Transmitter/receiver for optical parallel transmission and board for optical module

[0002] The present invention relates to an optical parallel transmission transmitter/receiver used for optical communication, and an optical module substrate having optical elements (light-receiving element/light-emitting elements) and optical fibers.

[0003] Along with an increase in required transmission capacity, the optical parallel data transmission technology for optical communication systems is becoming promising. An optical communication system using the optical parallel data transmission technology is divided into three sections: a transmission section, optical fiber transmission line, and reception section. In the transmission section, a plurality of electronic signals forming a bit sequence are input, subjected to signal processing, waveform shaping, and amplification, and output as optical signals through a current driving circuit and light-emitting element. In the reception section, the optical signals are converted into electrical signals by light-receiving elements, and the signals are subjected to amplification and signal processing to restore the original electrical signal bit sequence (Latest Materials of Optical Communication Technology III, “Optical parallel Data Transmission Scheme and Hardware Configuration”, pp. 191-192).

[0004] To realize an optical communication system using the optical parallel data transmission scheme, it is necessary to {circle around (1)} accurately and easily align the optical axes of an optical element array and optical fiber array and fix them, and {circle around (2)} hermetically seal the optical element array which readily degrades due to a change in humidity or temperature. A technique is known for this purpose in which a bundle fiber is inserted between a plurality of optical elements and a plurality of optical fibers to optically couple the optical elements to the optical fibers (Japanese Patent Laid-Open No. 5-188250).

[0005] Additionally, as described in transactions “the 1995 IEICE Conference C-185”, a structure is known in which a V-groove is formed in the upper surface of a silicon substrate, a light-emitting element is positioned and fixed at a predetermined position on the distal end side of the V-groove, and an optical fiber is arranged in the V-groove, thereby matching the optical axes of the optical fiber and light-emitting element.

[0006] From the viewpoint of facilitation and automation of the manufacturing process, a structure has been proposed in which optical coupling to light-emitting elements or light-receiving elements is achieved using a ferrule in which optical fiber strands are inserted and fixed (Japanese Patent Application No. 9-83004).

[0007] As an element technique for optical parallel transmission, for example, Japanese Patent Laid-Open No. 7-209556 discloses an optical transmission/reception module which integrates an LD (Laser Diode) array, PD (PhotoDiode) array, optical fiber array for optically coupling the LD array and PD array, LD IC, and PD IC. In this optical transmission/reception module, to facilitate alignment between the LD array, the PD array, and the optical fiber array, an optical module substrate made of silicon and having a plurality of V-grooves is used, and the optical fiber is formed by inserting a plurality of optical fibers into the V-grooves in the optical module substrate. Silicon is used for the optical module substrate because working of V-grooves can be easily and accurately realized.

[0008] However, when a plurality of optical fibers and a plurality of optical elements (light-receiving elements or light-emitting elements) are to be optically coupled using the conventional system, operation becomes hard. For, e.g., a 12-fiber array, operation is greatly complicated unless shift due to rotation is taken into consideration, unlike a case wherein a single optical fiber is connected to an optical element.

[0009] In addition, when not only an optical fiber array but also a light-emitting element array (e.g., a laser array) or light-receiving element array is mounted on an optical module substrate, the alignment operation is to be further facilitated, and the size of light-emitting module or light-receiving module is to be reduced, the optical module substrate according to the prior art has the following problems.

[0010] A laser beam emitted from each of a plurality of exit regions of a laser array diverges to some extent. For this reason, when the laser array is mounted on the mounting surface of an optical module substrate, the laser beam emitted from each exit region is partially reflected by the mounting surface of the optical module substrate. As a consequence, the coupling efficiency of the optical fibers of the optical fiber array lowers, and light reflected by the mounting surface generates noise.

[0011] Leakage light from a reflection region opposing each of the plurality of exit regions is also reflected by the mounting surface. As a consequence, the light reflected by the mounting surface generates noise.

[0012] When a light-emitting element array or light-receiving element array is to be mounted on an optical module substrate, normally, printed interconnections for electrically connecting the light-emitting element array and driving circuit and the like, or the light-receiving element array and amplification circuit and the like must be formed on the optical module substrate. Especially, when the optical module substrate is formed from a conductive material such as silicon, interconnections cannot be directly formed on the surface by metallizing. hence, an insulating film is formed on the surface, and interconnections are formed on this insulating film. With this arrangement, however, operation errors occur in the light-emitting module due to the parasitic capacitance generated between the interconnections and the optical module substrate through the insulating film, or noise is generated in the light-receiving module.

[0013] It is an object of the present invention to provide a structure capable of easily realizing operation of optically coupling a plurality of optical fibers and a plurality of optical elements. It is another object of the present invention to provide an optical module substrate which prevents any operation error of a light-emitting module or reduce noise in a light-receiving module.

[0014] In order to achieve the above object, according to the present invention, there is provided an optical parallel transmission receiver in which a plurality of light-receiving elements and a plurality of optical fibers are optically coupled via guide pins, characterized by comprising a pair of guide pins, fiber holding means (e.g., a ferrule) for holding the pair of guide pins in parallel and holding the plurality of optical fibers (e.g., a tape-like optical fibers) between the pair of guide pins at a predetermined interval, and light-receiving element holding means for holding the plurality of light-receiving elements (e.g., a light-receiving element array) between the pair of guide pins and holding one end of each of the pair of guide pins so as to make a plane including light-receiving surfaces of the light-receiving elements perpendicular to longitudinal axes of the guide pins, wherein the fiber holding means and the light-receiving element holding means are integrally held by resin molding.

[0015] There is also provided an optical parallel transmission transmitter in which a plurality of light-emitting elements and a plurality of optical fibers are optically coupled via guide pins, characterized by comprising a pair of guide pins, fiber holding means for holding the pair of guide pins in parallel and holding the plurality of optical fibers between the pair of guide pins at a predetermined interval, and light-emitting element holding means for holding the plurality of light-emitting elements between the pair of guide pins and holding one end of each of the pair of guide pins so as to align optical axes of the light-emitting elements with core axes of the optical fibers, wherein the fiber holding means and the light-emitting element holding means are integrally held by resin molding.

[0016] According to the present invention, there is also provided an optical parallel transmission receiver in which a plurality of light-receiving elements and a plurality of optical fibers are optically coupled via a pair of guide pins, characterized by comprising light-receiving element holding means for holding the plurality of light-receiving elements and holding one end of each of the pair of guide pins so as to make light-receiving surfaces of the light-receiving elements cross core axes of the optical fibers, wherein the light-receiving element holding means is formed from an insulator.

[0017] The light-receiving element holding means may comprise a light-receiving element array in which the plurality of light-receiving elements are arranged in an array, a preamplifier IC connected to the light-receiving element array and including a plurality of reception circuits, and a heat-conductive lead frame which is in contact with the preamplifier IC at one part and has a heat dissipation portion formed at the other part.

[0018] The light-receiving element holding means may comprise a guide pin holding portion for holding the guide pins, a first holding portion for holding the light-receiving element array, and a second holding portion for holding the preamplifier IC, the first holding portion may be positioned with reference to the guide pin holding portion, and when the light-receiving element array is held by the first holding portion, the light-receiving element array may be positioned with respect to the guide pins to be inserted to the guide pin holding portion.

[0019] The light-receiving element holding means may comprise a first plate member and a second plate member, which sandwich the lead frame, the first plate member having a pair of through holes which form the guide pin holding portions, and a pair of opening portions which expose part of the lead frame and form the first holding portion and the second holding portion.

[0020] The light-receiving element array may comprise back-incident-type light-receiving elements each having a light-receiving surface on an opposite side of a surface having an electrode connected to the preamplifier IC, the first holding portion may have an opening extending to a back side of the light-receiving element holding means, the back-incident-type light-receiving elements may be arranged to make the light-receiving surfaces expose to the back side of the light-receiving element holding means, and the plurality of optical fibers may be optically coupled to the light-receiving surfaces of the back-incident-type light-receiving elements through the pair of guide pins on the back side of the light-receiving element holding means.

[0021] According to the present invention, there is provided an optical parallel transmission transmitter in which a plurality of light-emitting elements and a plurality of optical fibers are optically coupled via a pair of guide pins, comprising light-emitting element holding means for holding the plurality of light-emitting elements and holding one end of each of the pair of guide pins so as to arrange optical axes of the light-emitting elements and core axes of the optical fibers, wherein the light-emitting element holding means may be formed from an insulator.

[0022] The light-emitting element holding means may comprise a light-emitting element array in which the plurality of light-emitting elements are arranged in an array, a driver IC array connected to the light-emitting element array and having a plurality of driving circuits, and a heat-conductive lead frame which is in contact with the driver IC array at one part and has a heat dissipation portion formed at the other part.

[0023] The light-emitting element holding means may comprise a guide pin holding portion for holding the guide pins, a first holding portion for holding the light-emitting element array, and a second holding portion for holding the driver IC array, and a light-receiving element may be arranged between the first holding portion and the second holding portion.

[0024] The light-emitting element holding means may comprise a first plate member and a second plate member, which sandwich the lead frame, the first plate member having a pair of grooves which form the guide pin holding portion, and a pair of opening portions which expose part of the lead frame and form the first holding portion and the second holding portion.

[0025] The light-emitting element array may be mounted faceup on the lead frame via an insulating submount.

[0026] The lead frame may be separated into two parts which are held by the first plate member and the second plate member while being spaced apart at a predetermined interval, and the light-emitting element array may be mounted on one part of the lead frame while the driver IC array may be mounted on the other part of the lead frame.

[0027] The light-emitting element holding means may comprise a guide pin holding portion for holding the guide pins on one surface, a first holding portion for holding the light-emitting element array, and a second holding portion for holding the driver IC array, and the driver IC array having a plurality of driving circuits may be in contact with the light-emitting element holding means.

[0028] According to the present invention, there is also provided an optical module substrate for mounting a laser array having a plurality of emission regions, and an optical fiber array formed by arraying a plurality of optical fibers optically coupled to the plurality of emission regions, respectively, characterized in that a groove portion is formed in a mounting surface for mounting the laser array at a portion corresponding to each of the plurality of emission regions of the laser array.

[0029] When the groove portion is formed in the mounting surface for mounting the laser array at a portion corresponding to each emission region, reflection of a laser beam emitted from the emission region by the mounting surface is reduced.

[0030] According to the present invention, there is provided an optical module substrate for mounting a laser array having a plurality of emission regions, and an optical fiber array formed by arraying a plurality of optical fibers optically coupled to the plurality of emission regions, respectively, which may be characterized in that a groove portion is formed in a mounting surface for mounting the laser array at a portion corresponding to each of a plurality of reflection regions respectively opposing the plurality of emission regions of the laser array.

[0031] When the groove portion is formed in the mounting surface for mounting the laser array at the portion corresponding to each reflection region, reflection of leakage light leaking from the reflection region by the mounting surface is reduced.

[0032] According to the present invention, there is also provided an optical module substrate for mounting a laser array having a plurality of emission regions, and an optical fiber array formed by arraying a plurality of optical fibers optically coupled to the plurality of emission regions, respectively, which may be characterized in that a groove portion is formed in a mounting surface for mounting the laser array at a portion corresponding to each of the plurality of emission regions of the laser array and a portion corresponding to each of a plurality of reflection regions respectively opposing the plurality of emission regions of the laser array.

[0033] When the groove portion is formed in the mounting surface for mounting the laser array at the portion corresponding to each emission region, reflection of a laser beam emitted from the emission region by the mounting surface is reduced. In addition, when the groove portion is formed in the mounting surface for mounting the laser array at the portion corresponding to each reflection region, reflection of leakage light leaking from the reflection region by the mounting surface is reduced.

[0034] According to the present invention, there is also provided a light-emitting module characterized by comprising a laser array having a plurality of emission regions, an optical fiber array formed by arraying a plurality of optical fibers optically coupled to the plurality of emission regions, respectively, an optical module substrate for mounting the laser array and the optical fiber array, a driving circuit for driving the laser array, and a base for mounting the optical module substrate and the driving circuit, wherein the optical module substrate comprises any one of the above optical module substrates.

[0035] When any one of the above optical module substrates is used, reflection of a laser beam emitted from the emission region of the laser array by the mounting surface is reduced, or reflection of leakage light leaking from the reflection region of the laser array by the mounting surface is reduced.

[0036] According to the present invention, there is also provided an optical module substrate for mounting a light-emitting element array formed by arraying a plurality of light-emitting elements and an optical fiber array formed by arraying a plurality of optical fibers optically coupled to the plurality of light-emitting elements, respectively, characterized in that the optical module substrate is formed from an insulating ceramic.

[0037] When the optical module substrate is formed from an insulating material, no insulating film need be formed between printed interconnections and the optical module substrate, and a parasitic capacitance is prevented. In addition, when the optical module substrate is formed from a ceramic, the workability and working accuracy are ensured.

[0038] According to the present invention, there is also provided an optical module substrate for mounting a light-receiving array formed by arraying a plurality of light-receiving elements and an optical fiber array formed by arraying a plurality of optical fibers optically coupled to the plurality of light-receiving elements, respectively, characterized in that the optical module substrate is formed from an insulating ceramic.

[0039] When the optical module substrate is formed from an insulating material, no insulating film need be formed between printed interconnections and the optical module substrate, and a parasitic capacitance is prevented. In addition, when the optical module substrate is formed from a ceramic, the workability and working accuracy are ensured.

[0040] The optical module substrate of the present invention is preferably characterized in that the insulating ceramic is an insulating ceramic selected from the group consisting of alumina ceramic, zirconia ceramic, calcium titanate ceramic, silicon nitride ceramic, and aluminum nitride ceramic.

[0041] The optical module substrate of the present invention may be characterized in that the substrate comprises a reflection surface for reflecting light emerging from an end face of each of the plurality of optical fibers of the optical fiber array and making the light incident on a corresponding one of the light-receiving elements of the light-receiving element array, and the reflection surface makes an angle of substantially 45° with respect to a mounting surface for mounting the optical fiber array.

[0042] In an optical module substrate made of silicon, it is difficult to form a reflection surface that makes an angle of 45° with respect to the mounting surface because of the problem of crystal surface. However, in the optical module substrate made of a ceramic, the reflection surface that makes an angle of 45° with respect to the mounting surface can be easily accurately formed, and the optical coupling efficiency between the light-receiving element array and the optical fiber array can be easily improved.

