Device for maintaining laser transmission efficiency by adjusting VBG crystal through temperature control

Abstract

The invention provides a device for maintaining laser transmission efficiency through temperature control adjustment of a VBG crystal, the VBG crystal and a temperature detector are arranged in a heat conduction structural member, the heat conduction structural member is used for conducting heat with the VBG crystal, and the temperature detector is used for detecting the real-time temperature of the VBG crystal; the TEC unit is used for conducting heat with the heat conducting structural member; the temperature controller is used for receiving the real-time temperature of the VBG crystal and can drive the TEC unit to work according to a received temperature setting instruction; the laser light path unit is used for receiving a laser beam obtained after incident laser irradiates the VBG crystal, and collimating and splitting the laser beam to obtain emergent laser and sampling laser; the photoelectric detector is used for performing power detection on the sampling laser and converting the sampling laser into an electric signal; and the regulation and control unit is used for giving a temperature setting instruction to the temperature controller and selectively regulating the temperature setting instruction according to the electric signal, so that stable output of emergent laser is realized by regulating the temperature of the VBG crystal.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of optical technology, and in particular to a device for temperature control adjustment of VBG crystal to maintain laser transmission efficiency. BACKGROUND

[0002] In modern optical systems, ultra-narrow band spectral filtering technology has become the core link to ensure signal purity. Especially in the fields of quantum precision measurement, atomic physics and optical communication, the noise suppression of laser light source directly determines the system limit performance. Taking neutral atom optical lattice clock as an example (such as ytterbium, strontium atomic system), its stability has reached 10 -18 orders of magnitude, but the broadband background noise of the lattice laser will introduce Hz-level frequency shift through the exchange of Stark effect, which seriously restricts the precision. The volume Bragg grating (VBG) has become an ideal solution to suppress broadband spectral noise because of its high angular selectivity (<200 μrad bandwidth) and GHz-level filtering bandwidth (typical value 10-30 GHz), which generally has a 20 dB / decade roll-off. Such technology is also suitable for scenarios that require extreme spectral purity, such as atomic interferometer and high-resolution molecular spectroscopy.

[0003] Although the theoretical filtering performance of VBG is excellent, its environmental sensitivity has become a fatal shortcoming for engineering application. The Bragg wavelength λ B of VBG is determined by the grating period Λ and the refractive index n of the medium (λ B = 2nΛ), and both n and Λ drift with temperature (typical temperature drift coefficient ≈10 -5 / ℃), and temperature fluctuations will change the diffraction efficiency through thermal expansion / refractive index change, resulting in a dramatic fluctuation in transmission efficiency of the subsequent optical path (such as fiber coupler). This instability is particularly prominent in portable systems that need to run for a long time, such as space optical clocks, mobile atomic interferometers, etc.

[0004] Mechanical adjustment of the incident angle can generally compensate for temperature drift, but this requires the system structure to include moving elements, which not only increases the complexity of the system and reduces the robustness of the system, but also introduces laser pointing offset to the subsequent optical path, affecting the laser transmission efficiency in the subsequent optical path (such as the efficiency of single-mode polarization maintaining fiber coupling). Therefore, developing a non-mechanical method to adjust the dynamic stability of VBG will be the key to its wide application in mobile precision measurement and precision spectroscopy equipment. SUMMARY

[0005] Therefore, in order to at least partially solve at least one of the above-mentioned technical problems, the present disclosure provides a device for temperature control adjustment of VBG crystal to maintain laser transmission efficiency in a non-mechanical manner. In order to achieve the above-mentioned purpose, the technical solution of the present disclosure is as follows:

