Optical semiconductor device

Abstract

A Fabry-Perot laser (1) and an electric field absorption modulator (2) are formed over a semiconductor substrate (9). The Fabry-Perot laser (1) has an active layer (11) and generates laser light. The electric field absorption modulator (2) has an absorption layer (14) connected to the active layer (11) and modulates the laser light. The mesa width of the Fabry-Perot laser (1) abruptly changes to the mesa width of the electric field absorption modulator (2) at a connection portion (3) of the Fabry-Perot laser (1) and the electric field absorption modulator (2).

Description

Technical Field

[0001] This disclosure relates to optical semiconductor devices. Background Technology

[0002] In recent years, the speed of optical communication has been rapidly developing. Especially in data centers or AI networks, a large number of high-speed optical modulators are needed for relatively short-distance communication of approximately 2km or less. As for existing ultra-high-speed modulators, most of them use electric field absorption (EA) modulators integrated with distributed feedback (DFB) lasers.

[0003] The parameter that most significantly affects the characteristics of an EA modulator-integrated DFB laser is the difference Δλ between the absorption wavelength of the EA modulator and the oscillation wavelength of the DFB laser. The temperature dependence of the absorption wavelength of the EA modulator is approximately 0.5 nm / ℃, caused by band structure changes due to thermal expansion of the semiconductor. On the other hand, the temperature dependence of the oscillation wavelength of the DFB laser is approximately 0.1 nm / ℃. This is because, although the oscillation wavelength is determined by the period of the diffraction grating, the changes in thermal expansion and refractive index caused by temperature are less than the changes in the band structure. Therefore, the Δλ of the EA modulator-integrated DFB laser has a large temperature dependence, thus temperature regulators are frequently used.

[0004] On the other hand, the temperature dependence of the oscillation wavelength of a Fabry-Perot (FP) laser without a diffraction grating is determined by the band structure and threshold, and is approximately 0.5 nm / ℃. Since this is roughly the same temperature dependence as the absorption wavelength of an EA modulator, the temperature dependence of Δλ is small, and consequently, the temperature dependence of the characteristics is also small. Therefore, an EA modulator-integrated FP laser does not require a temperature regulator.

[0005] However, in order to operate as an FP laser, a reflective structure for reflecting the laser needs to be provided at the connection between the FP laser and the EA modulator. To address this, a solution of providing a slot between the FP laser and the EA modulator has been proposed (for example, see Patent Document 1).

[0006] Patent Document 1: Japanese Patent Application Publication No. 2005-019533

[0007] However, light travels while diffusing from the portion of the waveguide that is interrupted by the trench. To recouple this light to the waveguide, it is necessary to control the mode field diameter on the laser side, implement focusing functions such as SSC on the modulator side, and ensure that the light is incident at the focal length in this focusing section. Balancing the design of this focusing and the reflectivity is very difficult. Furthermore, during semiconductor fabrication, deviations in processing depth occur, affecting the thickness of the grown epitaxial layer. Moreover, it is difficult to measure the depth during processing. Therefore, reflectivity control based on trench depth is not simple in manufacturing. Summary of the Invention

[0008] This disclosure was made to solve the aforementioned problems, with the aim of obtaining an optical semiconductor device with low temperature dependence of characteristics and simple manufacturing process.

[0009] The optical semiconductor device disclosed herein includes: a semiconductor substrate; a Fabry-Perot laser formed on the semiconductor substrate, having an active layer and generating laser light; and an electric field absorption modulator formed on the semiconductor substrate, having an absorption layer connected to the active layer and modulating the laser light, wherein at the connection between the Fabry-Perot laser and the electric field absorption modulator, the mesa width of the Fabry-Perot laser abruptly changes to the mesa width of the electric field absorption modulator.

[0010] In this disclosure, a reflective structure is implemented to reflect laser light at the junction of a Fabry-Perot laser and an electric field absorption modulator. By utilizing the reflective structure to provide optical feedback, the Fabry-Perot laser can operate with low temperature dependence on its characteristics. Furthermore, since the mesa width is easy to control, reflectivity control based on the mesa width is also easy. As a result, an optical semiconductor device with low temperature dependence on its characteristics and simple manufacturing process can be obtained. Attached Figure Description

[0011] Figure 1 This is a top view of the optical semiconductor device according to Embodiment 1.

