Semiconductor laser device and method of manufacturing the same

Abstract

To provide a semiconductor laser element capable of stabilizing the wavelength of light and improving efficiency, and to provide a method of manufacturing the same.SOLUTION: A semiconductor laser device including a laser region that laser-oscillates light, an amplification region that amplifies the light, an active region that extends to the laser region and the amplification region, a first antireflection film that is provided on an end face of the laser region opposite to the amplification region, and a second antireflection film that is provided on an end face of the amplification region opposite to the laser region, in which an area of the active region in the amplification region is larger than an area of the active region in the laser region in plan view.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a semiconductor laser device and a method for manufacturing the same. [Background technology]

[0002] Distributed Feedback (DFB) laser elements are known as semiconductor laser elements. For example, elements that integrate a DFB laser and a semiconductor optical amplifier (SOA) have been developed (Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] H. Ishii et al. “Spectral Linewidht Reduction in Widely Wavelength Tunable DFB Laser Array” IEEE Journal of Selected Topics in Quantum Electronics,Vol.15,No.3,May / June 2009 Summary of the Invention [Problem to be solved by the invention]

[0004] Light emitted from the end facet of an SOA is used in optical communications, etc. Light emitted from the end facet of the DFB section is lost. To increase efficiency, the output of light emitted from the end facet of the DFB section can be reduced and the optical output from the SOA can be increased. By providing a high-reflection film on the end facet of the DFB section, the output from the end facet of the DFB section can be reduced and the output from the SOA can be increased. However, the wavelength of the light varies depending on the positional relationship between the high-reflection film and the diffraction grating, which reduces wavelength stability. Therefore, the objective is to provide a semiconductor laser device that can stabilize the wavelength of light and increase efficiency, and a method for manufacturing the same. [Means for solving the problem]

[0005] A semiconductor laser element according to the present disclosure comprises a laser region that generates laser oscillation of light, an amplification region that amplifies the light, an active region extending to the laser region and the amplification region, a first antireflection film provided on an end face of the laser region opposite the amplification region, and a second antireflection film provided on an end face of the amplification region opposite the laser region, wherein, in a planar view, an area of ​​the active region in the amplification region is larger than an area of ​​the active region in the laser region. [Effects of the Invention]

[0006] According to the present disclosure, it is possible to provide a semiconductor laser element that can stabilize the wavelength of light and increase efficiency, and a method for manufacturing the same. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a plan view illustrating a semiconductor laser device according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view illustrating an example of a semiconductor laser device. [Figure 3A] FIG. 3A is a cross-sectional view illustrating an example of a semiconductor laser device. [Figure 3B] FIG. 3B is a cross-sectional view illustrating an example of a semiconductor laser device. [Figure 4] FIG. 4 is a flowchart illustrating a method for manufacturing a semiconductor laser device. [Figure 5] FIG. 5 is a plan view illustrating a method for manufacturing a semiconductor laser device. [Figure 6] FIG. 6 is a cross-sectional view illustrating a semiconductor laser device according to a comparative example. [Figure 7A] FIG. 7A is an enlarged view of the vicinity of the end face. [Figure 7B] FIG. 7B is an enlarged view of the vicinity of the end face. [Figure 8] FIG. 8 is a diagram illustrating an example of the spectrum. [Figure 9A]FIG. 9A is a diagram illustrating the power conversion efficiency of the laser region. [Figure 9B] FIG. 9B is a diagram illustrating the power conversion efficiency of the laser region. [Figure 10A] FIG. 10A is a diagram illustrating the power conversion efficiency of the entire semiconductor laser device. [Figure 10B] FIG. 10B is a diagram illustrating the power conversion efficiency of the entire semiconductor laser device. [Figure 11A] FIG. 11A is a diagram illustrating the relationship between the power input ratio and the optical output. [Figure 11B] FIG. 11B is a diagram illustrating the relationship between the power input ratio and the optical output. [Figure 12A] FIG. 12A is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 12B] FIG. 12B is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 13A] FIG. 13A is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 13B] FIG. 13B is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 13C] FIG. 13C is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 13D] FIG. 13D is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 13E] FIG. 13E is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 14A] FIG. 14A is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 14B] FIG. 14B is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 14C] FIG. 14C is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 14D] FIG. 14D is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 14E] FIG. 14E is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 15A] FIG. 15A is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 15B] FIG. 15B is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 15C] FIG. 15C is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 15D] FIG. 15D is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 15E] FIG. 15E is a diagram illustrating the relationship between the power input ratio and the power conversion efficiency. [Figure 16A] FIG. 16A is a diagram illustrating the relationship between the power input ratio and the length of the mesa portion. [Figure 16B] FIG. 16B is a diagram illustrating the relationship between the power input ratio and the length of the mesa portion. [Figure 16C] FIG. 16C is a diagram illustrating the relationship between the power input ratio and the length of the mesa portion. [Figure 16D] FIG. 16D is a diagram illustrating the relationship between the power input ratio and the length of the mesa portion. [Figure 16E] FIG. 16E is a diagram illustrating the relationship between the power input ratio and the length of the mesa portion. [Figure 17A] FIG. 17A is a diagram illustrating the relationship between the power input ratio and the length of the mesa portion. [Figure 17B] FIG. 17B is a diagram illustrating the relationship between the power input ratio and the length of the mesa portion. [Figure 17C] FIG. 17C is a diagram illustrating the relationship between the power input ratio and the length of the mesa portion. [Figure 17D] FIG. 17D is a diagram illustrating the relationship between the power input ratio and the length of the mesa portion. [Figure 17E] FIG. 17E is a diagram illustrating the relationship between the power input ratio and the length of the mesa portion. [Figure 18A] FIG. 18A is a diagram illustrating the relationship between the power input ratio and the length of the mesa portion. [Figure 18B] FIG. 18B is a diagram illustrating the relationship between the power input ratio and the length of the mesa portion. [Figure 18C] FIG. 18C is a diagram illustrating the relationship between the power input ratio and the length of the mesa portion. [Figure 18D] FIG. 18D is a diagram illustrating the relationship between the power input ratio and the length of the mesa portion. [Figure 18E] FIG. 18E is a diagram illustrating the relationship between the power input ratio and the length of the mesa portion. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Description of the embodiments of the present disclosure] First, the contents of the embodiments of the present disclosure will be listed and described.

