Mechanism to make a heat sink in contact with a pluggable transceiver, a pluggable optical transceiver and a cage assembly providing the same

[0001] This application claims the benefit of U.S. provisional application No. 60/996,924, filed Dec. 11, 2007, which claims priority from Japanese application, JP2007-329668, filed on Dec. 21, 2007, which are both incorporated herein by reference in their entirety.

[0002] 1. Field of the Invention

[0003] The present invention relates to a mechanism to dissipate heat from a pluggable optical transceiver, in particular, the invention relates to a structure of a heat sink provided in a cage that receives the pluggable optical transceiver.

[0004] 2. Related Prior Art

[0005] An optical transceiver transmits and receives optical signals through an optical connector engaged therewith by using optically active devices, such as a semiconductor light-emitting device and a semiconductor light-receiving device. An optical transceiver generally has a body that houses a plurality of electronic components, electronic circuits and circuit boards, and also includes an optical receptacle that receives the optical connector. A hot-pluggable optical transceiver is a type of optical transceiver. Such a transceiver is inserted into or extracted from a cage. The cage is arranged on a host board to engage an electrical plug of the transceiver with an optical connector located in the far end of the cage without the need to turn off the power of the host system.

[0006] FIG. 6 schematically illustrates one type of the pluggable transceiver called an XFP. FIG. 6 illustrates a state where the XFP transceiver 3 is to be installed within the host board 1. Japanese Patent Application published as JP-2007-156461A discloses an XFP transceiver 3. As illustrated in FIG. 6, the host board 1 includes a bezel 1a and a metal cage 2 that exposes an opening 2a at the front end thereof with respect to the bezel 1a of the host board 1. The XFP transceiver 3 is inserted into or extracted from the opening 2a. The rear end of the transceiver 3 includes an electrical plug 4. The transceiver 3 may electrically communicate with the host board 1 by engaging this plug 4 with an optical connector 5 provided in the far end of the cage 2.

[0007] The top of the cage 2 provides a heat sink 6 to dissipate heat from the transceiver 3 set in the cage 2. A clip 7 fastens the heat sink with the cage 2. The contact surfaces of the transceiver 3 and the heat sink 6, such as the roughness of the top surface of the transceiver 3 and that of the bottom surface of the heat sink 6, influence the heat-dissipating efficiency.

[0008] Recent transmission speeds in optical communication systems exceed 10 Gbps and sometimes reach 100 Gbps. Such speeds inevitably accompany greater power consumption in electronic and optical devices. An effective heat-dissipating mechanism is always required. To obtain efficient heat conduction between solids, such as the contact surfaces between a housing of the transceiver and a heat sink of the cage, it may be necessary to increase the contact area and to make the contact surfaces as smooth as possible. However, the process to obtain such smooth surfaces is cost-ineffective. Further, outer dimensions of the transceiver, which are primarily defined by acceptable standards, do not permit the contact area to be optionally increased.

[0009] Another known method of securing effective thermal contact between metals includes placing a viscous paste or a resin sheet with less hardness between the contact surfaces. Although resin is inherently inferior in thermal conductivity, resin in a form of powder is applicable for merging metals or ceramics with good thermal conductivity by forming the resin in a thin sheet. Such thermo-conducting sheet merges metals or ceramics with good thermal conductivity. Such a thermo-conducting sheet, is applicable as a gap-filler. The thermo-conducting sheet may be placed between contact surfaces of two members rigidly fixed with respect to each other. The thermo-conducting sheet may remove air gaps and equivalently increase the contact area between the members. Accordingly, the thermo-conducting sheet may secure efficient heat transmission between members. However, it is insufficient for effective heat transmission to merely set the thermo-conducting sheet between the members. Additional actions in applying adequate pressure to the members is necessary for effective heat transmission.

[0010] In a conventional pluggable optical transceiver, heat-dissipation occurs only by the physical contact between the housing of the transceiver and the heat sink without any thermo-conducting sheet. In other cases where the heat generation in the transceiver is comparably less, the housing of the transceiver itself may perform the heat-dissipating function without coming in contact with the heat sink. However, recent pluggable optical transceivers increasingly generate more heat as the transmission speeds increase and the transmission distance increases. The increases in speed and distance inevitably require heat sinks and an effective heat-dissipating path from the transceiver to the heat sink.

[0011] As discussed, the pluggable optical transceiver, as its name indicates, is inserted into or extracted from the cage. Therefore, an arrangement that does not interfere with the insertion or the extraction of the transceiver is necessary for the thermal contact between the housing of the transceiver and the heat sink. When the transceiver is inserted into the cage, the heat sink provided in the cage must be apart from the housing until the transceiver is set in the intended position to secure smooth insertion. Embodiments of the present invention provide such a mechanism between the housing of the transceiver and the heat sink.

