JP5772466B2 - OPTICAL SEMICONDUCTOR DEVICE, OPTICAL TRANSMITTER MODULE, OPTICAL TRANSMISSION SYSTEM, AND OPTICAL SEMICONDUCTOR DEVICE MANUFACTURING METHOD - Google Patents

Description

  The present invention relates to an optical semiconductor element, an optical transmission module, an optical transmission system, and an optical semiconductor element manufacturing method.

  Conventionally, an optical semiconductor element such as a semiconductor laser has been used in communication.

  In response to the increase in communication volume accompanying the spread of the Internet and the like, an increase in communication speed and an increase in communication capacity in optical communication or optical transmission have been attempted.

  For example, it is required to transmit an optical fiber transmission system having a communication speed of 40 Gb / s or more, or 25 gigabits of data by bundling 4 waves by CWDM to a communication amount of 100 gigabits.

  It is expected that the generation of the optical signal for performing the communication described above is performed by direct modulation using a semiconductor laser operating in an uncooled state. An example of such a semiconductor laser is a distributed feedback laser (DFB laser).

  In order to perform direct modulation at a high frequency using a DFB laser, it is required that the relaxation oscillation frequency is high, which is the frequency of a current signal at which the response of light to the injected current sharply decreases. The relaxation oscillation frequency can be increased by reducing the volume of the active layer of the semiconductor laser. For example, some DFB lasers can be modulated at 40 Gb / s at room temperature by shortening the resonator length to 100 μm.

  Further, since the relaxation oscillation frequency is proportional to the square root of the differential gain of the DFB laser, the relaxation oscillation frequency can be increased by increasing the differential gain. Specifically, the differential gain is increased by adjusting the detuning, which is the difference between the gain peak wavelength at which the maximum gain of the active layer in the DFB laser is obtained and the oscillation wavelength, by changing the period of the diffraction grating. Things have been done.

JP 2010-157691 A Japanese Patent Application Laid-Open No. 11-135876 JP 2011-40632 A

K. Nakahara et al. , “High Extension Ratio Operation at 40-Gb / s Direct Modulation in 1.3-μm InGaAlAs-MQW RWG DFB Lasers”, OFC / NFOEC 2006, Lecture Number OWC5

  Here, when the operating temperature of the DFB laser changes, the oscillation wavelength and the gain peak wavelength also change. In the DFB laser, the temperature change coefficient of the gain peak wavelength is larger than the temperature change coefficient of the oscillation wavelength.

  Therefore, when the operating temperature of the DFB laser changes, the above-mentioned detuning changes, so that there arises a problem that the relaxation oscillation frequency changes with temperature.

  In this specification, in order to solve the above-described problem, an object of the present invention is to provide an optical semiconductor element in which a change in relaxation oscillation frequency with temperature is small.

  Another object of the present specification is to provide an optical transmission module including an optical semiconductor element in which a change in relaxation oscillation frequency due to temperature is small in order to solve the above-described problem.

  Another object of the present specification is to provide an optical transmission system including an optical transmission module having an optical semiconductor element in which a change in relaxation oscillation frequency due to temperature is small in order to solve the above-described problem.

  Furthermore, in this specification, in order to solve the above-mentioned problem, it aims at providing the manufacturing method of the optical semiconductor element with a small change with the temperature of a relaxation oscillation frequency.

  According to one mode of the optical semiconductor element disclosed in the present specification, the optical semiconductor device includes a mesa portion having an active layer and a buried layer that embeds the mesa portion, and the buried layer has a temperature change in the refractive index of the active layer. A refractive index adjustment region having a temperature change coefficient of a refractive index larger than a coefficient and a refractive index larger than the refractive index of the active layer, wherein the refractive index adjustment region is in the height direction of the buried layer In the above, the active layer is disposed at a position at least partially overlapping.

  In addition, according to one mode of the optical transmission module disclosed in the present specification, the optical transmission module includes a mesa portion having an active layer and a buried layer that embeds the mesa portion, and the buried layer has a refractive index of the active layer. A refractive index adjustment region having a refractive index adjustment region having a refractive index greater than the refractive index of the active layer, and having a refractive index adjustment region greater than the refractive index of the active layer. An optical semiconductor element disposed at a position at least partially overlapping the active layer in the vertical direction, and a drive unit that supplies current to the active layer, wherein the optical semiconductor element emits light toward the optical fiber. Is sent out.

  Further, according to one mode of the optical transmission system disclosed in the present specification, the optical transmission system includes a mesa portion having an active layer and a buried layer that embeds the mesa portion, and the buried layer has a refractive index of the active layer. A refractive index adjustment region having a refractive index adjustment region having a refractive index greater than the refractive index of the active layer, and having a refractive index adjustment region greater than the refractive index of the active layer. An optical transmission module having an optical semiconductor element disposed at a position at least partially overlapping the active layer in the vertical direction, and a drive unit that supplies current to the optical semiconductor element, and is transmitted from the optical transmission module And an optical receiving module for receiving light from the optical fiber.

  Furthermore, according to one mode of the method for manufacturing an optical semiconductor element disclosed in the present specification, a step of forming a mesa portion having an active layer on a substrate and a step of forming a buried layer so as to bury the mesa portion. The buried layer has a refractive index adjustment region having a temperature change coefficient of a refractive index larger than that of the active layer and having a refractive index larger than that of the active layer. And forming a buried layer so that the refractive index adjustment region is disposed at a position at least partially overlapping the active layer in the height direction of the buried layer.

  According to one mode of the optical semiconductor element disclosed in the present specification described above, changes in relaxation oscillation frequency due to temperature are reduced.

  Moreover, according to one form of the optical transmission module disclosed in the present specification described above, changes in relaxation oscillation frequency due to temperature are reduced.

  Moreover, according to one form of the optical transmission system disclosed in the present specification described above, changes in relaxation oscillation frequency due to temperature are reduced.

  Furthermore, according to one embodiment of the method for manufacturing an optical semiconductor element disclosed in the present specification, it is possible to manufacture an optical semiconductor element in which a change in relaxation oscillation frequency due to temperature is small.

  The objects and advantages of the invention will be realized and obtained by means of the elements and combinations particularly pointed out in the appended claims.

  Both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention as claimed.