[0009] One aspect of the present disclosure is a semiconductor laser device comprising: (1) a laser region that generates laser oscillation of light; an amplification region that amplifies the light; an active region extending into the laser region and the amplification region; a first antireflection film provided on an end face of the laser region opposite the amplification region; and a second antireflection film provided on an end face of the amplification region opposite the laser region, wherein, in a planar view, the area of ​​the active region in the amplification region is larger than the area of ​​the active region in the laser region. Because reflections are less likely to occur at the end face of the laser region, the effect of reflections on the wavelength of light emitted from the amplification region is reduced. The wavelength can be stably controlled. Because the power input to the amplification region is greater than the power input to the laser region, efficiency can be improved. (2) In the above (1), the area of ​​the active region in the amplification region may be four or more times the area of ​​the active region in the laser region. Since the power input to the amplification region is greater than the power input to the laser region, efficiency can be improved. (3) In the above (1) or (2), the active region in the amplification region may be longer than the active region in the laser region, and the width of the active region in the amplification region may be greater than the width of the active region in the laser region. Since the power input to the amplification region is greater than the power input to the laser region, efficiency can be improved. (4) In any of the above (1) to (3), the length of the laser region may be 400 μm or more and 1200 μm or less. The laser region operates stably, the loss of optical output is reduced, and multimodes are less likely to occur. (5) In any of the above (1) to (4), the length of the active region in the laser region may be 0.6 times or less the length of the semiconductor laser element. This reduces optical loss. The amplification region is lengthened, improving efficiency. (6) In any of (1) to (5) above, the active layer may be provided in the laser region and the amplification region, and the active region may be a mesa, the mesa including the active layer, and may extend to the laser region and the amplification region. The area of ​​the mesa in the amplification region may be larger than the area of ​​the mesa in the laser region. The power input to the mesa in the amplification region may be larger than the power input to the mesa in the laser region. This results in higher efficiency. (7) In the above (6), the laser region and the amplification region may include a first semiconductor layer, the active layer, and a second semiconductor layer stacked in this order, the first semiconductor layer having a first conductivity type, the second semiconductor layer having a second conductivity type, the first semiconductor layer and the active layer forming the mesa, and the second semiconductor layer being provided on the mesa. A pin junction is formed in the mesa, allowing current to flow through the active layer. Light oscillates in the laser region, and light is amplified in the amplification region. (8) In the above (6) or (7), buried layers may be provided on both sides of the mesa in the laser region and the amplification region. By concentrating the current flow in the mesa, efficiency is increased. (9) In any of (6) to (8) above, a first electrode may be provided in the laser region and overlapping a portion of the mesa provided in the laser region, and a second electrode may be provided in the amplification region and overlapping a portion of the mesa provided in the amplification region. The area of ​​the mesa in the amplification region is larger than the area of ​​the mesa in the laser region. By overlapping the first electrode with the wider portion of the mesa, larger power is input. By overlapping the second electrode with the narrower portion of the mesa, smaller power is input. This increases efficiency. (10) In any one of (1) to (9) above, the light amplified by the amplification region may have an output of 200 mW or more. The higher the output, the higher the efficiency. (11) A method for manufacturing a semiconductor laser device, comprising the steps of: designing a laser region that oscillates light into a laser beam and an amplification region that amplifies the light; forming the laser region and the amplification region based on the design of the laser region and the design of the amplification region; forming a first antireflection film on an end face of the laser region opposite the amplification region; and forming a second antireflection film on an end face of the amplification region opposite the laser region, wherein the laser region and the amplification region include an active region; and the designing step is a design step in which the power input to the active region in the amplification region is greater than the power input to the active region in the laser region. Because reflections are less likely to occur at the end facets of the laser region, the effect of reflections on the wavelength of light emitted from the amplification region is reduced. The wavelength can be stably controlled. Because the power input to the amplification region is greater than the power input to the laser region, efficiency can be improved.

[0010] [Details of the embodiments of the present disclosure] Specific examples of semiconductor laser devices and manufacturing methods thereof according to embodiments of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0011] <Embodiment> 1 is a plan view illustrating a semiconductor laser device 100 according to an embodiment, and FIG. 2 is a cross-sectional view illustrating the semiconductor laser device 100.

[0012] 1 and 2, the semiconductor laser device 100 is an element that integrates a DFB laser and an SOA, and has a laser region 10 that functions as a DFB laser and an amplification region 12 that functions as an SOA. The laser region 10 and the amplification region 12 are adjacent to each other. Although the semiconductor laser device 100 may include elements other than the laser region 10 and the amplification region 12, the following example assumes that it has the laser region 10 and the amplification region 12.

[0013] The laser region 10 extends parallel to the X1-axis direction in FIG. 1. The amplification region 12 extends parallel to the X2-axis direction. The Y-axis direction is the width direction of the semiconductor laser device 100. The Z-axis direction is the thickness direction of the semiconductor laser device 100. The X1-axis, Y-axis, and Z-axis are perpendicular to each other. The X2-axis is parallel to the X1-Y plane and is inclined from the X1-axis. The length L1 of the laser region 10 in the X1-axis direction is, for example, not less than 400 μm and not more than 1200 μm. The length L2 of the amplification region 12 in the X1-axis direction is longer than the length L1. The length Lt of the semiconductor laser device 100 is the sum of the lengths L1 and L2, and is, for example, not less than 1000 μm and not more than 2500 μm.

[0014] The semiconductor laser element 100 has an end face 11 and an end face 13. The end face 11 is an end face of the laser region 10. The end face 13 is an end face of the amplification region 12. The end face 11 and the end face 13 are parallel to the YZ plane. The end face 11 and the end face 13 face each other. The semiconductor laser element 100 has a mesa 31 (active region). The mesa 31 extends from the end face 11 to the end face 13.

[0015] The semiconductor laser device 100 has an anti-reflection coating (AR coating) 20 and an anti-reflection coating 21. The anti-reflection coating 20 (first anti-reflection coating) is provided on the facet 11 and covers the facet 11. The anti-reflection coating 20 covers at least the facet of the mesa 31 of the facet 11. The anti-reflection coating 20 may cover the entire facet 11. The anti-reflection coating 20 may cover the facet of the mesa 31 of the facet 11 and its surroundings. The anti-reflection coating 20 covers a range of the facet 11 in which the intensity of light guided through the mesa 31 is distributed. The anti-reflection coating 21 (second anti-reflection coating) is provided on the facet 13 and covers the facet 13. The anti-reflection coating 21 covers at least the facet of the mesa 31 of the facet 13. The anti-reflection coating 21 may cover the entire facet 13. The anti-reflection coating 21 may cover the end face of the mesa 31 and its surroundings on the end face 13. The anti-reflection coating 21 covers the range of the end face 13 where the intensity of light guided through the mesa 31 is distributed. For light with a wavelength of around 1300 nm, the reflectance of the anti-reflection coatings 20 and 21 is less than 30%, such as 10% or less or 1% or less. The anti-reflection coating includes multiple films, such as a first film covering the end face and a second film covering the first film. Examples of the first and second films are shown below, with the notation first film / second film. Titanium(IV) oxide (TiO2) / silicon oxide (SiO2) Aluminum oxide (Al2O3) / Undoped titanium oxide (i-TiO2) Titanium oxynitride (TiON) / SiO2 Tantalum oxide (Ta2O5) / SiO2 A structure in which antireflection films are provided on both end facets 11 and 13 may be referred to as AR / AR.

