Semiconductor laser device

Abstract

To provide a semiconductor laser element capable of controlling the wavelength of light and improving optical output.SOLUTION: A semiconductor laser device comprising: a laser region configured to laser-oscillate light; an amplification region adjacent to the laser region and configured to amplify the light; and a resistor provided in the laser region and configured to heat the laser region, wherein the resistor includes a first portion and a second portion, the second portion is connected to the first portion, is closer to a boundary between the laser region and the amplification region than the first portion, and has a higher resistance per unit length than the first portion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a semiconductor laser device. [Background technology]

[0002] Some semiconductor laser devices integrate multiple elements. For example, a device is known that integrates a distributed Bragg reflector (DBR) laser and a phase adjustment region (Non-Patent Document 1). A heater is provided in the phase adjustment region, and the phase of the light is adjusted by controlling the temperature. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] T. Kameda et al. “A DBR Laser Employing Passive-Section Heaters,with 10.8 nm Tuning Range and 1.6 MHz Linewidth” IEEE Photonics Technology Letters,Vol.5,No.6,pp.608-610,June 1993 Summary of the Invention [Problem to be solved by the invention]

[0004] An element has also been developed that integrates a distributed feedback (DFB) laser and a semiconductor optical amplifier (SOA) that amplifies light. A heater installed in the laser region controls the temperature of the laser region and changes the wavelength of the laser light. Stable wavelength control can be achieved by uniformly heating the laser region. However, this can cause the temperature of the SOA to rise, resulting in a decrease in optical output. Therefore, the objective of this study is to provide a semiconductor laser element that can control the wavelength of light and improve optical output. [Means for solving the problem]

[0005] A semiconductor laser element according to the present disclosure comprises a laser region that oscillates light into laser oscillation, an amplification region adjacent to the laser region that amplifies the light, and a resistor provided in the laser region for heating the laser region, the resistor having a first portion and a second portion, the second portion being connected to the first portion and being closer to a boundary between the laser region and the amplification region than the first portion, and the resistance per unit length of the second portion being higher than the resistance per unit length of the first portion. [Effects of the Invention]

[0006] According to the present disclosure, it is possible to provide a semiconductor laser element that is capable of controlling the wavelength of light and improving the optical output. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a plan view illustrating the semiconductor laser device according to the first embodiment. [Figure 2A] FIG. 2A is a cross-sectional view illustrating an example of a semiconductor laser device. [Figure 2B] FIG. 2B is a cross-sectional view illustrating an example of a semiconductor laser device. [Figure 3] FIG. 3 is a cross-sectional view illustrating an example of a semiconductor laser device. [Figure 4A] FIG. 4A is a diagram illustrating the heating efficiency. [Figure 4B] FIG. 4B is a diagram illustrating power. [Figure 5] FIG. 5 is a plan view illustrating a semiconductor laser device according to a comparative example. [Figure 6] FIG. 6 is a diagram illustrating the temperature distribution. [Figure 7A] FIG. 7A is a cross-sectional view illustrating a method for manufacturing a semiconductor laser device. [Figure 7B] FIG. 7B is a cross-sectional view illustrating a method for manufacturing a semiconductor laser device. [Figure 7C]FIG. 7C is a cross-sectional view illustrating a method for manufacturing a semiconductor laser device. [Figure 8A] FIG. 8A is a cross-sectional view illustrating a method for manufacturing a semiconductor laser device. [Figure 8B] FIG. 8B is a cross-sectional view illustrating a method for manufacturing the semiconductor laser device. [Figure 8C] FIG. 8C is a cross-sectional view illustrating a method for manufacturing a semiconductor laser device. [Figure 9A] FIG. 9A is a cross-sectional view illustrating a method for manufacturing a semiconductor laser device. [Figure 9B] FIG. 9B is a cross-sectional view illustrating a method for manufacturing the semiconductor laser device. [Figure 9C] FIG. 9C is a cross-sectional view illustrating a method for manufacturing a semiconductor laser device. [Figure 10] FIG. 10 is a cross-sectional view illustrating a semiconductor laser device according to a modified example. [Figure 11] FIG. 11 is a plan view illustrating the semiconductor laser device according to the second embodiment. [Figure 12] FIG. 12 is a plan view illustrating the semiconductor laser device according to the third embodiment. [Figure 13] FIG. 13 is a plan view illustrating the semiconductor laser device according to the fourth embodiment. [Figure 14] FIG. 14 is a plan view illustrating the semiconductor laser device according to the fifth embodiment. 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 adjacent to the laser region that amplifies the light; and a resistor provided in the laser region for heating the laser region, the resistor having a first portion and a second portion, the second portion connected to the first portion and closer to the boundary between the laser region and the amplification region than the first portion, and the resistance per unit length of the second portion being higher than the resistance per unit length of the first portion. The laser region near the boundary with the amplification region is strongly heated. The temperature is low in the amplification region, rises sharply near the boundary, and is high in the laser region. This allows for control of the wavelength of light and improvement of optical output. (2) In the above (1), the width of the first portion may be greater than the width of the second portion. The resistance per unit length of the second portion is higher than the resistance per unit length of the first portion. This allows for control of the wavelength of light and improvement of light output. (3) In the above (1) or (2), the second portion may include a tapered portion, and the width of the tapered portion may decrease from the laser region to the amplification region. The resistance per unit length of the second portion is higher than the resistance per unit length of the first portion. This allows for control of the wavelength of light and improvement of optical output. (4) In any of (1) to (3) above, the second portion may be provided in the laser region, and an end of the second portion may be located at the boundary between the laser region and the amplification region. Since the temperature of the amplification region is less likely to rise, the optical output can be improved. By changing the temperature of the laser region, the wavelength of the light can be controlled. (5) In any one of (1) to (3) above, the second portion may be provided in the laser region and the amplification region. By uniformly heating the laser region, the temperature is changed uniformly. This allows for precise control of the wavelength of light. (6) In any of (1) to (5) above, the resistor may include two of the first portions and two of the second portions, one of the two first portions being connected to one of the two second portions, one of the two second portions being connected to the other of the two second portions, and the other of the two second portions being connected to the other of the two first portions. This allows for control of the wavelength of light and improvement of light output. (7) In any one of (1) to (6) above, the first portion may be longer than the second portion in the extension direction of the laser region. The temperature of the entire laser region can be controlled to set the wavelength to a desired value. (8) In any of (1) to (7) above, a first semiconductor layer may be provided in the laser region and the amplification region, and a second semiconductor layer may be provided in the laser region and embedded in the first semiconductor layer, and a diffraction grating may be formed where the first semiconductor layer and the second semiconductor layer are aligned. The wavelength of light can be controlled by changing the temperature of the diffraction grating with a resistor and adjusting the refractive index. (9) In the above (8), an active layer stacked on the first semiconductor layer and a third semiconductor layer stacked on the active layer may be provided, the first semiconductor layer having a first conductivity type, the third semiconductor layer having a second conductivity type, the first semiconductor layer and the active layer forming a mesa, the mesa extending to the laser region and the amplification region, the third semiconductor layer being provided on the mesa, and the resistor being provided on the third semiconductor layer, directly above the mesa or at a position spaced apart from the mesa.

