Semiconductor laser device and method for manufacturing a semiconductor laser device

Abstract

The semiconductor laser device (1A, 1B, 1C) comprises two semiconductor laser elements (6, 8) that emit laser light with mutually different oscillation wavelengths and mutually orthogonal polarizations, a birefringent crystal (3) into which the laser light emitted by the two semiconductor laser elements (6, 8) is incident in parallel, and which is arranged with its crystal axis tilted with respect to the optical axis of the laser light, and a lens (2) that focuses the laser light that has passed through the crystal (3) externally.

Description

Technical Field

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

[0002] Conventionally, as a method for multiplexing laser beams of different wavelengths and outputting them coaxially in a semiconductor laser device, Patent Document 1 discloses that a multiplexer called MMI (Multi-Mode Interference) is provided inside a semiconductor optical integrated device. By providing an MMI, laser beams output from laser elements oscillating at different wavelengths are multiplexed by the MMI and can be output coaxially to the outside of the semiconductor optical integrated device. In the technology disclosed in Patent Document 1, an EAM (Electro-Absorption Modulator) is disposed after multiplexing by the MMI, and the laser beam modulated by the EAM is output to the outside of the semiconductor optical integrated device. Prior Art Documents Patent Documents

[0003] Patent Document 1 Japanese Patent No. 7195156 Summary of the Invention Problem to be Solved by the Invention

[0004] However, optical loss occurs when multiplexing is performed using an MMI. Possible causes of the optical loss in the MMI include mode mismatch of the MMI, scattering loss of the MMI, absorption loss of the MMI, and the like. As an example, the loss is approximately 3 dB. Therefore, the laser beam output from each laser element is affected by the loss in the MMI, which poses the problem that the output of the laser element cannot be extracted as it is.

[0005] This disclosure aims to provide a semiconductor laser device that achieves low-loss laser light multiplexing compared to the case using MMI, in order to solve the above-mentioned problems. [Means for solving the problem]

[0006] The semiconductor laser device according to this disclosure comprises two semiconductor laser elements that output laser light with mutually different oscillation wavelengths and mutually orthogonal polarizations; a birefringent crystal into which the laser light output by the two semiconductor laser elements is incident in parallel, and which is arranged with its crystal axis tilted with respect to the optical axis of the laser light; a lens that focuses the laser light that has passed through the crystal externally; a cap; and a stem on which the semiconductor laser elements are arranged. The cap and stem are marked with alignment marks that serve as a reference for assembling the device. The alignment marks on the cap are positioned to indicate the direction of the crystal axis, and by aligning the alignment marks on the stem with the alignment marks on the cap, the relative rotation angle between the cap and the stem is defined, and the relative relationship between the crystal axis and the polarization direction of the laser light is adjusted. ru. [Effects of the Invention]

[0007] According to this disclosure, it is possible to provide a semiconductor laser device that achieves low-loss laser light multiplexing compared to the case using MMI. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a side cross-sectional view of a semiconductor laser device according to Embodiment 1. [Figure 2] Figure 2 is a top view showing a part of the configuration of the semiconductor laser device according to Embodiment 1. [Figure 3] Figure 3 is a side cross-sectional view of the cap according to Embodiment 1. [Figure 4] Figure 4 is a top view of the cap according to Embodiment 1. [Figure 5] Figure 5 is a schematic diagram showing the capping process of a semiconductor laser apparatus according to Embodiment 1. [Figure 6A] Figure 6A is a top view showing an example in which a D-cut is added to the top of the cap according to Embodiment 1. [Figure 6B]Figure 6B is a side cross-sectional view showing an example in which a D-cut is added to the top of the cap according to Embodiment 1. [Figure 7] Figure 7 is a side cross-sectional view of a semiconductor laser apparatus according to Embodiment 2. [Figure 8] Figure 8 is a top view showing a part of the configuration of the semiconductor laser device according to Embodiment 2. [Figure 9] Figure 9 is a side cross-sectional view of the cap according to Embodiment 2. [Figure 10] Figure 10 is a schematic diagram showing the capping process of a semiconductor laser apparatus according to Embodiment 2. [Figure 11] Figure 11 is a side cross-sectional view of a semiconductor laser device according to Embodiment 3. [Figure 12] Figure 12 is a top view showing a part of the configuration of a semiconductor laser device according to Embodiment 3. [Modes for carrying out the invention]

[0009] To provide a more detailed explanation of this disclosure, the forms for implementing this disclosure will be described below with reference to the attached drawings.

