Electro-optic connector module

[0002] Connectors that join optical fibers to create a low loss, separable optical interface have been available and in use for a number of years. These connectors use a variety of ferrule types, alignment schemes and latching mechanisms for joining solitary strands of single-mode and multi-mode optical fiber as well as a multiplicity of fibers in a ribbon form. An example of the second is typified by the “MT” style array ferrules. Each of these connectors join the fibers end to end using a variety of alignment techniques. For single fiber joints, an alignment ferrule generally surrounds and guides the fiber-ends together.

[0003] One application of optical connector technology is to provide an optical path for signals from board to board, or shelf to shelf within equipment chassis. This optical path is provided by passing optical fibers perpendicularly through a backplane, using so-called “pass through”optical connectors. A right angle mounting of connectors join the optical fibers from an optical module on the daughtercard to optical fibers in cables running out of a card rack. This right angle mounting relies upon a blind mating of the fibers and must conform to standard cable management conventions such as minimum bend radius that contribute to box volume requirements behind the, backplane.

[0004] As the need for bandwidth capacity increases, “Optical Backplanes” usually in the form of laminated fiber matrices that overlay the backplane or that supplement the backplane are also being used. These optical backplanes, likewise have their fibers terminated to standard “pass through” optical connectors as previously described.

[0005] With the recent advent of Vertical Cavity Surface Emitting Laser (VCSEL) transceiver arrays however, an opportunity exists to launch into fibers perpendicularly to or from the daughtercards or other printed circuit boards within the subrack. Typically, standard separable alignment techniques used for multi-fiber arrays, are used to connect the fibers to the VCSELs.

[0006] The current implementations of “optical backplane” or intra-box optical connections suffer from both reliability and performance limitations. Depending on the particular alignment mechanism used and the quality of the assembly, optical power losses can occur at the connection that degrade the signal.

[0007] Alignment tolerances required for optical connections are on the order of micrometers. These tight tolerance are difficult to achieve in a blind-mate connection. In addition, if multiple fibers are blind-mate aligned by pins or posts, the alignment tolerance due to stack up is not the same for all fiber pairs. This can induce uneven losses across the fibers and create skew among the signals in the fiber array. Moreover, if the daughtercard and backplane remain slightly out of perpendicularity after mating, the fiber surfaces will be further out of alignment with each other, inducing further losses.

[0008] In optical interconnect design, it is very important to have control and statistical knowledge of the losses in the optical path. This is because the design of the optical link tries to optimize the balance between providing enough optical power to achieve link performance goals, while trying to meet eye safety, thermal and cost goals.

[0009] Another limitation of current implementations results from the environment typically encountered by the optical connectors. These connections are typically within an equipment rack and are not easily cleaned. Dust and dirt are oftentimes carried by cooling fans or other motion within the equipment rack. As a result, mate and de-mate cycles of the connectors can then accumulate this debris on the mating surfaces, thus reducing the coupling efficiency of the optical connection. Some optical connector suppliers provide hinged shutters on portions of their connectors to minimize the contamination issues however, some dirt and dust can still get through during handling. In addition, shutters can also make the fibers more difficult to reach when cleaning is required.

[0010] Yet another limitation results from the nature of the “pass through” optical interface onto the equipment backplane. A 90 degree turn by the optical fiber on the backplane is required. Current optical fiber technology requires the design to maintain a bend radius of greater than one inch to avoid optical loss and mechanical fatigue that can cause breakage. Fixtures that control the fiber bend radius are typically used. These fixtures gradually turn the fiber parallel to the backplane in order to plug to an overlay. Alternatively, fibers may be looped from one perpendicular “pass through” to another to effect slot to slot connectivity. Both of these options, however, consume considerable space behind the traditional electrical backplane while radius fixtures add additional cost to the system.

[0011] In addition, using standard separable alignment techniques to connect fibers to VCSELs encounter the same sort of alignment and dust concerns previously stated. Moreover, these methods also consume a certain amount of length in the fiber that can be difficult to fit between card slots on a standard backplane.

[0012] One solution described in the following disclosure provides an electro-optical connector including a routing substrate with an optical transceiver mounted on the routing substrate. An optical fiber is connected to the optical transceiver and means are provided on the routing substrate to electrically connect to a circuit board. With such an arrangement, blind-mates at the optical connection are avoided while the tight alignment tolerances required by optical connections can be performed in a factory setting using precise alignment techniques thus minimizing optical losses due to misalignment of the fiber ends. As a result, losses in the optical path may be better controlled by a system designer.

