Semiconductor laser element and laser module

Abstract

To reduce the disturbance in an output light far view field pattern.SOLUTION: A semiconductor laser element 1 comprises a first emitter 31, and a second emitter 51. The first emitter 31 has a thickness which is different from that of the second emitter 51 so that the average value of indexes DB1 and DB2 given by the formulae (1) and (2) becomes 5% or below, where F1(θ) is a far view field pattern only for the first emitter, and F2(θ) is a far view field pattern only for the second emitter; F01(θ) is a far view field pattern of light emitted by the first and second emitter and also a far view field pattern of one of two modes corresponding to basis modes, and F02(θ) a far view field pattern of the other mode.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a semiconductor laser element and a laser module. [Background technology]

[0002] A semiconductor laser element is known in which a plurality of emitters (light emitting portions), each of which includes an active layer, are stacked along a stacking direction (see, for example, Patent Document 1). In such a semiconductor laser element, light from the plurality of emitters can be used as output light, and high output can be achieved. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-90063 Summary of the Invention [Problem to be solved by the invention]

[0004] In the semiconductor laser element described above, interference of light from multiple emitters may cause disturbance in the far-field pattern of the output light in the stacking direction. Such disturbance can cause spatial unevenness in the output light, deviation from the optical design, and the like, and therefore needs to be suppressed.

[0005] An object of the present invention is to provide a semiconductor laser element and a laser module capable of suppressing disturbance in the far-field pattern of output light. [Means for solving the problem]

[0006] A semiconductor laser device of the present invention comprises a first element portion and a second element portion stacked on the first element portion along a stacking direction, the first element portion including a first active layer and a pair of first guide layers sandwiching the first active layer, and has a first emitter that emits light along the optical axis direction, and a pair of first cladding layers sandwiching the pair of first guide layers, the second element portion including a second active layer and a pair of second guide layers sandwiching the second active layer, and has a second emitter that emits light along the optical axis direction, and a pair of second cladding layers sandwiching the pair of second guide layers, and a thickness of the first emitter differs from a thickness of the second emitter such that an average value of an index DB1 expressed by formula (1) and an index DB2 expressed by formula (2) is 5% or less.

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[0007] In this semiconductor laser element, the thickness of the first emitter is different from the thickness of the second emitter such that the average value of the index DB1 and the index DB2 is 5% or less. This makes it possible to suppress interference between the light emitted from the first emitter and the second emitter, and to suppress disturbance in the far-field pattern of the output light.

[0008] The thickness of the first emitter may be different from the thickness of the second emitter such that the average value of the index DB1 and the index DB2 is 3% or less, in which case the interference of the light emitted from the first emitter and the second emitter can be effectively suppressed.

[0009] The thickness of the first emitter may be different from the thickness of the second emitter such that the average value of the index DB1 and the index DB2 is 1% or less. In this case, the interference of the light emitted from the first emitter and the second emitter can be more effectively suppressed.

[0010] The thickness of the first emitter may be different from the thickness of the second emitter by making the total thickness of the pair of first guide layers different from the total thickness of the pair of second guide layers. In this case, the degree of freedom in designing the thicknesses of the first and second active layers can be increased, and for example, the thicknesses of the first and second active layers can be made equal to each other.

[0011] The thickness of the first emitter may be different from the thickness of the second emitter such that the index P expressed by the formula (3) is equal to or greater than 25. In this case, interference between the light emitted from the first emitter and the second emitter can be suppressed.

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[0012] The thickness of the first emitter may be different from the thickness of the second emitter such that the index P is equal to or greater than 40. In this case, interference between the light emitted from the first emitter and the second emitter can be effectively suppressed.

[0013] The thickness of the first emitter may be different from the thickness of the second emitter such that the index P is equal to or greater than 125. In this case, interference between the light emitted from the first emitter and the second emitter can be more effectively suppressed.

[0014] The absolute difference between the thickness of the first emitter and the average thickness of the first and second emitters may be 10% or less of the average thickness, which can prevent a deterioration in the quality of the output light due to an excessive difference in thickness between the first and second emitters.

[0015] The semiconductor laser device of the present invention further includes a third element portion stacked on the second element portion along the stacking direction, the third element portion including a third active layer and a pair of third guide layers sandwiching the third active layer, a third emitter that emits light along the optical axis direction, and a pair of third cladding layers sandwiching the pair of third guide layers, and the thickness of the third emitter may be different from the thickness of the second emitter such that the average value of the index DB3 expressed by formula (4) and the index DB4 expressed by formula (5) is 5% or less. In this case, interference of the light emitted from the second emitter and the third emitter can be suppressed.

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[0016] The semiconductor laser element of the present invention further includes a substrate, and the first emitter and the second emitter are stacked on the substrate such that the first emitter is located on a first side closer to the substrate than the second emitter, and the thickness of the first emitter may be thinner than the thickness of the second emitter. In this case, it is possible to avoid a situation in which the above-mentioned optical interference suppression effect is impaired due to the influence of distortion caused in the first emitter and the second emitter by a force acting from the substrate. The laser module of the present invention includes the semiconductor laser element and a mount member on which the semiconductor laser element is mounted, and the semiconductor laser element is fixed to the mount member on a second side opposite to the first side, and the thermal expansion coefficient of the mount member is smaller than the thermal expansion coefficient of the substrate. In this laser module, it is possible to avoid a situation in which the above-mentioned optical interference suppression effect is impaired due to the influence of distortion caused in the first emitter and the second emitter by a force acting from the substrate and the mount member.

[0017] A laser module of the present invention includes the semiconductor laser element and a mount member on which the semiconductor laser element is mounted, the semiconductor laser element further includes a substrate, the first emitter and the second emitter are stacked on the substrate such that the first emitter is located on a first side closer to the substrate than the second emitter, the semiconductor laser element is fixed to the mount member on a second side opposite to the first side, the mount member has a thermal expansion coefficient larger than that of the substrate, and the first emitter is thicker than the second emitter. This laser module can avoid a situation in which the above-mentioned optical interference suppression effect is impaired due to the influence of distortion caused in the first emitter and the second emitter by forces acting from the substrate and the mount member.

[0018] The semiconductor laser element of the present invention comprises a first element portion and a second element portion stacked on the first element portion along a stacking direction, the first element portion including a first active layer and a pair of first guide layers sandwiching the first active layer, and has a first emitter that emits light along the optical axis direction, and a pair of first cladding layers sandwiching the pair of first guide layers, the second element portion being stacked on the first emitter along the stacking direction, and including a second active layer and a pair of second guide layers sandwiching the second active layer, and has a second emitter that emits light along the optical axis direction, and a pair of second cladding layers sandwiching the pair of second guide layers, and the thickness of the first emitter differs from the thickness of the second emitter such that an index P represented by equation (6) is 25 or greater.