[0043] According to the present invention, there is also provided a light-emitting module characterized by comprising a light-emitting element array formed by arraying a plurality of light-emitting elements, an optical fiber array formed by arraying a plurality of optical fibers optically coupled to the plurality of light-emitting elements, respectively, an optical module substrate for mounting the light-emitting element array and the optical fiber array, a driving circuit for driving the light-emitting element array, and a base for mounting the optical module substrate and the driving circuit, wherein the optical module substrate comprises the optical module substrate formed from an insulating ceramic.

[0044] When the optical module substrate formed from an insulating ceramic is used, a parasitic capacitance is prevented, and the workability and working accuracy of the optical module substrate are ensured.

[0045] According to the present invention, there is also provided a light-receiving module characterized by comprising a light-receiving element array formed by arraying a plurality of light-receiving elements to output an electrical signal corresponding to a light-receiving amount of each of the plurality of light-receiving elements, an optical fiber array formed by arraying a plurality of optical fibers optically coupled to the plurality of light-receiving elements, respectively, an optical module substrate for mounting the light-receiving element array and the optical fiber array, an amplification circuit for amplifying the electrical signal output from the light-receiving element array, and a base for mounting the optical module substrate and the amplification circuit, wherein the optical module substrate comprises the optical module substrate formed from an insulating ceramic.

[0046] When the optical module substrate formed from an insulating ceramic is used, a parasitic capacitance is prevented, and the workability and working accuracy of the optical module substrate are ensured.

[0047] FIG. 1 is a perspective view showing an optical parallel transmission receiver according to an embodiment of the present invention immediately after resin molding;

[0048] FIG. 2 is a perspective view showing a PD subcarrier 3 usable for the optical parallel transmission receiver according to an embodiment of the present invention, which is viewed from an MT ferrule 2 side;

[0049] FIG. 3 is a perspective view showing the PD subcarrier 3 usable for the optical parallel transmission receiver according to an embodiment of the present invention, which is viewed from the rear side;

[0050] FIG. 4 is a perspective view showing a subassembly combining guide pins 1, MT ferrule 2, and PD subcarrier 3 usable for the optical parallel transmission receiver according to an embodiment of the present invention, which is viewed from the MT ferrule 2 side;

[0051] FIG. 5 is a perspective view showing the subassembly shown in FIG. 4, which is upside down and viewed from the PD subcarrier 3 side;

[0052] FIG. 6 is a perspective view showing the subassembly shown in FIG. 4, from which the MT ferrule 2 is detached;

[0053] FIG. 7 is a perspective view showing a state before bending connecting lead pins 3einto an almost S shape while omitting the half of a lid 2cof the MT ferrule 2 for the illustrative convenience so as to indicate the connection state between optical fibers and light-receiving elements usable for the optical parallel transmission receiver according to an embodiment of the present invention;

[0054] FIG. 8 is an exploded perspective view showing the MT ferrule together with the guide pins usable for the optical parallel transmission receiver according to an embodiment of the present invention;

[0055] FIG. 9 is a perspective view showing a metal lead frame as a constituent component of the PD subcarrier 3 usable for the optical parallel transmission receiver according to an embodiment of the present invention;

[0056] FIG. 10 is a perspective view showing a state wherein the metal lead frame usable for the optical parallel transmission receiver according to an embodiment of the present invention is sandwiched and fixed between a first flat plate 3band a second flat plate 3c;

[0057] FIG. 11 is a perspective view showing a state wherein the connecting lead pins 3eshown in FIG. 10 are bent;

[0058] FIG. 12 is a perspective view showing, together with the guide pins 1 and MT ferrule 2, a state wherein a light-receiving element array 3fand preamplifier IC 3gare mounted on die pad portions 3j1 and 3j2 shown in FIG. 11, respectively, and connected by wire bonding;

[0059] FIG. 13 is a perspective view showing, together with the MT ferrule 2, the PD subcarrier 3 using back-incident-type light-receiving elements, which is usable for the optical parallel transmission receiver according to an embodiment of the present invention;

[0060] FIG. 14 is a perspective view showing the PD subcarrier 3 shown in FIG. 13, which is viewed from the lower side;

[0061] FIG. 15 is a perspective view showing the connection state between the light-receiving element array 3fand the preamplifier IC 3gwhich are usable for the optical parallel transmission receiver according to an embodiment of the present invention;

[0062] FIG. 16 is a perspective view showing a connection method according to another embodiment, which is usable for the optical parallel transmission receiver according to an embodiment of the present invention;

[0063] FIG. 17 is a perspective view showing an optical parallel transmission transmitter immediately after resin molding, which is usable for an optical parallel transmission transmitter according to the first embodiment of the present invention;

[0064] FIG. 18 is an exploded perspective view showing the internal structures of an MT ferrule 12 and LD subcarrier 13 before resin molding, which are usable for the optical parallel transmission transmitter according to the first embodiment of the present invention;

[0065] FIG. 19 is a perspective view showing a state wherein the lid of the LD subcarrier 13 usable for the optical parallel transmission transmitter according to the first embodiment of the present invention is omitted;

[0066] FIG. 20 is a perspective view showing the LD subcarrier 13 usable for the optical parallel transmission transmitter according to the first embodiment of the present invention together with a lead frame 14 and ceramic substrate 16 (corresponding to the optical parallel transmission transmitter shown in FIG. 19 from which the MT ferrule 12 is omitted);

[0067] FIG. 21 is an exploded perspective view showing the MT ferrule together with guide pins usable for the optical parallel transmission transmitter according to the first embodiment of the present invention;

[0068] FIG. 22 is a perspective view showing the guide pins and MT ferrule shown in FIG. 21, which are viewed from the lower side;

[0069] FIG. 23 is a perspective view showing a metal lead frame as a constituent component of the LD subcarrier 13 usable for the optical parallel transmission transmitter according to the first embodiment of the present invention;

[0070] FIG. 24 is a perspective view showing a state wherein the metal lead frame usable for the optical parallel transmission transmitter according to the first embodiment of the present invention is sandwiched and fixed between a first flat plate 13band a second flat plate 13c;

[0071] FIG. 25 is a perspective view showing a state wherein the structure shown in FIG. 24 is viewed from a driver IC array mounting portion 13j1 side;

[0072] FIG. 26 is a perspective view showing, together with guide pins 11, a state wherein a light-emitting element array 13f,driver IC array 13g,and monitor light-receiving element 13pare mounted on the die pad portions 13j1 and 13j2 and 13mshown in FIG. 24, respectively;

[0073] FIG. 27 is a perspective view showing the optical parallel transmission transmitter according to the first embodiment of the present invention before resin molding, which is usable for an optical parallel transmission transmitter according to the second embodiment and is viewed from a ceramic substrate 26 side while detaching a lid 23eof the LD subcarrier;

[0074] FIG. 28 is a perspective view showing a state wherein a lid 22cof an MT ferrule 22 is also detached from the optical parallel transmission transmitter shown in FIG. 27;

[0075] FIG. 29 is a perspective view showing the state wherein the lid 22cand lid 23eare detached, which is viewed from the MT ferrule 22 side;

[0076] FIG. 30 is a perspective view showing an LD subcarrier 23 usable for the optical parallel transmission transmitter according to the second embodiment of the present invention together with a lead frame 24 and ceramic substrate 26;

[0077] FIG. 31 is a perspective view showing a state wherein the lid 23eof the LD subcarrier 23 of the optical parallel transmission transmitter according to the second embodiment of the present invention shown in FIG. 30 is removed;

[0078] FIG. 32 is a perspective view showing, together with the MT ferrule 22, the LD subcarrier 23 having no lid 23e,which is usable for the optical parallel transmission transmitter according to the second embodiment of the present invention;

[0079] FIG. 33 is a perspective view showing, together with guide pins 21, the LD subcarrier 23 having no lid 23e,which is usable for the optical parallel transmission transmitter according to the second embodiment of the present invention;

[0080] FIG. 34 is a perspective view showing a first flat plate 23b,second flat plate 23c,and two lead frames held by them, which are usable for the optical parallel transmission transmitter according to the second embodiment of the present invention;

[0081] FIG. 35 is a perspective view showing a state wherein a light-emitting element array 23f,driver IC array 23g,and monitor light-receiving element 23pare removed from the first flat plate 23bshown in FIG. 34;

[0082] FIG. 36 is a perspective view showing a metal lead frame as a constituent component of the LD subcarrier 23 usable for the optical parallel transmission transmitter according to the second embodiment of the present invention;

[0083] FIG. 37 is a perspective view showing the LD subcarrier 23 having no lid 23e,together with the guide pins 21 and MT ferrule 22, which are usable for the optical parallel transmission transmitter according to the second embodiment of the present invention;

[0084] FIG. 38 is a sectional view showing the MT ferrule 22 and LD subcarrier 23, which are usable for the optical parallel transmission transmitter according to the second embodiment of the present invention and are taken along a plane perpendicular to the optical fiber array surface;

[0085] FIG. 39 is a perspective view showing the optical parallel transmission transmitter before resin molding, which is usable for the optical parallel transmission transmitter according to the second embodiment of the present invention and is viewed from the ceramic substrate 26 side while omitting an MT ferrule 32;

[0086] FIG. 40 is a perspective view showing a state wherein a lid 33eof the optical parallel transmission transmitter shown in FIG. 39 is removed;

[0087] FIG. 41 is a perspective view showing an LD subcarrier 33 usable for an optical parallel transmission transmitter according to the third embodiment of the present invention;

[0088] FIG. 42 is a perspective view showing the LD subcarrier 33 usable for the optical parallel transmission transmitter according to the third embodiment of the present invention.

[0089] FIG. 43 is a perspective view showing the LD subcarrier 33 usable for the optical parallel transmission transmitter according to the third embodiment of the present invention;

[0090] FIG. 44 is a perspective view showing the LD subcarrier 33 usable for the optical parallel transmission transmitter according to the third embodiment of the present invention;

[0091] FIG. 45 is a perspective view showing the lid 33eof the LD subcarrier 33 usable for the optical parallel transmission transmitter according to the third embodiment of the present invention;

[0092] FIG. 46 is a perspective view showing the lid 33eof the LD subcarrier 33 usable for the optical parallel transmission transmitter according to the third embodiment of the present invention;

[0093] FIG. 47 is a perspective view showing the lid 33eof the LD subcarrier 33 usable for the optical parallel transmission transmitter according to the third embodiment of the present invention;

[0094] FIG. 48 is a perspective view showing the lid 33eof the LD subcarrier 33 usable for the optical parallel transmission transmitter according to the third embodiment of the present invention;

[0095] FIG. 49 is a perspective view showing the lid 33eof the LD subcarrier 33 usable for the optical parallel transmission transmitter according to the third embodiment of the present invention;

[0096] FIG. 50 is an exploded perspective view of a light-emitting module;

[0097] FIG. 51 is a perspective view of the light-emitting module;

[0098] FIG. 52 is a perspective view of a base;

[0099] FIG. 53 is a perspective view of an optical fiber array;

[0100] FIG. 54 is a perspective view of the optical fiber array;

[0101] FIG. 55 is a perspective view of a semiconductor laser array;

[0102] FIG. 56 is a perspective view of a platform;

[0103] FIG. 57 is a perspective view of a wiring board;

[0104] FIG. 58 is a perspective view of a platform;

[0105] FIG. 59 is a perspective view of a platform; and

[0106] FIG. 60 is a view showing a state wherein an optical fiber array and photodiode array are mounted on the platform.

[0107] An embodiment of the present invention will be described below with reference to the accompanying drawings. The same reference numerals denote the same elements throughout the drawings, and a detailed description thereof will be omitted.

[0108] FIG. 1 is a perspective view showing an optical parallel transmission receiver according to an embodiment of the present invention immediately after resin molding. For the optical parallel transmission receiver according to this embodiment, a pair of guide pins 1, an MT ferrule 2 for holding multiple optical fibers, and a PD subcarrier 3 for holding light-receiving elements are resin-molded together with a lead frame 4, thereby constructing a mold package 5.

[0109] After that, leads extending from the sides and rear side of the mold package 5 are cut in front of support leads, and tie bars between the leads are cut.

[0110] In this embodiment, the mold package 5 is used to fix the elements. However, a metal package or plastic package may be used to fix the elements.

[0111] FIGS. 2 and 3 are perspective views showing the optical parallel transmission receiver according to this embodiment before resin molding. FIG. 2 is a perspective view showing the PD subcarrier 3 viewed from the MT ferrule 2 side. FIG. 3 is a perspective view showing the PD subcarrier 3 viewed from the rear side. FIGS. 2 and 3 are schematic views aiming at clarity. For example, only some wires for connecting the PD subcarrier 3 and a ceramic substrate 6 are illustrated.

[0112] The guide pins 1 and lead frame 4 are held by a mold for resin molding whereby the relative position between the guide pins 1, MT ferrule 2, PD subcarrier 3, lead frame 4, and ceramic substrate 6, which are fixed by the mold package 5, is accurately realized. At this stage, the guide pins 1, MT ferrule 2, and PD subcarrier 3 are accurately assembled with reference to the guide pins 1.

[0113] The guide pins 1 are normally formed from a metal and have a length longer than at least the total length of the MT ferrule 2 and PD subcarrier 3 combined with each other. Another MT ferrule (not shown) is inserted on the guide pins 1 projecting from the MT ferrule 2. To facilitate insertion, the distal ends of the guide pins 1 are tapered. The guide pins 1 inserted into the MT ferrule 2 are not fixed. However, to prevent the other MT ferrule from removing the guide pins 1 when the other MT ferrule is detached, the guide pins 1 are held in the MT ferrule 2 by a certain force. A plurality of V-grooves are formed between the guide pins 1 at a predetermined interval in parallel to the longitudinal direction of the guide pins 1. A plurality of optical fibers are fixed in the grooves. Hence, the plurality of optical fibers are arrayed at a predetermined pitch that normally matches the standard of the other MT ferrule.

[0114] The MT ferrule 2 has at least a function of holding a plurality of optical fibers and guide pins. For this purpose, the MT ferrule 2 has fiber holding portions corresponding to the number of optical fibers to be held and pin holding portions corresponding to the number of guide pins to be held. The detailed structure will be described later with reference to FIG. 8.