[0006] According to an embodiment of the present disclosure, a device for maintaining laser transmission efficiency of a VBG crystal by temperature control is provided, comprising: a heat conduction structure, in which a VBG crystal and a temperature detector are arranged, the heat conduction structure being used for heat conduction with the VBG crystal, and the temperature detector being arranged in close contact with the VBG crystal and used for detecting real-time temperature of the VBG crystal; a TEC unit, in contact with an end surface of the heat conduction structure and used for heat conduction with the heat conduction structure; a temperature controller, connected with the temperature detector and the TEC unit, used for receiving the real-time temperature of the VBG crystal detected by the temperature detector, and capable of driving the TEC unit to work according to a received temperature setting instruction; a laser light path unit, used for receiving a laser beam obtained after incident laser irradiates the VBG crystal, and obtaining emergent laser and sampling laser after collimating and beam splitting the laser beam; a photoelectric detector, used for power detection of the sampling laser and conversion of the sampling laser into an electric signal; and a regulation unit, connected with the photoelectric detector and the temperature controller, used for giving a temperature setting instruction to the temperature controller, and capable of adjusting the temperature setting instruction according to the electric signal, so as to realize stable output of the emergent laser by adjusting the temperature of the VBG crystal.

[0007] According to an embodiment of the present disclosure, the laser light path unit comprises: a laser coupler, used for receiving a laser beam obtained after incident laser irradiates the VBG crystal, and coupling the laser beam into a fiber link; a laser collimator, used for outputting the laser beam input by the fiber link as a collimated beam; and a beam splitter, used for splitting the collimated beam into the emergent laser and the sampling laser.

[0008] According to an embodiment of the present disclosure, the temperature controller drives the TEC unit to work according to the real-time temperature value of the VBG crystal and the size of a temperature setting value given by the regulation unit.

[0009] According to an embodiment of the present disclosure, when the real-time temperature value of the VBG crystal is greater than the temperature setting value given by the regulation unit, the temperature controller drives the TEC unit to cool the heat conduction structure, so as to reduce the temperature of the VBG crystal.

[0010] According to an embodiment of the present disclosure, when the real-time temperature value of the VBG crystal is less than the temperature setting value given by the regulation unit, the temperature controller drives the TEC unit to heat the heat conduction structure, so as to increase the temperature of the VBG crystal.

[0011] According to the embodiment of the present disclosure, the device for temperature control and adjustment of VBG crystal to maintain laser transmission efficiency comprises a first working mode. In the first working mode, the regulation unit gives a temperature setting instruction to the temperature controller. After receiving the temperature setting instruction, the temperature controller automatically stabilizes the temperature of the VBG crystal to the set temperature by using the real-time temperature of the VBG crystal detected and fed back by the receiving temperature detector.

[0012] According to the embodiment of the present disclosure, the power of the outgoing laser changes accordingly with the change of the temperature of the VBG crystal. The power information of the outgoing laser is obtained by the photodetector and transmitted to the regulation unit to obtain the working temperature of the VBG crystal when the laser transmission efficiency is the highest.

[0013] According to the embodiment of the present disclosure, the device for temperature control and adjustment of VBG crystal to maintain laser transmission efficiency comprises a second working mode. In the second working mode, the regulation unit obtains a light power error signal according to the preset target outgoing light power and the outgoing light power actually measured by the photodetector, and automatically adjusts the temperature setting instruction to the temperature controller according to the light power error signal, thereby changing the working temperature of the VBG crystal, improving the laser transmission efficiency, and finally stabilizing the actual outgoing light power to the target outgoing light power.

[0014] According to the embodiment of the present disclosure, the VBG crystal is made of photosensitive glass, and the body grating function is realized by periodically modulating the refractive index inside the VBG crystal; the photodetector comprises a photosensitive probe and a transimpedance amplifier, the photosensitive probe converts the optical signal into a current signal, and the transimpedance amplifier converts the current signal into a voltage signal.

[0015] According to the embodiment of the present disclosure, the laser coupler comprises a coupling lens and a single-mode polarization maintaining optical fiber; the laser collimator comprises a collimating lens and a single-mode polarization maintaining optical fiber; the beam splitter can customize the splitting ratio, and the beam splitter adopts a combination of a half-wave plate and a polarization beam splitter, or adopts a non-polarization beam splitter. BRIEF DESCRIPTION OF DRAWINGS

[0016] The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of the embodiments of the present disclosure taken in conjunction with the accompanying drawings, in which:

[0017] Figure 1 The figure is a schematic diagram of the device for temperature control and adjustment of VBG crystal to maintain laser transmission efficiency according to the embodiment of the present disclosure.