[0010] Embodiment 1. Figure 1 is a side cross-sectional view of the semiconductor laser apparatus 1A according to Embodiment 1. Figure 2 is a top view showing a part of the configuration of the semiconductor laser apparatus 1A according to Embodiment 1. The x-axis, y-axis, and z-axis in the figures represent the following directions, respectively.

[0011] x-axis direction: The direction of polarization of the laser light output from the first semiconductor laser element 6, i.e., the direction of vibration of the electric field. Y-axis direction: The direction of polarization of the laser light output from the second semiconductor laser element 8, i.e., the direction of vibration of the electric field. z-axis direction: The direction of the optical axis of the laser beam output from the CAN package to the outside. "CAN package" refers to the small package containing the cap 4 of the semiconductor laser device 1A.

[0012] A semiconductor laser device 1A includes a first semiconductor laser element 6 and a second semiconductor laser element 8, which are two semiconductor laser elements. The first semiconductor laser element 6 and the second semiconductor laser element 8 are designed to oscillate laser beams at mutually different wavelengths, for example, 1550 nm and 1530 nm. Each of the semiconductor laser elements 6 and 8 is bonded to a carrier 5 via a submount 7 serving as a pedestal thereof. The carrier 5 is disposed on the upper surface of a stem 9. The submount 7 and the carrier 5 are made of a material with high thermal conductivity. The carrier 5 has an L-shape when viewed from the +z direction. The light emission point of the first semiconductor laser element 6 and the light emission point of the second semiconductor laser element 8 are arranged in a straight line along the x-axis direction. In the carrier 5 shown in FIG. 2, a recess is provided to accommodate the side surface portion of the second semiconductor laser element 8, thereby providing a structure in which the light emission points are arranged in a straight line along the x-axis direction. Laser beams of mutually different wavelengths, which are respectively parallel along the z-axis direction, are output from the first semiconductor laser element 6 and the second semiconductor laser element 8. In the present disclosure, the meaning of the term "parallel" is not necessarily strictly defined, and it is sufficient that the laser beams are output in an array, enter a subsequent crystal in this state, and fall within a range where the two laser beams are coaxially combined by the walk-off effect of the crystal described later.

[0013] Figure 3 is a side cross-sectional view of the cap 4. The cap 4, crystal 3, and lens 2 are integrally constructed. The cap 4 is cylindrical, and the crystal 3 and lens 2 are held and fixed inside it. This configuration in which the crystal 3 and lens 2 are held and fixed is referred to as "integrally constructed." For the birefringent crystal 3, examples include calcite (CaCO3), quartz (SiO2), yttrium vanadate (YVO4), and rutile (TiO2), but it is not limited to these; any birefringent crystal can be used. The crystal axis of the crystal 3 is positioned at an angle to the z-axis, which is the optical axis of the laser beam. The cap 4 is marked with an alignment mark 11. Figure 4 is a top view of the cap 4. The lens 2 is positioned on the plane of the paper, and the crystal 3 is located in the direction away from the plane of the paper relative to the lens 2. The alignment mark 11 is provided to indicate a plane that includes the optical axis of the laser beam and the crystal axis of the crystal 3. Alignment marks 11 are marked with triangles (△) at both ends of the plane containing the optical axis and crystal axis of cap 4.

