Adjustable Gain Amplifier and Its Gain Adjustment Method

Abstract

The present application discloses an adjustable gain amplifier and a gain adjustment method thereof. Among them, the amplifier includes: a pump light source, a coupler, a first polarization beam splitter, an optical rotator, a second polarization beam splitter, a quarter-wave plate, a first mirror, a second mirror, a gain medium, a third mirror, and a fourth mirror, where: the first polarization beam splitter and the second polarization beam splitter are configured to allow light beams with different polarization states to be transmitted and output, the first mirror can be controlled to move between a first position and a second position, the fourth mirror can be controlled to move between a third position and a fourth position, and by adjusting the positions of the first mirror and / or the fourth mirror, it is controlled whether the light beam is vertically incident and returns along the original path, so as to change the number of times the light beam passes through the gain medium in the amplifier, and realize the adjustment of the gain of the output light beam. The present application solves the technical problem of poor adjustability of existing amplifiers.

Description

Technical Field

[0001] This application relates to the field of optics, and more particularly, to an adjustable gain amplifier and a method for adjusting its gain. Background Art

[0002] The MOPA structure can endow required parameters such as pulse width, repetition frequency, line width, etc. when the seed light is weak, and then amplify it through a subsequent amplifier without changing the characteristics of the seed light, so as to obtain a laser with parameters meeting the requirements and high power. Many seed sources, such as ultrafast seed sources, gain-switch seed sources, etc., have very low output power, so the amplifier is required to have extremely high gain.

[0003] The MOPA scheme is generally divided into two types: fiber and solid. The fiber scheme has the advantages of high gain and compact structure, but it is difficult to achieve high peak power output due to the damage threshold and nonlinear effects of the fiber. The solid scheme is divided into two types: regenerative amplifier and multi-pass amplifier. The regenerative amplifier has a complex structure and high cost. The problem of the multi-pass amplifier is that those with a simple structure have low gain, and those with high gain have a complex structure. However, neither of them can make immediate adjustments to the changes in the seed light.

[0004] In view of the problem of poor adjustability of the existing amplifier, no effective solution has been proposed yet. Summary of the Invention

[0005] Embodiments of this application provide an adjustable gain amplifier and a method for adjusting its gain to at least solve the technical problem of poor adjustability of the existing amplifier.

[0006] According to one aspect of the embodiments of the present application, an adjustable gain amplifier is provided, including a pump light source, a coupler, a first polarization beam splitter, an optical rotator, a second polarization beam splitter, a quarter-wave plate, a first mirror, a second mirror, a gain medium, a third mirror, and a fourth mirror, wherein: the pump light source is coupled into the gain medium via the coupler; the seed light is aligned with the input end of the first polarization beam splitter and transmits through, the transmission output end of the first polarization beam splitter is aligned with one end of the optical rotator, and the reflection output end of the first polarization beam splitter is aligned with the first output end of the amplifier; the optical rotator is used to adjust the polarization state of the seed light, and the adjusted beam outputs from the other end of the optical rotator and then is aligned with the input end of the second polarization beam splitter and transmits through, the transmission output end of the second polarization beam splitter is aligned with one end of the quarter-wave plate, and the reflection output end of the second polarization beam splitter faces the first mirror, wherein the first mirror can be controlled to move between a first position and a second position. When the first mirror is moved to the first position, the beam output from the reflection output end of the second polarization beam splitter can be made to vertically incident on the first mirror and return along the original path. When the first mirror is moved to the second position, the transmission output end of the second polarization beam splitter can be aligned with the second output end of the amplifier; the other end of the quarter-wave plate is aligned with the second mirror, and the position of the second mirror is configured to make the beam output from the other end of the quarter-wave plate incident non-vertically, so that the reflected beam is incident on the gain medium. The beam amplified by the gain medium is aligned with the third mirror, wherein the position of the third mirror is configured to make the beam amplified by the gain medium incident non-vertically, so that the reflected beam passes through the gain medium again; the beam passing through the gain medium again after being reflected by the third mirror is aligned with the fourth mirror, wherein the fourth mirror can be controlled to move between a third position and a fourth position. When the fourth mirror is moved to the third position, the beam can be made to vertically incident on the fourth mirror and return along the original path. When the fourth mirror is moved to the fourth position, the beam can be aligned with the third output end of the amplifier; wherein, the amplification gains of the beams output from the first output end, the second output end, and the third output end are different. By moving the first mirror and / or the fourth mirror, the beam can be output from any one of the first output end, the second output end, and the third output end, so as to realize the adjustment of the beam gain.

[0007] According to another aspect of the embodiments of the present application, an adjustable gain amplifier is further provided, including: a pump light source, a coupler, a first polarization beam splitter, an optical rotator, a second polarization beam splitter, a quarter-wave plate, a first mirror, a second mirror, a gain medium, a third mirror, and a fourth mirror, wherein: the first polarization beam splitter and the second polarization beam splitter are configured to allow the transmission and output of light beams with different polarization states, the first mirror can be controlled to move between a first position and a second position, and the fourth mirror can be controlled to move between a third position and a fourth position; the pump light source is coupled into the gain medium via the coupler; the seed light modulated to a first polarization state is input through the input end of the first polarization beam splitter and is allowed to output from the transmission output end, and after entering the optical rotator, it is changed into a light beam with a second polarization state. The light beam with the second polarization state is input through the input end of the second polarization beam splitter and is allowed to output from the transmission output end, and after entering the quarter-wave plate, it is changed into a light beam with a third polarization state. The light beam with the third polarization state is incident on the second mirror non-vertically and then reflected into the gain medium for power amplification. The amplified light beam with the third polarization state is incident on the third mirror non-vertically and then passes through the gain medium again for secondary amplification. When the fourth mirror is moved to the fourth position, the light beam with the third polarization state after secondary amplification is output from the third output end of the amplifier; when the fourth mirror is moved to the third position, the light beam with the third polarization state after secondary amplification is incident on the fourth mirror vertically and then returns along the original path, passes through the gain medium for three times of amplification, and then is incident on the third mirror non-vertically and passes through the gain medium again for four times of amplification. The light beam with the third polarization state after four times of amplification is incident on the second mirror non-vertically, is reflected to the quarter-wave plate and then is changed into a light beam with the fourth polarization state after four times of amplification. The light beam with the fourth polarization state after four times of amplification is input through the transmission output end of the second polarization beam splitter and is allowed to output from the reflection output end. When the first mirror is moved to the second position, the light beam with the fourth polarization state after four times of amplification is output from the second output end of the amplifier;When the first reflector is moved to the first position, the fourth polarization state beam amplified four times is perpendicularly incident on the first reflector and then returns along the original path. After being input through the reflection output end of the second polarization beam splitter, it is allowed to be output from the transmission output end. It is incident on the quarter-wave plate and then outputs the fifth polarization state beam amplified four times, which is changed to the beam of the third polarization state. After passing through the second reflector once and the gain medium twice, it outputs the fifth polarization state beam amplified six times. The fifth polarization state beam amplified six times is perpendicularly incident on the fourth reflector at the third position and then returns along the original path. After passing through the gain medium twice and the second reflector once, it outputs the fifth polarization state beam amplified eight times. The fifth polarization state beam amplified eight times returns along the original path to the quarter-wave plate and is changed to the second polarization state beam amplified eight times. The second polarization state beam amplified eight times is input through the transmission output end of the second polarization beam splitter and is allowed to be output from the input end. After the second polarization state beam amplified eight times is incident on the optical rotator, it is changed to the sixth polarization state beam amplified eight times. After being input through the transmission output end of the first polarization beam splitter and being allowed to be output from the reflection output end, it is output from the first output end of the amplifier.;

[0008] According to another aspect of the embodiments of the present application, an amplifier gain adjustment method is further provided, including: receiving a power monitoring signal, where the power monitoring signal includes the power value of the current seed light; determining whether the power value of the current seed light is less than a threshold; if so, sending a control signal to move the position of the first reflector and / or the fourth reflector, and controlling whether the beam returns along the original path after being perpendicularly incident by adjusting the position of the first reflector and / or the fourth reflector, so as to change the number of times the beam passes through the gain medium in the amplifier and realize the adjustment of the gain of the output beam.