[0013] Another solution described in the following disclosure provides an apparatus for transferring a signal between an optical fiber and a circuit board. The apparatus includes an electro-optical module with an optical connection between the optical fiber and the electro-optical module. The apparatus further includes a separable, electrical connection between the electro-optical module and the circuit board and driver electronics electrically connected to the electro-optical module. With such an arrangement, mate and de-mate cycles of the apparatus are performed at the separable, electrical connection rather than at the optical connection between the fiber and the electro-optical module. As a result, optical losses suffered at the connector due to contamination introduced during mate and de-mate cycles are eliminated as are future misalignments at the optical connection due to wear and tear on the alignment features. Moreover, strict cleaning procedures typically required at optical connections are avoided.

[0014] A third solution described in the following disclosure provides an electro-optical system including first and second circuit boards and first and second electro-optical modules. A first separable, electrical interface is provided between the first circuit board and the first electro-optical module and a second separable, electrical interface is provided between the second circuit board and the second electro-optical module. The system further includes first and second driver electronics electrically connected to a respective first or second electro-optical module and an optical fiber connected between the first and second electro-optical modules. With such an arrangement, bends in the optical fiber are no longer required thus eliminating the need for fixtures controlling the bend radius. In addition, space taken up behind the traditional electrical backplane by radius fixtures and looping of fibers is also eliminated.

[0015] The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of an Electro-Optic Connector Module, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. For clarity and ease of description, the drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

[0016] FIG. 1 is a block diagram of an electro-optical connection according to an embodiment of the invention.

[0017] FIG. 2 is a pictorial representation of one embodiment of an electro-optical module.

[0018] FIG. 3 is a pictorial representation of an alternate embodiment of the electro-optical module.

[0019] FIG. 4 is a pictorial representation of an electro-optical connection system.

[0020] FIG. 5 is an exploded view of a general purpose z-axis pressure mount connector fixture.

[0021] FIG. 6 is a cross-sectional view of the connector fixture of FIG. 5

[0022] FIG. 7 is a cut-away view of the connector fixture of FIG. 6.

[0023] FIG. 8 is a pictorial representation of an alternate embodiment of a connector fixture used to mate the electro-optical module with a circuit board.

[0024] FIG. 9 is a cross-sectional view of the connector fixture of FIG. 7.

[0025] FIG. 10 is an exploded view of the connector fixture of FIG. 7 when used in conjunction with the electro-optical module of FIG. 2.

[0026] FIG. 11 is an exploded view of the connector fixture of FIG. 7 when used in conjunction-with the electro-optical module of FIG. 3.

[0027] FIG. 12 is a pictorial representation of an alternate embodiment for routing the optical fibers.

[0028] FIG. 13 is a pictorial representation of a connector fixture used in combination with the electro-optical module of FIG. 4.

[0029] The electro-optical connection 10 of FIG. 1 includes a circuit board 12, an electro-optical module 24 and an optical fiber or an array of optical fibers 22. The circuit board 12 and the electro-optical module 24 are connected through a separable, electrical connection 18. The electro-optical module 24 and the optical fiber 22 are connected through a semi-permanent optical connection 26.

[0030] The electro-optical module 24 is shown to include a routing substrate 14 and an optical interface 16. The routing substrate is connected to the optical interface 16 through a fixed connection 20.

[0031] In the configuration of FIG. 1, an electrical signal passes from a signal trace (not shown) within the circuit board 12 through the separable, electrical interface 18 to the electro-optical module 24. Within the electro-optical module 24, the electrical signal is passed from the routing substrate 14, through the fixed connection 20 to an optical interface 16. The optical interface 16 converts the electrical signal to an optical signal which is transferred to the optical fiber 22 through the semi-permanent optical connection 26. The electro-optical connection system 10 also operates in reverse wherein an optical signal traveling through the optical fiber 22 to the optical interface 16 is converted to an electrical signal. The electrical signal passes through the fixed connection 20 to the routing substrate 14 and through the separable, electrical interface 18 to a signal trace on the circuit board 12.

[0032] Generally, in an electro-optical connection system, the separable interface in the system is a mating between two optical fiber ends. Here, however, the separable interface is provided by an electrical connection, thus avoiding the problems encountered with fiber to fiber connections such as alignment issues and dust contamination. The semi-permanent connection between the optical fiber and the electro-optical module can be provided in a controlled factory setting allowing for better alignment and, when done in a dust free environment, minimal risks of contamination. The semi-permanent nature of the connection is generally provided to enable future servicing and repairs to the connection and/or components.