[0115] The PD subcarrier 3 is constructed by two, first flat plate 3band second flat plate 3cforming a pair of through holes 3aand formed from a plastic, and a metal lead frame having, at some portions, heat dissipation lead pins 3dand connecting lead pins 3eand sandwiched between the first flat plate 3band the second flat plate 3c,and is attached between the MT ferrule 2 and the ceramic substrate 6 with reference to the guide pins 1. To accurately position the PD subcarrier 3 with respect to the MT ferrule 2, the through holes 3aeach for receiving one end of a corresponding one of the guide pins 1 are formed in the PD subcarrier 3 to extend from the surface of the PD subcarrier 3, which opposes the MT ferrule 2, to the opposite surface (FIG. 3). A light-receiving element array 3fand preamplifier IC 3gare accurately mounted on the PD subcarrier 3 with reference to the through holes 3a.For this reason, the plurality of optical fibers attached to the MT ferrule 2 and the plurality of light-receiving element arrays 3fmounted on the PD subcarrier 3 can be easily accurately optically coupled only by inserting the PD subcarrier 3 on the guide pins 1. The heat dissipation lead pins 3dextending from both sides of the PD subcarrier 3 effectively dissipate heat from the preamplifier, which is transmitted through the metal lead frame. Grounding is also possible using the heat dissipation lead pins 3d.After the PD subcarrier 3 is packaged, the connecting lead pins 3eare bent into an almost S shape (FIG. 3) and easily connected to the ceramic substrate 6 by wire bonding. In this embodiment, the PD subcarrier 3 and ceramic substrate 6 are connected by wires. However, the connecting lead pins 3eand electrode terminals on the ceramic substrate 6 may be directly connected.

[0116] The lead frame 4 comprises a support lead 4awhich forms a rectangular frame, a die pad 4bon which the ceramic substrate 6 is mounted, and lead pins 4cfor connecting the die pad 4band support lead 4a.

[0117] The ceramic substrate 6 is mounted on the die pad 4bof the lead frame 4. The ceramic substrate 6 need not be strictly positioned as far as it is connected to the PD subcarrier 3 by wires. Electronic circuits (signal processing circuit, waveform shaping circuit, amplification circuit, and the like) necessary for driving the light-receiving elements are formed on the upper surface of the ceramic substrate 6.

[0118] FIG. 4 is a perspective view showing a subassembly combining the guide pins 1, MT ferrule 2, and PD subcarrier 3 usable in this embodiment, which is viewed from the MT ferrule 2 side. FIG. 5 is a perspective view showing the subassembly shown in FIG. 4, which is turned over and viewed from the PD subcarrier 3 side. FIG. 6 is a perspective view showing the subassembly shown in FIG. 4, from which the MT ferrule 2 is removed. FIG. 7 is a perspective view showing a state before bending the connecting lead pins 3einto an almost S shape while omitting the half of a lid 2cof the MT ferrule 2 for the illustrative convenience so as to indicate the connection state between the optical fibers and the light-receiving elements. To clearly indicate details, wires for connecting the connecting lead pins 3eand preamplifier 3fand wires for connecting the light-receiving element array 3fand preamplifier IC 3gare not illustrated.

[0119] As an important point, the plurality of optical fibers (e.g., a fiber array) and the plurality of light-receiving elements (e.g., a light-receiving element array) are accurately positioned using the guide pins as a mechanical reference such that the optical fibers and the light-receiving surfaces of the light-receiving elements are perpendicular (optically coupled) to each other. It is difficult to accurately position optical fibers and light-receiving elements held by separate members on the μm order. However, accurate positioning is realized through the guide pins by accurately forming holes for fixing the guide pins in the two members.

[0120] The guide pins 1, MT ferrule 2, and PD subcarrier 3, which construct this subassembly, will be sequentially described on the basis of FIGS. 4 to 7 with reference to FIGS. 8 to 11.

[0121] The guide pins 1 are normally formed into a long columnar shape to obtain the function of positioning a plurality of members (MT ferrule 2 and PD subcarrier 3 in this embodiment) to which the guide pins 1 are inserted (FIGS. 7 and 8). As for the material, the guide pins 1 are formed from a material that does not deform and curve under the use environment of the receiver, e.g., stainless steel. The projecting amount of the guide pins 1 from the MT ferrule 2 is calculated in consideration of connection and optical axis alignment to the MT connector or MT ferrule on the partner side, which is inserted to the guide pins 1. The length of each guide pin 1 is determined on the basis of the calculated value.

[0122] The MT ferrule 2 comprises the lid 2cand a fiber holding member 2d(FIGS. 6 and 8). The two plate members, i.e., the lid 2cand fiber holding member 2dare abutted against each other. The pair of guide pins 1 and the plurality of optical fibers are held between the abutment surfaces. For this purpose, each of the lid 2cand fiber holding member 2dhas a pair of trapezoidal grooves which form a pair of through holes 2afor receiving the pair of guide pins 1, and the fiber holding member 2dhas V-grooves 2bfor holding the plurality of optical fibers (FIGS. 6 and 8). Since these grooves are formed parallel to each other, the guide pins 1 inserted into the MT ferrule 2 and all the optical fibers held by the MT ferrule 2 are held in parallel. A recess 2eis formed on a side where the MT ferrule 2 opposes the PD subcarrier 3 so as to prevent interference with wires for connecting the light-receiving element array 3fand preamplifier IC 3g.

[0123] The PD subcarrier 3 comprises th e first flat plate 3b,second flat plate 3c,and lead frame (FIGS. 6 and 11). The first flat plate 3bis formed from a plastic material and has a rectangular outline. A first opening portion 3hfor mounting the preamplifier IC 3gis formed on the upper side (or lower side) of the central portion of the first flat plate 3b.A second opening portion 3ifor mounting the light-receiving element array 3fholding a plurality of upper-incident-type light-receiving elements is formed on the lower side (or upper side). The first opening portion 3hhas a sufficient size to accommodate the preamplifier IC 3g.The second opening portion 3ihas an opening shape conforming to the shape of the light-receiving element array 3fsuch that the optical fibers held by the MT ferrule 2 and the light-receiving element array 3fare accurately positioned with respect to the guide pins 1. For this purpose, hexagonal projecting portion s having the holes 3afor receiving the guide pins 1 for positioning are formed on both sides of the second opening portion 3i.The lead frame includes the large number of connecting lead pins 3eextending in one direction (e.g., downward), the small number of heat dissipation lead pins 3dextending in different directions (e.g., lateral directions), and die pad portions 3j1 and 3j2 on which the light-receiving element array 3fand preamplifier IC 3gare placed, and is sandwiched between the two first flat plate 3band second flat plate 3c(FIGS. 6 and 11). One end of each of the connecting lead pins 3eis bent into an almost S shape and directed to the ceramic substrate 6 so as to connect a signal source, ground, VDD, or VGC. The other end extends to the first opening portion 3h(FIGS. 4 and 11). The preamplifier IC 3gis formed into an almost parallelepiped chip shape (FIGS. 4 and 9) and has electrodes (not shown) formed on the upper surface. For this reason, the preamplifier IC 3gcan be easily connected to the other end of each connecting lead pin 3eby wire bonding. The second flat plate 3chas a function of sandwiching the lead frame with the first flat plate 3band fixing the lead frame and has, as opening portions, only the through holes 3afor receiving the guide pins 1 (FIG. 5). The guide pins 1 extend through not only the first flat plate 3bbut also the second flat plate 3c.Hence, the metal lead frame sandwiched between the plates has recess portions for passing the guide pins 1 (FIG. 9). The preamplifier IC 3gand light-receiving element array 3fare not in contact with the second flat plate 3cand come into surface contact with the metal lead frame (FIG. 9). For this reason, e.g., heat from the preamplifier IC 3gcan be efficiently dissipated through the lead pins 3d.

[0124] The structures of the MT ferrule 2 and PD subcarrier 3, which construct the subassembly, will be described next in more detail with reference to FIGS. 8 to 11.

[0125] FIG. 8 is an exploded perspective view showing the MT ferrule together with the guide pins. A pair of trapezoidal grooves are formed in parallel in the lower surface of the lid 2cof the MT ferrule 2, i.e., the surface opposing the fiber holding member 2d,in regions close to the side portions. The depth of the grooves is calculated and determined such that the guide pins 1 do not move in the through holes 2athat are formed when the lid 2cis combined with the fiber holding member 2d.A flat surface is formed between the trapezoidal grooves and presses the upper surfaces of the optical fibers held by the fiber holding member 2d.The fiber holding member 2dhas trapezoidal grooves with the same shape as that of the grooves in the lid 2cat positions corresponding to the trapezoidal grooves formed in the lid 2c.Hence, when the two members are stacked, the through holes 2afitted on the guide pins 1 are formed. The V-grooves 2bin number corresponding to the number of optical fibers to be held are formed in parallel between the two trapezoidal grooves formed in the upper surface of the fiber holding member 2d(FIG. 8). The V-grooves 2bare formed using the trapezoidal grooves as a mechanical reference. An optical fiber longer than each V-groove 2bis arranged in each V-groove 2b.The lid 2cis fixed to the fiber holding member 2dwith an adhesive while keeping the guide pins 1 removed, and after that, the guide pins 1 are inserted. After the optical fibers are held by the lid 2cand fiber holding member 2d,the lengths of optical fibers projecting from the V-grooves 2bare uniformed by end face polishing.

[0126] FIG. 9 is a perspective view showing the metal lead frame as a constituent component of the PD subcarrier 3. The light-receiving element array 3fand preamplifier IC 3gindicated by the alternate long and two-dashed lines are shown to indicate the positional relationship between the lead frame and the die pad portions 3j1 and 3j2 on which the light-receiving element array 3fand preamplifier IC 3gare placed. As shown in FIG. 9, the two die pad portions 3j1 and 3j2 are formed adjacent to each other. The connecting lead pins 3eextend close to the die pad portion 3j1 where the preamplifier IC 3gis placed. For this reason, the wires required to connect the light-receiving element array 3fand preamplifier IC 3g,and the preamplifier IC 3gand connecting lead pins 3eare short, and wire bonding is easy. For wire bonding, electrode pads on the light-receiving element array 3fand preamplifier IC 3gmay be heated to a predetermined temperature, e.g., 170° C. using the heat conduction effect through the lead frame. The four lead pins 3dextending in the lateral directions perpendicular to the longitudinal direction of the connecting lead pins 3eare mainly provided for heat dissipation. However, a ground function may be imparted using these terminals. Recess portions 3kfor passing the guide pins 1 are formed between the pairs of lead pins 3dextending in the lateral directions.

[0127] In this embodiment, a single lead frame is used. However, separate lead frames may be prepared for the light-receiving element array and preamplifier IC. When separate lead frames are used, thermal influence from the preamplifier IC 3gwhich generates a large amount of heat on the light-receiving element array 3fcan be eliminated.

[0128] FIG. 10 is a perspective view showing a state wherein the above-described metal lead frame is sandwiched and fixed between the first flat plate 3band second flat plate 3c.FIG. 11 is a perspective view showing a state wherein the connecting lead pins 3eshown in FIG. 10 are bent.

[0129] As an important point, the second opening portion 3ifor receiving the light-receiving element array 3fis highly accurately (at an accuracy of 1 μm or less) positioned and formed in consideration of the outer dimensions of the light-receiving element array 3fwith reference to the positioning holes 3afor receiving the guide pins 1. The accuracy required herein can be obtained by resin molding (e.g., plastic insert molding or transfer molding). Hence, in realizing the high accuracy, a plastic can be advantageously used as the material of the first flat plate 3band second flat plate 3c.In addition, the plastic material has no problem of parasitic capacitance and improves the performance, as compared to the conventional silicon substrate accurately microfabricated. Furthermore, since the material is inexpensive, the cost of products is expected to be lower.

[0130] On the other hand, the positional accuracy of the first opening portion 3hcan be lower than that of the second opening portion 3ibecause there is no restriction for optical coupling to optical fibers, and the preamplifier IC 3gis connected to the light-receiving element array 3fand connecting lead pins 3eby wire bonding. For this reason, the first opening portion 3his formed to have a relatively large size (to have a width of about 2 mm although the width of the preamplifier IC mounting surface is about 1 mm) such that the jig (e.g., a collet) for wire bonding can be used without any problem. The interval between the first opening portion 3hand the second opening portion 3iis preferably small because of the requirement for connection using short wires. However, the width is set so large (e.g., about 0.5 mm) as to maintain the strength capable of standing resin molding. That is, it is most important to accurately form the second opening portion 3i.The four corners of the second opening portion 3icorrespond to the corner portions of the light-receiving element array 3f.To eliminate the influence of odd shapes of the corner portions of the light-receiving element array 3fto be accommodated in the second opening portion 3i,the portions corresponding to the corner portions are largely cut. As is known, chips and flashes easily form at the corners of an array (normally a semiconductor chip) to readily make odd shapes. Hexagonal projecting portions for positioning the guide pins 1 and preventing interference of bonding wire are formed on both sides of the second opening portion 3i.The through holes 3afor receiving the guide pins 1 are formed in the hexagonal projecting portions. By forming the guide pin positioning projecting portions into a hexagonal shape, a space that allows the wire bonding jig to access is ensured to facilitate wire bonding between the light-receiving element array 3fand the preamplifier IC 3g.To easily insert the guide pins 1, the inlets of the through holes 3aare tapered.

[0131] FIG. 12 is a perspective view showing, together with the guide pins 1 and MT ferrule 2, a state wherein the light-receiving element array 3fand preamplifier IC 3gare mounted on the die pad portions 3j1 and 3j2 shown in FIG. 11, respectively, and connected by wire bonding.

[0132] In the MT ferrule 2, all optical fibers are accurately positioned with reference to the through holes 2ain which the guide pins 1 are to be inserted and fixed. Similarly, in the PD subcarrier 3, all the light-receiving elements of the light-receiving element array 3fare accurately positioned with reference to the through holes 3ain which the guide pins 1 are to be inserted and fixed. Hence, only by inserting the guide pins 1 into the through holes 2aand 3a,the plurality of optical fibers and the plurality of light-receiving elements are accurately optically coupled.

[0133] The optical parallel transmission receiver according to an embodiment of the present invention has been described with reference to FIGS. 1 to 12. However, the present invention is not limited to the above embodiment, and various changes and modifications can be made.

[0134] For example, in this embodiment, the light-receiving element array 3fuses a light-receiving element array structure using front-incident-type light-receiving elements (FIG. 12). However, so-called back-incident-type light-receiving elements may be employed.

[0135] FIG. 13 is a perspective view showing, together with the MT ferrule 2, the PD subcarrier 3 using back-incident-type light-receiving elements. FIG. 14 is a perspective view showing the PD subcarrier 3 shown in FIG. 13, which is viewed from the back side. The differences from the above-described embodiment are as follows. First, since interference of wire bonding need not be prevented, no hexagonal projecting portions are formed on the MT ferrule 2 and first flat plate 3b.Second, to receive light emerging from the optical fibers by the opposite surface (lower surface) of the upper surface on which the electrode pads are formed, the second flat plate 3calso has an opening portion.

