Semiconductor laser

Abstract

A semiconductor laser (10) according to the present invention comprises: an active region (11) having an active layer (114); non-active regions (12) disposed at both ends of the active region in a light wave-guiding direction; and diffraction gratings (13) disposed in the non-active regions and within ranges that are a predetermined length from both ends of the active region in the light wave-guiding direction.　As a result, the present invention can provide a semiconductor laser capable of suppressing a deterioration in laser characteristics due to spatial hole burning, and also capable of suppressing a decrease in the optical confinement ratio or improving the optical confinement ratio.

Description

semiconductor laser

[0001] The present invention relates to a semiconductor laser having a diffraction grating.

[0002] A diffraction grating is formed in a semiconductor laser to oscillate in a single longitudinal mode, and for example, a DFB laser (e.g., Non-Patent Document 1), a DR laser (e.g., Non-Patent Document 2), or a DBR laser (e.g., Non-Patent Document 3) is used. When these semiconductor lasers are introduced into optical interconnects for short-distance communications, a configuration with a short active layer length (short active layer length laser) is expected to reduce power consumption.

[0003] In a configuration with a short active layer length, loss due to light emission (mirror loss) increases, and to satisfy the oscillation conditions, the reflectivity at both ends must be increased. The reflectivity of a diffraction grating increases as the value of the product of the coupling coefficient and the length increases. Therefore, diffraction gratings with a large coupling coefficient are used in lasers with short active layer lengths (Non-Patent Documents 2 and 3). In DFB lasers and DR lasers in which a diffraction grating is formed on the active layer, if the diffraction grating has a high coupling efficiency, the electric field localizes in a part of the active layer, causing unstable laser oscillation (spatial hole burning). On the other hand, in DBR lasers, no diffraction grating is formed on the active layer, so localization of the electric field does not occur.

[0004] K. Utaka et al., “λ / 4-Shifted InGaAsP / InP DFB Lasers,” IEEE Journal of Quantum Electrons, Vol. QE-22, No. 7, pp. 1042 (1986). E. Kanno et al., “Twin-mirror membrane distributed-reflector lasers using 20-μm-long active region on substrate Sis,” Opt. no. 2, pp. 1268-1277, Jan. 2018.K. Takeda et al., “Continuous-wave Operation of Ultra-short Cavity Distributed Bragg Reflector Lasers on Si Substrates,” Proc. CSW, paper ThD1-2, Toyama, Japan, June 2016.

[0005] However, while DBR lasers can suppress degradation of laser characteristics due to spatial hole burning because localization of the electric field does not occur, there is a problem in that light confinement in the active region is lower than in DFB lasers and DR lasers.

[0006] In order to solve the above-mentioned problems, the semiconductor laser according to the present invention comprises an active region having an active layer, non-active regions disposed at both ends of the active region in the light guide direction, and diffraction gratings disposed in the non-active region and within a range of a predetermined length from both ends of the active region in the light guide direction.

[0007] According to the present invention, it is possible to provide a semiconductor laser that can suppress the deterioration of laser characteristics due to spatial hole burning, suppress the decrease in optical confinement ratio, or improve the optical confinement ratio.

[0008] FIG. 1 is a schematic top view showing the configuration of a semiconductor laser according to a first embodiment of the present invention. FIG. 2A is a schematic side cross-sectional view taken along line IIA-IIA' showing the configuration of a semiconductor laser according to the first embodiment of the present invention. FIG. 2B is a schematic cross-sectional view taken along line IIB-IIB' showing the configuration of a semiconductor laser according to the first embodiment of the present invention. FIG. 2C is a schematic cross-sectional view taken along line IIA-IIC' showing the configuration of a semiconductor laser according to the first embodiment of the present invention. FIG. 3A is a diagram for explaining the effects of the semiconductor laser according to the first embodiment of the present invention. FIG. 3B is a diagram for explaining the effects of the semiconductor laser according to the first embodiment of the present invention.

[0009] First Embodiment A semiconductor laser according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 3B.

[0010] <Configuration of Semiconductor Laser> As shown in FIGS. 1 and 2A, a semiconductor laser 10 according to this embodiment includes an active region 11 and a non-active region 12.

[0011] The active region 11 includes an active layer 114 .

[0012] The non-active regions 12 are arranged on both sides of the active region 11 in the light guide direction.

[0013] A diffraction grating 13 is formed in the non-active region 12 and in regions extending a predetermined distance from both ends of the active region 11 in the light guide direction.

