Optical semiconductor device and optical transceiver

Abstract

An optical semiconductor device according to the present disclosure comprises: a stem having a main surface and an annular wall part extending from the main surface; a pedestal part joined to the inner surface of the wall part; a semiconductor laser chip mounted on the pedestal part; a pattern provided on the pedestal part and electrically connected to the semiconductor laser chip; and a lead pin extending from a part of the main surface of the stem that is surrounded by the wall part and connected to the pattern by a wire.

Description

Optical semiconductor device and optical transceiver

[0001] The present disclosure relates to an optical semiconductor device and an optical transceiver.

[0002] Patent Document 1 discloses a semiconductor optical modulator. In this semiconductor optical modulator, a temperature control module and a first support block are mounted on a metal stem. A first dielectric substrate is mounted on the side of the first support block. A second support block is mounted on the cooling surface of the temperature control module. A second dielectric substrate is mounted on the side of the second support block, and a semiconductor optical modulator chip is mounted on the second dielectric substrate.

[0003] International Publication No. 2010 / 140473

[0004] For example, as shown in Patent Document 1, in a conventional CAN-type optical module, an EML (Electro-absorption Modulator Laser Diode) chip and a TEC (Thermoelectric Cooler) are bonded to the surface of a plate-shaped metal stem. The TEC is a thermo-module for maintaining a constant temperature of the EML chip. In this structure, the paths for heat dissipation from the inside of the CAN to the outside include the back surface of the stem, the side surface of the stem, and the side surface of the cap. However, an FPC (Flexible Printed Circuit) is generally connected to the back surface of the stem. This makes heat dissipation from the back surface of the stem difficult. In addition, because the stem is generally thin, approximately 1.3 mm, the side surface of the stem has high thermal resistance. Furthermore, because the side surface of the cap is generally far from the heat source and is thin, the thermal resistance is high. As a result, there is a risk that the amount of heat dissipation may be limited.

[0005] An object of the present disclosure is to provide an optical semiconductor device and an optical transceiver that can improve heat dissipation.

[0006] The optical semiconductor device according to the present disclosure comprises a stem having a main surface and an annular wall extending from the main surface, a base joined to an inner surface of the wall, a semiconductor laser chip mounted on the base, a pattern provided on the base and electrically connected to the semiconductor laser chip, and a lead pin extending from a portion of the main surface of the stem surrounded by the wall and connected to the pattern by a wire.

[0007] The optical semiconductor device according to the present disclosure comprises a stem having a main surface and an annular wall extending from the main surface, a base joined to the inner surface of the wall, and a semiconductor laser chip mounted on the base, wherein more than half of the base is housed in a recess formed by the main surface and the wall in a direction perpendicular to the main surface of the stem.

[0008] In the optical semiconductor device according to the present disclosure, the pedestal on which the semiconductor laser chip is mounted is bonded to the inner surface of the wall of the stem, thereby improving heat dissipation.

[0009] 10 is a perspective view of an optical semiconductor device according to a first embodiment. FIG. 11 is a front view of a semi-finished product according to the first embodiment. FIG. 12 is a perspective view of an optical semiconductor device according to a comparative example. FIG. 13 is a front view of an optical semiconductor device according to the first embodiment. FIG. 14 is a perspective view of an optical semiconductor device according to a second embodiment. FIG. 15 is a perspective view of an optical semiconductor device according to a third embodiment. FIG. 16 is a front view of a semi-finished product according to the third embodiment. FIG. 17 is an enlarged view of an optical semiconductor device according to the third embodiment. FIG. 18 is a front view of an optical semiconductor device according to the third embodiment. FIG. 19 is a perspective view of an optical semiconductor device according to a fourth embodiment. FIG. 19 is a diagram illustrating a bonding material according to a fifth embodiment. FIG. 19 is a front view of a semi-finished product according to a sixth embodiment. FIG. 19 is a diagram illustrating laser light without a collimating lens. FIG. 19 is a diagram illustrating laser light with a collimating lens. FIG. 19 is a perspective view schematically illustrating a configuration of an optical transceiver according to a seventh embodiment. FIG. 19 is a plan view schematically illustrating the configuration of an optical semiconductor device and a heat dissipation block according to the seventh embodiment.