[0018] Figure 2 The figure is a schematic diagram of different working modes of the device for temperature control and adjustment of VBG crystal to maintain laser transmission efficiency according to the embodiment of the present disclosure.

[0019] Figure 3 The figure is a schematic diagram of the relationship between the actually measured VBG crystal diffraction efficiency, fiber coupling efficiency and the working temperature of the VBG crystal.

[0020] Figure 4 A schematic diagram of the relationship between the diffraction efficiency of the VBG crystal, the frequency of the incident laser, and the temperature offset of the VBG crystal is theoretically calculated.

[0021] Figure 5 A schematic diagram of the relationship between the diffraction efficiency of the VBG crystal, the incident angle of the incident laser, and the temperature offset of the VBG crystal is theoretically calculated. DETAILED DESCRIPTION

[0022] The present disclosure provides a device for temperature control and adjustment of a VBG crystal to maintain laser transmission efficiency. In order to solve the problem of reduced diffraction efficiency caused by system temperature drift environment, change of incident laser directivity, or change of incident laser wavelength in the actual application of the VBG crystal, in the application environment where the optical system cannot be artificially mechanically adjusted, the best working state of the VBG crystal is found and maintained through active temperature control, so as to maintain the best efficiency of the overall optical path and ensure the stability and high efficiency of the laser signal in the transmission process. The device for temperature control and adjustment of a VBG crystal to maintain laser transmission efficiency has the advantages of being simple and effective, low in cost, and can realize accurate temperature control to ensure the characteristics of the crystal and maintain high-efficiency laser link transmission efficiency.

[0023] In order to make the purpose, technical scheme and advantages of the present disclosure clearer and more apparent, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the drawings.

[0024] In the embodiments of the present disclosure, a device for temperature control and adjustment of a VBG crystal to maintain laser transmission efficiency is provided, as shown in Figure 1 The device comprises:

[0025] A heat conduction structure 10 is provided with a VBG crystal 1 and a temperature detector 9, the heat conduction structure 10 is used for heat conduction with the VBG crystal 1, and the temperature detector 9 is arranged in close contact with the VBG crystal 1 and is used for detecting the real-time temperature of the VBG crystal 1;

[0026] A TEC unit 8 is in contact with the end face of the heat conduction structure 10 and is used for heat conduction with the heat conduction structure 10;

[0027] A temperature controller 7 is connected with the temperature detector 9 and the TEC unit 8, is used for receiving the real-time temperature of the VBG crystal 1 detected by the temperature detector 9, and can drive the TEC unit 8 to work according to the received temperature setting instruction;

[0028] A laser light path unit is used for receiving a laser beam obtained after the incident laser irradiates the VBG crystal 1, and obtaining an outgoing laser and a sampling laser after collimating and beam splitting processing of the laser beam;

[0029] Photodetector 5 is used to detect the power of the sampled laser and convert the sampled laser into an electrical signal;

[0030] The control unit 6 is connected to the photodetector 5 and the temperature controller 7. The control unit 6 is used to give a temperature setting command to the temperature controller 7, and can selectively adjust the temperature setting command according to the electrical signal, thereby achieving stable output of the emitted laser by adjusting the temperature of the VBG crystal 1.

[0031] According to an embodiment of this disclosure, the laser optical path unit includes a laser coupler 2, a laser collimator 3, and a beam splitter 4. The laser coupler 2 is used to receive the laser beam obtained after the incident laser irradiates the VBG crystal 1, and couple the laser beam into the optical fiber link; the laser collimator 3 is used to output the laser beam input from the optical fiber link as a collimated beam; and the beam splitter 4 is used to split the collimated beam into an output laser and a sampling laser.