[0016] The mesa 31 extends from the facet 11 to the facet 13, and is provided in the laser region 10 and the amplification region 12. Light is generated in the mesa 31 and propagates along the mesa 31.

[0017] The mesa 31 includes a portion 31a and a portion 31b. The portion 31b includes a tapered portion 31c. The portion 31a is located in the laser region 10 and is parallel to the X1-axis direction. The width of the portion 31a in the direction perpendicular to the X1-axis direction is W1. The portion 31b is located in the amplification region 12 and is parallel to the X2-axis direction. The width of the portion 31b in the direction perpendicular to the X2-axis direction is W2. The width W2 is equal to or greater than the width W1 and may be greater than the width W1. The width W1 is, for example, 2 μm. The width W2 is, for example, 4 μm. The tapered portion 31c has a tapered shape. The width of the tapered portion 31c increases with increasing distance from the portion 31a.

[0018] The length of portion 31a in the X1-axis direction is defined as L3. The length of portion 31b in the X2-axis direction is defined as L4. Length L3 is equal to length L1 of laser region 10, and is, for example, 400 μm or more and 1200 μm or less. Because portion 31b is tilted from the X1 axis, length L4 is longer than length L2 of amplification region 12 in the X1 direction. Length L4 is, for example, 700 μm or more and 2100 μm or less. Lengths L3 and L4 are determined based on power conversion efficiency, optical output, etc., and may take values ​​outside the above ranges. Length L4 of portion 31b may be longer than length L3 of portion 31a.

[0019] Fig. 2 illustrates a cross section including the mesa 31. As shown in Fig. 2, the semiconductor laser device 100 has a substrate 30 (first semiconductor layer), a semiconductor layer 32 (third semiconductor layer), a cladding layer 33 (first semiconductor layer), an optical confinement layer 34, an active layer 36, an optical confinement layer 38, a cladding layer 40 (second semiconductor layer), and a contact layer 42 (second semiconductor layer).

[0020] On one surface of the substrate 30, a cladding layer 33, an optical confinement layer 34, an active layer 36, an optical confinement layer 38, a cladding layer 40, and a contact layer 42 are stacked in this order in the Z-axis direction.

[0021] In the laser region 10, multiple semiconductor layers 32 are periodically arranged along the X1-axis direction and are embedded in the substrate 30 and the cladding layer 33. The cladding layers 33 and the semiconductor layers 32 are alternately arranged to form a diffraction grating 35. The period P1 of the diffraction grating 35 is, for example, 200 nm. The period is the pitch between adjacent semiconductor layers 32. The semiconductor layers 32 are not provided in the amplification region 12. In other words, the diffraction grating 35 is provided in the laser region 10, but not in the amplification region 12.

[0022] 3A and 3B are cross-sectional views illustrating a semiconductor laser device 100. FIG. 3A illustrates a cross section taken along line AA in FIG. 1. FIG. 3B illustrates a cross section taken along line BB in FIG. 1. As shown in FIGS. 3A and 3B, the semiconductor laser device 100 has a mesa 31, a trench 37, and a buried layer 39. The buried layers 39 are provided on both sides of the mesa 31. The trench 37 is provided outside the buried layer 39. The trench 37 and the buried layer 39 extend along the mesa 31.

[0023] The central portion of the substrate 30 in the Y-axis direction protrudes in the Z-axis direction compared to the portion outside the central portion of the substrate 30. As shown in Fig. 3A, in the laser region 10, a semiconductor layer 32, a cladding layer 33, an optical confinement layer 34, an active layer 36, and an optical confinement layer 38 are stacked in the central portion of the substrate 30. As shown in Fig. 3B, in the amplification region 12, the cladding layer 33, the optical confinement layer 34, the active layer 36, and the optical confinement layer 38 are stacked in the central portion of the substrate 30. The layers from the central portion of the substrate 30 to the optical confinement layer 38 form a mesa 31.

[0024] A semiconductor layer 44 and a semiconductor layer 46 are stacked on both sides of the mesa 31 in the Y-axis direction, between the mesa 31 and the trench 37. The semiconductor layer 44 and the semiconductor layer 46 are buried on both sides of the mesa 31 to form a buried layer 39. A cladding layer 40 is provided on the mesa 31 and the semiconductor layer 46. A contact layer 42 is provided on the cladding layer 40.

[0025] 3A and 3B, the trench 37 is a recessed portion in the Z-axis direction, penetrating through layers from the contact layer 42 to the semiconductor layer 44 and extending partway through the substrate 30. The semiconductor layer 44, the semiconductor layer 46, the cladding layer 40, and the contact layer 42 are provided outside the trench 37 in the Y-axis direction. The mesa 31, the inside of the trench 37, and the portion outside the trench 37 are covered with an insulating film 50. The insulating film 50 has an opening above the mesa 31. The insulating film 50 is made of an insulator such as silicon oxide (SiO2) and silicon nitride (SiN).

[0026] The substrate 30 is a semiconductor substrate and is made of, for example, n-type (first conductivity type) indium phosphide (n-InP). The semiconductor layer 32 is made of, for example, n-type indium gallium arsenide phosphide (n-InGaAsP). The emission wavelength of the semiconductor layer 32 is, for example, 1.0 μm or more and 1.15 μm or less. The cladding layer 33 is made of, for example, n-InP. The substrate 30, the semiconductor layer 32, and the cladding layer 33 are doped with, for example, silicon (Si). The refractive index of the semiconductor layer 32 is different from the refractive indexes of the substrate 30 and the cladding layer 33.

[0027] The active layer 36 has a multi-quantum well (MQW) structure and includes multiple well layers and multiple barrier layers. The multiple well layers and multiple barrier layers are alternately stacked. The well layers and barrier layers are formed of, for example, undoped InGaAsP. The emission wavelength is, for example, 1.25 μm or more and 1.6 μm or less. The optical confinement layers 34 and 38 are formed of, for example, InGaAsP. The refractive indexes of the optical confinement layers 34 and 38 are lower than the refractive index of the active layer 36 and higher than the refractive indexes of the cladding layers 33 and 40. The active layer 36, the optical confinement layers 34, and the optical confinement layers 38 form a separate confinement heterostructure (SCH) structure.

[0028] The cladding layer 40 is formed of, for example, p-type (second conductivity type) indium phosphide (p-InP). The contact layer 42 has a p-InGaAs layer and a p-GaInAsP layer. An InGaAs layer and a GaInAsP layer are stacked in this order on the cladding layer 40. The p-type semiconductor layer is doped with, for example, zinc (Zn).

[0029] The semiconductor layer 44 is made of, for example, p-InP, and the semiconductor layer 46 is made of, for example, n-InP.

[0030] 2, the semiconductor laser device 100 has an electrode 22, an electrode 23 (first electrode), and an electrode 24 (second electrode). The electrode 22 is provided in the laser region 10 and the amplification region 12, and is in contact with the surface of the substrate 30 opposite to the active layer 36, and is electrically connected to the substrate 30.