1 is a diagram illustrating a first embodiment of an optical semiconductor device disclosed in this specification. FIG. It is the X1-X1 sectional view taken on the line of FIG. (A) is a figure which shows the electric field distribution of the waveguide mode which propagates the optical semiconductor element of FIG. 1, (B) is the electric field distribution of the waveguide mode which propagates the optical semiconductor element which does not have a refractive index adjustment area | region. FIG. It is a figure which shows the electric field distribution of the light in the near field and far field of an optical semiconductor element. It is a figure which shows the modification of the optical semiconductor element of 1st Embodiment. It is a figure which shows 2nd Embodiment of the optical semiconductor element disclosed to this specification. It is the X2-X2 sectional view taken on the line of FIG. 1 is a diagram illustrating an embodiment of an optical transmission system disclosed in this specification. FIG. It is a figure which shows the process (the 1) of 1st Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 2) of 1st Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 3) of 1st Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 4) of 1st Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 5) of 1st Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 6) of 1st Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 7) of 1st Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 8) of 1st Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 1) of 2nd Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 2) of 2nd Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 3) of 2nd Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 4) of 2nd Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 5) of 2nd Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 6) of 2nd Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 7) of 2nd Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 8) of 2nd Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 9) of 2nd Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 10) of 2nd Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 11) of 2nd Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification. It is a figure which shows the process (the 12) of 2nd Embodiment of the manufacturing method of the optical semiconductor element disclosed to this specification.

  Hereinafter, after further describing the problem to be solved in the present specification, the form of the optical semiconductor element disclosed in the present specification will be described in detail.

  First, problems to be solved in this specification will be described below.

  As described above, when the relaxation oscillation frequency of the DFB laser is increased by using detuning, generally, the oscillation wavelength of the laser is arranged on the shorter wavelength side than the gain peak wavelength to increase the differential gain. For example, the oscillation wavelength is arranged on the short wavelength side about 10 to 20 nm with respect to the gain peak wavelength.

  The oscillation wavelength or gain peak wavelength of the laser varies depending on the refractive index of the material that affects the optical path length. This refractive index varies with the temperature of the material. Therefore, the oscillation wavelength or gain peak wavelength of the laser also changes due to a change in refractive index accompanying a change in operating temperature. For example, in the case of a DFB laser formed using an InP-based compound semiconductor, the temperature change coefficient of the oscillation wavelength is about 0.08 nm / K, and the temperature change coefficient of the gain peak wavelength is about 0.42 nm. / K.

  For example, it is assumed that the operating temperature range of the DFB laser is 25 ° C. to 85 ° C. In this case, when the operating temperature changes from 25 ° C. on the low temperature side to 85 ° C. on the high temperature side, the temperature change amount of the gain peak wavelength is about 25.2 nm, whereas the temperature change amount of the oscillation wavelength is about 4%. .8 nm.

  The above detuning is set at any temperature within the operating temperature range of the DFB laser. Here, when the detuning is set at an operating temperature on the low temperature side of 25 ° C., the detuning is larger than the value of 25 ° C. in the DFB laser that has become high temperature in the uncooled operation. As a result, the absolute value of the gain decreases as the differential gain decreases, and the relaxation oscillation frequency may decrease as the laser output decreases.

  On the other hand, when the detuning is set at an operating temperature on the high temperature side of 85 ° C., the oscillation wavelength may shift to a longer wavelength side than the gain peak wavelength in the DFB laser that has become low temperature in the uncooled operation. . As a result, the differential gain decreases and the relaxation oscillation frequency decreases.

  Therefore, in order to prevent a change in relaxation oscillation frequency due to a change in operating temperature, it is preferable that the temperature change coefficient of the laser oscillation wavelength and the temperature change coefficient of the gain peak wavelength are close to each other. That is, it is preferable that the temperature change coefficient of the refractive index of the element portion that determines the oscillation wavelength is close to the temperature change coefficient of the refractive index of the element portion that determines the gain peak wavelength.

  Here, the temperature change coefficient of the refractive index at the gain peak wavelength is mainly determined by the material for forming the active layer in which gain is generated. Therefore, to change the temperature change coefficient of the refractive index, the material for forming the active layer is changed. It may be difficult to do so.

  Therefore, the present specification aims to reduce the change in relaxation oscillation frequency due to temperature by bringing the temperature change coefficient of the oscillation wavelength closer to the temperature change coefficient of the gain peak wavelength.

  Hereinafter, a preferred first embodiment of an optical semiconductor device disclosed in this specification will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and equivalents thereof.

  FIG. 1 is a diagram showing a first embodiment of an optical semiconductor device disclosed in this specification. 2 is a cross-sectional view taken along line X1-X1 of FIG.

  The optical semiconductor element 10 of this embodiment is a distributed feedback semiconductor laser. The optical semiconductor element 10 includes a mesa unit 20 formed on the substrate 11 and a buried layer 30 that embeds both sides of the mesa unit 20. The mesa unit 20 is vertically long, and the buried layer 30 is disposed along the longitudinal direction of the mesa unit 20 so as to cover the side surface of the mesa unit 20. Further, non-reflective layers may be disposed on both sides of the optical semiconductor element 10 in the longitudinal direction. Here, the longitudinal direction of the optical semiconductor element 10 coincides with the longitudinal direction of the mesa unit 20.

  First, the mesa unit 20 will be described below.

  The mesa unit 20 includes a diffraction grating layer 21 formed on the substrate 11, a guide layer 22 disposed on the diffraction grating layer 21, an etching stopper layer 23 disposed on the guide layer 21, and the etching stopper layer 23. And an active layer 24 disposed on the substrate.

  The active layer 25 oscillates when a current is injected. The period of the diffraction grating of the diffraction grating layer 21 determines the oscillation wavelength. A phase shift 21 a is arranged at the center in the longitudinal direction of the diffraction grating layer 21. The guide layer 22 has a refractive index lower than that of the active layer 25.

  The mesa unit 20 includes a first cladding layer 25 disposed on the active layer 24, a second cladding layer 26 disposed on the first cladding layer 25, and a contact disposed on the second cladding layer 26. Layer 27. The first electrode 13 is disposed on the contact layer 27, and the second electrode 14 is disposed under the substrate 11.

  The resistivity of the second cladding layer 26 is lower than that of the first cladding layer 25, and the current from the first electrode 13 is injected into the active layer 24 through the first cladding layer 25.

  As the active layer 25, a quantum well structure or a bulk structure can be used. As a material for forming the active layer 25, a compound semiconductor or the like can be used.

  Next, the buried layer 30 will be described below.

  The buried layer 30 is preferably electrically semi-insulating or insulating and serves to inject current into the active layer 24.

The buried layer 30 includes a current blocking layer 31 that covers the side surface of the mesa unit 20 and the substrate 11. The current blocking layer 31 is preferably a semi-insulator or an insulator. The resistivity of the current blocking layer 31 is, for example, in the range of 1 × 10 ⁶ to 1 × 10 ⁸ Ωcm in the case of a semi-insulator, and more than 1 × 10 ⁸ Ωcm in the case of an electrical insulator. In particular, it is preferably larger than 1 × 10 ¹⁰ Ωcm in order to prevent a current flow from the mesa portion 20 to the buried layer 30.

