semiconductor laser element

Abstract

This semiconductor laser element (100) comprises: a semiconductor laser unit (1); a transition unit (2) which is adjacent to the semiconductor laser unit in a first direction (Y) and on which light emitted from the semiconductor laser unit is incident; and a spot size conversion unit (3) which is adjacent to the transition unit in the first direction (Y) and on which light emitted from the transition unit is incident. The semiconductor laser unit, the transition unit, and the spot size conversion unit each include: a semiconductor substrate (5) having a first surface (5A) extending along the first direction (Y) and a second direction (X); and a first cladding layer (6), active layer (11), and second cladding layer (12, 22, 32) laminated on the first surface in order from the first surface side in a third direction (Z) orthogonal to the first surface. The transition unit and the spot size conversion unit each further include a waveguide layer (22, 33) that contacts a portion of the upper surface of the second cladding layer and that has a higher refractive index than the active layer and second cladding layer.

Description

[Technical Field]

[0001] The present disclosure relates to a semiconductor laser element, and more particularly to a semiconductor laser element integrated with a spot size converter (hereinafter referred to as SSC). [Background technology]

[0002] In recent years, the amount of communication traffic in optical communications has been continuously increasing, and there is a demand for increased communication capacity. Therefore, there is a demand for semiconductor laser elements used as light sources for optical communications to be low-cost elements that operate at high frequencies and have high output power.

[0003] In the semiconductor laser element described in Patent Publication No. 2021-27310 (Patent Document 1), in order to provide an element that operates at high frequencies and has high output, the frequency response is improved by narrowing the current injection section and confining light to a narrow region using a core layer structure with a high refractive index layer inserted.

[0004] The semiconductor laser device described in JP 2016-96310 A (Patent Document 2) includes a semiconductor laser portion including a quantum well layer, and an SSC including a waveguide layer monolithically butt-connected to one end (emission end) of the quantum well layer of the semiconductor laser portion. With this semiconductor laser device, the increase in the divergence angle of the laser light emitted from the semiconductor laser portion is suppressed compared to the semiconductor laser device described in Patent Document 1, and coupling efficiency is improved. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-27310 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-96310 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method for manufacturing a semiconductor laser device described in Patent Document 2 requires the sequential steps of forming a quantum well layer on the entire surface of a semiconductor substrate, then partially removing the quantum well layer in the region where the SSC is to be formed, and then forming a waveguide layer in the region from which the quantum well layer has been removed. This manufacturing method requires a relatively large number of steps, resulting in relatively high manufacturing costs.

[0007] A primary object of the present disclosure is to provide a semiconductor laser device that includes an SSC but that can be manufactured at reduced cost compared to conventional semiconductor laser devices that include an SSC. [Means for solving the problem]

[0008] The semiconductor laser device according to the present disclosure includes a semiconductor laser portion, a transition portion adjacent to the semiconductor laser portion in a first direction and on which light emitted from the semiconductor laser portion is incident, and a spot size converter adjacent to the transition portion in the first direction and on which the light emitted from the transition portion is incident. Each of the semiconductor laser portion, the transition portion, and the spot size converter includes a semiconductor substrate having a first surface extending along the first direction and a second direction perpendicular to the first direction, and a first cladding layer, an active layer, and a second cladding layer stacked on the first surface in this order from the first surface side in a third direction perpendicular to the first surface. In the semiconductor laser portion, the second cladding layer is in contact with the active layer. The refractive index of the second cladding layer is lower than the refractive index of the active layer. Each of the transition portion and the spot size converter further includes a waveguide layer in contact with a portion of an upper surface of the second cladding layer and having a refractive index higher than those of the active layer and the second cladding layer. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a semiconductor laser element that includes an SSC but has reduced manufacturing costs compared to conventional semiconductor laser elements that include an SSC. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view of a semiconductor laser device according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIGS. 2 and 3. [Figure 5] FIG. 4 is a cross-sectional view taken along line VV in FIGS. 2 and 3. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIGS. 2 and 3. [Figure 7] FIG. 7 is a cross-sectional view taken along line VII-VII in FIGS. 2 and 3. [Figure 8] 4 is a flowchart for explaining a first step of a method for manufacturing the semiconductor laser device according to the first embodiment. [Figure 9] FIG. 10 is a cross-sectional view of a semiconductor laser device according to a second embodiment. [Figure 10] FIG. 10 is a cross-sectional view taken along line XX in FIG. 9. [Figure 11] 10 is a cross-sectional view taken along line XI-XI in FIG. 9. [Figure 12] 10 is a flowchart illustrating a first step of a method for manufacturing a semiconductor laser device according to a second embodiment. [Figure 13] FIG. 10 is a cross-sectional view of a semiconductor laser device according to a third embodiment. [Figure 14] FIG. 14 is a cross-sectional view taken along line XIV-XIV in FIG. [Figure 15] FIG. 14 is a cross-sectional view taken along line XV-XV in FIG. [Figure 16] FIG. 16 is a cross-sectional view taken along line XVI-XVI in FIG. [Figure 17] 10 is a flowchart illustrating a first step of a method for manufacturing a semiconductor laser device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Figures 1 to 6, 8 to 11, and 13 to 16 show a Cartesian coordinate system having an X direction (second direction), a Y direction (first direction), and a Z direction (third direction) that are orthogonal to each other.

[0012] In this embodiment, when geometric terms and terms expressing position, direction, and magnitude relationships, such as "orthogonal," "along," "equal," and "constant," are used, these terms allow for variations based on manufacturing errors.

[0013] Embodiment 1 <Configuration of the semiconductor laser element 100> 1, the semiconductor laser device 100 according to the first embodiment includes a semiconductor laser portion 1, a transition portion 2, and a spot size conversion portion (SSC) 3. The semiconductor laser device 100 is a device in which the semiconductor laser portion 1, the transition portion 2, and the SSC 3 are monolithically integrated.

[0014] The semiconductor laser portion 1 includes a multiple quantum well layer and is configured to emit light. The transition portion 2 is configured to receive the light emitted from the semiconductor laser portion 1. The transition portion 2 is adjacent to the semiconductor laser portion 1 in the Y direction. In other words, the transition portion 2 is directly connected to the semiconductor laser portion 1 in the Y direction. The SSC3 is configured to receive the light emitted from the transition portion 2. The SSC3 is adjacent to the transition portion 2 in the Y direction. In other words, the SSC3 is directly connected to the transition portion 2 in the Y direction. <Configuration of semiconductor laser section 1> As shown in Figures 1 to 4, the semiconductor laser portion 1 includes a semiconductor substrate 5, a first cladding layer 6, a diffraction grating layer 7, an active layer 11, a second cladding layer 12, a fourth cladding layer 15, an insulating layer 16, a first electrode 17, an electrode pad 18, and a second electrode 19.

[0015] The semiconductor substrate 5 has a first surface 5A and a second surface 5B located on the opposite side to the first surface 5A. The first surface 5A and the second surface 5B extend along the X direction and the Y direction, respectively. The semiconductor substrate 5 is made of, for example, p-type InP.

[0016] The first cladding layer 6, the active layer 11, and the second cladding layer 12 are provided on the first surface 5A and are stacked in this order from the first surface 5A side in the Z direction. The first cladding layer 6, the active layer 11, and the second cladding layer 12 form a pin junction. The first cladding layer 6 and the second cladding layer 12 are provided to sandwich the active layer 11 in the Z direction. The first cladding layer 6 and the second cladding layer 12 each contact the active layer 11. The active layer 11 includes a multiple quantum well layer. In other words, the active layer 11 has a multiple quantum well structure in which multiple quantum well layers and multiple barrier layers are alternately stacked in the Z direction.