[0009] Based on any of the above embodiments, the moving methods of the first reflector and the fourth reflector include any one of the following: the first reflector can be driven to move parallel between the first position and the second position, where the first position blocks the optical path and makes the incident beam perpendicularly incident and reflected, and the second position does not block the optical path, and the perpendicular incident path of the beam is aligned with the second output end of the amplifier; and / or the fourth reflector can be driven to move parallel between the third position and the fourth position, where the third position blocks the optical path and makes the incident beam perpendicularly incident and reflected, and the fourth position does not block the optical path, and the perpendicular incident path of the beam is aligned with the third output end of the amplifier; and / or the first reflector can be driven to move rotationally between the first position and the second position, where the first position blocks the optical path and makes the incident beam perpendicularly incident and reflected, and the second position blocks the optical path and makes the beam incident non-perpendicularly and reflected, and the reflection path is aligned with the second output end of the amplifier; and / or the fourth reflector can be driven to move rotationally between the third position and the fourth position, where the third position blocks the optical path and makes the incident beam perpendicularly incident and reflected, and the fourth position blocks the optical path and makes the beam incident non-perpendicularly and reflected, and the reflection path is aligned with the third output end of the amplifier.

[0010] Based on any of the above embodiments, the amplifier further includes: a power meter, a controller, a first mirror moving device, and a fourth mirror moving device; the power meter is connected to the seed light input end through a beam splitter, and is used to monitor the power of the seed light and generate a power monitoring signal to be sent to the controller; the controller is electrically connected to the power meter, the first mirror moving device, and the fourth mirror moving device respectively, and is used to receive the power monitoring signal and send a movement control signal to the first mirror moving device and / or the fourth mirror moving device according to the power monitoring signal, so as to control the first mirror to move between a first position and a second position, and control the fourth mirror to move between a third position and a fourth position.

[0011] Based on any of the above embodiments, the controller is configured to: receive the power monitoring signal, and determine the power value of the current seed light; judge the relationship between the power value of the current seed light and a first threshold and a second threshold, where the first threshold is greater than the second threshold; if the power value of the current seed light is greater than the first threshold, send a movement control signal to the fourth mirror moving device to move the fourth mirror to the fourth position, so that the light beam is output from the third output end; if the power value of the current seed light is between the first threshold and the second threshold, send movement control signals to the first mirror moving device and the fourth mirror moving device to move the fourth mirror to the third position and the first mirror to the second position, so that the light beam is output from the second output end; if the power value of the current seed light is less than the second threshold, send movement control signals to the first mirror moving device and the fourth mirror moving device to move the fourth mirror to the third position and the first mirror to the first position, so that the light beam is output from the first output end.

[0012] Based on any of the above embodiments, in the amplifier, when the fourth mirror moves to the fourth position, the seed light modulated to the first polarization state is input through the input end of the first polarization beam splitter and is allowed to output from the transmission output end. After entering the optical rotator, it is changed into a beam of the second polarization state. The beam of the second polarization state is input through the input end of the second polarization beam splitter and is allowed to output from the transmission output end. After entering the 1 / 4 wave plate, it is changed into a beam of the third polarization state. The beam of the third polarization state is incident on the second mirror non-vertically and then reflected into the gain medium for power amplification. The amplified beam of the third polarization state is incident on the third mirror non-vertically and then passes through the gain medium again for secondary amplification. The beam of the third polarization state after secondary amplification is output from the third output end of the amplifier; when the fourth mirror moves to the third position and the first mirror moves to the second position, the beam of the third polarization state after secondary amplification is incident on the fourth mirror vertically and then returns along the original path. After passing through the gain medium for three times of amplification, it is incident on the third mirror non-vertically and then passes through the gain medium again for four times of amplification. The beam of the third polarization state after four times of amplification is incident on the second mirror non-vertically, is reflected to the 1 / 4 wave plate and then is changed into a beam of the fourth polarization state after four times of amplification. The beam of the fourth polarization state after four times of amplification is input through the transmission output end of the second polarization beam splitter and is allowed to output from the reflection output end. The beam of the fourth polarization state after four times of amplification is output from the second output end of the amplifier; when the fourth mirror moves to the third position and the first mirror moves to the first position, the beam of the fourth polarization state after four times of amplification is incident on the first mirror vertically and then returns along the original path. After being input through the reflection output end of the second polarization beam splitter, it is allowed to output from the transmission output end. After entering the 1 / 4 wave plate, it outputs a beam of the fifth polarization state after four times of amplification, which is changed into a beam of the third polarization state. After passing through the second mirror once and the gain medium twice, it outputs a beam of the fifth polarization state after six times of amplification. The beam of the fifth polarization state after six times of amplification is incident on the fourth mirror at the third position vertically and then returns along the original path. After passing through the gain medium twice and the second mirror once, it outputs a beam of the fifth polarization state after eight times of amplification. The beam of the fifth polarization state after eight times of amplification returns to the 1 / 4 wave plate and then is changed into a beam of the second polarization state after eight times of amplification. The beam of the second polarization state after eight times of amplification is input through the transmission output end of the second polarization beam splitter and is allowed to output from the input end. After entering the optical rotator, it is changed into a beam of the sixth polarization state after eight times of amplification. After being input through the transmission output end of the first polarization beam splitter and being allowed to output from the reflection output end, it is output from the first output end of the amplifier.

[0013] Based on any of the above embodiments, the amplifier further includes a seed light input port and an amplified light output port. The seed light is input through the seed light input port and then aligned with the input end of the first polarization beam splitter. The first output end, the second output end and the third output end are converged by mirrors and then output from the amplified light output port.

[0014] Based on any of the above embodiments, the amplifier further includes an isolator, and the seed light is aligned with the input end of the first polarization beam splitter after passing through the isolator.

[0015] Based on any of the above embodiments, the amplifier further includes a lens, which is arranged between the optical paths of the second mirror and the gain medium and is used for focusing the light beam.

[0016] Based on any of the above embodiments, the amplifier further includes a half-wave plate, which is arranged between the optical paths of the optical rotator and the second polarization beam splitter and is used for adjusting the polarization state of the incoming and outgoing polarized light.

[0017] Based on any of the above embodiments, the third mirror is a dichroic mirror, which is arranged between the optical paths of the gain medium and the coupler and is used for transmitting the light beam emitted by the pump light source to enter the gain medium and reflecting the light beam amplified by the gain medium to return to the gain medium again.

[0018] Based on any of the above embodiments, the gain medium is a non-polarization absorption laser crystal.

[0019] Based on any of the above embodiments, the gain adjustment method further includes: judging the relationship between the power value of the current seed light and the first threshold and the second threshold, where the first threshold is greater than the second threshold; if the power value of the current seed light is greater than the first threshold, then sending a fourth control signal to control the fourth mirror to move to the fourth position so as to output the light beam with the third gain from the third output end; if the power value of the current seed light is between the first threshold and the second threshold, then sending a third control signal to control the fourth mirror to move to the third position and sending a second control signal to control the first mirror to move to the second position so as to output the light beam with the second gain from the second output end; if the power value of the current seed light is less than the second threshold, then sending a third control signal to control the fourth mirror to move to the third position and sending a first control signal to control the first mirror to move to the first position so as to output the light beam with the first gain from the first output end; wherein, the first gain is greater than the second gain is greater than the third gain.