  The buried layer 30 includes a lower buried region 32, a refractive index adjusting region 33, and an upper buried region 34. Each region is sequentially stacked on the substrate 11 via the current blocking layer 31.

  The passivation layer 12 is disposed on the upper embedded region 34 so as to straddle the mesa portion 20.

  The refractive index adjustment region 33 has a refractive index temperature change coefficient larger than the refractive index temperature change coefficient of the active layer 24 and has a refractive index larger than the refractive index of the active layer 24. Further, at least a part of the refractive index adjustment region 33 is disposed at a position overlapping the active layer 24 in the height direction of the buried layer 30. Here, the height direction of the buried layer 30 coincides with the direction in which the lower buried region 32, the refractive index adjusting region 33, and the upper buried region 34 are stacked.

  The lower buried region 32 and the upper buried region 34 are preferably electrically semi-insulating or insulating. Further, the refractive index of the lower buried region 32 and the upper buried region 34 is smaller than the refractive index of the active layer 24, which means that the waveguide mode electric field propagating through the optical semiconductor element 10 spreads to the buried layer 30 side. It is preferable in preventing.

  The refractive index adjustment region 33 is a part of the element portion including the active layer 24 that determines the oscillation wavelength in the optical semiconductor element 10, and increases the temperature change coefficient of the refractive index of the element portion that determines the oscillation wavelength. The element portion that determines the oscillation wavelength is a region in which a waveguide mode electric field propagating through the optical semiconductor device 10 is distributed. In this region, the diffraction grating layer 21 to the second cladding layer 26 of the mesa unit 20 are included. A portion of the buried layer 30 is included. Since the refractive index of each layer is not necessarily the same, the refractive index of the element portion that determines the oscillation wavelength means the equivalent refractive index of the region where the electric field of the waveguide mode is distributed. Therefore, the temperature change coefficient of the refractive index of the element portion that determines the oscillation wavelength means the temperature change coefficient of the equivalent refractive index of the region where the electric field of the waveguide mode is distributed. When the active layer 24 has a quantum well structure, the refractive index of the active layer 24 is an equivalent refractive index of a region composed of a well layer and a barrier layer.

  FIG. 3A is a diagram showing an electric field distribution of a waveguide mode propagating through the optical semiconductor element of FIG. FIG. 3A shows the distribution of the electric field strength E in the width direction of the optical semiconductor element 10. Here, the width direction of the optical semiconductor element 10 coincides with the width direction of the mesa unit 20, and the width direction of the mesa unit 20 is a direction orthogonal to the longitudinal direction of the mesa unit 20. Further, in the mesa portion 20 of FIG. 3A, constituent elements other than the active layer 24 are not shown.

  The electric field in the waveguide mode is distributed more in the mesa portion 20 particularly in the active layer 24, but a part is also distributed in the buried layer 30 portions on both sides of the mesa portion 20.

  Since the refractive index adjustment region 33 arranged in the buried layer 30 has a refractive index larger than that of the active layer 24, it induces that the electric field in the waveguide mode spreads toward the buried layer 30, and the electric field is refracted. Many are distributed in the rate adjustment region 33.

  Further, in the optical semiconductor element 10, the refractive index adjustment region 33 is disposed at a position that coincides with the active layer 24 in the height direction of the buried layer 30, and an electric field extends from the active layer 24 side to the refractive index adjustment region 33 side. Is easy to spread.

  The refractive index adjustment region 33 has a refractive index temperature variation coefficient larger than the refractive index temperature variation coefficient of the active layer 24, so that the equivalent refractive index temperature variation coefficient of the region where the electric field of the waveguide mode is distributed is set. Increase.

  In this way, the optical semiconductor element 10 induces the spread of light into the refractive index adjustment region 33 and effectively increases the temperature change coefficient of the equivalent refractive index in the region where the electric field of the waveguide mode is distributed. .

  FIG. 3B is a diagram illustrating an electric field distribution of a waveguide mode that propagates through an optical semiconductor element that does not have a refractive index adjustment region. In the optical semiconductor element shown in FIG. 3B, the buried layer has no buried refractive index adjustment region, and has a buried layer 300 having a smaller refractive index than the active layer.

  As shown in FIG. 3A, the optical semiconductor element 10 has an amount of electric field spreading from the mesa portion 20 to the buried layer side due to the presence of the refractive index adjustment region 33 having a large refractive index. It is bigger than the case.

  The oscillation wavelength λ of the optical semiconductor element 10 is represented by λ = 2 × neq × Λ. Here, neq is the equivalent refractive index of the region where the electric field of the waveguide mode is distributed, and Λ is the period of the diffraction grating of the diffraction grating layer 21. In the optical semiconductor element 10, since the temperature change coefficient of the equivalent refractive index neq is large, the temperature change coefficient of the oscillation wavelength is also large. As a result, the temperature change coefficient of the oscillation wavelength approaches the temperature change coefficient of the gain peak wavelength.

  As described above, in the optical semiconductor element 10, the refractive index of the refractive index adjustment region 33 is made larger than the refractive index of the active layer 24 in order to broaden the electric field distribution. Therefore, the resistivity of the refractive index adjustment region 33 may be lower than that of the active layer 24. Therefore, in the optical semiconductor element 10, the above-described current blocking layer 31 is disposed between the refractive index adjustment region 33 and the mesa unit 20, so that the refractive index adjustment region 33 and the mesa unit 20 do not come into contact with each other. Is prevented from flowing from the mesa unit 20 to the refractive index adjustment region 33.

  Thus, from the viewpoint of preventing current from flowing from the mesa unit 20 to the refractive index adjustment region 33, the thickness of the current blocking layer 31 is preferably 500 nm or more.

  On the other hand, the distance between the refractive index adjustment region 33 and the mesa unit 20 is preferably short in order to induce the spread of light from the mesa unit 20 to the refractive index adjustment region 33 side. From this viewpoint, the thickness of the current blocking layer 31 is preferably 0.2 μm or less.

  Next, specific examples of materials for forming the active layer 24 and the refractive index adjustment region 33 will be described below.

  When the active layer 24 is formed of a III-V group compound, the refractive index adjustment region 33 uses indium / antimony (InSb), gallium / antimony (GaSb), aluminum / antimony (AlSb), or a mixed crystal thereof. It is preferable to be formed.