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[0019] In this semiconductor laser element, the thickness of the first emitter is different from the thickness of the second emitter such that the index P is equal to or greater than 25. This makes it possible to suppress interference between the lights emitted from the first emitter and the second emitter, and to suppress disturbance in the far-field pattern of the output light. Effect of the Invention

[0020] According to the present invention, it is possible to provide a semiconductor laser element and a laser module capable of suppressing disturbance in the far-field pattern of output light. [Brief description of the drawings]

[0021] [Figure 1] 1 is a cross-sectional view of a semiconductor laser element according to an embodiment. [Diagram 2] 1A is a graph showing a far-field pattern of output light from a semiconductor laser device according to a comparative example, and FIG. 1B is a graph showing a far-field pattern of output light from a semiconductor laser device according to an embodiment. [Diagram 3] 6(a) and 6(b) are graphs showing examples of calculations of changes in the far-field pattern with respect to the index DBa. [Figure 4] 13 is a graph showing the relationship between an index P and an index DBa. [Diagram 5] FIG. 1 is a cross-sectional view of a simplified semiconductor laser device. [Figure 6] FIG. 11 is a cross-sectional view of a semiconductor laser element according to a modified example. [Figure 7] FIG. 2 is a diagram showing a mounting state of a semiconductor laser element. [Figure 8] 11A and 11B are diagrams illustrating another example of a mounting state of a semiconductor laser element. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following description, the same or corresponding elements are designated by the same reference numerals, and duplicated description will be omitted.

[0023] 1, the semiconductor laser device 1 includes a substrate 2, a first element portion 3, a first tunnel junction layer 4, a second element portion 5, a second tunnel junction layer 6, a third element portion 7, and a cap layer 8. The first element portion 3, the first tunnel junction layer 4, the second element portion 5, the second tunnel junction layer 6, the third element portion 7, and the cap layer 8 are stacked in this order on the substrate 2 along a stacking direction D2 (thickness direction of the substrate 2). Each of these layers can be formed on the substrate 2 by epitaxial growth.

[0024] The semiconductor laser element 1 is an end-emission type laser diode that emits output light L0 from one end face in an optical axis direction D1 (length direction of the substrate 2) perpendicular to the stacking direction D2 along the optical axis direction D1. The semiconductor laser element 1 is configured as a multi-junction type (stack type) in which a plurality of emitters (a first emitter 31, a second emitter 51, and a third emitter 71), each including an active layer, are stacked via tunnel junctions (a first tunnel junction layer 4 and a second tunnel junction layer 6). The semiconductor laser element 1 can be used for flash LiDAR (Light Detection and Ranging) and the like that require a relatively high pulse output.

[0025] The substrate 2 is a semiconductor substrate made of n-type GaAs. The first element portion 3 has a first emitter 31 and a pair of first cladding layers 35, 36. The first emitter 31 includes a first active layer 32 and a pair of first guide layers 33, 34. The first guide layers 33, 34 sandwich the first active layer 32 in the stacking direction D2. The first cladding layers 35, 36 sandwich the first active layer 32 and the first guide layers 33, 34 in the stacking direction D2. The first cladding layer 35, the first guide layer 33, the first active layer 32, the first guide layer 34, and the first cladding layer 36 are stacked on the substrate 2 in this order. A buffer layer is provided between the first cladding layer 35 and the substrate 2.

[0026] The first active layer 32 includes a barrier layer and a pair of quantum well layers sandwiching the barrier layer in the stacking direction D2, and has a double quantum well structure. 0.28The quantum well layer is made of GaAs and has a thickness of 5 nm. 0.1 Al 0.049 It is made of GaAs and has a thickness of 8 nm.

[0027] Each of the first guide layers 33 and 34 is made of Al 0.28 It is made of GaAs and has a thickness of (70-d) nm. In this example, d=4, and the first guide layers 33, 34 have a thickness of 66 nm. That is, the total thickness of the first guide layers 33, 34 is 132 nm, and the first emitter 31 has a thickness of 153 nm. The refractive index of the first guide layers 33, 34 is lower than that of the first active layer 32 and higher than that of the first cladding layers 35, 36. The first cladding layer 35 is made of n-type Al 0.37 The first cladding layer 36 is made of GaAs and has a thickness of 1600 nm. 0.37 The first tunnel junction layer 4 is made of GaAs and has a thickness of 2000 nm. The first tunnel junction layer 5 is made of GaAs and has a thickness of 225 nm.

[0028] The second element section 5 is stacked on the first element section 3 via the first tunnel junction layer 4. The second element section 5 has a second emitter 51 and a pair of second cladding layers 55, 56. The second emitter 51 includes a second active layer 52 and a pair of second guide layers 53, 54. The second guide layers 53, 54 sandwich the second active layer 52 in the stacking direction D2. The second cladding layers 55, 56 sandwich the second active layer 52 and the second guide layers 53, 54 in the stacking direction D2. The second cladding layer 55, the second guide layer 53, the second active layer 52, the second guide layer 54, and the second cladding layer 56 are stacked on the first tunnel junction layer 4 in this order. That is, the second emitter 51 is stacked on the first emitter 31 via the first cladding layer 36, the first tunnel junction layer 4, and the second cladding layer 55.

[0029] The second active layer 52 has the same structure as the first active layer 32. That is, the second active layer 52 includes a barrier layer and a pair of quantum well layers sandwiching the barrier layer in the stacking direction D2, and has a double quantum well structure. 0.28The quantum well layer is made of GaAs and has a thickness of 5 nm. 0.1 Al 0.049 The second active layer 52 is made of GaAs and has a thickness of 8 nm. The thickness of the second active layer 52 is equal to the thickness of the first active layer 32.

[0030] Each of the second guide layers 53 and 54 is made of Al 0.28 The second guide layers 53 and 54 are made of GaAs and have a thickness of 70 nm. That is, the total thickness of the second guide layers 53 and 54 is 140 nm, and the second emitter 51 has a thickness of 161 nm. The refractive index of the second guide layers 53 and 54 is lower than that of the second active layer 52 and higher than that of the second cladding layers 55 and 56. The second cladding layer 55 is made of n-type Al 0.37 The second cladding layer 56 is made of GaAs and has a thickness of 2000 nm. 0.37 The second tunnel junction layer 6 is made of GaAs and has a thickness of 2000 nm. The second tunnel junction layer 7 is made of GaAs and has a thickness of 225 nm.

[0031] The third element section 7 is stacked on the second element section 5 via the second tunnel junction layer 6. The third element section 7 has a third emitter 71 and a pair of third cladding layers 75, 76. The third emitter 71 includes a third active layer 72 and a pair of third guide layers 73, 74. The third guide layers 73, 74 sandwich the third active layer 72 in the stacking direction D2. The third cladding layers 75, 76 sandwich the third active layer 72 and the third guide layers 74, 74 in the stacking direction D2. The third cladding layer 75, the third guide layer 73, the third active layer 72, the third guide layer 74, and the third cladding layer 76 are stacked on the second tunnel junction layer 6 in this order. That is, the third emitter 71 is stacked on the second emitter 51 via the second cladding layer 56, the second tunnel junction layer 6, and the third cladding layer 75.

[0032] The third active layer 72 has the same structure as the first active layer 32 and the second active layer 52. That is, the third active layer 72 includes a barrier layer and a pair of quantum well layers sandwiching the barrier layer in the stacking direction D2, and has a double quantum well structure. 0.28The quantum well layer is made of GaAs and has a thickness of 5 nm. 0.1 Al 0.049 The third active layer 72 is made of GaAs and has a thickness of 8 nm. The thickness of the third active layer 72 is equal to the thickness of the first active layer 32 and the second active layer 52.