[0010] [Details of the embodiments of the present disclosure] Specific examples of semiconductor laser devices 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 equivalent to the claims.

[0011] First Embodiment FIG. 1 is a plan view illustrating a semiconductor laser device 100 according to an embodiment. FIGS. 2A to 3 are cross-sectional views illustrating the semiconductor laser device 100. The X-axis direction is the light propagation direction. The Y-axis direction is the width direction. The Z-axis direction is the thickness direction. The X-axis direction, Y-axis direction, and Z-axis direction are perpendicular to each other.

[0012] As shown in Fig. 1, the semiconductor laser device 100 is an element that integrates a DFB laser and an SOA. That is, the semiconductor laser device 100 has a laser region 10 that functions as a DFB laser and an amplification region 12 that functions as an SOA. The dashed line in Fig. 1 represents the boundary 13 between the laser region 10 and the amplification region 12. The laser region 10 and the amplification region 12 extend parallel to the X-axis direction and are adjacent to each other. The length of the laser region 10 in the X-axis direction is defined as L1. The length of the amplification region 12 in the X-axis direction is defined as L2.

[0013] A high-reflection coating (HR coating) 14 and an anti-reflection coating (AR coating) 16 are provided on the end faces of the semiconductor laser device 100. The high-reflection coating 14 is provided on the surface of the laser region 10 opposite to the amplification region 12. The anti-reflection coating 16 is provided on the surface of the amplification region 12 opposite to the laser region 10.

[0014] The semiconductor laser element 100 has a mesa 31. The mesa 31 extends in the X-axis direction. The mesa 31 is provided in the laser region 10 and the amplification region 12, and extends in the X-axis direction from the end face in contact with the high-reflection film 14 of the semiconductor laser element 100 to the end face in contact with the anti-reflection film 16. The width W0 of the mesa 31 is, for example, 2 μm. Light propagates through the mesa 31. In the laser region 10, the light undergoes laser oscillation. In the amplification region 12, the laser light is amplified.

[0015] 2A shows a cross section taken along line AA in FIG. 1. FIG. 2B shows a cross section taken along line BB in FIG. 1. FIG. 3 shows an enlarged view of a portion of FIG. 2B. As shown in FIG. 2A, the semiconductor laser device 100 has a substrate 30, a semiconductor layer 32, 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. On one surface of the substrate 30, the cladding layer 33, the optical confinement layer 34, the active layer 36, the optical confinement layer 38, the cladding layer 40, and the contact layer 42 are stacked in this order in the Z-axis direction. The substrate 30 and the cladding layer 33 correspond to a first semiconductor layer. The cladding layer 40 and the contact layer 42 correspond to a third semiconductor layer.