The active layer 24 may be formed using InP, InAs, or GaAs which is a III-V group compound. The refractive index of InP is 3.2@1310 nm, 3.17@1550 nm. Further, the temperature change coefficient of the refractive index of InP is ^{8.64 × 10 -5 /K@1310nm,8.56×10 -5 / K} @ 1550nm. The refractive index of InAs is 4.19@1310 nm, 3.98@1550 nm. Further, the temperature change coefficient of the refractive index of InAs is ^{37.74 × 10 -5 /K@1310nm,35.80×10 -5 / K} @ 1550nm. The refractive index of GaAs is 3.41@1310 nm, 3.38@1550 nm. Further, the temperature change coefficient of the refractive index of GaAs is ^{15.34 × 10 -5 /K@1310nm,15.20×10 -5 / K} @ 1550nm.

The refractive index of indium antimony is 4.13@1310 nm, 4.08@1550 nm. Further, the temperature change coefficient of the refractive index of the indium antimonide is ^{66.08 × 10 -5 /K@1310nm,65.28×10 -5 / K} @ 1550nm. The refractive index of gallium antimony is 3.88@1310 nm and 3.86@1550 nm. Further, the temperature change coefficient of the refractive index of gallium antimonide is ^{37.64 × 10 -5 /K@1310nm,37.44×10 -5 / K} @ 1550nm.

  The refractive index adjustment region 33 may have a crystal structure, but may have a polycrystalline or amorphous structure. For example, the refractive index adjustment region 33 may be formed of an amorphous dielectric. The refractive index adjustment region 33 having a crystal structure can be formed using a metal organic chemical vapor deposition method (MOVPE method). The refractive index adjustment region 33 having a polycrystalline or amorphous structure can be formed using a CVD or PVD method.

  Similarly, the current blocking layer 31 or the lower buried region 32 or the upper buried region 34 may have a crystal structure, but may have a polycrystalline or amorphous structure.

  As described above, when the refractive index adjustment region 33 is arranged in the buried layer 30, when the equivalent refractive index of the element portion that determines the oscillation wavelength increases, the equivalent refractive index of the element portion that determines the gain peak wavelength also affects. Receive and grow. However, since the gain peak wavelength is shifted by the same amount as the oscillation wavelength, the refractive index adjustment region 33 does not change the relative wavelength relationship between the gain peak wavelength and the oscillation wavelength.

  FIG. 4 is a diagram showing the electric field distribution of light in the near field and the far field of the optical semiconductor element.

  In FIG. 4, the near-field electric field distribution P <b> 1 in the optical semiconductor element 10 and the far-field electric field distribution Q <b> 1 in which light is transmitted to free space are indicated by solid lines. Also, in FIG. 4, the near-field electric field distribution P2 and the far-field electric field distribution Q2 in the optical semiconductor element shown in FIG. 3B are indicated by chain lines.

  As described with reference to FIG. 3, the optical semiconductor element 10 has a large spread of the electric field distribution of the waveguide mode propagating in the near field, so that the light in the far field transmitted from the optical semiconductor element 10 to the free space is transmitted. On the contrary, the expansion of the electric field strength of the above becomes small.

  As shown in FIG. 4, in the optical semiconductor element 10, the spread of the electric field distribution of light in the far field becomes narrower than in the case of FIG. Accordingly, when the light transmitted from the optical semiconductor element 10 is transmitted through an optical fiber, the spread of the electric field distribution of the light in the far field is narrow, so that the light transmitted from the optical semiconductor element 10 is coupled with the optical fiber. Will improve.

  According to the above-described optical semiconductor device of the present embodiment, the temperature change coefficient of the oscillation wavelength approaches the temperature change coefficient of the gain peak wavelength, so that changes due to the temperature of the relaxation oscillation frequency can be reduced.

  In addition, since the change in relaxation oscillation frequency due to temperature is small, detuning can be easily set in consideration of changes in oscillation wavelength and gain peak wavelength accompanying temperature change.

  Next, a modified example of the above-described optical semiconductor device of the first embodiment will be described below with reference to the drawings.

  FIG. 5 is a view showing a modified example of the optical semiconductor element of the first embodiment.

  In the optical semiconductor device 10 of this modification, the buried layer 30 does not have a current block layer, but has a buried region 35 in which the current block layer, the lower buried region, and the upper buried region are integrated. This is different from the first embodiment described above.

  The embedded region 35 is disposed so as to sandwich the refractive index adjustment region 33 and cover the side surface of the mesa unit 20 from above the substrate 11.

  A part of the buried region 35 is disposed between the refractive index adjustment region 33 and the mesa unit 20, and the refractive index adjustment region 33 and the mesa unit 20 are prevented from coming into contact with each other.

  The optical semiconductor element 10 of this modification is obtained, for example, by forming the current blocking layer, the lower buried region, and the upper buried region using the same material in the first embodiment.

  Next, a second embodiment of the above-described optical semiconductor element will be described below with reference to FIGS. For points that are not particularly described in the second embodiment, the description in detail regarding the first embodiment is applied as appropriate. Moreover, the same code | symbol is attached | subjected to the same component.

  FIG. 6 is a diagram illustrating a second embodiment of the optical semiconductor element disclosed in this specification. 7 is a cross-sectional view taken along line X2-X2 of FIG.

  The optical semiconductor element 10 of this embodiment is a distributed reflection type semiconductor laser. In the optical semiconductor device 10 of the present embodiment, the relaxation gain frequency is increased by increasing the differential gain by making the volume of the active layer 24 smaller than that of the first embodiment. Specifically, the dimension in the longitudinal direction of the mesa unit 20 is shorter than that in the first embodiment.

  However, if the length of the active layer 24 in the longitudinal direction is shortened, the laser oscillation current threshold value may increase or oscillation may become unstable. Thus, in the present embodiment, the distributed reflection regions are arranged on both sides in the longitudinal direction of the mesa unit 20 to prevent the occurrence of problems by shortening the longitudinal dimension of the active layer 24.

  As shown in FIG. 7, the optical semiconductor element 10 includes a front distributed reflection region 10a, an active region 10b where the active layer 24 is disposed, and a rear distributed reflection region 10c.

  The active region 10b has a mesa portion 20 and a buried layer 30 portion, and has the same structure as the above-described optical semiconductor device of the first embodiment. However, the diffraction grating layer 21 in the active region 10b does not have a phase shift.

  The forward distributed reflection region 10a is different in the structure of the mesa portion 20 from the active region 10b, and has a core layer 28 that does not generate a gain instead of the active layer. The core layer 28 propagates light generated in the active layer 24. A third cladding layer 29 is disposed on the core layer 28. The substrate 11, the diffraction grating layer 21, the guide layer 22, the etching stopper layer 23, the second cladding layer 26, and the contact layer 27 are formed integrally with the active region 10b.

  On the other hand, the structure of the portion of the buried layer 30 in the front distributed reflection region 10a is the same as that of the active region 10b and is formed integrally with the active region 10b. In the buried layer 30, the refractive index adjustment region 33 is disposed at a position that coincides with the active layer 24 or the core layer 28 in the height direction.

