Multi-path polarization phase active control system and method of aperture-division coherent synthesis system

Abstract

The invention discloses a multi-path polarization phase active control system and method of a sub-aperture coherent synthesis system, and relates to the technical field of sub-aperture coherent synthesis, the system comprises a detection module and a control module, the detection module samples coherent synthesis light, synthesizes and detects sampled light and reference light, and controls the control module to control the coherent synthesis light. A first detection signal and a second detection signal are obtained, the control system demodulates the first detection signal to obtain a phase error signal corresponding to each beam splitting light, and each phase modulator is controlled to work based on the phase error signal corresponding to each beam splitting light so as to adjust the phase of each beam splitting light. And demodulating the second detection signal to obtain a polarization error signal corresponding to each beam splitting light, and respectively controlling each polarization controller to work based on the polarization error signal corresponding to each beam splitting light so as to adjust the polarization of each beam splitting light. According to the invention, multi-path polarization phase active control with high control speed can be realized under the condition of low system complexity.

Description

Technical Field

[0001] The present application relates to the technical field of sub-aperture coherent combination, and particularly to a multi-channel polarization phase active control system and method for a sub-aperture coherent combination system. Background Art

[0002] Coherent combination technology can improve the laser power while maintaining the beam quality, and is an effective technical path to break through the output power limit of a single aperture of high-energy lasers. Coherent combination technology requires that the polarization of each laser beam is the same and the phases are synchronized. Among them, for the same polarization, there are two solutions: a fully polarization-maintaining laser amplification system and active polarization control for a non-polarization-maintaining laser amplification system. On the one hand, fully polarization-maintaining fiber devices are expensive and the process is complex, resulting in a higher cost for the fully polarization-maintaining laser amplification system. On the other hand, the nonlinear effect threshold in the fully polarization-maintaining fiber amplifier is lower, which limits the output power level of the fully polarization-maintaining laser amplification system. Therefore, the solution of active polarization control for a non-polarization-maintaining laser amplification system has the advantages of reducing costs and increasing the output power, which is of great significance for the design and implementation of a coherent combination system. Phase synchronization usually adopts an active phase control method to correct the phase noise caused by factors such as thermal effects, mechanical vibrations, air flow disturbances, and power supply noise to achieve phase synchronization.

[0003] Both active polarization control and active phase control are based on certain error detection means and optimization algorithms to control the polarization controller and phase modulator, so that the polarization of each laser beam is the same and the phases are synchronized. At present, single-channel polarization control and multi-channel phase control technologies are relatively mature. Although theoretically multi-channel polarization control can be directly extended based on single-channel polarization control, multiple single-channel control modules (including detection devices and control circuits) need to be set up to detect each laser beam separately and further control the polarization of each laser beam separately. Obviously, this requires a multiple increase in detection devices and control circuits, greatly increasing the system complexity, and the system complexity increases with the increase in the number of laser beams. The technology of sampling and detecting the light beam only once and controlling multiple polarizations simultaneously can greatly simplify the system structure, but there are great technical challenges. For example, only sampling and detecting the combined light of multiple laser beams once to generate a detection signal, and further based on the detection signal, using gradient optimization algorithms such as SPGD (Stochastic Parallel Gradient Descent) to control the polarization of each laser beam simultaneously. However, due to the randomness and blind optimization characteristics of the SPGD algorithm, the control speed decreases with the increase in the number of laser beams and is difficult to apply to large-scale systems. In addition, there is currently no solution for actively controlling multiple polarization phases simultaneously. Summary of the Invention

[0004] The purpose of this application is to provide a multi-channel polarization phase active control system and method for a sub-aperture coherent combination system, which can simultaneously achieve multi-channel polarization phase active control. The system complexity and control speed do not change with the number of laser beams. Under the condition of low system complexity, high-speed multi-channel polarization phase active control is achieved.

[0005] To achieve the above object, this application provides the following solutions.

