Laser system, laser and laser output control method

Abstract

The present disclosure provides a kind of laser system, laser and laser output control method, applied to optical technology field.System includes: light source module, light source module is semiconductor laser, for output laser beam, the spectrum of laser beam includes first specified wavelength and second specified wavelength;Body bragg grating, for receiving laser beam, the part of laser beam is diffracted, to obtain the diffraction light of first specified wavelength, and the diffraction light of first specified wavelength is reflected to light source module, also for the part of laser beam is transmitted;Transmission grating, for receiving transmission beam, the part of transmission beam is diffracted, to obtain the diffraction light of second specified wavelength, and the diffraction light of second specified wavelength is reflected to light source module, also for the part of transmission beam is transmitted, the central wavelength of output beam after transmission is first specified wavelength and second specified wavelength.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optics, and particularly relates to a laser system, a laser, and a laser output control method. BACKGROUND

[0002] Dual-wavelength laser is a laser that can simultaneously emit two wavelengths, which can be widely applied to the fields of interference measurement, spectrum analysis, free-space optical communication, nonlinear frequency conversion, and laser medical treatment.

[0003] At present, the output of dual-wavelength laser is mainly achieved in the following ways: 1. A semiconductor laser chip capable of dual-wavelength output is designed and manufactured, which is difficult to achieve and poses challenges to existing semiconductor technology, and is not conducive to large-scale production; 2. Dual-wavelength output is achieved by using a single laser output system with a single feedback cavity, a single laser output system with two feedback cavities, or multiple laser output systems with a single feedback cavity. This method makes the overall structure of the laser complex due to the need to add frequency selection elements and filters; 3. Dual-wavelength laser output is achieved by coupling the beams output by two independent laser output systems with different central wavelengths into one beam, but the spatial mode matching of the two laser output systems is often difficult to achieve in practice.

[0004] It can be seen that the existing methods for achieving dual-wavelength laser output have the defects of complex structure and difficulty in implementation. SUMMARY

[0005] The embodiments of the application aim to provide a laser system, a laser, and a laser output control method, which can achieve dual-wavelength laser output based on an easily integrated structure.

[0006] In a first aspect, the embodiments of the application provide a laser system, which comprises:

[0007] A light source module, configured to output a laser beam, wherein the spectrum of the laser beam comprises a first specified wavelength and a second specified wavelength;

[0008] A volume Bragg grating, configured to receive the laser beam, diffract a part of the laser beam to obtain diffracted light of the first specified wavelength, and reflect the diffracted light of the first specified wavelength to the light source module;

[0009] The volume Bragg grating is further configured to transmit a part of the laser beam, and the central wavelength of the transmitted beam after transmission is the first specified wavelength;

[0010] a transmission grating configured to receive the transmission beam, diffract a portion of the transmission beam to obtain diffracted light of the second designated wavelength, and reflect the diffracted light of the second designated wavelength to the light source module;

[0011] The transmission grating is further configured to transmit a portion of the transmission beam, and a central wavelength of the output beam after transmission is the first designated wavelength and the second designated wavelength.

[0012] In some embodiments, the light source module comprises:

[0013] a semiconductor laser chip configured to emit the laser beam;

[0014] a collimation module comprising a fast-axis collimation lens and a slow-axis collimation lens, the collimation module configured to receive the laser beam and collimate a divergence angle of the laser beam.

[0015] In some embodiments, the system further comprises:

[0016] a temperature control module configured to control a temperature of the volume Bragg grating to change a refractive index of the volume Bragg grating to adjust the first designated wavelength.

[0017] In some embodiments, the system further comprises:

[0018] an angle adjustment module configured to adjust a beam incidence angle of the transmission grating to adjust the second designated wavelength.

[0019] In some embodiments, the beam incidence angle of the transmission grating is a self-collimation diffraction angle of the transmission grating.

[0020] In a second aspect, an embodiment of the present application provides a laser, comprising the laser system provided by the first aspect of the present application.

[0021] In a third aspect, an embodiment of the present application provides a laser output control method, applied to the laser system provided by the first aspect of the present application, and the method comprises:

[0022] controlling the light source module to output a laser beam, a spectrum of the laser beam comprising a first designated wavelength and a second designated wavelength.