[0010] An optical semiconductor device and an optical transceiver according to each embodiment will be described with reference to the drawings. The same or corresponding components are designated by the same reference numerals, and repeated description may be omitted.

[0011] 1 is a perspective view of an optical semiconductor device 100 according to a first embodiment. The optical semiconductor device 100 includes a stem 10, a semi-finished product 20 joined to the stem 10, and a plurality of lead pins 40. The stem 10 has a main surface 11 and an annular wall portion 12 extending from the main surface 11. A recess 14 is formed in the stem 10 by the main surface 11 and the wall portion 12. In other words, the stem 10 can also be said to be cup-shaped. The stem 10 is formed from a metal such as iron or SPC (Steel Plate Cold).

[0012] 2 is a front view of a semi-finished product 20 according to the first embodiment. The semi-finished product 20 includes a pedestal and a semiconductor laser chip 30 mounted on the pedestal. The pedestal includes, for example, a pedestal 21 and a thermo-module 22 provided on the pedestal 21 and mounting the semiconductor laser chip 30 thereon. The pedestal 21 is made of a ceramic such as aluminum nitride or alumina. The thermo-module 22 is, for example, a TEC. The pedestal 21 is bonded to the wall 12 of the stem 10. That is, the pedestal is bonded to the inner surface of the wall 12.

[0013] The thermo-module 22 further has mounted thereon a thermistor 25 and a submount 26. The semiconductor laser chip 30 is mounted on the thermo-module 22 via the submount 26. The semiconductor laser chip 30 is, for example, an EML chip.

[0014] 3 is a perspective view of an optical semiconductor device 800 according to a comparative example. In the optical semiconductor device 800, a thermo module 22 is mounted on a plate-shaped stem 810, and a carrier 870 is mounted on the cooling surface of the thermo module 22. A semiconductor laser chip 30 is mounted on the carrier 870. In the optical semiconductor device 800, the stem 810 is thin, about 1.3 mm thick. Therefore, the side surfaces of the stem 810 have high thermal resistance. Furthermore, as mentioned above, it is difficult to dissipate heat from the back surface of the stem 810 and the side surfaces of the cap.

[0015] In contrast, in this embodiment, the base 21 on which the semiconductor laser chip 30 is mounted is bonded to the inner surface of the wall 12 of the stem 10. This improves heat dissipation. Specifically, by providing the wall 12, a large heat dissipation area can be secured on the side surface of the stem 10, and a large contact area can also be secured between the stem 10 and the base 21. This reduces the thermal resistance of the path from the semiconductor laser chip 30, which is a heat-generating body, to the outside via the thermo module 22, thereby improving heat dissipation, particularly from the side surface of the stem 10. Furthermore, improved heat dissipation can reduce the power required to cool the optical semiconductor device 100.

[0016] It is preferable that the portion of the inner surface of the wall portion 12 to which the base 21 is joined is flat. It is also preferable that the portion 13 of the wall portion 12 of the stem 10 to which the base is joined is thicker than the other portions. This further improves heat dissipation. The recess 14 formed by the main surface 11 and the wall portion 12 of the stem 10 is, for example, D-shaped when viewed from a direction perpendicular to the main surface 11. It can also be said that the recess 14 has a shape like a wafer with an orientation flat. Such a stem 10 can be easily produced using a mold.

[0017] Returning to the explanation of Fig. 2, a pattern electrically connected to the semiconductor laser chip 30 is provided on the base. Specifically, patterns 23 and 28 are provided on the base 21, and a pattern 24 is provided on the thermo module 22. In the example of Fig. 2, the pattern 23 is electrically connected to the electrode of the semiconductor laser chip 30 by a wire 44. The patterns 23 and 28 are, for example, electrode patterns for DC lines, GND, etc. The pattern 24 is, for example, an electrode pattern for GND, etc.

[0018] A through via 27 is formed in the base 21. The surface of the base 21 on which the thermo module 22 is provided is electrically connected to the stem 10 via the through via 27. In other words, the pattern 28 on the surface of the base 21, which is electrically connected to the through via 27, is electrically connected to the stem 10, which is GND, by the through via 27. The pattern 28 and the pattern 24 on the surface of the thermo module 22 are connected by a wire 44. This strengthens the GND.