[0012] Figure 2 This is a cross-sectional view of the optical semiconductor device according to Embodiment 1 along the resonant direction.

[0013] Figure 3 This is a perspective view of the optical semiconductor device involved in Embodiment 1.

[0014] Figure 4 This is a cross-sectional view of an FP laser.

[0015] Figure 5 This is a cross-sectional view of the EA modulator.

[0016] Figure 6 This is a top view of the optical semiconductor device involved in Embodiment 1, cut at the height of the core layer.

[0017] Figure 7 This is a top view showing a modified example of the optical semiconductor device according to Embodiment 1.

[0018] Figure 8 This is a top view of the optical semiconductor device involved in Embodiment 2, cut at the height of the core layer.

[0019] Figure 9 This is a graph showing the change in the overlap integral of the optical mode when the width of the absorption layer of the EA modulator is varied.

[0020] Figure 10 This is a top view of the optical semiconductor device involved in Embodiment 3, cut at the height of the core layer.

[0021] Figure 11 This is a top view of a modified example of the optical semiconductor device according to Embodiment 3, with the core layer height cut off.

[0022] Figure 12 This is a graph showing the change in the overlap integral of the optical modes when the width of the active layer of an FP laser is varied.

[0023] Figure 13 This is a perspective view of the optical semiconductor device involved in Embodiment 4.

[0024] Figure 14 This is a top view of the optical semiconductor device involved in Embodiment 4, cut at the height of the core layer.

[0025] Figure 15 This is a top view of a modified example of the optical semiconductor device according to Embodiment 4, with the core layer height cut off.

[0026] Figure 16 This is a cross-sectional view of the optical semiconductor device according to Embodiment 5.

[0027] Figure 17 This is a cross-sectional view of the optical semiconductor device according to Embodiment 6.

[0028] Figure 18 This is a cross-sectional view showing a modified example of the optical semiconductor device according to Embodiment 6.

[0029] Figure 19 This is a graph showing the change in effective refractive index when the width of the core is varied.

[0030] Figure 20 This is a graph showing the change in the overlap integral of the optical pattern when the width of the core is varied.

[0031] Figure 21 This is a graph showing the change in the overlap integral of the optical modes as the thickness of the core layer of an FP laser varies.

[0032] Figure 22 This is a graph showing the change in the overlap integral of the optical mode when the refractive index of the core layer of the EA modulator is changed. Detailed Implementation

[0033] The optical semiconductor device according to the embodiments will be described with reference to the accompanying drawings. The same or corresponding components are labeled with the same reference numerals, and repeated descriptions are sometimes omitted.

[0034] Implementation Method 1

[0035] Figure 1 This is a top view showing the optical semiconductor device according to Embodiment 1. A Fabry-perot (FP) laser 1 and an Electro-Absorption (EA) modulator 2 are integrated on a single chip and interconnected at a connection portion 3. The FP laser 1 and the EA modulator 2 are each formed into a mesa via a slot 4. An electrode 5 is formed on the upper surface of the FP laser 1. An electrode 6 is formed on the upper surface of the EA modulator 2. By using the connection portion 3 and the rear end face 7 of the chip as a Fabry-perot resonator, the FP laser 1 can generate laser light without using a diffraction grating. The EA modulator 2 modulates the laser light. The modulated laser light is emitted from the front end face 8 of the chip into an optical fiber or the like.

[0036] Furthermore, when the laser is directly modulated using the current supplied to the FP laser 1, the high-frequency characteristics deteriorate due to relaxation oscillations. On the other hand, the EA modulator 2 does not exhibit the typical laser-specific bandwidth degradation. Therefore, by modulating the laser generated by the FP laser 1 with the EA modulator 2, high-speed operation becomes possible.