[0023] In some embodiments, before the controlling the light source module to output a laser beam, the method further comprises:

[0024] controlling a beam incidence angle of the transmission grating to be a self-collimation diffraction angle of the transmission grating.

[0025] In some embodiments, the laser system further comprises a temperature control module, and the method further comprises:

[0026] controlling the temperature control module to control the temperature of the volume Bragg grating to change the refractive index of the volume Bragg grating to adjust the first specified wavelength.

[0027] In some embodiments, the laser system further comprises an angle adjustment module, and the method further comprises:

[0028] controlling the angle adjustment module to adjust the beam incidence angle of the transmission grating to adjust the second specified wavelength.

[0029] In the embodiments of the present application, the spectrum of the laser beam output by the light source module of the laser system includes a first specified wavelength and a second specified wavelength. After the laser beam output by the light source module is received by the volume Bragg grating in the system, the volume Bragg grating diffracts a part of the received laser beam to obtain diffracted light of the first specified wavelength, and reflects the diffracted light of the first specified wavelength to the light source module to form a first laser resonant cavity, narrows the spectrum of the laser beam output by the light source module, and locks the center wavelength of the transmitted beam that has passed through the volume Bragg grating as the first specified wavelength. The transmitted beam is received by the transmission grating, the transmission grating diffracts a part of the transmitted beam to obtain diffracted light of the second specified wavelength, and reflects the diffracted light of the second specified wavelength to the light source module to form a first laser resonant cavity, narrows the spectrum of the laser beam output by the light source module, and locks another center wavelength of the output beam that has passed through the transmission grating as the second specified wavelength, i.e. the center wavelength of the output beam of the laser system is the first specified wavelength and the second specified wavelength. In this way, the dual-wavelength laser output can be realized based on the structure of "light source module-volume Bragg grating-transmission grating" which is easy to integrate. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a structural schematic diagram of a laser system provided by the embodiments of the present application;

[0031] Figure 2 is another structural schematic diagram of a laser system provided by the embodiments of the present application;

[0032] Figure 3 is a flowchart of a laser output control method provided by the embodiments of the present application. DETAILED DESCRIPTION

[0033] In order to make the application purposes, features and advantages of the present application more obvious and easy to understand, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0034] Please refer to Figure 1 FIG. 1 is a structural schematic diagram of a laser system provided by the embodiments of the present application. The first aspect of the embodiments of the present application provides a laser system 100. The system 100 comprises:

[0035] A light source module 10, the light source module 10 is configured to output a laser beam L1, and the spectrum of the laser beam L1 comprises a first specified wavelength and a second specified wavelength;

[0036] A volume Bragg grating 20, the volume Bragg grating 20 is configured to receive the laser beam L1, diffract a part of the laser beam L1 to obtain diffracted light L2 of the first specified wavelength, and reflect the diffracted light L2 of the first specified wavelength to the light source module 10;

[0037] The volume Bragg grating 20 is further configured to transmit a part of the laser beam L1, and the center wavelength of the transmitted beam L3 after transmission is the first specified wavelength;

[0038] A transmission grating 30, the transmission grating 30 is configured to receive the transmitted beam L3, diffract a part of the transmitted beam L3 to obtain diffracted light L4 of the second specified wavelength, and reflect the diffracted light L4 of the second specified wavelength to the light source module 10;

[0039] The transmission grating 30 is further configured to transmit a part of the transmitted beam L3, and the center wavelength of the output beam L5 after transmission is the first specified wavelength and the second specified wavelength.

[0040] The light source module 10 in the system 100 is configured to output a laser beam L1, and the spectrum of the laser beam L1 comprises two wavelengths that the system 100 needs to output: a first specified wavelength and a second specified wavelength. Specifically, when designing and selecting the light source module 10, a high-power semiconductor light source output device whose output spectrum comprises the first specified wavelength and the second specified wavelength can be selected as the light source module 10.

[0041] In the system 100, the component receiving the laser beam L1 output by the light source module 10 is the volume Bragg grating 20. The volume Bragg grating 20 (VBG) is a new type of grating element. It is formed by causing the refractive index of photosensitive glass to change permanently through the thermal action of ultraviolet light, thereby forming an internal refractive index distribution in the photosensitive glass according to a certain rule.

