Semiconductor laser, method for designing diffraction grating layer of semiconductor laser, and method for manufacturing semiconductor laser

Abstract

The semiconductor laser (10) of the present invention is a distributed feedback semiconductor laser in which a diffraction grating layer (106) is arranged in a waveguide structure having an active layer (104), and the diffraction grating layer has a uniform diffraction grating (1061) and a plurality of phase shift portions (1062) that shift the phase of light guided through the waveguide structure, and the length of the phase shift portion is a value obtained by dividing the period by a predetermined integer of 2 or more, and the integer is set so that the difference between the threshold gain of the fundamental mode and the threshold gain of the first mode among the oscillation modes of the distributed feedback semiconductor laser is maximized. As a result, the present invention can provide a semiconductor laser that can stably operate in a single mode with a simple configuration.

Description

[Technical Field]

[0001] The present invention relates to a semiconductor laser that operates in a single mode, a method for designing a diffraction grating layer of the semiconductor laser, and a method for manufacturing the semiconductor laser. [Background technology]

[0002] In recent years, communication traffic has been increasing rapidly in data center networks and high-performance computing systems. Photonic integrated circuits (PICs) used in short-distance links of 2 km or less in these networks and systems are expected to operate with low power consumption.

[0003] The semiconductor laser used in this circuit (PIC) must have low power consumption, sufficient optical output to couple with optical fibers or optical waveguides, and oscillate in only a single longitudinal mode.

[0004] To meet these requirements, a distributed feedback laser diode (DFB-LD) is used. A typical InP-based DFB-LD has a phase shift section at the center of a uniform diffraction grating. Here, the shift amount in the phase shift section is π / 2, which corresponds to λ / 4 in the length of the diffraction grating. Therefore, this DFB laser is called a λ / 4-shifted DFB-LD. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-107958 [Non-patent literature]

[0006] [Non-Patent Document 1] T. Aihara, et al., “Membrane III-V / Si DFB Laser Using Uniform Grating and Width-Modulated Si Waveguide,” J. Lightw. Technol., vol. 38, no. 11, pp. 2961-2967, June 2020. Summary of the Invention [Problem to be solved by the invention]

[0007] However, spatial hole burning (SHB) is a problem with λ / 4-shifted DFB-LDs. In SHB, the light intensity distribution in the laser cavity causes a carrier distribution, resulting in a decrease in carrier density in the center of the active layer. This causes the refractive index in the center of the active layer to be higher than that near both ends. In other words, the effective Bragg wavelength in the center of the active layer is longer than that near both ends. As a result, the non-uniformity of the reflected wavelength and the decrease in reflectivity cause the laser oscillation mode to become unstable.

[0008] Furthermore, when a high optical confinement structure is adopted in a λ / 4 shifted DFB-LD to reduce power consumption, the influence of SHB increases.

[0009] For example, when a membrane structure (Non-Patent Document 1) with a thin film (350 nm or less) of III-V semiconductor material on an SiO2 / Si substrate is applied to a λ / 4 shifted DFB-LD, although it has a very high optical confinement coefficient, the influence of the SHB effect is large, making single-mode operation difficult.

[0010] In order to achieve stable single-mode operation of a λ / 4-shifted DFB-LD, a configuration for modulating the effective refractive index or the distribution of the diffraction grating has been disclosed (Patent Document 1). However, realizing this configuration requires a complex fabrication process and high costs. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, the semiconductor laser according to the present invention is a distributed feedback semiconductor laser in which a diffraction grating layer is disposed in a waveguide structure having an active layer, the diffraction grating layer having a uniform diffraction grating and a plurality of phase shift portions that shift the phase of light guided through the waveguide structure, and the lengths of the phase shift portions are Uniform diffraction grating The period is a value obtained by dividing the period by a predetermined integer of 2 or more, and the integer is set so that the difference between the threshold gain of the fundamental mode and the threshold gain of the first mode among the oscillation modes of the distributed feedback semiconductor laser becomes maximum.