[0016] The semiconductor layer 32 (second semiconductor layer) is embedded in the substrate 30 and the portion of the cladding layer 33 that is included in the laser region 10. A plurality of semiconductor layers 32 are periodically arranged along the X-axis direction. In the laser region 10, the cladding layers 33 and the semiconductor layers 32 are alternately arranged to form a diffraction grating 35. The semiconductor layer 32 is not provided in the amplification region 12. The diffraction grating 35 is provided in the laser region 10, but not in the amplification region 12.

[0017] 2B, the semiconductor laser device 100 has a mesa 31 and a trench 37. The trenches 37 are provided on both sides of the mesa 31 in the Y-axis direction.

[0018] As shown in FIG. 3 , the central portion of the substrate 30 in the Y-axis direction protrudes in the Z-axis direction compared to the portion of the substrate 30 outside the central portion. A semiconductor layer 32, 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 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. A semiconductor layer 44 and a semiconductor layer 46 are stacked on both sides of the mesa 31 in the Y-axis direction. The semiconductor layer 44 and the semiconductor layer 46 form a buried structure. 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.

[0019] 2B, trench 37 is a recessed portion in the Z-axis direction, penetrates through the semiconductor layers from contact layer 42 to semiconductor layer 44, and extends partway through substrate 30. Outside trench 37 in the Y-axis direction, semiconductor layer 44, semiconductor layer 46, cladding layer 40, and contact layer 42 are provided. Mesa 31, the inside of trench 37, and the portion outside trench 37 are covered with insulating film 54. Insulating film 54 has an opening above mesa 31. Insulating film 54 is made of an insulator such as silicon oxide (SiO2) and silicon nitride (SiN).

[0020] 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.

[0021] 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.

[0022] 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-InGaAsP layer. A p-InGaAs layer and a p-InGaAsP layer are stacked in this order on the cladding layer 40. The p-type semiconductor layer is doped with, for example, zinc (Zn).

[0023] The semiconductor layer 44 is made of, for example, p-InP, and the semiconductor layer 46 is made of, for example, n-InP.

[0024] 2A, the semiconductor laser device 100 has an electrode 50, an electrode 52, and a heater 60. The electrodes 50 and 52 are provided in the laser region 10 and the amplification region 12. As shown in FIG. 1, the heater 60 (resistor) is provided in the laser region 10, but not in the amplification region 12. The heater 60 heats the laser region 10.

[0025] 2A and 2B, an electrode 50 is provided on the surface of the substrate 30 opposite the active layer 36. The electrode 50 contacts the lower surface of the substrate 30 and is electrically connected to the substrate 30. The electrode 50 is made of metal.

[0026] The electrode 52 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 53 is provided on the electrode 52, and extends from above the mesa 31 to one trench 37 and beyond the trench 37. The wiring layer 53 is in contact with the electrode 52 on the mesa 31 through an opening in the insulating film 54. The electrode 52 and the wiring layer 53 are electrically connected to the contact layer 42. The wiring layer 53 is provided on the insulating film 54 in positions other than the mesa 31, and is insulated from the semiconductor layer by the insulating film 54.

[0027] The electrode 52 is made of metal and is, for example, a laminate of a gold (Au) layer, a tin (Sn) layer, and an Au layer stacked from the side closest to the contact layer 42. The wiring layer 53 is made of, for example, Au.

[0028] 2B , the heater 60 is provided on the upper surface of the insulating film 54 and is located on the mesa 31. The wiring layer 65 extends from above the mesa 31 to one trench 37 and beyond the trench 37. The wiring layer 65 is provided on the upper surface of the heater 60 above the mesa 31, and is provided on the upper surface of the insulating film 54 outside the mesa 31. The heater 60 and the wiring layer 65 are insulated from the electrode 52, the wiring layer 53, and the semiconductor layer by the insulating film 54.

[0029] The heater 60 is made of metal and is, for example, a laminate of a platinum (Pt) layer, a titanium (Ti) layer, a tungsten (W) layer, and an alloy layer of titanium and tungsten (TiW) layer stacked from the side closest to the contact layer 42. The heater 60 has a thickness of, for example, 0.1 μm or more and 1.0 μm or less. The wiring layer 65 is made of, for example, Au.

[0030] 1, the heater 60 has a portion 62 (first portion) and a portion 64 (second portion). The portion 62 is provided in the laser region 10 and extends parallel to the X-axis direction. The portion 64 is provided in the laser region 10 and is located closer to the amplification region 12 than the portion 62. The portion 64 is connected to the portion 62 and extends from the tip of the portion 62 to the boundary 13 in the X-axis direction.