[0042] The volume Bragg grating 20 is first used to diffract a portion of the laser beam L1 to obtain diffracted light L2 of a first specified wavelength, and reflect the diffracted light L2 of the first specified wavelength to the light source module 10, so that a first resonant cavity is formed between the volume Bragg grating 20 and the light source module 10. The resonant cavity refers to the area in which the laser is reflected back and forth between two "mirrors". In the system 100, the resonant cavity is composed of the light source module 10 and the volume Bragg grating 20. When the laser beam L1 repeatedly reflects in this area, only light of a specific wavelength will be enhanced, which is called "mode competition".

[0043] Under the action of mode competition, the spectrum of the laser beam L1 output by the light source module 10 is compressed, so that the center wavelength of a portion of the laser beam L1, i.e., the transmitted light beam L3 transmitted by the volume Bragg grating 20, is locked to the first specified wavelength. That is, by setting the wavelength of the diffracted light L2 reflected by the volume Bragg grating 20 back to the light source module 10 to be the first specified wavelength, the first center wavelength in the output light beam L5 of the system 100 is locked to the first specified wavelength.

[0044] Specifically, in the embodiment of the present application, the diffracted light L2 reflected by the volume Bragg grating 20 back to the light source module 10 is the -1 order diffracted light of the volume Bragg grating 20. That is, the wavelength of the -1 order diffracted light of the volume Bragg grating 20 is the first specified wavelength required in the output light beam L5 of the system 100. When designing the parameters (grating period number and average refractive index) of the volume Bragg grating 20 and the optical path design (beam incidence angle of the volume Bragg grating 20) of the system 100, the skilled person can proceed according to the following formula:

[0045] λ1=2Λn|cosθ1| (1)

[0046] wherein λ1 is the wavelength of the -1 order diffracted light L2 of the volume Bragg grating 20, θ1 is the beam incidence angle of the volume Bragg grating 20, Λ is the grating period number of the volume Bragg grating 20, and n is the average refractive index of the volume Bragg grating 20.

[0047] The person skilled in the art can understand that, when designing the parameters (grating period number and average refractive index) of the Bragg grating 20 and the optical path design (beam incidence angle of the volume Bragg grating 20) of the system 100, the first specified wavelength is taken as λ1 in formula (1) for design.

[0048] In the system 100, the component receiving the transmitted beam L3 output by the volume Bragg grating 20 is a transmission grating 30. The transmission grating 30 is an optical element for dispersing composite light by using the principle of multi-slit diffraction.

[0049] The transmission grating 30 is first used to diffract a part of the transmitted beam L3 output by the volume Bragg grating 20 to obtain diffracted light L4 of the second specified wavelength, and reflect the diffracted light L4 of the second specified wavelength to the light source module 10, so that a second resonant cavity is formed between the volume Bragg grating 20 and the light source module 10, and in the system 100, the resonant cavity is composed of the light source module 10 and the transmission grating 30.

[0050] Under the action of mode competition, the spectrum of the laser beam L1 output by the light source module 10 is narrowed, so that another center wavelength of the part of the transmitted beam L3, which is transmitted by the transmission grating 30 and is also the output beam L5 of the system 100, is locked as the second specified wavelength. That is, by setting the wavelength of the diffracted light L4 reflected back to the light source module 10 by the transmission grating 30 as the second specified wavelength, the second center wavelength of the output beam L5 of the system 100 is locked as the second specified wavelength. In this way, the center wavelength of the output beam L5 of the system 100 is the first specified wavelength and the second specified wavelength, and the dual-wavelength output of the system 100 is realized.

[0051] Specifically, in the embodiment of the present application, the diffracted light L4 reflected back to the light source module 10 by the transmission grating 30 is the -1 order diffracted light of the transmission grating 30. That is, the wavelength of the -1 order diffracted light L4 of the transmission grating 30 is the second specified wavelength required in the output beam of the system 100. The person skilled in the art can design the parameters (number of grating lines per millimeter) of the transmission grating 30 and the optical path design (beam incidence angle of the transmission grating 30) of the system 100 according to the following formula:

[0052] λ2=2dsinθ2 (2)

[0053] Wherein, λ2 is the wavelength of the -1 order diffracted light of the transmission grating 30, θ2 is the beam incidence angle of the transmission grating 30, and d is the number of grating lines per millimeter of the transmission grating 30.

