A feedback system for active polarization control of fiber laser and a non-polarization maintaining fiber laser system

Abstract

The application discloses a feedback system for active polarization control of a fiber laser and a non-polarization-maintaining fiber laser system, and relates to the field of fiber lasers. The feedback system comprises an electric detection array sampling module, a calculation feedback module and a programmable gate array. The electric detection array sampling module extracts a fundamental mode component from a sampled main light beam to obtain N*N fundamental mode electric signals of the main light beam. The calculation feedback module inputs convergence parameters of a polarization convergence algorithm to the programmable gate array. The programmable gate array takes the average value of the fundamental mode electric signals at preset positions in the N*N fundamental mode electric signals as a feedback signal under the control of the calculation feedback module, and drives the non-polarization-maintaining fiber laser system to perform real-time polarization control by using the polarization convergence algorithm according to the feedback signal and the convergence parameters. The application can improve the polarization extinction ratio and control bandwidth of polarization control.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fiber lasers, in particular to a feedback system for active polarization control of fiber lasers and a non-polarization-maintaining fiber laser system. BACKGROUND

[0002] All-fiber lasers have the characteristics of high brightness, high conversion efficiency, good beam quality, excellent heat dissipation, and good reliability, and have been widely used in various fields. Compared with polarization-maintaining fiber lasers, non-polarization-maintaining fiber laser systems have the characteristics of high nonlinear threshold, simple process, and low price, and are more conducive to large-scale deployment for coherent synthesis. Using fiber laser active polarization control technology, high polarization extinction ratio laser can be output in a non-polarization-maintaining fiber system.

[0003] In a non-polarization-maintaining fiber high-power system, the polarization pre-compensation scheme is generally used for active polarization control, that is, the polarization state of the seed light is changed to control the polarization state of the output light. The power sample of the output light passing through the polarizer of the target polarization direction is used as the feedback signal, and the polarization state of each seed light is controlled using the Stochastic Parallel Gradient Descent (SPGD) algorithm to maximize the feedback signal.

[0004] In a high-power laser system, gain fibers and energy transfer fibers usually use large-mode-area fibers to improve the power limit of fiber lasers, so the output light usually contains uncontrollable high-order mode components, and the high-order mode components cannot be controlled by the polarization pre-compensation scheme, which will seriously affect the control efficiency and convergence bandwidth of the polarization control. While improving the fundamental mode ratio of the laser, how to design the sampling method of the output laser is also an important point to improve the polarization control effect.

[0005] The existing fiber laser feedback light sampling scheme does not have a sampling method for selecting the fundamental mode. SUMMARY

[0006] The purpose of the present application is to provide a feedback system for active polarization control of fiber lasers and a non-polarization-maintaining fiber laser system, which can improve the polarization extinction ratio and control bandwidth of the polarization control.

[0007] To achieve the above purpose, the present application provides the following scheme:

[0008] In a first aspect, the present application provides a feedback system for active polarization control of fiber lasers, which is applied to a non-polarization-maintaining fiber laser system, the non-polarization-maintaining fiber laser system uses active polarization control to change the polarization state of the seed light and emits a main light beam; the feedback system comprises an electric detection array sampling module, a calculation feedback module, and a programmable gate array.

[0009] The electric detection array sampling module is connected with the calculation feedback module and the programmable gate array; the electric detection array sampling module is in the form of an N*N array, and N is a positive integer; the programmable gate array is internally provided with a polarization convergence algorithm.

[0010] The electric detection array sampling module is used to extract the fundamental mode component from the sampled main light beam to obtain N*N fundamental mode electric signals of the main light beam. The calculation feedback module is used to input the convergence parameters of the polarization convergence algorithm to the programmable gate array. The programmable gate array is used to drive the non-polarization maintaining fiber laser system to perform real-time polarization control by using the polarization convergence algorithm according to the average value of the fundamental mode electric signal at a preset position in the N*N fundamental mode electric signals as a feedback signal and the convergence parameters under the control of the calculation feedback module.

[0011] In a second aspect, the application provides a non-polarization maintaining fiber laser system, which comprises a polarization controller, a sampling mirror and the feedback system for active polarization control of a fiber laser as described above. The polarization controller is used to change the polarization state of the seed light by active polarization control to emit a main light beam. The sampling mirror is used to sample the emitted main light beam and transmit the sampled main light beam to the feedback system. The feedback system is used to drive the polarization controller to perform real-time polarization control according to the sampled main light beam.