[0014] Lens 2 is an optical element with an incident surface and an exit surface, a certain thickness, and is made of glass with a refractive index n, where n is greater than the refractive index of air. Lens 2 is manufactured using common lens manufacturing methods such as polishing or molding. The incident and exit surfaces of lens 2 have anti-reflective coatings formed on their surfaces for the oscillation wavelengths of the semiconductor laser elements 6 and 8. Lens 2 is designed so that the laser light that passes through it is focused outside of cap 4. This couples the laser light to a focal point placed outside cap 4, such as an optical fiber.

[0015] The stem 9 has, on its upper surface, main members constituting the semiconductor laser device 1A such as the carrier 5 and the semiconductor laser elements 6 and 8 disposed. On the other hand, a plurality of pins called leads 10 are disposed on the lower surface thereof. Main members including the submount 7 have electrical terminals such as an anode terminal or a cathode terminal. For example, the electrical terminals and the leads 10 are connected by wires or ribbons that are not shown in the figure. It is possible to electrically access the main members from the outside of the CAN package via the leads 10.

[0016] Next, the operation of the semiconductor laser elements 6 and 8 will be described. When a current is applied to the first semiconductor laser element 6, for example, a TE-polarized laser beam with a wavelength of 1550 nm is output, and the electric field is oriented in a direction (x-axis direction) perpendicular to the traveling direction of the light. When a current is applied to the second semiconductor laser element 8, for example, a TE-polarized laser beam with a wavelength of 1530 nm is output, and the electric field is oriented in a direction (y-axis direction) perpendicular to the traveling direction of the light. Here, since the active layers of the first semiconductor laser element 6 and the second semiconductor laser element 8 are arranged in directions orthogonal to each other, the laser beams output from the respective elements have polarizations orthogonal to each other and enter the crystal 3.

[0017] Among the laser beams incident on the crystal 3, the output beam from the first semiconductor laser element 6, which has an ordinary light component, travels straight through the crystal 3 as it is and is incident on the lens 2. Among the laser beams incident on the crystal 3, the output beam from the second semiconductor laser element 8, which has an extraordinary light component, after being incident on the crystal 3, travels inclined by a predetermined angle, is coaxially coupled with the ordinary light beam, and is incident on the lens 2. The laser beam incident on the lens 2 is two orthogonal laser beams of two different wavelengths, that is, a laser beam having two orthogonally polarized waves with wavelengths of 1550 nm and 1530 nm. The distance d between the two laser beams incident on the crystal 3 and the length L of the crystal 3 in the optical axis direction have the relationship represented by the following mathematical formula (1).

[0018] d=Ltanρ ···(1)

[0019] ρ is called the walk-off angle, and it relates to a phenomenon called walk-off, in which different polarization components propagate in different directions when passing through a birefringent crystal. The walk-off angle represents the angle between the propagation directions of the normal wave and the abnormal wave. This disclosure uses this phenomenon called walk-off in a birefringent crystal 3.

[0020] The laser light input to lens 2 is focused at lens 2 and output coaxially to a focusing target outside cap 4 (not shown), such as an optical fiber, where it is coupled. As a result, laser light with wavelengths of 1530 nm and 1550 nm is generated.

[0021] Next, the effect of the alignment marks 11 on the cap 4 and stem 9 on the assembly process will be explained. Figure 5 is a schematic diagram showing the capping process of the semiconductor laser device 1A. To clearly show the positional relationship between the stem 9 and the cap 4, the semiconductor laser device 1A is shown as a side view during assembly. The capping process is the process of joining the cap 4 to the stem 9. In the process preceding this capping process, components such as the semiconductor laser elements 6 and 8 are pre-mounted on the stem 9. Here, the two light-emitting points of the semiconductor laser elements 6 and 8 are positioned on a straight line connecting the alignment marks 11 pre-mounted on the stem 9, or on a straight line parallel to that line. In the capping process, the cap 4 needs to be joined to the stem 9 after its position or angle has been appropriately adjusted.