[0019] 1, a plurality of lead pins 40 extend from a portion of the main surface 11 of the stem 10 that is surrounded by the wall portion 12. The plurality of lead pins 40 penetrate the stem 10 to the back surface opposite the main surface 11. Each of the plurality of lead pins 40 is provided in a through hole that penetrates the stem 10 from the main surface 11 to the back surface. In the through hole, the space between the stem 10 and the lead pin 40 is filled with glass 42.

[0020] 4 is a front view of the optical semiconductor device 100 according to the first embodiment. Fig. 4 shows the optical semiconductor device 100 after capping, mainly showing the portion above the upper end of the stem 10. The pattern 23 and the plurality of lead pins 40 are connected by wires 44. The lead pins 40 and the base protrude beyond the wall 12 of the stem 10 in a direction perpendicular to the main surface 11 of the stem 10. Specifically, a portion of the base 21 on the cap 50 side by a length L1 protrudes beyond the wall 12.

[0021] In this embodiment, assembly can be performed by pre-assembling the semi-finished product 20 having the base 21, thermo module 22, thermistor 25, submount 26, and semiconductor laser chip 30, and then joining the semi-finished product 20 to the flat portion of the wall 12. At this time, the four sides of the portion of the base 21 that protrudes beyond the wall 12 of the stem 10 can be held with a pyramidal collet or the like and joined to the flat portion of the wall 12. Therefore, assembly can be easily performed.

[0022] In this embodiment, the portion of the pattern 23 that protrudes beyond the wall 12 and the portion of the lead pin 40 that protrudes beyond the wall 12 are connected by a wire 44. This allows the wire 44 to be driven from the front, i.e., from a direction perpendicular to the surface of the base 21, after the semi-finished product 20 is mounted on the stem 10, making assembly even easier.

[0023] The cap 50 is provided on the end face 12a of the wall 12 of the stem 10 opposite the main surface 11. The cap 50 covers the recess 14 formed by the main surface 11 and the wall 12. The cap 50 is a lens cap having a lens 51. After the cap 50 is mounted, X- and Y-axis adjustments are performed. The X- and Y-axes are, for example, axes parallel to the main surface 11, the X-axis is a direction along the surface of the thermo module 22, and the Y-axis is a direction perpendicular to the surface of the thermo module 22.

[0024] In this embodiment, in order to ensure a sufficient contact area between the stem 10 and the base, for example, more than half of the base may be housed in the recess 14 of the stem 10 in the direction perpendicular to the main surface 11 of the stem 10. In other words, if the length of the base 21 shown in Figure 2 is L0, then L0 / 2 > L1. However, if heat dissipation can be ensured, L0 / 2 ≤ L1 may be satisfied.

[0025] The shape of the stem 10 is not limited to that shown in FIG. 1, and may be any shape that allows the base portion to be joined to the inner surface of the wall portion 12.

[0026] The above-described modifications can be applied as appropriate to the optical semiconductor devices and optical transceivers according to the following embodiments. Note that the optical semiconductor devices and optical transceivers according to the following embodiments have many points in common with the first embodiment, so the following description will focus on the differences from the first embodiment.

[0027] Second Embodiment. FIG. 5 is a perspective view of an optical semiconductor device 200 according to a second embodiment. In this embodiment, the structure of the stem 210 differs from that of the first embodiment. In this embodiment, a portion of the wall 212 of the stem 210 to which the pedestal 21 is bonded protrudes in a direction perpendicular to the main surface 11 relative to the remaining portion. Specifically, the wall 212 of the stem 210 includes an annular wall 215 and a pedestal bond 216 provided to contact the inner surface of the annular wall 215. The height of the annular wall 215 from the main surface 11 is uniform. The pedestal bond 216 protrudes in a direction perpendicular to the main surface 11 relative to the annular wall 215, and the pedestal 21 is bonded to the pedestal bond 216. The stem 210 is a stem base made of a metal material, for example, a material with high thermal conductivity, such as Cu, plated with Au.

[0028] In this embodiment, the end surface 215a of the annular wall portion 215 opposite to the main surface 11 serves as the welding surface of the cap 50. The annular wall portion 215 and the pedestal joint portion 216 are formed as a single component. However, the annular wall portion 215 and the pedestal joint portion 216 may be separate components.

