Semiconductor laser

Abstract

The invention relates to a semiconductor laser. A semiconductor laser having excellent characteristics is provided. The semiconductor laser includes: a first conductive type semiconductor layer and a second conductive type semiconductor layer; a first electrode and a second electrode electrically connected to the first conductive type semiconductor layer or the second conductive type semiconductor layer; a diffraction grating layer; an insulating film disposed in a portion of a space between the second electrode and the second conductive type semiconductor layer; a mesa structure; and a first region and a second region in a direction in which the mesa structure extends. A first diffraction grating region in the diffraction grating layer of the first region and a second diffraction grating region in the diffraction grating layer of the second region form a resonator. The first region has a normalized coupling coefficient higher than a normalized coupling coefficient of the second region. The following in the first region is smaller than in the second region: a current supplied from the second electrode to the mesa structure per unit area.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority to Japanese Patent Application No. 2024-046659 filed on March 22, 2024 and Japanese Patent Application No. 2023-205737 filed on December 6, 2023. The disclosures of these prior applications are considered part of and incorporated by reference into this patent application. Technical Field

[0003] The present disclosure relates generally to semiconductor lasers. Background Art

[0004] Semiconductor lasers are widely used as light sources for optical communications. A distributed feedback semiconductor laser (DFB laser) is a type of semiconductor laser. The DFB laser includes a diffraction grating. In addition, the diffraction grating may include a structure having a phase shift portion for characteristic improvement. By forming an anti-reflection film (low-reflection film) on two facets of the semiconductor laser and arranging a λ / 4 offset portion in the diffraction grating, a stable single-wavelength operation can be obtained. Two regions having different reflectivities from each other with respect to the Bragg reflected light beam can be arranged in the resonator direction to increase the output of one facet. Summary of the invention

[0005] A structure can combine regions with high reflectivity and low reflectivity relative to the Bragg wavelength. The electrode into which the drive current is injected can be arranged to extend across two regions with different reflectivities from each other. Therefore, the two regions with different reflectivities have approximately the same injection current density. Compared with the region with low reflectivity, the region with high reflectivity has a low photon density and therefore has a high carrier density and a low refractive index. The region with high reflectivity also has a large gain. A low refractive index can lead to a degradation of the side mode suppression ratio (SMSR) and a decrease in yield. A large gain can lead to a decrease in light extraction efficiency and a degradation of the relative noise intensity characteristic.

[0006] An object of the present invention is to provide a semiconductor laser having excellent characteristics.

[0007] Some implementations described herein include a semiconductor laser including: a first conductive type semiconductor layer; an active layer formed on the first conductive type semiconductor layer; a second conductive type semiconductor layer formed on the active layer; a first electrode electrically connected to the first conductive type semiconductor layer; a second electrode electrically connected to the second conductive type semiconductor layer; a diffraction grating layer placed on one of the first conductive type semiconductor layer side or the second conductive type semiconductor layer side when viewed from the active layer; an insulating film placed in a portion of the space between the second electrode and the second conductive type semiconductor layer; a mesa structure including at least one of the active layer or the second conductive type semiconductor layer; and a first region and a second region in a direction in which the mesa structure extends. The diffraction grating layer of the first region includes a first diffraction grating region. The diffraction grating layer of the second region includes a second diffraction grating region. The first diffraction grating region and the second diffraction grating region form a resonator. The first region has a normalized coupling coefficient higher than the normalized coupling coefficient of the second region. The following item in the first region is smaller than that in the second region: current supplied from the second electrode to the mesa structure per unit area. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a top view for illustrating a semiconductor laser implemented according to a first example of the present disclosure.

[0009] Figure 2 It is along Figure 1 A schematic cross-sectional view of the semiconductor laser shown is taken along line II-II.

[0010] Figure 3 It is along Figure 1 A schematic cross-sectional view of the semiconductor laser shown is taken along line III-III.

[0011] Figure 4 is another top view of the semiconductor laser implemented according to the first example.

[0012] Figure 5 is a top view of a semiconductor laser according to Modification Example 1 of the first example implementation.

[0013] Figure 6 is a top view of a semiconductor laser according to Modification Example 2 of the first example implementation.

[0014] Figure 7 is a schematic cross-sectional view of a semiconductor laser according to a second embodiment of the present disclosure.

[0015] Figure 8 is a top view of a semiconductor laser implemented according to the second example.

[0016] Fig. 9is a schematic cross-sectional view of a semiconductor laser implemented according to a third example of the present disclosure.

[0017] Fig.10 is a top view of a semiconductor laser implemented according to the third example.

[0018] Fig.11 is a top view of a semiconductor laser implemented according to a fourth example of the present disclosure.

[0019] Fig.12 It is along Fig.11 A schematic cross-sectional view of the semiconductor laser shown is taken along line XII-XII.

[0020] Fig.13 is another top view of the semiconductor laser implemented according to the fourth example.

[0021] Fig.14 is a top view of a semiconductor laser implemented according to a fifth example of the present disclosure.

[0022] Fig.15 It is along Fig.14 A schematic cross-sectional view of a semiconductor laser shown is taken along line XV-XV.

[0023] Fig.16 It is along Fig.14 A schematic cross-sectional view of the semiconductor laser shown is taken along line XVI-XVI.

[0024] Fig.17 It is along Fig.14 A schematic cross-sectional view of the semiconductor laser shown is taken along line XVII-XVII.

[0025] Fig.18 is another top view of the semiconductor laser implemented according to the fifth example.

[0026] Fig.19 is a top view of a semiconductor laser implemented according to a sixth example of the present disclosure.

[0027] Fig. 20 It is along Fig.19 A schematic cross-sectional view of a semiconductor laser taken along line XX-XX is shown.

[0028] Fig.21 is another top view of the semiconductor laser implemented according to the sixth example. DETAILED DESCRIPTION

[0029] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. Components represented by the same reference numerals throughout the drawings have the same or equivalent functions, and repeated descriptions of these components are omitted. Note that the size of the figures is not always scaled to scale.

[0030] Figure 1 is a top view for illustrating a semiconductor laser 1 implemented according to a first example of the present disclosure. Figure 2 Shown along Figure 1 Schematic cross-sectional view taken along line II-II. Figure 3 Shown along Figure 1 Schematic cross-sectional view taken along line III-III. Figure 4 1 is a top view for illustrating the semiconductor laser 1, and is an explanatory diagram for illustrating the position of each region included in the semiconductor laser 1. The semiconductor laser 1 may include a first electrode 2 on its rear surface and a second electrode 3 on its front surface. The first electrode 2 and the second electrode 3 may be metal layers. By injecting current between the first electrode 2 and the second electrode 3, the front facet 40 ( Figure 1 and Figure 2 The first electrode 2 may be an electrode electrically connected to a first conductive type semiconductor layer described later. The second electrode 3 may be an electrode electrically connected to a second conductive type semiconductor layer described later. The low-reflective facet coating film 4 may be formed on each facet in a direction in which a mesa structure described later extends (hereinafter referred to as a "first direction D1"), that is, a front facet 40 ( Figure 1 and Figure 2 The left side facet) and the back facet 50 ( Figure 1 and Figure 2 The reflectivity of the low-reflection facet coating film 4 may be equal to or less than 1%.

