Feedback system for active polarization control of fiber laser and non-polarization-maintaining fiber laser system

Abstract

The invention discloses a feedback system for active polarization control of fiber laser and a non-polarization-maintaining fiber laser system, and relates to the field of fiber laser. 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, and N * N fundamental mode electric signals of the main light beam are obtained; the calculation feedback module inputs convergence parameters of the polarization convergence algorithm to the programmable gate array; and under the control of the calculation feedback module, the programmable gate array drives the non-polarization-maintaining fiber laser system to perform real-time polarization control by using a polarization convergence algorithm according to the feedback signal and the convergence parameter by taking the average value of the fundamental mode electric signals at the preset position in the N * N fundamental mode electric signals as the feedback signal. The polarization extinction ratio and the control bandwidth of polarization control can be improved.

Description

Technical Field

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

[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, low price, etc., and are more conducive to large-scale deployment under coherent synthesis. Using fiber laser active polarization control technology, lasers with high polarization extinction ratio can be output in non-polarization-maintaining fiber systems.

[0003] In non-polarization-maintaining fiber high-power systems, polarization pre-compensation schemes are currently commonly used for active polarization control, that is, the polarization state of the output light is controlled by changing the polarization state of the seed light. The power sampling of the output light passing through the polarizer in the target polarization direction is used as the feedback signal, and the Stochastic Parallel Gradient Descent (SPGD) algorithm is used to control the polarization state of each seed light to maximize the feedback signal.

[0004] In high-power laser systems, gain fibers and energy transfer fibers usually use large mode field fibers to increase the upper power limit of fiber lasers. Therefore, the output light usually contains unsuppressible high-order mode components, and these high-order mode components cannot be controlled by polarization pre-compensation schemes, which will seriously affect the control efficiency and convergence bandwidth of polarization control. While increasing the proportion of the laser fundamental mode, how to design the sampling method of the output laser is also the key to improving the polarization control effect.

[0005] There is no sampling method for screening the fundamental mode in the existing fiber laser feedback light sampling scheme. Summary of the invention

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

[0007] To achieve the above objectives, this application provides the following solutions:

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

[0009] The electric detection array sampling module is connected to the calculation feedback module and the programmable gate array respectively; the electric detection array sampling module is in the form of an N×N array, where N is a positive integer; and the programmable gate array has a built-in polarization convergence algorithm.

[0010] The electric detection array sampling module is used to extract the fundamental mode component from the sampled main beam to obtain N×N fundamental mode electrical signals of the main beam. The calculation feedback module is used to input the convergence parameters of the polarization convergence algorithm into the programmable gate array. The programmable gate array is used to use 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 under the control of the calculation feedback module, and according to the feedback signal and the convergence parameters, use the polarization convergence algorithm to drive the non-polarization-maintaining fiber laser system to perform real-time polarization control.

[0011] In a second aspect, the present application provides a non-polarization-maintaining fiber laser system, comprising: a polarization controller, a sampling mirror, and the above-mentioned feedback system for active polarization control of fiber laser. The polarization controller uses active polarization control to change the polarization state of the seed light and emit a main beam; the sampling mirror samples the emitted main beam and transmits the sampled main beam to the feedback system; the feedback system is used to drive the polarization controller according to the sampled main beam to perform real-time polarization control.

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

[0013] The present application provides a feedback system for active polarization control of fiber laser and a non-polarization-maintaining fiber laser system. The fundamental mode component in the main light beam can be extracted by using an N×N array of electrical detection array sampling modules, and feedback control is performed based on the fundamental mode component, thereby avoiding the influence of high-power laser high-order modes on polarization control and improving the polarization extinction ratio and control bandwidth of polarization control. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0015] Figure 1 A schematic structural diagram of a non-polarization-maintaining fiber laser system provided in one embodiment of the present application.