[0020] The present application discloses an adjustable gain amplifier, which includes: a pump light source, a coupler, a first polarization beam splitter, an optical rotator, a second polarization beam splitter, a quarter-wave plate, a first mirror, a second mirror, a gain medium, a third mirror, and a fourth mirror, wherein: the first polarization beam splitter and the second polarization beam splitter are configured to allow light beams with different polarization states to be transmitted and output, the first mirror can be controlled to move between a first position and a second position, the fourth mirror can be controlled to move between a third position and a fourth position, and whether the light beam is incident vertically and returns along the original path is controlled by adjusting the positions of the first mirror and / or the fourth mirror, so as to change the number of times the light beam passes through the gain medium in the amplifier, and realize the adjustment of the gain of the output light beam. The present application solves the technical problem of poor adjustability of existing amplifiers.

[0021] Conventional pulsed solid amplifiers all try to increase the number of round trips of the seed light in the crystal as much as possible to achieve the effect of increasing the gain. In the use of pulsed lasers, it is often necessary to switch the repetition frequency of the seed. At low repetition frequencies, the seed power is low, and a high gain is required to amplify the seed light as soon as possible; at high repetition frequencies, the seed power is high, and when the number of round trips is not much, the population of the upper energy level in the crystal has been depleted, and the seed continues to travel back and forth in the crystal without being amplified, which will only cause the seed light to be absorbed by the crystal, resulting in gain saturation. Increasing the pump light power can solve the problem of premature gain saturation after the seed power increases, but it will also cause the population of the upper energy level in the crystal not to be converted into seed light with the highest efficiency at low repetition frequencies and low power, the ASE becomes larger, resulting in an increase in the heat in the crystal, and further increasing the thermal lens effect of the crystal. The level of the seed power causes different pump light conversion efficiencies, so different numbers of round trips are required as the seed power changes to maximize the amplification power. The present application proposes a new multi-pass amplifier, which changes the number of round trips of the seed light in the gain medium by changing the position of the mirror, enabling the amplifier to switch between eight-pass, four-pass, and two-pass, and thus optimizing the gain effect of the amplifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings described herein are used to provide a further understanding of the present application, and constitute a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application, and do not constitute an improper limitation of the present application. In the drawings:

[0023] Figure 1 is a schematic structural diagram of an optional adjustable gain amplifier according to an embodiment of the present application;

[0024] Figure 2 is a schematic structural diagram of an optional adjustable gain amplifier according to an embodiment of the present application;

[0025] Figure 3 is a schematic structural diagram of an optional adjustable gain amplifier according to an embodiment of the present application;

[0026] Figure 4 It is a flowchart of a method for adjusting the gain of an amplifier according to an embodiment of the present application. Detailed implementation manners

[0027] In order to enable those skilled in the art to better understand the solution of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0028] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily need to be used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application described here can be implemented in an order other than those illustrated or described here. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0029] Embodiment 1

[0030] According to an embodiment of the present application, a structural embodiment of an adjustable gain amplifier is provided. It should be noted that the arrows shown in the figure can represent the transmission direction of the light beam. Although multiple components or components with a specific order are drawn in the structural schematic diagram of the accompanying drawings, the present application is not limited thereto. In all embodiments of the present application, unless the front-back relationship of certain components or components in the transmission path is specially limited, the positions of other components in the present application can be exchanged as long as the technical problems of the present application can be solved.

[0031] Figure 1 It is a schematic structural diagram of an optional adjustable gain amplifier according to an embodiment of the present application; as Figure 1 shown, the adjustable gain amplifier includes: a pump light source, a coupler, a first polarization beam splitter, an optical rotator, a second polarization beam splitter, a quarter-wave plate, a first mirror, a second mirror, a gain medium, a third mirror, and a fourth mirror, where:

[0032] The pump light source is coupled into the gain medium through the coupler;

[0033] The seed light is aligned with the input end of the first polarization beam splitter and transmitted through. The transmitted output end of the first polarization beam splitter is aligned with one end of the optical rotator, and the reflected output end of the first polarization beam splitter is aligned with the first output end of the amplifier.

[0034] The optical rotator is used to adjust the polarization state of the seed light. The adjusted light beam is output from the other end of the optical rotator and then aligned with the input end of the second polarization beam splitter and transmitted through. The transmitted output end of the second polarization beam splitter is aligned with one end of the quarter-wave plate, and the reflected output end of the second polarization beam splitter faces the first mirror. Among them, the first mirror can be controlled to move between a first position and a second position. When the first mirror is moved to the first position, the light beam output from the reflected output end of the second polarization beam splitter can be made to vertically incident on the first mirror and then return along the original path. When the first mirror is moved to the second position, the transmitted output end of the second polarization beam splitter can be aligned with the second output end of the amplifier.

[0035] The other end of the quarter-wave plate is aligned with the second mirror. The position of the second mirror is configured such that the light beam output from the other end of the quarter-wave plate is incident non-vertically, and the reflected light beam is incident on the gain medium. The light beam amplified by the gain medium is aligned with the third mirror. Among them, the position of the third mirror is configured such that the light beam amplified by the gain medium is incident non-vertically, and the reflected light beam passes through the gain medium again.

[0036] The light beam that passes through the gain medium again after being reflected by the third mirror is aligned with the fourth mirror. Among them, the fourth mirror can be controlled to move between a third position and a fourth position. When the fourth mirror is moved to the third position, the light beam can be made to vertically incident on the fourth mirror and then return along the original path. When the fourth mirror is moved to the fourth position, the light beam can be aligned with the third output end of the amplifier.

[0037] Among them, the amplification gains of the light beams output from the first output end, the second output end, and the third output end are different. By moving the first mirror and / or the fourth mirror, the light beam is output from any one of the first output end, the second output end, and the third output end, so as to realize the adjustment of the light beam gain.

[0038] The present application discloses an adjustable gain amplifier, which includes: a pump light source, a coupler, a first polarization beam splitter, an optical rotator, a second polarization beam splitter, a quarter-wave plate, a first mirror, a second mirror, a gain medium, a third mirror, and a fourth mirror, wherein: the first polarization beam splitter and the second polarization beam splitter are configured to allow light beams with different polarization states to be transmitted and output; the first mirror can be controlled to move between a first position and a second position, and the fourth mirror can be controlled to move between a third position and a fourth position. By adjusting the positions of the first mirror and / or the fourth mirror, it is controlled whether the light beam is vertically incident and returns along the original path, so as to change the number of times the light beam passes through the gain medium in the amplifier, and realize the adjustment of the gain of the output light beam. The present application solves the technical problem of poor adjustability of the existing amplifier.

[0039] Among them, in the first polarization beam splitter and the second polarization beam splitter, the three ports through which the light beams enter and exit are respectively named: the input end, the transmission output end, and the reflection output end. Although limitations such as input and output are used in the naming, due to the reversibility of the optical path transmission, the input end can equally serve as the output end, and the output end can equally serve as the input end. Specifically, the transmission output end corresponds to the end that transmits the P-polarized light, and the reflection output end corresponds to the end that reflects the S-polarized light. Both the first polarization beam splitter and the second polarization beam splitter can be configured to allow light with a specific polarization direction to pass through. The optical rotator is used to change the polarization state of the light, specifically the polarization direction. The seed light can be linearly polarized light, or circularly polarized light or elliptically polarized light. After passing through the optical rotator, the polarization direction of the seed light changes, so that when the light beam returns along the original path after passing through all the subsequent optical paths, it can no longer be input from the transmission output end of the first polarization beam splitter and output through the input end, ensuring that the light beam does not return to the seed light. Of course, for the safety of the optical path, an isolator can also be provided between the seed light and the first polarization beam splitter to block the path of the light beam transmitting towards the seed light. One alignment means that the spatial optical path of the light beam can be transmitted from one side to the other side, not necessarily limited to being transmitted or input from the central position of one side to the central position of the other side. As long as the light beam can be transmitted from one side to the other side, it can even be transmitted or input from the corner position of one side to the corner position of the other side. The quarter-wave plate can convert any state of polarized light into linearly polarized light, or convert linearly polarized light into linearly polarized light, circularly polarized light, or elliptically polarized light under specified conditions.