[0006] In a first aspect, this application provides a multi-channel polarization phase active control system for a sub-aperture coherent combination system, including: a detection module and a control module; The detection module is used to sample the coherent combined light output by the sub-aperture coherent combination system to obtain sampled light, perform two syntheses on the sampled light and the reference light to obtain a first combined light and a second combined light, and respectively detect the first combined light and the second combined light to obtain a first detection signal and a second detection signal; the reference light is a beam of light output by a beam splitter in the sub-aperture coherent combination system and collimated, the first combined light is the combined light obtained by combining the sampled light and the reference light, and the second combined light is the combined light obtained by combining the sampled light and the reference light with a 90-degree phase shift. The control module includes a control system, multiple phase modulators, and multiple polarization controllers. The phase modulators and the polarization controllers correspond one-to-one to the other split beams output by the beam splitter except the reference light. The phase modulators are applied with modulation signals, and the modulation angular frequencies of the modulation signals applied to different phase modulators are different; the control system is used to demodulate the first detection signal to obtain a phase error signal corresponding to each split beam, and respectively control the operation of each phase modulator based on the phase error signal corresponding to each split beam to adjust the phase of each split beam, and then demodulate the second detection signal to obtain a polarization error signal corresponding to each split beam, and respectively control the operation of each polarization controller based on the polarization error signal corresponding to each split beam to adjust the polarization of each split beam.

[0007] Optionally, the detection module includes a sampling mirror, a synthesizer, a first detector, and a second detector; the sampling mirror is used to sample the coherent combined light output by the sub-aperture coherent combination system to obtain sampled light; the synthesizer is used to perform two syntheses on the sampled light and the reference light to obtain a first combined light and a second combined light; the first detector is used to detect the first combined light to obtain a first detection signal; the second detector is used to detect the second combined light to obtain a second detection signal.

[0008] Optionally, the synthesizer is a 90° optical mixer; The first detector includes a first polarizer, a first focusing lens, and a first photodetector. The first polarizer is configured to convert the first combined light into a first combined polarized light. The first focusing lens is configured to focus the first combined polarized light to obtain a first combined focused light. The first photodetector is configured to perform photoelectric conversion on the first combined focused light to obtain a first detection signal. The second detector includes a second polarizer, a second focusing lens, and a second photodetector. The second polarizer is configured to convert the second combined light into a second combined polarized light. The second focusing lens is configured to focus the second combined polarized light to obtain a second combined focused light. The second photodetector is configured to perform photoelectric conversion on the second combined focused light to obtain a second detection signal.

[0009] Optionally, the sub-aperture coherent combining system includes: a laser module and a beam combining module. The laser module includes a seed laser, a first laser amplifier, a beam splitter, a plurality of second laser amplifiers, a plurality of first collimators, and a second collimator. The seed laser is configured to emit seed laser light. The first laser amplifier is configured to amplify the seed laser light to obtain amplified laser light. The beam splitter is configured to split the amplified laser light to obtain a plurality of split light beams and an output light beam. The second laser amplifiers and the first collimators correspond to the split light beams one by one. The second laser amplifier is configured to amplify the split light beam to obtain an amplified split light beam. The first collimator is configured to collimate the amplified split light beam to obtain a collimated split light beam. The second collimator is configured to collimate the output light beam to obtain the reference light. The beam combining module is configured to perform coherent combination on all the collimated split light beams.

[0010] Optionally, the phase modulator and the polarization controller are located between the beam splitter and the second laser amplifier. The phase modulator is configured to modulate the phase of the split light beam to obtain a phase-modulated split light beam. The polarization controller is configured to control the polarization of the phase-modulated split light beam to obtain a polarization-controlled split light beam. After all the polarization-controlled split light beams are amplified by the second laser amplifier and collimated by the first collimator, they are combined by the beam combining module into the coherent combined light.