[0033] Referring now to FIG. 2, a pictorial representation of an electro-optical connection 30 between a circuit board 12 and an optical fiber 22a, 22bis shown to include one embodiment of the electro-optical module 24. Here, the circuit board 12 is functionally shown as a daughtercard. Here, the optical fiber is shown as an input/output fiber pair 22a, 22bhowever an optical fiber array can be substituted as well as any other desirable configuration of the optical fibers. Also shown is a backplane 29. The electro-optical module 24 is shown spaced from the daughtercard in a unmated position.

[0034] The electro-optical module 24 is shown to include a routing substrate 14 and an optical interface mounted on a front surface of the routing substrate 14. The optical fiber pair 22a, 22bis connected to the optical interface 16 by a semi-permanent optical connection 26. In this way, the electro-optical module 24 provides a means for launching into an optical fiber positioned perpendicular to the circuit board 12.

[0035] Referring also to FIG. 2A, the separable, electrical connection 18 is provided on a back surface of the routing substrate 14. The separable, electrical connection 18 is preferably provided by a z-axis, pressure mount connector. Here, the separable, electrical connection 18 is shown as an array of self-retained pressure connectors 34 located on the back surface of the routing substrate 14. These pressure connectors 34, an exemplary one shown in FIG. 2B, are small metallic structures which are pressed into plated through holes (not shown) in the routing substrate 14. Surface contacts 36a, 36b(FIG. 2B) contact pads (not shown) on the surface of circuit board 12. These multiple contact surfaces 36a, 36bprovide multiple points of contact with the circuit board 12 surface pads thus providing a reliable electrical contact.

[0036] One benefit of using these small pressure connectors 34 is that small contact pads can be used on the circuit board surface and further, small plated through holes or vias can be used on the routing substrate 14. The small dimensions of these features allow for the separable, electrical connection 18 between the circuit board 12 and the routing substrate 14 to be optimized for low electrical parasitics.

[0037] In an alternate embodiment, a so-called mezzanine or stacking connector configured to provide the desired electrical signal properties can be used as the separable, electrical connection 18 between the circuit board 12 and the routing substrate 14. These connectors typically provide an electrical connection between two parallel circuit board surfaces.

[0038] Referring back to FIG. 2, the optical interface 16 includes an optical transceiver (not shown) and an optical/mechanical connection between the optical transceiver and optical fiber pair 22a, 22b. Typically, the optical transceiver responds to an analog signal rather than a digital signal as is typically communicated through a circuit board. Here, to provide and/or interpret the analog signal, driver electronics 28 for the optical transceiver are mounted on the circuit board 12. Typically, these driver electronics 28 are digital to analog converters packaged in an Application Specific Integrated Circuit (ASIC). The driver electronics 28 convert a digital signal being passed through the signal trace on the circuit board 12 to an analog current which drives the optical transceiver and vice versa.

[0039] The mechanical connection between the optical fibers and the optical transceiver can generally be done in a controlled factory setting. Alignment of the fibers to the optical transceiver performed in a dust free environment eliminates contamination at the end of the fiber, thus minimizing optical losses. A permanent connection can be provided between the optical fibers and the optical transceiver or a semi-permanent optical connection 26 as described in conjunction with FIG. 1.

[0040] In a preferred embodiment, the optical transceiver is an array of VCSEL elements. A VCSEL converts between an analog electrical signal and an optical signal. In an alternate embodiment, other opto-electrical (O/E) sources may be used in conjunction with photo detectors to provide the optical transceiver component of the optical interface 16.

[0041] Referring now to FIG. 3, a pictorial representation of an electro-optical connection 40 between a circuit board 12 and an optical fiber is shown to include an alternate embodiment of the electro-optical module 24′.

[0042] The electro-optical module 24′ includes a routing substrate 14. Mounted on a back surface of the routing substrate is a separable, electrical connection 18. An optical interface 16 is mounted on the front surface of the routing substrate with the optical fiber pair 22a, 22bbeing connected to the optical interface 16 by a semi-permanent optical connection 26.

[0043] Here, further included in the electro-optical module 24′ are the driver electronics 28 for the optical source/driver which are mounted on the routing substrate 14. Mounting the driver electronics 28 on the routing substrate 14 frees up additional space on the daughtercard. In addition, it eases the transmission of the analog signals from the driver electronics to the optical source/driver.

[0044] In an alternate embodiment (not shown) the optical interface 16 can be mounted on the driver electronics 28 rather than on the routing substrate 14.