[0022] The procedure for recognizing, adjusting, and joining components during the capping process is described below. First, two alignment marks 11 on the cap 4 are recognized by a camera installed in a mounting device (not shown). Next, a straight line is drawn connecting the two recognized alignment marks 11. Similarly, a straight line is drawn connecting the two alignment marks 11 on the stem 9. If the inclinations of these two straight lines differ, the cap 4 is rotated in the θz direction. Rotation adjustment in the θz direction is performed until the straight line connecting the alignment marks 11 on the cap 4 and the straight line connecting the alignment marks 11 on the stem 9 coincide. After the rotation adjustment is complete, the cap 4 is brought closer to the stem 9 and joined to complete the mounting process.

[0023] The relationship between the two laser beams and the crystal 3 inherently requires adjustment, thus necessitating adjustment of the rotation direction of the cap 4. For this reason, active alignment is commonly performed, which involves adjusting the positional relationship with the crystal 3 while actually emitting laser light. However, according to this disclosure, it is possible to adjust the positional relationship between the semiconductor laser elements 6 and 8 and the crystal 3 by mechanical adjustment, thus enabling passive alignment, i.e., alignment without emitting laser light. This simplifies the capping process.

[0024] As described above, according to Embodiment 1, with this configuration, laser light with different oscillation wavelengths output from two semiconductor laser elements 6 and 8 is coaxially coupled by the birefringent crystal 3. The light is then focused by the lens 2 and output to the outside of the CAN package. Since MMI, which was a source of light loss in the prior art, is unnecessary, the technology of this disclosure achieves lower-loss optical coupling compared to cases using MMI. Furthermore, in the capping process, simple assembly using passive alignment is achieved by aligning the alignment marks 11 of the stem 9 and the cap 4. This simplifies the capping process.

[0025] In Embodiment 1, a case was described in which a drive current is applied to both the first semiconductor laser element 6 and the second semiconductor laser element 8 to output laser light of two wavelengths with orthogonal polarization, but the invention is not limited to this. For example, a drive current may be applied only to the first semiconductor laser element 6, or only to the second semiconductor laser element 8. By selectively applying current to either semiconductor laser element, it is possible to output laser light of one wavelength and appropriately select and extract the wavelength of the laser light output coaxially.

[0026] Furthermore, while Embodiment 1 describes a simple configuration example, it is not limited to this. For example, a temperature control mechanism for the semiconductor laser elements 6 and 8 may be provided to stabilize the oscillation wavelength of the laser light output from the semiconductor laser elements 6 and 8. In this case, for example, a Peltier element can be placed between the upper surface of the stem 9 and the member on which the semiconductor laser elements 6 and 8 are mounted, and the semiconductor laser elements 6 and 8 can be stabilized at a predetermined temperature, thereby controlling the oscillation wavelength to be stabilized. In this case, each of the two wavelengths of laser light output from the CAN package can be output with a stable oscillation wavelength.

[0027] Furthermore, although the first embodiment described using a simple configuration for the semiconductor laser elements 6 and 8, it is also possible to use an EML, which is a semiconductor optical integrated element that integrates an EAM and a semiconductor laser that outputs single-wavelength light, such as a distributed feedback semiconductor laser element (DFB-LD: Distributed Feedback Laser Diode: also called a DFB laser). In such a case, modulation operation becomes possible in the EML, making it possible to extract two modulated laser beams of different wavelengths from the CAN package, which opens up possibilities for applications such as optical communication.

[0028] Furthermore, while Embodiment 1 described a case where triangles (△) are placed on both ends of the stem 9 and cap 4 as alignment marks 11, the design is not limited to this shape. For example, any shape such as a circle (○), cross (×), or square (□) can be applied as long as the shape can be visually confirmed by the camera. Alternatively, as shown in Figures 6A and 6B, a shape called a D-cut 12 may be placed on the top of the cap 4. This provides the same alignment effect as the triangle alignment marks 11. Moreover, the design is applicable even if it is not limited to this shape, as long as it can point to the plane containing the optical axis and the crystal axis of the crystal 3.