[0032] More specifically, such as Figure 1 As shown, in the temperature-controlled VBG crystal device for maintaining laser transmission efficiency disclosed in this invention, the connection relationships of each component are as follows: the incident laser acts on the input port 11 of the VBG crystal 1; the diffraction output port 12 of the VBG crystal 1 is connected to the input port 21 of the laser coupler 2; the output port 22 of the laser coupler 2 is connected to the input port 31 of the laser collimator 3; the output port 32 of the laser collimator 3 is connected to the input port 41 of the beam splitter 40; the output port 43 of the beam splitter 40 is connected to the input port 51 of the photodetector 5; the output port 52 of the photodetector 5 is connected to the input port 61 of the control unit 6; the output port 62 of the control unit 6 is connected to the input port 71 of the temperature controller 7; and the output port 73 of the temperature controller 7 is connected to the input port 81 of the TEC unit 8. The TEC unit 8 makes end-face contact with the heat-conducting structure 10. The temperature detector 9 is end-face connected to the VBG crystal 1 and is installed in the heat-conducting structure 10. The output port 91 of the temperature detector 9 is connected to the temperature controller 72 to form a temperature control closed-loop feedback circuit.

[0033] According to an embodiment of this disclosure, the temperature controller 7 drives the TEC unit 8 to operate based on the real-time temperature value of the VBG crystal 1 and the temperature setpoint given by the control unit 6. When the real-time temperature value of the VBG crystal 1 is greater than the temperature setpoint given by the control unit 6, the temperature controller 7 drives the TEC unit 8 to cool the heat-conducting structural component 10, thereby reducing the temperature of the VBG crystal 1. When the real-time temperature value of the VBG crystal 1 is less than the temperature setpoint given by the control unit 6, the temperature controller 7 drives the TEC unit 8 to heat the heat-conducting structural component 10, thereby increasing the temperature of the VBG crystal 1.

[0034] Specifically, in the temperature control closed loop feedback loop, the temperature detector 9 closely attached to the surface of the VBG crystal 1 collects the crystal temperature information in real time and transmits it to the temperature controller 7. The temperature controller 7 compares the measured temperature with the temperature set value given by the regulation unit 6, calculates the temperature error, and drives the TEC cooling fin to work according to the PID feedback algorithm of the temperature error signal. When the temperature is lower than the optimal working point, the TEC unit 8 heats the heat conduction structure through the hot end to increase the temperature; when the temperature is higher than the optimal working point, the TEC cools the heat conduction structure through the cold end. The TEC unit transmits heat or cold to the VBG crystal 1 through the heat conduction structure 10 through the hot end or the cold end, and then feedback adjusts the VBG crystal temperature, so that the VBG crystal temperature is finally stabilized at the working temperature point.

[0035] The incident laser (for example, the 813nm lattice light of the strontium atomic optical clock) which needs to be frequency filtered first enters the VBG crystal 1; the incident laser is diffracted in the VBG crystal 1, and the diffracted laser beam is coupled into the single-mode polarization maintaining optical fiber through the laser coupler 2; the laser is transmitted through the optical fiber link, and the output collimated light beam is emitted from the laser collimator 3; the collimated light beam is split into two beams by the beam splitter 4, one of which is used as the output laser, and the other is used as the sampling laser to enter the photodetector 5 for laser power monitoring; the photodetector 5 converts the optical signal into an electrical signal as the input of the regulation unit 6. The regulation algorithm in the regulation unit implements feedback control according to the working mode (overall open loop mode or closed loop mode).

[0036] According to the embodiment of the present disclosure, as shown in Figure 2 The device for maintaining the laser transmission efficiency of the temperature-controlled VBG crystal includes a first working mode and a second working mode, the first working mode is an open loop mode, and the second working mode is a closed loop working mode.

[0037] In the first working mode, the regulation unit 6 gives a temperature setting instruction to the temperature controller 7, and the temperature controller 7 receives the real-time temperature of the VBG crystal 1 detected and fed back by the receiving temperature detector 9, and automatically stabilizes the temperature of the VBG crystal 1 to the set temperature. The power of the output laser will change accordingly with the change of the temperature of the VBG crystal 1, and the power information of the output laser is obtained by the photodetector 5 and transmitted to the regulation unit 6, and by scanning different working temperature points of the VBG crystal 1, the working temperature or working condition of the VBG crystal 1 at which the laser transmission efficiency is the highest can be obtained.