[0029] In this embodiment, the annular wall portion 215 is lower than the wall portion 12 in the first embodiment, increasing the amount of protrusion of the semi-finished product 20 from the annular wall portion 215. In other words, if the length of the portion of the base 21 that protrudes from the annular wall portion 215 is L2, then L2 > L1. Generally, in an EML-CAN bridging substrate, die bonding is performed by gripping three sides of the substrate with a pyramidal collet. In this embodiment, too, by increasing L2, the three sides 21a, 21b, and 21c of the base 21 can be gripped with a pyramidal collet or the like to die bond the semi-finished product 20. This facilitates assembly. For example, L0 / 2 < L2 may be satisfied.

[0030] However, because the annular wall portion 215 is lower than the wall portion 12 of the first embodiment, the heat dissipation performance of the present embodiment is inferior to that of the first embodiment. In the present embodiment, the heat dissipation performance may be improved by setting L0 / 2>L2. In the present embodiment, the entire surface of the pedestal 21 is in contact with the pedestal joint portion 216. Therefore, if the annular wall portion 215 is set to the same height as the wall portion 12, the heat dissipation performance of the present embodiment is higher than that of the first embodiment.

[0031] Embodiment 3. Figure 6 is a perspective view of an optical semiconductor device 300 according to embodiment 3. In this embodiment, the structure of the stem 310 differs from that of embodiment 1. The wall portion 312 of the stem 310 has an annular wall portion 315 and a pedestal joint portion 316 that is provided in contact with the inner surface of the annular wall portion 315 and to which the pedestal 21 is joined. The annular wall portion 315 and the pedestal joint portion 316 are separate components. In other words, the flat portion to which the pedestal 21 is joined is configured as a separate component. The pedestal joint portion 316 can be formed, for example, from the same material as the annular wall portion 315.

[0032] In this embodiment, the entire pedestal portion including the base 21 and the thermo module 22 is housed in the recess 14 formed by the main surface 11 and the wall portion 312. This can improve heat dissipation.

[0033] 7 is a front view of a semi-finished product 320 according to the third embodiment. In this embodiment, the semi-finished product 320 is made up of the base 21, the thermo-module 22, thermistor 25, submount 26, semiconductor laser chip 30, and base joint 316. By holding the upper surface 316a of the base joint 316 with a suction collet or the like, the semi-finished product 320 can be joined to the annular wall 315. This allows for easy assembly.

[0034] 6, the upper surface of the lead pin 40 and the upper surface of the base 21 can be connected by a wire 44. This improves the ease of assembly. To achieve such a wire connection, a pattern may be formed on the upper surface of the base 21.

[0035] 8 is an enlarged view of optical semiconductor device 300 according to embodiment 3. When joining semifinished product 320, semifinished product 320 is pressed in the Z-axis direction, i.e., in a direction perpendicular to main surface 11, to join main surface 11 and pedestal joint portion 316. When joining with solder, the solder may also wet and spread between pedestal joint portion 316 and annular wall portion 315.

[0036] 9 is a front view of an optical semiconductor device 300 according to a third embodiment. FIG. 9 shows the optical semiconductor device 300 after capping, mainly showing the portion above the upper end of the stem 310. In this embodiment, the end face 315a of the annular wall portion 315 opposite the main surface 11 serves as the welding surface for the cap 50. Unlike the first embodiment, in this embodiment, the semifinished product 320 does not protrude from the end face 315a of the stem 310, and is completely contained within. This allows the height of the cap 50 to be reduced.

[0037] In this embodiment, an example has been described in which the annular wall portion 315 and the pedestal joint portion 316 are separate components, but the annular wall portion 315 and the pedestal joint portion 316 may be formed as a single component.

[0038] Furthermore, from the viewpoint of equalizing the thermal characteristics, it is desirable that the material of the pedestal joint 316 and the pedestal joint 216 of the second embodiment be the same as that of the other parts of the stems 210, 310. If the pedestal joint is made of a different material, there is a risk that the position of the light-emitting point of the semiconductor laser chip 30 will fluctuate greatly due to changes in the shape of the parts when the ambient temperature changes, due to increased stress and differences in the amount of deformation between the parts. This may result in a deterioration in the optical coupling efficiency of the optical fiber 70 due to fluctuations in the focal position of the lens 51.