[0054] The skilled in the art can understand that when designing the parameters (the number of grating lines per millimeter) of the transmission grating 30 and the optical path design (the beam incidence angle of the transmission grating 30) of the system 100, the second specified wavelength is taken as λ2 in formula (2) for design.

[0055] Through the laser system in the above embodiment, the laser beam output by the light source module is received by the volume Bragg grating in the system, the volume Bragg grating diffracts part of the received laser beam to obtain diffracted light of the first specified wavelength, and reflects the diffracted light of the first specified wavelength to the light source module to form a first laser resonant cavity, narrows the spectrum of the laser beam output by the light source module, and locks the center wavelength of the transmission beam transmitted through the volume Bragg grating as the first specified wavelength; the transmission beam is received by the transmission grating, the transmission grating diffracts part of the transmission beam to obtain diffracted light of the second specified wavelength, and reflects the diffracted light of the second specified wavelength to the light source module to form a second laser resonant cavity, narrows the spectrum of the laser beam output by the light source module, and locks another center wavelength of the output beam transmitted through the transmission grating as the second specified wavelength, that is, the center wavelength of the output beam of the high-power dual-wavelength narrow-linewidth semiconductor laser system is the first specified wavelength and the second specified wavelength. In this way, the dual-wavelength laser output can be realized based on the structure of “light source module-volume Bragg grating-transmission grating” which is easy to integrate.

[0056] In some embodiments, the transmission beam L3 transmitted through the volume Bragg grating 20 is the 0-order non-diffracted light of the volume Bragg grating 20, and the output beam L5 transmitted through the transmission grating 30 is the 0-order non-diffracted light of the transmission grating 30, that is, the output power of the volume Bragg grating 20 and the transmission grating 30 is determined by the 0-order non-diffracted light transmittance. Therefore, the volume Bragg grating 20 and the transmission grating 30 can respectively use photothermal refractive glass and high-purity fused quartz material, both of which have low light absorption and can realize high-power dual-wavelength laser output.

[0057] Please refer to Figure 2 , which is another structural schematic diagram of the laser system provided by the embodiment of the present application. In some embodiments, the light source module 10 comprises:

[0058] The semiconductor laser chip 11 is used for emitting a laser beam L1.

[0059] The collimation module comprises a fast-axis collimation lens 12 and a slow-axis collimation lens 13, and is used for receiving the laser beam L1 and collimating the divergence angle of the laser beam L1.

[0060] The light source module 10 includes a semiconductor laser chip 11 and a collimation module. The semiconductor laser chip 11 is used to emit a laser beam L1. At the same time, when the volume Bragg grating 20 and the transmission grating 30 reflect the diffracted light back to the light source module 10, the semiconductor laser chip 11, the volume Bragg grating 20 and the transmission grating 30 respectively form two different resonant cavities.

[0061] Between the light source module 10 and the volume Bragg grating 20, the system 100 also includes a collimation module. The collimation module includes a fast-axis collimating lens 12 and a slow-axis collimating lens 13 for collimating the divergence angle of the laser beam L1. The position of the fast-axis collimating lens 12 corresponds to the position of the semiconductor laser chip 11, and the position of the slow-axis collimating lens 13 corresponds to the position of the fast-axis collimating lens 12. The collimation module can prevent the laser beam L1 output from the semiconductor laser chip 11 from experiencing a certain degree of defocusing and deflection when received by the volume Bragg grating 20, thereby ensuring the stability and efficiency of the system 100 output.

[0062] In some embodiments, both sides of the fast-axis collimating lens 12 and the slow-axis collimating lens 13 are coated with anti-reflection coatings, and both the incident and exit surfaces of the fast-axis collimating lens 12 and the slow-axis collimating lens 13 are coated with anti-reflection coatings.