[0136] The light emerging from the optical fibers passes through the opening portion of the second flat plate 3cand becomes incident on the light-receiving surface of the back-incident-type light-receiving element array 3f.An electrical signal photoelectrically converted by the light-receiving element array 3fis transmitted to the preamplifier IC 3gthrough a wire. The signal transmitted to the preamplifier IC 3gis sent to the connecting lead pin 3ethrough wire connection. When the back-incident-type light-receiving element array 3fis used, the MT ferrule 2 and PD subcarrier 3 can have simple shapes.

[0137] In addition, in the above embodiment, the light-receiving elements and preamplifiers are connected by wires. However, one (e.g., the light-receiving element array) may be mounted on the other (e.g., the preamplifier IC) as a flip chip.

[0138] FIG. 15 is a perspective view showing the connection state between the light-receiving element array 3fand the preamplifier IC 3gused in the above-described embodiment. FIG. 16 is a perspective view showing a connection method according to another embodiment.

[0139] The difference between the two methods is that in the above embodiment, the light-receiving element array 3fand preamplifier IC 3gare arranged to be flush with each other, and the electrode pads are connected by wire bonding (FIG. 15) while in the connection structure according to another embodiment, wire bonding between the light-receiving element array 3fand the preamplifier IC 3gis unnecessary because back-incident-type light-receiving elements are directly mounted on preamplifier IC. (FIG. 16).

[0140] According to the connection method of another embodiment, the mounting area decreases, and crosstalk between adjacent channels decreases. For example, according to the wire bonding connection method shown in FIG. 15, the mounting area is 3.5 mm×3 mm. However, according to the flip chip connection method shown in FIG. 16, the mounting area is 3.5 mm×1.5 mm.

[0141] For crosstalk, experiments were conducted under the following conditions according to FIG. 15. When the input impedance of each channel was 100Ω, the input capacitance of each channel was 0.5 pF, and the capacitance between adjacent channel, which was generated by elements other than wire interconnections was 10 pF, the crosstalk amount for wire bonding correction was −66.7 dB at a frequency of 10 MHz while the crosstalk amount for flip chip connection was −84.0 dB. At a frequency of 100 MHz, the crosstalk amount for wire bonding correction was −46.7 dB while the crosstalk amount for flip chip connection was −64.0 dB. At a frequency of 1 GHz, the crosstalk amount for wire bonding correction was −27.4 dB while the crosstalk amount for flip chip connection was −44.0 dB. Assuming that a dielectric constant ∈_rof a resin to be packed is 3.69, a wire length L is 2.0×10⁻³[m], a wire radius r is 1.0×10⁻⁵[m], and an interwire distance d is 2.5×10⁻⁴[m], a coupling capacitance C between wire bonds is given by

[0142] C=(27.8×∈_r×L)×10⁻¹²/ln(d/r)[F]

[0143] The first, second, and third embodiments of an optical parallel transmission transmitter according to the present invention will be described next with reference to FIGS. 17 to 26, FIGS. 27 to 38, and FIGS. 39 to 49, respectively.

[0144] The basic differences between an optical parallel transmission transmitter and an optical parallel transmission receiver are as follows. First, the latter has a structure in which optical fibers and the light-receiving surfaces of light-receiving elements are perpendicular to each other while the former has a structure in which the exit directions of optical fibers and light-emitting elements are substantially the same. Second, the latter has the problem of optical axes of the core diameter (about 9 μm for a single-mode optical fiber) of an optical fiber and the light-receiving surface (about 100 μm²) while the former requires optical axis matching between a light-emitting element and the core diameter of an optical fiber, and therefore highly accurate positioning.

[0145] An optical parallel transmission transmitter according to the first embodiment will be described below. The same reference numerals denote components having the same functions throughout the drawings, and a detailed description thereof will be omitted.

[0146] FIG. 17 is a perspective view showing the optical parallel transmission transmitter immediately after resin molding. For this optical parallel transmission transmitter according to this embodiment, a pair of guide pins 11, an MT ferrule 12 for holding multiple optical fibers, and an LD subcarrier 13 for holding light-emitting elements are resin-molded together with a lead frame 14, thereby constructing a mold package 15.

[0147] After that, leads extending from the sides and rear side of the mold package 15 are cut in front of support leads, and tie bars between the leads are cut.

[0148] In this embodiment, the mold package 15 is used to fix the elements. However, a metal package or plastic package may be used to fix the elements.

[0149] FIGS. 18 and 19 show the optical parallel transmission transmitter according to this embodiment before resin molding. FIG. 18 is an exploded perspective view showing the internal structures of the MT ferrule 12 and LD subcarrier 13. FIG. 19 is a perspective view showing a state wherein the lid of the LD subcarrier 13 is omitted. FIGS. 18 and 19 are schematic views aiming at clarity. For example, wires for connecting the LD subcarrier 13 and a ceramic substrate 16 are not illustrated.

[0150] The guide pins 11 and lead frame 14 are held by a mold for resin molding whereby the relative position between the guide pins 11, MT ferrule 12, LD subcarrier 13, lead frame 14, and ceramic substrate 16, which are fixed by the mold package 15, is accurately realized. At this stage, the guide pins 11, MT ferrule 12, and LD subcarrier 13 are accurately assembled with reference to the guide pins 11.

[0151] The guide pins 11 are normally formed from a metal and have a length longer than at least the total length of the MT ferrule 12 and LD subcarrier 13 juxtaposed each other. Another MT connector (not shown) is inserted on the guide pins 11 projecting from the MT ferrule 12. To facilitate insertion, the distal ends of the guide pins 11 are tapered. The guide pins 11 inserted into the MT ferrule 12 are not fixed. However, to prevent the other MT connector from removing the guide pins 11 when the other MT connector is detached, the guide pins 11 are held in the MT ferrule 12 by a certain force. A plurality of V-grooves are formed between the guide pins 11 at a predetermined interval in parallel to the longitudinal direction of the guide pins 11. A plurality of optical fibers are fixed in the grooves. Hence, the plurality of optical fibers are arrayed at a predetermined pitch that normally matches the standard of the other MT connector.

[0152] The MT ferrule 12 has at least a function of holding a plurality of optical fibers and the guide pins 11. For this purpose, the MT ferrule 12 has fiber holding portions corresponding to the number of optical fibers to be held and pin holding portions corresponding to the number of guide pins 11 to be held. The detailed structure will be described later with reference to FIGS. 21 and 22.

[0153] The LD subcarrier 13 is constructed by two, first flat plate and second flat plate 13band 13cforming a pair of through holes 13aand formed from a plastic, a metal lead frame having, at some portions, heat dissipation lead pins 13dand sandwiched between the first flat plate 13band the second flat plate 13c,and a lid 13e,and is attached between the MT ferrule 12 and the ceramic substrate 16 with reference to the guide pins 11. To accurately position the LD subcarrier 13 with respect to the MT ferrule 12, the through holes 13aeach for receiving one end of a corresponding one of the guide pins 11 are formed in the LD subcarrier 13. A light-emitting element array 13fand driver IC array 13gare accurately mounted on the LD subcarrier 13 with reference to the through holes 13a.For this reason, the plurality of optical fibers attached to the MT ferrule 12 and the plurality of light-emitting element arrays 13fmounted on the LD subcarrier 13 can be easily accurately optically coupled only by inserting the LD subcarrier 13 on the guide pins 11. The heat dissipation lead pins 13dextending from both sides of the LD subcarrier 13 effectively dissipate heat from the driver, which is transmitted through the metal lead frame. Grounding is also possible using the heat dissipation lead pins 13d.In this embodiment, the LD subcarrier 13 and ceramic substrate 16 are connected by wires. The lid 13eis formed from a plastic material and fixed to the first flat plate 13bby bonding. After that, the guide pins 11 are inserted into the through holes 13a.The guide pins 11 need not be fixed in the through holes 13a.

[0154] The lead frame 14 comprises a support lead 14awhich forms a rectangular frame, a die pad 14bon which the ceramic substrate 16 is mounted, and lead pins 14cfor connecting the die pad 14band support lead 14a.

[0155] The ceramic substrate 16 is mounted on the die pad 14bof the lead frame 14. The ceramic substrate 16 need not be strictly positioned as far as it is connected to the LD subcarrier 13 by wires. Electronic circuits (signal processing circuit, waveform shaping circuit, amplification circuit, and the like) necessary for driving the light-emitting elements are formed on the upper surface of the ceramic substrate 16.

[0156] FIG. 20 is a perspective view showing the LD subcarrier 13 usable in this embodiment together with the lead frame 14 and ceramic substrate 16. This structure corresponds to the optical parallel transmission transmitter shown in FIG. 19 from which the MT ferrule 12 is omitted. To clearly indicate details, wires for connecting the ceramic substrate 16 and driver IC array 13gand wires for connecting the light-emitting element array 13fand driver IC array 13gare not illustrated.

[0157] As an important point, the plurality of optical fibers (e.g., a fiber array) and the plurality of light-emitting elements (e.g., a light-emitting element array) are more accurately positioned using the guide pins as a mechanical reference such that the optical axis of each optical fiber is aligned with that of a corresponding light-emitting element. It is difficult to accurately position optical fibers and light-emitting elements held by separate members on the μm order. However, accurate positioning is realized through the guide pins by accurately forming holes for fixing the guide pins in the two members.

[0158] The guide pins 11, MT ferrule 12, and LD subcarrier 13, which construct this subassembly, will be sequentially described on the basis of FIG. 20 with reference to FIGS. 21 to 26.

[0159] The guide pins 11 are normally formed into a long columnar shape to obtain the function of positioning a plurality of members (MT ferrule 12 and LD subcarrier 13 in this embodiment) to which the guide pins 11 are inserted (FIGS. 20 and 26). As for the material, the guide pins 11 are formed from a material that does not deform and curve under the use environment of the transmitter, e.g., stainless steel. The projecting amount of the guide pins 11 from the MT ferrule 12 is calculated in consideration of connection and optical axis alignment to the MT connector or MT ferrule on the partner side, which is inserted to the guide pins 11. The total length of each guide pin 11 is determined on the basis of the calculated value.

[0160] The MT ferrule 12 comprises the lid 12cand a fiber holding member 12d(FIGS. 21 and 22). The two plate members, i.e., the lid 12cand fiber holding member 12dare abutted against each other. The pair of guide pins 11 and a plurality of optical fibers 12eare held between the abutment surfaces. For this purpose, each of the lid 12cand fiber holding member 12dhas a pair of trapezoidal grooves which form a pair of through holes 12afor receiving the pair of guide pins 11, and the fiber holding member 12dhas V-grooves 12bfor holding the plurality of optical fibers 12e(FIGS. 21 and 22). Since these grooves are formed parallel to each other, the guide pins 11 inserted into the MT ferrule 12 and all the optical fibers 12eheld by the MT ferrule 12 are held in parallel. For the receiver, to make the optical axis of each optical fiber perpendicular to the light-receiving surface of a corresponding light-receiving element, the wires for connecting the light-receiving element array and preamplifier IC must be bypassed. In this case, however, such consideration is unnecessary because since the LD subcarrier 13 and MT ferrule 12 are arranged juxtaposed each other, and wire connection does not interfere.

[0161] The LD subcarrier 13 comprises the first flat plate 13b,second flat plate 13c,and lead frame (FIGS. 23 and 24). The first flat plate 13bis formed from a plastic material and has a rectangular outline. A first opening portion 13hfor mounting the driver IC array 13gis formed on the upper side (or lower side) of the central portion of the first flat plate 13b.A second opening portion 13ifor mounting the light-emitting element array 13fis formed on the lower side (or upper side). The first opening portion 13hhas a sufficient size to accommodate the driver IC array 13g.The second opening portion 13ihas an opening shape conforming to the shape of the light-emitting element array 13fsuch that the optical fibers held by the MT ferrule 12 and the light-emitting element array 13fare accurately positioned. Trapezoidal grooves are formed on both sides of the first opening portion 13hand second opening portion 13iso as to define the through holes 13afor receiving the guide pins 11. Unlike the lead frame for the receiver (FIG. 9), the lead frame of this embodiment (FIG. 23) does not have the number of connecting lead pins 3eextending in one direction (e.g., downward). However, the lead frame includes the small number of heat dissipation lead pins 13dextending in different directions (e.g., lateral directions) and die pad portions 13j1 and 13j2 on which the light-emitting element array 13fand driver IC array 13gare placed, and is sandwiched between the two first flat plate 13band second flat plate 13c(FIG. 26). The connecting lead pins 3eare unnecessary because the driver IC array 13gand ceramic substrate 16 are directly connected by wires. The driver IC array 13gis formed into an almost parallelepiped chip shape (FIGS. 20 and 26) and has electrodes (not shown) formed on the upper surface. For this reason, the driver IC array 13gcan be easily connected to the electrodes on the ceramic substrate 16 by wire bonding. The second flat plate 13chas a function of sandwiching the lead frame with the first flat plate 13band has no particular opening portions. Unlike the lead frame for the receiver (FIG. 12), since the guide pins 11 do not extend through the first flat plate 13band second flat plate 13c,the metal lead frame has not recess portions for passing the guide pins 11 (FIG. 23). The driver IC array 13gand light-emitting element array 13fare not in contact with the second flat plate 13cand come into surface contact with the metal lead frame (FIG. 23). For this reason, e.g., heat from the driver IC array 13gcan be efficiently dissipated through the lead pins 13d.

[0162] The structures of the MT ferrule 12 and LD subcarrier 13, which construct the subassembly, will be described next in more detail with reference to FIGS. 21 to 26.

[0163] FIG. 21 is an exploded perspective view showing the MT ferrule together with guide pins. FIG. 22 is a perspective view showing the guide pins and MT ferrule shown in FIG. 21, which are viewed from the lower side. A pair of trapezoidal grooves are formed in parallel in the lower surface of the lid 12cof the MT ferrule 12, i.e., the surface opposing the fiber holding member 12d,in regions close to the side portions. The depth of the grooves is calculated and determined such that the guide pins 11 do not move in the through holes 12athat are formed when the lid 12cis combined with the fiber holding member 12d.A flat surface is formed between the trapezoidal grooves and presses the upper surfaces of the optical fibers held by the fiber holding member 12d.The fiber holding member 12dhas trapezoidal grooves with the same shape as that of the grooves in the lid 12cat positions corresponding to the trapezoidal grooves formed in the lid 12c.Hence, when the two members are stacked, the through holes 12afitted on the guide pins 11 are formed. The V-grooves 12bin number corresponding to the number of optical fibers to be held are formed in parallel between the two trapezoidal grooves formed in the upper surface of the fiber holding member 12d(FIG. 22). The V-grooves 12bare formed using the trapezoidal grooves as a mechanical reference. An optical fiber longer than each V-groove 12bis arranged in each V-groove 12b.The lid 12cis fixed to the fiber holding member 12dwith an adhesive while keeping the guide pins 11 removed, and after that, the guide pins 11 are inserted. After the optical fibers are held by the lid 12cand fiber holding member 12d,the lengths of optical fibers 12eprojecting from the V-grooves 12bare uniformed by end face polishing.