[0012] Further, a method for designing a diffraction grating layer of a semiconductor laser according to the present invention is a method for designing a diffraction grating layer of a distributed feedback semiconductor laser, the method comprising the steps of: providing a diffraction grating layer in a waveguide structure having an active layer; and the diffraction grating layer having a uniform diffraction grating and a plurality of phase shift portions for shifting the phase of light guided through the waveguide structure, the method comprising the steps of: Uniform diffraction grating a step of setting a period and a predetermined integer, a step of calculating the length of the phase shift portion by dividing the period by the predetermined integer, a step of calculating a difference between a maximum value and a minimum value of a light intensity distribution in an element length direction based on the period and the length of the phase shift portion, and a step of calculating a value of the difference between the maximum value and the minimum value that is greater than a value of the difference between the maximum value and the minimum value of a distributed feedback semiconductor laser having one of the phase shift portions. Small and determining the period and the length of the phase shift portion so that [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a semiconductor laser that can operate stably in a single mode with a simple configuration, a method for designing a diffraction grating layer of a semiconductor laser, and a method for manufacturing a semiconductor laser. [Brief explanation of the drawings]

[0014] [Figure 1A] FIG. 1A is a schematic top view of a semiconductor laser according to a first embodiment of the present invention. [Figure 1B]FIG. 1B is a schematic cross-sectional view taken along line IB-IB' of the semiconductor laser according to the first embodiment of the present invention. [Figure 1C] FIG. 1C is a schematic cross-sectional view taken along line IC-IC' of the semiconductor laser according to the first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of a diffraction grating layer of a semiconductor laser according to the first embodiment of the present invention. [Figure 3] FIG. 3 is a diagram for explaining the operation of the semiconductor laser according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a diagram for explaining the operation of the semiconductor laser according to the first embodiment of the present invention. [Figure 5] FIG. 5 is a diagram for explaining the operation of the semiconductor laser according to the first embodiment of the present invention. [Figure 6A] FIG. 6A is a diagram for explaining the effect of the semiconductor laser according to the first embodiment of the present invention. [Figure 6B] FIG. 6B is a diagram for explaining the effect of the semiconductor laser according to the first embodiment of the present invention. [Figure 7A] FIG. 7A is a diagram for explaining the effect of the semiconductor laser according to the first embodiment of the present invention. [Figure 7B] FIG. 7B is a diagram for explaining the effect of the semiconductor laser according to the first embodiment of the present invention. [Figure 8] FIG. 8 is a diagram for explaining a method of designing the diffraction grating layer of the semiconductor laser according to the first embodiment of the present invention. [Figure 9A] FIG. 9A is a schematic top view of a semiconductor laser according to a second embodiment of the present invention. [Figure 9B] FIG. 9B is a schematic cross-sectional view taken along line IXB-IXB' of the semiconductor laser according to the second embodiment of the present invention. [Figure 9C] FIG. 9C is a schematic cross-sectional view taken along line IXC-IXC' of the semiconductor laser according to the second embodiment of the present invention. [Figure 10A] FIG. 10A is a schematic top view of an example of a semiconductor laser according to the second embodiment of the present invention. [Figure 10B] FIG. 10B is a schematic cross-sectional view taken along the line XB-XB' of an example of a semiconductor laser according to the second embodiment of the present invention. [Figure 10C] FIG. 10C is a schematic cross-sectional view taken along the line XC-XC' of an example of a semiconductor laser according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] First Embodiment A semiconductor laser according to a first embodiment of the present invention will be described with reference to FIGS. 1A to 8. FIG.

[0016] <Configuration of semiconductor laser> 1A to 1C, a semiconductor laser (hereinafter also referred to as "DFB-LD") 10 according to this embodiment includes an active layer 104 covered with InP on a Si substrate 101 / lower cladding (SiO2) 102, and has a membrane structure in which current is injected laterally (x direction in the figure) by a p-type InP layer 108 and an n-type InP layer 111 arranged to sandwich the active layer 104 in the horizontal direction (x direction in the figure). Here, a multi-quantum well (MQW) is used for the active layer 104.

[0017] In detail, semiconductor laser 10 includes, in order, Si substrate 101, lower cladding layer 102, InP lower layer 103, MQW 104 as an active layer, InP upper layer 105, diffraction grating layer 106, and upper cladding layer 107. Also, p-type InP layer 108 and n-type InP layer 111 are provided on either side of MQW 104 in the horizontal direction. P-type contact layer 109 / p-type electrode 110 and n-type contact layer 112 / n-type electrode 113 are provided on p-type InP layer 108 and n-type InP layer 111, respectively.

[0018] In this way, a waveguide structure is formed by the InP lower layer 103, the active layer (MQW) 104, and the InP upper layer 105, and the diffraction grating layer 106 is disposed (formed) on this waveguide structure. Here, the diffraction grating layer 106 may be disposed on either the lower surface or the upper surface of this waveguide structure.