[0063] In some embodiments, system 100 further includes:

[0064] An angle adjustment module is used to adjust the incident angle of the beam of the transmission grating 30 in order to adjust the second specified wavelength.

[0065] The system 100 includes an angle adjustment module for adjusting the incident angle of the beam of the transmission grating 30. According to the above formula (2), changing the incident angle θ2 of the beam of the transmission grating 30 can achieve the tuning of the wavelength λ2 of the diffracted light of the transmission grating 30. That is, by changing the incident angle of the beam of the transmission grating 30, the adjustment of the second specified wavelength can be achieved.

[0066] Specifically, the angle adjustment module can be a fixture for mounting the transmission grating 30. By adjusting the placement angle of the fixture, the incident angle of the beam of the transmission grating 30 can be changed, thereby achieving the tuning of the wavelength of the diffracted light of the transmission grating 30.

[0067] In some embodiments, the incident angle of the light beam of the transmission grating 30 is the autocollimation diffraction angle of the transmission grating 30.

[0068] When designing the optical path of system 100, or when adjusting the incident angle of the beam of transmission grating 30 using the angle adjustment module, the incident angle of the beam of transmission grating 30 can be designed or adjusted to the autocollimation diffraction angle of transmission grating 30. This allows transmission grating 30 to reflect the -1st order diffracted light L4 back to the light source module 10 along the incident optical path of the beam, reducing the loss of diffracted light of transmission grating 30, ensuring the overall power of system 100, and reducing the design difficulty of the optical path.

[0069] Those skilled in the art will understand that if the optical path design of the system 100 has been completed and the incident angle of the beam of the transmission grating 30 has been determined as the autocollimation diffraction angle of the transmission grating 30, then when the technician uses the angle adjustment module to adjust the incident angle of the beam of the transmission grating 30, the adjustable range is small, that is, the wavelength tuning range is also small, and it will not affect the optical path of the transmission grating 30 reflecting the -1st order diffracted light L4 back to the light source module 10. That is, the transmission grating 30 can still reflect the -1st order diffracted light L4 back to the light source module 10 along the incident optical path of the beam.

[0070] In some embodiments, system 100 further includes:

[0071] The temperature control module is used to control the temperature of the volume Bragg grating 20 to change the refractive index of the volume Bragg grating 20 in order to adjust the first specified wavelength.

[0072] System 100 includes a temperature control module for controlling the temperature of volume Bragg grating 20. As can be seen from the above formula (1), by changing the average refractive index n of volume Bragg grating 20, the wavelength λ1 of the diffracted light L2 of volume Bragg grating 20 can be tuned. Therefore, the temperature of volume Bragg grating 20 can be adjusted by the temperature control module to adjust the average refractive index n of volume Bragg grating 20, thereby achieving the tuning of the wavelength λ1 of the diffracted light of volume Bragg grating 20, that is, achieving the adjustment of the first specified wavelength.

[0073] Specifically, the temperature control module consists of a heating element and a temperature controller. The heating element is mounted on a fixture on which the volume Bragg grating 20 is placed. The temperature of the heating element is adjusted by the temperature controller, which in turn adjusts the temperature of the volume Bragg grating 20, thereby changing the refractive index of the material of the volume Bragg grating 20. This achieves the tuning of the wavelength λ1 of the diffracted light of the transmission grating 30, that is, the adjustment of the first specified wavelength.

[0074] The second aspect of this application provides a laser, which includes the laser system 100 provided in the first aspect of this application.

[0075] The laser provided in the second aspect of this application can achieve all the functions of the laser system 100 described above and achieve the same beneficial effects. To avoid repetition, it will not be described again here.

[0076] Please see Figure 3 This is a flowchart illustrating the laser output control method provided in an embodiment of this application. A third aspect of this application provides a laser output control method applied to the laser system 100 provided in the first aspect of this application. The method includes:

[0077] Step S100: Control the light source module 10 to output a laser beam L1. The spectrum of the laser beam L1 includes a first specified wavelength and a second specified wavelength.

[0078] From the perspective of a technician, when using system 100 to output dual-wavelength laser, it is only necessary to control the light source module 10 to output a laser beam L1 whose spectrum includes a first specified wavelength and a second specified wavelength.