[0031] The semiconductor laser 1 may have a semiconductor multilayer structure including a first conductive type semiconductor layer, an active layer, and a second conductive type semiconductor layer that may be grown sequentially. In a first exemplary implementation, on a substrate 5 of a first conductive type, semiconductor layers, i.e., a core layer 7, a cladding layer 9 of a second conductive type, and a contact layer 13 of a second conductive type may be grown sequentially. The substrate 5 corresponds to a first conductive type semiconductor layer. Another first conductive type semiconductor layer may be formed on the substrate 5. The core layer 7 may be a semiconductor layer including at least an active layer. For example, the core layer 7 may be a semiconductor layer obtained by sequentially growing a first conductive type light confinement layer, an active layer that may be formed by an "i" type multi-quantum well layer, and a second conductive type light confinement layer from the substrate 5 side to the second conductive type cladding 9 side. The core layer 7 may include layers other than these semiconductor layers. The active layer may be an n-type semiconductor layer. In a first exemplary implementation, the cladding 9 and the contact layer 13 form a second conductive type semiconductor layer. The diffraction grating layer 11 may be formed in the cladding layer 9 of the second conductive type. The semiconductor laser 1 may be a DFB laser. The first conductivity type and the second conductivity type here can be n-type and p-type respectively, but can be switched to each other. Figure 3 As shown, the semiconductor multilayer including the above layers may have a mesa structure 15. Here, a portion of the substrate 5 as well as the core layer 7, the cladding layer 9 and the contact layer 13 may be included in the mesa structure 15. The mesa structure 15 extends in a direction in which light can be taken out. Each side of the mesa structure 15 may be covered with a semi-insulating semiconductor buried layer 17. The buried layer 17 may be a multilayer of p-type and n-type semiconductor layers. Figure 1 The dotted line indicates the position of the boundary between the mesa structure 15 and the buried layer 17. The mesa structure 15 may have a constant width in a direction perpendicular to the first direction D1 in a plan view (hereinafter referred to as "second direction D2").

[0032] The semiconductor laser 1 may include an insulating film 14. The insulating film 14 may cover the surface of the semiconductor laser 1 except for some parts. The insulating film 14 may be a film of, for example, silicon oxide, silicon nitride, or resin. The insulating film 14 may include one or more opening regions in a portion of the space above the mesa structure 15, in which the second electrode 3 and the second conductive type semiconductor layer may contact each other. The second electrode 3 and the contact layer 13 of the second conductive type may be physically and electrically connected to each other via the opening region, and an electrical signal may be applied to the active layer (current may be injected into the active layer) via the second conductive type semiconductor layer. The opening region may be a hole for electrically connecting the second electrode 3 and the contact layer 13 of the second conductive type to each other, and therefore, may also be referred to as a "through hole 18" hereinafter. In a first example implementation, the through holes 18 may be aligned in the first direction D1. Each through hole 18 may have a width (length in the second direction D2) wider than the width of the mesa structure 15. However, the width of each through hole 18 may be the same as or narrower than the mesa width. The details of the through hole 18 are described later.

[0033] The diffraction grating layer 11 may include a plurality of first refractive index regions 11A and a plurality of second refractive index regions 11B. Specifically, the diffraction grating layer 11 may be of a floating type, and may be formed of a region having a first refractive index different from the refractive index of the cladding layer 9 of the second conductivity type and a region having a second refractive index in which the cladding layer 9 of the second conductivity type may be arranged in a cross-sectional view. That is, the diffraction grating layer 11 may have a structure in which the first refractive index regions 11A and the second refractive index regions 11B having the same length are alternately arranged. In this case, the first refractive index is higher than the second refractive index, but the second refractive index may be higher than the first refractive index.

[0034] The following region in the diffraction grating layer 11 may be referred to as a “diffraction grating region 12A”: in this region, the first refractive index region 11A and the second refractive index region 11B may have the same length and are arranged alternately. Meanwhile, the following region of the diffraction grating layer 11 may be referred to as a “non-diffraction grating region 12B”: in this region, only the first refractive index region 11A or only the second refractive index region 11B is arranged. In the first example implementation, the non-diffraction grating region 12B may be formed of the second refractive index region 11B. The diffraction grating region 12A in the first example implementation may have a uniform diffraction grating structure in which the first refractive index region 11A and the second refractive index region 11B have the same length in the first direction D1 and are arranged alternately. The Bragg wavelength of such a diffraction grating structure corresponds to the 1.3-μm band, but other Bragg wavelengths, such as the 1.55-μm band, may also be used.

[0035] like Figure 2As shown, the semiconductor laser 1 may include two regions. On the rear facet 50 side, a first region 10 including one diffraction grating region in the diffraction grating region 12A may be placed. On the front facet 40 side, a second region 20 in which a plurality of diffraction grating regions 12A and a plurality of non-diffraction grating regions 12B are alternately arranged may be placed. Here, the diffraction grating regions 12A and the non-diffraction grating regions 12B may be arranged so that a light beam having a Bragg wavelength transmitted from the first region 10 may be reflected into the second region 20. In order to strongly reflect a light beam having a specific wavelength (Bragg wavelength), it may be necessary to adjust the length (diffraction grating period) of the first refractive index region 11A and the second refractive index region 11B. In addition, the relationship between the diffraction grating period and the Bragg wavelength may depend on the effective refractive index. In a first example implementation, the first region 10 may have an effective refractive index greater than that of the second region 20. This may be because, when the second region 20 is regarded as a whole, the number of regions that do not have a diffraction grating structure (regions that are non-diffraction grating regions 12B) is large, and therefore the effective refractive index may be reduced by this amount. Taking into account the difference between the average effective refractive index of the first region 10 and the average effective refractive index of the second region 20, the diffraction grating region 12A and the non-diffraction grating region 12B to be arranged in the second region 20 may be determined. Here, the diffraction grating period of the diffraction grating region 12A arranged in the second region 20 may be different from or the same as the diffraction grating period of the diffraction grating region 12A arranged in the first region 10. In the case of adopting the same diffraction grating period, the length of each of the plurality of diffraction grating regions 12A and the plurality of non-diffraction grating regions 12B in the first direction D1 and the interval between the two regions may be adjusted so that the average diffraction grating period of the entire second region 20 reflects a light beam having a desired Bragg wavelength. Hereinafter, when special distinction may be required, the diffraction grating region 12A included in the first region 10 may be referred to as a "first diffraction grating region", and the diffraction grating region 12A included in the second region 20 may be referred to as a "second diffraction grating region". The diffraction grating region 12A and the non-diffraction grating region 12B included in the second region 20 may have different lengths in the first direction D1. It is preferred that each length is different, for example, under the condition of causing reflection at a desired Bragg wavelength, in order to suppress high-order diffraction backscattering relative to the Bragg wavelength.