[0019] The MQW 104 is an InGaAlAs-based MQW with a 1.3 μm wavelength composition corresponding to the O band, and the MQW 104 has a total layer thickness of 150 μm and a width of 600 μm.

[0020] The thickness of the InP lower layer 103 and the thickness of the InP upper layer 105 are each 40 μm, and the thickness of the p-type InP layer 108 and the n-type InP layer 111 are each 230 μm.

[0021] The upper clad layer 107 and the lower clad layer 102 are made of SiO2. X Alternatively, a material with a low refractive index such as BCB may be used.

[0022] The confinement factor Γ in the MQW104 in this configuration QW is around 23%.

[0023] The diffraction grating layer 106 is made of SiN and SiO2 in the element length direction (z direction in the drawing).

[0024] The diffraction grating layer 106 is configured by dividing a uniform diffraction grating 1061, i.e., a diffraction grating with a constant period and depth (hereinafter referred to as a "uniform diffraction grating"), into four regions by three phase shift portions 1062. The phase shift portions 1062 shift the phase of light guided through the waveguide structure, enabling single-mode oscillation of the semiconductor laser 10. Here, single-mode oscillation refers to oscillation with a high side mode suppression ratio (SMSR), for example, oscillation with an SMSR of 20 dB or more.

[0025] The diffraction grating layer 106 is formed by laminating SiO2 after selectively etching SiN on the InP upper layer 105. Here, the phase shift portion 1062 may be made of either SiN or SiO2.

[0026] FIG. 2 is a schematic diagram showing the detailed configuration of the diffraction grating layer 106.

[0027] In the uniform diffraction grating 1061, the length L1 of the two outer regions is equal, and the length L2 of the two inner regions is equal. gr =2(L1+L2).

[0028] The pitch (period) Λ of the uniform diffraction grating 1061 is λ B / 2 / n eff where λ B is the Bragg wavelength, which is 1.26 to 1.360 μm, which corresponds to the O-band wavelength range. eff is the average effective refractive index, which is about 2.91 to 2.93 in the O band in the configuration of the DFB-LD 10. Therefore, in this embodiment, the pitch is about 220 nm.

[0029] The length L of each phase shift section 1062 φ are equal, and L φ =Λ / K, where K is an integer constant greater than or equal to 2 (see below).

[0030] In addition, in order to obtain a sufficiently high output from the DFB-LD 10, the total length L gr is 500 μm. Therefore, the length L of the entire element is L gr +3L φ is.

[0031] Figure 3 shows the difference in threshold gain (Δg th ) is calculated as follows: where K is an integer.

[0032] The calculation is based on the transfer matrix theory model, λ B = 1.28 μm, n eff =2.93, κ=38cm -1 , Λ = 220 nm. L1 and L2 are gr was changed to 500 μm.

[0033] When L2=L1, the threshold gain difference is at its maximum (about 20 / cm) at about K=2. When L2=L1 / 2, the threshold gain difference is at its maximum (about 30 / cm) at about K=5. When L2=L1 / 3 to L1 / 4, the threshold gain difference is at its maximum (about 35 / cm) at about K=6.

[0034] In this way, the configuration of L1 and L2 changes the phase coefficient K at which the threshold gain difference is maximized, i.e., the optimal value of the phase coefficient K, and the maximum value of the threshold gain difference also changes. For example, from the above results, when L2=L1 / 3 to L1 / 4, the optimal value of the phase coefficient K is 6, and the threshold gain difference is maximized. Therefore, it is desirable that L2=L1 / 3 or less.

[0035] From the above, in the DFB-LD10, L2 = L1 / 3. gr = 500 μm, L1 = 187.5 μm and L2 = 62.5 μm.

[0036] FIG. 4 shows the calculation results of the dependence of the coupling coefficient κ of the uniform diffraction grating 1061 on the SiN layer thickness.

[0037] In the calculation, the difference in effective refractive index between SiN and SiO2 in the diffraction grating was calculated using the simulation software "FIMMWAVE" (Photon Design), and the coupling coefficient κ was derived.

[0038] For single mode operation, it is usually necessary to satisfy the condition κL<2. In this embodiment, L is about 500 μm, so κ<40 cm -1 From Figure 4, κ<40cm -1 The thickness of the SiN layer that satisfies the above requirement is preferably about 12 nm or less. In this embodiment, in consideration of increasing the laser output, the thickness of the SiN layer, ie, the depth of the diffraction grating layer 106, is set to 10 nm.

[0039] In the semiconductor laser 10 according to this embodiment, the length L of the three phase shift portions 1062 is φ The phase coefficient K that determines the phase coefficient K will be described with reference to FIG.