[0045] Referring now to FIG. 4, a pictorial representation of an electro-optical connection system 45 that provides an electro-optical connection between a first circuit board 12aand a second circuit board 12bis shown. Here, the electro-optical connection system 45 is shown to include two electro-optical modules 24a, 24b.

[0046] Included in the first electro-optical module 24ais a first routing substrate 14a. Mounted on the routing substrate 14ais a first optical interface 16alocated on a front surface and a second optical interface 16clocated on a lower back surface. Optical interfaces 16a, 16care provided on either side of the routing substrate 14ato enable the first circuit board 12 to communicate with circuit boards located on either side of the first circuit board 12 without requiring a bend in the optical fiber.

[0047] The first routing substrate 14aalso includes a separable, electrical connection 18aprovided on an upper back surface of the routing substrate 14a. Here, the separable, electrical connection 18ais shown as an array of self retained pressure connectors. The separable, electrical connection 18aprovides electrical contact between the electro-optical module 24aand the first circuit board 12a. The optical fiber pair 22a, 22bis connected to the optical interface 16aby a semi-permanent optical connection 26a. Mounted on the circuit board 12aare the driver electronics 28afor an optical transceiver included in the optical interface 16a.

[0048] A third optical interface 16bis connected at a distal end of the optical fiber pair 22a, 22bby a second semi-permanent optical connection 26b. The third optical interface 16bis mounted on a front surface of a second routing substrate 14b. A fourth optical interface 16dis mounted on a lower back surface of the second routing substrate 14bto enable the second circuit board 12bto communicate with another circuit board located on its other side. The second routing substrate 14bconnects to the second circuit board 12bthrough a separable, electrical interface 18b, also shown as an array of self retained pressure connectors, provided on an upper back surface of the routing substrate 14b. Mounted on the surface of the second circuit board 12bare the driver electronics 28bfor an optical transceiver included in the optical interface 16b.

[0049] In an alternate embodiment, the driver electronics 28a, 28bare mounted on their respective routing substrates 14a, 14brather than on the circuit boards 12a, 12b.

[0050] The electro-optical connection system 45 described above provides a solution to many of the problems faced by current electro-optical connection systems. Multiple mating cycles of traditional optical connectors degrade the performance of the connection and introduce, over time, additional signal losses into the system as guidance features aiding in the alignment between the two mating surfaces become worn. In addition, dirt and dust can become an increased contamination problem unless strict cleaning procedures are adhered to and even then, may still compound over time. Here, the wear and tear of multiple mate cycles are born by a separable, electrical connection 18 less susceptible to alignment issues and dirt and dust contamination. This system further eliminates the need to bend optical fibers perpendicularly to route them between daughtercards or adjacent backplanes thus eliminating significant volume associated with bend radius.

[0051] Referring now to FIG. 5, an exploded view of a general purpose, z-axis pressure mount connector fixture 75 is shown to include a circuit board receiving slot 51, an actuator 56, and a loading spring 54. The circuit board 12 engages an activation surface 62 when inserted into the receiving slot 51, causing the actuator to pivot around a pivot pin 52 included on the actuator 56. The pivoting action presses a face 53 against the loading spring 54, compressing the spring 54 thus, applying a perpendicular force against a first surface of a mezzanine board or daughtercard 70.

[0052] The perpendicular force applied by the loading spring 54 presses an opposing face of the mezzanine board 70 against a surface of the circuit board 12 thus engaging a z-axis pressure connector 71 with a corresponding mating surface.

[0053] For example, in one embodiment, the z-axis pressure connector 71 is an array of self-retained pressure connectors 34 (FIG. 2A). The corresponding mating surface is an array of pads located on the surface of the circuit board 12. The perpendicular force flattens the contact surfaces 36a, 36b(FIG. 2A) of each self-retained pressure connector 34 against a corresponding pad on the circuit board 12 thus providing an electrical connection between the mezzanine board 70 and the circuit board 12.

[0054] Referring now to FIG. 6, a cross-sectional view of the connector fixture 75 illustrates a preloaded position 58aof the actuator 56. Prior to insertion of the circuit board 12, the actuator 56 is in the preloaded position 58a. When the circuit board 12 is inserted into the slot 51 in the connector fixture, the circuit board 12 engages the actuator 56 causing the actuator 56 to rotate. The actuator 56 rotates around the pivot pin 52 until it locks into its loaded position 58b. In the loaded position 58b, a face 53 of the actuator 56 compresses the loading spring 54, thus applying a perpendicular force against the mezzanine board 70. The perpendicular force caused by the loading spring 54 causes the array of z-axis pressure connectors 71 to mate with a corresponding mating surface (not shown) on the circuit board 12.