  The rear distribution reflection region 10c has the same structure as the front distribution reflection region 10a. The size of the rear distribution reflection region 10c is longer than that of the front distribution reflection region 10a.

  In the optical semiconductor element 10, the first electrode 13 and the second electrode 14 are arranged at the position of the active region 10b in the longitudinal direction so that current is injected into the active region 10b. The light oscillated in the active region 10b is reflected by the front distributed reflection region 10a or the rear distributed reflection region 10c and returned to the active region 10b.

  According to the above-described optical semiconductor element 10 of the present embodiment, the relaxation oscillation frequency is increased while the change of the relaxation oscillation frequency due to temperature is reduced.

  Next, an optical transmission module having the optical semiconductor element disclosed in this specification and an optical transmission system including such an optical transmission module will be described below with reference to the drawings.

  FIG. 8 is a diagram illustrating an embodiment of an optical transmission system disclosed in this specification.

  The optical transmission system 40 of this embodiment includes an optical transmission module 50, an optical fiber 41 that propagates light transmitted from the optical transmission module 50, and an optical reception module 60 that receives light from the optical fiber 41.

  The optical transmission module 50 includes a semiconductor laser 51 that is the optical semiconductor device of the first embodiment or the second embodiment described above, a drive unit 52 that supplies current to the active layer of the optical semiconductor device 51, and a semiconductor laser 51 that emits light. And a lens 53 that couples the laser beam to the optical fiber 41.

  The optical transmission module 50 also includes an isolator 54 that prevents the reflected light from the optical fiber 41 from entering the semiconductor laser 51, and a monitor unit 55 that monitors the laser oscillation of the semiconductor laser 51.

  The optical transmission module 50 transmits an optical signal generated by direct modulation by the uncooled operation of the semiconductor laser 51 to the optical fiber 41.

  The optical receiver module 60 includes an optical receiver 61, a lens 63 that couples laser light transmitted from the optical fiber 41 to the optical receiver 61, and a drive unit 62 that drives the optical receiver 61.

  In the example shown in FIG. 8, a pair of optical transmission modules 50 and optical reception modules 60 are described, but the optical transmission system 40 may include a plurality of pairs of optical transmission modules 50 and optical reception modules 60. .

  According to the optical transmission system 40 of the present embodiment described above, since the optical transmission module 50 includes the semiconductor laser 51 in which the change of the relaxation oscillation frequency due to the temperature is small, in the uncooled operation, stable by direct modulation up to a high frequency range Transmitted light is possible.

  Next, a preferred embodiment of the above-described method for manufacturing an optical semiconductor device will be described below with reference to the drawings. This embodiment is an example of a method for manufacturing the optical semiconductor element shown in FIGS.

  First, as shown in FIG. 9, a mask 70 for forming a diffraction grating layer is formed on the substrate 11. In the present embodiment, an n-type doped InP substrate is used as the substrate 11. An electron beam exposure method was used to form the mask 70. The mask 70 has a length of 150 μm, and a mask portion 70 a for forming a phase shift of π radians (corresponding to λ / 4 shift) is provided at the center in the longitudinal direction. The period of the diffraction grating was 199.505 nm.

  Next, as shown in FIG. 10, the diffraction grating layer 21 is formed by etching the substrate 11 halfway using a mask 70. A phase shift 21 a is formed at the center in the longitudinal direction of the diffraction grating layer 21. In this embodiment, reactive ion etching (RIE) using an ethane / hydrogen mixed gas is used. The depth of the diffraction grating was 100 nm. Then, the mask 70 is removed.

  Next, as shown in FIG. 11, the guide layer 22, the etching stopper layer 23, the active layer 24, the first cladding layer 25, the second cladding layer 26, and the contact layer 27 include the diffraction grating layer 21. Formed in order on top. In this embodiment, each layer was formed using the MOVPE method. The guide layer 22 was formed using n-type doped GaInAsP, and had a composition wavelength of 1.20 μm and a thickness of 120 nm. The etching stopper layer 23 was formed using n-type doped InP and had a thickness of 20 nm. Note that the etching stopper layer 23 may not be formed.

  As the active layer 25, a quantum well structure was used. The quantum well structure was formed using an undoped AlGaInAs well layer and an undoped AlGaInAs barrier layer. Here, the undoped AlGaInAs well layer had a thickness of 6 nm and a compressive strain of 1.2%. The undoped AlGaInAs barrier layer had a composition wavelength of 1.05 μm and a thickness of 10 nm. The number of stacked quantum well structures was 15, and the emission wavelength (oscillation wavelength) was 1310 nm.

  In addition, an undoped AlGaInAs-SCH (Separate Composition Heterostructure) layer was provided above and below the quantum well structure so as to sandwich the quantum well structure. Here, the undoped AlGaInAs-SCH layer had a composition wavelength of 1.05 μm and a thickness of 20 nm.

  The first cladding layer 25 on the active layer 24 was formed using p-type doped InP and had a thickness of 250 nm. The second cladding layer 26 was formed using p-type InP doped with Zn and had a thickness of 2.5 μm. The contact layer 27 was formed using p-type GaInAs doped with Zn and had a thickness of 300 nm.

Next, as shown in FIG. 12, a striped mask 71 for forming a mesa portion is formed on the contact layer 27 over the entire length of the element. In the present embodiment, the mask 71 is formed by using a chemical vapor deposition (CVD) method and a photolithography technique. The mask 71 was formed using SiO ₂ and had a width of 1.3 μm and a thickness of 400 nm.

  Next, as shown in FIG. 13, using the mask 71, the mesa portion 20 is formed by etching from the portion of the contact layer 27 where the mask is not formed to the middle of the substrate 11 by etching. In the present embodiment, the substrate 11 is removed from the surface to a depth of 0.7 μm.

  Next, as shown in FIG. 14, the current blocking layer 31 is formed on the side surface of the mesa unit 20 and on the substrate 11. In the present embodiment, the current blocking layer 31 is formed using the MOVPE method. The current blocking layer 31 was formed using undoped AlInAs having semi-insulating properties, and the thickness was 0.2 μm.

  Next, as shown in FIG. 15, the lower buried region 32, the refractive index adjustment region 33, and the upper buried region 34 are sequentially stacked on the substrate 11 through the current blocking layer 31, and the buried layer 30 It is formed. The refractive index adjustment region 33 is formed so as to be disposed at a position overlapping the active layer 24 in the height direction of the buried layer 30, specifically at a position matching the active layer 24. In this embodiment, each layer was formed using the MOVPE method. The lower buried region 32 was formed using undoped InP and had a thickness of 0.5 μm. The refractive index adjustment region 33 was formed using undoped InSb and had a thickness of 0.25 μm. The upper buried region 34 was formed using undoped InP and had a thickness of 3.0 μm. Then, the mask 71 is removed.