[0164] FIG. 23 is a perspective view showing the metal lead frame as a constituent component of the LD subcarrier 13. The light-emitting element array 13fand driver IC array 13gindicated by the alternate long and two-dashed lines are shown to indicate the positional relationship between the lead frame and the die pad portions 13j1 and 13j2 on which the light-emitting element array 13fand driver IC array 13gare placed. As shown in FIG. 23, the two die pad portions 13j1 and 13j2 are formed adjacent to each other. For this reason, the wires required to connect the light-emitting element array 13fand driver IC array 13gare short, and wire bonding is easy. For wire bonding, electrode pads on the light-emitting element array 13fand driver IC array 13gmay be heated to a predetermined temperature, e.g., 170° C. using the heat conduction effect through the lead frame. The four lead pins 3dextending in the lateral directions are mainly provided for heat dissipation. However, a ground function may be imparted using these terminals.

[0165] In this embodiment, a single lead frame is used. However, separate lead frames may be prepared for the light-emitting element array and driver IC array. When separate lead frames are used, thermal influence from the driver IC array 13gwhich generates a large amount of heat on the light-emitting element array 13fcan be eliminated.

[0166] FIG. 24 is a perspective view showing a state wherein the above-described metal lead frame is sandwiched and fixed between the first flat plate 13band second flat plate 13c.FIG. 25 is a perspective view showing a state wherein the structure shown in FIG. 24 is viewed from the driver IC array mounting portion 13j1 side.

[0167] As an important point, the second opening portion 13ifor receiving the light-emitting element array 13fis highly accurately (at an accuracy of 1 μm or less) positioned and formed in consideration of the outer dimensions of the light-emitting element array 13fwith reference to the trapezoidal grooves which define the positioning holes 13afor receiving the guide pins 11. The accuracy required herein can be obtained by resin molding (e.g., plastic insert molding or transfer molding). Hence, in realizing the high accuracy, a plastic can be advantageously used as the material of the first flat plate 13band second flat plate 13c.In addition, the plastic material has no problem of parasitic capacitance and improves the performance, as compared to the conventional silicon substrate accurately microfabricated. Furthermore, since the material is inexpensive, the cost of products is expected to be lower.

[0168] On the other hand, the positional accuracy of the first opening portion 13hcan be lower than that of the second opening portion 13ibecause there is no restriction for optical coupling to optical fibers, and the driver IC array 13gis connected to the light-emitting element array 13fand ceramic substrate 16 by wire bonding. For this reason, the first opening portion 13his formed to have a relatively large size such that the jig (e.g., a collet) for wire bonding can be used without any problem. A monitor light-receiving element mounting portion 13mis formed between the first opening portion 13hand the second opening portion 13i.As an important point, the monitor light-receiving element mounting portion 13mis tilted with respect to a plane including the emitting portions of the light-emitting elements such that a monitor light-receiving element 13pmounted on the monitor light-receiving element mounting portion 13mobliquely receives light emitted from the light-emitting elements. For this reason, reflected light from the light-receiving surface of the monitor light-receiving element 13pdoes not enter any light-emitting element, so the performance of the light-emitting elements increases. To impart such a function to the monitor light-receiving element 13p,the monitor light-receiving element mounting portion 13mis tilted with respect to the exit surface of the light-emitting element array, and metallizing interconnections 13n1 and 13n2 extend on both sides of the monitor light-receiving element 13p.The monitor light-receiving element 13phas a light-receiving surface on its front surface, an electrode on the front surface, and another electrode on the back surface. For this reason, one metallizing interconnection 13n1 comes into contact with the back surface of the monitor light-receiving surface while the other metallizing interconnection 13n2 is spaced apart from the monitor light-receiving element 13pand connected by, e.g., wire bonding.

[0169] FIG. 26 is a perspective view showing, together with guide pins 11, a state wherein the light-emitting element array 13f,driver IC array 13g,and monitor light-receiving element 13pare mounted on the die pad portions 13j1 and 13j2 and 13mshown in FIG. 24, respectively. FIG. 26 aims at clarity and does not illustrate wires and the like.

[0170] In the MT ferrule 12 (not shown), all optical fibers are accurately positioned with reference to the through holes 12ain which the guide pins 11 are to be inserted and fixed. In the LD subcarrier 13, all the light-emitting elements of the light-emitting element array 13fare accurately positioned with reference to the through holes 13ain which the guide pins 11 are to be inserted and fixed. Hence, only by inserting the guide pins 11 into the through holes 12aand 13a,the plurality of optical fibers and the plurality of light-emitting elements are accurately optically coupled.

[0171] An optical parallel transmission transmitter according to the second embodiment will be described next with reference to FIGS. 17, and 27 to 38.

[0172] The basic differences between the optical parallel transmission transmitter according to the first embodiment and that according to the second embodiment are that the light-emitting element array is positioned not by openings but by grooves, and the lead frame of a LD subcarrier 23 is separated into two parts to the first flat plate of the LD subcarrier 23. As in the first embodiment, optical axis alignment between light-emitting elements and optical fibers is necessary, and more accurate positioning is required.

[0173] The optical parallel transmission transmitter according to the second embodiment will be described below. The same reference numerals denote components having the same functions throughout the drawings, and a detailed description thereof will be omitted.

[0174] The optical parallel transmission transmitter according to the second embodiment after resin molding has the shape shown in FIG. 17. The function and arrangement are the same as in the first embodiment, and a detailed description thereof will be omitted.

[0175] FIGS. 27 to 29 show the optical parallel transmission transmitter according to this embodiment before resin molding. FIG. 27 is a perspective view showing a state wherein a lid 23eis detached, which is viewed from a ceramic substrate 26 side. FIG. 28 is a perspective view showing a state wherein a lid 22cof an MT ferrule 22 is also detached from the optical parallel transmission transmitter shown in FIG. 27. FIG. 29 is a perspective view showing the state wherein the lid 22cand lid 23eare detached, which is viewed from the MT ferrule 22 side. FIGS. 27 to 29 are schematic views aiming at clarity, and, for example, wires for connecting the LD subcarrier 23 and ceramic substrate 26 are not illustrated.

[0176] In this embodiment, since the LD subcarrier 23 is formed from a plastic material, and transfer mold is used, a working accuracy of 1 μm or less can be realized. It is therefore effective for non-alignment assembly between the core diameter (about 9 μm) of a single-mode optical fiber and a light-emitting element.

[0177] Guide pins 21 and lead frame 24 are held by a mold for resin molding whereby the relative position between the guide pins 21, MT ferrule 22, LD subcarrier 23, lead frame 24, and ceramic substrate 26, which are fixed by a mold package (FIG. 17), is accurately realized. At this stage, the guide pins 21, MT ferrule 22, and LD subcarrier 23 are accurately assembled with reference to the guide pins 21.

[0178] The guide pins 21 are normally formed from a metal and have a length larger than at least the total length of the MT ferrule 22 and LD subcarrier 23 juxtaposed each other. Another MT ferrule (not shown) is inserted on the guide pins 21 projecting from the MT ferrule 22. To facilitate insertion, the distal ends of the guide pins 21 are tapered. The guide pins 21 inserted into the MT ferrule 22 are not fixed. However, to prevent the other MT ferrule from removing the guide pins 21 when the other MT ferrule is detached, the guide pins 21 are held in the MT ferrule 22 by a certain force. A plurality of V-grooves are formed between the guide pins 21 at a predetermined interval in parallel to the longitudinal direction of the guide pins 21. A plurality of optical fibers are fixed in the grooves. Hence, the plurality of optical fibers are arrayed at a predetermined pitch that normally matches the standard of the other MT ferrule.

[0179] The MT ferrule 22 has at least a function of holding a plurality of optical fibers and the guide pins 21. For this purpose, the MT ferrule 22 has fiber holding portions corresponding to the number of optical fibers to be held and pin holding portions corresponding to the number of guide pins 21 to be held. The detailed structure is substantially the same as that of the optical parallel transmission transmitter according to the first embodiment, and a detailed description thereof will be omitted (FIGS. 21 and 22).

[0180] The LD subcarrier 23 is constructed by two, first flat plate 23band second flat plate 23cforming part of a pair of through holes 23aand formed from a plastic, a metal lead frame having, at some portions, heat dissipation lead pins 23dand sandwiched between the first flat plate 23band the second flat plate 23c,and the lid 23e,and is arranged between the MT ferrule 22 and the ceramic substrate 26 with reference to the guide pins 21. To accurately position the LD subcarrier 23 with respect to the MT ferrule 22, the through holes 23aeach for receiving one end of a corresponding one of the guide pins 21 are formed in the LD subcarrier 23 (FIG. 30). A light-emitting element array 23fand driver IC array 23gare accurately mounted on the LD subcarrier 23 with reference to the through holes 23a.For this reason, the plurality of optical fibers attached to the MT ferrule 22 and the plurality of light-emitting element arrays 23fmounted on the LD subcarrier 23 can be easily accurately optically coupled only by inserting the LD subcarrier 23 on the guide pins 21. The heat dissipation lead pins 23dextending from both sides of the LD subcarrier 23 effectively dissipate heat from the driver, which is transmitted through the metal lead frame. Grounding is also possible using the heat dissipation lead pins 23d.In this embodiment, the LD subcarrier 23 and ceramic substrate 26 are connected by wires. The lid 23eis formed from a plastic material and fixed to the first flat plate 23bby bonding using a transparent resin or the like. After that, the guide pins 21 are inserted into the through holes 23a.The guide pins 21 need not be fixed in the through holes 23a.

[0181] The lead frame 24 comprises a support lead 24awhich forms a rectangular frame, a die pad 24bon which the ceramic substrate 26 is mounted, and lead pins 24cfor connecting the die pad 24band support lead 24a.

[0182] The ceramic substrate 26 is mounted on the die pad 24bof the lead frame 24. The ceramic substrate 26 need not be strictly positioned as far as it is connected to the LD subcarrier 23 by wires. Electronic circuits (signal processing circuit, waveform shaping circuit, amplification circuit, APC circuit, and the like) necessary for driving the light-emitting elements are formed on the upper surface of the ceramic substrate 26.

[0183] FIGS. 30 and 31 are perspective views showing the LD subcarrier 23 usable in this embodiment together with the lead frame 24 and ceramic substrate 26. To clearly indicate details, wires for connecting the ceramic substrate 26 and driver IC array 23gand wires for connecting the light-emitting element array 23fand driver IC array 23gare not illustrated.

[0184] As an important point, the plurality of optical fibers (e.g., a fiber array) and the plurality of light-emitting elements (e.g., a light-emitting element array) are more accurately positioned using the guide pins as a mechanical reference such that the optical axis of each optical fiber is aligned with that of a corresponding light-emitting element. It is difficult to accurately position optical fibers and light-emitting elements held by separate members on the μm order. However, accurate positioning is realized through the guide pins by accurately forming holes for fixing the guide pins in the two members.

[0185] The guide pins 21, MT ferrule 22, and LD subcarrier 23, which construct this subassembly, will be sequentially described on the basis of FIGS. 32 to 36.

[0186] FIG. 32 is a perspective view showing the LD subcarrier 23 having no lid 23etogether with the MT ferrule 22. FIG. 33 is a perspective view showing the LD subcarrier 23 having no lid 23etogether with guide pins 21. FIG. 34 is a perspective view showing the first flat plate 23b,second flat plate 23c,and two lead frames held by them, which construct the LD subcarrier 23. FIG. 35 is a perspective view showing a state wherein the light-emitting element array 23f,driver IC array 23g,and monitor light-receiving element 23pare removed from the first flat plate 23bshown in FIG. 34. FIG. 36 is a perspective view showing the metal lead frame as a constituent component of the LD subcarrier 23 according to the second embodiment.

[0187] The guide pins 21 are normally formed into a long columnar shape to obtain the function of positioning a plurality of members (MT ferrule 22 and LD subcarrier 23 in this embodiment) to which the guide pins 21 are inserted (FIG. 33). As for the material, the guide pins 21 are formed from a material that does not deform and curve under the use environment of the transmitter, e.g., stainless steel. The projecting amount of the guide pins 21 from the MT ferrule 22 is calculated in consideration of connection and optical axis alignment to the MT connector or MT ferrule on the partner side, which is inserted to the guide pins 21. The length of each guide pin 21 is determined on the basis of the calculated value.

[0188] The MT ferrule 22 comprises the lid 22cand a fiber holding member 22d(FIG. 32). The two plate members, i.e., the lid 22cand fiber holding member 22dare abutted against each other. The pair of guide pins 21 and a plurality of optical fibers 22eare held between the abutment surfaces. For this purpose, each of the lid 22cand fiber holding member 22dhas a pair of trapezoidal grooves which form a pair of through holes 22afor receiving the pair of guide pins 21, and the fiber holding member 22dhas V-grooves 22bfor holding the plurality of optical fibers 22e(FIGS. 21 and 22). Since these grooves are formed parallel to each other, the guide pins 21 inserted into the MT ferrule 22 and all the optical fibers 22eheld by the MT ferrule 22 are held in parallel. For the receiver, to make the optical axis of each optical fiber perpendicular to the light-receiving surface of a corresponding light-receiving element, the wires for connecting the light-receiving element array and preamplifier IC must be bypassed. In this case, however, such consideration is unnecessary because since the LD subcarrier 23 and MT ferrule 22 are arranged juxtaposed each other, and wire connection does not interfere.