[0040] Among them, the first mirror can be moved in the following way: for example, the first mirror is fixed on a substrate, and the substrate is horizontally moved or rotated by a motor, so as to control whether the light beam is vertically incident or not. When the first mirror moves to the first position, the light beam output from the reflection output end of the second polarization beam splitter is vertically incident on the first mirror and then returns along the original path; when the first mirror moves to the second position, the first mirror can be made not to be located on the transmission path of the light beam output from the reflection output end of the second polarization beam splitter, or the light beam output from the reflection output end of the second polarization beam splitter is not vertically incident on the first mirror and thus cannot return along the original path.

[0041] Among them, the gain medium is, for example, a laser crystal, and non-polarization absorption crystals such as Yb:YAG and Nd:YVO4 can be selected to amplify the energy of the light beam. The output wavelength of the seed light is in the bands of 1030nm, 1064nm, and 1342nm. The working wavelengths of the first polarization beam splitter and the second polarization beam splitter are in the bands of 1030nm, 1064nm, and 1342nm, and the polarization extinction ratio > 500:1. The optical rotator works in the bands of 1030nm, 1064nm, and 1342nm. The 1 / 4 wave plate works in the bands of 1030nm, 1064nm, and 1342nm. The first mirror, the second mirror, the third mirror, and the fourth mirror all work in the bands of 1030nm, 1064nm, and 1342nm. In the optimal solution, the angle of the coating on the mirror is matched with the angle of its incident light beam. For example, the second mirror and the third mirror are 45-degree mirrors, and the first mirror and the fourth mirror are 0-degree mirrors, so as to reduce the loss as much as possible. Of course, those skilled in the art can understand that the angle of the coating on the mirror may not be matched with the angle of its incident light beam, but the loss is higher, which does not affect the overall implementation of the solution of this application.

[0042] Optionally, the moving methods of the first mirror and the fourth mirror include any one of the following:

[0043] The first mirror can be driven to move parallel between the first position and the second position, where the first position blocks the optical path and makes the incident light beam vertically incident and reflected, and the second position does not block the optical path, and the vertically incident light path is aligned with the second output end of the amplifier; and / or

[0044] The fourth mirror can be driven to move parallel between the third position and the fourth position, where the third position blocks the optical path and makes the incident light beam vertically incident and reflected, and the fourth position does not block the optical path, and the vertically incident light path is aligned with the third output end of the amplifier; and / or

[0045] The first mirror can be driven to rotate between the first position and the second position, where the first position blocks the optical path and makes the incident light beam vertically incident and reflected, and the second position blocks the optical path and makes the light beam non-vertically incident and reflected, and the reflection path is aligned with the second output end of the amplifier; and / or

[0046] The fourth mirror can be driven to rotate between a third position and a fourth position, where the third position blocks the optical path and makes the incident light beam incident and reflected vertically, and the fourth position blocks the optical path and makes the light beam incident and reflected non-vertically, and the reflection path is aligned with the third output end of the amplifier.

[0047] Among them, the configurations of the moving modes of the first mirror and the fourth mirror can preferably be the same. Of course, they can also be selected differently according to the actual optical path design. For example, the first mirror can be configured to move parallelly, while the fourth mirror can be configured to rotate, or vice versa; in this application, the moving mode is only used to control whether the light beam returns along the original path, and its specific mechanical implementation method has nothing to do with the concept of adjustable gain in this application. Those skilled in the art can also select any other existing moving modes as long as it can be realized that the light beam returns along the original path at one position and does not return along the original path at another position.

[0048] Figure 2 It is a schematic structural diagram of an optional adjustable gain amplifier according to an embodiment of the present application; as Figure 2 shown, the amplifier further includes: a power meter, a controller, a first mirror moving device, and a fourth mirror moving device;

[0049] The power meter is connected to the seed light input end through a beam splitter, and is used to monitor the power of the seed light and generate a power monitoring signal to be sent to the controller;

[0050] The controller is electrically connected to the power meter, the first mirror moving device, and the fourth mirror moving device respectively, and is used to receive the power monitoring signal and send a moving control signal to the first mirror moving device and / or the fourth mirror moving device according to the power monitoring signal to control the first mirror to move between the first position and the second position, and control the fourth mirror to move between the third position and the fourth position.

[0051] Among them, the power meter includes any instrument capable of measuring the power of the light beam. The power meter monitors the average power of the seed light, thereby generating a power monitoring signal containing the power information of the seed light.

[0052] Optionally, the method of sending a moving control signal to the first mirror moving device and / or the fourth mirror moving device according to the power monitoring signal to control the first mirror to move between the first position and the second position and control the fourth mirror to move between the third position and the fourth position specifically includes:

[0053] Receiving the power monitoring signal and determining the current power value of the seed light;

[0054] Judging the relationship between the current power value of the seed light and a first threshold and a second threshold, where the first threshold is greater than the second threshold;

[0055] If the power value of the current seed light is greater than the first threshold, a movement control signal is sent to the fourth mirror moving device to move the fourth mirror to the fourth position so that the light beam is output from the third output end;

[0056] If the power value of the current seed light is between the first threshold and the second threshold, a movement control signal is sent to the first mirror moving device and the fourth mirror moving device to move the fourth mirror to the third position and the first mirror to the second position so that the light beam is output from the second output end;

[0057] If the power value of the current seed light is less than the second threshold, a movement control signal is sent to the first mirror moving device and the fourth mirror moving device to move the fourth mirror to the third position and the first mirror to the first position so that the light beam is output from the first output end.

[0058] Optionally, in the amplifier,

[0059] When the fourth mirror moves to the fourth position, the seed light modulated to the first polarization state is input through the input end of the first polarization beam splitter and is allowed to be output from the transmission output end, and then enters the optical rotator and is changed into a light beam in the second polarization state. The light beam in the second polarization state is input through the input end of the second polarization beam splitter and is allowed to be output from the transmission output end, and then enters the 1 / 4 wave plate and is changed into a light beam in the third polarization state. The light beam in the third polarization state is incident on the second mirror non-vertically and then reflected into the gain medium for power amplification. The amplified light beam in the third polarization state is incident on the third mirror non-vertically and then passes through the gain medium again for secondary amplification. The light beam in the third polarization state after secondary amplification is output from the third output end of the amplifier;

[0060] When the fourth mirror moves to the third position and the first mirror moves to the second position, the light beam in the third polarization state after secondary amplification is incident on the fourth mirror vertically and then returns along the original path, passes through the gain medium for three times of amplification and then is incident on the third mirror non-vertically and passes through the gain medium again for four times of amplification. The light beam in the third polarization state after four times of amplification is incident on the second mirror non-vertically, is reflected to the 1 / 4 wave plate and is changed into a light beam in the fourth polarization state after four times of amplification. The light beam in the fourth polarization state after four times of amplification is input through the transmission output end of the second polarization beam splitter and is allowed to be output from the reflection output end. The light beam in the fourth polarization state after four times of amplification is output from the second output end of the amplifier;

[0061] When the fourth reflector moves to the third position and the first reflector moves to the first position, the quadruple - amplified fourth - polarized light beam is incident perpendicularly on the first reflector and then returns along the original path. After being input through the reflection output end of the second polarization beam splitter, it is allowed to be output from the transmission output end. It is incident on the 1 / 4 - wave plate and then outputs a quadruple - amplified fifth - polarized light beam, which is changed into a third - polarized light beam. After passing through the second reflector once and the gain medium twice, a six - times - amplified fifth - polarized light beam is output. The six - times - amplified fifth - polarized light beam is incident perpendicularly on the fourth reflector at the third position and then returns along the original path. After passing through the gain medium twice and the second reflector once, an eight - times - amplified fifth - polarized light beam is output. The eight - times - amplified fifth - polarized light beam returns along the original path to the 1 / 4 - wave plate and is changed into an eight - times - amplified second - polarized light beam. The eight - times - amplified second - polarized light beam is input through the transmission output end of the second polarization beam splitter and is allowed to be output from the input end. After the eight - times - amplified second - polarized light beam is incident on the optical rotator, it is changed into an eight - times - amplified sixth - polarized light beam. After being input through the transmission output end of the first polarization beam splitter and being allowed to be output from the reflection output end, it is output from the first output end of the amplifier.