[0033] Each of the third guide layers 73 and 74 is made of Al 0.28 It is made of GaAs and has a thickness of (70+d) nm. In this example, d=4, and the third guide layers 73, 74 have a thickness of 74 nm. That is, the total thickness of the third guide layers 73, 74 is 148 nm, and the third emitter 71 has a thickness of 169 nm. The refractive index of the third guide layers 73, 74 is lower than that of the third active layer 72 and higher than that of the third cladding layers 75, 76. The third cladding layer 75 is made of n-type Al 0.37 The third cladding layer 76 is made of GaAs and has a thickness of 2000 nm. 0.37 The cap layer 8 is made of n-type GaAs and has a thickness of 2000 nm.

[0034] During operation of the semiconductor laser element 1, for example, a voltage is applied between electrodes provided on the surface of the substrate 2 opposite to the first element portion 3 and on the cap layer 8. As a result, light is generated in the first active layer 32, the second active layer 52, and the third active layer 72. The light generated in the first active layer 32 is confined in the first emitter 31 (the first active layer 32 and the first guide layers 33, 34), and is reflected by both end faces of the first emitter 31 in the optical axis direction D1, and is amplified while traveling back and forth between both end faces, and is emitted from one end face as laser light L1 along the optical axis direction D1. Similarly, the laser light L2 and L3 are output from the second emitter 51 and the third emitter 71 along the optical axis direction D1. The output light L0 of the semiconductor laser element 1 is composed of the laser light L1, L2, and L3. In this example, the oscillation wavelength of the laser light L1, L2, and L3 is 905 nm. In this manner, the first emitter 31, the second emitter 51, and the third emitter 71 output light in the same wavelength range.

[0035] As described above, in the semiconductor laser device 1, the first emitter 31, the second emitter 51, and the third emitter 71 have thicknesses of 153 nm, 161 nm, and 169 nm, respectively, and the thickness of the first emitter 31 is different from the thickness of the second emitter 51, and the thickness of the third emitter 71 is different from the thickness of the second emitter 51. More specifically, the total thickness (132 nm) of the first guide layers 33, 34 is different from the total thickness (140 nm) of the second guide layers 53, 54, so that the thickness of the first emitter 31 is different from the thickness of the second emitter 51. In addition, the total thickness (148 nm) of the third guide layers 73, 74 is different from the total thickness (140 nm) of the second guide layers 53, 54, so that the thickness of the third emitter 71 is different from the thickness of the second emitter 51. This makes it possible to suppress interference between the laser beams L1, L2, and L3 emitted from the first emitter 31, the second emitter 51, and the third emitter 71, and to suppress disturbance in the far-field pattern of the output beam L0. This point will be further described below.

[0036] FIG. 2(a) is a graph showing the far-field pattern (FFP) of the output light of the semiconductor laser device according to the comparative example, and FIG. 2(b) is a graph showing the far-field pattern of the output light of the semiconductor laser device 1 according to the embodiment. In FIG. 2(a) and FIG. 2(b), actual measurement data of the far-field pattern in the stacking direction D2 (crystal growth direction) is shown. The angle θ is the angle with respect to the optical axis direction D1 in the stacking direction D2. The far-field pattern is the light intensity distribution at a position sufficiently far from the light emission surface. The semiconductor laser device according to the comparative example differs from the semiconductor laser device 1 only in that the thicknesses of the first guide layers 33, 34 and the third guide layers 73, 74 are equal to the thickness of the second guide layers 53, 54. That is, the semiconductor laser device according to the comparative example corresponds to the case where the parameter d is set to 0 in the semiconductor laser device 1.

[0037] 2(a) and 2(b), in the comparative example, disturbances (unevenness) occurred in the far-field pattern, whereas in the semiconductor laser element 1 according to the embodiment, such disturbances did not occur. This is considered to be because, in the comparative example, beats occurred due to interference between the laser beams L1, L2, and L3 from the first emitter 31, the second emitter 51, and the third emitter 71, whereas in the semiconductor laser element 1 according to the embodiment, interference between the laser beams L1, L2, and L3 was suppressed. From this, it can be seen that by making the thicknesses of the first emitter 31, the second emitter 51, and the third emitter 71 different from each other, interference between the laser beams L1, L2, and L3 can be suppressed, and disturbances in the far-field pattern of the output beam L0 can be suppressed.

[0038] The following describes how to set the thicknesses of the first emitter 31, the second emitter 51, and the third emitter 71 in order to suppress the interference of the laser beams L1, L2, and L3. In the following, attention is focused on the effect of the interference of the laser beams L1 and L2 from the first emitter 31 and the second emitter 51 on the far-field pattern of the output beam L0.

[0039] The average value of the index DB1 expressed by the formula (7) and the index DB2 expressed by the formula (8) is defined as the index DBa. That is, DBa = (DB1 + DB2) / 2. The index DBa represents the percentage of the area surrounded by the far-field pattern of the output light L0 that is modulated by interference.

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[0040] In formulas (7) and (8), θ is the angle with respect to the optical axis direction D1. The integral range is the entire range of the radiation angle (illumination angle), for example, from -90° to +90°. 01 (θ) and F 02(θ) is a far-field pattern in the normalized stacking direction D2, and both are normalized so that the integral value over the entire range of the radiation angle in the stacking direction D2 is 1. F1(θ) is a far-field pattern of the laser light L1 emitted from the first emitter 31 when it is assumed that the second emitter 31 and the third emitter 71 (emitters other than the first emitter 31) do not exist and only the first emitter 31 exists alone. F2(θ) is a far-field pattern of the laser light L2 emitted from the second emitter 51 when it is assumed that the first emitter 31 and the third emitter 71 (emitters other than the second emitter 51) do not exist and only the second emitter 51 exists alone.

[0041] When the third emitter 71 is not present and only the first emitter 31 and the second emitter 51 are present, the light (output light L0) emitted from the first emitter 31 and the second emitter 51 has two modes corresponding to the fundamental mode. The mode with the smaller propagation constant is defined as the first mode, and the mode with the larger propagation constant is defined as the second mode. When the thickness of the first emitter 31 is thinner than the thickness of the second emitter 51, F 01 (θ) is the far-field pattern of the first mode, F 02 (θ) is the far-field pattern of the second mode. When the thickness of the first emitter 31 is greater than the thickness of the second emitter 51, F 01 (θ) is the far-field pattern of the second mode, F 02 (θ) is the far-field pattern of the first mode.

[0042] That is, when only two emitters, the first emitter 31 and the second emitter 51, are present, the output light L0 has two modes as the fundamental mode. Of these two modes, the mode with the smaller propagation constant is the first mode, and the mode with the larger propagation constant is the second mode. In the semiconductor laser device 1, the thickness of the first emitter 31 is thinner than the thickness of the second emitter 51. Therefore, F 01 (θ) is the far-field pattern of the first mode, F 02 (θ) is the far-field pattern of the second mode. When the thickness of the first emitter 31 is greater than the thickness of the second emitter 51 as in the modified example described later, F01 (θ) is the far-field pattern of the second mode, F 02 (θ) is the far-field pattern of the first mode. Hereinafter, the far-field patterns F1(θ), F2(θ), and F 01 (θ),F 02 The notation (θ) in (θ) etc. will be omitted as appropriate.

[0043] The reason for changing the far-field patterns to be compared according to the magnitude relationship between the thicknesses of the first emitter 31 and the second emitter 51 is as follows. When the thicknesses of the first emitter 31 and the second emitter 51 are different, the far-field patterns when the first emitter 31 and the second emitter 51 exist alone have different widths. In addition, the far-field pattern when the first emitter 31 and the second emitter 51 exist alone has a base width different from the two modes that appear when the first emitter 31 and the second emitter 51 exist simultaneously. The indices DB1 and DB2 calculated by the formulas (7) and (8) are affected not only by interference but also by the difference in width of the far-field patterns. Therefore, in order to accurately evaluate the degree of interference, far-field patterns with similar base widths are compared.