Next, as shown in FIG. 16, the passivation layer 12 is formed on the mesa portion 20 and the buried layer 30. In the present embodiment, the passivation layer 12 is formed using SiO ₂ .

  Then, the first electrode 13 is formed after the portion of the passivation layer 12 where the first electrode is to be formed is removed using a normal lithography technique and etching technique. A second electrode 14 is formed below the substrate 11.

  Then, non-reflective layers 15a and 15b are formed on both surfaces of the element in the longitudinal direction, and the manufacture of the optical semiconductor element 10 is completed.

In the optical semiconductor element 10 formed as described above, the refractive index of the active layer 24 was 3.49, and the temperature change coefficient of the refractive index was 32 × 10 ⁻⁵ K ⁻¹ . The equivalent refractive index of the active layer 24, the etching stopper layer 23, and the first cladding layer 25 was 3.32, and the temperature change coefficient of the refractive index was 21.6 × 10 ⁻⁵ K ⁻¹ . The refractive index of the refractive index adjustment region 33 was 4.13, and the temperature change coefficient of the refractive index was 66.1 × 10 ⁻⁵ K ⁻¹ . The equivalent refractive index of the refractive index adjustment region 33, the lower embedded region 32, and the upper embedded region 34 was 3.29, and the temperature change coefficient of the refractive index was 60.8 × 10 ⁻⁵ K ⁻¹ .

  Further, in the optical semiconductor element 10, the temperature change coefficient of the oscillation wavelength increased 2.25 times compared to the case where the refractive index adjustment region was not disposed in the buried layer.

  Next, a second embodiment of a preferable method for manufacturing the above-described optical semiconductor element will be described below with reference to the drawings. This embodiment is an example of a method for manufacturing the optical semiconductor element shown in FIGS.

  First, as shown in FIG. 17, a mask 72 for forming a diffraction grating layer is formed on the substrate 11. In the present embodiment, an n-type doped InP substrate is used as the substrate 11. A two-beam interference exposure method was used to form the mask 72. In the future, the length of the portion 11a of the substrate 11 serving as the front distributed reflection region is set to 25 μm, the length of the portion 11b of the substrate 11 serving as the active region is set to 100 μm, and the length of the portion 11c of the substrate 11 serving as the rear distributed reflection region. Was 75 μm. The period of the diffraction grating was the same in the portions 11a, 11b, and 11c, and was 236.055 nm.

  Next, as shown in FIG. 18, the diffraction grating layer 21 is formed by etching the substrate 11 halfway using a mask 72. In this embodiment, reactive ion etching (RIE) using an ethane / hydrogen mixed gas is used. The depth of the diffraction grating was 100 nm. Then, the mask 72 is removed.

  Next, as shown in FIG. 19, a guide layer 22, an etching stopper layer 23, an active layer 24, and a first cladding layer 25 are formed in order on the diffraction grating layer 21. In this embodiment, each layer was formed using the MOVPE method. The guide layer 22 was formed using n-type doped GaInAsP, and had a composition wavelength of 1.20 μm and a thickness of 120 nm. The etching stopper layer 23 was formed using n-type doped InP and had a thickness of 20 nm.

  As the active layer 25, a quantum well structure was used. The quantum well structure was formed using an undoped GaInAsP well layer and an undoped GaInAsP barrier layer. Here, the undoped GaInAsP well layer had a thickness of 5.1 nm and a compressive strain of 1.2%. The undoped GaInAsP barrier layer had a composition wavelength of 1.20 μm and a thickness of 10 nm. The number of stacked quantum well structures was 15, and the emission wavelength (oscillation wavelength) was 1550 nm.

  In addition, an undoped GaInAsP-SCH (Separate Composition Heterostructure) layer was provided above and below the quantum well structure so as to sandwich the quantum well structure. Here, the undoped GaInAsP-SCH layer had a composition wavelength of 1.15 μm and a thickness of 20 nm. The first cladding layer 25 on the active layer 24 was formed using p-type doped InP and had a thickness of 250 nm.

Next, as shown in FIG. 20, a mask 73 is formed on the first cladding layer 25 of the portion 11b of the substrate 11 that will become an active region in the future. In the present embodiment, the mask 73 is formed using a chemical vapor deposition (CVD) method and a photolithography technique. The mask 71 was formed using SiO ₂ and had a width of 400 nm. In the future, no mask is formed in the region of the first cladding layer 25 of the portions 11a and 11b of the substrate 11 that will be the front distributed reflection region and the rear distributed reflection region.

  Next, as shown in FIG. 21, using the mask 73, the first cladding layer 25 and the active layer 24 where the mask is not formed are removed by etching, and the etching stopper layer 23 is exposed.

Next, as shown in FIG. 22, the core layer 28 and the third cladding layer 29 are sequentially formed on the exposed etching stopper layer 23. The core layer 28 is bonded to the active layer 24 by batting. Similarly, the third clad layer 29 is butted with the first clad layer 25. In this embodiment, each layer was formed using the MOVPE method. The core layer 28 was formed using undoped GaInAsP, and had a composition wavelength of 1.25 μm and a thickness of 230 nm. The third cladding layer 29 was formed using undoped InP and had a thickness of 250 nm. The core layer 28 and the third cladding layer 29 do not grow on the mask layer 73 made of SiO ₂ by selective growth, but grow only on the exposed etching stopper layer 23 made of n-type doped InP. Then, the mask layer 73 is removed.

  Next, as shown in FIG. 23, the second cladding layer 26 and the contact layer 27 are formed in order on the first cladding layer 25 and the third cladding layer 29. In this embodiment, each layer was formed using the MOVPE method. The second cladding layer 26 was formed using p-type InP doped with Zn and had a thickness of 2.5 μm. The contact layer 27 was formed using p-type GaInAs doped with Zn and had a thickness of 300 nm.

Next, as shown in FIG. 24, a striped mask 74 for forming a mesa portion is formed on the contact layer 27 over the entire length of the element. In the present embodiment, the mask 74 is formed using a CVD method and a photolithography technique. The mask 74 was formed using SiO ₂ and had a width of 1.5 μm and a thickness of 400 nm.

  Next, as shown in FIG. 25, the mesa portion 20 is formed by removing a portion from the contact layer 27 where the mask is not formed to the middle of the substrate 11 by etching using a mask 74. In the present embodiment, the substrate 11 is removed from the surface to a depth of 0.7 μm.

  Next, as illustrated in FIG. 26, the current blocking layer 31 is formed on the side surface of the mesa unit 20 and the substrate 11. In the present embodiment, the current blocking layer 31 is formed using the MOVPE method. The current blocking layer 31 was formed using Fe-doped InP having semi-insulating properties, and the thickness was 0.2 μm.