[0038] In the second working mode, the regulating unit 6 obtains a light power error signal according to the preset target output light power and the actual output light power measured by the photodetector 5, and automatically adjusts a temperature setting instruction to the temperature controller 7 according to the light power error signal, so as to change the working temperature of the VBG crystal 1, improve the laser transmission efficiency, and finally stabilize the actual output light power to the target output light power.

[0039] In actual working conditions, when the system environment drifts, the diffraction efficiency of the VBG crystal 1 will decrease, and the device can greatly inhibit the influence of environmental temperature drift and keep the diffraction efficiency of the VBG crystal 1 unchanged by controlling the temperature of the VBG crystal 1. When the incident laser direction drifts or the incident laser wavelength changes, the diffraction efficiency of the VBG crystal 1 will decrease, and the device of the present disclosure can restore the diffraction efficiency of the VBG crystal 1 by modifying the working stable point of the VBG crystal.

[0040] According to the embodiment of the present disclosure, the VBG crystal 1 is made of photosensitive glass, and the internal body grating function is realized by periodically modulating the refractive index.

[0041] According to the embodiment of the present disclosure, the photodetector 5 includes a photosensitive probe and a transimpedance amplifier, the photosensitive probe converts the optical signal into a current signal, and the transimpedance amplifier converts the current signal into a voltage signal.

[0042] According to the embodiment of the present disclosure, the laser coupler 2 includes a coupling lens and a single-mode polarization maintaining optical fiber; and the laser collimator 3 includes a collimating lens and a single-mode polarization maintaining optical fiber.

[0043] According to the embodiment of the present disclosure, the beam splitter 4 can customize the splitting ratio, and the beam splitter 4 can adopt a combination of a half-wave plate and a polarization beam splitter, or can adopt a non-polarization beam splitter.

[0044] According to the embodiment of the present disclosure, the control algorithm in the regulating unit is executed by a host computer.

[0045] According to the embodiment of the present disclosure, the temperature controller 7 receives the signal of the temperature sensor 9, executes the built-in PID algorithm, and outputs a current to drive the TEC unit to work.

[0046] According to the embodiment of the present disclosure, the TEC (Thermionic Energy Converter) unit 8 is a semiconductor device, which can be called a semiconductor refrigerator. When the TEC unit 8 is powered on, a cold end and a hot end are formed, and the direction of the cold end and the hot end can be changed by adjusting the current direction.

[0047] According to the embodiment of the present disclosure, the temperature sensor 9 can use a thermistor or a thermocouple.

[0048] The heat-conducting structural component 10 can be a custom-machined copper block, with a VBG crystal 1 and a temperature detector 9 installed inside, and the external heat-conducting surface making end-face contact with the TEC unit 8.

[0049] Another aspect of this disclosure provides a device for temperature-controlled adjustment of a VBG crystal to maintain laser transmission efficiency, comprising:

[0050] S1: Detects the real-time temperature of VBG crystal 1;

[0051] S2: Receive the laser beam obtained after the incident laser irradiates the VBG crystal 1, and collimate and split the laser beam to obtain the output laser and the sampling laser.

[0052] S3: Power detection of the sampled laser to convert the sampled laser into an electrical signal; and

[0053] S4: The electrical signal is detected and the temperature of the VBG crystal 1 is adjusted to achieve stable output of the emitted laser.

[0054] Specifically, the operating mode is switched to the first operating mode, i.e., the overall on / off mode. The scanning range and scanning step size for the operating temperature point are set, for example, a scanning range of 22℃-27℃ and a scanning step size of 0.5℃. The temperature controller executes a PID temperature control algorithm according to the temperature setting command to adjust the operating state of the TEC unit and regulate the temperature of the VBG crystal. After the VBG crystal temperature stabilizes at the set temperature point, the sampled laser signal collected in real time by the photodetector is recorded. After the scan is completed, the relationship curve between the emitted laser-related voltage signal and the VBG crystal operating temperature point can be obtained. Figure 3 The figure shows the relationship between the measured diffraction efficiency of the VBG crystal, the fiber coupling efficiency of the diffracted light, and the operating temperature of the VBG crystal. The VBG crystal exhibits an optimal operating temperature for diffraction efficiency, while the fiber coupling efficiency remains almost constant. The maximum VBG diffraction efficiency obtained is better than 95%, corresponding to an optimal operating temperature of 24.5℃.