[0062] Among them, the first polarization state can be linear polarization, circular polarization or elliptical polarization. Taking the first polarization state as linear polarization as an example, the optical rotator changes the first polarization state into the second polarization state, where the polarization direction in the second polarization state is different from that in the first polarization state. For example, the linearly polarized light is rotated by a predetermined angle. After passing through the 1 / 4 - wave plate for the first time, the second polarization state, which was still linearly polarized originally, can be changed into a circularly polarized third polarization state, and a circularly polarized double - amplified light beam is output from the third output end. After passing through the 1 / 4 - wave plate for the second time, the originally circularly polarized third polarization state becomes linearly polarized perpendicular to the polarization direction in the second polarization state, and a quadruple - amplified fourth - polarized light beam perpendicular to the second polarization state is obtained, and the quadruple - amplified fourth - polarized light beam perpendicular to the second polarization state is output from the second output end. After passing through the 1 / 4 - wave plate for the third time, the originally fourth - polarized state with a perpendicular polarization direction can be changed into a circularly polarized fifth polarization state. After passing through the 1 / 4 - wave plate for the fourth time, the originally circularly polarized fifth polarization state becomes the second polarization state with the same polarization direction as that in the second polarization state. At this time, the light beam has passed through the gain medium 8 times and has been amplified 8 times. Therefore, the eight - times - amplified second - polarized light beam is incident on the optical rotator after passing through the second polarization beam splitter, and is rotated by the predetermined angle again to obtain an eight - times - amplified sixth - polarized light beam. The polarization direction of the sixth - polarized light beam is different from that of the first - polarized light beam and cannot pass through the first polarization beam splitter. Therefore, it is output from the reflection output end of the first polarization beam splitter.

[0063] Among them, the specific gain adjustment process is as follows: judge the strength of the seed light, and then:

[0064] When the seed light is very weak, the seed light passes through the isolator, outputs horizontally polarized light, passes through the polarization beam splitter 1, passes through the optical rotator, and then passes through the 1 / 2 wave plate. Adjust the wave plate direction to maintain horizontal polarization output. The 1 / 4 wave plate converts the horizontal polarization into circular polarization. The seed light passes through the crystal for amplification and then reaches the mirror 2, and then returns along the original path. It passes through the 1 / 4 wave plate for the second time, and the polarization direction becomes vertically polarized. It is reflected by the polarization beam splitter 2 to the mirror 3. Then it returns along the original path of the mirror, passes through the 1 / 4 wave plate for the third time, repeats the above process, and the amplified light passes through the 1 / 4 wave plate for the fourth time, becoming horizontally polarized. It passes through the 1 / 2 wave plate and the optical rotator for the second time and becomes vertically polarized, and finally outputs from the polarization beam splitter 1, achieving eight-pass amplification.

[0065] When the seed light is slightly stronger, move the mirror 3 through the motor. The seed light directly outputs from the polarization beam splitter 2 to achieve four-pass amplification.

[0066] When the seed light is the strongest, move the mirror 2 through the motor. The seed light directly outputs from the lens to achieve two-pass amplification.

[0067] Optionally, the amplifier further includes at least one of the following structures:

[0068] The amplifier includes a seed light input port and an amplified light output port. The seed light is input from the seed light input port and then aligned with the input end of the first polarization beam splitter. The first output end, the second output end, and the third output end are converged by the mirror and then output from the amplified light output port; and / or

[0069] The amplifier further includes an isolator. The seed light passes through the isolator and then is aligned with the input end of the first polarization beam splitter; the working wavelength of the isolator is in the 1030nm, 1064nm, 1342nm bands.

[0070] The amplifier further includes a lens, which is arranged between the optical path of the second mirror and the gain medium and is used for focusing the light beam; and / or

[0071] The amplifier further includes a 1 / 2 wave plate, which is arranged between the optical path of the optical rotator and the second polarization beam splitter and is used for adjusting the polarization state of the incoming and outgoing polarized light.

[0072] Optionally, the third mirror is a dichroic mirror, which is arranged between the optical path of the gain medium and the coupler and is used for transmitting the light beam emitted by the pump light source to enter the gain medium and reflecting the light beam amplified by the gain medium to return to the gain medium; the gain medium is a non-polarization absorption laser crystal.

[0073] Optionally, the specific gain adjustment process is: judge the relationship between the current power value of the seed light and the first threshold and the second threshold, where the first threshold is greater than the second threshold;

[0074] If the power value of the current seed light is greater than the first threshold, a fourth control signal is issued to control the fourth mirror to move to the fourth position, so as to output a beam with a third gain from the third output end;

[0075] If the power value of the current seed light is between the first threshold and the second threshold, a third control signal is issued to control the fourth mirror to move to the third position, and a second control signal is issued to control the first mirror to move to the second position, so as to output a beam with a second gain from the second output end;

[0076] If the power value of the current seed light is less than the second threshold, a third control signal is issued to control the fourth mirror to move to the third position, and a first control signal is issued to control the first mirror to move to the first position, so as to output a beam with a first gain from the first output end;

[0077] Wherein, the first gain is greater than the second gain which is greater than the third gain.

[0078] In other embodiments of the present application, especially in the embodiment where the amplifier includes a seed light input port and an amplified light output port that gathers the first output end, the second output end, and the third output end, the fourth mirror moves between the third position and the fourth position at a first frequency, so that a beam combining multiple gains can be output from the amplified light output port. In a more complex scheme, the fourth mirror moves between the third position and the fourth position at a first frequency, and the first mirror moves between the first position and the second position at a second frequency, and a beam combining multiple gain values can be output. When the first frequency and the second frequency are high, the more gain values the beam combines, and when the first frequency and the second frequency are low, the fewer gain values the beam combines. Therefore, the embodiments of the present application also provide an adjustment method for outputting a combined gain beam, specifically including determining the values of the first frequency and / or the second frequency according to the required beam gain value combination degree, so that the fourth mirror moves between the third position and the fourth position at the first frequency, and the first mirror moves between the first position and the second position at the second frequency.

[0079] Embodiment 2

[0080] According to the embodiment of the present application, a structural embodiment of an adjustable gain amplifier is also provided. It should be noted that the arrows shown in the figure can represent the transmission direction of the beam. Although multiple components or components with a specific sequence are drawn in the structural schematic diagram of the accompanying drawing, the present application is not limited thereto. In all embodiments of the present application, unless the front-back relationship of certain components or components in the transmission path is specially defined, the positions of other components in the present application can be swapped as long as the technical problems of the present application can be solved.