[0029] Furthermore, while Embodiment 1 described the case where the alignment mark 11 is applied to the stem 9, the invention is not necessarily limited to this, and the alignment mark 11 may also be applied to the lens 2. In this case as well, it is clear that the same effect can be obtained by adjusting and joining the alignment mark 11 applied to the lens 2 and the alignment mark 11 applied to the stem 9.

[0030] Furthermore, while Embodiment 1 describes one example of the assembly process for the cap 4 to the stem 9, it is not limited to this method. To add to this, when adjusting the rotation direction of the stem 9 and the cap 4, a method was described in which straight lines are drawn based on the alignment marks 11 for each, and the angle between these lines is compared to make the adjustment, but it is not necessarily limited to this method.

[0031] Furthermore, while Embodiment 1 described a case where the laser beam is focused by lens 2, the invention is not limited to this. The lens should be designed to produce the appropriate laser beam according to the requirements of the system to which the semiconductor laser device 1A is applied. For example, the beam may be collimated, i.e., made into parallel light. In this case, collimated laser beams of different wavelengths can be output coaxially to the outside of the CAN package.

[0032] Embodiment 2. In Embodiment 2, the following configuration is used to ensure that the laser light output from the two semiconductor laser elements 6 and 8 is incident parallel to the crystal 3 with orthogonal polarization relationships. The active layers of the two semiconductor laser elements 6 and 8 are arranged parallel to the stem 9. A flip-up mirror 14 is used to change the optical path of the laser light output from the semiconductor laser elements 6 and 8 by 90°. A λ / 2 plate 13, i.e., a half-wave plate, is inserted downstream of the optical path of one of the laser beams to rotate the polarization direction by 90°. As a result, the polarization directions become orthogonal to each other and can be incident on the crystal 3. The other configurations and effects are the same as in Embodiment 1.

[0033] Figure 7 is a side cross-sectional view showing an example of the configuration of the semiconductor laser device 1B according to Embodiment 2. Figure 8 is a top view showing a part of the configuration of the semiconductor laser device 1B according to Embodiment 2. In the figures, the x-axis, y-axis, and z-axis directions refer to the following directions, respectively.

[0034] x-axis direction: The direction of the optical axis of the laser beam immediately after it is emitted from the first semiconductor laser element 6. Y-axis direction: A direction perpendicular to both the direction of the optical axis of the laser light immediately after it is emitted from the second semiconductor laser element 8, and the direction of polarization of the laser light, i.e., the direction of vibration of the electric field. z-axis direction: The direction of the optical axis of the laser beam output from the CAN package to the outside.

[0035] The two semiconductor laser elements 6 and 8 each emit lasers at different wavelengths. The semiconductor laser elements 6 and 8 are joined to the stem 9 via a submount 7 that serves as a base. The submount 7 is made of a material with good thermal conductivity. The semiconductor laser elements 6 and 8 are arranged along the x-axis. A flip-up mirror 14 is placed downstream of the optical path of the laser light output from each semiconductor laser element 6 and 8. The flip-up mirror 14 reflects the laser light from the semiconductor laser elements 6 and 8 by 90°. The laser light that has passed through the flip-up mirror 14 travels to the upper side of Figure 7. Also, in Figure 8, the two flipped-up laser beams travel towards the foreground of the paper. Here, each laser beam is incident parallel to the crystal 3.

[0036] Figure 9 is a side cross-sectional view of the cap 4. The cap 4, crystal 3, λ / 2 plate 13, and lens 2 are integrally constructed. The cap 4 is cylindrical, and the crystal 3, λ / 2 plate 13, and lens 2 are pre-held and fixed inside it. The λ / 2 plate 13 is positioned on the optical axis of the laser beam output from the second semiconductor laser element 8 and is used to rotate the polarization direction of the laser beam by 90°.