[0036] In order to obtain high single wavelength characteristics, it may be necessary to form a resonator by the first region 10 and the second region 20. In order to form a resonator by the first region 10 and the second region 20, it may be necessary to shift the phase of the diffraction grating region of the first region 10 and the phase of the diffraction grating region of the second region 20 by π. Here, the phase of the diffraction grating region refers to the phase of the diffraction grating structure. For example, when the first region 10 and the second region 20 have the same effective refractive index, it may only be required that the phase of the second diffraction grating region (the diffraction grating region 12A of the second region 20) is simply shifted by π relative to the phase of the first diffraction grating region (the diffraction grating region 12A of the first region 10). However, in the first example implementation, the first region 10 and the second region 20 may have different effective refractive indices. Therefore, the phase of the second diffraction grating region may need to be different from the phase obtained by shifting the phase of the first diffraction grating region by π. In the first example implementation, the phase of the first diffraction grating region and the phase of the second diffraction grating region may not be shifted by π, but a resonator can be formed by the first region 10 and the second region 20. Furthermore, in the first exemplary implementation, the low-reflection facet coating film 4 can be formed on two facets, and thus a very high single-wavelength characteristic can be achieved.

[0037] In the first example implementation, the normalized coupling coefficient κ1L1 of the first region 10 may be greater than the normalized coupling coefficient κ2L2 of the second region 20. The coupling coefficient κ may be determined according to the semiconductor multilayer and the diffraction grating structure. Here, for example, due to the difference in effective refractive index, the coupling coefficient κ1 of the first region 10 and the coupling coefficient κ2 of the second region 20 may be different. However, the difference may be small, and the main reason for the difference in the normalized coupling coefficient between the first region 10 and the second region 20 may be the length of the diffraction grating region 12A included in each region in the first direction D1. Here, the length L1 of the first region 10 may be the length of the first diffraction grating region in the first direction D1. The length L2 of the second region 20 may be the total length of the plurality of second diffraction grating regions. That is, the length L2 may be the total length of the plurality of diffraction grating regions 12A included in the second region 20 in the first direction D1. The non-diffraction grating region 12B does not reflect a light beam having a Bragg wavelength, and therefore the coupling coefficient κ of the non-diffraction grating region 12B may be actually regarded as 0. Therefore, the length L2 of the second region 20 contributing to the normalized coupling coefficient κL becomes the total length of the region in which the plurality of second diffraction grating regions are arranged. The normalized coupling coefficient κ1L1 of the first region 10 may be greater than the normalized coupling coefficient κ2L2 of the second region 20, and thus the light output intensity of the light beam output from the front facet 40 becomes greater than the light output intensity of the light beam output from the rear facet 50. When the normalized coupling coefficients of the first region 10 and the second region 20 are the same value, the light output intensities of the light beams output from the front facet 40 and the rear facet 50 are the same. In the present disclosure, the total length of the region in which the plurality of second diffraction grating regions are arranged may be set to be shorter than the length of the region in which the first diffraction grating regions may be arranged, so that the intensity of the light beam output from the front facet 40 may be increased. The "front" and "rear" used here may be merely names used for convenience, and the facet with a larger light output may be referred to as the front facet for short. In general optical communications, a larger light intensity may be preferred, and the light beam from the front facet may be used for communication. In addition, the total length of the plurality of second diffraction grating regions in the first direction D1 may be shorter than the total length of the plurality of non-diffraction grating regions 12B. With this structure, the effect of increasing the light output from the front side obtained by reducing the coupling coefficient κ2 of the second region 20 may be enhanced. Here, it is preferred that κ1L1 may be equal to or greater than 60% (i.e., κ2L2 is equal to or less than 40%) relative to the normalized coupling coefficient of the entire semiconductor laser 1.

[0038] Here, the resonator length of the semiconductor laser 1 may be the total length of the first region 10 and the second region 20 in the first direction D1. In the first example implementation, the resonator length substantially corresponds to the length between the front facet 40 and the rear facet 50. The first example implementation also aims to increase the light output intensity of the light beam output from the front facet 40 so as to be greater than the light output intensity of the light beam output from the rear facet 50. To this end, it is preferred that the first region 10 (more strictly speaking, the first diffraction grating region) is located on the rear side. For example, it is preferred that the first diffraction grating region is arranged in a region that is equal to or less than 40% of the resonator length from the rear end portion of the resonator (in this case, the rear facet 50). That is, the length of the first diffraction grating region in the direction in which the mesa structure extends may preferably be equal to or less than 40% of the length of the entire diffraction grating layer, and more preferably equal to or less than 30% thereof. However, when κ1L1 is less than 1, the oscillation threshold may increase, which may not be preferred from the viewpoint of power consumption. Therefore, κ1L1 may preferably be set to be equal to or greater than 1, and more preferably to be equal to or greater than 1.5.

[0039] Figure 4 1 is a top view of the semiconductor laser 1 and can be an explanatory diagram for illustrating the position of the opening region (through hole 18). For convenience of explanation, Figure 4 The second electrode 3 is omitted in the figure. Figure 4 It is also a perspective view of the diffraction grating layer 11 assuming that the diffraction grating layer 11 is transparent. The dot-dash line indicates the position of the through hole 18.

[0040] The through hole 18 may be an opening provided in the insulating film 14. The through hole 18 may be placed only in a portion of the top surface of the mesa structure 15 in the first region 10. In other words, the through hole 18 may be discretely placed in the first region 10. In the first region 10, the high resistance element 30 may be placed in a region other than the opening region in the region directly above the mesa structure 15 (hereinafter also referred to as a "non-opening region"). That is, the high resistance element 30 may be placed in a portion of the top surface of the mesa structure 15 in the first region 10. The phrase "high resistance" means that the resistance is higher than the contact layer 13. In the first example implementation, the high resistance element 30 may be a portion of the insulating film 14. However, the material of the high resistance element 30 and the material of the region of the insulating film 14 other than the high resistance element 30 may be different from each other. Examples of other materials are given later. The resistance of the high resistance element 30 may be higher than the resistance of the contact layer 13 of the second conductive type. In the opening region which is a region above the mesa structure 15 and in which the insulating film 14 may not be placed, the second electrode 3 and the second conductive type contact layer 13 may be in electrical and physical contact with each other. The shape of each through hole 18 may be a quadrilateral in a plan view, but is not limited thereto. For example, each through hole 18 may have a quadrilateral shape with rounded corners.