[0037] Figure 2 This is a cross-sectional view of the optical semiconductor device according to Embodiment 1 along the resonant direction. Figure 3This is a perspective view of the optical semiconductor device according to Embodiment 1. An FP laser 1 and an EA modulator 2 are formed on a semiconductor substrate 9. The FP laser 1 has an n-type cladding layer 10, an active layer 11, a p-type cladding layer 12, and a p-type contact layer 13 sequentially formed on the semiconductor substrate 9. An electrode 5 is formed on the p-type contact layer 13. The EA modulator 2 has an n-type cladding layer 10, an absorber layer 14, a p-type cladding layer 12, and a p-type contact layer 13 sequentially formed on the semiconductor substrate 9. An electrode 6 is formed on the p-type contact layer 13. An electrode 15 is formed on the entire lower surface of the semiconductor substrate 9. The absorber layer 14 is directly connected to the active layer 11 at the connection portion 3 without passing through other layers. That is, the active layer 11 and the absorber layer 14 are mated.

[0038] The semiconductor substrate 9 is made of, for example, n-InP. The active layer 11 is made of, for example, InGaAsP, AlGaInAs, etc. The absorber layer 14 is made of, for example, InGaAsP, AlGaInAs, etc. The n-type cladding layer 10 and the p-type cladding layer 12 are made of InP. The p-type contact layer 13 is made of, for example, InGaAs, InGaAsP, etc.

[0039] Figure 4 This is a cross-sectional view of an FP laser. The FP laser 1 is a buried structure formed by embedding a current blocking layer 16 into the side portion of a ridge structure, including an active layer 11. The current blocking layer 16 is made of, for example, a semi-insulating semiconductor such as Fe-InP. This buried structure becomes a mesa structure through a trench 4. The side portion of the mesa structure is covered by an insulating film 17. The insulating film 17 is made of, for example, SiN or SiO.

[0040] The mesa width of the FP laser 1 is the sum of the width of the ridge structure and the width of the embedded structure. The widths of the left and right current blocking layers 16 are 3 μm each. The active layer 11 has a refractive index of 3.5, a width of 1.5 μm, and a thickness of 200 nm. The n-type cladding 10 and the p-type cladding 12 have a refractive index of 3.2 and a thickness of 2 μm.

[0041] Figure 5 This is a cross-sectional view showing the EA modulator. The EA modulator 2 has a mesa structure including an absorption layer 14. The width of the mesa in the EA modulator 2 is the same as the width of the mesa structure. The sides of the mesa structure are covered by an insulating film 17. The absorption layer 14 has a refractive index of 3.4, a width of 1.5 μm, and a thickness of 200 nm. The insulating film 17 has a refractive index of 2.0 and a thickness of 0.5 μm.

[0042] Figure 6 This is a top view of the optical semiconductor device according to Embodiment 1, cut along the height of the core layer. This figure corresponds to... Figure 2A top view of the I-II cutting device. The mesa width of FP laser 1 is 8 μm. The mesa width of EA modulator 2 is 1.5 μm. The mesa widths of FP laser 1 and EA modulator 2 are constant until the connection part 3. Therefore, at the connection part 3, the mesa width of FP laser 1 changes abruptly to the mesa width of EA modulator 2.

[0043] Figure 7 This is a top view showing a modified example of the optical semiconductor device according to Embodiment 1. A spot size converter 18 is formed on the output side of the EA modulator 2. The spot size converter 18 changes the spot size of the emitted laser to match the size of the optical fiber. As a result, the laser can be efficiently guided into the optical fiber.

[0044] As explained above, in this embodiment, at the connection 3 between the FP laser 1 and the EA modulator 2, the mesa width of the FP laser 1 changes abruptly to that of the EA modulator 2. This increases the effective refractive index difference, thus enabling a reflective structure that reflects the laser light. By utilizing this reflective structure to provide light feedback, it can operate as a Fabry-Perot laser with low temperature dependence on its characteristics. Furthermore, the mesa width can be controlled using the width of the transfer mask during mesa processing. If the width of the transfer resist is not the desired width, it can be re-transferred. Therefore, mesa width dimensional control is easy, and reflectivity control based on mesa width dimensional control is also easy. As a result, an optical semiconductor device with low temperature dependence on its characteristics and simple manufacturing process can be obtained.