[0017] The materials constituting the multiple quantum well layers and barrier layers of active layer 11 can be selected arbitrarily depending on the emission wavelength. For example, if the emission wavelength of active layer 11 is 1.31 μm, each of the multiple quantum well layers and barrier layers of active layer 11 is made of, for example, InGaAsP.

[0018] The composition ratio of InGaAsP, a quaternary mixed crystal, is generally In 1-x Ga x As y P 1-y The refractive index of InGaAsP can be adjusted by adjusting the values ​​of x and y. 1-x Ga x As y P 1-y It is known that the refractive index of InGaAsP can be changed by adjusting the composition ratio of InGaAsP. The refractive index of InGaAsP is characterized in that it is lower than that of InP when its composition ratio is close to GaP, and higher than that of InP when its composition ratio is close to InAs.

[0019] By utilizing the above-described characteristics, the refractive index of the active layer 11 can be made higher than the refractive index of each of the first cladding layer 6 and the second cladding layer 12. The materials (composition ratios) constituting each of the first cladding layer 6 and the second cladding layer 12 can be selected from materials (composition ratios) that have a lower refractive index than the material constituting the active layer 11. The first cladding layer 6 is made of, for example, p-type InP. The second cladding layer 12 is made of, for example, n-type InP. The material constituting the active layer 11 may be a quaternary mixed crystal other than InGaAsP, such as AlInGaAs. Even in this case, the refractive indexes of the active layer 11, the first cladding layer 6, and the second cladding layer 12 can be set as described above by appropriately adjusting the composition ratio of the quaternary mixed crystal. When the material constituting the active layer 11 is AlInGaAs, the first cladding layer 6 may be made of p-type AlAs, and the second cladding layer 12 may be made of n-type AlAs.

[0020] The active layer 11 of the semiconductor laser portion 1 has a first end facet 11A located on the opposite side to the transition portion 2 in the Y direction. The first end facet 11A is a cleavage plane. The first end facet 11A is covered with a reflective film (HR (High Reflection) coating film) (not shown). The reflectance of the reflective film is, for example, about 95%.

[0021] The diffraction grating layer 7 is embedded inside the first cladding layer 6. The diffraction grating layer 7 is disposed closer to the active layer 11 in the Z direction than the semiconductor substrate 5. The diffraction grating layer 7 has a plurality of portions that are periodically arranged at intervals in the X direction. The first cladding layer 6 is disposed between the plurality of portions of the diffraction grating layer 7. The diffraction grating layer 7 and the first cladding layer 6 form a diffraction grating 10. The refractive index of the diffraction grating layer 7 is higher than the refractive index of the first cladding layer 6. The average refractive index of the diffraction grating 10 is higher than the refractive index of the first cladding layer 6 and lower than the refractive index of the active layer 11. The diffraction grating layer 7 is made of, for example, p-type InGaAsP.

[0022] As shown in FIG. 4, the fourth cladding layer 15 is provided on a part of the second cladding layer 12 in the X direction. The fourth cladding layer 15 is provided so as to overlap with the diffraction grating 10 in the Z direction. The fourth cladding layer 15 has a cross section along the X direction and the Z direction (hereinafter referred to as the X Z In the XZ cross section, the width in the X direction gradually narrows toward the second cladding layer 12 in the Z direction. In other words, in the XZ cross section, the fourth cladding layer 15 has an inverted mesa shape with respect to the second cladding layer 12. In the XZ cross section, the fourth cladding layer 15 is connected to the upper surface of the second cladding layer 12 and has a side surface that extends upward beyond the upper surface of the second cladding layer 12. The angle formed by the side surface of the fourth cladding layer 15 and the upper surface of the second cladding layer 12 with respect to the outside of the fourth cladding layer 15 is an acute angle. The width in the X direction of the fourth cladding layer 15 is constant, for example, in the Y direction. The refractive index of the fourth cladding layer 15 is lower than the refractive index of the active layer 11. The fourth cladding layer 15 is made of, for example, n-type InP.

[0023] The insulating layer 16 is provided so as to bury the periphery of the fourth cladding layer 15. The insulating layer 16 has a lower surface in direct contact with the side surface of the fourth cladding layer 15, an upper surface that is contiguous with the upper surface of the fourth cladding layer 15 of the semiconductor laser portion 1 so as to form the same plane as the upper surface of the fourth cladding layer 15, and a pair of inner side surfaces that face each other in the X direction. Each of the pair of inner side surfaces is in direct contact with the side surface of the fourth cladding layer 15. The inner angle between each of the pair of inner side surfaces of the insulating layer 16 and the lower surface of the insulating layer 16 is an acute angle. In the XZ cross section, the insulating layer 16 has a mesa shape. From the viewpoint of suppressing the penetration of heat and moisture from the outside to the inside of the semiconductor laser device 100, the insulating layer 16 is preferably made of a material that has relatively high heat resistance and relatively low moisture absorption. The insulating layer 16 is made of, for example, benzocyclobutene (hereinafter referred to as BCB). The insulating layer 16 is made of, for example, photosensitive BCB.

[0024] 2 and 3, in the YZ cross section, the shapes of the semiconductor substrate 5, the first cladding layer 6, the diffraction grating layer 7, the active layer 11, the second cladding layer 12, the fourth cladding layer 15, and the insulating layer 16 are each symmetrical with respect to the center line of the semiconductor laser portion 1, which passes through the center in the X direction and extends along the Y direction. As shown in Fig. 4, in the XZ cross section, the shapes of the semiconductor substrate 5, the first cladding layer 6, the diffraction grating layer 7, the active layer 11, the second cladding layer 12, the fourth cladding layer 15, and the insulating layer 16 are each symmetrical with respect to the center line of the semiconductor laser portion 1, which passes through the center in the X direction and extends along the Z direction.

[0025] The first electrode 17 is a fourth clad layer 15 The second electrode 19 is provided on the second surface 5B of the semiconductor substrate 5 and is electrically connected to the semiconductor substrate 5. The insulating layer 16 is provided on the fourth cladding layer 15 and is electrically connected to the fourth cladding layer 15. The electrode pad 18 is provided on the insulating layer 16 and is electrically connected to the first electrode 17. The second electrode 19 is provided on the second surface 5B of the semiconductor substrate 5 and is electrically connected to the semiconductor substrate 5.

[0026] <Configuration of Transition Section 2> 1 to 3 and 5, the transition section 2 includes a semiconductor substrate 5, a first cladding layer 6, an active layer 11, a second cladding layer 22, a waveguide layer 23, a third cladding layer 25, and an insulating layer 16. The semiconductor substrate 5, the first cladding layer 6, the active layer 11, and the insulating layer 16 of the transition section 2 each have the same structure as the semiconductor substrate 5, the first cladding layer 6, the active layer 11, and the insulating layer 16 of the semiconductor laser section 1, respectively. The semiconductor substrate 5, the first cladding layer 6, the active layer 11, and the insulating layer 16 of the transition section 2 are each provided as the same member as the semiconductor substrate 5, the first cladding layer 6, the active layer 11, and the insulating layer 16 of the semiconductor laser section 1, for example. In other words, the semiconductor substrate 5, first cladding layer 6, active layer 11, and insulating layer 16 of the transition portion 2 are formed simultaneously with the semiconductor substrate 5, first cladding layer 6, active layer 11, and insulating layer 16 of the semiconductor laser portion 1, in the manufacturing method of the semiconductor laser device 100. The following will mainly describe the configuration of the transition portion 2 that differs from the semiconductor laser portion 1.