[0044] 3(a) and 3(b) are graphs showing examples of calculations of the change in the far-field pattern with respect to the index DBa when the thickness of the first emitter 31 is thinner than the thickness of the second emitter 51. In FIG. 3(a), the far-field pattern F1 (far-field pattern in the absence of interference) is shown by a dashed line, and the far-field pattern F 01 In FIG. 3(b), the far-field pattern F2 (the far-field pattern in the absence of interference) is shown in dashed lines, and the far-field pattern F 02 In Fig. 3(a) and Fig. 3(b), the far field patterns F1, F2, F3, F4, F5, F6, F7, F8, F9, F10, F11, F12, F13, F14, F15, F16, F17, F18, F19, F20, F21, F22, F23, F24, F25, F26, F27, F28, F29, 01 ,F2,F 02 are shown in order from the bottom.

[0045] As shown in FIG. 3(a) and FIG. 3(b), when the index DBa is 10% or 30%, the far-field pattern F 01,F 02 On the other hand, when the index DBa is 1%, 3%, and 5%, the far-field pattern F 01 ,F 02 The smaller the index DBa, the smaller the far-field pattern F 01 ,F 02 The shape of the far-field patterns F1 and F2 approaches the far-field patterns F1 and F2, and the occurrence of disturbance is effectively suppressed. Therefore, by making the thickness of the first emitter 31 different from the thickness of the second emitter 51 so that the index DBa is 5% or less, the interference of the laser beams L1 and L2 emitted from the first emitter 31 and the second emitter 51 can be suppressed, and disturbance in the far-field pattern of the output light L0 can be suppressed. Specifically, the larger the difference (absolute difference) in thickness between the first emitter 31 and the second emitter 51, the greater the effect of suppressing the interference of the laser beams L1 and L2. Therefore, by setting the difference in thickness between the first emitter 31 and the second emitter 51 so that the index DBa is 5% or less, the interference of the laser beams L1 and L2 can be suppressed.

[0046] Also, as shown in FIG. 3(a), when the index DBa is 5%, the far-field pattern F 01 The peak of the far-field pattern F is slightly concave, whereas when the index DBa is 3% or less, 01 There is only one extreme value in the center of the far-field pattern F. Therefore, it is preferable that the index DBa is 3% or less. When the index DBa is 1%, the far-field pattern F 01 ,F 02 The shape of the far-field patterns F1 and F2 is almost the same as that of the far-field patterns F1 and F2. Therefore, it is more preferable that the index DBa is 1% or less.

[0047] A preferred upper limit value of the difference in thickness between the first emitter 31 and the second emitter 51 will be described. The greater the difference in thickness between the first emitter 31 and the second emitter 51, the greater the interference suppression effect. However, as described above, the difference in width between the far-field pattern when each of the first emitter 31 and the second emitter 51 exists alone becomes greater. If the difference in width between these far-field patterns is large, practical problems may occur. Therefore, the absolute difference between the thickness of the first emitter 31 and the average value of the thicknesses of the first emitter 31 and the second emitter 51 may be set to 10% or less of the average value. This is for the following reason. There is an approximately inversely proportional relationship between the widths of the far-field pattern and the near-field pattern. In addition, the width of the near-field pattern depends on the thickness of the guide layer. Although the degree of this dependence may vary depending on the structure, the region in which a change of about 10% occurs in the width of the near-field pattern for a change of about 10% in the thickness of the guide layer is wide. In practical terms, a change in the width of the far-field pattern of about ±10% can be tolerated. Therefore, the above conditions are set.

[0048] As an index related to the index DBa, an index P expressed by the formula (9) is set.

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[0049] FIG. 4 is a graph showing the relationship between the index P and the index DBa. In FIG. 4, a straight line A representing DBa=1.25 / P is shown. Each plot is a calculation result obtained by changing the structure of the first emitter 31 and the second emitter 51 in various ways. As shown in FIG. 4, many plots are located on the straight line A or in the vicinity of the straight line A, and there is a good correlation between the index DBa and the index P. The inventors of the present invention have found that there is a good correlation between the index DBa and the index P. From this graph, it can be seen that in order to make the index DBa 5% or less, the index P should be set to 25 or more, in order to make the index DBa 3% or less, the index P should be set to 40 or more, and in order to make the index DBa 1% or less, the index P should be set to 125 or more.

[0050] Propagation constants β1, β2 and coupling constant K 12 A calculation method of is explained. In the following calculation, the first emitter 31 and the second emitter 51 are analyzed as slab-type waveguides. First, consider the simplified semiconductor laser device 1A as shown in FIG. 5. In the semiconductor laser device 1A, the cladding layer 11, the first emitter 31, the cladding layer 12, the second emitter 51, and the cladding layer 13 are laminated in this order. The refractive index of the cladding layers 11, 12, and 13 is n0, and the thickness of the cladding layer 12 is D. It is assumed that the thickness of the cladding layers 11 and 13 is semi-infinite. The refractive index of the first guide layers 33 and 34 and the second guide layers 53 and 54 is n1, and the thickness of each of the first guide layers 33 and 34 and each of the second guide layers 53 and 54 is a. The oscillation wavelength of the first emitter 31 and the second emitter 51 is λ.

[0051] When the laser beams L1, L2 emitted from the first emitter 31 and the second emitter 51 are TE mode beams, the propagation constant β of the first emitter 31 and the second emitter 51 is calculated as follows. Equation (10) defines v, where k is the wave number in vacuum and is equal to 2π / λ.

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[0052] The coupling constant K between the first emitter 31 and the second emitter 51 when it is assumed that the thickness of each of the first emitter 31 and the second emitter 51 is equal to the average thickness of the first emitter 31 and the second emitter 51. 12 can be calculated as follows: Equations (13) and (14) define u and w.

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[0053] When the laser beams L1, L2 emitted from the first emitter 31 and the second emitter 51 have the TM mode, the propagation constant β of the first emitter 31 and the second emitter 51 is calculated by a calculation method in which formula (11) is replaced with formula (16) and formula (15) is replaced with formula (17) in the above calculation method. That is, the index DBa and the index P are calculated using either the calculation method when the laser beams L1, L2 have the TM mode or the calculation method when the laser beams L1, L2 have the TE mode.

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[0054] In the actual calculation, the propagation constant β and the coupling constant K 12 is calculated by the above calculation method using the following definitions without simplifying the semiconductor laser device 1: n1: Weighted average value of the refractive index of the guide layer and the active layer weighted by thickness so that the thicker the layer, the heavier the weight. n0: Weighted average value of the refractive index of the cladding layer weighted by thickness so that the thicker the layer, the heavier the weight. 2a: Average thickness of the two emitters (the sum of the thickness of the active layer and a pair of guide layers) D: The total thickness of the cladding layer and the tunnel junction layer disposed between the emitters

[0055] As described above, the thickness of the first emitter 31 and the second emitter 51 can be set using the index DBa and the index P. The influence of the interference of the laser beams L2 and L3 from the second emitter 51 and the third emitter 71 and the interference of the laser beams L1 and L3 from the first emitter 31 and the third emitter 71 on the far-field pattern of the output light L0 is similar to the influence of the interference of the laser beams L1 and L2 from the first emitter 31 and the second emitter 51 on the far-field pattern of the output light L0. However, since the distance between the first emitter 31 and the third emitter 71 in the stacking direction D2 is longer than the distance between the first emitter 31 and the second emitter 51 and the distance between the second emitter 51 and the third emitter 71, the influence of the interference of the laser beams L1 and L3 is sufficiently small compared to the influence of the interference of the laser beams L1 and L2 and the influence of the interference of the laser beams L2 and L3, and can be ignored.

