A semiconductor laser

Abstract

The application relates to the technical field of lasers, in particular to a semiconductor laser, which comprises a first laser module, a first light beam conversion lens, a first slow-axis conversion lens, a first volume Bragg grating and a half-wave plate arranged in sequence along a first light beam path; a second laser module, a second light beam conversion lens, a second slow-axis conversion lens and a second volume Bragg grating arranged in sequence along a second light beam path; a polarization beam splitter prism located at the intersection of the first light beam path and the second light beam path; and a third volume Bragg grating located on the side of the polarization beam splitter prism away from the half-wave plate; wherein the diffraction efficiency of the first volume Bragg grating is lower than that of the third volume Bragg grating, and the central wavelength of the first volume Bragg grating is the same as that of the third volume Bragg grating. The application is at least beneficial to inhibiting multimode resonance effect, improving the side mode suppression ratio and improving the spectral purity after line width narrowing.

Description

Technical Field

[0001] This invention belongs to the field of laser technology, and particularly relates to a semiconductor laser. Background Technology

[0002] High-power narrow-linewidth semiconductor lasers, with their high output power, sub-nanometer-level extremely narrow linewidth, good wavelength stability, and power stability, are widely used in pump fiber lasers, gas lasers, and disk lasers, playing an irreplaceable role in many fields such as laser processing and medical health.

[0003] Currently, external cavity feedback structures based on volume Bragg gratings are the main technical route for achieving linewidth narrowing and spectral locking in high-power semiconductor lasers. A freely rotating semiconductor laser is collimated and incident on a volume Bragg grating. A volume Bragg grating based on a specific diffraction center wavelength can significantly increase the optical gain at that wavelength. Under mode competition, a narrow linewidth laser output can ultimately be achieved. This structure can achieve good linewidth narrowing and spectral locking effects for semiconductor lasers with single emission units. However, for high-power, multi-emission unit Bar-strip semiconductor lasers, the Smile effect can easily lead to multimode resonance, reducing the side-mode suppression ratio and affecting the spectral purity after linewidth narrowing, ultimately impacting pump efficiency.

[0004] For high-power semiconductor lasers with bar structures, due to the effects of epitaxial growth and packaging stress, the multiple light-emitting units on the bar are no longer in an ideal straight line after being packaged into the heat sink. They are prone to significant bending, and there are positional differences among the light-emitting points, known as the Smile effect. The Smile effect increases the off-axis phase difference along the fast axis. As the Smile effect increases, the divergence angle of the laser along the fast axis direction will increase significantly, leading to a deterioration in the beam quality along the fast axis direction. This situation will seriously affect the spectral characteristics of the external cavity feedback semiconductor laser. The Smile effect causes the angles at which different light-emitting units on the bar are incident on the bulk Bragg to be different. Therefore, these light-emitting points generate different resonant wavelengths in the external cavity feedback structure. Although it still results in spectral narrowing, it will produce multimode resonance, with significant side-mode effects, affecting the purity of the spectrum after linewidth narrowing, reducing the side-mode suppression ratio, thus affecting the pump efficiency, bringing more ineffective waste heat to the system, and affecting the reliability of the laser system. Summary of the Invention

[0005] In view of this, the present invention aims to provide a semiconductor laser that at least helps to suppress multimode resonance effects, improve side-mode suppression ratio, and improve spectral purity after linewidth narrowing.

[0006] To achieve the above objectives, the technical solution created by this invention is implemented as follows:

[0007] This invention provides a semiconductor laser, comprising: a first laser module, a first beam conversion lens, a first slow-axis conversion lens, a first volume Bragg grating, and a half-wave plate arranged sequentially along a first beam path; a second laser module, a second beam conversion lens, a second slow-axis conversion lens, and a second volume Bragg grating arranged sequentially along a second beam path; a polarizing beam splitter located at the intersection of the first and second beam paths; and a third volume Bragg grating located on the side of the polarizing beam splitter away from the half-wave plate; wherein the first and second laser modules are both multi-emitting unit Bar strip structures, the first and second volume Bragg gratings are identical, the diffraction efficiency of the first volume Bragg grating is lower than that of the third volume Bragg grating, and the center wavelength of the first and third volume Bragg gratings are the same.