[0027] The first cladding layer 6, the active layer 11, the second cladding layer 22, the waveguide layer 23, and the third cladding layer 25 are provided on the first surface 5A and are stacked in this order from the first surface 5A side in the Z direction. The first cladding layer 6 and the second cladding layer 22 are provided so as to sandwich the active layer 11 in the Z direction. The first cladding layer 6 and the second cladding layer 22 are each in contact with the active layer 11. The second cladding layer 22 and the third cladding layer 25 are provided so as to sandwich the waveguide layer 23 in the Z direction. The second cladding layer 22 and the third cladding layer 25 are each in contact with the waveguide layer 23.

[0028] The waveguide layer 23 is provided on a portion of the second cladding layer 22 so as to overlap the active layer 11 of the transition section 2 in the Z direction. The waveguide layer 23 has a lower surface in direct contact with a portion of the upper surface of the second cladding layer 22 of the transition section 2, and an upper surface in direct contact with the entire lower surface of the third cladding layer 25. The waveguide layer 23 is sandwiched between insulating layers 16 in the X direction. The waveguide layer 23 further has a pair of side surfaces in contact with a pair of inner surfaces of the insulating layer 16 facing each other in the X direction.

[0029] 2, the width (thickness) of the waveguide layer 23 in the Z direction is wider (thicker) than the width (thickness) of the active layer 11 in the Z direction. As shown in FIGS. 2 and 5, the width of the waveguide layer 23 in the X direction is narrower than the width of the active layer 11 in the X direction. As shown in FIG. 2, in a cross section along the X and Y directions (hereinafter referred to as an XY cross section), the waveguide layer 23 is provided so that its width in the X direction gradually increases with increasing distance from the semiconductor laser portion 1 in the Y direction.

[0030] 5, in the XZ cross section, the waveguide layer 23 is provided so that its width in the X direction gradually narrows toward the second cladding layer 22 in the Z direction. In other words, in the XZ cross section, the waveguide layer 23 has an inverted mesa shape with respect to the second cladding layer 22. In the XZ cross section, the angle formed between the side surface of the waveguide layer 23 and the upper surface of the second cladding layer 12 outside the waveguide layer 23 is an acute angle. The width in the X direction of the active layer 11 of the transition section 2 is equal to the width in the X direction of the active layer 11 of the semiconductor laser section 1.

[0031] The minimum width in the X direction of one end of the waveguide layer 23 connected to the semiconductor laser portion 1 in the Y direction is equal to the minimum width in the X direction of the fourth cladding layer 15.

[0032] The third cladding layer 25 is provided on the waveguide layer 23. The third cladding layer 25 has a lower surface that is in direct contact with the upper surface of the waveguide layer 23, and an upper surface that is continuous to be flush with the upper surfaces of the fourth cladding layer 15 and the pair of insulating layers 16 of the semiconductor laser section 1. The third cladding layer 25 is sandwiched between the pair of insulating layers 16 in the X direction. The third cladding layer 25 further has a pair of side surfaces that are in contact with the pair of insulating layers 16, respectively.

[0033] 3 and 5, the width of the third cladding layer 25 in the X direction is narrower than the width of the active layer 11 in the X direction. As shown in FIG. 3, the third cladding layer 25 is provided so that the width in the X direction gradually increases with increasing distance from the semiconductor laser portion 1 in the Y direction in the XY cross section. As shown in FIG. 5, the third cladding layer 25 has an XZ Cut off In the XZ cross section, the width in the X direction gradually narrows toward the waveguide layer 23 in the Z direction. In other words, in the XZ cross section, the waveguide layer 23 and the third cladding layer 25 have an inverted mesa shape with respect to the second cladding layer 22. In the XZ cross section, the side surface of the third cladding layer 25 is continuous with, for example, the side surface of the waveguide layer 23 so as to form the same plane.

[0034] The refractive index of the second cladding layer 22 is higher than the refractive index (effective refractive index) of the active layer 11. The refractive index of the waveguide layer 23 is higher than the refractive index of each of the second cladding layer 22 and the third cladding layer 25. The refractive index of the third cladding layer 25 is higher than, for example, the refractive index of the fourth cladding layer 15. The second cladding layer 22 and the waveguide layer 23 are transparent to the light generated in the active layer 11. Here, transparent means that the transmittance of the light generated by the active layer 11 is 90% or more.

[0035] Each of the second cladding layer 22, the third cladding layer 25, and the waveguide layer 23 is one in which the composition ratio of any quaternary mixed crystal is appropriately adjusted so that each refractive index has the above relationship. The waveguide layer 23 is, for example, i-type InGaAsP. The second cladding layer 22 is, for example, n-type or i-type InGaAsP. The third cladding layer 25 may be, for example, n-type or i-type InP. By appropriately adjusting the composition ratio of each of the active layer 11, the second cladding layer 22, the third cladding layer 25, and the waveguide layer 23, the refractive index of the second cladding layer 22 becomes higher than the refractive index of the active layer 11 and lower than the refractive index of the waveguide layer 23. Note that the materials constituting the second cladding layer 22 and the waveguide layer 23 may be other quaternary mixed crystals than InGaAsP, and may be, for example, AlInGaAs or the like.

[0036] As shown in FIGS. 2 and 3, in the YZ cross section, the shape of each member constituting the transition portion 2 is symmetric with respect to the center line of the transition portion 2 that passes through the center in the X direction and extends along the Y direction. As shown in FIG. 5, in the XZ cross section, the shape of each member constituting the transition portion 2 is symmetric with respect to the center line of the transition portion 2 that passes through the center in the X direction and extends along the Z direction.

[0037] <Configuration of SSC3> The SSC 3 includes a semiconductor substrate 5, a first cladding layer 6, an active layer 11, a second cladding layer 32, a waveguide layer 33, a third cladding layer 35, a pair of fifth cladding layers 36, and a pair of insulating layers 16. The semiconductor substrate 5, the first cladding layer 6, and the active layer 11 of the SSC 3 each have the same structure as the semiconductor substrate 5, the first cladding layer 6, and the active layer 11 of the semiconductor laser section 1. The semiconductor substrate 5, the first cladding layer 6, the active layer 11, and the pair of insulating layers 16 of the SSC 3 are each provided as the same member as the semiconductor substrate 5, the first cladding layer 6, the active layer 11, and the pair of insulating layers 16 of the semiconductor laser section 1 and the transition section 2, for example. In other words, the semiconductor substrate 5, the first cladding layer 6, the active layer 11, and the pair of insulating layers 16 of the SSC3 are formed simultaneously with the semiconductor substrate 5, the first cladding layer 6, the active layer 11, and the pair of insulating layers 16 of the semiconductor laser section 1 and the transition section 2 in the manufacturing method of the semiconductor laser element 100.