[0056] By making the thickness of the third emitter 71 different from the thickness of the second emitter 51 so that the index DBb, which is the average value of the index DB3 expressed by equation (18) and the index DB4 expressed by equation (19), is 5% or less, interference between the laser beams L2 and L3 emitted from the second emitter 51 and the third emitter 71 can be suppressed, and disturbances in the far-field pattern of the output light L0 can be suppressed.

number

number

[0057] In formula (18) and formula (19), F3, F4, F 03 and F 04 are far-field patterns in the normalized stacking direction D2, and are normalized so that the integral value over the entire range of the radiation angle in the stacking direction D2 is 1. F3 is the far-field pattern of the laser light L3 emitted from the third emitter 71 when it is assumed that the first emitter 31 and the second emitter 51 do not exist and only the third emitter 71 exists alone. F4 is the far-field pattern of the laser light L2 emitted from the second emitter 51 when it is assumed that the first emitter 31 and the third emitter 71 do not exist and only the second emitter 51 exists alone.

[0058] When the first emitter 31 is not present and only the second emitter 51 and the third emitter 71 are present, the light (output light L0) emitted from the second emitter 51 and the third emitter 71 has two modes corresponding to the fundamental mode. The mode with the smaller propagation constant is defined as the third mode, and the mode with the larger propagation constant is defined as the fourth mode. When the thickness of the third emitter 71 is thinner than the thickness of the second emitter 51, F 03 is the far-field pattern of the third mode, and F 04 is the far-field pattern of the fourth mode. When the thickness of the third emitter 71 is greater than the thickness of the second emitter 51, F 03 is the far-field pattern of the fourth mode, and F 04is the far-field pattern of the third mode. In the semiconductor laser device 1, the thickness of the third emitter 71 is thicker than the thickness of the second emitter 51. Therefore, F 03 (θ) is the far-field pattern of the fourth mode, F 04 (θ) is the far-field pattern of the third mode.

[0059] The index P for the second emitter 51 and the third emitter 71 is expressed by the formula (20).

number

[0060] In the semiconductor laser device 1 according to the embodiment, the index P for the first emitter 31 and the second emitter 51, and the index P for the second emitter 51 and the third emitter 71 are approximately 190, which is greater than or equal to 125. That is, the index DBa is less than or equal to 1%. In addition, the difference in thickness between the first emitter 31 and the second emitter 51 is 8 nm, which is less than or equal to 10% of the average thickness of the first emitter 31 and the second emitter 51, that is, 157 nm, and is less than or equal to 10% of the average thickness of the first emitter 31, the second emitter 51, and the third emitter 71 (the average thickness of all the emitters), that is, 161 nm. The difference in thickness between the third emitter 71 and the second emitter 51 is 8 nm, which is less than 10% of the average thickness of the second emitter 51 and the third emitter 71, which is 165 nm, and is also less than 10% of the average thickness of the first emitter 31, the second emitter 51 and the third emitter 71, which is 161 nm. [Action and Effects]

[0061] In the semiconductor laser element 1, the thickness of the first emitter 31 is different from the thickness of the second emitter 51 so that the index DBa, which is the average value of the index DB1 and the index DB2, is 5% or less. By modulating the thicknesses of the first emitter 31 and the second emitter 51 in this manner, the effective refractive index and the propagation constant of the first emitter 31 and the second emitter 51 can be made different. As a result, the interference (resonant coupling of the propagation modes) of the laser beams L1 and L2 emitted from the first emitter 31 and the second emitter 51 can be suppressed, and the occurrence of disturbance in the far-field pattern of the output light L0 can be suppressed. As described above, the disturbance can cause spatial unevenness in the output light L0, deviation from the optical design, and the like. In addition, such unevenness and deviation can cause a decrease in yield. In contrast, in the semiconductor laser element 1, the disturbance can be suppressed, thereby improving the yield. Alternatively, the disturbance in the far-field pattern of the output light L0 can be suppressed by thickening the first cladding layer 36 and the second cladding layer 55 disposed between the first emitter 31 and the second emitter 51, but this increases the operating voltage. In contrast, the semiconductor laser device 1 can suppress the disturbance in the far-field pattern of the output light L0 while suppressing the increase in the operating voltage.

[0062] The thickness of the first emitter 31 is different from the thickness of the second emitter 51 such that the index DBa is 3% or less, more specifically, 1% or less, thereby making it possible to effectively suppress interference between the laser beams L1 and L2.

[0063] The total thickness of the first guide layers 33, 34 is different from the total thickness of the second guide layers, and thus the thickness of the first emitter 31 is different from the thickness of the second emitter 51. This increases the degree of freedom in designing the thicknesses of the first active layer 32 and the second active layer 52, and allows the first active layer 32 and the second active layer 52 to have the same thickness, for example.

[0064] The thickness of the first emitter 31 is different from the thickness of the second emitter 51 so that the index P is equal to or greater than 25. This makes it possible to suppress interference between the laser beams L1 and L2.

[0065] The thickness of the first emitter 31 is different from the thickness of the second emitter 51 so that the index P is equal to or greater than 40, more specifically, equal to or greater than 125. This makes it possible to effectively suppress interference between the laser beams L1 and L2.

[0066] The absolute difference between the thickness of the first emitter 31 and the average value of the thicknesses of the first emitter 31 and the second emitter 51 is 10% or less of the average value. This makes it possible to prevent a situation in which the quality of the output light L0 is reduced due to an excessive difference in thickness between the first emitter 31 and the second emitter 51.

[0067] The thickness of the third emitter 71 is different from the thickness of the second emitter 51 so that an index DBb, which is an average value of the indexes DB3 and DB4, is 5% or less. This makes it possible to suppress interference between the laser beams L2 and L3 emitted from the second emitter 51 and the third emitter 71. [Variations]

[0068] 6 includes a substrate 2, a first element portion 3, a first tunnel junction layer 4, a second element portion 5, and a cap layer 8, but does not include a second tunnel junction layer 6 or a third element portion 7. The first active layer 32 is made of In 0.1 Al 0.049 The first guide layers 33 and 34 are each made of GaAs and each have a thickness of 8 nm. 0.25 The first cladding layer 35 is made of GaAs and has a thickness of (100-h) nm. 0.35 The first cladding layer 36 is made of GaAs and has a thickness of 1600 nm. 0.35 The first tunnel junction layer 4 is made of GaAs and has a thickness of 1600 nm. The first tunnel junction layer 5 is made of GaAs and has a thickness of 200 nm.

[0069] The second active layer 52 is In 0.1 Al 0.049The second guide layers 53 and 54 are each made of GaAs and have a thickness of 8 nm. 0.25 The second cladding layer 55 is made of GaAs and has a thickness of (100+h) nm. 0.35 The second cladding layer 56 is made of GaAs and has a thickness of 1600 nm. 0.35 The first emitter 31 and the second emitter 51 have an oscillation wavelength of 905 nm.