[0041] As described above, the normalized coupling coefficient κ1L1 of the first region 10 may be higher than the normalized coupling coefficient κ2L2 of the second region 20. Therefore, the photon density of the first region 10 may be lower than the photon density of the second region 20. When the photon density is higher, the carrier consumption caused by stimulated emission may be greater. Therefore, in the case where the injection current density of the first region 10 and the second region 20 is equal to each other, the carrier density of the first region 10 may be higher than the carrier density of the second region 20. In the first example implementation, the first region 10 and the second region 20 may have equal injection current density because the second electrode 3 is placed to extend across the first region 10 and the second region 20. With a higher carrier density, the refractive index of the first region 10 may be lower and the gain may be greater. A decrease in the refractive index may result in degradation of the SMSR characteristics, and an increase in the gain may result in a decrease in the efficiency of the light output from the front facet 40 and degradation of the relative noise intensity characteristics. The present disclosure deals with this by setting the following item in the first region 10 to be smaller than that in the second region 20: the current supplied from the second electrode 3 to the mesa structure 15 per unit area. In the first example implementation, by limiting the area in which the current can be injected in the first region 10, the current per unit area in the first region 10 can be set to be smaller than that in the second region 20. Therefore, the injection current density of the first region 10 can be set lower than that of the second region 20, thereby preventing the carrier density of the first region 10 from increasing. In order to limit the area into which the current is injected, the through hole 18 of the first region 10 can be placed only in a part of the area directly above the mesa structure 15, rather than the entire area. In the area where the through hole 18 is not placed, the high resistance element 30 can be placed. In other words, in the top surface of the mesa structure 15 in the first region 10, the opening area (through hole 18) and the non-opening area (high resistance element 30) can be alternately arranged along the first direction D1. Current cannot be injected into the non-opening area, and thus the overall carrier density of the first region 10 can be reduced.

[0042] In the first region 10, the ratio of the opening area (through hole 18) to the area directly above the mesa structure 15 may preferably be equal to or less than 60%. The ratio of the opening area to the area directly above the mesa structure 15 may be referred to as the "aperture ratio" hereinafter. A more preferred aperture ratio may be equal to or greater than 20% and equal to or less than 50%. The term "aperture ratio" may be understood as the ratio of the planar size of the region (energized region) in which the second electrode 3 and the second conductive type semiconductor layer (contact layer 13) are in contact with each other to the entire planar size of the top surface of the mesa structure 15 in the first region 10. Figure 2In the embodiment, the second region 20 may include a region in which the high resistance element 30 is placed, which is close to the position where the second region 20 can be connected to the first region 10. However, compared with the opening area of ​​the second region 20, this area can be sufficiently small as a whole, and thus has little effect on the carrier density. In the first example implementation, the opening ratio of the first region 10 can be smaller than the opening ratio of the second region 20, thereby being able to reduce the influence of the difference in carrier density caused by the difference in the normalized coupling coefficient κL.

[0043] In the first example implementation, the plurality of vias 18 and the plurality of high resistance elements 30 disposed in the first region 10 may have the same length in the first direction D1, but are not limited thereto and may have different lengths. However, it may be desirable to discretely arrange the plurality of vias 18 to ensure uniform injection current in the first region 10. The desired minimum length between the plurality of vias 18 in the first direction D1 may be equal to or less than 1 / 5 of the length of the first region 10.

[0044] In the first example implementation, the first electrode 2 and the second electrode 3 may each be integrally formed to extend across the first region 10 and the second region 20, but is not limited thereto. As long as current can be injected into the electrodes in the first region 10 and the second region 20 at the same injection current density, separate electrodes may be provided for the first region 10 and the second region 20.

[0045] The semiconductor laser 1 implemented according to the first example realizes both high wavelength uniformity and high power characteristics of the output of the front facet 40 by forming a resonator by the first region 10 having a normalized coupling coefficient κ1L1 and the second region 20 having a normalized coupling coefficient κ2L2 (which may be lower than the normalized coupling coefficient κ1L1). The semiconductor laser 1 also realizes excellent SMSR characteristics and relative noise intensity characteristics by setting the aperture ratio of the through hole 18 of the first region 10 to be lower than the aperture ratio of the through hole 18 of the second region 20.

[0046] Figure 5 1 is a top view of the semiconductor laser 1 of the modified example 1 implemented according to the first example, and is an explanatory diagram for illustrating the mode of the through hole 18. The difference from the first example implementation is the shape of the through hole 18 and the high resistance element 30. In the modified example 1, the through holes 18 can each have a parallelogram shape in a plan view. In other words, the side surfaces forming the through hole 18 and the high resistance element 30 can be arranged to be inclined relative to the first direction D1 along which the light resonates. The inclination angles here are all constant, but may not be limited thereto and may be different from each other.

[0047] Figure 61 is a top view of the semiconductor laser 1 of the modified example 2 implemented according to the first example, and is an explanatory diagram for illustrating the pattern of the through hole 18. The difference from the first example implementation lies in the shapes of the through hole 18 and the high resistance element 30. The widths of the corresponding through holes 18 can be substantially the same in the second direction D2 of the mesa structure 15. The through holes 18 in the first region 10 can be hexagonal. Therefore, the shape of each through hole 18 can be a quadrilateral, a hexagon or other polygon, or a circle or an ellipse. A combination of these shapes can also be used. As long as the aperture ratio of the first region 10 is lower than the aperture ratio of the second region 20, the effect of the present disclosure can be obtained.

[0048] Figure 7 is a schematic cross-sectional view of a semiconductor laser 201 according to a second example implementation of the present disclosure taken along a first direction D1, and corresponds to a cross-sectional view taken along Figure 1 Schematic cross-sectional view taken along line II-II. Figure 8 2 is a top view of the semiconductor laser 201 and is an explanatory diagram for illustrating a mode of an opening region (through hole 218 ).

[0049] The semiconductor multilayer structure of the semiconductor laser 201 may be substantially the same as the structure of the semiconductor layer 1 implemented according to the first example, but the number of diffraction grating layers and the diffraction grating structure may be different. In the second example implementation, the first region 210 may include two layers, which may be a first diffraction grating layer 211A and a second diffraction grating layer 211B, wherein the first diffraction grating layer 211A is closer to the core layer 7 than the second diffraction grating layer 211B. The cladding layer 9 may be placed between the first diffraction grating layer 211A and the second diffraction grating layer 211B. On the other hand, the second region 220 may include only the first diffraction grating layer 211A. The λ / 4 phase shift portion 219 may be placed between the first region 210 and the second region 220. The λ / 4 phase shift portion 219 may also be placed in the second diffraction grating layer 211B. The first region 210 may have a uniform diffraction grating structure in which the first refractive index region 11A and the second refractive index region 11B may have the same length in the first direction D1 and may be alternately arranged except for the phase shift portion 219. In the first region 210, the first refractive index region 11A and the second refractive index region 11B included in the first diffraction grating layer 211A may have the same length and phase as the first refractive index region 11A and the second refractive index region 11B included in the second diffraction grating layer 211B. The second region 220 may have a uniform diffraction grating structure in which the first refractive index region 11A and the second refractive index region 11B have the same length in the first direction D1 and may be alternately arranged except for the phase shift portion 219. The first region 210 may include a first diffraction grating region formed of two diffraction grating layers (the first diffraction grating layer 211A and the second diffraction grating layer 211B). The second region 220 may include a second diffraction grating region formed of a single diffraction grating layer (first diffraction grating layer 211A). The first diffraction grating region and the second diffraction grating region form a resonator with the phase shift portion 219 sandwiched therebetween.