[0014] In detail, the active region 11 is formed by, in order, a substrate (e.g., Si) 111 and a dielectric layer (e.g., SiO ２ The semiconductor device includes a p-type semiconductor 116 on one side of the layer structure consisting of the i-type semiconductor layer 113, the active layer 114, and the i-type semiconductor layer 115, and an n-type semiconductor 117 on the other side. Here, the "side of the active layer" refers to the end face of the active layer 114 that is parallel to the direction of light propagation and perpendicular to the surface of the substrate. A p-type electrode 118 and an n-type electrode 119 are provided on the surfaces of the p-type semiconductor 116 and the n-type semiconductor 117, respectively.

[0015] This causes a current to be injected laterally into the active layer 114. Here, the "lateral direction" refers to a direction parallel to the substrate surface and perpendicular to the waveguide direction of light.

[0016] In the light guide direction, a diffraction grating 13 is formed on the surface of the i-type semiconductor layer 115 in regions up to a predetermined distance from both ends of the active region 11. Diffraction gratings 13 may also be formed on the surfaces of the p-type semiconductor 116 and the n-type semiconductor 117.

[0017] As an example of the layer structure, the active layer 114 is an InGaAsP-based multiple quantum well structure for the 1.55 μm wavelength band, with six quantum well layers. The active layer 114 is 150 nm thick. Each i-layer is made of undoped InP and 50 nm thick.

[0018] The p-type semiconductor 116 is, for example, Zn-doped (1×10 １８ cm －３ ) p-type InP. A p-type contact layer (e.g., InGaAs) may be provided between the p-type semiconductor 116 and the p-type electrode 118. The n-type semiconductor 117 is, for example, Si-doped (2×10 １８ cm －３ An n-type contact layer (e.g., InGaAs) may be provided between the n-type semiconductor 117 and the n-type electrode 119.

[0019] As shown in FIG. 2C, the non-active region 12 is formed by a substrate (e.g., Si) 111 and a dielectric layer (e.g., SiO ２ The diffraction grating 13 is formed on the surface of the i-type semiconductor layer 123.

[0020] In this way, in the semiconductor laser 10, the diffraction grating 13 is arranged in the non-active region 12 and within a range of a predetermined length from both ends of the active region 11 in the light guide direction.

[0021] <Effects> The effects of the semiconductor laser 10 according to this embodiment will be described with reference to FIGS. 3A and 3B.

[0022] In the semiconductor laser 10, the optical confinement ratio in the active region 11 was calculated relative to the length x (optical waveguide direction) where no diffraction grating is formed in the active region 11.

[0023] 3A shows the structure used in the calculation. A diffraction grating 13 is formed in the active region 11 at a predetermined distance from both ends thereof in the light guide direction, and in the inactive region 12. The length L of the active region 11 is ａ is 20 μm, and the length L of the inactive region 12 ｇ was set to 50 μm. In this case, no diffraction grating was formed within a range of x μm at the center of the active region 11 in the light guide direction. When x = 0 μm, it corresponds to a DR laser, and when x = 0 μm, it corresponds to a DBR laser. The equivalent refractive index of the region where the diffraction grating 13 is formed is set to 2.72, and the equivalent refractive index of the region where the diffraction grating is not formed is set to 2.66, and the coupling coefficient of the diffraction grating 13 is set to 1167 cm －１ The Bragg wavelength was set to 1550 nm.

[0024] The calculation results are shown in Figure 3B. The optical confinement ratio in the active region 11 is lower when x = 20 μm (corresponding to a DBR laser) than when x = 0 μm (corresponding to a DR laser), but when x = 18 μm, it is improved by 5% compared to when x = 20 μm (corresponding to a DBR laser). This shows that the optical confinement ratio can be improved by forming the diffraction grating 13 in regions 1 μm from both ends of the active region 11. In this way, the optical confinement ratio can be improved by forming the diffraction grating 13 in regions 5% of the length of the active region 11 from both ends of the active region 11.

[0025] Furthermore, when x is 2 μm to 14 μm, the value is higher than the value when x = 0 μm (corresponding to a DR laser). Therefore, by forming the diffraction grating 13 in regions 3 μm to 9 μm from both ends of the active region 11, the optical confinement ratio can be further improved. In this way, by forming the diffraction grating 13 in regions 15% to 45% of the length of the active region 11 from both ends of the active region 11, an optical confinement ratio equivalent to that of a DR laser can be obtained.

[0026] In this way, in the semiconductor laser 10, by forming the diffraction grating 13 in the region up to a predetermined distance from both ends of the active region as well as the inactive region 12, it is possible to obtain a high optical confinement ratio while avoiding localization of the electric field.

[0027] The semiconductor laser according to this embodiment can suppress the deterioration of laser characteristics due to spatial hole burning caused by localized electric fields, and can also suppress the decrease in optical confinement ratio, or can improve the optical confinement ratio.