[0055] The operating mode is switched to the second operating mode, and the target output optical power or the voltage setpoint corresponding to the target output power is preset. The photodetector collects the voltage signal of the sampled laser in real time. When the laser diffraction efficiency decreases due to factors such as system temperature drift, changes in incident laser directionality, or changes in incident laser wavelength, the voltage signal of the photodetector deviates from the voltage setpoint. The control unit calculates the corresponding error signal and executes the PID feedback algorithm to automatically adjust the set temperature, thereby changing the operating temperature of the VBG crystal, improving the transmission efficiency of the optical link, and ultimately stabilizing the actual output optical power to the target output optical power. For example, VBG crystal 1 is designed with an incident angle of 5°, a center wavelength of 813.427nm, an average refractive index of 1.49, a refractive index modulation amount of 0.000065, and a grating thickness of 22mm.Figure 4 As shown, the relationship between the theoretical calculation of the VBG diffraction efficiency and the temperature offset of the VBG crystal at a specific laser frequency is reflected. When there is no frequency offset, the frequency is v0, and after the offset, the frequency is v. When the incident laser frequency is offset, the maximum VBG crystal diffraction efficiency can be restored by adjusting the VBG temperature. When the incident laser frequency is offset (v-v0=-3GHz), the peak diffraction efficiency before the offset can be restored by adjusting the working temperature of the VBG crystal 1 (reduced by 0.136℃), and the corresponding temperature compensation coefficient is 22.1GHz / ℃. As shown, Figure 5 As shown, the incident angle of the incident laser is θ0when there is no offset, and the incident angle is θafter the offset. When the incident angle of the incident laser is offset (θ-θ0=0.1mrad), the peak diffraction efficiency before the offset can be restored by adjusting the temperature of the VBG crystal 1 (reduced by 0.146℃), and the corresponding temperature compensation coefficient is -0.687mrad / ℃.

[0056] The device and method for controlling and adjusting the VBG crystal to maintain the fiber coupling efficiency have simple structure, low cost, no need for customization, and high feasibility of scheme implementation. The device can significantly improve the fiber coupling efficiency, eliminate the influence of environmental temperature fluctuation, change of incident laser directivity, or change of incident light wavelength on the transmission efficiency of the laser link, and improve the system stability and reliability. The method can improve the diffraction efficiency of the VBG crystal without manual mechanical adjustment of the optical link, is convenient for maintenance of the laser link, and has good experimental environment adaptability.

[0057] Thus far, the embodiments of the present disclosure have been described in detail with reference to the accompanying drawings. It should be noted that the implementation manners not shown or described in the drawings or the text are known to those skilled in the art, and are not described in detail. In addition, the definitions of the elements and methods described above are not limited to the various specific structures, shapes or manners mentioned in the embodiments, and can be simply changed or replaced by those skilled in the art.

[0058] The above-described specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above-described specific embodiments are only specific embodiments of the present disclosure and are not used to limit the present disclosure. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A device for temperature-controlled adjustment of a VBG crystal to maintain laser transmission efficiency, comprising: A heat-conducting structural component (10) is provided with a VBG crystal (1) and a temperature detector (9). The heat-conducting structural component (10) is used to conduct heat with the VBG crystal (1). The temperature detector (9) is attached to the VBG crystal (1) and is used to detect the real-time temperature of the VBG crystal (1). The TEC unit (8) is in contact with the end face of the heat-conducting structure (10) and is used to conduct heat with the heat-conducting structure (10); Temperature controller (7) is connected to temperature detector (9) and TEC unit (8) to receive the real-time temperature of VBG crystal (1) detected by temperature detector (9) and to drive TEC unit (8) to work according to the received temperature setting command. The laser optical path unit is used to receive the laser beam obtained after the incident laser irradiates the VBG crystal (1), and to collimate and split the laser beam to obtain the output laser and the sampling laser. Photodetector (5) is used to detect the power of the sampled laser and convert the sampled laser into an electrical signal; as well as The control unit (6) is connected to the photodetector (5) and the temperature controller (7). The control unit (6) is used to give a temperature setting command to the temperature controller (7) and can selectively adjust the temperature setting command according to the electrical signal, thereby achieving stable output of the emitted laser by adjusting the temperature of the VBG crystal (1).