[0011] In a second aspect, the present application provides a multi-channel polarization phase active control method for a sub-aperture coherent combining system, which works based on the multi-channel polarization phase active control system of the above-mentioned sub-aperture coherent combining system, and includes: Obtaining a first detection signal and a second detection signal output by the detection module; Demodulate the first detection signal to obtain a phase error signal corresponding to each sub-beam of light, and respectively control the operation of each phase modulator based on the phase error signal corresponding to each sub-beam of light to adjust the phase of each sub-beam of light; Demodulate the second detection signal to obtain a polarization error signal corresponding to each sub-beam of light, and respectively control the operation of each polarization controller based on the polarization error signal corresponding to each sub-beam of light to adjust the polarization of each sub-beam of light.

[0012] Optionally, demodulating the first detection signal to obtain a phase error signal corresponding to each sub-beam of light specifically includes: demodulating the first detection signal by using a coherent radio frequency demodulation method to obtain a phase error signal corresponding to each sub-beam of light; Demodulating the second detection signal to obtain a polarization error signal corresponding to each sub-beam of light specifically includes: demodulating the second detection signal by using a coherent radio frequency demodulation method to obtain a polarization error signal corresponding to each sub-beam of light.

[0013] Optionally, the calculation formula for the phase error signal is: ; Wherein, is the phase error signal corresponding to the th sub-beam of light; is the integration time; is the modulation angular frequency of the th sub-beam of light; is the time; is the first detection signal at time; is the voltage conversion coefficient of the photodetector; is the power of the th sub-beam of light irradiating on the detection surface of the photodetector; is the first-kind Bessel function of the first order; is the phase modulation depth of the th sub-beam of light; is the number of sub-beams of light; is the power of the th sub-beam of light irradiating on the detection surface of the photodetector; is the first-kind Bessel function of the zero order; is the phase of the th sub-beam of light in the main polarization direction; phase of the The calculation formula for the polarization error signal is: ; Among them, is the polarization error signal corresponding to the th split beam; is the power of the th split beam irradiated on the detection surface of the photodetector, and the 0th split beam is the reference light.

[0014] Optionally, each phase modulator is controlled to work based on the phase error signal corresponding to each split beam to adjust the phase of each split beam. Specifically, for each split beam, the phase modulator corresponding to the split beam is controlled to work based on the phase error signal corresponding to the split beam, and the phase of the split beam is adjusted to the updated phase; The calculation formula for the updated phase is: ; Among them, is the updated phase of the th split beam; is the phase of the th split beam; is the feedback coefficient; is the phase error signal corresponding to the th split beam.

[0015] Optionally, each polarization controller is controlled to work based on the polarization error signal corresponding to each split beam to adjust the polarization of each split beam. Specifically, for each split beam, with the polarization error signal corresponding to the split beam as the input, the SPGD algorithm is used to control the polarization controller corresponding to the split beam to work to adjust the polarization of the split beam.

[0016] According to the specific embodiments provided by the present application, the present application has the following technical effects.