[0016] Figure numerals: electrical detection array sampling module-1, calculation feedback module-2, programmable gate array-3, polarization controller-4, sampling mirror-5, polarization beam splitter-6, beam expansion system-7, detection array-8. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0018] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0019] In an exemplary embodiment, Figure 1 As shown, a feedback system for active polarization control of fiber laser is provided, and the feedback system 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 the seed light and emit the main beam. The feedback system includes: an electric detection array sampling module 1, a calculation feedback module 2 and a programmable gate array 3. The electric detection array sampling module 1 is connected to the calculation feedback module 2 and the programmable gate array 3 respectively; the electric detection array sampling module 1 is in the form of an N×N array, where N is a positive integer; the programmable gate array 3 has a built-in polarization convergence algorithm.

[0020] The electric detection array sampling module 1 is used to extract the fundamental mode component from the sampled main beam to obtain N×N fundamental mode electrical signals of the main 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 use 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 under the control of the calculation feedback module 2, and according to the feedback signal and the convergence parameters, use the polarization convergence algorithm to drive the non-polarization-maintaining fiber laser system to perform real-time polarization control.

[0021] The present application uses an electrical detection array sampling module 1 for sampling. By analyzing multiple sampling signals, the fundamental mode component of the output optical power can be screened out as a feedback electrical signal for polarization control to eliminate the influence of high-order modes on polarization control.

[0022] As an optional implementation, the method for determining the fundamental mode electrical signal at the preset position includes: when the feedback system is initially operated, the calculation feedback module 2 starts from the array center of N×N fundamental mode electrical signals, selects 1 fundamental mode electrical signal, 2 fundamental mode electrical signals, 3 fundamental mode electrical signals, ..., N×N fundamental mode electrical signals in turn, and outputs them to the programmable gate array 3 after each selection; the programmable gate array 3 sequentially drives the non-polarization-maintaining fiber laser system to perform real-time polarization control using a polarization convergence algorithm based on the input fundamental mode electrical signal and convergence parameters. The polarization extinction ratio measured by real-time polarization control selects the fundamental mode electrical signal input by the programmable gate array 3 when the polarization extinction ratio is the highest (indicating the polarization control effect) as the fundamental mode electrical signal at the preset position. The fundamental mode electrical signal at the preset position 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) camera array; the photoelectric detection array is an N×N clock-synchronized photoelectric detection array; the CCD camera array includes N×N pixels.

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

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

[0026] Exemplarily, the photoelectric detection array is a gallium arsenide photoelectric array. Further, the present 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 view the N×N fundamental mode electrical signals in real time, and control the programmable gate array 3 to screen the average value of M signals among the N×N fundamental mode electrical signals as the feedback signal. In addition, the convergence parameters of the polarization convergence algorithm of the programmable gate array 3 can also be controlled, such as the gain coefficient, the integration time, etc. Exemplarily, the calculation feedback module 2 is an industrial computer, such as Figure 1 PC in.

[0028] As an optional implementation, the field-programmable gate array 3 (FPGA) is equipped with a programmed SPGD polarization control convergence algorithm, which receives N×N electrical signals detected by the sampling photoelectric array, and uses the average value of M of the signals as a feedback signal under the control of an industrial computer. The convergence parameters input by the industrial computer are used to apply the SPGD algorithm to the seed light, driving several electro-optical ceramic crystals in the polarization controller 4 to complete real-time polarization control of the main light beam.

[0029] As an optional implementation, refer to Figure 1 The non-polarization-maintaining fiber laser system includes: a polarization controller 4; the polarization controller 4 uses active polarization control to change the polarization state of the seed light and emit the main light beam. The polarization controller 4 is an electro-optical ceramic crystal polarization controller, a squeezed fiber polarization controller or a semiconductor polarization controller. Figure 1 The Seed in it represents the seed light source, which emits seed light.

[0030] Figure 1 It is also shown that the non-polarization-maintaining fiber laser system further includes: a sampling mirror 5; after the emitted main beam is sampled by the sampling mirror 5, it is transmitted to the electrical detection array sampling module 1. The sampling mirror 5 obtains the sampled main beam after two reflections of light.

[0031] Please still refer to Figure 1 The light beam output by the polarization controller 4 is pre-amplified and mainly amplified to obtain a main light beam.