[0012] One aspect of the present invention relates to a mechanism to dissipate heat from a pluggable optical transceiver set in a cage to a heat sink assembled with the cage. Such heat dissipation may be through a thermo-conducting sheet placed between the optical transceiver and the heat sink. The mechanism includes at least a projection in a rear end of the optical transceiver, at least a rail with a pocket provided in the heat sink, and a mechanism, provided in the cage and the heat sink, to cause a downward force on the heat sink. In the present embodiment, the projection first lifts the heat sink upward against the downward force by running along the rail when the transceiver is inserted into the cage. The projection is finally set within the pocket to cause a thermo-conducting sheet to come in contact with the optical transceiver when the optical transceiver is set in a final position within the cage.

[0013] The mechanism of the invention enables the thermo-conducting sheet to be apart from the surface of the transceiver until the optical transceiver is set in its final position. This may prevent the thermo-conducting sheet from being scraped by the transceiver and peeled off. Moreover, because the downward force caused in the heat sink occurs at the final position of the transceiver, the effective heat-dissipating path may be secured from the optical transceiver to the heat sink.

[0014] Another aspect of the present invention relates to a pluggable optical transceiver to be set in a cage that provides a heat sink to dissipate heat from the optical transceiver through a thermo-conducting sheet. The heat sink is applied with a downward force from the cage when the cage is free from the transceiver and includes a first rail with a first pocket and a second rail with a second pocket. The optical transceiver includes a first projection and a second projection with a surface to come in contact with the thermo-conducting sheet. The second projection is not overlapped with the first projection in a direction along which the optical transceiver is inserted into the cage. The first projection first runs on the first rail of the heat sink to lift the heat sink upward when the transceiver is inserted into the cage. The first projection is set within the first pocket and the second projection is set within the second pocket such that the heat sink comes in contact with a surface of the transceiver by putting the thermo-conducting sheet there between when the optical transceiver is set in an intended position within the cage.

[0015] A third aspect of the present invention relates to a cage assembly for a pluggable optical transceiver. The cage assembly includes a cage and a heat sink. The cage provides an aperture in a top thereof and an elastic member to causing a downward force on the heat sink. The heat sink is provided with a thermo-conducting sheet and is exposed in the cage by the aperture of the cage. The heat sink is movable within the aperture in vertical direction, while unable to move substantially in a horizontal direction. The heat sink also provides a rail with a pocket in a surface where the thermo-conducting sheet is attached thereto. In the cage assembly according to this embodiment, a projection provided in the optical transceiver runs along the rail to lift the heat sink upward against the downward force when the optical transceiver is inserted into the cage. The pocket receives the projection to cause the thermo-conducting sheet to contact the optical transceiver when the transceiver is set in the intended position within the cage.

[0022] Next, embodiments according to the present invention are described in detail as referring to drawings. FIG. 1A is a perspective view schematically showing the heat-dissipating mechanism according to an embodiment of the invention, and FIG. 1B is a cross section of the heat-dissipating mechanism.

[0023] The fundamental structure of the heat-dissipating mechanism is similar to conventional mechanisms such as those shown in FIG. 6. Referring to FIG. 1A, the host system 10 provides a host board 11 where a metal cage 12 is arranged thereon. A pluggable optical transceiver 13 is inserted into or extracted from the cage 12. The host system 10 includes a bezel 11a. The front end of the cage 12 provides an opening 12a that is exposed from the bezel 11a to receiver the transceiver 13.

[0024] The cage 12 has a box shape with an aperture 12c in the top 12b thereof to expose a heat sink 15. The heat sink 15 is assembled with the cage 12 such that the heat sink 15 is movable in up and down directions. The cross section of the side rib 16 controls the up and down motion of the heat sink 15, as depicted in FIG. 1B. The side rib 16 cooperates with tabs 17 formed in the side 12d of the cage 12.

[0025] The optical transceiver 13 has a metal housing 14. When the transceiver 13 is set within the cage 12, the top 14a of the housing 14 comes in thermal contact with the heat sink 15. FIG. 1B also illustrates an electrical plug 24 in the rear end of the transceiver 13. This plug 24 is mated with the connector 22 arranged in the far end of the cage 12 to secure the communication with the host system 10. Such communication may include supply of electric power from the host system to the transceiver 13 and transmission of electrical signals between the transceiver 13 and the host system 10.