  Next, as shown in FIG. 27, the lower buried region 32, the refractive index adjustment region 33, and the upper buried region 34 are sequentially stacked on the substrate 11 via the current blocking layer 31. It is formed. The refractive index adjustment region 33 is formed so as to be disposed at a position overlapping the active layer 24 in the height direction of the buried layer 30, specifically at a position matching the active layer 24. In this embodiment, each layer was formed using the MOVPE method. The lower buried region 32 was formed using undoped InP and had a thickness of 0.5 μm. The refractive index adjustment region 33 was formed using undoped GaInS (registered trademark) b and had a thickness of 0.25 μm. The upper buried region 34 was formed using undoped InP and had a thickness of 3.0 μm. Then, the mask 74 is removed.

Next, as shown in FIG. 28, the passivation layer 12 is formed on the mesa portion 20 and the buried layer 30. In the present embodiment, the passivation layer 12 is formed using SiO ₂ .

  Then, the first electrode 13 is formed after the portion of the passivation layer 12 where the first electrode is to be formed is removed using a normal lithography technique and etching technique. A second electrode 14 is formed below the substrate 11.

  Then, non-reflective layers 15a and 15b are formed on both surfaces of the element in the longitudinal direction, and the manufacture of the optical semiconductor element 10 is completed.

In the optical semiconductor element 10 formed as described above, the refractive index of the active layer 24 was 3.44, and the temperature change coefficient of the refractive index was 30 × 10 ⁻⁵ K ⁻¹ . The equivalent refractive index of the active layer 24, the etching stopper layer 23, and the first cladding layer 25 was 3.25, and the temperature change coefficient of the refractive index was 23.7 × 10 ⁻⁵ K ⁻¹ . The refractive index of the refractive index adjustment region 33 was 4.08, and the temperature change coefficient of the refractive index was 65.3 × 10 ⁻⁵ K ⁻¹ . The equivalent refractive index of the refractive index adjusting region 33, the lower buried region 32, and the upper buried region 34 was 3.24, and the temperature change coefficient of the refractive index was 61.32 × 10 ⁻⁵ K ⁻¹ .

  Moreover, in the optical semiconductor element 10, the temperature change coefficient of the oscillation wavelength increased twice as compared with the case where the refractive index adjustment region was not arranged in the buried layer.

  In the present invention, the optical semiconductor element, the optical transmission module, the optical transmission system, and the manufacturing method of the optical semiconductor element of the above-described embodiments can be appropriately changed without departing from the gist of the present invention. In addition, the configuration requirements of one embodiment can be applied to other embodiments as appropriate.

  For example, in the first embodiment of the manufacturing method described above, the active layer is formed using an AlGaInAs compound semiconductor, and in the second embodiment, the active layer is formed using a GaInAsP compound semiconductor. However, the active layer of the first embodiment may be formed using a GaInAsP-based compound semiconductor, and the active layer of the second embodiment may be formed using an AlGaInAs-based compound semiconductor.

  In the first embodiment of the manufacturing method described above, the current blocking layer is formed using an AlInAs compound semiconductor, and in the second embodiment, the current blocking layer is formed using an InP compound semiconductor. However, the current blocking layer of the first embodiment may be formed using an InP-based compound semiconductor, and the current blocking layer of the second embodiment may be formed using an AlInAs-based compound semiconductor. The current blocking layer may be formed using a dielectric.

  In each embodiment of the manufacturing method described above, the substrate or the active layer is formed using a compound semiconductor containing InP, but the substrate or the active layer uses another compound semiconductor such as GaAs / AlGaAs / GaInP. May be formed.

  Moreover, in each embodiment of the manufacturing method described above, a substrate having n-type conductivity is used, but a substrate having p-type conductivity is used, and a conductivity opposite to that of each embodiment is provided thereon. You may form the element structure which has.

  In each embodiment of the manufacturing method described above, the n-type doped InP substrate is used, but a semi-insulating substrate may be used. Alternatively, the optical semiconductor element may be formed using a method of bonding onto a silicon substrate.

  In each of the above-described embodiments, the diffraction grating has a surface diffraction grating structure formed on the surface of the substrate, but may have a buried diffraction grating structure.

  In each of the embodiments described above, the diffraction grating layer is disposed on the substrate side with respect to the active layer. However, the diffraction grating layer may be disposed on the side opposite to the substrate with respect to the active layer. good.

  In the first embodiment described above, the phase shift is disposed at the center in the longitudinal direction of the diffraction grating layer. However, the phase shift may be disposed at a position other than the center as long as it is within the diffraction grating layer. . Further, the value of the phase shift is not limited to π radians, and may be an arbitrary value within the design range.

  In the second embodiment described above, the active region, the front distributed reflection region, and the rear distributed reflection region have the same diffraction grating depth, and the coupling coefficient between the propagating light and the diffraction grating is the same. there were. However, depending on the element design, the active region, the front distributed reflection region, and the rear distributed reflection region may have different coupling coefficients between the propagating light and the diffraction grating.

  In the second embodiment described above, the front distributed reflection area is provided. However, depending on the element design, the front distributed reflection area may not be provided.

  In each of the embodiments described above, the peak-to-valley ratio of the diffraction grating is 50%, but the peak-to-valley ratio may be other values depending on the element design.

  Furthermore, although the optical semiconductor element of each of the embodiments described above is a semiconductor laser having a diffraction grating layer, the optical semiconductor element disclosed in this specification is a Fabry-Perot semiconductor laser having no diffraction grating. May be. Since such a Fabry-Perot type semiconductor laser has a narrow spread of the electric field distribution of light in the far field, the coupling between the light transmitted from the laser and the optical fiber is improved. From the same viewpoint, the optical semiconductor element disclosed in this specification may be a semiconductor optical amplifier.

  All examples and conditional words mentioned herein are intended for educational purposes to help the reader deepen and understand the inventions and concepts contributed by the inventor. All examples and conditional words mentioned herein are to be construed without limitation to such specifically stated examples and conditions. Also, such exemplary mechanisms in the specification are not related to showing the superiority and inferiority of the present invention. While embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions or modifications can be made without departing from the spirit and scope of the invention.

  Regarding the above-described embodiments, the following additional notes are disclosed.

(Appendix 1)
A mesa portion having an active layer;
An embedded layer for embedding the mesa portion;
With
The buried layer has a refractive index adjustment region having a refractive index temperature change coefficient larger than the refractive index temperature change coefficient of the active layer and having a refractive index larger than the refractive index of the active layer;
The refractive index adjustment region is an optical semiconductor element disposed at a position at least partially overlapping the active layer in the height direction of the buried layer.