[0038] Furthermore, the second cladding layer 32, the waveguide layer 33, and the third cladding layer 35 of the SSC3 each have the same structure as the second cladding layer 22, the waveguide layer 23, and the third cladding layer 25 of the transition section 2, respectively. The second cladding layer 32, the waveguide layer 33, and the third cladding layer 35 of the SSC3 are provided as the same members as the second cladding layer 22, the waveguide layer 23, and the third cladding layer 25 of the transition section 2, respectively, for example. In other words, the second cladding layer 32, the waveguide layer 33, and the third cladding layer 35 of the SSC3 are formed simultaneously with the second cladding layer 22, the waveguide layer 23, and the third cladding layer 25 of the transition section 2, respectively, in the manufacturing method of the semiconductor laser device 100. Below, the configuration of the SSC3 that differs from the semiconductor laser section 1 and the transition section 2 will be mainly described.

[0039] Each of the second cladding layer 32, the waveguide layer 33, the third cladding layer 35, and the fifth cladding layer 36 of the SSC 3 has a second end face 3B located on the opposite side to the transition section 2 in the Y direction. The second end face 3B is a cleavage plane. The second end face 3B is an emission surface from which the semiconductor laser device 100 emits laser light. The second end face 3B is covered with an antireflection film (AR (AntiReflection) coating film) not shown. The second end face 3B is coupled to an external optical system such as an optical fiber.

[0040] As described above, the SSC 3 includes a pair of fifth cladding layers 36. As shown in FIGS. 2, 3, 6, and 7, the pair of fifth cladding layers 36 are provided so as to sandwich the waveguide layer 33 in the X direction. As shown in FIGS. 6 and 7, each of the pair of fifth cladding layers 36 is provided on the second cladding layer 32. In the XZ cross section, the waveguide layer 33 is surrounded by the second cladding layer 32, the third cladding layer 35, and the pair of fifth cladding layers 36. The pair of fifth cladding layers 36 are provided so as to sandwich the waveguide layer 33 and the third cladding layer 35 in the X direction, for example.

[0041] 2 and 3, in the YZ cross section, the width in the X direction of each of the pair of fifth cladding layers 36 gradually increases with increasing distance from the transition section 2 in the Y direction. In the YZ cross section, the shape of each of the pair of fifth cladding layers 36 is, for example, triangular. In the YZ cross section, the width in the X direction of each of the pair of fifth cladding layers 36 is, for example, equal to each other.

[0042] 2, in the YZ cross section, the width of the waveguide layer 33 in the X direction gradually narrows with increasing distance from the transition portion 2 in the Y direction. In other words, in the YZ cross section, the width of the waveguide layer 33 in the X direction gradually narrows toward the second end face 3B in the Y direction. The width of the waveguide layer 33 in the X direction is narrowest at the second end face 3B. The minimum width of the waveguide layer 33 in the X direction is narrower than the minimum width of the waveguide layer 23 in the X direction.

[0043] 3, in the YZ cross section, the width of the third cladding layer 35 in the X direction gradually narrows with increasing distance in the Y direction from the transition section 2. The minimum width of the third cladding layer 35 in the X direction is narrower than the minimum width of the third cladding layer 25 in the X direction.

[0044] As shown in Figures 6 and 7, each of the pair of fifth cladding layers 36 has a lower surface in contact with a portion of the upper surface of the second cladding layer 32, an inner surface in direct contact with each side surface of the waveguide layer 33 and the third cladding layer 35, an outer surface in direct contact with each side surface of one insulating layer 16, and an upper surface that is continuous with and flush with the upper surfaces of the third cladding layer 35 and the pair of insulating layers 16.

[0045] 6 and 7, in the XZ cross section, the width in the X direction of each of the pair of fifth cladding layers 36 is constant, for example, in the Z direction. In the XZ cross section, the width in the X direction of each of the pair of fifth cladding layers 36 is, for example, equal to each other.

[0046] The refractive index of the second cladding layer 32 is higher than the refractive index (effective refractive index) of the active layer 11. The refractive index of the waveguide layer 33 is higher than the refractive index of each of the second cladding layer 32 and the third cladding layer 35. The refractive index of the fifth cladding layer 36 is lower than the refractive index of the waveguide layer 33.

[0047] The second cladding layer 32, the third cladding layer 35, the fifth cladding layer 36, and the waveguide layer 33 are each made of any quaternary mixed crystal with the above-mentioned composition ratios appropriately adjusted so that the refractive indices of each layer satisfy the above-mentioned relationships. The waveguide layer 33 is, for example, i-type InGaAsP. The second cladding layer 32 may be, for example, n-type InGaAsP or i-type InGaAsP. The third cladding layer 35 may be, for example, n-type InP or i-type InP. The fifth cladding layer 36 may be, for example, i-type InP.

[0048] 2 and 3, in the YZ cross section, the shapes of the members constituting SSC3 are symmetrical with respect to the center line of SSC3, which passes through the center in the X direction and extends along the Y direction. As shown in Figures 6 and 7, in the XZ cross section, the shapes of the members constituting SSC3 are symmetrical with respect to the center line of SSC3, which passes through the center in the X direction and extends along the Z direction.

[0049] <Method of Manufacturing Semiconductor Laser Device 100> Next, an example of a method for manufacturing the semiconductor laser device 100 will be described. The method for manufacturing the semiconductor laser device 100 includes, for example, a first step of forming device regions to become a plurality of semiconductor laser devices 100 on the first surface 5A of the semiconductor substrate 5, and a second step of singulating each of the plurality of semiconductor laser devices 100. As shown in Fig. 8, the first step includes, for example, a step (S1) of forming a first cladding layer 6, a diffraction grating 10, and an active layer 11 on the first surface 5A of the semiconductor substrate 5, a step (S2) of forming second cladding layers 22, 32 and waveguide layers 23, 33 on the active layer 11 of the transition portion 2 and SSC3, a step (S3) of forming a second cladding layer 12 on the active layer 11 of the semiconductor laser portion 1, and a step (S4) of forming a fourth cladding layer 15 on the semiconductor laser portion 1 and a third cladding layer 16 on the transition portion 2 and SSC3. The first step includes a step (S4) of forming the second cladding layer 12 and the fourth cladding layer 15 in the peripheral portion other than the central portion of the semiconductor laser section, and a step (S5) of removing the second cladding layers 22 and 32, the waveguide layers 23 and 33, and the third cladding layers 25 and 35 in the peripheral portion other than the central portions of the transition section 2 and SSC3, a step (S6) of forming a fifth cladding layer 36 in the peripheral portion of SSC3, and a step (S7) of forming an insulating layer 16, a first electrode 17, a second electrode 19, etc. In the first step, steps (S1) to (S7) are performed in order. In the second step, for example, a step of forming a cleavage plane in each of the second cladding layer 32, the waveguide layer 33, the third cladding layer 35, and the fifth cladding layer 36 to form a second end facet 3B.

[0050] In step (S1), first cladding layer 6 is formed over the entire first surface 5A of semiconductor substrate 5, and then diffraction grating 10 is formed only in the region where semiconductor laser portion 1 is to be formed, and then active layer 11 is formed only in the region where active layer 11 is to be formed. Methods for forming each include, for example, vapor phase growth, photolithography, and etching. As described above, the materials constituting the multiple quantum well layer and barrier layer of active layer 11 can be selected arbitrarily depending on the emission wavelength, and are, for example, quaternary mixed crystal semiconductor materials.