[0031] The pads 56 are formed from the same metal layer as the wiring layer 65 and are electrically connected to the heater 60. One of the two pads 56 is connected to the portion 62. The other pad 56 is connected to the portion 64.

[0032] The planar shapes of portion 62 and portion 64 of heater 60 are rectangular. The width of portion 62 in the Y-axis direction is W1. The width of portion 64 is W2. The width W1 of portion 62 is larger than the width W2 of portion 64. The length of portion 62 in the X-axis direction is L3. The length of portion 64 is L4. The length L3 of portion 62 is larger than the length L4 of portion 64.

[0033] Because portion 64 is thinner than portion 62, the electrical resistance per unit length of portion 64 is higher than the electrical resistance per unit length of portion 62. Because portion 62 is longer than portion 64, the overall electrical resistance of portion 62 is higher than the overall electrical resistance of portion 64.

[0034] The mesa 31 of the semiconductor laser device 100 includes an active layer 36. At the position overlapping the mesa 31, the n-type substrate 30 and cladding layer 33, the i-type active layer 36, the p-type cladding layer 40, and the contact layer 42 form a pin (positive-intrinsic-negative) junction. Outside the mesa 31, the p-type cladding layer 40, the n-type semiconductor layer 46, the p-type semiconductor layer 44, and the n-type substrate 30 are stacked to form a pnpn junction. In other words, a current confinement structure including the mesa 31 is formed. Current flows easily through the mesa 31 and is difficult to flow outside the mesa 31.

[0035] When a voltage is applied to the electrodes 50 and 52, a current flows selectively through the mesa 31. Carriers are injected into the active layer 36 and recombine to generate light. The light propagates through the mesa 31, resulting in laser oscillation at a wavelength corresponding to the period of the diffraction grating 35. The laser light is reflected by the high-reflection film 14. The laser light is amplified in the amplification region 12, passes through the anti-reflection film 16, and is emitted to the outside of the semiconductor laser device 100.

[0036] The semiconductor laser element 100 is a tunable laser element, and can change the wavelength of the emitted light. When a current flows through the heater 60, the heater 60 generates heat, and the laser region 10 is heated. The refractive index of the diffraction grating 35 changes in response to the change in temperature. The wavelength of the laser light changes.

[0037] As an example, let us assume that the semiconductor laser device 100 is used for optical communications. The wavelength range of the emitted light is assumed to be approximately 4.5 nm, from 1295.56 nm to 1300.05 nm. The wavelength of the laser light changes by approximately 0.1 nm for a temperature change of 1 degree. To change the wavelength within this range, it is sufficient to be able to change the temperature within a 45-degree range, for example, from 30 degrees to 75 degrees.

[0038] 4A is a diagram illustrating the heating efficiency. The horizontal axis represents the length L1 of the laser region 10. The vertical axis represents the heating efficiency. The heating efficiency is the temperature change relative to the power input to the heater 60.

[0039] FIG. 4B is a diagram illustrating power. The horizontal axis represents the length L1 of the laser region 10. The vertical axis represents the power input to the heater 60 to change the wavelength by 4.5 nm. In this example, the wavelength change per degree of temperature is 0.1 nm / °C, and the wavelength change is 4.5 nm. To achieve a wavelength shift of 4.5 nm, the temperature is changed by 45 degrees. FIG. 4B shows the power required for a temperature change of 45 degrees.

[0040] The longer the laser region 10, the lower the heating efficiency and the more power required to achieve a 4.5 nm wavelength shift. The shorter the laser region 10, the higher the heating efficiency and the lower the power required. To reduce power, simply shorten the laser region 10. If the laser region 10 is too short, operation becomes unstable.

[0041] The semiconductor laser device 100 is designed taking into consideration heating efficiency and power. For example, the length L1 of the laser region 10 is 350 μm or more and 800 μm or less. The length L2 of the amplification region 12 is 200 μm or more and 1500 μm or less. Laser oscillation of light and amplification of laser light are possible. The length L3 of the portion 62 of the heater 60 is shorter than the length L1 of the laser region 10, e.g., 100 μm shorter than L1. The length L4 of the portion 64 of the heater 60 is, e.g., 50 μm or more and 200 μm or less, and shorter than the length L3 of the portion 62. The width W1 of the portion 62 is, e.g., 1.5 μm or more and 10 μm or less. The width W2 of the portion 64 is, e.g., 1.5 μm or more and 10 μm or less, and shorter than the width W1. The thickness of the heater 60 is, e.g., 0.1 μm or more and 1.0 μm or less.

[0042] The wavelength is changed by heating the laser region 10. On the other hand, if the temperature of the amplification region 12 increases, there is a risk of a decrease in output power. By concentrating the heating on the laser region 10 and not increasing the temperature of the amplification region 12, it is possible to achieve both wavelength change and high output power.