[0045] Implementation Method 2

[0046] Figure 8 This is a top view of the optical semiconductor device according to Embodiment 2, cut at the height of the core layer. The waveguide width of the active layer 11 of the FP laser 1 is constant. On the other hand, the waveguide width of the absorption layer 14 of the EA modulator 2 varies towards the connection portion 3 between the FP laser 1 and the EA modulator 2. Specifically, the absorption layer 14 of the EA modulator 2 has a straight portion 14a with a constant waveguide width and a tapered portion 14b disposed between the straight portion 14a and the connection portion 3, the waveguide width of which narrows towards the connection portion 3. For example, the length of the tapered portion 14b in the resonator direction is 30 μm, and the waveguide width narrows from 1.5 μm to 1.0 μm towards the connection portion 3. Therefore, at the connection portion 3, the waveguide width of the absorption layer 14 is narrower than the waveguide width of the active layer 11.

[0047] Figure 9This diagram illustrates the change in the overlap integral of the optical mode when the width of the absorption layer of the EA modulator is varied. The active layer 11 of the FP laser 1 has a constant width of 1500 nm. When the width of the absorption layer 14 of the EA modulator 2 is varied, the overlap integral between the FP laser 1 and the EA modulator 2 changes. By returning a portion of the (1-overlap integral) component to the FP laser 1, the amplification of the light required for laser oscillation can be obtained.

[0048] As explained above, in this embodiment, the waveguide width of the active layer 11 at the connection portion 3 is different from the waveguide width of the absorption layer 14, thereby enabling a reflective structure that reflects the laser light. By utilizing the reflective structure to provide light feedback, it can operate as a Fabry-Perot laser with low temperature dependence on its characteristics. Furthermore, since the waveguide width is easy to control, reflectivity control based on the waveguide width is also easy. As a result, an optical semiconductor device with low temperature dependence on its characteristics and simple manufacturing process can be obtained.

[0049] Implementation Method 3

[0050] Figure 10 This is a top view of the optical semiconductor device according to Embodiment 3, cut at the height of the core layer. The waveguide width of the absorption layer 14 of the EA modulator 2 is constant. On the other hand, the waveguide width of the active layer 11 of the FP laser 1 varies towards the connection portion 3 between the FP laser 1 and the EA modulator 2. Specifically, the active layer 11 of the FP laser 1 has a straight portion 11a with a constant waveguide width and a tapered portion 11b disposed between the straight portion 11a and the connection portion 3, the waveguide width of which widens towards the connection portion 3. For example, the length of the tapered portion 11b in the resonator direction is 30 μm, and the waveguide width increases from 1.5 μm to 3.0 μm towards the connection portion 3. Therefore, at the connection portion 3, the waveguide width of the absorption layer 14 is narrower than the waveguide width of the active layer 11.

[0051] Figure 11 This is a top view of a modified example of the optical semiconductor device according to Embodiment 3, cut at the height of the core layer. The active layer 11 of the FP laser 1 has a straight portion 11a with a constant waveguide width and a tapered portion 11b disposed between the straight portion 11a and the connecting portion 3, the waveguide width of which narrows towards the connecting portion 3. For example, the length of the tapered portion 11b in the resonator direction is 30 μm, and the waveguide width narrows from 1.5 μm to 1.0 μm towards the connecting portion 3. Therefore, at the connecting portion 3, the waveguide width of the absorption layer 14 is wider than the waveguide width of the active layer 11.

[0052] Figure 12This is a graph showing the change in the overlap integral of the optical mode when the width of the active layer of the FP laser is varied. The width of the absorber layer 14 of the EA modulator 2 is constant at 1500 nm. When the width of the active layer 11 of the FP laser 1 is varied, the overlap integral between the FP laser 1 and the EA modulator 2 changes. By returning a portion of the (1-overlap integral) component to the FP laser 1, a gain for laser oscillation can be obtained.

[0053] As explained above, in this embodiment, the waveguide width of the active layer 11 at the connection portion 3 is different from the waveguide width of the absorption layer 14, thereby enabling a reflective structure that reflects the laser light. By utilizing the reflective structure to provide light feedback, it can operate as a Fabry-Perot laser with low temperature dependence on its characteristics. Furthermore, since the waveguide width is easy to control, reflectivity control based on the waveguide width is also easy. As a result, an optical semiconductor device with low temperature dependence on its characteristics and simple manufacturing process can be obtained.