[0037] Next, we will explain only the differences in the operation of the semiconductor laser elements 6 and 8 compared to Embodiment 1. By applying a current to the first semiconductor laser element 6, laser light with TE polarization, for example, a wavelength of 1550 nm, is output, and the electric field of the light is in a direction perpendicular to the direction of light propagation, i.e., the z-axis direction. By applying a current to the second semiconductor laser element 8, laser light with TE polarization, for example, a wavelength of 1530 nm, is output, and the electric field of the light is in a direction perpendicular to the direction of light propagation, i.e., the z-axis direction. Here, the optical path is folded back by 90° by the flip-up mirror 14 in the subsequent stage, changing the direction of the laser light, and the direction of the electric field of the light becomes the x-axis direction perpendicular to the direction of light propagation. The laser light from the first semiconductor laser element 6 is incident on the crystal 3 in this polarization state and behaves as an ordinary ray, similar to Embodiment 1. On the other hand, the polarization of the laser light from the second semiconductor laser element 8 is rotated by 90° by the λ / 2 plate 13, and the direction of the electric field of the light becomes the y-axis direction perpendicular to the direction of light propagation. In this polarization, the laser light incident on crystal 3 becomes an extraordinary ray, and as an extraordinary ray, it behaves in the same manner as described in Embodiment 1. As a result, laser light with orthogonal polarizations at wavelengths of 1530 nm and 1550 nm, focused by lens 2, is output coaxially.

[0038] Next, we will explain the effect of the alignment marks 11 attached to the cap 4 and stem 9 on the assembly process. Note that we will omit explanations of parts that are common with Embodiment 1 and only explain the differences. Figure 10 is a schematic diagram illustrating an example of the procedure for the capping process of the semiconductor laser apparatus 1B according to Embodiment 2. To clarify the positional relationship between the stem 9 and the cap 4, the semiconductor laser apparatus 1B during assembly is shown as a side view. The capping process is the process of joining the cap 4 to the stem 9. In the previous process, components such as semiconductor laser elements 6 and 8 and a flip-up mirror 14 are already mounted on the stem 9. Here, the laser light emitted from the semiconductor laser elements 6 and 8 and then propagating toward the viewer in the direction of the paper by the flip-up mirror 14 is positioned on a straight line connecting the alignment marks 11 attached to the stem 9 in advance, or on a straight line parallel to that line. In the capping process, the cap 4 needs to be joined to the stem 9 after its position or angle has been appropriately adjusted.

[0039] The procedures for recognizing, adjusting, and joining the components in the capping process are described in the same way as in Embodiment 1. Passive alignment, i.e., alignment can be achieved without emitting laser light, thus simplifying the assembly process.

[0040] As described above, according to Embodiment 2, laser light with different oscillation wavelengths output from two semiconductor laser elements 6 and 8 is coaxially coupled by a birefringent crystal 3. Subsequently, it is focused by the lens 2 and output to the outside of the CAN package. In Embodiment 2 as well, since MMI, which was a source of light loss in the conventional technology, is not required, it has the effect of achieving low-loss optical coupling compared to when MMI is used. Furthermore, in the capping process, by aligning the alignment marks 11 of the stem 9 and the cap 4, simple assembly by passive alignment is achieved. This has the effect of simplifying the assembly process.

[0041] Embodiment 3. In Embodiment 3, the following configuration is used to ensure that the laser light output from the two semiconductor laser elements 6 and 8 is incident parallel to the crystal 3 with orthogonal polarization relationships. The active layers of the two semiconductor laser elements 6 and 8 are arranged parallel to the stem 9, and the positions of the semiconductor laser elements 6 and 8 are perpendicular to the stem 9 so that the laser light output from each semiconductor laser element 6 and 8 is perpendicular to the stem 9. A flip-up mirror 14 is provided downstream of the optical paths of the semiconductor laser elements 6 and 8 to change the optical path of the laser light by 90°. As a result, the polarization directions are orthogonal to each other and the laser light is incident parallel to the crystal 3. Other configurations and effects are the same as in Embodiment 2.