[0055] Referring now to FIG. 7, a cut-away view of the connector fixture 50 exposes an actuator retract spring 60. The actuator retract spring 60 aids in rotating the actuator 56 back to its preloaded position 58awhen the circuit board 12 is removed. Specifically, when the circuit board 12 is removed from the slot 51, the actuator retract spring 60 exerts a force against the actuator 56 causing it to rotate in a clockwise direction until it comes to rest in its preloaded position 58a(FIG. 6).

[0056] Referring now to FIG. 8, a pictorial representation of an alternate embodiment of a connector fixture 50′ used to mate the electro-optical module 24 with the circuit board 12 is shown. The connector fixture 50′ is shown to include a channel 67 through which the optical fiber pair 22a, 22bpasses. The circuit board 12 is inserted into slot 51 in the connector fixture 50′. Once inserted, the actuator 56 (FIG. 5) within the body of the connector fixture pivots around the pivot pin 52 causing the loading spring to exert a force against the routing substrate 14 which, in turn, presses the routing substrate 14 against the circuit board 12.

[0057] Referring now to FIG. 9, a cross-sectional view of the connector fixture 50′ illustrates both a preloaded position 58aand a loaded position 58bof the actuator 56. Prior to insertion of the circuit board 12, the actuator 56 is in the preloaded position 58a. As the circuit board 12 is inserted into the slot 51 in the connector fixture, the circuit board 12 presses against an activation surface 62 on the actuator 56. The force against the activation surface 62 causes the actuator 56 to rotate, here, counter-clockwise around the pivot pin 52 until it locks into its loaded position 58b. In the loaded position 58b, a face 53 of the actuator 56 compresses the loading spring 54, thus applying a perpendicular force against the routing substrate 14. The perpendicular force caused by the loading spring 54 causes the array of self-retained pressure connectors 18 to mate with surface pads (not shown) on the circuit board 12.

[0058] Referring now to FIGS. 10 and 11 exploded views of the connector fixture are shown when used in conjunction with the electro-optical module 24 of FIG. 2 (FIG. 10) and with the electro-optical module 24′ of FIG. 3 (FIG. 11). In both FIGS. 10 and 11, the pivot pin 52 can be seen to extend across the length of the actuator 56 extending beyond each side face 55a, 55bof the actuator 56. These extended portions of the pivot pin 52 rest within grooves 64a, 64bin a bottom portion of the connector fixture body 49a. The top portion of the connector fixture body 49bincludes a similar groove 65a, (65bis not visible). The actuator 56 then rotates within these grooves 64a, 64b65a, 65baround the pivot pin 52. Also provided are wells 66 on each side of the bottom portion 49aof the connector fixture body to provide clearance for the actuator 56 as it rotates.

[0059] In the configuration of FIG. 10, the loading spring 54 presses against the routing substrate 14 when the actuator 56 is in the loaded position 58b(FIG. 8). In the configuration of FIG. 11 however, the loading spring 54 presses against the driver electronics package 28 when the actuator 56 is in the loaded position 58b(FIG. 8). An optional reinforcement plate (not shown) can also be used in conjunction with the loading spring 54 to protect the driver electronics package 28 from being damaged by the spring 54.

[0060] Referring now to FIG. 12 a pictorial representation of an alternate embodiment for routing the optical fiber pair 22a, 22bis shown. Here, the backplane 29 includes a backplane cutout 72 through which a routing substrate 74 extends. The optical interface 16 is mounted on the substrate 74 however here, the optical fibers are routed on a back side of the backplane 29. This embodiment enables easy maintenance from the back side of the backplane 29 and greater flexibility in routing the optical fibers.

[0061] For example, using the backplane cutout 72 configuration, routing of optical fibers need not be limited between adjacent daughtercards but rather may be extended between daughtercards that are not adjacent as intermediate daughtercards would not be an obstacle to the routing. Typically, a “daughtercard connector void” is provided where the optical fibers pass by the daughtercard. A “daughtercard connector void” is a location on the daughtercard where no connector is located providing a space between the edge of the daughtercard and the surface of the backplane. It is through this space that the optical fiber passes.

[0062] Referring now to FIG. 13, a pictorial representation of a connector fixture 50″ used in combination with the electro-optical module 24a(FIG. 4) is shown. The connector fixture 50″ is shown to include a second channel 76 through which a second optical fiber pair 22c, 22dpass. The second optical fiber pair 22c, 22dare semi-permanently connected to a second optical interface 16c(FIG. 4) located on a lower back surface of the first routing substrate 14a(FIG. 4).

[0063] While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.