[0054] Implementation Method 4

[0055] Figure 13 This is a perspective view of the optical semiconductor device involved in Embodiment 4. Figure 14 This is a top view of the optical semiconductor device according to Embodiment 4, cut at the height of the core layer. The FP laser 1 is a buried structure formed by embedding a current blocking layer 16 into the side portion of a ridge structure including the active layer 11. On the other hand, the EA modulator 2 is a high mesa structure including an absorption layer 14. A portion of the front end face of the FP laser 1 is connected to the EA modulator 2. Since the mesa width of the FP laser 1 is wider than the mesa width of the EA modulator 2, there is a portion of the front end face of the FP laser 1 that is not connected to the EA modulator 2. A reflective film 19 for reflecting laser light is formed on this portion of the front end face.

[0056] By reflecting a portion of the optical mode of the FP laser 1 back to the FP laser 1 using the reflective film 19, the mirror loss of the FP laser 1 can be reduced, and the gain required for laser oscillation can be obtained. Furthermore, the reflective film 19 is easy to form. As a result, an optical semiconductor device with low temperature dependence of characteristics and simple fabrication can be obtained.

[0057] Figure 15 This is a top view of a modified example of the optical semiconductor device according to Embodiment 4, cut at the height of the core layer. A reflective film 19 is also formed between the active layer 11 and the absorber layer 14. For example... Figure 14 As shown, without forming a reflective film 19 between the active layer 11 and the absorber layer 14, manufacturing is easy and the waveguide structure can be maintained. On the other hand, as Figure 15As shown, when a reflective film 19 is formed between the active layer 11 and the absorber layer 14, manufacturing becomes more difficult, but a high reflectivity can be obtained.

[0058] Implementation Method 5

[0059] Figure 16 This is a cross-sectional view showing the optical semiconductor device according to Embodiment 5. At the connection portion 3 between the FP laser 1 and the EA modulator 2, a waveguide layer 20 is formed between the active layer 11 of the FP laser 1 and the absorption layer 14 of the EA modulator 2. The waveguide layer 20 is made of, for example, a semiconductor such as InP or an insulating film such as SiO, and the active layer 11 and the absorption layer 14 have different refractive indices.

[0060] The active layer 11 of the FP laser 1 has an effective refractive index of 3.371, and the waveguide layer 20 of the insulating film has an effective refractive index of 1.636. The overlap integral is 95.142%. Due to the large difference in effective refractive index, 12% of the optical mode within the core layer is reflected. By adjusting the refractive index of the waveguide layer 20, the reflectivity can be easily controlled. Furthermore, the waveguide layer 20 is easily formed. As a result, an optical semiconductor device with low temperature dependence and simple fabrication can be obtained. Moreover, the waveguide layer 20 can also be a structure composed of multiple layers with different refractive indices stacked together. Figure 16 In the waveguide layer 20, a groove is formed. However, it is not limited to this. A p-type cladding layer 12 made of InP can be formed on the waveguide layer 20, or a cladding layer made of a semiconductor material other than InP can be formed.

[0061] Implementation Method 6

[0062] Figure 17 This is a cross-sectional view showing the optical semiconductor device according to Embodiment 6. A low-reflectivity film 21 is formed on the front end face of the chip that emits laser light. A high-reflectivity film 22 is formed on the rear end face of the chip, opposite to the front end face. The low-reflectivity film 21 and the high-reflectivity film 22 are, for example, formed by alternating layers of Si and SiO. The reflectivity of the laser light from the low-reflectivity film 21 is lower than that from the high-reflectivity film 22. As a result, since the laser light modulated by the EA modulator 2 does not return to the FP laser 1, the operation of the FP laser 1 is stable, thereby improving the modulation characteristics. Other structures and effects are the same as in Embodiment 1.