[0040] In order to operate the DFB-LD10 in a single mode with high SMSR, the threshold gain difference (Δg th ) must be the largest.

[0041] Figure 5 shows the calculation results of the phase coefficient dependence of the threshold gain of each of the main mode (solid line in the figure) and the first side mode (dashed line in the figure), where the phase coefficient K is an integer.

[0042] The calculation is based on the transfer matrix theory model, similar to the calculation above (Figure 3), and λ B = 1.28 μm, n eff =2.93, κ=38cm -1 , Λ=220 nm. Also, L1=187.5 μm, L2=62.5 μm.

[0043] The threshold gain of the main mode decreases as the phase factor K increases from 2 to 4, and increases slightly when the phase factor K is 4 or more. On the other hand, the threshold gain of the first side mode increases as the phase factor K increases from 2 to 6, and decreases when the phase factor K is 6 or more. Here, the threshold gain difference between the main mode and the first side mode (Δg th ) reaches a maximum of about 35 / cm when the phase coefficient K is 6.

[0044] Therefore, since K=6, the length of the three phase shift parts 1062 is L φ =Λ / 6=λ B / 12 / n eff Therefore, in this embodiment, the DFB-LD 10 is called a "λ / 12 shift" DFB-LD. φ =37nm.

[0045] <Effects> In this embodiment, the effect of the λ / 12 shifted DFB-LD 10 with the phase coefficient K=6 based on the above results will be described with reference to FIGS. 6A to 7B.

[0046] 6A shows the simulation results of the spectrum of the λ / 12 shifted DFB-LD 10. For comparison, FIG. 6B shows the simulation results of the spectrum of a conventional semiconductor laser (λ / 4 shifted DFB-LD).

[0047] The spectrum of the DFB-LD was calculated based on the transmittance of the DFB-LD based on the transfer matrix method, where λ B = 1.28 μm, n eff =2.93, κ=38cm -1 , Λ=220 nm. In the λ / 12 shifted DFB-LD 10, L1=187.5 μm and L2=62.5 μm.

[0048] In addition, in this calculation, the structure of the diffraction grating of the DFB-LD is symmetrical in the element length direction (z direction in the figure), so the same spectrum is output from both output end faces.

[0049] As shown in Figure 6A, the λ / 12-shifted DFB-LD 10 achieves a single-mode oscillation spectrum with an SMSR of 20 dB or more, which is similar to the spectrum of the λ / 4-shifted DFB-LD shown in Figure 6B.

[0050] Further, detailed effects of the semiconductor laser 10 according to this embodiment will be described with reference to FIGS. 7A and 7B.

[0051] 7A shows the calculation results of the optical intensity distribution in the element length direction (z direction in the figure) of the λ / 12-shifted DFB-LD 10. For comparison, FIG. 7B shows the calculation results of the optical intensity distribution in the element length direction (z direction in the figure) of a conventional λ / 4-shifted DFB-LD.

[0052] The calculation was performed based on the transfer matrix method for a λ / 12 shifted DFB-LD 10 having the same configuration as above.

[0053] The SHB effect, which affects the mode uniformity of DFB-LDs, strongly depends on the optical intensity distribution. That is, the SHB effect decreases when the optical intensity distribution is constant, whereas it increases as the optical intensity distribution changes.

[0054] Here, to quantify the uniformity of the light intensity distribution, the difference (ΔI) between the maximum and minimum values ​​of the standardized light intensity distribution is used.

[0055] In the λ / 4-shifted DFB-LD, as shown in Figure 7B, the optical intensity is approximately 0.4 at both ends (z = 0, 500 μm), increases up to the center (z = 250 μm) where the phase shifter is located, and reaches a maximum value (1.0) at the center. At this time, ΔI is approximately 0.62.

[0056] As shown in FIG. 7A, in the λ / 12-shifted DFB-LD 10, the optical intensity is approximately 0.55 at both ends (z=0, 500 μm), increases up to the center (z=250 μm) where the phase shift section 1062 is located, and reaches a maximum value (1.0). The change in optical intensity also reaches a peak at the portion where the phase shift section 1062 is located (z=187.5 μm, 312.5 μm). At this time, ΔI is approximately 0.5. This value is 21% lower than that of the λ / 4-shifted DFB-LD.