[0189] A pair of trapezoidal grooves are formed in parallel in the lower surface of the lid 22cof the MT ferrule 22, i.e., the surface opposing the fiber holding member 12d,in regions close to the side portions. The depth of the grooves is calculated and determined such that the guide pins 21 do not move in the through holes 22athat are formed when the lid 22cis combined with the fiber holding member 22d.A flat surface is formed between the trapezoidal grooves and presses the upper surfaces of the optical fibers held by the fiber holding member 22d.The fiber holding member 22dhas trapezoidal grooves with the same shape as that of the grooves in the lid 22cat positions corresponding to the trapezoidal grooves formed in the lid 22c.Hence, when the two members are stacked, the through holes 22afitted on the guide pins 21 are formed. The V-grooves 22bin number corresponding to the number of optical fibers to be held are formed in parallel between the two trapezoidal grooves formed in the upper surface of the fiber holding member 22d(FIG. 21). The V-grooves 22bare formed using the trapezoidal grooves as a mechanical reference. An optical fiber longer than each V-groove 22bis arranged in each V-groove 22b.The lid 22cis fixed to the fiber holding member 22dwith adhesive while keeping the guide pins 21 removed, and after that, the guide pins 21 are inserted. After the optical fibers are held by the lid 22cand fiber holding member 22d,the lengths of optical fibers 22eprojecting from the V-grooves 22bare uniformed by end face polishing.

[0190] The LD subcarrier 23 comprises the first flat plate 23b,second flat plate 23c,lead frame, and lid 23e(FIGS. 29 and 32). The first flat plate 23bis formed from a plastic material and has a rectangular outline. A first groove portion 23hfor mounting the driver IC array 23gis formed on the upper side (or lower side) of the central portion of the first flat plate 23b.A second groove portion 23ifor mounting the light-emitting element array 23fis formed on the lower side (or upper side). The first groove portion 23hhas a sufficient size to accommodate the driver IC array 23g.The second groove portion 23ihas an opening shape conforming to the shape of the light-emitting element array 23fsuch that the optical fibers held by the MT ferrule 22 and the light-emitting element array 23fare accurately positioned. Trapezoidal grooves are formed on both sides of the first groove portion 23hand second groove portion 23iso as to define the holes 23afor receiving the guide pins 21. Unlike the lead frame for the receiver (FIG. 9), the lead frame of this embodiment (FIG. 36) does not have the number of connecting lead pins 3eextending in one direction (e.g., downward). However, the lead frame includes the small number of heat dissipation lead pins 23dextending in different directions (e.g., lateral directions) and die pad portions 23j1 and 23j2 on which the light-emitting element array 23fand driver IC array 23gare placed, and is sandwiched between the two first flat plate 23band second flat plate 23c(FIG. 26). The connecting lead pins 3eare unnecessary because the driver IC array 23gand ceramic substrate 26 are directly connected by wires. The driver IC array 23gis formed into an almost parallelepiped chip shape (FIGS. 32 and 36) and has electrodes (not shown) formed on the upper surface. For this reason, the driver IC array 23gcan be easily connected to the electrodes on the ceramic substrate 26 by wire bonding. The second flat plate 23chas a function of sandwiching the lead frame with the first flat plate 23band has no particular opening portions. Unlike the lead frame for the receiver (FIG. 12), since the guide pins 21 do not extend through the first flat plate 23band second flat plate 23c,the metal lead frame has not recess portions for passing the guide pins 21 (FIG. 36). The driver IC array 23gis not in contact with the second flat plate 23cand comes into surface contact with the metal lead frame (FIG. 36). For this reason, e.g., heat from the driver IC array 23gcan be efficiently dissipated through the lead pins 23d.

[0191] In addition, the light-emitting element array 23fis mounted, via a submount 23q,on the light-emitting element mounting surface 23j2 of the lead frame spaced apart from the driver IC array 23g(FIGS. 35 and 36). The LD subcarrier 23 has at least a function of adjusting the light-emitting position of the light-emitting element array 23fin accordance with the optical axes of the optical fibers. Hence, when the light-emitting element array 23fwhose light-emitting elements have a sufficient height is used, the submount 23qcan be omitted.

[0192] The light-emitting element array 23fand driver IC array 23gindicated by the alternate long and two-dashed lines (FIG. 36) are shown to indicate the positional relationship between the lead frame and the die pad portions 23j1 and 23j2 on which the light-emitting element array 23fand driver IC array 23gare placed. A gap (space) is formed between the two die pad portions 23j1 and 23j2, though they are sufficiently close to each other. For this reason, wires required to connect the light-emitting element array 23fand driver IC array 23gare short, and wire bonding is easy. In addition, thermal interference is prevented. For wire bonding, electrode pads on the light-emitting element array 23fand driver IC array 23gare heated to a predetermined temperature, e.g., 170° C. using the heat conduction effect through the lead frame. The four lead pins 3dextending in the lateral directions are mainly provided for heat dissipation. However, a ground function may be imparted using these terminals.

[0193] As an important point, the second groove portion 23i(FIG. 35) for receiving the light-emitting element array 23fis highly accurately (at an accuracy of 1 μm or less) positioned and formed in consideration of the outer dimensions of the light-emitting element array 23fwith reference to the trapezoidal grooves which define the positioning holes 23afor receiving the guide pins 21. The accuracy required herein can be obtained by resin molding (e.g., plastic insert molding or transfer molding). Hence, in realizing the high accuracy, a plastic can be advantageously used as the material of the first flat plate 23band second flat plate 23c.In addition, the plastic material has no problem of parasitic capacitance and improves the performance, as compared to the conventional silicon substrate accurately microfabricated. Furthermore, since the material is inexpensive, the cost of products is expected to be lower.

[0194] On the other hand, the positional accuracy of the first groove portion 23hcan be lower than that of the second opening portion 23ibecause there is no restriction for optical coupling to optical fibers, and the driver IC array 23gis connected to the light-emitting element array 23fand ceramic substrate 26 by wire bonding. For this reason, the first opening portion 23his formed to have a relatively large size such that the jig (e.g., a collet) for wire bonding can be used without any problem. A monitor light-receiving element mounting portion 23mis formed between the first groove portion 23hand the second groove portion 23i(FIG. 35).

[0195] As an important point, the monitor light-receiving element mounting portion 23mis tilted with respect to a plane including the emitting portions of the light-emitting elements such that the monitor light-receiving element 23pmounted on the monitor light-receiving element mounting portion 23mobliquely receives light emitted from the light-emitting elements. For this reason, reflected light from the light-receiving surface of the monitor light-receiving element 23pdoes not enter any light-emitting element, so the performance of the light-emitting elements increases. To impart such a function to the monitor light-receiving element 23p,the monitor light-receiving element mounting portion 23mis tilted with respect to the exit surface of the light-emitting element array, and metallizing interconnections 23n1 and 23n2 extend on both sides of the monitor light-receiving element 23p.The monitor light-receiving element 23phas a light-receiving surface on its front surface, an electrode on the front surface, and another electrode on the back surface. For this reason, one metallizing interconnection 23n1 comes into contact with the back surface of the monitor light-receiving surface while the other metallizing interconnection 23n2 is spaced apart from the monitor light-receiving element 23pand connected by, e.g., wire bonding. In this embodiment, grooves are formed instead of opening potions, unlike the first embodiment. The light-emitting element array 23fand driver IC array 23gcan be more accurately mounted by automatic recognition positioning using, e.g., the grooves as a marker.

[0196] According to the optical parallel transmission receiver of the second embodiment, the assembly can be improved, and additionally, cost reduction or cost reduction by decreasing the number of components is possible. In addition, since the accuracy of the MT ferrule, the accuracy of light-emitting elements, and their array accuracy can be substantially increased, non-alignment assembly is enabled by arranging the light-emitting elements using the guide pins of the MT ferrule as a mechanical reference. Furthermore, lens alignment operation can also be omitted by bad joint.

[0197] The structures of the MT ferrule 22 and LD subcarrier 23 constructing the subassembly of an optical parallel transmission transmitter according to a modification to the second embodiment will be described next on the basis of FIGS. 37 and 38 with reference to FIGS. 27 to 36.

[0198] FIG. 37 is a perspective view showing the LD subcarrier 23 having no lid 23etogether with the guide pins 21 and MT ferrule 22. FIG. 38 is a sectional view showing the MT ferrule 22 and LD subcarrier 23 which are taken along a plane perpendicular to the optical fiber array surface.

[0199] The difference from the optical parallel transmission transmitter according to the second embodiment is that the guide pins are arranged at a predetermined angle with respect to the optical axis (FIG. 38). When such a structure is employed, light incident on the optical fibers can be prevented from being reflected to the light-emitting element.

[0200] The guide pins 21, MT ferrule 22, and LD subcarrier 23, which construct the optical parallel transmission transmitter according to this modification, will be sequentially described below.

[0201] The guide pins 21 and MT ferrule 22 are basically the same as those used in the second embodiment, and a detailed description thereof will be omitted.

[0202] The LD subcarrier 23 comprises the first flat plate 23b,second flat plate 23c,lead frame, and lid 23e,as in the second embodiment. The difference from the second embodiment is that the through holes 23afor receiving the guide pins 21 are tilted with respect to the lead frame. For this reason, grooves for defining the through holes 23ahave a predetermined gradient with respect to the plane including the die pad portion of the lead frame. The degree of gradient is calculated and determined such that the light emitted from the light-emitting elements becomes incident on the cores of the optical fibers and is generally set to about 8°. With this arrangement, only by inserting the guide pins 21 projecting from the MT ferrule 22 into the through holes 23a,positioning is done such that light emitted from each of the plurality of light-emitting elements becomes incident on the core of a corresponding one of the plurality of optical fibers, so the two optical elements can be easily automatically and accurately optically coupled.

[0203] The first flat plate 23bhaving the tilted grooves is formed from a plastic material and has a rectangular outline. The first groove portion 23hfor mounting the driver IC array 23gis formed on the upper side (or lower side) of the central portion of the first flat plate 23b.The second groove portion 23ifor mounting the light-emitting element array 23fis formed on the lower side (or upper side). The first groove portion 23hhas a sufficient size to accommodate the driver IC array 23g.The second groove portion 23ihas an opening shape conforming to the shape of the light-emitting element array 23fsuch that the optical fibers held by the MT ferrule 22 and the light-emitting element array 23fare accurately positioned. Trapezoidal grooves are formed on both sides of the first groove portion 23hand second groove portion 23iso as to define the holes 23afor receiving the guide pins 21. Unlike the lead frame for the receiver (FIG. 9), the lead frame of this embodiment (FIG. 36) does not have the number of connecting lead pins 3eextending in one direction (e.g., downward). However, the lead frame includes the small number of heat dissipation lead pins 23dextending in different directions (e.g., lateral directions) and die pad portions 23j1 and 23j2 on which the light-emitting element array 23fand driver IC array 23gare placed, and is sandwiched between the two first flat plate 23band second flat plate 23c(FIG. 26). The connecting lead pins 3eare unnecessary because the driver IC array 23gand ceramic substrate 26 are directly connected by wires. The driver IC array 23gis formed into an almost parallelepiped chip shape (FIGS. 32 and 36) and has electrodes (not shown) formed on the upper surface. For this reason, the driver IC array 23gcan be easily connected to the electrodes on the ceramic substrate 26 by wire bonding. The second flat plate 23chas a function of sandwiching the lead frame with the first flat plate 23band has no particular opening portions. Unlike the lead frame for the receiver (FIG. 12), since the guide pins 21 do not extend through the first flat plate 23band second flat plate 23c,the metal lead frame has not recess portions for passing the guide pins 21 (FIG. 36). The driver IC array 23gis not in contact with the second flat plate 23cand comes into surface contact with the metal lead frame (FIG. 36). For this reason, e.g., heat from the driver IC array 23gcan be efficiently dissipated through the lead pins 23d.

[0204] In addition, the light-emitting element array 23fis mounted, via the submount 23q,on the light-emitting element mounting surface 23j2 of the lead frame spaced apart from the driver IC array 23g(FIGS. 35 and 36). The LD subcarrier 23 has at least a function of adjusting the light-emitting position of the light-emitting element array 23fin accordance with the optical axes of the optical fibers. Hence, when the light-emitting element array 23fwhose light-emitting elements have a sufficient height is used, the submount 23qcan be omitted.

[0205] The light-emitting element array 23fand driver IC array 23gindicated by the alternate long and two-dashed lines (FIG. 36) are shown to indicate the positional relationship between the lead frame and the die pad portions 23j1 and 23j2 on which the light-emitting element array 23fand driver IC array 23gare placed. A gap (space) is formed between the two die pad portions 23j1 and 23j2, though they are sufficiently close to each other. For this reason, the wires required to connect the light-emitting element array 23fand driver IC array 23gare short, and wire bonding is easy. In addition, thermal interference is prevented. For wire bonding, electrode pads on the light-emitting element array 23fand driver IC array 23gare heated to a predetermined temperature, e.g., 170° C. using the heat conduction effect through the lead frame. The four lead pins 3dextending in the lateral directions are mainly provided for heat dissipation. However, a ground function may be imparted using these terminals.

[0206] As an important point, the second groove portion 23i(FIG. 35) for receiving the light-emitting element array 23fis highly accurately (at an accuracy of 1 Am or less) positioned and formed in consideration of the outer dimensions of the light-emitting element array 23fwith reference to the trapezoidal grooves which define the positioning holes 23afor receiving the guide pins 21. The accuracy required herein can be obtained by resin molding (e.g., plastic insert molding or transfer molding). Hence, in realizing the high accuracy, a plastic can be advantageously used as the material of the first flat plate 23band second flat plate 23c.In addition, the plastic material has no problem of parasitic capacitance and improves the performance, as compared to the conventional silicon substrate accurately microfabricated. Furthermore, since the material is inexpensive, the cost of products is expected to be lower.

[0207] On the other hand, the positional accuracy of the first groove portion 23hcan be lower than that of the second opening portion 23ibecause there is no restriction for optical coupling to optical fibers, and the driver IC array 23gis connected to the light-emitting element array 23fand ceramic substrate 26 by wire bonding. For this reason, the first opening portion 23his formed to have a relatively large size such that the jig (e.g., a collet) for wire bonding can be used without any problem. The monitor light-receiving element mounting portion 23mis formed between the first groove portion 23hand the second groove portion 23i(FIG. 35). As an important point, the monitor light-receiving element mounting portion 23mis tilted with respect to a plane including the emitting portions of the light-emitting elements such that the monitor light-receiving element 23pmounted on the monitor light-receiving element mounting portion 23mobliquely receives light emitted from the light-emitting elements. For this reason, reflected light from the light-receiving surface of the monitor light-receiving element 23pdoes not enter any light-emitting element, so the performance of the light-emitting elements increases. To impart such a function to the monitor light-receiving element 23p,the monitor light-receiving element mounting portion 23mis tilted with respect to the exit surface of the light-emitting element array, and metallizing interconnections 23n1 and 23n2 extend on both sides of the monitor light-receiving element 23p.The monitor light-receiving element 23phas a light-receiving surface on its front surface, an electrode on the front surface, and another electrode on the back surface. For this reason, one metallizing interconnection 23n1 comes into contact with the back surface of the monitor light-receiving surface while the other metallizing interconnection 23n2 is spaced apart from the monitor light-receiving element 23pand connected by, e.g., wire bonding.