[0012] According to the specific embodiments provided by the application, the application has the following technical effects:

[0013] The application provides a feedback system for active polarization control of a fiber laser and a non-polarization maintaining fiber laser system. The electric detection array sampling module in the form of an N*N array can extract the fundamental mode component in the main light beam, and the feedback control is performed according to the fundamental mode component, thereby avoiding the influence of the high-order mode of high-power laser on the polarization control and improving the polarization extinction ratio and control bandwidth of the polarization control. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the application or the related art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings described below are only some embodiments of the application, and other drawings can also be obtained by those skilled in the art without any creative effort.

[0015] Figure 1 The structure diagram of the non-polarization maintaining fiber laser system provided by an embodiment of the application.

[0016] The drawings are as follows: electric detection array sampling module-1, calculation feedback module-2, programmable gate array-3, polarization controller-4, sampling mirror-5, polarization beam splitter-6, beam expanding system-7, detection array-8. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0018] The above purposes, features and advantages of the present application will be more apparent and understandable. The present application will be further described in detail below with reference to the drawings and specific embodiments.

[0019] In one exemplary embodiment, as shown in Figure 1 a feedback system for fiber laser active polarization control is provided, which is applied to a non-polarization maintaining fiber laser system, and the non-polarization maintaining fiber laser system uses active polarization control to change the polarization state of seed light and output a main light beam. The feedback system comprises an electrical detection array sampling module 1, a calculation feedback module 2 and a programmable gate array 3. The electrical detection array sampling module 1 is connected with the calculation feedback module 2 and the programmable gate array 3 respectively; the electrical detection array sampling module 1 is in the form of an N×N array, where N is a positive integer; and the programmable gate array 3 is built-in with a polarization convergence algorithm.

[0020] The electrical detection array sampling module 1 is used to extract the fundamental mode component from the sampled main light beam and obtain N×N fundamental mode electrical signals of the main light beam. The calculation feedback module 2 is used to input the convergence parameters of the polarization convergence algorithm to the programmable gate array 3. The programmable gate array 3 is used to, under the control of the calculation feedback module 2, take the average value of the fundamental mode electrical signal at a preset position in the N×N fundamental mode electrical signals as a feedback signal, and use the polarization convergence algorithm to drive the non-polarization maintaining fiber laser system to perform real-time polarization control according to the feedback signal and the convergence parameters.

[0021] The present application uses the electrical detection array sampling module 1 to perform sampling, and by analyzing a plurality of sampling signals, the fundamental mode component of the output light power can be screened out as a feedback electrical signal for polarization control, so as to exclude the influence of high-order modes on polarization control.

[0022] As an optional implementation, the determination mode of the preset-position base mode electrical signal includes: when the feedback system is initially operated, the feedback module 2 sequentially selects 1 base mode electrical signal, 2 base mode electrical signals, 3 base mode electrical signals, …, N×N base mode electrical signals from the center of the array of N×N base mode electrical signals, and outputs to the programmable gate array 3 after each selection; the programmable gate array 3 uses the polarization convergence algorithm to drive the non-polarization maintaining fiber laser system to perform real-time polarization control according to the input base mode electrical signal and the convergence parameter. The polarization extinction ratio measured by the real-time polarization control is selected as the base mode electrical signal input by the programmable gate array 3 when the polarization extinction ratio is the highest (indicating the polarization control effect), which is the preset-position base mode electrical signal. The preset-position base mode electrical signal is the basis for the operation of this feedback system.

[0023] As an optional implementation, the electrical detection array sampling module 1 includes: a detection array 8; the detection array 8 is a photoelectric detection array or a CCD (Charge Coupled Device, charge coupled device) camera array; the photoelectric detection array is an N×N clock-synchronized photoelectric detection array; and the CCD camera array includes N×N pixels.

[0024] The electrical detection array sampling module 1 further includes a polarization beam splitter 6 (Polarizing Beam Splitter, PBS) and a beam expansion system 7. The sampled main light beam passes through the polarization beam splitter 6 and then enters the beam expansion system 7 for beam expansion. The expanded main light beam extracts the base mode component through the photoelectric detection array or the CCD camera array and performs photoelectric conversion to obtain N×N base mode electrical signals of the main light beam. The N×N base mode electrical signals are divided into two paths, one of which is input to the calculation feedback module 2, and the other of which is input to the programmable gate array 3.