[0063] Figure 18 This is a cross-sectional view showing a modified example of the optical semiconductor device according to Embodiment 6. A spot size converter 18 is formed on the output side of the EA modulator 2. In this case, the same effect can be obtained by forming a low reflectivity film 21 and a high reflectivity film 22. Alternatively, the low reflectivity film 21 and the high reflectivity film 22 can also be formed in Embodiments 2 to 5.

[0064] In typical FP lasers, the cleaved end face is usually used directly as the reflective structure instead of being coated. In this case, both the front and rear end faces have a reflectivity of 30%. When a coating with a reflectivity of 90% or more is applied to the rear end face, the reflectivity becomes 10%, resulting in the same mirror loss as described above. Therefore, the reflectivity of the laser under the reflective structure of the connection portion 3 in embodiments 1-6 is preferably 10% or more. Furthermore, if the reflectivity of the reflective structure of the connection portion 3 has wavelength selectivity, the temperature dependence of the oscillation wavelength of the FP laser 1 deviates from the temperature dependence of the EA modulator 2, leading to a deterioration in temperature characteristics. Therefore, the reflective structure of the connection portion 3 is preferably low in wavelength selectivity.

[0065] Figure 19 This diagram illustrates the change in effective refractive index when the core width is varied. The current blocking layer 16 on the ridge side of the FP laser 1 is made of InP, and the insulating film 17 on the ridge side of the EA modulator 2 is made of SiO. Even with the same core width, there is a difference in effective refractive index. The difference in effective refractive index is related to the overlap integral of the FP laser 1 and the EA modulator 2. By returning a portion of the (1-overlap integral) component to the FP laser 1, the gain for laser oscillation can be obtained. Therefore, by controlling the refractive index of the ridge side material, the reflectivity can be adjusted.

[0066] Figure 20 This is a diagram showing the change in the overlap integral of the optical mode when the width of the core is varied. It illustrates the cases where the material of the ridge side connects the semiconductor waveguides to each other and the cases where the material of the ridge side connects the semiconductor waveguides to the waveguides of the insulating film. Different ridge side materials result in a higher gain for laser oscillation. Therefore, to improve the reflectivity at the connection 3 between the FP laser 1 and the EA modulator 2, it is preferable that the material covering the ridge side of the FP laser 1 is different from the material covering the ridge side of the EA modulator 2.

[0067] Figure 21 This diagram illustrates the change in the overlap integral of the optical modes when the thickness of the core layer of the FP laser is varied. If the thickness of the active layer 11 of the FP laser 1 is varied relative to the 300 nm thickness of the absorption layer 14 of the EA modulator 2, the overlap integral of the FP laser 1 and the EA modulator 2 changes. Therefore, to improve the reflectivity at the junction 3 between the FP laser 1 and the EA modulator 2, it is preferable that the thickness of the active layer 11 of the FP laser 1 is different from the thickness of the absorption layer 14 of the EA modulator 2.

[0068] Figure 22This diagram illustrates the change in the overlap integral of the optical modes when the refractive index of the core layer of the EA modulator is changed. If the refractive index of the absorption layer 14 of the EA modulator 2 is changed relative to the refractive index of the active layer 11 of the FP laser 1 (3.56), the overlap integral of the FP laser 1 and the EA modulator 2 changes. Therefore, to improve the reflectivity at the junction 3 between the FP laser 1 and the EA modulator 2, it is preferable that the refractive index of the active layer 11 of the FP laser 1 is different from the refractive index of the absorption layer 14 of the EA modulator 2.

[0069] Explanation of reference numerals in the attached figures

[0070] 1...FP laser; 2...EA modulator; 3...connector; 9...semiconductor substrate; 11...active layer; 11a, 14a...linear section; 11b, 14b...tapered section; 14...absorption layer; 16...current blocking layer; 19...reflective film; 20...waveguide layer; 21...low reflectivity film; 22...high reflectivity film.

Claims

1. An optical semiconductor device, characterized in that, have: Semiconductor substrate; A Fabry-Perot laser, formed on the semiconductor substrate, having an active layer, and generating laser light; and An electric field absorption modulator, formed on the semiconductor substrate, has an absorption layer connected to the active layer and modulates the laser. At the connection between the Fabry-Perot laser and the electric field absorption modulator, the width of the Fabry-Perot laser's mesa changes abruptly to the width of the electric field absorption modulator's mesa.