[0043] (Comparative Example) 5 is a plan view illustrating a semiconductor laser device 110 according to a comparative example. The heater 60 of the semiconductor laser device 110 has a certain width. The heater 60 is provided in the laser region 10.

[0044] (Temperature distribution) FIG. 6 is a diagram illustrating the temperature distribution. The horizontal axis represents the position in the X-axis direction of the semiconductor laser element. The thick dashed line represents the 550 μm point. The position from 0 to 550 μm is the amplification region 12. The position from 550 μm to 1000 μm is the laser region 10. That is, in this example, the length of the semiconductor laser element in the X-axis direction is 1000 μm, the length L2 of the amplification region 12 is 550 μm, and the length L1 of the laser region 10 is 450 μm. The vertical axis in FIG. 6 represents the temperature. The temperature of the laser region 10 is increased from 30 degrees to 75 degrees.

[0045] The temperature distribution was calculated for each of the comparative example and the first embodiment. Table 1 shows an example of the design of the semiconductor laser device used in the calculation of the temperature distribution. [Table 1]

[0046] Table 1 shows, from left to right, design examples of a semiconductor laser element 110a, a semiconductor laser element 110b, and a semiconductor laser element 100. The semiconductor laser elements 110a and 110b correspond to comparative examples. In the semiconductor laser element 110a, the heater 60 protrudes into the amplification region 12. In the semiconductor laser element 110b, the heater 60 extends to the boundary 13 between the laser region 10 and the amplification region 12, and does not protrude into the amplification region 12.

[0047] In the semiconductor laser element 110a and the semiconductor laser element 110b, the overall length of the heater 60 is L3, the width is W1, and the electrical resistance is R1. The length L3 of the heater 60 in the semiconductor laser element 110a is 600 μm. The length L3 of the heater 60 in the semiconductor laser element 110b is 450 μm. The width W1 of the heater 60 in the semiconductor laser element 110a and the semiconductor laser element 110b is 3.05 μm. The electrical resistance R1 of the heater 60 in the semiconductor laser element 110a is 205 Ω. The voltage V1 applied to the heater 60 in the semiconductor laser element 110a is 20.5 V, and the current flowing through the heater 60 is 0.1 A. The overall power P1 consumed by the heater 60 in the semiconductor laser element 110a is 2.05 W. The electrical resistance R1 of the heater 60 in the semiconductor laser element 110b is 155 Ω. The voltage V1 applied to the heater 60 of the semiconductor laser element 110b is 15.5 V, and the current flowing through the heater 60 is 0.1 A. The power P1 consumed by the heater 60 of the semiconductor laser element 110b as a whole is 1.55 W.

[0048] In the semiconductor laser device 100, the length L3 of the portion 62 of the heater 60 is 400 μm, and the width W1 of the portion 62 is 4.10 μm. The length L4 of the portion 64 of the heater 60 is 50 μm, and the width W2 of the portion 64 is 2.23 μm. The electrical resistance R1 of the portion 62 is 102.5 Ω, and the electrical resistance R2 of the portion 64 is 23.5 Ω. The voltage V1 applied to the portion 62 is 10.25 V, and the voltage V2 applied to the portion 64 is 2.35 V. A current of 0.1 A flows through the entire heater 60. The power P1 consumed by the portion 62 is 1.025 W. The power P2 consumed by the portion 64 is 0.235 W. The total power consumption is 1.26 W.

[0049] 6, the dashed line indicates the calculation results for the comparative examples (110a and 110b), and the solid line indicates the calculation results for the semiconductor laser device 100 according to the first embodiment.

[0050] In the semiconductor laser element 110a, the heater 60 protrudes from the laser region 10 to the amplification region 12. The entire laser region 10 can be uniformly heated to a temperature of approximately 75 degrees. However, the portion of the amplification region 12 close to the laser region 10 is also heated, causing the temperature to rise. This may result in a decrease in optical output.

[0051] In the semiconductor laser element 110b, the heater 60 is provided only in the laser region 10. The temperature of the amplification region 12 does not easily rise. However, the temperature of the laser region 10 is uneven. In the part of the laser region 10 close to the amplification region 12, the temperature does not reach the target value of 75 degrees. It is difficult to stably control the wavelength.

[0052] In the semiconductor laser device 100, the heater 60 has a portion 62 and a portion 64. The portion 64 extends to the boundary 13 between the laser region 10 and the amplification region 12, and has a width W2 smaller than that of the portion 62. The resistance per unit length of the portion 64 is higher than that of the portion 62. When a current flows, the amount of heat generated per unit length of the portion 64 is greater than that of the portion 62. Therefore, the portion where the portion 64 is provided is heated more strongly than the portion where the portion 62 is provided.