[0031] As shown in FIGS. 1 and 2, the electrodes 23 and 24 are located on the upper surface of the semiconductor laser device 100. The electrode 23 is provided in the laser region 10 and overlaps with a portion 31a of the mesa 31. The electrode 24 is provided in the amplification region 12 and overlaps with a portion 31b of the mesa 31. The electrodes 23 and 24 are spaced apart from each other. The antireflection film 20 may cover a portion of the electrode 23 or a portion of the electrode 22. Here, the "part of the electrode" refers to the portion of the electrode that is included in the facet 11. The antireflection film 21 may cover a portion of the electrode 24 or a portion of the electrode 22. Here, the "part of the electrode" refers to the portion of the electrode that is included in the facet 13.

[0032] 3A, the electrode 23 is provided on the mesa 31, on the surface of the contact layer 42 opposite the cladding layer 40, and is in contact with this surface. The wiring layer 25 is provided on the electrode 23, and is also provided inside the trench 37 and in a portion outside the trench 37. The wiring layer 25 is in contact with the electrode 23 on the mesa 31 through an opening in the insulating film 50. The electrode 23 and the wiring layer 25 are electrically connected to the contact layer 42.

[0033] 3B , the electrode 24 is provided on the mesa 31, on the surface of the contact layer 42 opposite the cladding layer 40, and is in contact with this surface. The wiring layer 26 is provided on the electrode 24, and is also provided inside the trench 37 and in a portion outside the trench 37. The wiring layer 26 is in contact with the electrode 24 on the mesa 31 through an opening in the insulating film 50. The electrode 24 and the wiring layer 26 are electrically connected to the contact layer 42.

[0034] The electrodes 23 and 24 are made of metal and are, for example, laminates of a gold (Au) layer, a tin (Sn) layer, and an Au layer stacked in this order from the side closest to the contact layer 42. The wiring layers 25 and 26 are made of, for example, Au. The electrode 22 is made of metal.

[0035] Mesa 31 is an active region and includes active layer 36. At the position overlapping mesa 31, p-type cladding layer 40 and contact layer 42, i-type active layer 36, n-type cladding layer 33, and substrate 30 are stacked, and these semiconductor layers form a pin (positive-intrinsic-negative) junction. On both sides of mesa 31, p-type cladding layer 40, n-type semiconductor layer 46, p-type semiconductor layer 44, and n-type substrate 30 are stacked, forming a pnpn junction. A current confinement structure is formed, allowing current to flow easily into mesa 31 and difficult to flow outside mesa 31.

[0036] When a voltage is applied to electrodes 22 and 23, a current flows selectively through mesa 31 in laser region 10. When a voltage is applied to electrodes 22 and 24, a current flows selectively through mesa 31 in amplification region 12. Carriers are injected into active layer 36 and recombine to generate light. The light propagates along mesa 31 to both sides of laser region 10, causing laser oscillation at a wavelength according to the period of diffraction grating 35.

[0037] Laser light is indicated by arrows in Figure 2. Light propagating from laser region 10 toward facet 11 is designated as B1. Light propagating from laser region 10 toward amplification region 12 is designated as B2. Light propagating from amplification region 12 toward facet 13 is designated as B3.

[0038] Laser light B1 propagates from the laser region 10 to the facet 11, passes through the antireflection film 20, and is emitted to the outside of the semiconductor laser device 100. Laser light B2 enters the amplification region 12 from the laser region 10, is amplified in the amplification region 12, and becomes laser light B3. Laser light B3 propagates along the mesa 31 to the facet 13, passes through the antireflection film 21, and is emitted to the outside of the semiconductor laser device 100. The intensity of laser light B2 is approximately equal to that of laser light B1. Because laser light B3 is amplified by the amplification region 12, it has a higher intensity than laser light B1 and B2.

[0039] The semiconductor laser device 100 is used as a light source for optical communication, for example. The light B3 emitted from the end face 13 is used for optical communication. The light B1 emitted from the end face 11 is not used for applications such as optical communication.

[0040] The semiconductor laser element 100 is required to have an optical output of, for example, 200 mW or more and wavelength stability. The output of the output light B3 is amplified to a target level by the amplification region 12. To improve communication quality, the wavelength of the output light B3 is required to maintain a target value without discontinuous changes during operation. The semiconductor laser element 100 may be a wavelength-tunable laser element. When a current flows through a heater (not shown), the heater generates heat, heating the laser region 10. The refractive index of the diffraction grating 35 changes in response to changes in temperature. The wavelength of the laser light changes.

[0041] (Manufacturing method) 4 is a flowchart illustrating a method for manufacturing the semiconductor laser device 100. The laser region 10 is designed (step S10). The amplification region 12 is designed (step S12). The device is manufactured based on the design (step S14).

[0042] In designing the laser region 10, the pitch P1 of the diffraction grating 35, the cavity length L3, the width W1 of the portion 31a of the mesa 31, and other factors are designed taking into consideration the drive conditions and oscillation wavelength of the DFB laser. In designing the amplification region 12, the length L4 and width W2 of the portion 31b of the mesa 31 are designed taking into consideration the drive conditions of the SOA and the target value of the optical output. The design is performed so that the power Wsoa input to the mesa 31 in the amplification region 12 is greater than the power Wdfb input to the mesa 31 in the laser region 10 (steps S10 and S12). Specifically, when viewed in a plan view as shown in FIG. 1, the design is performed so that the area of ​​the mesa 31 in the amplification region 12 is greater than the area of ​​the mesa 31 in the laser region 10. "Planar view" means viewed from the direction in which the semiconductor layers are stacked (the Z-axis direction).

[0043] In step S14, the following processes are performed: A semiconductor layer 32 is epitaxially grown on the upper surface of the substrate 30 in the laser region 10 by metal organic chemical vapor deposition (MOCVD). The semiconductor layer 32 in the laser region 10 is shaped like islands by etching. A cladding layer 33 is epitaxially grown so as to bury the semiconductor layer 32. The diffraction grating 35 shown in FIG. 2 is formed. An optical confinement layer 34, an active layer 36, and an optical confinement layer 38 are epitaxially grown in this order in the laser region 10 and the amplification region 12. A p-type cladding layer is epitaxially grown on the upper surface of the optical confinement layer 38.

[0044] 5 is a plan view illustrating a method for manufacturing the semiconductor laser device 100. As shown in FIG. 5, a mesa 31 is formed by etching. Semiconductor layers 44 and 46 are grown on both sides of the mesa 31 to embed the mesa. A p-type InP layer is epitaxially grown on the mesa 31 and the semiconductor layer 46. The p-type InP layer and the p-type cladding layer of the mesa 31 form the cladding layer 40. A contact layer 42 is epitaxially grown on the upper surface of the cladding layer 40.

[0045] On both sides of the mesa 31, etching is performed from the contact layer 42 to partway through the substrate 30 to form trenches 37. The electrodes 23 and 24 are formed on the top surface of the contact layer 42 of the mesa 31 by, for example, vacuum deposition and lift-off.