[0050] Due to the second diffraction grating layer 211B included therein, the coupling coefficient κ of the first region 210 is higher than that of the second region 220. In the second exemplary implementation, the normalized coupling coefficient κ1L1 of the first region 210 may be higher than the normalized coupling coefficient κ2L2 of the second region 220, so as to set the light intensity of the light output from the front facet 40 to be higher than the light intensity of the light output from the rear facet 50. Here, "L1" represents the entire length of the first region 210 in the first direction D1. "L2" represents the entire length of the second region 220. The length L1 may be equal to or less than half of the entire length of the semiconductor laser 201. That is, although in the first exemplary implementation, the main reason for the difference in the normalized coupling coefficient κL between the first region 10 and the second region 20 may be the difference in the total length of the diffraction grating region 12A, in the second exemplary implementation, the main reason may be the difference in the number of diffraction grating layers and the difference in length between the first region 210 and the second region 220. The number of diffraction grating layers is not limited to two as long as the number of diffraction grating layers in the first region 210 is greater than the number of diffraction grating layers in the second region 220. For example, the number of diffraction grating layers in the first region 210 and the number of diffraction grating layers in the second region 220 may be three and two, respectively.

[0051] The second example implementation is also different from the first example implementation in the structure of the high resistance element 230. In the first example implementation, the high resistance element 30 placed in the top surface of the mesa structure 15 of the first region 210 can be continuous in the second direction D2. On the other hand, in the second example implementation, the width of the opening region in the direction (second direction D2) perpendicular to the direction (first direction D1) in which the mesa structure 15 extends in a plan view can be wider in some parts and narrower in other parts. The high resistance element 230 can be placed on each side of the part in which the opening region can have a narrower width. According to this structure, although the current injected from a part of the second electrode 3 located in the opening region also reaches below the high resistance element 230 to inject current there, the injection current density below the high resistance element 230 can be lower than the injection current density below the opening region (through hole 218). On the other hand, in the second region 220, the high resistance element 230 can be placed only where the second region 220 can be connected to the first region 210, and the opening region (through hole 218) can be placed in most of the second region 220. In other words, in the first region 210, a region in which the top surface of the mesa structure 15 may have an opening (wider width portion) that is completely opened in the second direction D2 and a region in which the top surface of the mesa structure 15 may have an opening (narrower width portion) that is partially opened in the second direction D2 may be alternately arranged. On the other hand, in the second region 220, an opening region (one of the through holes 218) may be placed in the entire region directly above the mesa structure 15. Therefore, the opening ratio of the through hole 218 of the first region 210 may be lower than that of the second region 220. As a result, the injection current density of the first region 210 becomes lower than that of the second region 220, and thus the same effect as that achieved in the first example may be obtained.

[0052] It should be understood that the same effect can be obtained by applying the structure of the through hole 18 and the high resistance element 30 shown in the first example implementation and its modified example to the semiconductor laser 201. Similarly, the structure of the high resistance element 230 shown in the second example implementation can be combined with the first example implementation.

[0053] Fig. 9 is a schematic cross-sectional view of a semiconductor laser 301 implemented according to a third example of the present disclosure taken along a first direction D1, and corresponds to a cross-sectional view taken along Figure 1 Schematic cross-sectional view taken along line II-II. Fig.10 31 is a top view of the semiconductor laser 301 and may be an explanatory diagram for illustrating a mode of an opening region (through hole 318 ).

[0054] The semiconductor multilayer structure of the semiconductor laser 301 may be substantially the same as the structure of the semiconductor layer 1 implemented according to the first example, but the diffraction grating structure is different. In the third example implementation, the diffraction grating structure may be formed by forming protrusions and depressions on the surface of the diffraction grating layer 311 placed on the core layer 7. The cladding 9 may be placed in the concave region. The protrusion region corresponds to the first refractive index region 11A, and the depression region corresponds to the second refractive index region 11B. The height of each protrusion of the diffraction grating structure of the first region 310 (the depth of each depression) may be greater than the height of each protrusion in the diffraction grating structure of the second region 320. The height or depth may be defined in the stacking direction of the semiconductor layer growth. The λ / 4 phase shift portion 319 may be placed between the first region 310 and the second region 320. The first region 310 may have a uniform diffraction grating structure in which the first refractive index region 11A and the second refractive index region 11B have the same length in the first direction and are arranged alternately. The second region 320 may have a uniform diffraction grating structure in which. The first refractive index region 11A and the second refractive index region 11B may have the same length in the first direction and may be arranged alternately. The first region 310 may have a first diffraction grating region in which the diffraction grating structure may be deep. The second region 320 may have a second diffraction grating region in which the depth of the diffraction grating structure may be shallower than the depth in the first region 310. The first diffraction grating region and the second diffraction grating region form a resonator, wherein the phase shift portion 319 is sandwiched between the first diffraction grating region and the second diffraction grating region.

[0055] Since the diffraction grating structure is deep, the coupling coefficient κ of the first region 310 is higher than that of the second region 320. In the third example implementation, the normalized coupling coefficient κ1L1 of the first region 310 may be higher than the normalized coupling coefficient κ2L2 of the second region 320, so as to set the light intensity of the light output from the front facet 40 to be higher than the light intensity of the light output from the rear facet 50. Here, "L1" represents the entire length of the first region 310 in the first direction D1. "L2" represents the entire length of the second region 320. The length L1 may be equal to or less than half of the entire length of the semiconductor laser 301. That is, although in the first example implementation, the main reason for the difference in the normalized coupling coefficient κL between the first region 10 and the second region 20 is the difference in the total length of the diffraction grating region 12A, in the third example implementation, the main reason may be the difference in the depth of the diffraction grating structure and the difference in length between the first region 310 and the second region 320.

[0056] The third example implementation is also different from the first example implementation in the material of the high resistance element 330. Although the high resistance element 30 may be the insulating film 14 in the first example implementation, the high resistance element 330 may be formed of an insulating material different from the insulating film 314 in the third example implementation. For example, in the case where the insulating film 314 is a silicon oxide film, the high resistance element 330 may be formed of silicon nitride or resin. The material of the high resistance element 330 is not limited thereto, and a high resistance element formed of another material may be placed as long as the resistance of the high resistance element is at least higher than that of the contact layer 13.