2. The device for maintaining laser transmission efficiency by temperature-controlled adjustment of VBG crystal according to claim 1, wherein the laser optical path unit comprises: A laser coupler (2) is used to receive the laser beam obtained after the incident laser irradiates the VBG crystal (1) and couple the laser beam into the optical fiber link; A laser collimator (3) is used to output a collimated laser beam input from an optical fiber link; and The beam splitter (4) is used to split the collimated beam into an output laser and a sampling laser.

3. The device for maintaining laser transmission efficiency by temperature control adjustment of VBG crystal according to claim 1 or 2, wherein the temperature controller (7) drives the TEC unit (8) to work according to the real-time temperature value of the VBG crystal (1) and the temperature set value given by the control unit (6).

4. The device for maintaining laser transmission efficiency by temperature control adjustment of VBG crystal according to claim 1 or 2, wherein when the real-time temperature value of the VBG crystal (1) is greater than the temperature set value given by the control unit (6), the temperature controller (7) drives the TEC unit (8) to cool down the heat-conducting structure (10) so as to reduce the temperature of the VBG crystal (1).

5. The device for maintaining laser transmission efficiency by temperature control adjustment of VBG crystal according to claim 1 or 2, wherein when the real-time temperature value of the VBG crystal (1) is less than the temperature set value given by the control unit (6), the temperature controller (7) drives the TEC unit (8) to heat up the heat-conducting structure (10) to increase the temperature of the VBG crystal (1).

6. The device for maintaining laser transmission efficiency of VBG crystal by temperature control according to claim 1 or 2 includes a first working mode. In the first working mode, the control unit (6) gives a temperature setting command to the temperature controller (7). After receiving the temperature setting command, the temperature controller (7) uses the real-time temperature of the VBG crystal (1) detected and fed back by the temperature detector (9) to automatically stabilize the temperature of the VBG crystal (1) to the set temperature.

7. The device for maintaining laser transmission efficiency by temperature control adjustment of VBG crystal according to claim 6, wherein the power of the emitted laser will change accordingly with the temperature change of VBG crystal (1), the power information of the emitted laser is obtained by photodetector (5) and transmitted to control unit (6) to obtain the working temperature of VBG crystal (1) when the laser transmission efficiency is the highest.

8. The device for maintaining laser transmission efficiency by temperature control adjustment of VBG crystal according to claim 1 or 2 includes a second working mode. In the second working mode, the control unit (6) obtains an optical power error signal based on the preset target output optical power and the actual output optical power measured by the photodetector (5), and automatically adjusts the temperature setting command to the temperature controller (7) according to the optical power error signal, thereby changing the working temperature of VBG crystal (1), improving laser transmission efficiency, and finally stabilizing the actual output optical power to the target output optical power.

9. The device for maintaining laser transmission efficiency by temperature-controlled adjustment of the VBG crystal according to claim 1 or 2, wherein: The VBG crystal (1) is made of photosensitive glass, and its internal refractive index is periodically modulated to realize the volume grating function; The photodetector includes a photosensitive probe and a transimpedance amplifier. The photosensitive probe converts the optical signal into a current signal, and the transimpedance amplifier converts the current signal into a voltage signal.

10. The device for maintaining laser transmission efficiency by temperature-controlled adjustment of VBG crystal according to claim 2, wherein the laser coupler includes a coupling lens and a single-mode polarization-maintaining fiber; the laser collimator includes a collimating lens and a single-mode polarization-maintaining fiber; the beam splitter can be customized in terms of splitting ratio, and the beam splitter adopts a combination of a half-wave plate and a polarization beam splitter, or adopts a non-polarization beam splitter.

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