[0057] As described above, the λ / 12-shifted DFB-LD 10 has a smaller optical intensity difference (ΔI) in the cavity than the λ / 4-shifted DFB-LD, and therefore can reduce the effects of SHB. Therefore, the λ / 12-shifted DFB-LD 10 has excellent stability of the single mode of the spectrum. Here, the smaller the optical intensity difference (ΔI), the more the effects of SHB can be reduced.

[0058] <Design method of diffraction grating for semiconductor laser> An example of a method for designing the diffraction grating layer 106 of the semiconductor laser 10 according to this embodiment will be described with reference to Fig. 8. Fig. 8 shows a flowchart for explaining an example of a method for designing the diffraction grating layer 106 of the semiconductor laser 10.

[0059] First, the period of the uniform diffraction grating of the semiconductor laser 10 and a predetermined integer equal to or greater than 2 as the phase coefficient K are set (step S1).

[0060] Next, the period of the uniform diffraction grating is divided by a coefficient K to calculate the length of the phase shift portion (step S2).

[0061] Next, as described above (Figures 7A and 7B), the difference (ΔI) between the maximum and minimum values ​​of the light intensity distribution in the waveguide (element length) direction is calculated based on the period of the uniform diffraction grating and the length of the phase shift section (step S3).

[0062] Next, the calculated value of ΔI is compared with a predetermined value (step S4). Here, the predetermined value is the value of ΔI of a distributed feedback semiconductor laser having one phase shift unit (for example, ΔI=0.62 in FIG. 7B).

[0063] Finally, the period of the uniform diffraction grating and the length of the phase shift portion when the calculated value of ΔI is less than a predetermined value are determined as the period of the uniform diffraction grating 1061 and the length of the phase shift portion 1062 of the semiconductor laser 10 (step S5).

[0064] If the calculated value of ΔI is equal to or greater than a predetermined value, the period of the uniform diffraction grating of the semiconductor laser 10 and the value of the coefficient K are changed, and the same steps are repeated (steps S1 to S4).

[0065] Here, the predetermined value may be a value that has the effect of reducing SHB (for example, ΔI=0.5 in FIG. 7A). In this case, the period of the uniform diffraction grating and the length of the phase shift portion when the calculated value of ΔI is equal to or less than the predetermined value may be determined as the period of the uniform diffraction grating 1061 and the length of the phase shift portion 1062 of the semiconductor laser 10. Alternatively, the period of the uniform diffraction grating and the length of the phase shift portion may be determined so that the value of ΔI becomes the minimum value.

[0066] <Method of manufacturing semiconductor laser> After the diffraction grating is designed as described above, the designed diffraction grating layer 106 is formed using a known distributed feedback semiconductor laser fabrication process, thereby manufacturing the semiconductor laser 10.

[0067] <Second embodiment> Next, a semiconductor laser according to a second embodiment of the present invention will be described with reference to FIGS. 9A to 10C.

[0068] <Configuration of semiconductor laser> 9A to 9C, the semiconductor laser 20 according to this embodiment includes a Si waveguide 214 in the lower cladding 202. The other configurations are the same as those of the first embodiment.

[0069] The Si waveguide 214 is arranged to couple the laser light of the DFB-LD with other Si-based elements (e.g., Si photonic devices) in the PIC. The Si waveguide 214 is arranged below the MQW 204, i.e., below the InP lower layer 203, and the distance between the Si waveguide 214 and the InP lower layer 203 is 100 nm.

[0070] The width of the Si waveguide 214 is 800 nm or more, and the layer thickness is 150 to 220 nm. For example, when the width of the Si waveguide 214 is 3 μm or more and the layer thickness is 150 nm, the confinement factor Γ in the MQW 204 is QW This value is about 19%. QW In this way, even with a configuration that has a Si waveguide, the DFB-LD can obtain high output power.

[0071] In the semiconductor laser according to this embodiment, the DFB-LD operates stably in a single mode, similar to the first embodiment.

[0072] According to this embodiment, the DFB-LD and other Si-based elements in the PIC can be optically coupled and integrated well.

[0073] In the semiconductor laser according to the present embodiment, an example in which the Si waveguide 214 is provided in the lower cladding 202 has been described, but the present invention is not limited to this. As shown in Figures 10A to 10C, the Si waveguide 314 may be provided in the upper cladding 307. Furthermore, the Si waveguide may be provided in both the lower cladding and the upper cladding.

[0074] In the embodiment of the present invention, a DFB-LD with a membrane structure in which current is injected in the horizontal direction (x direction) is shown as an example, but a DFB-LD in which current is injected in the normal vertical direction (y direction) may also be used. Here, the membrane structure has greater optical confinement than the normal structure, so the effect of the present invention is greater.