[0057] The insulating film 314 may be placed on the top surface of the mesa structure 15, except for a portion of the top surface. In the second region 320, the second electrode 3 may be in contact with the contact layer 13 in the entire region directly above the mesa structure 15. That is, the aperture ratio of the second region 320 may be 100%. On the other hand, in the first region 310, the high resistance element 330 may be discretely placed between the second electrode 3 and the contact layer 13. In other words, the opening region (through hole 318) in which the second electrode 3 and the contact layer 13 may be in contact with each other may be discretely placed. Therefore, the aperture ratio of the first region 310 may be lower than that of the second region 320. As described in the first example implementation, the preferred aperture ratio of the first region 310 is, for example, equal to or greater than 20% and equal to or less than 50%. Similarly, in the third example implementation, the injection current density of the first region 310 may be less than the injection current density of the second region 320, and the same effect as in the first example implementation may be obtained accordingly.

[0058] Fig.11 is a top view of a semiconductor laser 401 implemented according to a fourth example of the present disclosure. Fig.12 It is along Fig.11 A schematic cross-sectional view taken along line XII-XII. Fig.13 4 is another top view of the semiconductor laser 401, and is an explanatory diagram for illustrating the positions of the regions included therein. The main difference from the semiconductor laser 1 according to the first example implementation may be the difference in the shape of the opening region (through hole 418) of the first region 410 and the high resistance element 430, and the difference in the placement of the window structure 460 between the first region 410 and the rear facet 50 and between the second region 420 and the front facet 40. The rest of the semiconductor multilayer structure may be the same as in the first example implementation.

[0059] The window structure 460 may be formed of a semiconductor material having an effective refractive index lower than that of the active layer included in the core layer 7. For example, the material of the window structure 460 may be the same as that of the buried layer 17. The window structure 460 may have an effect of reducing the light returned to the core layer 7, and thereby further improve the SMSR characteristics, such as yield. The window structure 460 may not be included in the mesa structure 415. The end facets of the mesa structure 415 in the first direction D1 may be in contact with the window structure 460. The window structure 460 may be placed from one end to the other end of the semiconductor laser 401 in the second direction D2.

[0060] In the first region 410, the opening region (through hole 418) may be substantially quadrilateral in a plan view. The through hole 418 may be arranged so that the center of the through hole 418 and the center of the mesa structure 415 are offset from each other in the second direction D2. That is, the through hole 418 only partially overlaps with the mesa structure 415. The high resistance element 430 (here, the insulating film 414) may be placed in an area where the through hole 418 and the mesa structure 415 do not overlap each other. Therefore, the through hole 418 and the high resistance element 430 may not need to be alternately arranged in a discrete manner. In the second region 420, the high resistance element 430 may not be placed directly above the mesa structure 415, except near the connection portion where the mesa structure 415 may be connected to the window structure 460. Therefore, the aperture ratio of the second region 420 may be higher than that of the first region 410.

[0061] The insulating film 414 may be placed above the window structure 460. The insulating film 414 may also be placed in a portion of the first region 410 and a portion of the second region 420 to serve as a high resistance element 430. In the first region 410, the through hole 418 may be discretely placed as in the first example implementation. The second electrode 3 may also be placed on a portion of the top surface of the window structure 460. The above-mentioned effects may also be obtained in the fourth example implementation.

[0062] Fig.14 is a top view of a semiconductor laser 501 according to a fifth embodiment of the present disclosure. Fig.15 It is along Fig.14 Schematic cross-sectional view taken along line XV-XV of . Fig.16 It is along Fig.14 Schematic cross-sectional view taken along line XVI-XVI of . Fig.17 It is along Fig.14 Schematic cross-sectional view taken along line XVII-XVII. Fig.185 is another top view of the semiconductor laser 501 and is an explanatory diagram for illustrating the positions of the regions included therein. The semiconductor laser 501 may have a planar buried heterostructure (PBH) structure in which a second conductivity type cladding layer 509 and a second conductivity type contact layer 513 may be placed generally above a mesa structure 515.

[0063] The semiconductor laser 501 may have a semiconductor multilayer structure in which a first conductive type semiconductor layer, an active layer, and a second conductive type semiconductor layer may be sequentially grown. In a fifth exemplary implementation, on a substrate 505 of the first conductive type, semiconductor layers may be sequentially grown, which may be a buffer layer 516 of the first conductive type, a core layer 507, a cladding layer 509 of the second conductive type, and a contact layer 513 of the second conductive type. The substrate 505 and the buffer layer 516 correspond to the first conductive type semiconductor layer. The core layer 507 may be a semiconductor layer including at least an active layer. For example, the core layer 507 may be a semiconductor layer obtained by sequentially growing an optical confinement layer of the first conductive type, an active layer that may be formed by an "i" type multi-quantum well layer, and a second conductive type optical confinement layer from the substrate 505 side. The core layer 507 may include layers other than these semiconductor layers. The active layer may be an n-type semiconductor layer. In the fifth exemplary implementation, the cladding layer 509 and the contact layer 513 form a second conductive type semiconductor layer. The diffraction grating layer 511 may be formed in the buffer layer 516. The semiconductor laser 501 may be a DFB laser. The first conductivity type and the second conductivity type here may be n-type and p-type, respectively, but may be interchangeable. Fig.16 As shown, a portion of the buffer layer 516 forms a mesa structure 515 together with the core layer 507. The mesa structure 515 extends in the first direction D1. Each side of the mesa structure 515 can be covered with a semi-insulating semiconductor buried layer 517. The buried layer 517 can be a multilayer of p-type and n-type semiconductor layers. The cladding layer 509 and the contact layer 513 can be placed above the mesa structure 515 and the buried layer 517. Fig.14 The dotted line indicates the position of the boundary between the mesa structure 515 and the buried layer 517. The mesa structure 515 may have a constant width in a second direction D2 perpendicular to the first direction D1 in a plan view.

[0064] The diffraction grating layer 511 may have the same structure as that of the diffraction grating layer 11 in the first example implementation, except that it is placed below the core layer 507 (on the substrate 505 side). That is, the first region 510 may include a first diffraction grating region, which may be a uniform diffraction grating region 12A. The second region 520 may include a plurality of diffraction grating regions 12A (second diffraction grating regions) and a plurality of non-diffraction grating regions 12B. The first diffraction grating region of the first region and the second diffraction grating region of the second region form a resonator. As described above, the phase of the diffraction grating structure considering the optical path length of the first region and the second region may be shifted by a π phase shift.