[0079] After the laser beam L1 output by the light source module 10 is received by the volume Bragg grating in the system 100, the volume Bragg grating 20 diffracts a portion of the received laser beam L1 to obtain diffracted light L2 of a first specified wavelength, and reflects the diffracted light L2 of the first specified wavelength back to the light source module 10 to form a first laser resonant cavity, thus narrowing the spectrum of the laser beam L1 output by the light source module 10. The center wavelength of the transmitted beam L3 transmitted through the volume Bragg grating 20 is locked to the first specified wavelength. The transmitted beam L3 is received by the transmission grating 30, which diffracts a portion of the transmitted beam L3 to obtain diffracted light L4 of a second specified wavelength, and reflects the diffracted light L4 of the second specified wavelength back to the light source module 10 to form a second laser resonant cavity, thus narrowing the spectrum of the laser beam L1 output by the light source module 10. The other center wavelength of the output beam L5 transmitted through the transmission grating 30 is locked to the second specified wavelength. That is, the center wavelength of the output beam L5 of the system 100 is the first specified wavelength and the second specified wavelength.

[0080] In some embodiments, before controlling the light source module 10 to output the laser beam L1, the method further includes:

[0081] The incident angle of the beam in the transmission grating 30 is controlled to be the autocollimation diffraction angle of the transmission grating 30.

[0082] In some embodiments, the laser system 100 further includes a temperature control module, and the method further includes:

[0083] The temperature control module controls the temperature of the volume Bragg grating 20 to change the refractive index of the volume Bragg grating 20 in order to adjust the first specified wavelength.

[0084] In some embodiments, the laser system 100 further includes an angle adjustment module, and the method further includes:

[0085] The control angle adjustment module adjusts the incident angle of the beam of the transmission grating 30 to adjust the second specified wavelength.

[0086] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, because according to the present invention, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0087] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0088] The above is a description of the laser system, laser, and laser output control method provided by the present invention. For those skilled in the art, based on the ideas of the embodiments of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A laser system, characterized in that, The system includes: A light source module, which is used to output a laser beam, wherein the spectrum of the laser beam includes a first specified wavelength and a second specified wavelength; A volume Bragg grating is used to receive the laser beam, diffract a portion of the laser beam to obtain diffracted light of the first specified wavelength, and reflect the diffracted light of the first specified wavelength to the light source module. The volume Bragg grating is also used to transmit a portion of the laser beam, and the center wavelength of the transmitted beam after transmission is the first specified wavelength. A transmission grating is used to receive the transmitted light beam, diffract a portion of the transmitted light beam to obtain diffracted light of the second specified wavelength, and reflect the diffracted light of the second specified wavelength to the light source module. The transmission grating is also used to transmit a portion of the transmission beam, and the center wavelength of the output beam after transmission is the first specified wavelength and the second specified wavelength. The incident angle of the beam of the transmission grating is the autocollimation diffraction angle of the transmission grating. A temperature control module is used to control the temperature of the volume Bragg grating to change the refractive index of the volume Bragg grating in order to adjust the first specified wavelength. An angle adjustment module is used to adjust the incident angle of the light beam of the transmission grating in order to adjust the second specified wavelength.

2. The system according to claim 1, characterized in that, The light source module includes: A semiconductor laser chip, wherein the semiconductor laser chip is used to emit the laser beam; The collimation module includes a fast-axis collimating lens and a slow-axis collimating lens. The collimation module is used to receive the laser beam and collimate the divergence angle of the laser beam.

3. A laser, characterized in that, The laser includes the laser system as described in any one of claims 1-2.

4. A laser output control method, characterized in that, Applied to the laser system as described in any one of claims 1-2, the method comprises: The incident angle of the light beam in the transmission grating is controlled to be the autocollimation diffraction angle of the transmission grating; The control light source module outputs a laser beam, the spectrum of which includes a first specified wavelength and a second specified wavelength; The temperature control module controls the temperature of the volume Bragg grating to change the refractive index of the volume Bragg grating in order to adjust the first specified wavelength. The angle adjustment module is controlled to adjust the incident angle of the light beam of the transmission grating in order to adjust the second specified wavelength.

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