[0017] The present application provides a multi-channel polarization phase active control system and method for a sub-aperture coherent synthesis system, including: a detection module and a control module. The detection module samples the coherent synthesis light output by the sub-aperture coherent synthesis system to obtain sampled light, synthesizes the sampled light and a reference light twice to obtain a first synthesized light and a second synthesized light, and respectively detects the first synthesized light and the second synthesized light to obtain a first detection signal and a second detection signal. The control module includes a control system, a plurality of phase modulators and a plurality of polarization controllers. The phase modulators and the polarization controllers correspond one-to-one to the other split light beams output by the beam splitter except the reference light. The phase modulators are applied with modulation signals, and the modulation angular frequencies of the modulation signals applied by different phase modulators are different. The control system demodulates the first detection signal to obtain a phase error signal corresponding to each split light beam, and respectively controls the operation of each phase modulator based on the phase error signal corresponding to each split light beam to adjust the phase of each split light beam. Then, the second detection signal is demodulated to obtain a polarization error signal corresponding to each split light beam, and respectively controls the operation of each polarization controller based on the polarization error signal corresponding to each split light beam to adjust the polarization of each split light beam. By setting the sampled light and the reference light to be synthesized twice, and setting the phase modulators to be applied with modulation signals, and the modulation angular frequencies of the modulation signals applied by different phase modulators are different, the first detection signal and the second detection signal can be obtained through one sampling and detection. Subsequently, by demodulating the first detection signal and the second detection signal, the operation of the multi-channel phase modulators and the polarization controllers can be controlled simultaneously, so as to only sample and detect the light beam once and control the multi-channel polarization phase simultaneously, thereby realizing the multi-channel polarization phase active control. Moreover, it is not necessary to detect each laser beam separately, reducing the system complexity and simplifying the system structure. At the same time, in the multi-channel polarization active control, the light beam is only sampled and detected once and the multi-channel polarization is controlled simultaneously, and the control is based on the polarization error signal, avoiding the blind optimization of the traditional optimization algorithm. The system complexity and the control speed do not change with the number of laser beams, so that the multi-channel polarization phase active control with high control speed is realized under the condition of low system complexity. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0019] Figure 1 It is a schematic optical path structure diagram of a multi-channel polarization phase active control system for a sub-aperture coherent synthesis system provided in Embodiment 1 of the present application.

[0020] Figure 2 Schematic diagram of the simulation results of the 7-channel sub-aperture coherent combination system arranged in a hexagon provided in Embodiment 1 of the present application; among them, Figure 2 in (a) is the simulation result when the reference light only coincides with the central split beam in the near field; Figure 2 in (b) is the simulation result when the reference light coincides with each split beam in the near field.

[0021] Figure 3 Schematic flow diagram of a multi-channel polarization phase active control method for a sub-aperture coherent combination system provided in Embodiment 2 of the present application.

[0022] Figure 4 Schematic structural diagram of a computer device provided in Embodiment 3 of the present application. Detailed implementation manners

[0023] Next, the technical solutions in the embodiments of the present application will be clearly and completely described 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.

[0024] Embodiment 1.

[0025] This embodiment provides a multi-channel polarization phase active control system for a sub-aperture coherent combination system, including: a detection module and a control module.

[0026] The detection module is used to sample the coherent combined light output by the sub-aperture coherent combination system to obtain sampled light, perform two syntheses on the sampled light and the reference light to obtain a first combined light and a second combined light, and respectively detect the first combined light and the second combined light to obtain a first detection signal and a second detection signal. The reference light is a beam of light output by the beam splitter in the sub-aperture coherent combination system and collimated. The first combined light is the combined light obtained by combining the sampled light and the reference light, and the second combined light is the combined light obtained by combining the sampled light and the reference light with a 90-degree phase shift.

[0027] The control module includes a control system, a plurality of phase modulators, and a plurality of polarization controllers. The phase modulators and the polarization controllers correspond one by one to the split light beams other than the reference light output by the beam splitter. A modulation signal is applied to the phase modulators, and the modulation angular frequencies of the modulation signals applied to different phase modulators are different. The control system is used to demodulate the first detection signal to obtain the phase error signal corresponding to each split light beam, and respectively control the operation of each phase modulator based on the phase error signal corresponding to each split light beam to adjust the phase of each split light beam. Then, the second detection signal is demodulated to obtain the polarization error signal corresponding to each split light beam, and respectively control the operation of each polarization controller based on the polarization error signal corresponding to each split light beam to adjust the polarization of each split light beam.

[0028] This embodiment provides a multi-channel polarization-phase active control system for a sub-aperture coherent combination system, which is a multi-channel polarization-phase active control system applicable to a sub-aperture coherent combination system. Currently, a foreign research team has achieved simultaneous control of polarization and phase of 5 non-polarization-maintaining lasers based on the multi-dither method, and achieved high-power coherent combination of 3 2.4 kW lasers based on the multi-dither method. However, the technical details of this multi-dither method are unknown, and it has only been verified in a common-aperture coherent combination system. It is not clear whether it can be used in a sub-aperture coherent combination system and how to use it in a sub-aperture coherent combination system, which limits its application scope. To overcome the above technical difficulties, this embodiment proposes a multi-channel polarization-phase active control system applicable to a sub-aperture coherent combination system based on the multi-dither method, which can apply the multi-channel polarization-phase active control technology in a sub-aperture coherent combination system and expand the application scope of the multi-dither method.