2. The optical semiconductor device according to claim 1, characterized in that, The mesa width of the Fabry-Perot laser and the mesa width of the electric field absorption modulator are both constant and do not change up to the connection portion.

3. The optical semiconductor device according to claim 1 or 2, characterized in that, The Fabry-Perot laser is an embedded structure formed by embedding a current blocking layer into the side of a ridge structure, including the active layer. The electric field absorption modulator has a high-platform structure including the absorption layer. The width of the mesa of the Fabry-Perot laser is the width of the embedded structure. The width of the platform of the electric field absorption modulator is the width of the high platform structure.

4. A photonic semiconductor device, characterized in that, have: Semiconductor substrate; A Fabry-Perot laser, formed on the semiconductor substrate, having an active layer, and generating laser light; and An electric field absorption modulator, formed on the semiconductor substrate, has an absorption layer connected to the active layer and modulates the laser. The waveguide width of the active layer or the absorption layer varies toward the connection between the Fabry-Perot laser and the electric field absorption modulator, at which the waveguide width of the active layer differs from that of the absorption layer.

5. The optical semiconductor device according to claim 4, characterized in that, The absorption layer has: a straight portion with a constant waveguide width; and a tapered portion disposed between the straight portion and the connecting portion, wherein the waveguide width narrows towards the connecting portion. At the connection point, the waveguide width of the absorbing layer is narrower than the waveguide width of the active layer.

6. The optical semiconductor device according to claim 4, characterized in that, The active layer has: a straight portion with a constant waveguide width; and a tapered portion disposed between the straight portion and the connecting portion, wherein the waveguide width widens as it moves toward the connecting portion. At the connection point, the waveguide width of the absorbing layer is narrower than the waveguide width of the active layer.

7. The optical semiconductor device according to claim 4, characterized in that, The active layer has: a straight portion with a constant waveguide width; and a tapered portion disposed between the straight portion and the connecting portion, wherein the waveguide width narrows as it moves toward the connecting portion. At the connection point, the waveguide width of the absorbing layer is wider than the waveguide width of the active layer.

8. The optical semiconductor device according to claim 3, characterized in that, A portion of the front face of the Fabry-Perot laser is connected to the electric field absorption modulator. A reflective film for reflecting the laser is formed on the front end surface.

9. The optical semiconductor device according to claim 8, characterized in that, The reflective film is also formed between the active layer and the absorbent layer.

10. An optical semiconductor device, characterized in that, have: Semiconductor substrate; A Fabry-Perot laser is formed on the semiconductor substrate, has an active layer, and generates laser light; An electric field absorption modulator is formed on the semiconductor substrate, has an absorption layer connected to the active layer, and modulates the laser. as well as A waveguide layer, formed between the active layer and the absorption layer at the junction of the Fabry-Perot laser and the electric field absorption modulator, has a different refractive index than the active layer and the absorption layer.

11. The optical semiconductor device according to any one of claims 1 to 10, characterized in that, It also has: A low-reflectivity film is formed on the front end of the chip from which the laser is emitted; and A high-reflectivity film is formed on the rear side of the chip, opposite to the front side of the chip. The reflectivity of the laser light from the low-reflectivity film is lower than that from the high-reflectivity film.

12. The optical semiconductor device according to any one of claims 1 to 11, characterized in that, The reflectivity of the laser at the connection point is more than 10%.

13. The optical semiconductor device according to any one of claims 1 to 12, characterized in that, The material covering the ridge side of the Fabry-Perot laser is different from the material covering the ridge side of the electric field absorption modulator.

14. The optical semiconductor device according to any one of claims 1 to 13, characterized in that, The thickness of the active layer of the Fabry-Perot laser is different from the thickness of the absorption layer of the electric field absorption modulator.

15. The optical semiconductor device according to any one of claims 1 to 14, characterized in that, The refractive index of the active layer of the Fabry-Perot laser is different from the refractive index of the absorption layer of the electric field absorption modulator.

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