(Appendix 2)
The optical semiconductor element according to appendix 1, wherein the refractive index adjustment region is not in contact with the mesa portion.

(Appendix 3)
The optical semiconductor element according to appendix 2, wherein a semi-insulator layer is disposed between the refractive index adjustment region and the mesa portion.

(Appendix 4)
The optical semiconductor element according to appendix 2, wherein an electrical insulator layer is disposed between the refractive index adjustment region and the mesa portion.

(Appendix 5)
5. The optical semiconductor device according to claim 1, wherein the refractive index adjustment region is disposed at a position that coincides with the active layer in a height direction of the buried layer.

(Appendix 6)
The active layer comprises a III-V group compound;
The optical semiconductor element according to any one of appendices 1 to 5, wherein the refractive index adjustment region has indium / antimony, gallium / antimony, aluminum / antimony, or a mixed crystal thereof.

(Appendix 7)
The optical semiconductor element according to any one of appendices 1 to 6, wherein the mesa portion includes a diffraction grating layer.

(Appendix 8)
A mesa portion having an active layer;
An embedded layer for embedding the mesa portion;
With
The buried layer has a refractive index adjustment region having a refractive index temperature change coefficient larger than the refractive index temperature change coefficient of the active layer and having a refractive index larger than the refractive index of the active layer;
The refractive index adjustment region is an optical semiconductor element disposed at a position at least partially overlapping the active layer in the height direction of the buried layer;
A driver for supplying current to the active layer;
With
An optical transmission module in which the optical semiconductor element transmits light toward an optical fiber.

(Appendix 9)
A mesa portion having an active layer;
An embedded layer for embedding the mesa portion;
With
The buried layer has a refractive index adjustment region having a refractive index temperature change coefficient larger than the refractive index temperature change coefficient of the active layer and having a refractive index larger than the refractive index of the active layer;
The refractive index adjustment region is an optical semiconductor element disposed at a position at least partially overlapping the active layer in the height direction of the buried layer;
A drive unit for supplying current to the optical semiconductor element;
An optical transmission module having
An optical fiber for propagating light transmitted from the optical transmission module;
An optical receiver module for receiving light from the optical fiber;
Optical transmission system equipped with.

(Appendix 10)
Forming a mesa portion having an active layer on a substrate;
Forming a buried layer so as to embed the mesa portion, wherein the buried layer has a temperature change coefficient of a refractive index larger than a temperature change coefficient of a refractive index of the active layer and is refracted by the active layer; And forming a buried layer so that the refractive index adjustment region is disposed at a position at least partially overlapping the active layer in the height direction of the buried layer. And a process of
A method for manufacturing an optical semiconductor device comprising:

DESCRIPTION OF SYMBOLS 10 Opto-semiconductor element 10a Front distribution reflection area 10b Active area 10c Back distribution reflection area 11 Substrate 12 Passivation layer 13 1st electrode 14 2nd electrode 15a, 15b Non-reflection layer 20 Mesa part 21 Diffraction grating layer 21a Phase shift 22 Guide layer 23 Etching stopper layer 24 Active layer 25 First clad layer 26 Second clad layer 27 Contact layer 28 Core layer 29 Third clad layer 30 Buried layer 31 Current blocking layer 32 Lower buried region 33 Refractive index adjusting region 34 Upper buried region 35 Buried Area 40 Optical transmission system 41 Optical fiber 50 Optical transmission module 51 Semiconductor laser 52 Drive unit 53 Lens 54 Isolator 55 Monitor unit 60 Optical reception module 61 Optical reception unit 62 Drive unit 63 Lens 70 Mask 71 Mask 7 Mask 73 mask 74 mask

Claims (8)

A mesa portion having an active layer;
An embedded layer for embedding the mesa portion;
With
The buried layer has a refractive index adjustment region having a refractive index temperature change coefficient larger than the refractive index temperature change coefficient of the active layer and having a refractive index larger than the refractive index of the active layer;
The refractive index adjustment region is disposed at a position at least partially overlapping the active layer in the height direction of the buried layer, and has a temperature change coefficient of the oscillation wavelength smaller than the temperature change coefficient of the gain peak wavelength. Semiconductor element.   The optical semiconductor element according to claim 1, wherein the refractive index adjustment region is not in contact with the mesa portion.   The optical semiconductor element according to claim 1, wherein the refractive index adjustment region is disposed at a position that coincides with the active layer in a height direction of the buried layer. The active layer comprises a III-V group compound;
The optical semiconductor element according to any one of claims 1 to 3, wherein the refractive index adjustment region has indium antimony, gallium antimony, aluminum antimony, or a mixed crystal thereof.   The optical semiconductor element according to claim 1, wherein the mesa portion includes a diffraction grating layer. A mesa portion having an active layer;
An embedded layer for embedding the mesa portion;
With
The buried layer has a refractive index adjustment region having a refractive index temperature change coefficient larger than the refractive index temperature change coefficient of the active layer and having a refractive index larger than the refractive index of the active layer;
The refractive index adjustment region is disposed at a position at least partially overlapping the active layer in the height direction of the buried layer, and has a temperature change coefficient of the oscillation wavelength smaller than the temperature change coefficient of the gain peak wavelength. A semiconductor element;
A driver for supplying current to the active layer;
With
An optical transmission module in which the optical semiconductor element transmits light toward an optical fiber. A mesa portion having an active layer;
An embedded layer for embedding the mesa portion;
With
The buried layer has a refractive index adjustment region having a refractive index temperature change coefficient larger than the refractive index temperature change coefficient of the active layer and having a refractive index larger than the refractive index of the active layer;
The refractive index adjustment region is disposed at a position at least partially overlapping the active layer in the height direction of the buried layer, and has a temperature change coefficient of the oscillation wavelength smaller than the temperature change coefficient of the gain peak wavelength. A semiconductor element;
A drive unit for supplying current to the optical semiconductor element;
An optical transmission module having
An optical fiber for propagating light transmitted from the optical transmission module;
An optical receiver module for receiving light from the optical fiber;
Optical transmission system equipped with. A method for manufacturing an optical semiconductor element, wherein the temperature change coefficient of the oscillation wavelength is smaller than the temperature change coefficient of the gain peak wavelength,
Forming a mesa portion having an active layer on a substrate;
Forming a buried layer so as to embed the mesa portion, wherein the buried layer has a temperature change coefficient of a refractive index larger than a temperature change coefficient of a refractive index of the active layer and is refracted by the active layer; And forming a buried layer so that the refractive index adjustment region is disposed at a position at least partially overlapping the active layer in the height direction of the buried layer. And a process of
A method for manufacturing an optical semiconductor device comprising:

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