[0026] FIG. 1B illustrates a thermo-conducting sheet 18 arranged between a bottom 15a of the heat sink 15 and the top 14a of the housing 14 to secure a heat conducting path from the transceiver 13 to the heat sink 15. In FIG. 1B, the heat sink 15 includes the thermo-conducting sheet 18. In order to maintain the effective thermal conduction from the housing 14 to the heat sink 15 so that the effectiveness is not deteriorated, the thermo-conducting sheet 18 should be adhered to both the top 14a of the housing 14 and the bottom 15a of the heat sink 15. The thermo-conducting sheet 18 may be made of softened material with good thermal conductivity.

[0027] Specifically, the thermo-conducting sheet 18 may be made of resin such as silicone rubber, or may be made of a hybridized material of organic and inorganic material. Such material may contain, as a thermal conductive filler, metal powder of copper, aluminum, silver or stainless steel; or minute particles of oxide metal such as of aluminum oxide, titanium oxide or silicon oxide, nitride metal such as boron nitride, aluminum nitride, or chromium nitride; or other carbonized metal. The thickness of the thermo-conducting sheet 18 may be approximately from 0.3 to 1.0 mm. Such a thermo-conducting sheet may be easily available in the market.

[0028] The optical transceiver 13, as already described, is a type of pluggable transceiver which is insertable into and extractable from the cage 12. The transceiver 13 should not scrape off or not peel off the thermo-conducting sheet 18 at the insertion or the extraction. The transceiver 13 according to the present embodiment includes the projection 19 at both sides of the top 14a of the housing 14 and the heat sink 15 includes a rail 20 at both sides of the bottom 15a thereof that receives the projection 19. Both the projection 19 and the rail 20 are formed in respective surfaces to interfere with the thermo-conducting sheet 18.

[0029] The elastic tab 17 applies a downward force to the heat sink 15. When the transceiver 13 is inserted into the cage 12, the projection 19 lifts up the heat sink 15 against the downward force, as the projection 19 abuts against the bottom 15a of the heat sink 15. That is, the thermo-conducting sheet 18 may be at a distance from the top 14a of the housing 14 without being in contact until the transceiver 13 is set in the final intended position in the cage 12.

[0030] At the final position of the transceiver 13 in the cage 12, the rail 20 receives the projection 19, at which the heat sink 15 is pressed downward by the elastic force caused by the side tab 17, as denoted by the dotted line position in FIG. 1B. Thus, the bottom 15a of the heat sink 15 is pressed against the top 14a of the housing. Accordingly, the thermo-conducting sheet 18 is arranged between the heat sink 15 and the housing 14. The mechanism described above may secure the effective heat-dissipating path from the transceiver 13 to the heat sink 15 without scraping or peeling off the thermo-conducting sheet 18 between the housing 14 and the heat sink 15.

[0031] FIGS. 2A to 2D illustrate the projection 19 on the top 14a of the housing 14 and the rail 20 in the bottom 15a of the heat sink 15, respectively. FIGS. 2A and 2B are side and top views of the housing 14, respectively, while, FIGS. 2C and 2D are bottom and side views of the heat sink 15, respectively. The top 14a of the housing 14 includes two types of projections, 19a and 19b, each including front and rear slopes 19c. A distance between rear projections 19a is smaller than a distance between front projections 19b, as illustrated in FIG. 2B. That is, the rear projections 19a are positioned inwardly with respect to the front projection 19b, which are positioned outwardly with respect to a center longitudinal axis. The two projections, 19a and 19b, do not overlap with each other along the longitudinal direction of the transceiver 13. Moreover, the respective projections, 19a and 19b, have sloping sides in both longitudinal sides which facilitate the mating of the projections with the rail 20 of the heat sink 15.

[0032] The rail 20 on both, sides of the heat sink 15 provides two tracks, 20a and 20b. Each track receives a respective projection, 19a or 19b, of the housing 14. Here, only a center portion of the bottom 15a of the heat sink 15 includes the thermo-conducting sheet 18, and both side walls of the transceiver 13 include the side rib 16. The first inner track 20a receives the first projection 19a at the rear projection of the housing 14. The second outer track 20b, arranged outside of the first track 20a, receives the second projection 19b at the front projection. The rear end of the first track 20a includes the pocket 20d where the first projection 19a is set therein. The rear end of the second track 20b includes the second pocket 20e where the second projection 19b is set therein. The ends of respective tracks, 20a and 20b, provide a slope 20c to facilitate the slide of the projection, 19a or 19b, thereon.

[0033] FIGS. 3A to 3E schematically illustrate the mating mechanism between the projections, 19a and 19b, and the tracks, 20a and 20b. When the transceiver 13 is free from the cage 12, the heat sink 15 is pressed downward by the elastic tab 17 of the cage 12. Accordingly, it is necessary to lift the heat sink 15 upward against the downward force caused by the tab 17 when the transceiver 13 is inserted into the cage 12.