[0051] In step (S2), second cladding layers 22, 32 and waveguide layers 23, 33 are formed only in the regions where the transition section 2 and SSC 3 are to be formed. Methods for forming these cladding layers and waveguide layers include, for example, vapor deposition, photolithography, and etching. As described above, the materials (composition ratios) constituting each of the second cladding layers 22, 32 and the waveguide layers 23, 33 are appropriately adjusted so that the refractive index of the second cladding layers 22, 32 is higher than the refractive index of the active layer 11 and lower than the refractive index of the waveguide layers 23, 33.

[0052] In step (S3), second cladding layer 12 is formed only in the region where semiconductor laser portion 1 is to be formed. Methods for forming these cladding layers include, for example, vapor deposition, photolithography, and etching. As described above, the materials (composition ratio) constituting second cladding layer 12 are appropriately adjusted so that the refractive index of second cladding layer 12 is lower than the refractive index of active layer 11.

[0053] In step (S4), a fourth cladding layer 15 is formed in the region where the semiconductor laser section 1 is to be formed, and third cladding layers 25, 35 are formed in the regions where the transition section 2 and SSC 3 are to be formed. Methods for forming these cladding layers include, for example, vapor deposition, photolithography, and etching. As described above, the material (composition ratio) constituting the fourth cladding layer 15 is appropriately adjusted so that the refractive index of the fourth cladding layer 15 is lower than the refractive index of the active layer 11. The material (composition ratio) constituting the third cladding layers 25, 35 is appropriately adjusted so that the refractive index of the third cladding layers 25, 35 is lower than the refractive index of the waveguide layers 23, 33.

[0054] In step (S5), the second cladding layer 12 and the fourth cladding layer 15 in the peripheral portion other than the central portion of the semiconductor laser portion 1, and the second cladding layers 22 and 32, the waveguide layers 23 and 33, and the third cladding layers 25 and 35 in the peripheral portions other than the central portions of the transition portion 2 and the SSC 3 are removed to form a mesa structure. Methods for forming these cladding layers include photolithography and etching.

[0055] In step (S6), a fifth cladding layer 36 is formed on the second cladding layer 32 of the SSC 3 on both sides of the waveguide layer 33 and the third cladding layer 35 in the X direction. Methods for forming this cladding layer include, for example, vapor deposition, photolithography, and etching. As described above, the materials (composition ratio) constituting the fifth cladding layer 36 are appropriately adjusted so that the refractive index of the fifth cladding layer 36 is lower than the refractive index of the waveguide layer 33.

[0056] In step (S7), the insulating layer 16, the first electrode 17, the electrode pad 18, and the second electrode 19 are each formed. Methods for forming the insulating layer 16, the first electrode 17, the electrode pad 18, and the second electrode 19 include, for example, a film formation process, a photolithography process, a resin coating process, and an etching process.

[0057] <Operation of the semiconductor laser device 100> Next, the operation of the semiconductor laser device 100 will be described. When a drive current flows between the first electrode 17 and the second electrode 19 and carriers are injected into the active layer 11 of the semiconductor laser portion 1, inversion amplification occurs in the active layer 11, generating stimulated emission light. Furthermore, due to the effect of the diffraction grating 10 embedded under the active layer 11, laser oscillation occurs with the semiconductor laser portion 1 acting as a cavity. As a result, the semiconductor laser device 100 functions as an AR / HR coated distributed feedback laser.

[0058] 4 to 7, the transition of the optical propagation mode (waveguide) within the semiconductor laser device 100 will be specifically described below. Region I in Fig. 4, region J in Fig. 5, region K in Fig. 6, and region L in Fig. 7 show the distribution of the optical propagation mode on each XZ cross section. Based on the light intensity distribution on each XZ cross section, the optical propagation mode is defined as a region where the intensity is equal to or greater than a predetermined value relative to its maximum value.

[0059] Region I in Figure 4 shows the distribution of the optical propagation mode in the semiconductor laser section 1 on the XZ cross section. As shown in region I, in the semiconductor laser section 1, the optical propagation mode in the XZ cross section is distributed in a small, approximately circular shape centered on the active layer 11. The fourth cladding layer 15 is connected to only a portion of the second cladding layer 12. In other words, the connection region between the fourth cladding layer 15 and the second cladding layer 12 is narrower than the connection region between the active layer 11 and the second cladding layer 12. The current injected from the fourth cladding layer 15 through the second cladding layer 12 to the active layer 11 is limited to passing through the connection region between the fourth cladding layer 15 and the second cladding layer 12. Therefore, the region in the active layer 11 where population inversion occurs is limited to just below the connection region. Furthermore, in the semiconductor laser section 1, the refractive index of the active layer 11 is higher than the refractive indexes of the first cladding layer 6 and the second cladding layer 12 arranged around it. As a result, in the semiconductor laser portion 1, the optical propagation mode (waveguide) has a distribution in a relatively small, approximately circular shape with the active layer 11 at the center in the XZ cross section.

[0060] Furthermore, the cross-sectional shape of the fourth cladding layer 15 in the XZ cross section is an inverted mesa shape, and the fourth cladding layer 15 is connected to only a part of the second cladding layer 12 at the bottom of the inverted mesa shape. In this case, the width in the X direction of the connection region between the fourth cladding layer 15 and the second cladding layer 12 is narrower than when the cross-sectional shape of the fourth cladding layer 15 in the XZ cross section is a shape other than an inverted mesa shape, for example, a forward mesa shape. Therefore, the width in the X direction of the region where current is injected from the fourth cladding layer 15 through the second cladding layer 12 to the active layer 11 also becomes narrower, and the distribution of the optical propagation mode in the XZ cross section becomes narrower.

[0061] Light generated in the active layer 11 of the semiconductor laser section 1 is input to the active layer 11 of the transition section 2. Region J in FIG. 5 indicates the optical propagation mode in the transition section 2. As shown as region J in FIG. 5, the optical propagation mode in the transition section 2 is distributed between the active layer 11 and the waveguide layer 23. The second cladding layer 22 and the waveguide layer 23 of the transition section 2 are transparent to the light generated in the active layer 11, and the refractive index of the second cladding layer 22 is higher than the refractive index of the active layer 11, and the refractive index of the waveguide layer 23 is higher than the refractive index of the second cladding layer 22. As a result, as shown as region J in FIG. 5, the optical propagation mode gradually transitions from the active layer 11 to the waveguide layer 23 in the transition section 2. The optical propagation mode transitions to the waveguide layer 23 before reaching the SSC3.

[0062] Region K in FIG. 6 indicates an optical propagation mode formed in SSC3 closer to the transition section 2 than the center in the Y direction. Region L in FIG. 7 indicates an optical propagation mode formed in SSC3 closer to the second end face 3B than the center in the Y direction. As shown by region K in FIG. 6, the optical propagation mode on the transition section 2 side of SSC3 is distributed mainly in the waveguide layer 33. On the other hand, as shown by region L in FIG. 7, the optical propagation mode on the second end face 3B side of SSC3 is distributed so as to spread to the second cladding layer 32, the third cladding layer 35, and the fifth cladding layer 36, which are arranged to surround the waveguide layer 33. This is because the width of the waveguide layer 33 of SSC3 in the X direction gradually narrows toward the second end face 3B of the waveguide layer 33 in the Y direction. As a result, the divergence angle of the light emitted from the second end face 3B of SSC3 can be suppressed, thereby increasing the coupling efficiency between the semiconductor laser device 100 and an external optical system. Therefore, the coupling efficiency between the semiconductor laser device 100 and the external optical system is improved compared to a semiconductor laser device not provided with the SSC 3.