[0053] As shown by the solid line in Figure 6, a steep temperature distribution is obtained from the amplification region 12 to the laser region 10. The temperature of almost the entire laser region 10 reaches the target value of 75 degrees. The temperature changes rapidly near the boundary between the laser region 10 and the amplification region 12. The temperature of the amplification region 12 is maintained at 45 degrees. This allows for stable wavelength control and high optical output.

[0054] (Manufacturing method) 7A to 9C are cross-sectional views illustrating a method for manufacturing the semiconductor laser device 100, showing the laser region 10. FIG.

[0055] As shown in FIG. 7A, 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 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. 2A is formed. In the laser region 10 and the amplification region 12, an optical confinement layer 34, an active layer 36, and an optical confinement layer 38 are epitaxially grown in this order. A cladding layer 40a is epitaxially grown on the upper surface of the optical confinement layer 38.

[0056] As shown in FIG. 7B, a mesa 31 is formed by etching. The mesa 31 extends from the cladding layer 40a to a portion of the substrate 30. As shown in FIG. 7C, 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 InP layer and the cladding layer 40a form the cladding layer 40. A contact layer 42 is epitaxially grown on the upper surface of the cladding layer 40.

[0057] As shown in Figure 8A, 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. As shown in Figure 8B, an electrode 52 is formed on the top surface of the contact layer 42 of the mesa 31 by, for example, vacuum deposition and lift-off.

[0058] 8C, an insulating film 54a is formed by, for example, plasma enhanced CVD (PECVD). The insulating film 54a 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 54a above the mesa 31. A wiring layer 53 is formed on the surfaces of the electrode 52 and the insulating film 54a by, for example, plating.

[0059] 9A, an insulating film is formed to cover the insulating film 54a and the wiring layer 53. The formed insulating film forms the insulating film 54 together with the insulating film 54a.

[0060] As shown in Fig. 9B, a heater 60 is formed on the surface of the insulating film 54, above the mesa 31, by vacuum deposition and lift-off. As shown in Fig. 9C, a wiring layer 65 is formed by, for example, plating. After polishing the back surface of the substrate 30, an electrode 50 is formed on the substrate 30. In this way, the semiconductor laser device 100 is formed.

[0061] According to the first embodiment, as shown in FIG. 1, the semiconductor laser device 100 has a laser region 10 and an amplification region 12. A heater 60 is provided in the laser region 10 and has a portion 62 and a portion 64. The portion 64 is located closer to the boundary 13 between the laser region 10 and the amplification region 12 than the portion 62, and extends, for example, from the tip of the portion 62 to the boundary 13. The width W1 of the portion 62 is larger than the width W2 of the portion 64. The electrical resistance per unit length of the portion 64 is higher than the electrical resistance per unit length of the portion 62. The portion of the laser region 10 near the boundary 13 is heated more strongly than the portion of the laser region 10 away from the boundary 13. The amplification region 12 is not provided with the heater 60, and is therefore less likely to be heated.

[0062] As shown in the example of Figure 6, a steep temperature distribution is obtained. The temperature of the amplification region 12 is low and is maintained at room temperature (e.g., 30°C). As one approaches the boundary 13 from the amplification region 12, the temperature rises rapidly and reaches 75°C. The temperature in almost the entire laser region 10 is higher than that of the amplification region 12, e.g., 75°C. The wavelength of the laser light can be changed by adjusting the temperature of the laser region 10 using the heater 60. Since the temperature of the amplification region 12 is maintained low, the optical output is less likely to decrease. It is possible to control the optical wavelength and improve the optical output.

[0063] By changing the temperature by 45 degrees, the wavelength can be changed by 4.5 nm. The semiconductor laser element 100 can cover a band from 1295.5 nm to 1300.05 nm, for example. By controlling the wavelength with the heater 60, it is possible to compensate for wavelength errors between multiple chips. The power consumption required to change the temperature by 45 degrees is 1.26 W. This makes it possible to reduce power consumption compared to the comparative example. The temperature variable range may be above 45 degrees or below 45 degrees.

[0064] The width of the heater 60 changes discontinuously between width W1 and width W2. The electrical resistance also changes suddenly between portion 62 and portion 64. This simplifies the design of the heater 60 and the analysis of the temperature distribution. The width W1 of portion 62 of the heater 60 is, for example, 4.10 μm. The width W2 of portion 64 is, for example, 2.23 μm. The width W2 may be, for example, more than half the width W1, or less than half the width W1.

[0065] The end of portion 64 is located at the boundary 13 between the laser region 10 and the amplification region 12. Because the heater 60 is not provided in the amplification region 12, the amplification region 12 is less likely to heat up and its temperature does not easily rise. This allows for increased optical output. The heater 60 is provided from the boundary 13 to the laser region 10, so it is heated. Because the temperature of the laser region 10 changes, the wavelength of the light can be controlled.