[0070] Table 1 shows the results of numerical calculations when the parameter h is changed in the semiconductor laser device 1B. It can be seen from Table 1 that as the parameter h increases, the index P increases and the index DBa decreases, suppressing the disturbance in the far-field pattern of the output light L0. In this way, the semiconductor laser device 1B can also suppress the disturbance in the far-field pattern of the output light L0, as in the above embodiment. [Table 1]

[0071] As another modification, the semiconductor laser device 1B may be configured as follows: the first guide layers 33, 34 each have a thickness of (400-h) nm, the first cladding layers 35, 36 each have a thickness of 800 nm, the second guide layers 53, 54 each have a thickness of (400+h) nm, and the second cladding layers 55, 56 each have a thickness of 800 nm. This modification of the semiconductor laser device 1B is otherwise configured similarly to the semiconductor laser device 1B.

[0072] Table 2 shows the results of numerical calculations when the parameter h is changed in the modified semiconductor laser element 1B. It can be seen from Table 2 that as the parameter h increases, the index P increases and the index DBa decreases, suppressing the disturbance in the far-field pattern of the output light L0. In this way, the modified semiconductor laser element 1B can also suppress the disturbance in the far-field pattern of the output light L0, as in the above embodiment. [Table 2]

[0073] Tables 3 to 6 show the results of calculating the thickness modulation amount (a1-a2)n1 / λ value at which the index P is 40 in the semiconductor laser device 1A shown in FIG. 5 described above. Tables 3, 4, 5, and 6 show the cases where the normalized refractive index difference (n1-n0) / n1 is 0.02, 0.03, 0.04, and 0.05, respectively. In Tables 3 to 6, 2a1 is the thickness of the first emitter 31, 2a2 is the thickness of the second emitter 51, and 2a0 is the average value of the thicknesses of the first emitter 31 and the second emitter 51. n1 is the refractive index of the first emitter 31 and the second emitter 51. a0n1 / λ represents the average thickness of the emitter normalized by the wavelength and the refractive index, and (Dn1 / λ)×(a0n1 / λ) represents the product of the average thickness of the emitter normalized by the wavelength and the refractive index and the thickness of the cladding layer normalized by the wavelength and the refractive index. In Tables 3 to 6, columns listing numerical values ​​indicate that the thicknesses of the first emitter 31 and the second emitter 51 can be set so that the index P is 40. The same applies to Tables 7 to 10 described later. With such a semiconductor laser device 1A, as in the above embodiment, it is possible to suppress the occurrence of disturbances in the far-field pattern of the output light L0. [Table 3] [Table 4] [Table 5] [Table 6]

[0074] Tables 7 to 10 show the results of calculating the thickness modulation amount (a1-a2)n1 / λ value at which the index P is 125 in the semiconductor laser device 1A shown in Fig. 5 described above. Tables 7, 8, 9, and 10 show the cases where the normalized refractive index difference (n1-n0) / n1 is 0.02, 0.03, 0.04, and 0.05, respectively. [Table 7] [Table 8] [Table 9] [Table 10]

[0075] As shown in FIG. 7, the semiconductor laser element 1 can be mounted on a mount member 15 to configure a laser module 100. That is, the laser module 100 includes the semiconductor laser element 1 and the mount member 15 on which the semiconductor laser element 1 is mounted. In the semiconductor laser element 1, the first emitter 31, the second emitter 51, and the third emitter 71 are stacked on the substrate 2 such that the first emitter 31 is located on a first side (lower side in FIG. 7) closer to the substrate 2 than the second emitter 51, and the second emitter 51 is located on the first side than the third emitter 71. The semiconductor laser element 1 is fixed on the mount member 15 on the first side. The semiconductor laser element 1 is joined to the mount member 15 by, for example, solder. The mount member 15 is, for example, a heat sink made of copper. Since the semiconductor laser element 1 has a tendency to generate a large amount of heat due to the presence of multiple emitters, it is preferable to ensure heat dissipation by using a heat sink.

[0076] The effective refractive indexes of the first emitter 31, the second emitter 51, and the third emitter 71 (optical waveguide) are affected by the strain occurring therein. Therefore, the difference in the effective refractive index introduced by making the thicknesses of the first emitter 31, the second emitter 51, and the third emitter 71 different can be canceled by the influence of the strain. For example, in the semiconductor laser element 1, a stack (a stack consisting of the first element portion 3, the first tunnel junction layer 4, the second element portion 5, the second tunnel junction layer 6, the third element portion 7, and the cap layer 8) formed by epitaxial growth on the substrate 2 has compressive strain in the in-plane direction due to the force acting from the substrate 2. When compressive strain in the in-plane direction exists, the effective refractive index of the TE mode changes in a decreasing direction. Since the strain is relaxed as it goes away from the substrate 2, the effective refractive index becomes relatively larger as the layer goes away from the substrate 2. Therefore, it is preferable to increase the thickness of an emitter farther from the substrate 2 so that the effective refractive index when it exists alone is larger, that is, so that the propagation constant is larger. In this respect, in the laser module 100, the second emitter 51 is thicker than the first emitter 31, and the third emitter 71 is thicker than the second emitter 51. As a result, the thicknesses of the first emitter 31, the second emitter 51, and the third emitter 71 are modulated in a direction in which the difference in effective refractive index caused by the distortion is emphasized. As a result, it is possible to avoid a situation in which the above-mentioned optical interference suppression effect is impaired due to the influence of the distortion caused in the first emitter 31, the second emitter 51, and the third emitter 71 by the force acting from the substrate 2.

[0077] In the laser module 100 shown in Fig. 8, the semiconductor laser element 1 is fixed on a mount member 15 on a second side (upper side in Fig. 8) opposite to the first side. The mount member 15 is made of a material having a smaller thermal expansion coefficient than the material constituting the substrate 2, and the thermal expansion coefficient of the mount member 15 is smaller than the thermal expansion coefficient of the substrate 2. In this case, the distortion generated in the laminate on the substrate 2 can be smaller the farther away from the substrate 2. This is because the effect of the force acting on the laminate from the substrate 2 due to the difference in lattice constants is larger than the effect of the force acting on the laminate from the mount member 15 due to the difference in thermal expansion coefficients, or the directions of these forces are opposite. In the laser module 100, the second emitter 51 is thicker than the first emitter 31, and the third emitter 71 is thicker than the second emitter 51, so that it is possible to avoid a situation in which the above-mentioned optical interference suppression effect is impaired due to the influence of distortion caused in the first emitter 31, the second emitter 51, and the third emitter 71 by the forces acting from the substrate 2 and the mounting member 15.

[0078] As another modification, in the laser module 100 shown in FIG. 8, the thermal expansion coefficient of the mount member 15 may be greater than that of the substrate 2. In this modification, the first emitter 31 is made thicker than the second emitter 51, and the second emitter 51 is made thicker than the third emitter 71. When the thermal expansion coefficient of the mount member 15 is greater than that of the substrate 2, the effect of the force acting on the laminate from the mount member 15 becomes greater than the effect of the force acting on the laminate from the substrate 2, and the distortion generated in the laminate may become greater the farther away from the substrate 2. In the laser module 100 of this modification, the first emitter 31, the second emitter 51, and the third emitter 71 are thicker in this order, so that it is possible to avoid a situation in which the above-mentioned optical interference suppression effect is impaired due to the effect of distortion generated in the first emitter 31, the second emitter 51, and the third emitter 71 by the force acting from the substrate 2 and the mount member 15.