[0081] An embodiment of the present application discloses an adjustable gain amplifier, including: a pump light source, a coupler, a first polarization beam splitter, an optical rotator, a second polarization beam splitter, a quarter-wave plate, a first mirror, a second mirror, a gain medium, a third mirror, and a fourth mirror, wherein: the first polarization beam splitter and the second polarization beam splitter are configured to allow light beams with different polarization states to be transmitted and output, the first mirror can be controlled to move between a first position and a second position, and the fourth mirror can be controlled to move between a third position and a fourth position;

[0082] The pump light source is coupled into the gain medium via the coupler;

[0083] The seed light modulated to a first polarization state is input through the input end of the first polarization beam splitter and is allowed to be output from the transmission output end, and after entering the optical rotator, it is changed into a light beam with a second polarization state. The light beam with the second polarization state is input through the input end of the second polarization beam splitter and is allowed to be output from the transmission output end, and after entering the quarter-wave plate, it is changed into a light beam with a third polarization state. The light beam with the third polarization state is incident on the second mirror non-vertically and then reflected into the gain medium for power amplification. The amplified light beam with the third polarization state is incident on the third mirror non-vertically and then passes through the gain medium again for secondary amplification. When the fourth mirror is moved to the fourth position, the secondarily amplified light beam with the third polarization state is output from the third output end of the amplifier;

[0084] When the fourth mirror is moved to the third position, the secondarily amplified light beam with the third polarization state is incident on the fourth mirror vertically and then returns along the original path, passes through the gain medium for three times of amplification and then is incident on the third mirror non-vertically and passes through the gain medium again for four times of amplification. The light beam with the third polarization state amplified four times is incident on the second mirror non-vertically, is reflected to the quarter-wave plate and then is changed into a light beam with the fourth polarization state amplified four times. The light beam with the fourth polarization state amplified four times is input through the transmission output end of the second polarization beam splitter and is allowed to be output from the reflection output end. When the first mirror is moved to the second position, the light beam with the fourth polarization state amplified four times is output from the second output end of the amplifier;

[0085] When the first mirror is moved to the first position, the fourth polarization state beam amplified four times is vertically incident on the first mirror and then returns along the original path. After being input from the reflection output end of the second polarization beam splitter, it is allowed to output from the transmission output end. It is incident on a quarter-wave plate and then outputs the fifth polarization state beam amplified four times, which is changed to a beam of the third polarization state. After passing through the second mirror once and the gain medium twice, it outputs the fifth polarization state beam amplified six times. The fifth polarization state beam amplified six times is vertically incident on the fourth mirror at the third position and then returns along the original path. After passing through the gain medium twice and the second mirror once, it outputs the fifth polarization state beam amplified eight times. The fifth polarization state beam amplified eight times returns along the original path to the quarter-wave plate and is changed to the second polarization state beam amplified eight times. The second polarization state beam amplified eight times is input from the transmission output end of the second polarization beam splitter and is allowed to output from the input end. After the second polarization state beam amplified eight times is incident on the optical rotator, it is changed to the sixth polarization state beam amplified eight times. After being input from the transmission output end of the first polarization beam splitter and being allowed to output from the reflection output end, it outputs from the first output end of the amplifier.

[0086] Figure 3 is a schematic structural diagram of an optional adjustable gain amplifier according to an embodiment of the present application; as Figure 3 shown, the device includes a seed, an isolator, a polarization beam splitter 1, an optical rotator, a half-wave plate, a polarization beam splitter 2, a quarter-wave plate, a mirror 1, a lens, a laser crystal, a dichroic mirror, a coupling mirror 1, a coupling mirror 2, a mirror 2, and a mirror 3.

[0087] Overall working process: When the seed light is very weak, the seed light passes through the isolator, outputs horizontally polarized light, passes through the polarization beam splitter 1, passes through the optical rotator, and then passes through the half-wave plate. The wave plate direction is adjusted to maintain horizontally polarized output. The quarter-wave plate converts the horizontally polarized light into circularly polarized light. The seed light is amplified by the crystal and reaches the mirror 2, and then returns along the original path. It passes through the quarter-wave plate for the second time, and the polarization direction becomes vertically polarized. It is reflected by the polarization beam splitter 2 to the mirror 3. Then it returns along the original path from the mirror, passes through the quarter-wave plate for the third time, repeats the above process, and the amplified light passes through the quarter-wave plate for the fourth time and becomes horizontally polarized. It passes through the half-wave plate and the optical rotator for the second time and becomes vertically polarized, and finally outputs from the polarization beam splitter 1, achieving eight-pass amplification.

[0088] When the seed light is slightly stronger, the mirror 3 is moved by a motor, and the seed light is directly output from the polarization beam splitter 2, achieving four-pass amplification.

[0089] When the seed light is the strongest, the mirror 2 is moved by a motor, and the seed light is directly output from the lens, achieving two-pass amplification.

[0090] The seed outputs wavelengths in the 1030nm, 1064nm, and 1342nm bands.

[0091] Isolator, the isolator has a working wavelength in the bands of 1030nm, 1064nm, and 1342nm.

[0092] Polarizing beam splitter, the polarizing beam splitters 1 and 2 have a working wavelength in the bands of 1030nm, 1064nm, and 1342nm, and the polarization extinction ratio > 500:1.

[0093] Optical rotator, the optical rotator operates in the bands of 1030nm, 1064nm, and 1342nm.

[0094] Wave plate, the 1 / 2 wave plate and 1 / 4 wave plate operate in the bands of 1030nm, 1064nm, and 1342nm.

[0095] Mirror, the mirrors 1, 2, and 3 operate in the bands of 1030nm, 1064nm, and 1342nm. Mirror 1 is a 45-degree mirror, and mirrors 2 and 3 are 0-degree mirrors.

[0096] Laser crystal, the laser crystal is a non-polarization absorption crystal such as Yb:YAG, Nd:YVO4, etc.

[0097] In addition, it should be noted that different from Embodiment 1 which focuses on describing the structure of the tunable gain amplifier, this embodiment focuses on describing the transmission process of the light beam in the tunable gain amplifier, and the positional relationship of each component in the optical path is defined through the description of the light beam transmission process. Thus, Embodiment 2 and Embodiment 1 are interoperable in technical content, and the components described therein have been given the same names as those in Embodiment 1 as much as possible. Therefore, all the specific implementation manners in Embodiment 1 can be unconditionally applied to Embodiment 2, and many technical details are omitted due to space limitations.

[0098] Embodiment 3

[0099] This application also provides a method embodiment of an amplifier gain adjustment method. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although the logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than here.

[0100] Figure 4 is a flowchart of an amplifier gain adjustment method according to an embodiment of the present application, applied to as Figures 1-3In the amplifier shown, the amplifier may be any of the optional amplifiers described in the embodiments of the present application. In an optional solution, the amplifier at least includes a pump light source, a coupler, a first polarization beam splitter, an optical rotator, a second polarization beam splitter, a quarter-wave plate, a first mirror, a second mirror, a gain medium, a third mirror, and a fourth mirror, where: the first polarization beam splitter and the second polarization beam splitter are configured to allow light beams with different polarization states to be transmitted and output, the first mirror can be controlled to move between a first position and a second position, the fourth mirror can be controlled to move between a third position and a fourth position, and whether the light beam is vertically incident and returns along the original path is controlled by adjusting the positions of the first mirror and / or the fourth mirror, so as to change the number of times the light beam passes through the gain medium in the amplifier, and the adjustment of the gain of the output light beam is realized.