[0008] Furthermore, the diffraction efficiency of the first-body Bragg grating is in the range of 7% to 13%.

[0009] Furthermore, the diffraction efficiency of the third-body Bragg grating is in the range of 92% to 98%.

[0010] Furthermore, the first laser module emits first linearly polarized light, which includes P-polarized light and S-polarized light. In the first linearly polarized light, the degree of polarization of the P-polarized light is greater than that of the S-polarized light. The first linearly polarized light sequentially passes through a first beam conversion lens, a first slow-axis conversion lens, and a first volume Bragg grating to achieve spectral locking and linewidth narrowing. It then passes through a half-wave plate to convert the degree of polarization, forming first converted linearly polarized light. In the first converted linearly polarized light, the degree of polarization of the S-polarized light is greater than that of the P-polarized light. The S-polarized light in the first converted linearly polarized light is reflected by a polarizing beam splitter and then directed towards the third optical path. The P-polarized light in the first converted linearly polarized light is transmitted through a polarizing beam splitter and then directed towards the third volume Bragg grating. The third volume Bragg grating reflects the P-polarized light in the first converted linearly polarized light back to the first beam path to suppress laser self-excitation. The second laser module... The first beam emits a second linearly polarized light, which includes P-polarized light and S-polarized light. The second linearly polarized light is the same as the first linearly polarized light. After passing through a second beam conversion lens, a second slow-axis conversion lens, and a second volume Bragg grating in sequence, the second linearly polarized light achieves spectral locking and linewidth narrowing, forming a second converted linearly polarized light. In the second converted linearly polarized light, the degree of polarization of the P-polarized light is greater than that of the S-polarized light. The S-polarized light in the second converted linearly polarized light is reflected by a polarizing beam splitter and then directed towards a third volume Bragg grating. The P-polarized light in the second converted linearly polarized light is transmitted through a polarizing beam splitter and then directed towards a third optical path. The third volume Bragg grating reflects the S-polarized light in the second converted linearly polarized light back to the second beam path to suppress the laser self-excitation effect. The S-polarized light in the first converted linearly polarized light and the P-polarized light in the second converted linearly polarized light are combined to form the output beam.

[0011] Furthermore, the center wavelengths of both the first laser module and the second laser module are in the range of 777nm to 783nm, and the center wavelength of the first volume Bragg grating is in the range of 779.9nm to 780.1nm.

[0012] Furthermore, the thickness of the first-body Bragg grating is no greater than the thickness of the third-body Bragg grating.

[0013] Furthermore, the thickness of both the first-body Bragg grating and the third-body Bragg grating is 3 mm.

[0014] Compared with existing technologies, the present invention achieves the following beneficial effects: The semiconductor laser provided by the present invention, based on an external cavity feedback combining a low-diffraction-efficiency volume Bragg grating and a high-diffraction-efficiency volume Bragg grating, can effectively suppress the multimode resonance effect under the external cavity feedback structure, improve the side-mode suppression ratio, and improve the spectral purity after linewidth narrowing. Specifically, the present invention collimates two freely rotating semiconductor laser beams (a first linearly polarized beam and a second linearly polarized beam) through a beam conversion lens and a slow-axis conversion lens, respectively, and then incident them onto a low-diffraction-efficiency volume Bragg grating to achieve spectral locking and linewidth narrowing without crosstalk between them. Furthermore, combining the linear polarization characteristics of semiconductor lasers, by introducing a polarization beam splitter and a half-wave plate, the polarization state in the first converted linearly polarized beam is converted, resulting in a higher polarization state in the first converted linearly polarized beam. In this system, the S-polarized light dominates. Thus, after the first converted linearly polarized light is incident on the polarization beam splitter, the dominant S-polarized light is reflected into the three optical paths. The dominant P-polarized light in the second converted linearly polarized light, after passing through the polarization beam splitter, combines with the dominant S-polarized light to form a high-power output beam. Furthermore, the S-polarized light in the second converted linearly polarized light and the P-polarized light in the first converted linearly polarized light are incident on a high-diffraction-efficiency volume Bragg grating (a third-body Bragg grating). The high-diffraction-efficiency volume Bragg grating feeds this portion of the laser back into the laser cavity, suppressing other spectra outside the main peak, thereby suppressing multimode resonance, improving the side-mode suppression ratio, and increasing the spectral purity after linewidth narrowing. This results in better spectral locking, improved pump efficiency, reduced ineffective waste heat generated by the pump light, and ultimately, improved reliability of the laser system. Attached Figure Description