[0079] The present invention is not limited to the above-mentioned embodiment and modified examples. For example, the material and shape of each component are not limited to the above-mentioned material and shape, and various materials and shapes can be adopted. In the above-mentioned embodiment, the thickness of the first active layer 32 is different from the thickness of the second active layer 52, so that the thickness of the first emitter 31 may be different from the thickness of the second emitter 51. In this case, the total thickness of the first guide layers 33 and 34 may be equal to the total thickness of the second guide layer.

[0080] In the above embodiment, the thicknesses of the first emitter 31, the second emitter 51, and the third emitter 71 are different from each other, but it is sufficient that the thicknesses of at least two emitters are different from each other. From the viewpoint of suppressing interference, it is preferable that the thicknesses are different between the adjacent first emitter 31 and the second emitter 51, and between the adjacent second emitter 51 and the third emitter 71. In the above embodiment, the first emitter 31 is thinner than the second emitter 51, and the third emitter 71 is thicker than the second emitter 51, but the first emitter 31 and the third emitter 71 may be thinner than the second emitter 51. For example, the thicknesses of the first emitter 31 and the third emitter 71 may be equal to each other. Alternatively, the first emitter 31 and the third emitter 71 may be thicker than the second emitter 51. In the above embodiment, three emitters (waveguides) are provided: the first emitter 31, the second emitter 51, and the third emitter 71. However, four or more emitters may be provided. The first active layer 32, the second active layer 52, and the third active layer 72 may have a multiple quantum well structure. In this case, the thickness of the barrier layer may be changed as appropriate. [Explanation of symbols]

[0081] 1...semiconductor laser element, 2...substrate, 15...mounting member, 31...first emitter, 32...first active layer, 33,34...first guide layer, 35,36...first cladding layer, 51...second emitter, 52...second active layer, 53,54...second guide layer, 55,56...second cladding layer, 71...third emitter, 72...third active layer, 73,74...third guide layer, 100...laser module, D1...optical axis direction, D2...stacking direction.

Claims

1. A first element portion; a second element portion stacked on the first element portion along a stacking direction, The first element portion is a first emitter including a first active layer and a pair of first guide layers sandwiching the first active layer, the first emitter emitting light along an optical axis direction; a pair of first cladding layers sandwiching the pair of first guide layers; The second element portion is a second emitter including a second active layer and a pair of second guide layers sandwiching the second active layer, the second emitter emitting light along the optical axis direction; a pair of second cladding layers sandwiching the pair of second guide layers; a thickness of the first emitter is different from a thickness of the second emitter such that an average value of an index DB1 expressed by formula (1) and an index DB2 expressed by formula (2) is 5% or less; A semiconductor laser device, wherein an absolute difference between a thickness of the first emitter and an average value of thicknesses of the first emitter and the second emitter is 10% or less of the average value. [0010] [0025] In the formulas (1) and (2), θ is an angle with respect to the optical axis direction, and F １ (θ), F ２ (θ), F ０１ (θ) and F ０２ (θ) is the normalized far-field pattern in the stacking direction, F １ (θ) is the far field pattern of light emitted from the first emitter assuming that the second emitter is not present and only the first emitter is present, F ２ (θ) is the far field pattern of light emitted from the second emitter if the first emitter were not present and only the second emitter were present; When only the first emitter and the second emitter are present, the light emitted from the first emitter and the second emitter has two modes corresponding to a fundamental mode. If the mode having a smaller propagation constant is defined as a first mode and the mode having a larger propagation constant is defined as a second mode, When the thickness of the first emitter is smaller than the thickness of the second emitter, F ０１ (θ) is the far-field pattern of the first mode, F ０２ (θ) is the far field pattern of the second mode, When the thickness of the first emitter is greater than the thickness of the second emitter, F ０１ (θ) is the far-field pattern of the second mode, F ０２ (θ) is the far field pattern of the first mode.

2. 2. The semiconductor laser device according to claim 1, wherein a thickness of the first emitter is different from a thickness of the second emitter such that an average value of the index DB1 and the index DB2 is 3% or less.

3. 2. The semiconductor laser device according to claim 1, wherein a thickness of the first emitter is different from a thickness of the second emitter such that an average value of the index DB1 and the index DB2 is 1% or less.

4. 4. The semiconductor laser element according to claim 1, wherein a total thickness of the pair of first guide layers is different from a total thickness of the pair of second guide layers, such that a thickness of the first emitter is different from a thickness of the second emitter.

5. 5. The semiconductor laser device according to claim 1, wherein a thickness of the first emitter is different from a thickness of the second emitter such that an index P expressed by formula (3) is 25 or more. [0030] In the formula (3), β １ is the propagation constant of the first emitter, and β ２ is the propagation constant of the second emitter, K １２ is a coupling constant between the first emitter and the second emitter when the thickness of each of the first emitter and the second emitter is assumed to be equal to the average thickness of the first emitter and the second emitter.

6. 6. The semiconductor laser device of claim 5, wherein a thickness of the first emitter is different from a thickness of the second emitter such that the index P is 40 or more.

7. 6. The semiconductor laser device of claim 5, wherein a thickness of the first emitter differs from a thickness of the second emitter such that the index P is 125 or greater.

8. a third element portion stacked on the second element portion along the stacking direction, The third element portion is a third emitter including a third active layer and a pair of third guide layers sandwiching the third active layer, the third emitter emitting light along the optical axis direction; a pair of third cladding layers sandwiching the pair of third guide layers; 8. The semiconductor laser element according to claim 1, wherein a thickness of the third emitter is different from a thickness of the second emitter such that an average value of an index DB3 expressed by formula (4) and an index DB4 expressed by formula (5) is 5% or less. [0045] [0050] In the formula (4) and the formula (5), F ３ (θ) is the far-field pattern of light emitted from the third emitter assuming that the first emitter and the second emitter are not present and only the third emitter is present, F ４ (θ) is the far field pattern of light emitted from the second emitter if the first emitter and the third emitter were not present and only the second emitter were present; When the first emitter is not present and only the second emitter and the third emitter are present, the light emitted from the second emitter and the third emitter has two modes corresponding to a fundamental mode. If the mode having a smaller propagation constant is defined as a third mode and the mode having a larger propagation constant is defined as a fourth mode, When the thickness of the third emitter is smaller than the thickness of the second emitter, F ０３ (θ) is the far-field pattern of the third mode, F ０４ (θ) is the far field pattern of the fourth mode, When the thickness of the third emitter is greater than the thickness of the second emitter, F ０３ (θ) is the far-field pattern of the fourth mode, F ０４ (θ) is the far field pattern of the third mode.

9. A first element portion; a second element portion stacked on the first element portion along a stacking direction, The first element portion is a first emitter including a first active layer and a pair of first guide layers sandwiching the first active layer, the first emitter emitting light along an optical axis direction; a pair of first cladding layers sandwiching the pair of first guide layers; The second element portion is a second emitter that is stacked on the first emitter along a stacking direction, includes a second active layer and a pair of second guide layers sandwiching the second active layer, and emits light along the optical axis direction; a pair of second cladding layers sandwiching the pair of second guide layers; a thickness of the first emitter is different from a thickness of the second emitter such that an index P represented by formula (6) is 25 or more; A semiconductor laser device, wherein an absolute difference between a thickness of the first emitter and an average value of thicknesses of the first emitter and the second emitter is 10% or less of the average value. [006] In the formula (6), β １ is the propagation constant of the first emitter, and β ２ is the propagation constant of the second emitter, K １２ is a coupling constant between the first emitter and the second emitter when the thickness of each of the first emitter and the second emitter is assumed to be equal to the average thickness of the first emitter and the second emitter.