[0208] The optical parallel transmission transmitter according to the second embodiment and its modification have been described with reference to FIGS. 17 and 27 to 38. However, the present invention is not limited to the above embodiment, and various changes and modifications can be made.

[0209] An optical parallel transmission transmitter according to the third embodiment will be described next with reference to FIGS. 17 and 39 to 49.

[0210] The basic differences between the optical parallel transmission transmitter according to the first embodiment and that according to the third embodiment are that a first flat plate 33band lid 33econstructing an LD subcarrier 23 are formed from ceramic substrates, and a monitor light-receiving element 33pis arranged on the lid 33e.The difference between the second embodiment and the third embodiment is that light-emitting elements and monitor light-receiving element 33pare separated and independently mounted on separate components in the third embodiment. As common subjects of the first, second, and third embodiments, optical axis alignment between light-emitting elements and the core diameters of optical fibers is necessary, and more accurate positioning is required.

[0211] The optical parallel transmission transmitter according to the third embodiment will be described below. The same reference numerals denote components having the same functions throughout the drawings, and a detailed description thereof will be omitted.

[0212] The optical parallel transmission transmitter according to the third embodiment after resin molding has the shape shown in FIG. 17. The function and arrangement are the same as in the above embodiment, and a detailed description thereof will be omitted.

[0213] FIGS. 39 and 40 show the optical parallel transmission transmitter according to this embodiment before resin molding. FIG. 39 is a perspective view showing the optical parallel transmission transmitter before resin molding, which is viewed from a ceramic substrate 26 side while omitting an MT ferrule 32. FIG. 40 is a perspective view showing a state wherein the lid 33eof the optical parallel transmission transmitter shown in FIG. 39 is detached. FIGS. 39 and 40 are schematic views aiming at clarity, and, for example, wires for connecting the LD subcarrier 33 and ceramic substrate 36 are not illustrated.

[0214] Guide pins 31 and lead frame 34 are held by a mold for resin molding whereby the relative position between the guide pins 31, MT ferrule 32, LD subcarrier 33, lead frame 34, and ceramic substrate 36, which are fixed by a mold package (FIG. 17), is accurately realized. At this stage, the guide pins 31, MT ferrule 32, and LD subcarrier 33 are accurately assembled with reference to the guide pins 31.

[0215] The guide pins 31 are normally formed from a metal and have a length longer than at least the total length of the MT ferrule 32 and LD subcarrier 33 juxtaposed each other. Another MT connector (not shown) is inserted on the guide pins 31 projecting from the MT ferrule 32. To facilitate insertion, the distal ends of the guide pins 31 are tapered. The guide pins 31 inserted into the MT ferrule 32 are not fixed. However, to prevent the other MT connector from removing the guide pins 31 when the other MT connector is detached, the guide pins 31 are held in the MT ferrule 32 by a certain force. A plurality of V-grooves are formed between the guide pins 31 at a predetermined interval in parallel to the longitudinal direction of the guide pins 31. A plurality of optical fibers are fixed in the grooves. Hence, the plurality of optical fibers are arrayed at a predetermined pitch that normally matches the standard of the other MT ferrule.

[0216] Although not illustrated in FIG. 39, the MT ferrule 32 has the same function as that of the optical parallel transmission receiver according to the first embodiment and has at least a function of holding a plurality of optical fibers and the guide pins 21. For this purpose, the MT ferrule 32 has fiber holding portions corresponding to the number of optical fibers to be held and pin holding portions corresponding to the number of guide pins 31 to be held. The detailed structure is substantially the same as that of the optical parallel transmission transmitter according to the first embodiment, and a detailed description thereof will be omitted (FIGS. 21 and 22).

[0217] The LD subcarrier 33 according to the third embodiment is more advantageous than the LD subcarriers 13 and 23 of the first and second embodiments because the number of components is smaller, and the structure is simple. A lead frame for the LD subcarrier 33 is unnecessary. Hence, the LD subcarrier 33 is constructed by the first flat plate 33band lid 33eand is attached between the MT ferrule 32 and the ceramic substrate 36 with reference to the guide pins 31. To accurately position the LD subcarrier 33 with respect to the MT ferrule 32, through holes 33aeach for receiving one end of a corresponding one of the guide pins 31 are formed in the LD subcarrier 33. A light-emitting element array 33f(FIG. 40) and driver IC array 33gare accurately mounted on the LD subcarrier 33 with reference to the through holes 33a.For this reason, the plurality of optical fibers attached to the MT ferrule 32 and the plurality of light-emitting element arrays 33fmounted on the LD subcarrier 33 can be easily accurately optically coupled. In this embodiment, the LD subcarrier 33 and ceramic substrate 36 are connected by wires. The lid 33eis formed from a ceramic material and fixed to the first flat plate 33bby bonding. After that, the guide pins 31 are inserted into the through holes 33aand fixed.

[0218] The lead frame 34 comprises a support lead 34awhich forms a rectangular frame, a die pad 34bon which the ceramic substrate 36 is mounted, and lead pins 34cfor connecting the die pad 34band support lead 34a.

[0219] The ceramic substrate 36 is mounted on the die pad 34bof the lead frame 34. The ceramic substrate 36 need not be strictly positioned as far as it is connected to the LD subcarrier 33 by wires. Electronic circuits (signal processing circuit, waveform shaping circuit, amplification circuit, APC circuit, and the like) necessary for driving the light-emitting elements are formed on the upper surface of the ceramic substrate 36.

[0220] FIGS. 41 to 44 are perspective views showing the LD subcarrier 33 usable in this embodiment. FIGS. 45 to 49 are perspective views showing the lid 33eof the LD subcarrier 33 usable in this embodiment. To clearly indicate details, wires for connecting the light-emitting element array 33fand driver IC array 33gare not illustrated.

[0221] As an important point, the plurality of optical fibers (e.g., a fiber array) and the plurality of light-emitting elements (e.g., a light-emitting element array) are more accurately positioned using the guide pins as a mechanical reference such that the optical axis of each optical fiber is aligned with that of a corresponding light-emitting element. It is difficult to accurately position optical fibers and light-emitting elements held by separate members on the μm order. However, accurate positioning is realized through the guide pins by accurately forming holes for fixing the guide pins in the two members.

[0222] The LD subcarrier 33 usable in the third embodiment will be described below in more detail. As important points, a ceramic material is used for the LD subcarrier, and a monitor light-receiving element is attached to the lower surface of the lid.

[0223] The LD subcarrier 33 comprises the first flat plate 33band lid 33e.The first flat plate 33bis formed from a ceramic material having a rectangular outline. The LD subcarrier 33 has no opening portions, unlike the LD subcarriers 13 and 23 (FIGS. 24 and 35) according to the first and second embodiments. A pair of trapezoidal grooves are formed in a flat substrate. A first region 33ifor mounting the light-emitting element array 33fis formed on the upper side (or lower side) of the central portion. A second region 33h(not shown) for mounting the driver IC array 33gis formed on the lower side (or upper side). The second region 33hhas a sufficient size to accommodate the driver IC array 33g.The LD subcarrier according to this embodiment has no lead frame, unlike the receiver or the LD subcarriers according to the first and second embodiments. The driver IC array 33gis formed into an almost parallelepiped chip shape (FIGS. 41 to 44) and has electrodes (not shown) formed on the front surface. For this reason, the driver IC array 33gcan be easily connected to the electrodes on the ceramic substrate 36 by wire bonding. Predetermined metallizing patterns 33n1 and 33n2 are formed on the upper surface of the lid 33e.A mounting portion 33q(FIG. 49) is provided at a position corresponding to the light-emitting elements of the light-emitting element array 33f.

[0224] When the ceramic is used for the first flat plate 33band lid 33e,the problem of parasitic capacitance is less serious, and the performance improves as compared to the conventional silicon substrate accurately microfabricated. In addition, since the ceramic is more inexpensive than silicon, the cost of products is expected to be lower.

[0225] On the other hand, the positional accuracy of the first region 33hcan be lower than that of the first region 33ibecause there is no restriction for optical coupling to optical fibers, and the driver IC array 33gis connected to the light-emitting element array 33fand ceramic substrate 36 by wire bonding. For this reason, the first region 33iis formed to have a relatively large size such that the jig (e.g., a collet) for wire bonding can be used without any problem. A monitor light-receiving element 33pis arranged at a corresponding portion of the lid 33earranged between the first region 33hand second region 33i(FIG. 41).

[0226] As an important point, the monitor light-receiving element mounting portion 33qis tilted with respect to a plane including the emitting portions of the light-emitting elements such that the monitor light-receiving element 33pmounted on the mounting portion 33qobliquely receives light emitted from the light-emitting elements (FIGS. 41 and 47). For this reason, reflected light from the light-receiving surface of the monitor light-receiving element 33pdoes not enter any light-emitting element, so the performance of the light-emitting elements increases. To impart such a function to the monitor light-receiving element 33p,the monitor light-receiving element mounting portion 33qis tilted with respect to the exit surface of the light-emitting element array 33f,and metallizing interconnections 33n1 and 33n2 extend on both sides of the monitor light-receiving element 33p(FIGS. 47 and 49). The monitor light-receiving element 33phas a light-receiving surface on its front surface, an electrode on the front surface, and another electrode on the back surface. For this reason, one metallizing interconnection 33n1 comes into contact with the back surface of the monitor light-receiving surface while the other metallizing interconnection 33n2 is spaced apart from the monitor light-receiving element 33pand connected by, e.g., wire bonding.

[0227] According to the optical parallel transmission transmitter of the third embodiment, the mounting area 23m(FIG. 35) allocated to the monitor light-receiving element in the second embodiment can be effectively used without damaging the required function. In addition, high-level functional pattern design can be realized on a ceramic substrate. Hence, the degree of freedom in design can be increased. Furthermore, since the lid 33ehas not only the guide holding function but also the region 33qon the lower surface where the monitor light-receiving element can be mounted, the substrate layout mounted on the light-emitting elements obtains a margin.

[0228] The present invention is not limited to the above embodiment, and various changes and modifications can be made.

[0229] A light-emitting module according to an embodiment of the present invention will be described next with reference to the accompanying drawings. The light-emitting module according to this embodiment includes an optical module substrate according to an embodiment of the present invention. The arrangement of the light-emitting module according to this embodiment will be described first. FIG. 50 is an exploded perspective view of the light-emitting module according to this embodiment. FIG. 51 is a perspective view of the light-emitting module according to this embodiment.

[0230] In a light-emitting module 110 according to this embodiment, as shown in FIGS. 50 and 51, a platform 114 (optical module substrate), optical fiber array 116, semiconductor laser array 118, LSI 120 (driving circuit), and wiring board 122 are mounted on a base 112, the optical fiber array 116 and semiconductor laser array 118 are covered with a fixing piece 124, and a heat dissipation fin 126 is provided on the lower surface side of the base 112. Each constituent component will be described below in detail.

[0231] FIG. 52 is a perspective view of the base 112. The base 112 is made of a metal having a high heat transfer rate, such as copper, or a ceramic and has an almost parallelepiped shape having a volume sufficiently larger than that of the platform 114, optical fiber array 116, semiconductor laser array 118, or LSI 120. A recessed platform mounting region 112afor mounting the platform 114, projecting LSI mounting region 112bfor mounting the LSI 120, and a recessed wiring board mounting region 112cfor mounting the wiring board 122 are formed on the upper surface of the base 112. A recessed portion 112dto fit on a projecting portion 124a(FIG. 50) of the fixing piece 124 is formed in the upper surface of the base 112. When the projecting portion 124aof the fixing piece 124 is fitted in the recessed portion 112d,the fixing piece 124 can be fixed to the base 112, and the semiconductor laser array 118 and the like can be packaged.

[0232] FIG. 53 is a perspective view of the optical fiber array 116 viewed from the upper surface side.

[0233] FIG. 54 is a perspective view of the optical fiber array 116 viewed from the lower surface side. The optical fiber array 116 has a structure in which 12 optical fibers 116bwith the same lengths are arrayed on a substrate 116ain parallel at equal intervals, and two pins 116cwith the same length are arranged outside the 12 optical fibers 116bso as to be parallel to the optical fibers 116b.More specifically, 12 optical fiber reception V-grooves extending from one side surface side to the other side surface side opposing the side surface are formed in the substrate 116ain parallel at equal intervals. Each of the 12 optical fibers 116bis inserted to a corresponding one of the optical fiber reception V-grooves and bonded. The length of the optical fibers 116bequals that of the optical fiber reception V-grooves. The optical fibers 116bare arrayed such that the two end portions become flush with the two side surfaces of the substrate 116a.Two pin reception grooves are formed in the substrate 116aso as to sandwich the optical fiber reception V-grooves. Each of the two pins 116cis inserted to a corresponding one of the pin reception grooves. The pins 116care longer than the pin reception grooves. Each pin 116cis arranged such that one end portion projects from the side surface of the substrate 116a.A glass plate having an opening at the center is placed on the optical fibers 116b.

[0234] As shown in FIG. 55, the semiconductor laser array 118 is constructed by sequentially stacking a cladding layer 118b,active layer 118c,and cladding layer 118d on a substrate 118aand forming an emitting surface 118eand reflection surface 118f,which oppose each other, in parallel to the stacking direction. At portions of the incident surface 118e,where the active layer 118cis located, 12 emission regions 118gare formed. At portions of the reflection surface 118f,where the active layer 118cis located, 12 reflection regions 118hare formed to oppose the 12 emission regions 118g,respectively. Hence, each of the reflection regions 118hand a corresponding one of the 12 emission regions 118gconstruct a laser resonator, and a laser beam is emitted from each of the 12 emission regions.

[0235] FIG. 56 is a perspective view of the platform 114. The platform 114 is made of silicon and has an almost flat plate shape. An optical fiber array mounting region 114afor mounting the optical fiber array 116, a semiconductor laser array mounting region 114bfor mounting the semiconductor laser array 118, and a linear groove portion 114cfor partitioning the optical fiber array mounting region 114aand the semiconductor laser array mounting region 114bare formed on one major surface (to be referred to as a mounting surface hereinafter) of the platform 114.

[0236] In the optical fiber array mounting region 114a,groove portions 114dand 114ewhere the optical fibers 116band two pins 116cof the optical fiber array 116 are to be arranged are formed perpendicular to the groove portion 114c.