[0066] 1, portion 62 is longer than portion 64. Portion 62 uniformly heats the portion of laser region 10 away from boundary 13. Short, narrow portion 64 strongly heats the area near boundary 13. The temperature of the entire laser region 10 can be controlled to achieve the desired wavelength.

[0067] As shown in FIG. 2A, the laser region 10 and the amplification region 12 are provided with a substrate 30, a cladding layer 33, an active layer 36, a cladding layer 40, and a contact layer 42. In the laser region 10, a semiconductor layer 32 is embedded in the substrate 30 and the cladding layer 33. The portion where the substrate 30 and the cladding layer 33 are aligned with the semiconductor layer 32 functions as a diffraction grating 35. The temperature of the diffraction grating 35 can be changed by a heater 60. The refractive index of the diffraction grating 35 changes in response to a change in temperature, and the oscillation wavelength of the light also changes.

[0068] 3, the mesa 31 includes a substrate 30, a cladding layer 33, and an active layer 36. A cladding layer 40 and a contact layer 42 are provided on the mesa 31. A heater 60 is provided on the contact layer 42, directly above the mesa 31. The width in the Y-axis direction can be reduced in the portion sandwiched between the trenches 37. The heater 60 is insulated from the electrode 52 and the semiconductor layer by an insulating film 54.

[0069] An n-type substrate 30 and cladding layer 33, an i-type active layer 36, a p-type cladding layer 40, and a contact layer 42 are stacked. A pin junction is formed. Carriers are injected into the active layer 36 by applying a voltage to the electrodes 50 and 52. The active layer 36 generates light. The light propagates through the mesa 31. The wavelength of the laser light is controlled by the diffraction grating 35 in the laser region 10. The laser light is amplified in the amplification region 12.

[0070] (Variation) FIG. 10 is a cross-sectional view illustrating a semiconductor laser device 120 according to a modified example. Description of the same configuration as in the first embodiment will be omitted. The heater 60 is located on the upper surface of the insulating film 54, outside the mesa 31. The heater 60 is separated from the wiring layer 53 and is not electrically connected. There is no need to provide an insulating film. The number of processes is reduced.

[0071] Second Embodiment FIG. 11 is a plan view illustrating a semiconductor laser device 200 according to the second embodiment. The same components as those in the first embodiment will not be described. The heater 60 has a portion 62 (first portion) and a portion 66 (second portion). The portion 66 is connected to the portion 62 and is provided in a portion of the laser region 10 close to the boundary 13. The tip of the portion 66 is located at the boundary 13. The portion 66 has a tapered shape. The width of the portion 66 decreases with increasing distance from the portion 62. The width W3 of the portion of the portion 66 that contacts the portion 62 is equal to the width W1 of the portion 62. The width W4 of the tip of the portion 66 is, for example, approximately the same as the width W2 of the portion 64 in FIG. 1.

[0072] According to the second embodiment, the portion 66 of the heater 60 is a tapered portion. The width of the portion 66 decreases as it approaches the boundary 13. The electrical resistance per unit length of the portion 66 is higher than that of the portion 62, and increases as it approaches the boundary 13. The area near the boundary 13 is easily heated, and the temperature changes rapidly. This allows for wavelength control and improved light output.

[0073] The current density in the heater 60 changes continuously in the portion 66. The current is less likely to concentrate, and the heater 60 is less likely to break.

[0074] <Third embodiment> FIG. 12 is a plan view illustrating a semiconductor laser device 300 according to the third embodiment. Description of the same configuration as in the first or second embodiment will be omitted. The heater 60 has a portion 62 (first portion), a portion 64, and a portion 66 (these two are second portions). The portions 62, 66, and 64 are arranged in this order from the laser region 10 toward the amplification region 12. The portion 66 is connected to the tip of the portion 62. The portion 64 is connected to the tip of the portion 66. The tip of the portion 64 is located at the boundary 13.

[0075] According to the third embodiment, heater 60 has portions 62, 64, and 66. The electrical resistance per unit length of portions 64 and 66 is higher than the electrical resistance per unit length of portion 62. The temperature changes rapidly near boundary 13. Wavelength control and improved light output are possible.

[0076] The portion 66 is located between the portion 62 and the portion 64 and has a tapered shape. Since the current density changes continuously in the portion 66, the heater 60 is less likely to break.

[0077] <Fourth embodiment> FIG. 13 is a plan view illustrating a semiconductor laser device 400 according to the fourth embodiment. Description of the same configuration as any of the first to third embodiments will be omitted. The heater 60 has a portion 62 and a portion 64. The portion 64 extends from the laser region 10 to the amplification region 12. The tip of the portion 64 is located in the amplification region 12. The length L5 of the portion of the portion 64 located in the amplification region 12 may be, for example, half or more of the length L4 of the entire portion 64, or may be half or less of L4.