[0034] At the initial position of the transceiver 13 in the cage 12, as shown in FIG. 3A, the first projection 19a slides on the slope 20c in the front end of the first track 20a and slips there under. Thus, the first projection 19a abuts against the bottom 15a of the heat sink 15 to lift the front end of the heat sink 15 upward. Because the front end of the heat sink 15 is lifted upward, the insertion of the transceiver 13 into the cage 12 may be facilitated.

[0035] Subsequent to the initial position shown in FIG. 3A, the transceiver 13 is further pushed into the cage until the first projection 19a is in a midway in the cage 12 as shown in FIG. 3B. The other front projection 19b also comes in contact with the bottom 15a of the heat sink 15, which orients the heat sink 15 substantially horizontal.

[0036] FIG. 3C illustrates a status where the transceiver 13 is set in a position just before the final position. In FIG. 3C, the two projections, 19a and 19b, still come in contact with the respective tracks, 20a and 20b, and are not yet set within the pockets, 20d and 20e. By pushing the transceiver 13 slightly into the cage 12 past the position shown in FIG. 3C, only the first projection 19a is set within the first pocket 20d of the first track 20a, while, the front projection 19b is still left on the second track 20b. This position orients the heat sink 15 as inclined with the front end of the heat sink 15 lifted up again against the downward force caused by the elastic tab 17.

[0037] At the final position of the transceiver 13 in the cage 12, the second and front projection 19b is also set into the second pocket 20e. At this position, the thermo-conducting sheet 18 between the housing 14 and the heat sink 15 is pressed by the downward force of the heat sink 15 by the elastic tab 17. When the transceiver 13 is extracted from the cage 12, the mechanism described above may also operate to extract the transceiver from the heat sink 15.

[0038] That is, the second front projection 19b is first set on the second track 20b to lift the front end of the heat sink 15 upward against the downward force of the tab 17, as shown in FIG. 3D. Next, the first projection 19a, in addition to the second front projection 19b, is set on the first track 20a, which levels the heat sink 15 as shown in FIG. 3C. Finally, only the first projection 19a is left in contact with the heat sink 15.

[0039] Thus, according to the embodiment described above, the transceiver 13 may be inserted into or extracted from the cage 12 without touching the top 14a of the housing 14 to the thermo-conducting sheet 18 until the transceiver 13 is set in the final portion in the cage 12. At the final portion, the plug 24 mates with the connector 22. The thermo-conducting sheet 18 may be prevented from being scraped or peeled off by the transceiver 13. Similarly, when the transceiver 13 is extracted from the cage 12, the mechanism according to an embodiment of the invention first separates the thermo-conducting sheet 18 from the housing 14, and second extracts the transceiver 12 from the cage 13.

[0040] FIGS. 4A to 4C, and FIGS. 5A and 5B illustrate an arrangement to assemble the heat sink 15 with the cage 12 which enables a downward force to be applied to the heat sink 15. FIGS. 4A to 4C are cross sections taken along the longitudinal direction of the transceiver 13.

[0041] As explained above, the heat sink 15 is assembled with the cage 12 such that the top of the heat sink 15 includes a plurality of fins exposed through the aperture 12c of the cage 12. The plurality of fins are vertically movable but substantially unable to move horizontally. The front and rear edges defining the aperture 12c are bent downward and a tip of the bent portion extends inside the aperture 12c to form a tip tab 12e. The bottom corners of the front and rear ends of the heat sink 15 include a step hooked on the tip tab 12e. When the cage 12 is free from the transceiver 13, the heat sink 15 receives the downward force of the tab 17 in the side of the cage 12. The downward force may be compensated by the tip tab 12e. When the cage 12 receives the transceiver 13, the heat sink 15 is lifted upward by the projections, 19a and 19b, of the top 14a of the housing 14, as illustrated in the position shown by the dotted lines in FIGS. 4B and 4C.

[0042] FIGS. 5A and 5B show the side tab 17 of the cage 12 which causes the downward force on the heat sink 15. This side tab 17 is integrally formed with the cage 12 by cutting the cage 12 at several points in the sides defining the aperture 12c with a preset interval. The cut portions may be bent inward to form an arched cross section. The side rib 16 of the heat sink 15 in the upper surface thereof abuts against this arched side tab 17 which causes the downward force when the cage 12 is free from the transceiver 13. When the transceiver 13 is set within the cage 12, the heat sink 15 is lifted upward against the downward force applied to the upper surface of the side rib 16 by the arched tab 17.

[0043] While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.