[0101] As Figure 4 shown, the method for adjusting the gain of the amplifier includes the following steps:

[0102] Receiving a power monitoring signal, where the power monitoring signal includes the power value of the current seed light;

[0103] Judging whether the power value of the current seed light is less than a threshold;

[0104] If so, sending a control signal to move the position of the first mirror and / or the fourth mirror, and controlling whether the light beam is vertically incident and returns along the original path by adjusting the positions of the first mirror and / or the fourth mirror, so as to change the number of times the light beam passes through the gain medium in the amplifier, and the adjustment of the gain of the output light beam is realized.

[0105] Optionally, the method further includes:

[0106] Judging the relationship between the power value of the current seed light and a first threshold and a second threshold, where the first threshold is greater than the second threshold;

[0107] If the power value of the current seed light is greater than the first threshold, sending a fourth control signal to control the fourth mirror to move to the fourth position to output a light beam with a third gain from the third output end;

[0108] If the power value of the current seed light is between the first threshold and the second threshold, sending a third control signal to control the fourth mirror to move to the third position, and sending a second control signal to control the first mirror to move to the second position to output a light beam with a second gain from the second output end;

[0109] If the power value of the current seed light is less than the second threshold, sending a third control signal to control the fourth mirror to move to the third position, and sending a first control signal to control the first mirror to move to the first position to output a light beam with a first gain from the first output end;

[0110] Among them, the first gain is greater than the second gain which is greater than the third gain.

[0111] It should be noted here that the steps related to gain adjustment in Embodiment 1 and Embodiment 2 can be unconditionally applied to this Embodiment 3. Due to space limitations, they will not be elaborated here.

[0112] The above embodiments of the present application list multiple optional embodiments, only for describing the details of the technical solutions, and the order of their descriptions does not represent the superiority or inferiority of the embodiments.

[0113] In the above embodiments of the present application, the descriptions of each embodiment have their own emphases. For the parts not detailed in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0114] In several embodiments provided by the present application, it should be understood that the disclosed technical content can be implemented in other ways. Among them, the device embodiments described above are only illustrative. For example, the division of the units can be a logical function division. In actual implementation, there can be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections to each other can be through some interfaces. The indirect couplings or communication connections of the units or modules can be in electrical or other forms.

[0115] The units described as separate components may or may not be physically separated. The components displayed as units may or may not be physical units, that is, they can be located in one place or distributed to multiple units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0116] In addition, the functional units in each embodiment of the present application can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above integrated units can be implemented in the form of hardware or in the form of software functional units.

[0117] The above are only the preferred embodiments of the present application. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present application, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. An adjustable gain amplifier, characterized in that: It includes a pump light source, a coupler, a first polarization beam splitter, an optical rotator, a second polarization beam splitter, a quarter-wave plate, a first mirror, a second mirror, a gain medium, a third mirror, and a fourth mirror, where: The pump light source is coupled into the gain medium via the coupler; The seed light is aligned with the input end of the first polarization beam splitter and transmits through it. The transmission output end of the first polarization beam splitter is aligned with one end of the optical rotator, and the reflection output end of the first polarization beam splitter is aligned with the first output end of the amplifier; The optical rotator is used to adjust the polarization state of the seed light. The adjusted beam outputs from the other end of the optical rotator and then is aligned with the input end of the second polarization beam splitter and transmits through it. The transmission output end of the second polarization beam splitter is aligned with one end of the quarter-wave plate, and the reflection output end of the second polarization beam splitter faces the first mirror. Among them, the first mirror can be controlled to move between a first position and a second position. When the first mirror is moved to the first position, the beam output from the reflection output end of the second polarization beam splitter can be made to vertically incident on the first mirror and return along the original path. When the first mirror is moved to the second position, the transmission output end of the second polarization beam splitter can be aligned with the second output end of the amplifier; The other end of the quarter-wave plate is aligned with the second mirror. The position of the second mirror is configured such that the beam output from the other end of the quarter-wave plate is incident non-vertically, and the reflected beam is incident on the gain medium. The beam amplified by the gain medium is aligned with the third mirror. Among them, the position of the third mirror is configured such that the beam amplified by the gain medium is incident non-vertically, and the reflected beam passes through the gain medium again; The beam that passes through the gain medium again after being reflected by the third mirror is aligned with the fourth mirror. Among them, the fourth mirror can be controlled to move between a third position and a fourth position. When the fourth mirror is moved to the third position, the beam can be made to vertically incident on the fourth mirror and return along the original path. When the fourth mirror is moved to the fourth position, the beam can be aligned with the third output end of the amplifier; Among them, the amplification gains of the beams output from the first output end, the second output end, and the third output end are different. By moving the first mirror and / or the fourth mirror, the beam can be output from any one of the first output end, the second output end, and the third output end, so as to realize the adjustment of the beam gain.

2. The amplifier according to claim 1, characterized in that, The moving modes of the first mirror and the fourth mirror include any one of the following: The first mirror can be driven to move parallel between the first position and the second position, where the first position blocks the optical path and makes the incident beam vertically incident and reflected, and the second position does not block the optical path, and the vertical incident path of the beam is aligned with the second output end of the amplifier; and / or The fourth mirror can be driven to move parallel between the third position and the fourth position, where the third position blocks the optical path and makes the incident beam vertically incident and reflected, and the fourth position does not block the optical path, and the vertical incident path of the beam is aligned with the third output end of the amplifier; or The first reflector can be driven to rotate between a first position and a second position, where in the first position, the optical path is blocked and the incident beam is vertically incident and reflected, and in the second position, the optical path is blocked and the beam is non-vertically incident and reflected, and the reflection path is aligned with the second output end of the amplifier; and / or The fourth reflector can be driven to rotate between a third position and a fourth position, where in the third position, the optical path is blocked and the incident beam is vertically incident and reflected, and in the fourth position, the optical path is blocked and the beam is non-vertically incident and reflected, and the reflection path is aligned with the third output end of the amplifier.

3. The amplifier according to claim 1, wherein The amplifier further includes: a power meter, a controller, a first reflector moving device, and a fourth reflector moving device; The power meter is connected to the seed light input end through a beam splitter, and is used to monitor the power of the seed light and generate a power monitoring signal to be sent to the controller; The controller is electrically connected to the power meter, the first reflector moving device, and the fourth reflector moving device respectively, and is used to receive the power monitoring signal and send a movement control signal to the first reflector moving device and / or the fourth reflector moving device according to the power monitoring signal to control the first reflector to move between the first position and the second position, and control the fourth reflector to move between the third position and the fourth position.

4. The amplifier according to claim 3, characterized in that, The controller is configured to: Receive the power monitoring signal and determine the power value of the current seed light; Judge the relationship between the power value of the current seed light and a first threshold and a second threshold, where the first threshold is greater than the second threshold; If the power value of the current seed light is greater than the first threshold, send a movement control signal to the fourth reflector moving device to move the fourth reflector to the fourth position so that the beam is output from the third output end; If the power value of the current seed light is between the first threshold and the second threshold, send movement control signals to the first reflector moving device and the fourth reflector moving device to move the fourth reflector to the third position and the first reflector to the second position so that the beam is output from the second output end; If the power value of the current seed light is less than the second threshold, send movement control signals to the first reflector moving device and the fourth reflector moving device to move the fourth reflector to the third position and the first reflector to the first position so that the beam is output from the first output end.