[0065] Fig.18 5 is a top view of the semiconductor laser 501 and is an explanatory diagram for illustrating the position of the through hole 518. For convenience of explanation, Fig.18 The second electrode 3 may be omitted in the figure. Fig.18 It is also a perspective view of the diffraction grating layer 511 assuming that the diffraction grating layer 511 is transparent. The dot-dash line indicates the position of the opening area (through hole 518). In the second area 520, one of the through holes 518 can be placed above the mesa structure 515. Fig.16 As shown, one of the through holes 518 overlaps the entire mesa structure 515 in the second direction D2. On the other hand, in the first region 510, another through hole in the through holes 518 may not be placed directly above the mesa structure 515, but may be placed in a region deviating from the mesa structure 515 (see Fig.17 ). In other words, in the first region 510, the opening region may be placed so as to be offset from the region directly above the mesa structure 515 in a plan view, and the high resistance element 530 may be placed so as to overlap the region directly above the mesa structure 515 in a top view. The PBH structure places the second conductive type semiconductor layer (here, the cladding layer 509 and the contact layer 513) generally above the mesa structure 515, and therefore, although the mesa structure 515 and the other through hole in the through hole 518 are offset from each other in the second direction D2, the current injected from the second electrode 3 still flows into the mesa structure 515. However, the distance between the other through hole in the through hole 518 and the top surface of the mesa structure 515 in the first region 510 may be longer than the distance between one through hole in the through hole 518 and the top surface of the mesa structure 515 in the second region 520, with the result that the effective current injection density may be lower in the first region 510.

[0066] In the present disclosure, the ratio of the area directly above the mesa structure occupied by the opening area can be defined as the aperture ratio. That is, the aperture ratio may not be defined by the ratio of the area in which the mesa structure can be in contact with the electrode. In the fifth example implementation, the aperture ratio of the first region 510 in which the opening area does not overlap with the mesa structure 515 in a plan view may be 0%. That is, the high resistance element 530 may be placed in the entire area directly above the mesa structure 515. On the other hand, the second region 520 may have an aperture ratio of substantially 100%. In this way, the effect of the present disclosure is obtained by setting the aperture ratio of the first region that may have a high normalized coupling coefficient to be lower than the aperture ratio of the second region without requiring the opening region to overlap with the mesa structure.

[0067] In the first region 510, another through hole in the through holes 518 may partially overlap with the region directly above the mesa structure 515, such as Fig.13 shown.

[0068] Fig.19 is a top view of a semiconductor laser 601 implemented according to a sixth example of the present disclosure. Fig. 20 It is along Fig.19 A schematic cross-sectional view taken along line XX-XX. Fig.21 615 is another top view of the semiconductor laser 601, and may be an explanatory diagram for illustrating the location of the region included therein. The semiconductor laser 601 may be a ridge-type semiconductor laser, in which the active layer may not be included in the mesa structure. The semiconductor multilayer structure in the sixth example implementation may be the same as the semiconductor multilayer structure in the first example implementation. The difference may be that the mesa structure 615 does not include the core layer 7 that may include the active layer. In the sixth example implementation, the mesa structure 615 may include a cladding layer 9, a diffraction grating layer 11, and a contact layer 13.

[0069] As in the first example implementation, the normalized coupling coefficient of the first region 610 may be higher than that of the second region 620. Fig.21 As shown, the aperture ratio of the first region 610 may be lower than the aperture ratio of the second region 620. The above-mentioned effect can also be obtained in the sixth exemplary implementation.

[0070] The above effects can also be obtained by combining the above embodiments and modified examples. For example, any one of a buried semiconductor laser, a PBH semiconductor laser, and a ridge semiconductor laser can be used. Any one of the placement, number of layers, depth, etc. of the diffraction grating structure can be used as a structure for changing the normalized coupling coefficient between the first region and the second region. The shape and position of the (multiple) opening regions and the (multiple) high-resistance elements of the first region can be the shape and position of any one of the above multiple examples. However, Fig.18The examples shown may only apply to the PBH structure. Conversely, applying the other examples to the PBH structure will produce the same effect. The diffraction grating layer may be placed above or below the active layer in the stacking direction in which the semiconductor layer may grow.

[0071] The present invention improves the high power characteristics, high wavelength uniformity, SMSR characteristics and relative noise intensity characteristics of a semiconductor laser with a mesa structure. The embodiment of the present disclosure achieves this by providing a first region with a high normalized coupling coefficient and a second region with a normalized coupling coefficient lower than the first region and setting the aperture ratio of the first region to be lower than the aperture ratio of the second region. The low aperture ratio makes the injection current density of the first region lower than the injection current density of the second region. The first diffraction grating region of the first region and the second diffraction grating region of the second region form a resonator. The phase of the diffraction grating structure considering the optical path length of the first region and the second region can be offset by a π phase shift. The first region may include a first diffraction grating region, in which the first refractive index region and the second refractive index region for reflecting Bragg wavelength light may have the same length and may be arranged alternately. The second region may include a second diffraction grating region and a non-diffraction grating region, in which the first refractive index region and the second refractive index region may have the same length and may be arranged alternately, and the non-diffraction grating region may transmit Bragg wavelength light. The non-diffraction grating region may be formed only by the first refractive index region or only by the second refractive index region. The second region may include a plurality of diffraction grating regions and a plurality of non-diffraction grating regions. The structure for setting the normalized coupling coefficient of the first region to be higher than the normalized coupling coefficient of the second region may not be limited to the above structure. For example, by setting the number of diffraction grating layers of the first region to be greater than the number of diffraction grating layers of the second region, the normalized coupling coefficient of the first region may be higher than the normalized coupling coefficient of the second region. This may also be achieved by setting the depth of the diffraction grating structure of the first region to be deeper than the depth of the diffraction grating structure of the second region. The aperture ratio of the first region may be equal to or less than 60%, more preferably equal to or greater than 20% and equal to or less than 50%. The high resistance element may be placed in a non-diffraction grating region in which no through hole (opening) is formed. In the first region, the opening region and the high resistance element may be arranged alternately in the direction of light propagation (the direction in which the mesa structure extends). The opening region of the first region may be placed to overlap only partially with the region directly above the mesa structure. The high resistance element may be an insulator, such as silicon oxide, silicon nitride or resin. The high resistance element may not need to completely cover the region directly above the mesa structure. By forming a portion in which the width of the opening area in the second direction can be smaller, the planar size of the opening can be reduced. A low-reflection facet coating film can be formed on the front facet side and the rear facet side of the semiconductor laser. The semiconductor laser can also have a window structure at each facet. Any of a buried semiconductor laser, a PBH semiconductor laser, and a ridge-type semiconductor laser can be used. The semiconductor laser disclosed herein oscillates at a wavelength in the 1.3μm band or the 1.55μm band. However, other wavelength bands can also be used. The diffraction grating layer can be placed above or below the active layer.

[0072] While there have been described certain embodiments of what are presently considered to be the present invention, it will be understood that various modifications may be made thereto and the appended claims are intended to cover all such modifications which fall within the true spirit and scope of the present invention.

[0073] The above disclosure provides illustration and description, but is not intended to be exhaustive or to limit the implementation to the precise form disclosed. Modifications and variations may be made based on the above disclosure, or may be obtained from the practice of the implementation. In addition, any implementation described herein may be combined, unless the above disclosure explicitly provides reasons why one or more implementations cannot be combined.