[0015] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0016] Figure 1 This is a schematic diagram of the structure of the semiconductor laser described in an embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0019] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0021] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] refer to Figure 1This invention provides a semiconductor laser, comprising: a first laser module 11, a first beam switching lens 12, a first slow-axis switching lens 13, a first volume Bragg grating 14, and a half-wave plate 15 arranged sequentially along a first beam path; a second laser module 21, a second beam switching lens 22, a second slow-axis switching lens 23, and a second volume Bragg grating 24 arranged sequentially along a second beam path; a polarizing beam splitter 16 located at the intersection of the first and second beam paths; and a third volume Bragg grating 17 located at the polarizing beam splitter 16. On the side away from the half-wave plate 15; wherein, the first laser module 11 and the second laser module 21 are both multi-emitting unit Bar strip structures, the first body Bragg grating 14 and the second body Bragg grating 24 are the same, the diffraction efficiency of the first body Bragg grating 14 is lower than that of the third body Bragg grating 17, the diffraction efficiency of the second body Bragg grating 24 is lower than that of the third body Bragg grating 17, and the center wavelength of the first body Bragg grating 14 is the same as that of the third body Bragg grating 17, and the center wavelength of the second body Bragg grating 24 is the same as that of the third body Bragg grating 17. The center wavelengths of the low-diffraction-efficiency body Bragg grating and the high-diffraction-efficiency body Bragg grating must be the same because: only when the center wavelengths are the same will the center wavelength of the laser after wavelength locking be consistent; otherwise, two center wavelengths will be generated, resulting in spectral linewidth broadening and affecting the purity of the spectrum.

[0023] The first laser module 11 and the second laser module 21 are both used to output laser light. The first beam conversion lens 12 and the second beam conversion lens 22 are the same, and their function is to rotate the laser beam by 90° to achieve the interchange of the fast axis and the slow axis, and at the same time to collimate the laser fast axis divergence angle. The first slow axis collimating lens and the second slow axis collimating lens are the same, and their function is to collimate the laser slow axis divergence angle. The first volume Bragg grating 14 and the second volume Bragg grating 24 are mainly used for external cavity feedback for high-power lasers to achieve linewidth narrowing and optimize spectral characteristics. The half-wave plate 15 is used to adjust the linear polarization degree of the laser. The polarization beam splitter prism 16 is used to achieve polarization separation of the beam, which can achieve the effect of P-polarized beam transmission and S-polarized beam reflection. The third volume Bragg grating 17 is used to narrow the spectral linewidth. The third volume Bragg grating 17 is mainly used for external cavity feedback for low-power lasers to achieve linewidth narrowing and optimize spectral characteristics.

[0024] In some embodiments, the first laser module 11 is a single bar structure, which may have 19 laser emitting units with a period of 500 μm between the laser emitting units. The second laser module 21 has the same structure as the first laser module 11.

[0025] Furthermore, the diffraction efficiency of the first-body Bragg grating 14 is in the range of 7% to 13%.

[0026] Furthermore, the diffraction efficiency of the third-body Bragg grating 24 is in the range of 92% to 98%.