[0032] The beneficial effects brought by the feedback system of this application are as follows:

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

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

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

[0036] In an exemplary embodiment, Figure 1 As shown, a non-polarization-maintaining fiber laser system is provided, including: a polarization controller 4, a sampling mirror 5 and the above-mentioned feedback system for active polarization control of fiber laser. The polarization controller 4 uses active polarization control to change the polarization state of the seed light and emit a main beam. After sampling from the emitted main beam, the sampling mirror 5 transmits the sampled main beam to the feedback system. The feedback system is used to drive the polarization controller 4 to perform real-time polarization control according to the sampled main beam.

[0037] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0038] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this 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, which uses active polarization control to change the polarization state of the seed light and emit a main light beam; the feedback system includes: an electrical detection array sampling module, a calculation feedback module and a programmable gate array; The electric detection array sampling module is connected to the calculation feedback module and the programmable gate array respectively; the electric detection array sampling module is in the form of an N×N array, where N is a positive integer; the programmable gate array has a built-in polarization convergence algorithm; 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 electrical signals of the main light beam; The calculation feedback module is used for inputting the convergence parameters of the polarization convergence algorithm into 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 using a polarization convergence algorithm based on the feedback signal and the convergence parameter, with the average value of the fundamental mode electrical signal at a preset position among N×N fundamental mode electrical signals as a feedback signal under the control of the calculation feedback module.

2. The feedback system for active polarization control of optical fiber laser according to claim 1, characterized in that: The method for determining the fundamental mode electrical signal at the preset position includes: When the feedback system is initially operated, the calculation feedback module starts from the array center of N×N fundamental mode electrical signals, selects 1 fundamental mode electrical signal, 2 fundamental mode electrical signals, 3 fundamental mode electrical signals, ..., N×N fundamental mode electrical signals in sequence, and outputs them to the programmable gate array after each selection; the programmable gate array drives the non-polarization-maintaining fiber laser system to perform real-time polarization control using a polarization convergence algorithm according to the input fundamental mode electrical signal and the convergence parameter in sequence; The polarization extinction ratio is measured through real-time polarization control, and the fundamental mode electrical signal input by the programmable gate array when the polarization extinction ratio is the highest is selected as the fundamental mode electrical signal of the preset position.

3. The feedback system for active polarization control of optical fiber laser according to claim 1, characterized in that: The electrical 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 includes N×N pixels.

4. The feedback system for active polarization control of optical fiber laser according to claim 3, characterized in that: The electrical detection array sampling module also includes: a polarization beam splitter and a beam expansion system; The sampled main beam passes through a polarization beam splitter and then enters a beam expansion system for beam expansion; The expanded main light beam extracts the fundamental mode component through a photoelectric detection array or a CCD camera array and performs photoelectric conversion to obtain N×N fundamental mode electrical signals of the main light beam.

5. The feedback system for active polarization control of optical fiber laser according to claim 1, characterized in that: The polarization convergence algorithm includes a stochastic parallel gradient descent algorithm or a root mean square propagation algorithm.

6. The feedback system for active polarization control of optical fiber laser according to claim 1, characterized in that: The non-polarization-maintaining fiber laser system comprises: a polarization controller; The polarization controller uses active polarization control to change the polarization state of the seed light and emit the main light beam.

7. The feedback system for active polarization control of optical fiber laser according to claim 6, characterized in that: The non-polarization-maintaining fiber laser system further includes: a sampling mirror; The outgoing main light beam is sampled by the sampling mirror and then transmitted to the electrical detection array sampling module.

8. The feedback system for active polarization control of optical fiber laser according to claim 6, characterized in that: The polarization controller is an electro-optical ceramic crystal polarization controller, a squeezed fiber polarization controller or a semiconductor polarization controller.

9. The feedback system for active polarization control of optical fiber laser according to claim 1, characterized in that: The convergence parameters include: gain coefficient and integration time.

10. 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 a feedback system for active polarization control of a fiber laser according to any one of claims 1 to 9; The polarization controller uses active polarization control to change the polarization state of the seed light and emit the main light beam; After the sampling mirror samples the emitted main light beam, the sampled main light beam is transmitted to the feedback system; The feedback system is used to drive the polarization controller according to the sampled main light beam to perform real-time polarization control.

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