[0025] When the CCD camera array is used to extract the base mode component and perform photoelectric conversion, the brightness of the N×N pixels represents the intensity of the N×N base mode electrical signals.

[0026] For example, the photoelectric detection array is a gallium arsenide photoelectric array. Further, the application can select corresponding photoelectric detection elements as the detection array according to the wavelength range of the light beam.

[0027] As an optional implementation, the calculation feedback module 2 can perform real-time viewing on the N×N base mode electrical signals, and control the programmable gate array 3 to screen the average value of M signals in the N×N base mode electrical signals as the feedback signal, and in addition, can control the convergence parameters of the polarization convergence algorithm of the programmable gate array 3, such as the gain coefficient, the integration time, etc. For example, the calculation feedback module 2 is an industrial computer, such as a PC in Figure 1

[0028] ​As an optional implementation, a programmed SPGD polarization control convergence algorithm is loaded in a Field-Programmable Gate Array (FPGA), N*N electric signals detected by the sampling photoelectric array are accepted, the average value of M signals is used as a feedback signal through the control of an industrial computer, the SPGD algorithm is used for the seed light by using the convergence parameters input by the industrial computer, and a plurality of electro-optic ceramic crystals in the polarization controller 4 are driven to complete the real-time polarization control of the main light beam.

[0029] As an optional implementation, referring to Figure 1 , the non-polarization maintaining fiber laser system comprises a polarization controller 4; the polarization controller 4 changes the polarization state of the seed light by using active polarization control to emit the main light beam. The polarization controller 4 is an electro-optic ceramic crystal polarization controller, an extruded fiber polarization controller or a semiconductor polarization controller. Figure 1 In the figure, Seed represents a seed light source, which emits seed light.

[0030] Figure 1 In the figure, the non-polarization maintaining fiber laser system further comprises a sampling mirror 5; the emitted main light beam is sampled by the sampling mirror 5 and then transmitted to the electric detection array sampling module 1. The sampling mirror 5 obtains the sampled main light beam through twice reflection of light.

[0031] Still referring to Figure 1 , the light beam output by the polarization controller 4 is pre-amplified and main-amplified to obtain the main light beam.

[0032] The feedback system of the present application has the following beneficial effects:

[0033] 1. Compared with the traditional active polarization control scheme using a single detector for sampling feedback, the photoelectric detection array used in the present application can extract the fundamental mode in the output light beam for feedback control, avoiding the influence of high-order modes of high-power laser on polarization control and improving the polarization extinction ratio and control bandwidth of polarization control.

[0034] 2. Compared with the traditional polarization control scheme, the present application only needs to replace the sampling detection part of the optical path, and the original light source, polarization controller and polarization control algorithm do not need to be updated, greatly reducing the maintenance cost.

[0035] Based on the same inventive concept, the present application also provides a non-polarization maintaining fiber laser system using the feedback system for fiber laser active polarization control. The implementation scheme for solving the problem provided by the non-polarization maintaining fiber laser system is similar to the implementation scheme described in the feedback system, so the specific limitations in one or more non-polarization maintaining fiber laser system embodiments provided below can be referred to the limitations of the feedback system described above, which will not be repeated here.

[0036] In one exemplary embodiment, as shown in Figure 1 A non-polarization maintaining fiber laser system is provided, which includes a polarization controller 4, a sampling mirror 5 and the feedback system for active polarization control of fiber laser as described above. The polarization controller 4 is used to change the polarization state of the seed light by active polarization control, and the main light beam is emitted. The sampling mirror 5 transmits the sampled main light beam to the feedback system after sampling from the emitted main light beam. The feedback system is used to drive the polarization controller 4 to perform real-time polarization control according to the sampled main light beam.

[0037] The technical features of the above embodiments can be combined in any manner. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described, but as long as there is no contradiction, the combinations should be considered as within the scope of the present disclosure.

[0038] The principles and implementation modes of the present application are described by using specific examples in the present disclosure, and the above embodiments are only used to help understand the method of the present application and its core idea; meanwhile, for those skilled in the art, the specific implementation modes and application ranges can be changed according to the idea of the present application. In conclusion, the content of the present disclosure should not be understood as a limitation of the present application.