[0039] Fourth Embodiment Fig. 10 is a perspective view of an optical semiconductor device 400 according to a fourth embodiment. The optical semiconductor device 400 includes an RF (Radio Frequency) power supply lead pin 446. The RF power supply lead pin 446 is provided on a protrusion 417 formed on the main surface 11 of the stem 410. Note that a termination resistor and a capacitor for an LD (Laser Diode) are omitted from Fig. 10.

[0040] If the semiconductor laser chip 30 is an EML, it is necessary to add an RF feed line to the EA (Electro-Absorption) modulator. In this embodiment, an RF feed lead pin 446 is added to the center of the stem 410. In addition, an RF line 429 is provided on the submount 26. In this case, for good high-frequency characteristics, it is preferable that the RF feed lead pin 446 protruding from the glass 42 and the wire 44 connecting the RF feed lead pin 446 and the RF line 429 are short. In this embodiment, the provision of the protrusion 417 allows the RF feed lead pin 446 and the wire 44 connected to the RF feed lead pin 446 to be short.

[0041] In this embodiment, the wall portion 412 of the stem 410 includes, for example, an annular wall portion 415 and a pedestal joint portion 316 provided to contact the inner surface of the annular wall portion 415. The pedestal joint portion 316 protrudes from the annular wall portion 415 in a direction perpendicular to the main surface 11, and the pedestal 21 is joined to the pedestal 21. The annular wall portion 415 and the pedestal joint portion 316 are separate components. Therefore, similar to the third embodiment, the pedestal 21, the thermo-module 22, the thermistor 25, the submount 26, the semiconductor laser chip 30, and the pedestal joint portion 316 constitute a semi-finished product 320. The annular wall portion 415 and the pedestal joint portion 316 may be formed as a single component. Lowering the annular wall portion 415 makes it easier to connect the short wire 44 between the RF power supply lead pin 446 and the RF line 429.

[0042] 3 requires a carrier 870 and a bridging substrate 872 to shorten the RF power supply lead pin 45 and the wire. In contrast, in the present embodiment, the protrusion 417 allows the RF power supply lead pin 446 and the wire 44 connected to the RF power supply lead pin 446 to be shortened. This eliminates the need for the carrier 870 and the bridging substrate 872. This allows for a reduction in material costs.

[0043] The RF power supply lead pin 446 and the RF line 429 may be connected with a bonding material such as solder.

[0044] 11 is a diagram illustrating a bonding material 60 according to a fifth embodiment. In this embodiment, a fillet of the bonding material 60 is formed between the side surface of the base and the wall portion 12 of the stem 10. Specifically, a fillet of the bonding material 60 is formed between the side surface of the base 21 and the wall portion 12 of the stem 10.

[0045] By increasing the amount of bonding material 60 on the base 21 to form a fillet, the heat dissipation range is widened and the heat dissipation performance can be improved. This embodiment may be combined with any of the first to fourth embodiments.

[0046] 12 is a front view of a semi-finished product 520 according to a sixth embodiment. The optical semiconductor device 100 may further include a collimating lens 552 mounted on the base. The collimating lens 552 is provided, for example, in the semi-finished product 520 at a position where it can receive the laser light emitted by the semiconductor laser chip 30 on the thermo module 22.

[0047] 13 is a diagram illustrating the laser light 71 when there is no collimator lens 552. In this case, the optical semiconductor device 100 becomes a single-lens system with the lens 51, which is a condenser lens provided in the cap 50. In such a configuration, the components expand and contract due to the ambient temperature, which can cause a tracking error, in which the position of the light-emitting point of the semiconductor laser chip 30 shifts and the coupling efficiency to the optical fiber 70 decreases.

[0048] 14 is a diagram illustrating the laser light 72 when a collimating lens 552 is present. In this case, the optical semiconductor device 100 becomes a two-lens system consisting of the lens 51 and the collimating lens 552. In this case, the lens magnification is lower than in a single-lens system, and it is possible to reduce the decrease in coupling efficiency to the optical fiber 70 due to a shift in the position of the light-emitting point. Therefore, according to this embodiment, tracking errors can be suppressed. This embodiment may be combined with any of embodiments 1 to 5.