[0074] As used herein, satisfying a threshold may refer to a value being greater than a threshold, greater than or equal to a threshold, less than a threshold, less than or equal to a threshold, equal to a threshold, not equal to a threshold, etc., depending on the context.

[0075] Although the specific combination of features is cited in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of various implementations. In fact, many of these features can be combined in a manner that is not specifically cited in the claims and / or is not disclosed in the specification. Although each dependent claim listed below can only directly depend on one claim, the disclosure of various implementations includes the combination of each dependent claim with each other claim in the claim set. As used herein, the phrase "at least one" in the referenced item list refers to any combination of these items, including single members. For example, "at least one of a, b or c" is intended to cover a, b, c, ab, ac, bc and abc, and the combination of multiple items in the same item.

[0076] Unless explicitly stated, any element, behavior or instruction used in this article should not be interpreted as critical or essential. In addition, as used in this article, the article "one" and "an" are intended to include one or more projects, and can be used interchangeably with "one or more". In addition, as used in this article, the article "said" is intended to include one or more projects quoted in combination with the article "said", and can be used interchangeably with "one or more". In addition, the word "set" used in this article is intended to include one or more projects (for example, a combination of related projects, unrelated projects, or related and unrelated projects), and can be used interchangeably with "one or more". If only one project is intended to be used, the phrase "only one" or similar language is used. In addition, as used in this article, the term "having", "having", "containing" etc. is intended to be an open term. In addition, unless otherwise explicitly stated, the word "based on" is intended to represent "at least partially based on". In addition, as used in this article, the term "or" is inclusive when used in series, and can be used interchangeably with "and / or", unless otherwise explicitly stated (for example, if used in combination with "any one of ... or "only one of ... "). Additionally, for ease of description, spatially relative terms (such as "below," "lower," "above," "upper," etc.) may be used herein to describe the relationship of one element or feature to other elements or features shown in the figures. Spatially relative terms are intended to encompass different orientations of the device, equipment, and / or elements in use or operation in addition to the orientations shown in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein may be interpreted accordingly.

Claims

1. A semiconductor laser comprising: a first conductivity type semiconductor layer; an active layer formed on the first conductive type semiconductor layer; a second conductive type semiconductor layer formed on the active layer; a first electrode electrically connected to the first conductive type semiconductor layer; a second electrode electrically connected to the second conductive type semiconductor layer; a diffraction grating layer disposed on one of the first conductive type semiconductor layer side or the second conductive type semiconductor layer side when viewed from the active layer; an insulating film disposed in a portion of a space between the second electrode and the second conductive type semiconductor layer; a mesa structure comprising at least one of the active layer or the second conductive type semiconductor layer; as well as In the first area and the second area in the direction in which the mesa structure extends, wherein the diffraction grating layer of the first region comprises a first diffraction grating region, wherein the diffraction grating layer of the second region comprises a second diffraction grating region, wherein the first diffraction grating region and the second diffraction grating region form a resonator, wherein the first region has a normalized coupling coefficient that is higher than a normalized coupling coefficient of the second region, and wherein the following item is smaller in the first region than in the second region: a current supplied from the second electrode to the mesa structure per unit area.

2. The semiconductor laser according to claim 1, wherein the insulating film in a portion of the space above the mesa structure includes one or more opening regions in which the second electrode and the second conductive type semiconductor layer are in contact with each other, and The proportion of the one or more opening regions occupying an area directly above the mesa structure in the first region is lower than the proportion of the one or more opening regions occupying an area directly above the mesa structure in the second region.

3. The semiconductor laser according to claim 2, wherein in the first region, a high resistance element is placed in a non-opening region which is a portion of a region directly above the mesa structure that does not include the one or more opening regions. 4 . The semiconductor laser according to claim 3 , wherein the one or more opening regions and the non-opening regions are alternately arranged in a direction in which the mesa structure extends. 5 . The semiconductor laser according to claim 3 , wherein the one or more opening regions have one of a polygonal shape, a circular shape, or an elliptical shape in a plan view.

6. The semiconductor laser according to claim 3, wherein the one or more opening regions are parallelogram-shaped in plan view, and The one or more opening regions have side surfaces inclined in a direction in which the mesa structure extends.

7. The semiconductor laser according to claim 3, wherein the one or more opening regions have a portion having a wider width and a portion having a narrower width in a direction perpendicular to a direction in which the mesa structure extends in a plan view.

8. The semiconductor laser according to claim 3, wherein the high resistance element is formed of the insulating film. 9 . The semiconductor laser according to claim 3 , wherein the high resistance element includes one of silicon oxide, silicon nitride, or resin. 10 . The semiconductor laser according to claim 2 , wherein in the first region, a ratio of the one or more opening regions occupying a region directly above the mesa structure is equal to or less than 60%. 11 . The semiconductor laser according to claim 2 , wherein in the first region, a ratio of the one or more opening regions occupying a region directly above the mesa structure is equal to or greater than 20% and equal to or less than 50%.

12. The semiconductor laser according to claim 1, wherein the diffraction grating layer comprises a first refractive index region and a second refractive index region, wherein the first diffraction grating region of the first region comprises a diffraction grating region, in which the first refractive index regions and the second refractive index regions are alternately arranged, wherein the second region comprises a non-diffraction grating region in which one of the first refractive index region alone or the second refractive index region alone is placed, and The second region includes a plurality of the diffraction grating regions and a plurality of the non-diffraction grating regions.

13. The semiconductor laser according to claim 1, wherein the diffraction grating layer comprises a plurality of diffraction grating layers, and The number of diffraction grating layers in the first region is greater than the number of diffraction grating layers in the second region.

14. The semiconductor laser according to claim 1, wherein the diffraction grating layer includes two regions having diffraction grating depths different from each other, and The diffraction grating depth of the first region is deeper than the diffraction grating depth of the second region.

15. The semiconductor laser according to claim 1, wherein a low-reflection facet coating film is formed on each facet in a direction in which the mesa structure extends. 16 . The semiconductor laser according to claim 1 , wherein a window structure having a lower refractive index than the active layer is placed between each facet and the mesa structure in a direction in which the mesa structure extends.

17. The semiconductor laser according to claim 3, wherein the mesa structure comprises the active layer, and The semiconductor laser further comprises a semiconductor buried layer, and the semiconductor buried layer is located on each side surface of the mesa structure. 18 . The semiconductor laser according to claim 17 , wherein the second conductivity type semiconductor layer is placed over the mesa structure and the semiconductor buried layer.

19. The semiconductor laser according to claim 18, wherein in the first region, the opening region is positioned to be offset from a region directly above the mesa structure in a plan view, wherein in the first region, the high resistance element is placed so as to overlap with a region directly above the mesa structure in a plan view, and In the second region, the opening region is placed in a region directly above the mesa structure.

20. The semiconductor laser of claim 1, wherein the second electrode is positioned to extend across the first region and the second region.

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