[0046] An insulating film 50 is formed by, for example, plasma CVD (PECVD: Plasma Enhanced CVD). The insulating film 50 covers the mesa 31, the inside of the trench 37, and the contact layer 42 outside the trench 37. An opening is formed in the insulating film 50 above the mesa 31. A wiring layer 25 is formed on the surfaces of the electrode 23 and the insulating film 50 by, for example, plating. A wiring layer 26 is formed on the surfaces of the electrode 24 and the insulating film 50. A heater (not shown) is formed in the laser region 10 by vacuum deposition and lift-off. After the substrate 30 is polished from the back side, an electrode 22 is formed on the substrate 30.

[0047] The wafer is diced or cleaved to form a chip-type element. End face 11 and end face 13 are formed by this dicing or cleaving. As shown in FIG. 1, an anti-reflection coating 20 is formed on end face 11. An anti-reflection coating 21 is formed on end face 13. In this manner, the semiconductor laser element 100 is formed. When forming the anti-reflection coatings 20 and 21, the chip-type element is set in a film formation device using a jig. Depending on the shape of the jig, it is possible to change the area of ​​the end face on which the anti-reflection coating is formed. Depending on the shape of the jig, it is possible to change the area of ​​the electrode on which the anti-reflection coating is formed.

[0048] (Comparative Example) Fig. 6 is a cross-sectional view illustrating a semiconductor laser device 110 according to a comparative example. As shown in Fig. 6, a high-reflection coating (HR coating) 27 is provided on a facet 11 of the laser region 10. For light with a wavelength of around 1300 nm, the reflectance of the high-reflection coating 27 is higher than that of the anti-reflection coating, and is 70% or more or 99% or more. A structure in which a high-reflection coating is provided on facet 11 and an anti-reflection coating is provided on facet 13 is sometimes referred to as HR / AR.

[0049] The reflectivity of the high-reflectivity film 27 is set to 70% or more. Approximately 30% of the laser light B1 is emitted to the outside from the end face 11. 70% or more of the laser light B1 is reflected by the high-reflectivity film 27. The reflected light propagates toward the amplification region 12. Laser light B2 also travels from the laser region 10 toward the amplification region 12. The reflected light and light B2 are amplified in the amplification region 12 and emitted from the end face 13 as emitted light B3. According to the comparative example, since the laser light B1 is reflected, the loss of optical output is reduced. However, the wavelength becomes unstable.

[0050] 7A and 7B are enlarged views of the vicinity of facet 11, showing two different semiconductor laser elements. Facet 11 and facet 13 of the semiconductor laser element are formed by dicing or cleaving. In both the embodiment and the comparative example, an error of about ±5 μm may occur in the position of dicing or cleaving. Variation occurs in the position of facet 11 among multiple semiconductor laser elements, and the position of facet 11 and semiconductor layer 32 of diffraction grating 35 changes.

[0051] In the comparative example, laser light B1 is reflected by high-reflection film 27, generating reflected light. The phase of the reflected light changes depending on the positional relationship between end face 11 and diffraction grating 35. The change in the phase of the reflected light changes the wavelength of the composite wave of the reflected light and laser light B2, and also changes the wavelength of the amplified output light B3.

[0052] Figure 8 illustrates spectra for four semiconductor laser devices according to the comparative example. The horizontal axis represents the wavelength of light. The vertical axis represents the intensity of light. The solid, dotted, dashed, and dashed lines represent the spectra for four devices with different positions of the end facet 11 and the diffraction grating 35. The period P1 of the diffraction grating 35 is 200 nm. As shown in Figure 8, the peak wavelengths are different from one another. A change in the position of the end facet 11 over a range of approximately 5 μm results in a change in the peak wavelength of approximately 0.3 nm, and the wavelengths do not match between multiple devices. The spectrum indicated by the dashed-dotted line has two peaks Pa and Pb. In other words, resonance occurs at two different wavelengths. Mode hopping occurs during operation of the semiconductor laser device 110, causing discontinuous changes in the resonance state. In the comparative example, wavelength stability is reduced both among multiple devices and within a single device. Devices with wavelengths that differ from the design value are deemed defective, resulting in reduced yield.

[0053] In this embodiment, an anti-reflection coating 20 is provided on the end face 11. For example, approximately 99% of the laser light B1 is emitted from the end face 11, and the reflected light is 1% or less of the laser light B1. The intensity of the reflected light is lower than in the comparative example. Most of the light incident on the amplification region 12 is the emitted light B2 from the laser region 10. This reduces the effect of reflected light on the wavelength of the emitted light B3. Regardless of the position of the end face 11, the wavelength of the emitted light B3 is determined by the diffraction grating 35. This reduces wavelength variation between elements and makes mode hopping less likely to occur. The wavelength of the emitted light B3 is stabilized.

[0054] On the other hand, in the embodiment, the emitted light B1 from the laser region 10 passes through the anti-reflection film 20 and is emitted to the outside. Approximately half of the light emitted from the laser region 10 is lost. To increase the optical output, power is input to the amplification region 12 to amplify the light.

[0055] To improve the efficiency of the semiconductor laser device 100, the power input to the laser region 10 should be reduced and the power input to the amplification region 12 should be increased. As the power input to the laser region 10 decreases, the intensity of the emitted light B1 decreases, and the loss of optical output decreases. As the power input to the amplification region 12 increases, the optical output increases. In the design of FIG. 4 (steps S10 and S12), the power Wsoa input to the mesa 31 of the amplification region 12 is designed to be greater than the power Wdfb input to the mesa 31 of the laser region 10. An example of the design will be described below.

[0056] Table 1 shows examples of parameters of the semiconductor laser device 100 and the semiconductor laser device 110. In Table 1, DFB represents the laser region 10. SOA represents the amplification region 12. [Table 1]

[0057] As shown in Table 1, in both the semiconductor laser device 110 according to the comparative example and the semiconductor laser device 100 according to the embodiment, the threshold current density of the laser region 10 is 2.4 kA / cm -2 The bias current input to the laser region 10 is 15 times the threshold current Ith (15Ith). The length (cavity length) L3 of the mesa 31 of the laser region 10 is changed between 400 μm and 1200 μm in 200 μm increments. When the cavity length L3 is 800 μm, the electrical resistance of the laser region 10 is 1.2 Ω. The slope efficiency varies depending on the HR / AR structure and the AR / AR structure. The slope efficiency of the laser region 10 of the semiconductor laser element 110 is 0.4 W / A. The slope efficiency of the laser region 10 of the semiconductor laser element 100 is 0.2 W / A. The drive power Wdfb of the laser region 10 is determined depending on the optical output.

[0058] In both the comparative example and the embodiment, the power conversion efficiency PCEsoa in the amplification region 12 is set to 25%. The power conversion efficiency is the ratio of optical output power to input power. The driving power Wsoa of the amplification region 12 is determined according to the optical output power. The optical output power from the amplification region 12 is set to a range from 0 W to 0.7 W.