[0027] Furthermore, the first laser module 11 emits first linearly polarized light, which includes P-polarized light and S-polarized light. In the first linearly polarized light, the degree of polarization of the P-polarized light is greater than that of the S-polarized light. The first linearly polarized light passes sequentially through the first beam conversion lens 12, the first slow-axis conversion lens 13, and the first volume Bragg grating 14 to achieve spectral locking and linewidth narrowing. Then, it passes through the half-wave plate 15 to convert the degree of polarization, forming first converted linearly polarized light. In the first converted linearly polarized light, the degree of polarization of the S-polarized light is greater than that of the P-polarized light. The S-polarized light in the first converted linearly polarized light is reflected by the polarizing beam splitter 16 and then directed towards the third optical path. The P-polarized light in the first converted linearly polarized light is transmitted through the polarizing beam splitter 16 and then directed towards the third volume Bragg grating 17. The third volume Bragg grating 17 reflects the P-polarized light in the first converted linearly polarized light back to the first beam path to suppress the laser self-lasing effect and thus improve spectral purity. The second laser... Optical module 21 emits second linearly polarized light, which includes P-polarized light and S-polarized light. The first linearly polarized light is the same as the second linearly polarized light. The second linearly polarized light passes through the second beam conversion lens 22, the second slow-axis conversion lens 23, and the second volume Bragg grating 24 in sequence to achieve spectral locking and linewidth narrowing, forming second converted linearly polarized light. In the second converted linearly polarized light, the degree of polarization of the P-polarized light is greater than that of the S-polarized light. The S-polarized light in the second converted linearly polarized light is reflected by the polarizing beam splitter 16 and then directed to the third volume Bragg grating 17. The P-polarized light in the second converted linearly polarized light is transmitted through the polarizing beam splitter 16 and then directed to the third optical path. The third volume Bragg grating 17 reflects the S-polarized light in the second converted linearly polarized light back to the second beam path to suppress the laser self-excitation effect and thus improve spectral purity. The S-polarized light in the first converted linearly polarized light and the P-polarized light in the second converted linearly polarized light are combined to form the output beam.

[0028] In some embodiments, in the first linearly polarized light, the degree of polarization of the P-polarized light is 95% and the degree of polarization of the S-polarized light is 5%; in the second linearly polarized light, the degree of polarization of the P-polarized light is 95% and the degree of polarization of the S-polarized light is 5%.

[0029] It is understandable that although the first laser module 11 and the second laser module 21 exhibit linearly polarized light characteristics, they are a superposition of P-polarization and S-polarization states. Although the P-polarization state is dominant, the S-polarization state still exists.

[0030] Furthermore, the center wavelength of the first laser module 11 and the center wavelength of the second laser module 21 are both in the range of 777nm~783nm, and the center wavelength of the first volume Bragg grating 14 is in the range of 779.9nm~780.1nm.

[0031] In some embodiments, the spectral linewidth of the first laser module 11 is in the range of 4.6 nm to 5.2 nm, the divergence angle of the fast axis of the first linearly polarized light is in the range of 30° to 60°, and the divergence angle of the slow axis is in the range of 8° to 12°. Since the volume Bragg grating has angular selectivity, a smaller laser divergence angle is beneficial to obtaining a better spectral locking effect. Therefore, the divergence angle needs to be collimated before it is incident on the volume Bragg grating. Specifically, the beam is rotated 90° by a beam conversion lens with a focal length of 0.41 mm to realize the interchange of the fast axis and slow axis beams, and the fast axis divergence angle of the beam is collimated at the same time. Then, the slow axis divergence angle of the beam is collimated by a slow axis collimating lens with a focal length of 14 mm. After collimation, the divergence angles in both directions can reach the order of 10 mrad.

[0032] Furthermore, the thickness of the first volume Bragg grating 14 is no greater than the thickness of the third volume Bragg grating 17. This is because a thicker volume Bragg grating results in a narrower spectral linewidth after linewidth reduction, which is beneficial for achieving better spectral locking. The function of a high-diffraction-efficiency volume Bragg grating is to provide external cavity feedback for other spectra outside the main peak, suppressing multimode resonance effects, improving the side-mode suppression ratio, and enhancing the spectral purity after linewidth reduction, thereby achieving better spectral locking. When its thickness is lower than that of a low-diffraction-efficiency volume Bragg grating, the locked spectral linewidth will be wider, thus affecting the overall spectral linewidth narrowing effect.

[0033] Furthermore, the thickness of the first-body Bragg grating 14 and the thickness of the third-body Bragg grating 17 are both 3 mm.

[0034] This invention is beneficial for improving the side-mode suppression ratio, enhancing spectral purity, achieving better spectral locking, increasing pump efficiency, reducing ineffective waste heat generated by pump light, and ultimately improving the reliability of the laser system, thereby achieving an overall enhancement of laser reliability.