[0049] Seventh Embodiment. FIG. 15 is a perspective view illustrating a schematic configuration of an optical transceiver 1000 according to a seventh embodiment. The optical transceiver 1000 includes an optical semiconductor device 801, which is one of the optical semiconductor devices according to any one of the first to sixth embodiments. An integrated circuit for driving the optical semiconductor device 801 and the light-receiving device 805 is mounted on a substrate 903. The optical semiconductor device 801, the light-receiving device 805, and the substrate 903 are connected via a flexible printed circuit board 804. The optical semiconductor device 801 is equipped with a receptacle 600 for connecting to an optical fiber. The optical semiconductor device 801, the light-receiving device 805, and the substrate 903 are housed in a case 900 of the optical transceiver 1000. The case 900 is configured such that an upper housing 902 is attached to a lower housing 901.

[0050] In order to increase the amount of heat transfer between optical semiconductor device 801 and lower housing 901, it is desirable to attach heat dissipation block lower part 802 to optical semiconductor device 801, and to attach heat dissipation block lower part 802 to lower housing 901. In other words, heat dissipation block lower part 802 comes into contact with case 900 and wall part 12 of stem 10. For bonding between optical semiconductor device 801 and heat dissipation block lower part 802, and between heat dissipation block lower part 802 and lower housing 901, a highly thermally conductive insulator such as a sheet is used.

[0051] FIG. 16 is a plan view illustrating a schematic configuration of an optical semiconductor device 801 and a heat dissipation block according to the seventh embodiment. The heat dissipation block includes a lower heat dissipation block portion 802 and an upper heat dissipation block portion 803. The lower heat dissipation block portion 802 preferably has a semicircular structure that allows it to be fixed to the entire side surface of the stem 10. That is, the lower heat dissipation block portion 802 preferably has a semicircular notch formed therein that corresponds to the shape of the wall portion 12 of the stem 10. The lower heat dissipation block portion 802 contacts the wall portion 12 of the stem 10 at the semicircular notch. This ensures a large contact area between the stem 10 and the lower housing 901, improving the ability to radiate heat generated by the optical semiconductor device 801 to the outside of the optical transceiver 1000. This reduces power consumption.

[0052] The upper heat dissipation block 803 also comes into contact with the wall 12 of the stem 10. Like the lower heat dissipation block 802, the upper heat dissipation block 803 may have a semicircular structure that allows the stem 10 to be fixed along the entire length of its side surface. Furthermore, the upper heat dissipation block 803 has a fin-shaped portion, i.e., a portion that is machined into a fin shape. This allows for high heat dissipation from the entire periphery of the stem 10. This further improves the heat dissipation effect and reduces power consumption.

[0053] The technical features described in each embodiment may be used in appropriate combination.

[0054] REFERENCE SIGNS LIST 10 stem, 11 main surface, 12 wall portion, 12a end face, 13 portion to which pedestal portion is joined, 14 recess, 20 semi-finished product, 21 pedestal, 21a to 21c sides, 22 thermo module, 23 pattern, 24 pattern, 25 thermistor, 26 submount, 27 through via, 28 pattern, 30 semiconductor laser chip, 40 lead pin, 42 glass, 44 wire, 45 RF power supply lead pin, 50 cap, 51 lens, 60 bonding material, 70 optical fiber, 71 laser light, 72 laser light, 100 optical semiconductor device, 200 optical semiconductor device, 210 stem, 212 wall portion, 215 annular wall portion, 215a end face, 216 pedestal joining portion, 300 optical semiconductor device, 310 stem, 312 Wall portion, 315 Annular wall portion, 315a End surface, 316 Base joint portion, 316a Upper surface, 320 Semi-finished product, 400 Optical semiconductor device, 410 Stem, 412 Wall portion, 415 Annular wall portion, 417 Convex portion, 429 RF line, 446 RF power supply lead pin, 520 Semi-finished product, 552 Collimating lens, 800 Optical semiconductor device, 810 Stem, 870 Carrier, 872 Substrate, 600 Receptacle, 801 Optical semiconductor device, 802 Lower heat dissipation block, 803 Upper heat dissipation block, 804 Flexible printed circuit board, 805 Light receiving device, 900 Case, 901 Lower housing, 902 Upper housing, 903 Substrate, 1000 Optical transceiver

Claims

1. An optical semiconductor device comprising: a stem having a main surface and an annular wall extending from the main surface; a pedestal joined to an inner surface of the wall; a semiconductor laser chip mounted on the pedestal; a pattern provided on the pedestal and electrically connected to the semiconductor laser chip; and a lead pin extending from a portion of the main surface of the stem surrounded by the wall and connected to the pattern by a wire.