[0029] The multi-channel polarization-phase active control system of the sub-aperture coherent combination system in this embodiment mainly involves the multi-channel polarization-phase active control of the sub-aperture coherent combination system. As Figure 1 shown, the sub-aperture coherent combination system in this embodiment is first introduced. The sub-aperture coherent combination system includes: a laser module and a beam combination module. The laser module includes: a seed laser, a first laser amplifier, a beam splitter, N second laser amplifiers, N first collimators, and a second collimator, where N is the number of split light beams. The beam combination module includes: a beam combination system.

[0030] The seed laser emitted by the seed laser is divided into N + 1 paths after being amplified by the first laser amplifier. One of the paths is collimated by the second collimator and used as the reference light, and the remaining N paths are used as split light beams. After being amplified by the second laser amplifier and collimated by the first collimator respectively, the N split light beams are emitted and output by the first collimator and incident into the beam combination system to be combined into a single laser beam.

[0031] At this time, in this embodiment, the sub-aperture coherent combination system includes: a laser module and a beam combination module.

[0032] The laser module includes a seed laser, a first laser amplifier, a beam splitter, multiple second laser amplifiers, multiple first collimators, and a second collimator. The seed laser is used to emit seed laser light. The first laser amplifier is used to amplify the seed laser light to obtain amplified laser light. The beam splitter is used to split the amplified laser light to obtain multiple split beams of light and an output beam of light. The second laser amplifiers and the first collimators are in one-to-one correspondence with the split beams of light. The second laser amplifiers are used to amplify the split beams of light to obtain amplified split beams of light. The first collimators are used to collimate the amplified split beams of light to obtain collimated split beams of light. The second collimator is used to collimate the output beam of light to obtain reference light.

[0033] The beam combining module is used to perform coherent combination on all the collimated split beams of light.

[0034] It should be noted that the structure of the above sub-aperture coherent combination system is only an example of this embodiment. Of course, this embodiment can also be applied to sub-aperture coherent combination systems with other structures. The structure of the disclosed sub-aperture coherent combination system should not be construed as a limitation to this embodiment.

[0035] As Figure 1 shown, the multi-channel polarization phase active control system of the sub-aperture coherent combination system used in this embodiment will be introduced. The multi-channel polarization phase active control system of the sub-aperture coherent combination system includes: a detection module and a control module. The detection module includes: a sampling mirror, a 90° optical mixer, two polarizers, two focusing lenses, two photodetectors. The control module includes: a control system, N phase modulators, N polarization controllers. Among them, small-amplitude sinusoidal modulation signals with different modulation angular frequencies are applied to the phase modulators, and the modulation angular frequency and amplitude can be determined according to user requirements.

[0036] After the seed laser emitted by the seed laser source is amplified by the first laser amplifier, it is split into N + 1 paths by a beam splitter. One path is collimated by the second collimator and used as the reference light, and the remaining N paths are used as split beams. After being phase-modulated by the phase modulator, polarization-controlled by the polarization controller, and amplified by the second laser amplifier respectively, they are collimated by the first collimator and then emitted and output, and incident into the beam combining system to be combined into a single laser beam, obtaining the coherently combined light. After the beam combination, that is, after obtaining the coherently combined light, a small part of the power of the coherently combined light is extracted by a sampling mirror for detection to obtain the sampling light. The sampling light and the reference light are input into a 90° optical mixer together, and two different combined laser beams, namely the first combined light and the second combined light, are output. Then, after passing through the polarizer and the focusing lens respectively, they are incident on two photodetectors to generate different detection signals, namely the first detection signal and the second detection signal. Inside the 90° optical mixer, both the reference light and the sampling light are split into two parts. One part of the reference light is combined with one part of the sampling light to generate the first combined light. The first combined light passes through the polarizer and the focusing lens, and the first detection signal generated on the photodetector is denoted as , and the other part of the reference light first undergoes a 90° phase shift and then is combined with the other part of the sampling light to generate the second combined light. The second combined light passes through the polarizer and the focusing lens, and the second detection signal generated on the photodetector is denoted as . The two detection signals are input into the control system together, where is used for phase control, is used for polarization control. The phase error signals and polarization error signals of each split beam are demodulated by the coherent radio frequency demodulation method. Based on the phase error signals and polarization error signals, the control voltages of the phase modulator and the polarization controller are adjusted to change the phase and polarization of the split beams, and gradually achieve phase synchronization and polarization identity.