[0035] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0036] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A semiconductor laser, characterized in that, include: The first laser module, the first beam conversion lens, the first slow-axis conversion lens, the first volume Bragg grating, and the half-wave plate are arranged sequentially along the first beam path. The second laser module, the second beam conversion lens, the second slow-axis conversion lens, and the second volume Bragg grating are arranged sequentially along the second beam path. A polarizing beam splitter, wherein the polarizing beam splitter is located at the intersection of the first beam path and the second beam path; A third-body Bragg grating is located on the side of the polarizing beam splitter away from the half-wave plate; The first laser module emits first linearly polarized light, which includes P-polarized light and S-polarized light. In the first linearly polarized light, the degree of polarization of the P-polarized light is greater than that of the S-polarized light. The second laser module emits second linearly polarized light, which also includes P-polarized light and S-polarized light. The second linearly polarized light is the same as the first linearly polarized light. In the first linearly polarized light, the degree of polarization of the P-polarized light is 95%, and the degree of polarization of the S-polarized light is 5%. In the second linearly polarized light, the degree of polarization of the P-polarized light is 95%, and the degree of polarization of the S-polarized light is 5%. The function of the first beam switching lens and the second beam switching lens is to rotate the laser beam by 90° to achieve the interchange of the fast axis and the slow axis, and to collimate the divergence angle of the laser fast axis. Both the first and second laser modules are multi-emitting unit Bar structures. The first and second bulk Bragg gratings are identical. The diffraction efficiency of the first bulk Bragg grating is lower than that of the third bulk Bragg grating, and the center wavelengths of the first and third bulk Bragg gratings are the same. The diffraction efficiency of the first bulk Bragg grating is in the range of 7% to 13%, and that of the third bulk Bragg grating is in the range of 92% to 98%. The first and second bulk Bragg gratings achieve linewidth narrowing, while the third bulk Bragg grating is a high-diffraction-efficiency bulk Bragg grating. The function of the high-diffraction-efficiency bulk Bragg grating is to provide external cavity feedback for other spectra outside the main peak, suppress multimode resonance effects, improve the side-mode suppression ratio, and improve the spectral purity after linewidth narrowing.

2. The semiconductor laser according to claim 1, characterized in that, The first linearly polarized light sequentially passes through a first beam conversion lens, a first slow-axis conversion lens, and a first volume Bragg grating to achieve spectral locking and linewidth narrowing. Then, it passes through a half-wave plate to convert the degree of polarization, forming the first converted linearly polarized light. In the first converted linearly polarized light, the degree of polarization of the S-polarized light is greater than that of the P-polarized light. The S-polarized light in the first converted linearly polarized light is reflected by the polarization beam splitter and then directed towards the third optical path. The P-polarized light in the first converted linearly polarized light is transmitted through the polarization beam splitter and then directed towards the third volume Bragg grating. The third volume Bragg grating reflects the P-polarized light in the first converted linearly polarized light back to the first beam path to suppress the laser self-emission effect. The second linearly polarized light passes sequentially through the second beam conversion lens, the second slow-axis conversion lens, and the second volume Bragg grating to achieve spectral locking and linewidth narrowing, forming the second converted linearly polarized light. In the second converted linearly polarized light, the polarization degree of the P-polarized light is greater than that of the S-polarized light. The S-polarized light in the second converted linearly polarized light is reflected by the polarization beam splitter and then directed towards the third volume Bragg grating. The P-polarized light in the second converted linearly polarized light is transmitted through the polarization beam splitter and then directed towards the third optical path. The third volume Bragg grating reflects the S-polarized light in the second converted linearly polarized light back to the second beam path to suppress the laser self-emission effect. The S-polarized light in the first converted linearly polarized light and the P-polarized light in the second converted linearly polarized light are combined to form an output beam.

3. The semiconductor laser according to claim 1, characterized in that, The center wavelengths of the first laser module and the second laser module are both in the range of 777nm to 783nm, and the center wavelength of the first volume Bragg grating is in the range of 779.9nm to 780.1nm.

4. The semiconductor laser according to claim 1, characterized in that, The thickness of the first body Bragg grating is not greater than the thickness of the third body Bragg grating.

5. The semiconductor laser according to claim 4, characterized in that, The thickness of the first body Bragg grating and the thickness of the third body Bragg grating are both 3 mm.

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