[0059] In both the comparative example and the embodiment, the power conversion efficiency PCEdfb of the laser region 10 and the power conversion efficiency PCEall of the entire semiconductor laser device are calculated using the parameters in Table 1. The power conversion efficiency PCEdfb of the laser region 10 is expressed by equation (1). PCEdfb=Pdfb / Wdfb (1) Pdfb is the optical output of light B2 traveling from the laser region 10 to the amplification region 12. The power conversion efficiency PCEsoa of the amplification region 12 is expressed by equation (2) and is fixed at 25% as shown in Table 1. Psoa is the optical output of light B3 emitted from the amplification region 12 to the outside of the facet 13. PCEsoa=(Psoa-Pdfb) / Wsoa (2) The power conversion efficiency PCEall of the entire semiconductor laser device is expressed by equation (3). PCEall=Psoa / (Wdfb+Wsoa) (3) The power input ratio Wr between the amplification region 12 and the laser region 10 is expressed by equation (4). Wr=Wsoa / Wdfb (4)

[0060] 9A and 9B are diagrams illustrating the power conversion efficiency of the laser region 10. The horizontal axis represents the current (DFB current) flowing through the mesa 31 of the laser region 10. The vertical axis represents the power conversion efficiency PCEdfb of the laser region 10. In FIGS. 9A to 11B, black circles and thick solid lines represent an example where the length L3 (resonator length) of the mesa 31 in the laser region 10 is 400 μm. White circles and dotted lines represent an example where the resonator length L3 is 600 μm. Black squares and dashed lines represent an example where the resonator length L3 is 800 μm. White squares and dashed lines represent an example where the resonator length L3 is 1000 μm. Triangles and thin solid lines represent an example where the resonator length L3 is 1200 μm.

[0061] FIG. 9A shows the power conversion efficiency PCEdfb in the embodiment. As shown in FIG. 9A, in the embodiment, the power conversion efficiency PCEdfb of the laser region 10 is lower than the power conversion efficiency PCEsoa (25%) of the amplification region 12. Regardless of the value of the cavity length L3, the power conversion efficiency PCEdfb is at most approximately 15%. FIG. 9B shows the power conversion efficiency PCEdfb in the comparative example. As shown in FIG. 9B, in the comparative example, the power conversion efficiency PCEdfb of the laser region 10 can be higher than the power conversion efficiency PCEsoa of the amplification region 12, by up to approximately 30%. In FIGS. 9A and 9B, when the current is approximately 0.1 A or less, the shorter the cavity length L3, the higher the power conversion efficiency PCEdfb. When the current is large, the longer the cavity length L3, the higher the power conversion efficiency PCEdfb.

[0062] 10A and 10B are diagrams illustrating the power conversion efficiency PCEall of the entire semiconductor laser device. The horizontal axis represents the target value of the optical output from the amplification region 12. The vertical axis represents the power conversion efficiency PCEall of the entire semiconductor laser device.

[0063] 10A shows the power conversion efficiency PCEall in the embodiment. As shown in FIG. 10A, in the embodiment, the power conversion efficiency PCEall of the entire device is lower than the power conversion efficiency PCEsoa (25%) of the amplification region 12. For the same optical output, the shorter the cavity length L3, the higher the power conversion efficiency PCEall. Regardless of the value of the cavity length L3, the higher the optical output, the higher the power conversion efficiency PCEall becomes, approaching the power conversion efficiency PCEsoa of the amplification region 12.

[0064] 10B shows the power conversion efficiency PCEall in the comparative example. In the comparative example, the power conversion efficiency PCEall of the entire device is higher than the power conversion efficiency PCEsoa of the amplification region 12. For the same optical output, the longer the cavity length L3, the higher the power conversion efficiency PCEall. Regardless of the value of the cavity length L3, the higher the optical output, the lower the power conversion efficiency PCEall becomes, approaching the power conversion efficiency PCEsoa of the amplification region 12.

[0065] 11A and 11B are diagrams illustrating the relationship between the power input ratio Wr and the optical output. The horizontal axis represents the power input ratio Wr (=Wsoa / Wdfb). The vertical axis represents the target value of the optical output from the amplification region 12. FIG. 11A represents an embodiment. FIG. 11B represents a comparative example. As shown in FIGS. 11A and 11B, for the same cavity length L3, the optical output is proportional to the power input ratio Wr. The higher the target optical output, the higher the power input ratio Wr. In other words, by increasing the power input ratio Wr, a higher optical output can be obtained. For a given optical output, the shorter the cavity length L3, the higher the power input ratio Wr.

[0066] 12A and 12B are diagrams illustrating the relationship between the power input ratio Wr and the power conversion efficiency PCEall. The horizontal axis represents the power input ratio Wr. The vertical axis represents the power conversion efficiency PCEall of the entire semiconductor laser device. Fig. 12A represents an embodiment. Fig. 12B represents a comparative example.

[0067] As shown in FIG. 12A, in the embodiment, the power conversion efficiency PCEall increases as the power input ratio Wr increases. As the resonator length L3 becomes shorter, such as 800 μm, 600 μm, or 400 μm, the power input ratio Wr increases and the power conversion efficiency PCEall also increases. As shown in FIG. 12B, in the comparative example, the power conversion efficiency PCEall decreases as the power input ratio Wr increases. In both examples, the power conversion efficiency PCEall approaches a constant value (approximately 0.25) as the power input ratio Wr increases.

[0068] When compared at the same power input ratio Wr, the power conversion efficiency PCEall shown in Fig. 12A is lower than the power conversion efficiency PCEall shown in Fig. 12B. As the power input ratio Wr increases, the power conversion efficiency PCEall in Fig. 12A increases and the power conversion efficiency PCEall in Fig. 12B decreases. The difference in power conversion efficiency PCEall between the embodiment and the comparative example decreases.

[0069] As described above, in this embodiment, the larger the power input ratio Wr, the higher the power conversion efficiency PCEall. To make the power input ratio Wr greater than 1, the power Wsoa input to the amplification region 12 is made greater than the power Wdfb input to the laser region 10. Specifically, the area of ​​the mesa 31 in the amplification region 12 should be greater than the area of ​​the mesa 31 in the laser region 10. The length L3 and width W1 of the portion 31a of the mesa 31, and the length L4 and width W2 of the portion 31b of the mesa 31 are set to appropriate sizes.

[0070] In the following example, appropriate ranges for the length L3 of the portion 31a of the mesa 31 and the length L4 of the portion 31b are determined according to the length (total length Lt) of the semiconductor laser device 100.

[0071] The output power Psoa of the output light B3 from the amplification region 12 is expressed by equation (5), where g is the gain per unit length in the amplification region 12. Psoa = Pdfb × exp(g × L4) (5) By substituting Psoa expressed by equation (5) into equation (2), the length L4 is expressed by equation (6). L4=(1 / g)ln(Esoa×Wsoa / Pdfb+1) (6) The power conversion efficiency PCEall and the length L4 are calculated for each total length Lt and cavity length L3 of the semiconductor laser device 100. In this example, the gain g is set to 15 cm -1 Let's say.