Claims

1. A feedback system for active polarization control of fiber lasers, characterized in that, The feedback system is applied to a non-polarization maintaining fiber laser system, the non-polarization maintaining fiber laser system adopts active polarization control to change the polarization state of seed light, and emits a main light beam; the feedback system comprises an electric detection array sampling module, a calculation feedback module and a programmable gate array; The electric detection array sampling module is connected with the calculation feedback module and the programmable gate array; the electric detection array sampling module is in the form of an N×N array, N being a positive integer; the programmable gate array is internally provided with a polarization convergence algorithm; The electric detection array sampling module is used to extract fundamental mode components from the sampled main light beam, and obtain N×N fundamental mode electric signals of the main light beam; The calculation feedback module is used to input convergence parameters of the polarization convergence algorithm to the programmable gate array; The programmable gate array is used to, under the control of the calculation feedback module, take the average value of the fundamental mode electric signal at a preset position in the N×N fundamental mode electric signals as a feedback signal, and use the polarization convergence algorithm to drive the non-polarization maintaining fiber laser system to perform real-time polarization control according to the feedback signal and the convergence parameters; The determination mode of the fundamental mode electric signal at the preset position comprises: When the feedback system is initially operated, the calculation feedback module starts from the center of the N×N fundamental mode electric signal array, and sequentially selects 1 fundamental mode electric signal, 2 fundamental mode electric signals, 3 fundamental mode electric signals, …, N×N fundamental mode electric signals, and outputs to the programmable gate array after each selection; the programmable gate array sequentially uses the polarization convergence algorithm to drive the non-polarization maintaining fiber laser system to perform real-time polarization control according to the input fundamental mode electric signal and the convergence parameters; The polarization extinction ratio measured through the real-time polarization control is used to select the fundamental mode electric signal input by the programmable gate array when the polarization extinction ratio is the highest as the fundamental mode electric signal at the preset position.

2. The feedback system for active polarization control of fiber laser according to claim 1, characterized in that, The electric detection array sampling module comprises a detection array; The detection array is a photoelectric detection array or a CCD camera array; The photoelectric detection array is an N×N clock-synchronized photoelectric detection array; The CCD camera array comprises N×N pixels.

3. The feedback system for active polarization control of fiber laser according to claim 2, characterized in that, The electric detection array sampling module further comprises a polarization beam splitter and a beam expansion system; The sampled main light beam passes through the polarization beam splitter and then enters the beam expansion system for beam expansion; The expanded main light beam passes through the photoelectric detection array or the CCD camera array to extract the fundamental mode components and perform photoelectric conversion, thereby obtaining N×N fundamental mode electric signals of the main light beam.

4. The feedback system for active polarization control of fiber lasers according to claim 1, characterized in that, The polarization convergence algorithm comprises a stochastic parallel gradient descent algorithm or a root mean square propagation algorithm.

5. The feedback system for active polarization control of fiber laser according to claim 1, wherein, The non-polarization maintaining fiber laser system comprises a polarization controller; The polarization controller adopts active polarization control to change the polarization state of the seed light, and emits the main light beam.

6. The feedback system for active polarization control of fiber laser according to claim 5, wherein, The non-polarization maintaining fiber laser system further comprises a sampling mirror; The emitted main light beam is sampled by the sampling mirror and then transmitted to the electric detection array sampling module.

7. The feedback system for active polarization control of fiber laser according to claim 5, wherein, The polarization controller is an electro-optic ceramic crystal polarization controller, an extruded fiber polarization controller or a semiconductor polarization controller.

8. The feedback system for active polarization control of fiber laser according to claim 1, wherein, The convergence parameters comprise a gain coefficient and an integral time.

9. A non-polarization maintaining fiber laser system, characterized in that, The non-polarization maintaining fiber laser system comprises a polarization controller, a sampling mirror and the feedback system for active polarization control of a fiber laser according to any one of claims 1-8. The polarization controller adopts active polarization control to change the polarization state of the seed light, and the main light beam is emitted; The sampling mirror transmits the sampled main light beam to the feedback system after sampling the emitted main light beam; The feedback system is used to drive the polarization controller to perform real-time polarization control according to the sampled main light beam.

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