[0078] According to the fourth embodiment, the portion 64 of the heater 60 is provided near the boundary 13 between the laser region 10 and the amplification region 12. The portion of the laser region 10 close to the boundary 13 is heated by the portion 64. By uniformly heating the laser region 10 with the heater 60, the temperature changes uniformly throughout the laser region 10. The wavelength of light can be controlled with high precision. The heater 60 is provided only in the portion of the amplification region 12 close to the boundary 13. The temperature of the amplification region 12 is unlikely to rise. The wavelength can be controlled and the light output can be improved.

[0079] The heater 60 may have a tapered portion 66, and the portion 66 may be provided in the amplification region 12. The heater 60 may have a portion 64 and a portion 66. The portion 66 or the portion 64 may protrude into the amplification region 12.

[0080] Fifth Embodiment FIG. 14 is a plan view illustrating a semiconductor laser device 500 according to the fifth embodiment. The same configuration as in any of the first to fourth embodiments will not be described. The heater 60 includes a heater 60a (resistor) and a heater 60b (resistor). The heater 60a is provided on the mesa 31. The heater 60b is provided at a position away from the mesa 31 in the Y-axis direction. The heaters 60a and 60b are connected to each other and have a shape that moves back and forth in the X-axis direction. The heaters 60a and 60b each have a portion 62 and a portion 64. The portion 64 of the heater 60a and the portion 64 of the heater 60b are connected. The tips of the two portions 64 are located at the boundary 13.

[0081] According to the fifth embodiment, the heater 60 includes a heater 60a and a heater 60b. The temperature of the laser region 10 can be changed efficiently to control the wavelength of light. Two portions 64 of the heater 60 are provided near the boundary 13 of the laser region 10. The temperature changes rapidly near the boundary 13. This allows for wavelength control and improved light output. The heater 60 of the fifth embodiment is longer, for example, twice as long, than the heater 60 of the first embodiment. The current flowing through the heater 60 is reduced.

[0082] At least one of heater 60a and heater 60b may include portion 66. Portion 64 of heater 60 may protrude into amplification region 12.

[0083] 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]

[0084] 10 Laser Region 12 Amplified region 13 Boundary 14 Highly reflective coating 16 Anti-reflection coating 31 Mesa 30 boards 32, 44, 46 Semiconductor layer 33, 40, 40a cladding layer 34, 38 Optical confinement layer 35 Diffraction Grating 36 Active layer 37 Trench 42 Contact layer 50, 52 electrodes 53, 65 wiring layer 54, 54a insulating film 56 Pad 60, 60a, 60b Heater (resistor) 62, 64, 66 parts 100, 110, 120, 200, 300, 400, 500 Semiconductor laser element

Claims

1. a laser region that lases light; an amplification region adjacent to the laser region for amplifying the light; a resistor provided in the laser region for heating the laser region; The resistor has a first portion and a second portion; the second portion is connected to the first portion and is closer to the boundary between the laser region and the amplification region than the first portion; The semiconductor laser element has a resistance per unit length of the second portion higher than a resistance per unit length of the first portion.

2. 2. The semiconductor laser device according to claim 1, wherein the width of the first portion is greater than the width of the second portion.

3. the second portion includes a tapered portion; 3. The semiconductor laser device according to claim 1, wherein the width of the tapered portion decreases from the laser region toward the amplification region.

4. the second portion is provided in the laser region; 3. The semiconductor laser device according to claim 1, wherein an end of the second portion is located at a boundary between the laser region and the amplification region.

5. 3. The semiconductor laser device according to claim 1, wherein the second portion is provided in the laser region and the amplification region.

6. the resistor includes two of the first portions and two of the second portions; one of the two first portions and one of the two second portions are connected; the one of the two second portions is connected to the other of the two second portions; 3. The semiconductor laser device according to claim 1, wherein the other of the two second portions is connected to the other of the two first portions.

7. 3. The semiconductor laser device according to claim 1, wherein the first portion is longer than the second portion in the direction in which the laser region extends.

8. a first semiconductor layer provided in the laser region and the amplification region; a second semiconductor layer provided in the laser region and embedded in the first semiconductor layer; 3. The semiconductor laser device according to claim 1, wherein a portion where the first semiconductor layer and the second semiconductor layer are aligned forms a diffraction grating.

9. an active layer stacked on the first semiconductor layer; a third semiconductor layer stacked on the active layer, the first semiconductor layer has a first conductivity type; the third semiconductor layer has a second conductivity type; the first semiconductor layer and the active layer form a mesa; the mesa extends into the laser region and the amplifier region; the third semiconductor layer is provided on the mesa; 9. The semiconductor laser device according to claim 8, wherein the resistor is provided on the third semiconductor layer, directly above the mesa or at a position spaced apart from the mesa.

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