10. A first element portion; a second element portion stacked on the first element portion along a stacking direction; A substrate; The first element portion is a first emitter including a first active layer and a pair of first guide layers sandwiching the first active layer, the first emitter emitting light along an optical axis direction; a pair of first cladding layers sandwiching the pair of first guide layers; The second element portion is a second emitter including a second active layer and a pair of second guide layers sandwiching the second active layer, the second emitter emitting light along the optical axis direction; a pair of second cladding layers sandwiching the pair of second guide layers; a thickness of the first emitter is different from a thickness of the second emitter such that an average value of an index DB1 expressed by formula (1) and an index DB2 expressed by formula (2) is 5% or less; the first emitter and the second emitter are stacked on the substrate such that the first emitter is located on a first side closer to the substrate than the second emitter; A semiconductor laser device, wherein a thickness of the first emitter is thinner than a thickness of the second emitter. [0070] [0080] In the formulas (1) and (2), θ is an angle with respect to the optical axis direction, and F １ (θ), F ２ (θ), F ０１ (θ) and F ０２ (θ) is the normalized far-field pattern in the stacking direction, F １ (θ) is the far field pattern of light emitted from the first emitter assuming that the second emitter is not present and only the first emitter is present, F ２ (θ) is the far field pattern of light emitted from the second emitter if the first emitter were not present and only the second emitter were present; When only the first emitter and the second emitter are present, the light emitted from the first emitter and the second emitter has two modes corresponding to a fundamental mode. If the mode having a smaller propagation constant is defined as a first mode and the mode having a larger propagation constant is defined as a second mode, When the thickness of the first emitter is smaller than the thickness of the second emitter, F ０１ (θ) is the far-field pattern of the first mode, F ０２ (θ) is the far field pattern of the second mode, When the thickness of the first emitter is greater than the thickness of the second emitter, F ０１ (θ) is the far-field pattern of the second mode, F ０２ (θ) is the far field pattern of the first mode.

11. A semiconductor laser element; a mount member on which the semiconductor laser element is mounted, The semiconductor laser element is A first element portion; a second element portion stacked on the first element portion along a stacking direction; A substrate; The first element portion is a first emitter including a first active layer and a pair of first guide layers sandwiching the first active layer, the first emitter emitting light along an optical axis direction; a pair of first cladding layers sandwiching the pair of first guide layers; The second element portion is a second emitter including a second active layer and a pair of second guide layers sandwiching the second active layer, the second emitter emitting light along the optical axis direction; a pair of second cladding layers sandwiching the pair of second guide layers; a thickness of the first emitter is different from a thickness of the second emitter such that an average value of an index DB1 expressed by formula (1) and an index DB2 expressed by formula (2) is 5% or less; the first emitter and the second emitter are stacked on the substrate such that the first emitter is located on a first side closer to the substrate than the second emitter; the semiconductor laser element is fixed to the mount member at a second side opposite to the first side, the mounting member has a thermal expansion coefficient greater than the thermal expansion coefficient of the substrate; A laser module, wherein a thickness of the first emitter is greater than a thickness of the second emitter. [0097] [0010] In the formulas (1) and (2), θ is an angle with respect to the optical axis direction, and F １ (θ), F ２ (θ), F ０１ (θ) and F ０２ (θ) is the normalized far-field pattern in the stacking direction, F １ (θ) is the far field pattern of light emitted from the first emitter assuming that the second emitter is not present and only the first emitter is present, F ２ (θ) is the far field pattern of light emitted from the second emitter if the first emitter were not present and only the second emitter were present; When only the first emitter and the second emitter are present, the light emitted from the first emitter and the second emitter has two modes corresponding to a fundamental mode. If the mode having a smaller propagation constant is defined as a first mode and the mode having a larger propagation constant is defined as a second mode, When the thickness of the first emitter is smaller than the thickness of the second emitter, F ０１ (θ) is the far-field pattern of the first mode, F ０２ (θ) is the far field pattern of the second mode, When the thickness of the first emitter is greater than the thickness of the second emitter, F ０１ (θ) is the far-field pattern of the second mode, F ０２ (θ) is the far field pattern of the first mode.

12. A first element portion; a second element portion stacked on the first element portion along a stacking direction; A substrate; The first element portion is a first emitter including a first active layer and a pair of first guide layers sandwiching the first active layer, the first emitter emitting light along an optical axis direction; a pair of first cladding layers sandwiching the pair of first guide layers; The second element portion is a second emitter that is stacked on the first emitter along a stacking direction, includes a second active layer and a pair of second guide layers sandwiching the second active layer, and emits light along the optical axis direction; a pair of second cladding layers sandwiching the pair of second guide layers; a thickness of the first emitter is different from a thickness of the second emitter such that an index P represented by formula (6) is 25 or more; the first emitter and the second emitter are stacked on the substrate such that the first emitter is located on a first side closer to the substrate than the second emitter; A semiconductor laser device, wherein a thickness of the first emitter is thinner than a thickness of the second emitter. ##EQU00011## In the formula (6), β １ is the propagation constant of the first emitter, and β ２ is the propagation constant of the second emitter, K １２ is a coupling constant between the first emitter and the second emitter when the thickness of each of the first emitter and the second emitter is assumed to be equal to the average thickness of the first emitter and the second emitter.

13. A semiconductor laser element; a mount member on which the semiconductor laser element is mounted, The semiconductor laser element is A first element portion; a second element portion stacked on the first element portion along a stacking direction; A substrate; The first element portion is a first emitter including a first active layer and a pair of first guide layers sandwiching the first active layer, the first emitter emitting light along an optical axis direction; a pair of first cladding layers sandwiching the pair of first guide layers; The second element portion is a second emitter that is stacked on the first emitter along a stacking direction, includes a second active layer and a pair of second guide layers sandwiching the second active layer, and emits light along the optical axis direction; a pair of second cladding layers sandwiching the pair of second guide layers; a thickness of the first emitter is different from a thickness of the second emitter such that an index P represented by formula (6) is 25 or more; the first emitter and the second emitter are stacked on the substrate such that the first emitter is located on a first side closer to the substrate than the second emitter; the semiconductor laser element is fixed to the mount member at a second side opposite to the first side, the mounting member has a thermal expansion coefficient greater than the thermal expansion coefficient of the substrate; A laser module, wherein a thickness of the first emitter is greater than a thickness of the second emitter. ##EQU00012## In the formula (6), β １ is the propagation constant of the first emitter, and β ２ is the propagation constant of the second emitter, K １２ is a coupling constant between the first emitter and the second emitter when the thickness of each of the first emitter and the second emitter is assumed to be equal to the average thickness of the first emitter and the second emitter.

14. A semiconductor laser element according to claim 10 or 12, a mount member on which the semiconductor laser element is mounted, the semiconductor laser element is fixed to the mount member at a second side opposite to the first side, A laser module, wherein the mount member has a thermal expansion coefficient smaller than that of the substrate.

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