[0072] 13A to 15E are diagrams illustrating the relationship between the power input ratio Wr and the power conversion efficiency PCEall. The horizontal axis represents the power input ratio Wr. The vertical axis represents the power conversion efficiency PCEall of the entire device. In FIGS. 13A to 13E, the total length Lt is 1000 μm or more and less than 1500 μm. The cavity length L3 in FIGS. 13A to 13E is 400 μm, 600 μm, 800 μm, 1000 μm, and 1200 μm, respectively. In FIGS. 14A to 14E, the total length Lt is 1500 μm or more and less than 2000 μm. In FIGS. 15A to 15E, the total length Lt is 2000 μm or more and less than 2500 μm. In FIGS. 14A to 14E and 15A to 15E, the cavity length L3 is the same as in FIGS. 13A to 13E. The figure shows the possible ranges of the power input ratio Wr and the power conversion efficiency PCEall.

[0073] 16A to 18E are diagrams illustrating the relationship between the power input ratio Wr and the length L4 of the portion 31b of the mesa 31. The horizontal axis represents the power input ratio Wr. The vertical axis represents the length L4 of the mesa 31 in the amplification region 12. The total length Lt and the cavity length L3 are set to the same ranges as those in FIGS. 13A to 15E. The figures show the possible ranges of the power input ratio Wr and the length L4.

[0074] 13D and 13E, 16D and 16E, when the total length Lt is in the range of 1000 μm to 1500 μm and the resonator length L3 is 1000 μm or 1200 μm, the power input ratio Wr is less than 1. As shown in FIGS. 13A to 13C and 16A to 16C, when the resonator length L3 is 400 μm, 600 μm, or 800 μm, the power input ratio Wr can be 1 or greater. As shown in FIG. 16A, when Wr>1, the length L4 of portion 31b is approximately 700 μm or greater and approximately 1000 μm or less.

[0075] 14D and 14E, 17D and 17E, when the total length Lt is in the range of 1500 μm to 2000 μm and the resonator length L3 is 1000 μm or 1200 μm, the power input ratio Wr can be less than 1. As shown in FIGS. 14A to 14C and 17A to 17C, when the resonator length L3 is 400 μm, 600 μm, or 800 μm, the power input ratio Wr is greater than 1. When Wr>1, the length L4 of portion 31b is equal to or greater than approximately 700 μm and equal to or less than approximately 1500 μm.

[0076] 15A to 15E and 18A to 18E, when the total length Lt is in the range of 2000 μm to 2500 μm, the power input ratio Wr is greater than 1 regardless of whether the cavity length L3 is in the range of 400 μm to 1200 μm. The length L4 of the portion 31b is not less than approximately 800 μm and not more than approximately 2100 μm.

[0077] As the total length Lt is longer and the resonator length L3 is shorter, the length L4 of the portion 31b is longer, and the power input ratio Wr increases. This improves the power conversion efficiency PCEall. For example, the resonator length L3 may be 0.6 times, 0.5 times, or 0.4 times the total length Lt or less. When the total length Lt is 1500 μm or more and the resonator length L3 is 0.6 times or less the total length Lt, the power input ratio Wr is greater than 1 (FIGS. 14A to 14C, 17A to 17C, 15A to 15E, and 18A to 18E).

[0078] According to this embodiment, as shown in FIGS. 1 and 2, an anti-reflection coating 20 is provided on the end face 11, and an anti-reflection coating 21 is provided on the end face 13. Since light is less likely to be reflected from the end face 11, the effect of reflected light on wavelength is reduced. The wavelength of the output light B3 is determined by the diffraction grating 35. The wavelength can be stably controlled. Since the variation in wavelength between elements is reduced, yield is improved.

[0079] As shown in FIG. 1, the mesa 31 is provided in the laser region 10 and the amplification region 12. In a plan view, the area of ​​the mesa 31 in the amplification region 12 is larger than the area of ​​the mesa 31 in the laser region 10. The power Wsoa input to the amplification region 12 is larger than the power Wdfb input to the laser region 10, and the power input ratio Wr is larger than 1. As shown in FIG. 12A, an increase in the power input ratio Wr increases the power conversion efficiency PCEall of the semiconductor laser device 100. It is possible to stabilize the wavelength of light and increase efficiency.

[0080] The power input ratio Wr depends on the area ratio of the mesa 31 in the laser region 10 to the amplification region 12. The area of ​​the mesa 31 in the amplification region 12 may be two or more, three or more, four or more, five or more, eight or more, or ten or more times the area of ​​the mesa 31 in the laser region 10. If the driving voltages of the laser region 10 and the amplification region 12 are approximately the same, the power input ratio Wr will also be two or more, three or more, four or more, five or more, eight or more, or ten or more depending on the above area ratio. For example, the area of ​​the mesa 31 in the amplification region 12 is set to four or more times the area of ​​the mesa 31 in the laser region 10. In the example of FIG. 12B, when the power input ratio Wr is four or more, the power conversion efficiency PCEall is approximately 0.23 or more.

[0081] The length L4 of the mesa 31 in the amplification region 12 may be greater than the length L3 of the mesa 31 in the laser region 10. The width W2 of the mesa 31 in the amplification region 12 may be greater than the width W1 of the mesa 31 in the laser region 10. When the length L4 is greater than the length L3 and the width W2 is greater than the width W1, the area of ​​the mesa 31 in the amplification region 12 is greater than the area of ​​the mesa 31 in the laser region 10. The power input ratio Wr is greater than 1, and the power conversion efficiency PCEall is improved. Even when the length L4 is smaller than the length L3, if the width W2 is sufficiently larger than the width W1, the area of ​​the portion 31b is greater than the area of ​​the portion 31a. Even when the width W2 is smaller than the width W1, if the length L4 is sufficiently larger than the length L3, the area of ​​the portion 31b is greater than the area of ​​the portion 31a.

[0082] The emitted light B1 from the laser region 10 passes through the anti-reflection coating 20 and is emitted to the outside from the facet 11, resulting in loss. To reduce loss, the laser region 10 can be made smaller and the emitted light B1 reduced. However, if the cavity length L3 is shortened, the laser region 10 is less likely to operate stably as a DFB laser element. If the cavity length L3 is long, the loss of the emitted light B1 increases and there is a risk of multi-mode oscillation. For example, the cavity length L3 is set to 400 μm or more and 1200 μm or less. When the cavity length L3 is 400 μm or more, the laser region 10 operates stably as a DFB laser element. When the cavity length L3 is 1200 μm or less, loss is reduced and multi-mode oscillation is less likely to occur.