[0063] <Effects of the semiconductor laser element 100> Next, the effects of the semiconductor laser device 100 will be described in comparison with a comparative example. In a manufacturing method for a semiconductor laser device according to a comparative example in which the active layer of the laser portion of the semiconductor laser unit and the waveguide layer of the SSC are butt-connected in the Y direction, as in the semiconductor laser device described in Patent Document 1, it is necessary to remove the active layer formed in the SSC region, and then grow a semiconductor layer to become the waveguide layer in that region and further process it to form the waveguide layer that is butt-connected to the active layer.

[0064] In contrast, in the semiconductor laser device 100, the transition region 2 and the SSC3 each include a waveguide layer 33, and the waveguide layer 33 is in contact with a part of the upper surface of the second cladding layer 32 and has a higher refractive index than the active layer 11 and the second cladding layer 32. Therefore, the optical propagation mode transitions in the Z direction from the active layer 11 to the waveguide layer 23 in the transition region 2. Therefore, by growing semiconductor layers to become the waveguide layers 23, 33 on the active layer 11 without removing a part of the active layer 11 and further processing the semiconductor layers, the waveguide layers 23, 33 directly connected to the active layer 11 can be formed. Therefore, although the semiconductor laser device 100 includes the SSC3, the manufacturing cost can be reduced compared to the semiconductor laser device according to the comparative example.

[0065] In the semiconductor laser device 100, the refractive indexes of the active layer 11, the second cladding layer 22, and the waveguide layer 23, which are stacked in the Z direction in the transition section 2, are increased in this order. Therefore, in the transition section 2, the optical propagation mode can transition stepwise in the order of the active layer 11, the second cladding layer 22, and the waveguide layer 23.

[0066] In the semiconductor laser device 100, the transition section 2 and the SSC 3 are provided on the waveguide layers 23 and 33, respectively, and further include third clad layers 25 and 35 having a refractive index lower than that of the waveguide layers 23 and 33. The third clad layers 25 and 35 restrict the optical propagation mode from spreading above the waveguide layers 23 and 33 in the transition section 2 and the SSC 3, respectively.

[0067] In the semiconductor laser device 100, the semiconductor laser portion 1 further includes a fourth cladding layer 15 provided on a part of the second cladding layer 12, and a first electrode 17 provided on the fourth cladding layer 15 and electrically connected to the fourth cladding layer 15. The fourth cladding layer 15 is provided such that its width in the X direction gradually narrows toward the second cladding layer 12 in the Z direction. In other words, in the XZ cross section, the fourth cladding layer 15 has an inverted mesa shape with respect to the second cladding layer 12. Therefore, in the semiconductor laser device 100, the distribution of the optical propagation mode of the semiconductor laser portion 1 is narrower than in a semiconductor laser device in which the fourth cladding layer 15 does not have an inverted mesa shape with respect to the second cladding layer 12, and therefore the operating current can be reduced.

[0068] In the semiconductor laser device 100, the minimum width in the X direction of the waveguide layer 23 in the transition region 2 is equal to the minimum width in the X direction of the fourth cladding layer 15 in the semiconductor laser region 1. Furthermore, in the transition region 2, the width in the X direction of the waveguide layer 23 gradually narrows as it approaches the second cladding layer 22 in the Z direction, and the width in the X direction of the waveguide layer 23 gradually widens as it moves away from the semiconductor laser region 1 in the Y direction. Therefore, light incident on the transition region 2 from the semiconductor laser region 1 easily transits from the active layer 11 to the waveguide layer 23.

[0069] In the semiconductor laser device 100, in the SSC3, the width of the waveguide layer 33 in the X direction gradually narrows with increasing distance in the Y direction from the transition section 2. Therefore, the optical propagation mode on the second end facet 3B side of the SSC3 can be distributed so as to leak and spread to the second cladding layer 32, the third cladding layer 35, and the fifth cladding layer 36 that are arranged to surround the waveguide layer 33.

[0070] In the semiconductor laser device 100, the material constituting the second cladding layer 12 is InP, the material constituting the second cladding layers 22 and 32 is InGaAsP, and the material constituting the waveguide layers 23 and 33 is InGaAsP. By appropriately setting the composition of each InGaAsP, the refractive index of each of the waveguide layers 23 and 33 can be made higher than the refractive index of each of the second cladding layers 12, 22, and 32.

[0071] Embodiment 2 9 to 11, the semiconductor laser device 101 according to the second embodiment has basically the same configuration as the semiconductor laser device 100 according to the first embodiment, but differs from the semiconductor laser device 100 in that the semiconductor laser portion 1 includes a diffraction grating layer 8 embedded inside the fourth cladding layer 15 instead of the diffraction grating layer 7. The following mainly describes the differences between the semiconductor laser device 101 and the semiconductor laser device 100.

[0072] The diffraction grating layer 8 is provided on the second cladding layer 12. The diffraction grating layer 8 has a lower surface that is in direct contact with the upper surface of the second cladding layer 12, for example.

[0073] The average refractive index of the diffraction grating 10 made up of the diffraction grating layer 8 and the fourth cladding layer 15 is higher than the refractive index of the fourth cladding layer 15 and lower than the refractive index of the active layer 11 .

[0074] As shown in FIGS. 10 and 11 , the width T (thickness) of the diffraction grating layer 8 in the Z direction is equal to the width T (thickness) of the waveguide layer 23 in the Z direction. The width of the diffraction grating layer 8 in the X direction is narrower than the width of the active layer 11 in the X direction. The diffraction grating layer 8 is provided so that its width in the X direction gradually narrows toward the second cladding layer 12 in the Z direction. The material constituting the diffraction grating layer 8 is the same as the material constituting the waveguide layer 23. The refractive index of the diffraction grating layer 8 is higher than the refractive index of the fourth cladding layer 15. The diffraction grating layer 8 is made of, for example, InGaAsP.

[0075] The method for manufacturing the semiconductor laser device 101 basically comprises the same steps as the method for manufacturing the semiconductor laser device 100, but differs from the method for manufacturing the semiconductor laser device 100 in that the diffraction grating layer 8 is formed in the same step as the waveguide layers 23 and 33. Below, the differences between the method for manufacturing the semiconductor laser device 101 and the method for manufacturing the semiconductor laser device 100 will be mainly described.

[0076] As shown in FIG. 12, the first step of the manufacturing method of the semiconductor laser element 101 includes a step (S8) of forming the first cladding layer 6 and the active layer 11 on the first surface 5A of the semiconductor substrate 5, a step (S9) of forming the second cladding layers 22 and 32 and the waveguide layers 23 and 33 on the active layer 11 of the transition section 2 and the SSC 3, a step (S10) of forming the second cladding layer 12 on the active layer 11 of the semiconductor laser section 1, a step (S11) of forming the waveguide layers 23 and 33 and forming the diffraction grating layer 8, and a step (S12) of forming the fourth cladding layer 15 on the semiconductor laser section 1. The method includes a step (S12) of forming third cladding layers 25 and 35 on the transition section 2 and SSC3 while removing the second cladding layer 12 and fourth cladding layer 15 from the peripheral portion other than the central portion of the semiconductor laser section, and the second cladding layers 22 and 32, the waveguide layers 23 and 33, and the third cladding layers 25 and 35 from the peripheral portions other than the central portions of the transition section 2 and SSC3, a step (S14) of forming a fifth cladding layer 36 on the peripheral portion of SSC3, and a step (S15) of forming an insulating layer 16, a first electrode 17, a second electrode 19, etc. In the first step, steps (S8) to (S15) are performed in order.