[0237] In the semiconductor laser array mounting region 114b,printed interconnections 114ffor supplying a driving current to each of the 12 laser resonators of the semiconductor laser array 118 are formed. Especially, pad portions 114heach having a solder film 114gare formed at a portion immediately under the semiconductor laser array 118. Twelve groove portions 114iand 114jare formed at positions corresponding to the 12 emission regions 118gand 12 reflection regions 118hof the semiconductor laser array 118, respectively, in the semiconductor laser array mounting region 114b.More specifically, the 12 groove portions 114iextend, in the direction of laser beam emission, from portions corresponding to a portion immediately under the emission regions 118gwhen the semiconductor laser array 118 is mounted in the semiconductor laser array mounting region 114b.The 12 groove portions 114jextend, in the direction opposite to the laser beam emission direction, from portions corresponding to a portion immediately under the reflection regions 118hwhen the semiconductor laser array 118 is mounted in the semiconductor laser array mounting region 114b.The groove portions 114iand 114jcan be accurately formed by etching using photolithography.

[0238] When the optical fiber array 116 is mounted on the platform 114 such that the optical fibers 116band two pins 116care arranged in the groove portions 114dand 114e,and the semiconductor laser array 118 is mounted in correspondence with the pad portions 114h,the optical fiber array 116 and semiconductor laser array 118 are positioned, and light emitted from each of the 12 emission regions of the semiconductor laser array 118 can be made to directly (without being reflected) become incident from one end of a corresponding one of the 12 optical fibers 116band emerge from the other end. Consequently, each of the 12 emission regions of the semiconductor laser array 118 and a corresponding one of the 12 optical fibers 116bcan be optically coupled. In addition, the platform 114 is mounted in the platform mounting region 112aof the base 112. Hence, the optical fiber array 116 and semiconductor laser array 118 are mounted on the base 112 via the platform 114.

[0239] The LSI 120 incorporates a driving circuit for driving the semiconductor laser array 118. The LSI 120 and the plurality of laser resonators of the semiconductor laser array 118 are electrically connected by the printed interconnections 114fformed on the platform 114. Hence, the plurality of laser resonators of the semiconductor laser array 118 can be independently ON/OFF-controlled by a driving signal from the LSI 120. The LSI 120 is mounted in the LSI mounting region 112bof the base 112.

[0240] As shown in FIG. 57, in the wiring board 122, a plurality of pins 122care arranged around a substrate 122bhaving printed interconnections 122a.The pins 122cand LSI 120 are electrically connected through the printed interconnections 122a,and the LSI 120 can be externally controlled.

[0241] The heat dissipation fin 126 is formed from a metal having a high heat transfer rate, such as aluminum or copper, has a plurality of projecting portions formed on a flat plate having almost the same area as that of the base 112, and is in tight contact with the lower surface side of the base 112 (a surface on the opposite side of the surface having the platform 114 and the like), as shown in FIG. 50.

[0242] In the light-emitting module 110, the platform 114 and optical fiber array 116 are stacked to form an MT connector. An optical interface to an external optical transmission line is formed through this MT connector.

[0243] The function and effect of the light-emitting module according to this embodiment will be described next. In the light-emitting module 110 according to this embodiment, the groove portions 114iare formed in the mounting surface of the platform 114 at portions corresponding to the emission regions 118gof the semiconductor laser array 118. Hence, laser beams emitted from the emission regions 118gof the semiconductor laser array 118 and propagating while diverging in the direction of mounting surface of the platform 114 are not reflected by the mounting surface of the platform 114 and become incident on the groove portions 114iof the platform 114. Hence, reflection of the laser beams by the mounting surface is reduced. As a result, noise due to the reflected light decreases, and a light-emitting module free from noise is implemented.

[0244] Additionally, in the light-emitting module 110 according to this embodiment, the groove portions 114jare formed in the mounting surface of the platform 114 at portions corresponding to the reflection regions 118hof the semiconductor laser array 118. Hence, leakage light leaking from the reflection regions 118hof the semiconductor laser array 118 and propagating while spreading in the direction of mounting surface of the platform 114 is not reflected by the mounting surface of the platform 114 and becomes incident on the groove portions 114jof the platform 114. Hence, reflection of the leakage light by the mounting surface is reduced. As a result, noise due to the reflected light decreases, and a light-emitting module free from noise is implemented.

[0245] In the platform 114 of the light-emitting module 110 according to this embodiment, the 12 groove portions 114iare formed in correspondence with the 12 emission regions 118gof the semiconductor laser array 118, respectively. Instead, one integrated groove portion may be formed for the entire portion corresponding to the 12 emission regions 118gof the semiconductor laser array 118.

[0246] Similarly, in the platform 114 of the light-emitting module 110 according to this embodiment, the 12 groove portions 114jare formed in correspondence with the 12 reflection regions 118hof the semiconductor laser array 118, respectively. Instead, one integrated groove portion may be formed for the entire portion corresponding to the 12 reflection regions 118hof the semiconductor laser array 118.

[0247] A light-emitting module according to another embodiment of the present invention will be described next with reference to the accompanying drawings. In this embodiment, different platforms 214 and 232 are used in place of the platform 114 of the embodiment described with reference to FIGS. 50 to 57. The arrangement of the remaining parts is the same as in the above embodiment.

[0248] FIG. 58 is a perspective view of the platform 214. The platform 214 is formed from an insulating ceramic such as alumina ceramic and has an almost flat plate shape. An optical fiber array mounting region 214afor mounting an optical fiber array 116, a semiconductor laser array mounting region 214bfor mounting a semiconductor laser array 118, and a linear groove portion 214cfor partitioning the optical fiber array mounting region 214aand the semiconductor laser array mounting region 214bare formed on one major surface of the platform 214. In the optical fiber array mounting region 214a,groove portions 214dand 214ewhere optical fibers 116band two pins 116cof the optical fiber array 116 are to be arranged are formed perpendicular to the groove portion 214c.Hence, when the optical fiber array 116 is mounted on the platform 214 such that the optical fibers 116band two pins 116care arranged in the groove portions 214dand 214e,and the semiconductor laser array 118 is mounted such that the emitting surfaces are arranged along the edge of the groove portion 214c,the optical fiber array 116 and semiconductor laser array 118 are positioned, and light emitted from each of 12 light-emitting portions of the semiconductor laser array 118 can be made to directly (without being reflected) become incident from one end of a corresponding one of the 12 optical fibers 116band emerge from the other end. Consequently, each of the 12 light-emitting portions of the semiconductor laser array 118 and a corresponding one of the 12 optical fibers 116bcan be optically coupled. In addition, the platform 214 is mounted in a platform mounting region 112aof a base 112. Hence, the optical fiber array 116 and semiconductor laser array 118 are mounted on the base 112 via the platform 214. Printed interconnections 214f(to be described later) are formed on the upper surface of the platform 214.

[0249] An LSI 120 incorporates a driving circuit for driving the semiconductor laser array 118. The LSI 120 and the plurality of 1 light-emitting portions of the semiconductor laser array 118 are electrically connected by the printed interconnections 214fformed on the platform 214. Hence, the plurality of light-emitting portions of the semiconductor laser array 118 can be independently ON/OFF-controlled by a driving signal from the LSI 120. The LSI 120 is mounted in an LSI mounting region 112bof the base 112.

[0250] As shown in FIG. 57, in a wiring board 122, a plurality of pins 122care arranged around a substrate 122bhaving printed interconnections 122a.The pins 122cand LSI 120 are electrically connected through the printed interconnections 122a,and the LSI 120 can be externally controlled.

[0251] The heat dissipation fin 126 is formed from a metal having a high heat transfer rate, such as aluminum or copper, has a plurality of projecting portions formed on a flat plate having almost the same area as that of the base 112, and is in tight contact with the lower surface side of the base 112 (a surface on the opposite side of the surface having the platform 214 and the like), as shown in FIG. 50.

[0252] In the light-emitting module 110, the platform 214 and optical fiber array 116 are stacked to form an MT connector. An optical interface to an external optical transmission line is formed through this MT connector.

[0253] The function and effect of the light-emitting module according to this embodiment will be described next. In the light-emitting module 110 according to this embodiment, since the platform 214 is formed from an insulating ceramic, no insulating film need be formed between the printed interconnections 214fthe and platform 214, and a parasitic capacitance is prevented. As a consequence, operation errors due to such a parasitic capacitance are prevented. In addition, in the light-emitting module 110 according to this embodiment, since the platform 214 is formed from an insulating ceramic, the groove portions 214c,214d,and 214ecan be easily accurately formed on the platform 214. Hence, as compared to the platform 214 formed from silicon, the manufacturing cost does not increase, and the working accuracy does not lower, either.

[0254] The light-emitting module according to this embodiment has been described above. A light-receiving module can be constructed in almost the same way. More specifically, the semiconductor laser array 118 described with reference to FIG. 50 is replaced with a photodiode array 30 (light-receiving element array) for outputting an electrical signal corresponding to the light-receiving amount of each of 12 light-receiving portions, an amplification circuit for amplifying the electrical signal output from the photodiode array 30 is incorporated in the LSI 120, and the platform 214 is replaced with a platform 232 partially having a different shape, thereby constructing a light-receiving module according to an embodiment of the present invention. The differences from the light-emitting module 110 will be mainly described below in detail.

[0255] FIG. 59 is a perspective view of the platform 232 used for the light-receiving module. Like the platform 214, the platform 232 is formed from an insulating ceramic such as alumina ceramic and has an almost flat plate shape. An optical fiber array mounting region 232afor mounting an optical fiber array 116, a photodiode array mounting region 232bfor mounting the photodiode array 30, and a linear groove portion 232cfor partitioning the optical fiber array mounting region 232aand the photodiode array mounting region 232bare formed on one major surface of the platform 232. In the optical fiber array mounting region 232a,groove portions 232dand 232ewhere optical fibers 116band two pins 116cof the optical fiber array 116 are to be arranged are formed perpendicular to the groove portion 232c.The bottom surface of the groove portion 232dserves as the mounting surface for mounting the optical fiber array 116. Printed interconnections 232ffor electrically connecting the photodiode array 30 and an LSI 120 are formed on the upper surface of the platform 232. In addition, at a portion opposing the groove portion 232din the photodiode array mounting region 232b,a reflection surface 232gthat makes an angle of 45° with respect to the mounting surface is formed (detailed function will be described later).

[0256] FIG. 60 is a view showing a state wherein the optical fiber array 116 and photodiode array 30 are mounted on the platform 232. The optical fiber array 116 is mounted in the optical fiber array mounting region 232aof the platform 232. The photodiode array 30 is mounted in the photodiode array mounting region 232b.More specifically, the optical fiber array 116 is arranged such that the optical fibers 116bof the optical fiber array 116 are arranged on the mounting surface of the platform 232, and one end portion of each optical fiber 116bopposes the reflection surface 232g of the platform 232. The photodiode array 30 is arranged such that the light-receiving surface becomes parallel to the mounting surface and opposes the reflection surface 232gof the platform 232. Alignment is done such that each of the 12 light-receiving portions of the photodiode array 30 is optically coupled to a corresponding one of the 12 optical fibers 116bof the optical fiber array 116 via the reflection surface 232g.That is, light emerging from one end portion of each optical fiber 116bof the optical fiber array 116 is reflected by the reflection surface 232gof the platform 232 and becomes incident on a corresponding one of the 12 light-receiving portions of the photodiode array 30. Twelve lens portions 30aare monolithically formed on the light-receiving surface of the photodiode array 30 so as to efficiently receive light incident on the light-receiving surface of the photodiode array 30.

[0257] In the light-receiving module according to this embodiment as well, since the platform 232 is formed from an insulating ceramic, a parasitic capacitance is prevented, and consequently, noise due to such a parasitic capacitance is prevented.

[0258] In a silicon platform, it is relatively hard to form a reflection surface that makes an angle of 45° with respect to the mounting surface because of the problem of crystal surface. However, in the platform 232 made of a ceramic, the reflection surface that substantially makes an angle of 45° with respect to the mounting surface can be easily accurately formed. As a result, the light-receiving module according to this embodiment can easily improve the optical coupling efficiency between the optical fiber array 116 and the photodiode array 30.

[0259] In the light-emitting module 110 and light-receiving module according to the above embodiments, the platforms 214 and 232 are formed from alumina ceramic. Instead, an insulating ceramic such as zirconia ceramic, calcium titanate ceramic, silicon nitride ceramic, or aluminum nitride ceramic may be used.

[0260] Industrial Applicability

[0261] With the above-described arrangements, the present invention can provide a structure capable of easily realizing operation of optically coupling a plurality of optical fibers and a plurality of optical elements (light-receiving elements or light-emitting elements).

[0262] In the optical module substrate of the present invention, when a groove portion is formed in the mounting surface for mounting a laser array, at a portion corresponding to an emission region, reflection of a laser beam emitted from the emission region by the mounting surface is reduced. As a consequence, noise due to the reflected light is reduced, and a light-emitting module free from noise can be constructed.

[0263] In the optical module substrate of the present invention, when a groove portion is formed in the mounting surface for mounting a laser array, at a portion corresponding to a reflection region, reflection of leakage light leaking from the reflection region by the mounting surface is reduced. As a consequence, noise due to the reflected light is reduced, and a light-emitting module free from noise can be constructed.

[0264] In the light-emitting module of the present invention, when the above optical module substrate is used, reflection of a laser beam emitted from the emission region of the laser array by the mounting surface is reduced, or reflection of leakage light leaking from the reflection region of the laser array by the mounting surface is reduced. As a consequence, noise due to the reflected light can be reduced.

[0265] When the optical module substrate of the present invention is formed from an insulating ceramic, no insulating film need be formed between the optical module substrate and printed interconnections formed thereof, and a parasitic capacitance is prevented. As a result, operation errors of a light-emitting module having this optical module substrate are prevented, or noise in a light-receiving module having this optical module substrate is reduced.

[0266] When the optical module substrate of the present invention is formed from an insulating ceramic, a reflection surface that substantially makes an angle of 45° with respect to the mounting surface of the optical fiber array can be easily accurately formed, and the optical coupling efficiency between the light-receiving element array and the optical fiber array can be easily improved.

[0267] When the light-emitting module of the present invention has the optical module substrate formed from an insulating ceramic, a parasitic capacitance is prevented, and consequently, operation errors are prevented.

[0268] When the light-receiving module of the present invention has the optical module substrate formed from an insulating ceramic, a parasitic capacitance is prevented, and consequently, noise is reduced.