[0075] Although the embodiment of the present invention has been described as an example in which three phase shift sections are provided, the present invention is not limited to this, and a plurality of phase shift sections may be provided.

[0076] In the embodiment of the present invention, an example in which the lengths of the plurality of phase shift parts are equal has been shown, but this is not limiting, and the lengths of the plurality of phase shift parts may be different. Here, when the lengths of the plurality of phase shift parts are equal, simulations for designing an optimal structure can be simplified.

[0077] In the embodiments of the present invention, an example has been shown in which the diffraction grating structure of the DFB-LD is symmetrical in the element length direction. For example, in the diffraction grating, the length L1 of the two outer regions is equal and the length L2 of the two inner regions is equal. However, the present invention is not limited to this, and the diffraction grating structure of the DFB-LD may be asymmetrical in the element length direction. For example, the diffraction grating may have a configuration in which the length L1 of the two outer regions is different and the length L2 of the two inner regions is different. Here, a diffraction grating structure that is symmetrical in the element length direction can simplify simulations for designing an optimal structure.

[0078] In the embodiment of the present invention, a DFB-LD in the O-band wavelength band is shown as an example, but other wavelength bands are also possible. Also, although an example using an InGaAlAs-based MQW is shown, an MQW based on other materials such as InGaAsP may also be used.

[0079] 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. Anything that can exhibit the functions and effects of the semiconductor laser can be used. [Industrial Applicability]

[0080] The present invention can be applied to communication network systems and computing systems. [Explanation of symbols]

[0081] 10 Semiconductor laser 104 Active layer (MQW) 106 Diffraction Grating Layer 1061 Uniform Diffraction Grating 1062 Phase shift section

Claims

1. A distributed feedback semiconductor laser in which a diffraction grating layer is disposed in a waveguide structure having an active layer, the diffraction grating layer has a uniform diffraction grating and a plurality of phase shift portions that shift the phase of light guided through the waveguide structure; a length of the phase shift portion is a value obtained by dividing a period of the uniform diffraction grating by a predetermined integer of 2 or more, The integer is set so that the difference between the threshold gain of the fundamental mode and the threshold gain of the first mode among the oscillation modes of the distributed feedback semiconductor laser is maximized. A semiconductor laser characterized by:

2. The difference between the maximum and minimum values ​​of the light intensity distribution in the element length direction is smaller than the difference between the maximum and minimum values ​​of a distributed feedback semiconductor laser having one of the phase shift portions.

2. The semiconductor laser according to claim 1.

3. The predetermined integer is 6 3. The semiconductor laser according to claim 1 or 2.

4. the uniform diffraction grating is divided into four regions by three of the phase shift portions; The length of each of the two inner regions in the element length direction among the four regions of the uniform diffraction grating is 1 / 3 or less of the length of each of the two outer regions in the element length direction among the four regions.

2. The semiconductor laser according to claim 1.

5. An optical waveguide is provided at least either above or below the active layer.

3. The semiconductor laser according to claim 1 or 2.

6. the waveguide structure comprising, in order, a first semiconductor layer, the active layer, and a second semiconductor layer; a p-type semiconductor layer disposed in contact with one side surface of the active layer; an n-type semiconductor layer disposed in contact with the other side surface of the active layer; Equipped with The grating layer is disposed on either the lower surface or the upper surface of the waveguide structure.

3. The semiconductor laser according to claim 1 or 2.

7. A method for designing a diffraction grating layer of a distributed feedback semiconductor laser, the method comprising the steps of: providing a diffraction grating layer in a waveguide structure having an active layer; the diffraction grating layer having a uniform diffraction grating and a plurality of phase shift portions that shift the phase of light guided through the waveguide structure; setting the period of the uniform diffraction grating to a predetermined integer; calculating the length of the phase shift portion by dividing the period by the predetermined integer; calculating a difference between a maximum value and a minimum value of a light intensity distribution in a length direction of the element based on the period and the length of the phase shift portion; determining the period and the length of the phase shift portion so that the difference between the maximum value and the minimum value is smaller than the difference between the maximum value and the minimum value of a distributed feedback semiconductor laser including one of the phase shift portions; A method for designing a diffraction grating layer of a semiconductor laser comprising:

8. a step of forming a diffraction grating layer designed by the method for designing a diffraction grating layer of a semiconductor laser according to claim 7; 1. A method for manufacturing a semiconductor laser.

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