[0042] Figure 11 is a side cross-sectional view of the semiconductor laser apparatus 1C according to Embodiment 3. Figure 12 is a top view showing a part of the configuration of the semiconductor laser apparatus 1C according to Embodiment 3. The x-axis, y-axis, and z-axis in the figures represent the following directions, respectively.

[0043] x-axis direction: The direction of the optical axis of the laser beam immediately after it is emitted from the first semiconductor laser element 6. Y-axis direction: The direction of the optical axis of the laser beam immediately after it is emitted from the second semiconductor laser element 8. z-axis direction: The direction of the optical axis of the laser beam output from the CAN package to the outside.

[0044] The two semiconductor laser elements 6 and 8 each emit lasers at different wavelengths. The semiconductor laser elements 6 and 8 are joined to the stem 9 via a submount 7. The submount 7 is made of a material with good thermal conductivity. The two semiconductor laser elements 6 and 8 are arranged along the x-axis. A flip-up mirror 14 is placed downstream of the optical path of the laser light output from each semiconductor laser element 6 and 8. The flip-up mirror 14 reflects the laser light from the semiconductor laser elements 6 and 8 by 90°. The laser light that has passed through the flip-up mirror 14 travels to the upper side of Figure 11. Also, in Figure 12, the two flipped-up laser beams travel towards the foreground of the paper. Each laser beam is incident parallel to the crystal 3. The cap 4 used in Embodiment 3 is the same as the cap 4 shown in Embodiment 1.

[0045] Next, we will explain the differences in the operation of the semiconductor laser elements 6 and 8 compared to Embodiment 2. By applying a current to the first semiconductor laser element 6, laser light with TE polarization and a wavelength of, for example, 1550 nm is output, and the electric field of the light is in a direction perpendicular to the direction of light propagation, i.e., the z-axis direction. By applying a current to the second semiconductor laser element 8, laser light with TE polarization and a wavelength of, for example, 1530 nm is output, and the electric field of the light is in a direction perpendicular to the direction of light propagation, i.e., the z-axis direction. Here, the optical path is folded back by 90° by the flip-up mirror 14 downstream of the optical path, changing the direction of the laser light. In the case of the laser light from the first semiconductor laser element 6, the direction of the electric field of the light is in the x-axis direction perpendicular to the direction of light propagation, and in the case of the laser light from the second semiconductor laser element 8, the direction is in the y-axis direction perpendicular to the direction of light propagation. The laser light from the first semiconductor laser element 6 behaves as an ordinary ray, similar to Embodiment 1. The laser light from the second semiconductor laser element 8 behaves as an extraordinary ray, similar to Embodiment 1. As a result, focused laser light with orthogonal polarization at wavelengths of 1530 nm and 1550 nm is output coaxially from lens 2.

[0046] Next, we will explain the effect of the alignment marks 11 on the cap 4 and stem 9 on the assembly process. Here again, we will omit explanations of parts that are common with Embodiment 2 and only explain the differences. The capping process between the stem 9 and the cap 4 is the process of joining the cap 4 to the stem 9. The procedures for recognizing, adjusting, and joining the components in the capping process are the same as in Embodiment 1, and passive alignment, that is, alignment can be performed without emitting laser light, thus simplifying the assembly process.

[0047] As described above, according to Embodiment 3, laser light with different oscillation wavelengths output from two semiconductor laser elements 6 and 8 is coaxially coupled by a birefringent crystal 3. The light is then focused by the lens 2 and output to the outside of the CAN package. In Embodiment 3, as in the prior art, MMI, which was a source of light loss, is unnecessary, resulting in lower loss optical coupling compared to cases using MMI. Furthermore, in the capping process, simple assembly is achieved through passive alignment by aligning the alignment marks 11 of the stem 9 and the cap 4. This simplifies the assembly process.