[0077] In step (S8), first cladding layer 6 is formed over the entire first surface 5A of semiconductor substrate 5, and then active layer 11 is formed only in the region where active layer 11 is to be formed. Methods for forming first cladding layer 6 and active layer 11 include, for example, vapor phase growth, photolithography, and etching. As described above, the material constituting active layer 11 can be arbitrarily selected depending on the emission wavelength, and is, for example, a quaternary mixed crystal semiconductor material.

[0078] In step (S9), the second cladding layers 22, 32 are formed only in the regions where the transition section 2 and the SSC 3 are to be formed. Methods for forming the second cladding layers 22, 32 include, for example, vapor deposition, photolithography, and etching. As described above, the materials (composition ratios) constituting each of the second cladding layers 22, 32 are appropriately adjusted so that the refractive index of the second cladding layers 22, 32 is higher than the refractive index of the active layer 11 and lower than the refractive index of the waveguide layers 23, 33.

[0079] In step (S10), the second cladding layer 12 is formed only in the region where the semiconductor laser portion 1 is to be formed. of The method for forming the cladding layer includes, for example, vapor deposition, photolithography, and etching. As described above, the materials (composition ratio) constituting the second cladding layer 12 are appropriately adjusted so that the refractive index of the second cladding layer 12 is lower than the refractive index of the active layer 11.

[0080] In step (S11), the diffraction grating layer 8 is simultaneously formed in the region where the semiconductor laser section 1 is to be formed, and the waveguide layers 23, 33 are simultaneously formed in the regions where the transition section 2 and SSC 3 are to be formed. Methods for forming these layers include, for example, vapor deposition, photolithography, and etching. The materials (composition ratios) constituting each of the diffraction grating layer 8 and the waveguide layers 23, 33 are appropriately adjusted so that the refractive indexes of each of the diffraction grating layer 8 and the waveguide layers 23, 33 are higher than the refractive indexes of each of the second cladding layers 22, 32 and the fourth cladding layer 15.

[0081] In step (S12), a fourth cladding layer 15 is simultaneously formed in the region where the semiconductor laser portion 1 is to be formed, and third cladding layers 25, 35 are simultaneously formed in the regions where the transition portion 2 and SSC 3 are to be formed. Methods for forming these cladding layers include, for example, vapor deposition, photolithography, and etching. The materials (composition ratios) constituting the third cladding layers 25, 35 are appropriately adjusted so that the refractive index of the third cladding layers 25, 35 is lower than the refractive index of the waveguide layers 23, 33.

[0082] Steps (S13) to (S15) are carried out in the same manner as steps (S5) to (S7), respectively. In this manner, the semiconductor laser device 101 can be manufactured.

[0083] The semiconductor laser device 101 can operate in the same manner as the semiconductor laser device 100. The refractive index of the diffraction grating layer 8 is higher than that of the fourth cladding layer 15, but the average refractive index of the diffraction grating 10 consisting of the diffraction grating layer 8 and the fourth cladding layer 15 is lower than that of the active layer 11. In addition, the diffraction grating layer 8 is buried in the bottom of the fourth cladding layer 15, which has an inverted mesa shape. Therefore, the optical propagation mode in the semiconductor laser portion 1 does not spread to the diffraction grating 10, and has a distribution approximately equivalent to that of the semiconductor laser device 100.

[0084] Since the transition region 2 and SSC3 of the semiconductor laser device 101 have the same configuration as those of the semiconductor laser device 100, the optical propagation modes in each of the transition region 2 and SSC3 have distributions that are approximately the same as those of the semiconductor laser device 100.

[0085] In the manufacturing method of the semiconductor laser device 101, the diffraction grating layer 8 can be formed in the same process as the waveguide layers 23 and 33, and therefore the number of steps can be reduced compared to the manufacturing method of the semiconductor laser device 100. As a result, the manufacturing cost of the semiconductor laser device 101 can be further reduced compared to the manufacturing cost of the semiconductor laser device 100.

[0086] <Modification> In the semiconductor laser devices 100 and 101, the refractive index of each of the second cladding layers 22 and 32 may be equal to the refractive index of the active layer 11 as long as it is lower than the refractive index of each of the waveguide layers 23 and 33.

[0087] Embodiment 3 13 to 15, the semiconductor laser device 102 according to the third embodiment has basically the same configuration as the semiconductor laser device 100 according to the first embodiment, but differs from the semiconductor laser device 100 in that the second cladding layer 12 in the semiconductor laser portion 1 and the second cladding layers 22 and 32 in the transition portion 2 and SSC3 are disposed at the bottom of an inverted mesa structure that is narrower than the active layer 11, and the refractive index of the second cladding layer 12 in the semiconductor laser portion 1 is higher than the average refractive index of the active layer 11. The following will mainly describe the differences between the semiconductor laser device 102 and the semiconductor laser device 100.

[0088] As shown in FIG. 14 , the fourth cladding layer 15 and the second cladding layer 12 are provided on a portion of the active layer 11 in the X direction. The fourth cladding layer 15 is provided so as to overlap the entire second cladding layer 12 in the Z direction. The fourth cladding layer 15 and the second cladding layer 12 are provided so as to overlap the diffraction grating 10 in the Z direction. In a cross section along the X and Z directions (hereinafter referred to as an XZ cross section), the fourth cladding layer 15 and the second cladding layer 12 are provided so that their widths in the X direction gradually narrow toward the active layer 11 in the Z direction. In other words, in the XZ cross section, the fourth cladding layer 15 and the second cladding layer 12 have an inverted mesa shape. The fourth cladding layer 15 is made of, for example, n-type InP.

[0089] The refractive index of the second cladding layer 12 is higher than the average refractive index of the active layer 11. Preferably, the ratio of the refractive index of the second cladding layer 12 to the average refractive index of the active layer 11 is higher than 100% and not higher than 103%. The refractive index of the second cladding layer 12 is equal to the refractive index of the second cladding layers 22 and 32, for example. The material forming the second cladding layer 12 is the same as the material forming the second cladding layers 22 and 32, for example. The second cladding layer 12 is made of, for example, n-type InGaAsP.

[0090] Region I in FIG. 14 shows the distribution of the optical propagation mode in the semiconductor laser portion 1 on the XZ cross section. As shown in region I, in the semiconductor laser portion 1, the optical propagation mode in the XZ cross section is distributed in a small, approximately circular shape centered on the active layer 11. The second cladding layer 12 is connected to only a part of the active layer 11. That is, the width of the second cladding layer 12 in the X direction in the XZ cross section is narrower than that of the active layer 11. Therefore, in the semiconductor laser device 102, as described above, although the refractive index of the active layer 11 is slightly lower than the refractive index of the second cladding layer 12 that is in contact with the active layer 11, most of the optical propagation mode (waveguide) can be distributed in a relatively small, approximately circular shape centered on the active layer 11 without significantly reducing the coupling efficiency between the active layer 11 and the second cladding layer 12, similar to the semiconductor laser device 100.

[0091] 15, in the XZ cross section of the transition section 2, the second cladding layer 22 is provided so that its width in the X direction gradually narrows in the Z direction toward the active layer 11. In other words, in the XZ cross section, the third cladding layer 25, the waveguide layer 23, and the second cladding layer 22 have an inverted mesa shape.