[0028] In this embodiment, an example in which the length of the active region is 20 μm and the length of the inactive region is 50 μm has been shown, but this is not limiting. Even in a configuration in which the length of the active region is 20 μm and the length of the inactive region is 30 μm to 80 μm, the decrease in the optical confinement ratio can be suppressed or the optical confinement ratio can be improved. In other words, the same effect can be obtained when the length of the inactive region is about 1.5 to 4 times the length of the active region.

[0029] In this embodiment, the dielectric layer 112 is formed on the surface of the semiconductor layer (i-type semiconductor layer 115, i-type semiconductor layer 123), but the present invention is not limited thereto. For example, the dielectric layer 112 may be formed on the interface between the semiconductor layer (i-type semiconductor layer 113, i-type semiconductor layer 123).

[0030] In this embodiment, an example in which the diffraction grating is formed on a semiconductor layer has been described, but the present invention is not limited to this. ２ A diffraction grating made of SiN may be disposed on the surface of the semiconductor layer (i-type semiconductor layer 115, i-type semiconductor layer 123).

[0031] In this embodiment, an example has been shown in which a lateral current injection type laser is used as the semiconductor laser, but the present invention is not limited to this, and a laser in which current is injected in a direction perpendicular to the substrate surface may also be used.

[0032] In this embodiment, an example has been shown in which a lateral current injection type laser is used as the semiconductor laser, but the present invention is not limited to this, and a laser in which current is injected in a direction perpendicular to the substrate surface may also be used.

[0033] In this embodiment, an example has been shown in which an InGaAsP-based multiple quantum well structure for the 1.55 μm wavelength band is used for the active layer, but this is not limiting. Materials corresponding to other wavelength bands, such as the 1.3 μm wavelength band, may also be used. Furthermore, GaAs-based materials or GaN-based materials other than InP may also be used to correspond to other wavelengths.

[0034] In the embodiments of the present invention, examples of the structure, dimensions, materials, etc. of each component in the configuration and manufacturing method of the semiconductor laser are shown, but the present invention is not limited to these examples. Anything that can exhibit the functions and effects of the semiconductor laser can be used.

[0035] It should be noted that the present invention is not limited to the above-described embodiments, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention.

[0036] A part or all of the above-described embodiment or an example thereof can be described as, but is not limited to, the following supplementary notes.

[0037] (Supplementary Note 1) A semiconductor laser comprising: an active region having an active layer; inactive regions disposed at both ends of the active region in a light guiding direction; and a diffraction grating disposed in the inactive region and within a range of a predetermined length from both ends of the active region in the light guiding direction.

[0038] (Supplementary Note 2) The semiconductor laser according to Supplementary Note 1, wherein the predetermined length is 5% to 45% of the length of the active region in the waveguide direction of the light.

[0039] (Supplementary Note 3) The semiconductor laser according to Supplementary Note 1 or Supplementary Note 2, wherein the length of the inactive region is 1.5 to 4 times the length of the active region in the light guide direction.

[0040] (Supplementary Note 4) A semiconductor laser according to any one of Supplementary Notes 1 to 3, wherein the active region comprises a waveguide structure including, on a substrate, a first semiconductor layer, the active layer, and a second semiconductor layer, in that order; a p-type semiconductor layer disposed in contact with one of the surfaces of the active layer that is parallel to the waveguiding direction of the light and perpendicular to the substrate; and an n-type semiconductor layer disposed in contact with the other side surface of the active layer opposite to the one surface.

[0041] The present invention can be applied to optical semiconductor lasers in optical communication systems, particularly in optical interconnects for short-distance communication.

[0042] 10 Semiconductor laser 11 Active region 114 Active layer 12 Non-active region 13 Diffraction grating

Claims

1. A semiconductor laser comprising: an active region having an active layer; inactive regions disposed at both ends of the active region in the light guide direction; and a diffraction grating disposed in the inactive region and within a range of a predetermined length from both ends of the active region in the light guide direction.

2. The semiconductor laser according to claim 1, wherein the predetermined length is 5% to 45% of the length of the active region in the light guide direction.

3. A semiconductor laser according to claim 2, wherein the length of said inactive region in the light guide direction is 1.5 to 4 times the length of said active region.

4. A semiconductor laser according to claim 1 or claim 2, wherein the active region comprises: a waveguide structure comprising, in order on a substrate, a first semiconductor layer, the active layer, and a second semiconductor layer; a p-type semiconductor layer arranged in contact with one of the surfaces of the active layer that is parallel to the waveguiding direction of the light and perpendicular to the substrate; and an n-type semiconductor layer arranged in contact with the other side of the active layer opposite to the one surface.

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