[0048] Within the scope of this disclosure, it is possible to freely combine each embodiment, modify any component of each embodiment, or omit any component in each embodiment. [Industrial applicability]

[0049] This disclosure can be applied to semiconductor laser devices and methods for manufacturing semiconductor laser devices. [Explanation of Symbols]

[0050] 1A, 1B, 1C Semiconductor laser device, 2 Lens, 3 Crystal, 4 Cap, 5 Carrier, 6 First semiconductor laser element, 7 Submount, 8 Second semiconductor laser element, 9 Stem, 10 Lead, 11 Alignment mark, 12 D-cut, 13 λ / 2 plate, 14 Flip-up mirror.

Claims

1. Two semiconductor laser elements that emit laser light with mutually different oscillation wavelengths and mutually orthogonal polarizations, A crystal having birefringence, to which the laser light emitted by two semiconductor laser elements is incident in parallel, and which is arranged such that its crystal axis is tilted with respect to the optical axis of the laser light, A lens that focuses the laser light that has passed through the crystal externally, The cap and The system comprises a stem on which the semiconductor laser element is arranged, Alignment marks are provided on the cap and the stem to serve as a reference for assembling the device. The alignment marks provided on the cap are arranged to indicate the direction of the crystal axis of the crystal. By aligning the alignment mark on the stem with the alignment mark on the cap, the relative rotation angle between the cap and the stem is defined, and the relative relationship between the crystal axis and the polarization direction of the laser light is adjusted. A semiconductor laser device characterized by the following features.

2. The device includes a carrier with a shape that allows the orientations of the active layers of the two semiconductor laser elements to be arranged to be orthogonal to each other. The semiconductor laser apparatus according to claim 1, characterized in that it is a semiconductor laser apparatus.

3. The shape of the aforementioned carrier is L-shaped. The semiconductor laser apparatus according to claim 2, characterized by its features.

4. On the optical path of the laser beam, downstream of the two semiconductor laser elements, is a flip-up mirror that changes the optical path of the laser beam by 90°, For one of the aforementioned laser beams, a λ / 2 plate is provided downstream of the flip-up mirror to change the polarization direction by 90°. The semiconductor laser apparatus according to claim 1, characterized in that it is a semiconductor laser apparatus.

5. The semiconductor laser elements are arranged such that the optical axes of the laser beams are orthogonal to each other. On the optical path of the laser beam, a flip-up mirror is provided downstream of the two semiconductor laser elements to change the optical path of the laser beam by 90°. The semiconductor laser apparatus according to claim 1, characterized in that it is a semiconductor laser apparatus.

6. The alignment marks applied to the stem are provided to indicate a plane that includes the optical axis and the crystal axis of the crystal. A semiconductor laser apparatus according to any one of claims 1 to 5.

7. The aforementioned semiconductor laser element is an EML composed of a DFB laser and an EAM. A semiconductor laser apparatus according to any one of claims 1 to 5.

8. By simultaneously applying a drive current to the two semiconductor laser elements, The lens simultaneously outputs two orthogonal laser beams of two different wavelengths coaxially. A semiconductor laser apparatus according to any one of claims 1 to 5.

9. By applying a drive current to only one of the two semiconductor laser elements, The lens outputs laser light of a single wavelength. A semiconductor laser apparatus according to any one of claims 1 to 5.

10. The lens collimates the laser light to make it parallel. A semiconductor laser apparatus according to any one of claims 1 to 5.

11. A temperature control mechanism is provided to stabilize the oscillation wavelength of the laser light. A semiconductor laser apparatus according to any one of claims 1 to 5.

12. A method for manufacturing a semiconductor laser apparatus according to claim 1, comprising the cap for holding the crystal and the lens, and the stem on which at least the semiconductor laser element is arranged, The cap is joined to the stem using passive alignment. A method for manufacturing a semiconductor laser device, characterized by the following:

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