5. The amplifier according to claim 4, characterized in that, In the amplifier, When the fourth reflector moves to the fourth position, the seed light modulated to the first polarization state is input through the input end of the first polarization beam splitter and is allowed to be output from the transmission output end, is incident on the optical rotator and is changed into a beam of the second polarization state, the beam of the second polarization state is input through the input end of the second polarization beam splitter and is allowed to be output from the transmission output end, is incident on the 1 / 4 wave plate and is changed into a beam of the third polarization state, the beam of the third polarization state is non-vertically incident on the second reflector and then reflected into the gain medium for power amplification, the amplified beam of the third polarization state is non-vertically incident on the third reflector and then passes through the gain medium again for secondary amplification, and the beam of the third polarization state after secondary amplification is output from the third output end of the amplifier; When the fourth reflector moves to the third position and the first reflector moves to the second position, the third polarized light beam after double amplification is vertically incident on the fourth reflector and then returns along the original path. After passing through the gain medium for triple amplification, it is non-vertically incident on the third reflector and then passes through the gain medium for quadruple amplification again. The third polarized light beam after quadruple amplification is non-vertically incident on the second reflector and is reflected to the quarter-wave plate, where it is changed into the fourth polarized light beam after quadruple amplification. The fourth polarized light beam after quadruple amplification is input through the transmission output end of the second polarization beam splitter and is allowed to be output from the reflection output end. The fourth polarized light beam after quadruple amplification is output from the second output end of the amplifier; When the fourth reflector moves to the third position and the first reflector moves to the first position, the fourth polarized light beam after quadruple amplification is vertically incident on the first reflector and then returns along the original path. After being input through the reflection output end of the second polarization beam splitter, it is allowed to be output from the transmission output end. After being incident on the quarter-wave plate, the fifth polarized light beam after quadruple amplification is output, which is changed into the third polarized light beam. After passing through the second reflector once and the gain medium twice, the fifth polarized light beam after sixfold amplification is output. The fifth polarized light beam after sixfold amplification is vertically incident on the fourth reflector at the third position and then returns along the original path. After passing through the gain medium twice and the second reflector once, the fifth polarized light beam after eightfold amplification is output. The fifth polarized light beam after eightfold amplification returns along the original path to the quarter-wave plate and is changed into the second polarized light beam after eightfold amplification. The second polarized light beam after eightfold amplification is input through the transmission output end of the second polarization beam splitter and is allowed to be output from the input end. After the second polarized light beam after eightfold amplification is incident on the optical rotator, it is changed into the sixth polarized light beam after eightfold amplification. After being input through the transmission output end of the first polarization beam splitter and being allowed to be output from the reflection output end, it is output from the first output end of the amplifier.

6. The amplifier according to any one of claims 1-5, characterized in that, The amplifier further includes at least one of the following structures: The amplifier includes a seed light input port and an amplified light output port. The seed light is input through the seed light input port and then aligned with the input end of the first polarization beam splitter. The first output end, the second output end, and the third output end are converged by reflectors and then output from the amplified light output port; and / or The amplifier further includes an isolator. The seed light passes through the isolator and then is aligned with the input end of the first polarization beam splitter; and / or The amplifier further includes a lens, which is arranged on the optical path between the second reflector and the gain medium and is used for focusing the light beam; and / or The amplifier further includes a half-wave plate, which is arranged on the optical path between the optical rotator and the second polarization beam splitter and is used for adjusting the polarization state of the incoming and outgoing polarized light.

7. The amplifier according to any one of claims 1-5, wherein The third reflector is a dichroic mirror, which is arranged on the optical path between the gain medium and the coupler and is used for transmitting the light beam emitted by the pump light source to enter the gain medium and reflecting the light beam amplified by the gain medium to return it to the gain medium again; and / or The gain medium is a non-polarization absorption laser crystal.

8. An adjustable gain amplifier, characterized in that: Comprising: A pump light source, a coupler, a first polarization beam splitter, an optical rotator, a second polarization beam splitter, a quarter-wave plate, a first mirror, a second mirror, a gain medium, a third mirror, and a fourth mirror, wherein: the first polarization beam splitter and the second polarization beam splitter are configured to allow light beams of different polarization states to be transmitted and output, the first mirror can be controlled to move between a first position and a second position, and the fourth mirror can be controlled to move between a third position and a fourth position; The pump light source is coupled into the gain medium via the coupler; The seed light modulated to a first polarization state is input through the input end of the first polarization beam splitter and is allowed to be output from the transmission output end. After entering the optical rotator, it is changed into a light beam with a second polarization state. The light beam with the second polarization state is input through the input end of the second polarization beam splitter and is allowed to be output from the transmission output end. After entering the quarter-wave plate, it is changed into a light beam with a third polarization state. The light beam with the third polarization state is incident on the second mirror non-vertically and is reflected into the gain medium for power amplification. The amplified light beam with the third polarization state is incident on the third mirror non-vertically and then passes through the gain medium again for secondary amplification. When the fourth mirror is moved to the fourth position, the secondarily amplified light beam with the third polarization state is output from the third output end of the amplifier; When the fourth mirror is moved to the third position, the secondarily amplified light beam with the third polarization state is incident on the fourth mirror vertically and returns along the original path. After passing through the gain medium for three times of amplification, it is incident on the third mirror non-vertically and then passes through the gain medium again for four times of amplification. The light beam with the third polarization state amplified four times is incident on the second mirror non-vertically, is reflected to the quarter-wave plate and then is changed into a light beam with the fourth polarization state amplified four times. The light beam with the fourth polarization state amplified four times is input through the transmission output end of the second polarization beam splitter and is allowed to be output from the reflection output end. When the first mirror is moved to the second position, the light beam with the fourth polarization state amplified four times is output from the second output end of the amplifier; When the first mirror is moved to the first position, the light beam with the fourth polarization state amplified four times is incident on the first mirror vertically and returns along the original path. After being input through the reflection output end of the second polarization beam splitter, it is allowed to be output from the transmission output end. After entering the quarter-wave plate, it outputs a light beam with the fifth polarization state amplified four times, which is changed into a light beam with the third polarization state. After passing through the second mirror once and the gain medium twice, it outputs a light beam with the fifth polarization state amplified six times. The light beam with the fifth polarization state amplified six times is incident on the fourth mirror at the third position vertically and returns along the original path. After passing through the gain medium twice and the second mirror once, it outputs a light beam with the fifth polarization state amplified eight times. The light beam with the fifth polarization state amplified eight times returns to the quarter-wave plate along the original path and is changed into a light beam with the second polarization state amplified eight times. The light beam with the second polarization state amplified eight times is input through the transmission output end of the second polarization beam splitter and is allowed to be output from the input end. After the light beam with the second polarization state amplified eight times enters the optical rotator, it is changed into a light beam with the sixth polarization state amplified eight times. After being input through the transmission output end of the first polarization beam splitter and being allowed to be output from the reflection output end, it is output from the first output end of the amplifier.

9. A method for adjusting the amplifier gain, characterized in that: The amplifier is the amplifier described in any one of claims 1-8, and the method includes: Receiving a power monitoring signal, where the power monitoring signal contains the power value of the current seed light; Judging whether the power value of the current seed light is less than a threshold; If so, sending a control signal to move the position of the first mirror and / or the fourth mirror, and controlling whether the light beam is vertically incident and returns along the original path by adjusting the position of the first mirror and / or the fourth mirror, so as to change the number of times the light beam passes through the gain medium in the amplifier, and realizing the adjustment of the gain of the output light beam.

10. The method according to claim 9, characterized in that, The method further includes: Judging the relationship between the power value of the current seed light and a first threshold and a second threshold, where the first threshold is greater than the second threshold; If the power value of the current seed light is greater than the first threshold, sending a fourth control signal to control the fourth mirror to move to a fourth position, so as to output a light beam with a third gain from a third output end; If the power value of the current seed light is between the first threshold and the second threshold, sending a third control signal to control the fourth mirror to move to a third position, and sending a second control signal to control the first mirror to move to a second position, so as to output a light beam with a second gain from a second output end; If the power value of the current seed light is less than the second threshold, sending a third control signal to control the fourth mirror to move to a third position, and sending a first control signal to control the first mirror to move to a first position, so as to output a light beam with a first gain from a first output end; Wherein, the first gain is greater than the second gain is greater than the third gain.

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