[0083] As shown in Figure 11A, at a constant optical output, the shorter the cavity length L3, the higher the power input ratio Wr. As shown in Figure 10A, at a constant optical output, the shorter the cavity length L3, the higher the power conversion efficiency PCEall. For example, the cavity length L3 may be 400 μm or more, 600 μm or less, 800 μm or less, 1000 μm or less, or 1200 μm or less.

[0084] The cavity length L3 may be, for example, 0.6 times or less, 0.5 times or less, 0.4 times or less, or 0.3 times or less the total length Lt of the semiconductor laser device 100. When the total length Lt is 1500 μm or more, the cavity length L3 is 0.6 times or less Lt, i.e., 900 μm or less. As shown in FIGS. 14A to 14C and 17A to 17C, the power input ratio Wr is greater than 1. When the total length Lt is 2000 μm or more, the cavity length L3 is 0.6 times or less Lt, i.e., 1200 μm or less. As shown in FIGS. 15A to 15E and 18A to 18E, the power input ratio Wr is greater than 1. When the total length Lt is 2000 μm or more and the cavity length is 600 μm or less, the power input ratio Wr is greater than 4. In the amplification region 12, the length L4 of the mesa 31 is long, and the power conversion efficiency PCEall is high. However, it is better to limit the total length Lt to reduce the size of the semiconductor laser device 100. The total length Lt is set to, for example, 2500 μm or less, or 3000 μm or less.

[0085] The active region in the semiconductor laser device 100 is a mesa 31. As shown in FIG. 2, the mesa 31 includes an active layer 36 and extends to the laser region 10 and the amplification region 12. As shown in FIG. 1, a portion 31a of the mesa 31 is located in the laser region 10. A portion 31b of the mesa 31 is located in the amplification region 12. In a plan view, the area of ​​the portion 31b is larger than the area of ​​the portion 31a. The power Wsoa input to the portion 31b is larger than the power Wdfb input to the portion 31a. The power input ratio Wr becomes larger than 1, and the power conversion efficiency PCEall becomes higher.

[0086] As shown in Figures 3A and 3B, an n-type substrate 30, an i-type active layer 36, a p-type cladding layer 40, and a contact layer 42 are stacked to form a mesa 31. The mesa 31 includes a pin junction. Current can be injected into the active layer 36 of the mesa 31. Light oscillates in the laser region 10, and the light is amplified in the amplification region 12.

[0087] Buried layers 39 are provided on both sides of the mesa 31. The buried layers 39 include an n-type semiconductor layer 46 and a p-type semiconductor layer 44. A pnpn junction is formed on both sides of the mesa 31. The current confinement structure allows current to flow easily into the mesa 31 and makes it difficult for current to flow outside the mesa 31. By concentrating the current flow in the mesa 31, the power conversion efficiency PCEall is increased.

[0088] As shown in FIG. 1, electrode 23 overlaps portion 31a of mesa 31. Electrode 24 overlaps portion 31b of mesa 31. As shown in FIG. 2, electrode 22 is provided on the back surface of substrate 30. Current flows in the Z-axis direction. The current flowing through mesa 31 and the amount of power input depend on the area of ​​mesa 31. By making the area of ​​portion 31b larger than the area of ​​portion 31a, the power input ratio Wr becomes larger than 1. The power conversion efficiency PCEall increases.

[0089] As shown in Fig. 11A, the higher the optical output power, the larger the power input ratio Wr. As shown in Fig. 10A, the higher the optical output power, the higher the power conversion efficiency PCEall. The optical output power of light B3 after amplification by the amplification region 12 may be, for example, 200 mW or more, 300 mW or more, or 500 mW or more. The semiconductor laser device 100 functions as a highly efficient and high-output light source.

[0090] The reflectance of the interface between the semiconductor layer and air for light with a wavelength of around 1300 nm is about 30%. The reflectance of anti-reflection coating 20 and anti-reflection coating 21 is lower than the reflectance of the interface between the semiconductor and air, and is 30% or less, 10% or less, or 1% or less.

[0091] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present disclosure as described in the claims. [Explanation of symbols]

[0092] 10 Laser Region 12 Amplified region 20, 21 Anti-reflection coating 22, 23, 24 electrodes 25, 26 wiring layer 27 Highly reflective coating 30 boards 31 Mesa (active region) 31a, 31b part 31c Tapered section 32, 44, 46 Semiconductor layer 33, 40 Cladding layer 34, 38 Optical confinement layer 35 Diffraction Grating 36 Active layer 37 Trench 39 Buried Layer 42 Contact layer 50 insulating film 100, 110 Semiconductor laser element

Claims

1. a laser region that lases light; an amplification region that amplifies the light; an active region extending into the laser region and the amplifier region; a first antireflection film provided on an end surface of the laser region opposite to the amplification region; a second antireflection film provided on an end surface of the amplification region opposite to the laser region, A semiconductor laser element in which, in a plan view, the area of ​​the active region in the amplification region is larger than the area of ​​the active region in the laser region.

2. 2. The semiconductor laser device according to claim 1, wherein the area of ​​said active region in said amplification region is at least four times the area of ​​said active region in said laser region.

3. the active region in the amplification region is longer than the active region in the laser region; 3. The semiconductor laser device according to claim 1, wherein the width of said active region in said amplification region is larger than the width of said active region in said laser region.

4. 3. The semiconductor laser device according to claim 1, wherein the length of the laser region is 400 [mu]m or more and 1200 [mu]m or less.

5. 3. The semiconductor laser device according to claim 1, wherein the length of said active region in said laser region is 0.6 times or less the length of said semiconductor laser device.

6. an active layer provided in the laser region and the amplification region; the active region is a mesa; 3. The semiconductor laser device according to claim 1, wherein the mesa includes an active layer and extends to the laser region and the amplification region.

7. The laser region and the amplification region include a first semiconductor layer, the active layer, and a second semiconductor layer stacked in this order, the first semiconductor layer has a first conductivity type; the second semiconductor layer has a second conductivity type; the first semiconductor layer and the active layer form the mesa; 7. The semiconductor laser device according to claim 6, wherein the second semiconductor layer is provided on the mesa.

8. 7. The semiconductor laser device according to claim 6, further comprising buried layers provided on both sides of said mesa in said laser region and said amplification region.

9. a first electrode provided in the laser region and overlapping a portion of the mesa provided in the laser region; 7. The semiconductor laser device according to claim 6, further comprising: a second electrode provided in the amplification region and overlapping a portion of the mesa that is provided in the amplification region.

10. 3. The semiconductor laser device according to claim 1, wherein the light amplified by said amplification region has an output of 200 mW or more.

11. designing a laser region for lasing light and an amplifier region for amplifying said light; forming the laser region and the amplifier region based on a design of the laser region and a design of the amplifier region; forming a first anti-reflection film on an end surface of the laser region opposite to the amplification region; forming a second anti-reflection film on an end surface of the amplification region opposite to the laser region, the laser region and the amplifier region include an active region; a step of designing the active region in the amplification region so that the power input to the active region in the laser region is greater than the power input to the active region in the laser region;

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