[0092] 16, in the XZ cross section of the SSC3, the second cladding layer 32 is provided so that its width in the X direction gradually narrows in the Z direction toward the active layer 11. In other words, in the XZ cross section, the third cladding layer 35, the waveguide layer 33, and the second cladding layer 32 have an inverted mesa shape.

[0093] The method for manufacturing the semiconductor laser device 102 basically comprises the same steps as the method for manufacturing the semiconductor laser device 100, but differs from the method for manufacturing the semiconductor laser device 100 in that the second cladding layer 12 of the semiconductor laser portion 1 is formed in the same step as the second cladding layers 22, 32 of the transition portion 2 and the SSC 3. Below, the differences between the method for manufacturing the semiconductor laser device 102 and the method for manufacturing the semiconductor laser device 100 will be mainly described.

[0094] Semiconductor laser element 10 217, the first step of the manufacturing method includes a step (S16) of forming a first cladding layer 6, a diffraction grating layer 7, an active layer 11, and second cladding layers 12, 22, and 32 on the first surface 5A of the semiconductor substrate 5, a step (S17) of forming waveguide layers 23 and 33 on the active layer 11 of each of the transition section 2 and the SSC 3, and a step (S18) of forming a fourth cladding layer 15 in the semiconductor laser section 1 and third cladding layers 25 and 35 in the transition section 2 and the SSC 3. The method includes the steps of (S18) removing the second cladding layer 12 and the fourth cladding layer 15 in the peripheral portion other than the central portion of the semiconductor laser portion 1, and the second cladding layers 22 and 32, the waveguide layers 23 and 33, and the third cladding layers 25 and 35 in the peripheral portions other than the central portions of the transition portion 2 and SSC3, (S20) forming a fifth cladding layer 36 in the peripheral portion of SSC3, and (S21) forming an insulating layer 16, a first electrode 17, and a second electrode 19. In the first step, steps (S16) to (S21) are carried out in order.

[0095] In step (S16), first cladding layer 6 is formed over the entire first surface 5A of semiconductor substrate 5. Next, active layer 11 is formed only in the region where active layer 11 is to be formed. Next, second cladding layers 12, 22, and 32 are formed only in the regions where second cladding layers 12, 22, and 32 are to be formed. Methods for forming each layer include, for example, vapor phase growth, photolithography, and etching. As described above, the material constituting active layer 11 can be selected arbitrarily depending on the emission wavelength, and is, for example, a quaternary mixed crystal semiconductor material. The materials (composition ratios) constituting second cladding layers 12, 22, and 32 are appropriately adjusted so that the refractive index of second cladding layers 12, 22, and 32 is higher than the refractive index of active layer 11 and lower than the refractive index of waveguide layers 23 and 33.

[0096] In step (S17), the waveguide layers 23, 33 are formed only in the regions where the transition section 2 and the SSC 3 are to be formed. Methods for forming these waveguide layers include, for example, vapor deposition, photolithography, and etching. As described above, the materials (composition ratios) constituting the waveguide layers 23, 33 are appropriately adjusted so that the refractive index of the waveguide layers 23, 33 is higher than the refractive index of the second cladding layers 22, 32.

[0097] In step (S18), a fourth cladding layer 15 is formed in the region where the semiconductor laser section 1 is to be formed, and third cladding layers 25, 35 are formed in the regions where the transition section 2 and SSC 3 are to be formed. Methods for forming these cladding layers include, for example, vapor deposition, photolithography, and etching. As described above, the material (composition ratio) constituting the fourth cladding layer 15 is appropriately adjusted so that the refractive index of the fourth cladding layer 15 is lower than the refractive index of the active layer 11. The material (composition ratio) constituting the third cladding layers 25, 35 is appropriately adjusted so that the refractive index of the third cladding layers 25, 35 is lower than the refractive index of the waveguide layers 23, 33.

[0098] Steps (S19) to (S21) are carried out in the same manner as steps (S5) to (S7), respectively. In this manner, the semiconductor laser device 102 can be manufactured.

[0099] Although the embodiments of the present disclosure have been described above, the above-described embodiments can be modified in various ways. Furthermore, the scope of the present disclosure is not limited to the above-described embodiments. The scope of the present disclosure is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0100] 1 semiconductor laser portion, 2 transition portion, 3B second end facet, 5 semiconductor substrate, 5A first facet, 5B second facet, 6 first cladding layer, 7, 8 diffraction grating layer, 10 diffraction grating, 11 active layer, 11A first end facet, 12, 22, 32 second cladding layer, 15 fourth cladding layer, 16 insulating layer, 17 first electrode, 18 electrode pad, 19 second electrode, 23, 33 waveguide layer, 25, 35 third cladding layer, 36 fifth cladding layer, 100, 101, 102 semiconductor laser element.

Claims

1. a semiconductor laser portion; a transition portion adjacent to the semiconductor laser portion in a first direction and onto which light emitted from the semiconductor laser portion is incident; a spot size conversion portion adjacent to the transition portion in the first direction and on which the light emitted from the transition portion is incident, Each of the semiconductor laser portion, the transition portion, and the spot size conversion portion is a semiconductor substrate having a first surface extending along the first direction and a second direction perpendicular to the first direction; a first cladding layer, an active layer, and a second cladding layer stacked on the first surface in this order from the first surface side in a third direction orthogonal to the first surface, the second cladding layer is in contact with the active layer, the active layer of each of the transition portion and the spot size conversion portion is provided as the same material as the active layer of the semiconductor laser portion, In the transition section and the spot size conversion section, the refractive index of the second cladding layer is higher than the refractive index of the active layer; each of the transition section and the spot size conversion section further includes a waveguide layer in contact with a portion of an upper surface of the second cladding layer and having a refractive index higher than that of the active layer and the second cladding layer; the refractive index of the waveguide layer is higher than the refractive index of the second cladding layer; In the transition section, the width of the waveguide layer in the second direction gradually increases with increasing distance from the semiconductor laser section in the first direction, In the spot size conversion section, a width of the waveguide layer in the second direction is gradually narrowed with increasing distance from the transition section in the first direction, the spot size conversion portion further includes a pair of fifth cladding layers disposed to sandwich the waveguide layer in the second direction, In the semiconductor laser portion, the refractive index of the second cladding layer is higher than the refractive index of the active layer.

2. In the semiconductor laser portion, the second cladding layer is provided on a part of the active layer, The semiconductor laser unit a fourth clad layer provided on the second clad layer; an electrode provided on the fourth clad layer and electrically connected to the fourth clad layer, 2. The semiconductor laser device according to claim 1, wherein the fourth cladding layer and the second cladding layer are provided so that the widths in the second direction gradually narrow toward the active layer in the third direction.

3. In the transition portion, a width of the waveguide layer in the second direction is narrower than a width of the active layer in the second direction; In each of the transition section and the spot size conversion section, the width of the waveguide layer in the second direction gradually decreases toward the second cladding layer in the third direction, 3. The semiconductor laser device according to claim 2, wherein a minimum width of said waveguide layer of said transition section in said second direction is equal to a minimum width of said fourth cladding layer of said semiconductor laser section in said second direction.

4. 4. The semiconductor laser device according to claim 1, wherein the material forming said waveguide layer is InGaAsP.

5. 4. The semiconductor laser device according to claim 1, wherein the material forming said waveguide layer is AlInGaAs.

Images