2. An optical semiconductor device comprising: a stem having a main surface and an annular wall extending from the main surface; a pedestal joined to the inner surface of the wall; and a semiconductor laser chip mounted on the pedestal, wherein more than half of the pedestal is contained in a recess formed by the main surface and the wall in a direction perpendicular to the main surface of the stem.

3. The optical semiconductor device according to claim 1 or 2, wherein the portion of the wall of the stem to which the base is joined is thicker than the other portions.

4. The optical semiconductor device according to claim 3, wherein the recess formed by the main surface and the wall of the stem is D-shaped when viewed from a direction perpendicular to the main surface.

5. The optical semiconductor device according to claim 1, wherein more than half of said base portion is housed in a recess formed by said main surface and said wall portion in a direction perpendicular to said main surface of said stem.

6. The optical semiconductor device according to claim 1, characterized in that the lead pin and the base protrude beyond the wall in a direction perpendicular to the main surface of the stem, and the portion of the pattern protruding beyond the wall and the portion of the lead pin protruding beyond the wall are connected by the wire.

7. The optical semiconductor device according to claim 1, wherein the portion of the wall of the stem to which the base is joined protrudes in a direction perpendicular to the main surface more than the remaining portion.

8. An optical semiconductor device as described in claim 7, characterized in that the wall portion of the stem has: an annular wall portion; and a base joint portion provided in contact with the inner surface of the annular wall portion, protruding beyond the annular wall portion in a direction perpendicular to the main surface, and to which the base portion is joined.

9. The optical semiconductor device according to claim 8, wherein said annular wall portion and said pedestal joint portion are formed as a single component.

10. The optical semiconductor device according to claim 8, wherein said annular wall portion and said base joint portion are separate components.

11. An optical semiconductor device as claimed in any one of claims 1 to 5, characterized in that the wall portion of the stem has: an annular wall portion; and a base joint portion provided in contact with the inner surface of the annular wall portion and to which the base portion is joined.

12. The optical semiconductor device according to claim 11, wherein the entirety of said base is housed in a recess formed by said main surface and said wall portion.

13. The optical semiconductor device according to claim 11 or 12, wherein the annular wall portion and the base joint portion are separate components.

14. An optical semiconductor device as claimed in any one of claims 1 to 13, further comprising an RF power supply lead pin, said RF power supply lead pin being provided on a protrusion formed on said main surface of said stem.

15. An optical semiconductor device as claimed in any one of claims 1 to 14, further comprising a cap provided on the end face of the wall portion of the stem opposite the main surface, the cap covering a recess formed by the main surface and the wall portion.

16. An optical semiconductor device as claimed in any one of claims 1 to 15, characterized in that the pedestal portion comprises: a pedestal joined to the wall portion of the stem; and a thermo module provided on the pedestal and mounting the semiconductor laser chip thereon.

17. The optical semiconductor device according to claim 16, wherein the surface of the base on which the thermo module is provided is electrically connected to the stem through a through via formed in the base.

18. An optical semiconductor device according to any one of claims 1 to 17, characterized in that a fillet of bonding material is formed between the side surface of the base and the wall portion of the stem.

19. The optical semiconductor device according to any one of claims 1 to 18, further comprising a collimating lens mounted on the base portion.

20. An optical transceiver comprising an optical semiconductor device according to any one of claims 1 to 19.

21. An optical transceiver as described in claim 20, comprising: a case for housing the optical semiconductor device and a substrate connected to the optical semiconductor device; and a first heat dissipation block in contact with the case and the wall of the stem, wherein the first heat dissipation block has a semicircular notch formed therein corresponding to the shape of the wall of the stem, and the first heat dissipation block contacts the wall of the stem at the notch.

22. The optical transceiver according to claim 20 or 21, further comprising a second heat dissipation block having a fin shape and in contact with the wall of the stem.

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