[0037] At this time, in this embodiment, the detection module is used to sample the coherent combined light output by the sub-aperture coherent combining system to obtain sampled light, perform two syntheses on the sampled light and the reference light to obtain a first combined light and a second combined light, and respectively detect the first combined light and the second combined light to obtain a first detection signal and a second detection signal. The control module includes a control system, a plurality of phase modulators and a plurality of polarization controllers. The phase modulators and the polarization controllers correspond one-to-one to the split light beams other than the reference light output by the beam splitter. The phase modulators are applied with modulation signals, and the modulation angular frequencies of the modulation signals applied by different phase modulators are different. The phase modulators and the polarization controllers are located between the beam splitter and the second laser amplifier. The phase modulators are used to modulate the phases of the split light beams to obtain phase-modulated split light beams, and the polarization controllers are used to control the polarizations of the phase-modulated split light beams to obtain polarization-controlled split light beams. After all the polarization-controlled split light beams are amplified by the second laser amplifier and collimated by the first collimator, they are combined into coherent combined light by the combining module. The control system is used to demodulate the first detection signal to obtain the phase error signal corresponding to each split light beam, and respectively control the operations of the respective phase modulators based on the phase error signal corresponding to each split light beam to adjust the phases of each split light beam, and then demodulate the second detection signal to obtain the polarization error signal corresponding to each split light beam, and respectively control the operations of the respective polarization controllers based on the polarization error signal corresponding to each split light beam to adjust the polarizations of each split light beam.

[0038] Among them, the detection module includes a sampling mirror, a synthesizer, a first detector and a second detector. The sampling mirror is used to sample the coherent combined light output by the sub-aperture coherent combining system to obtain sampled light. The synthesizer is used to perform two syntheses on the sampled light and the reference light to obtain a first combined light and a second combined light. The first detector is used to detect the first combined light to obtain a first detection signal. The second detector is used to detect the second combined light to obtain a second detection signal.

[0039] Among them, the synthesizer is a 90° optical mixer. The first detector includes a first polarizer, a first focusing lens and a first photodetector. The first polarizer is used to convert the first combined light into a first combined polarized light. The first focusing lens is used to focus the first combined polarized light to obtain a first combined focused light. The first photodetector is used to perform photoelectric conversion on the first combined focused light to obtain a first detection signal. The second detector includes a second polarizer, a second focusing lens and a second photodetector. The second polarizer is used to convert the second combined light into a second combined polarized light. The second focusing lens is used to focus the second combined polarized light to obtain a second combined focused light. The second photodetector is used to perform photoelectric conversion on the second combined focused light to obtain a second detection signal.

[0040] In addition to using a 90° optical mixer, other optical path structures can also be used for the synthesis of the reference light and the sampling light, but it is necessary to ensure that there is a 90-degree phase difference between the reference light and the sampling light in the second synthesized light for polarization control.

[0041] The control system of this embodiment adopts the multi-dither method, and the execution steps of the multi-dither method are as follows (the integration time is , and its specific duration is determined according to user requirements): Collect the first detection signal and the second detection signal , from the moment to the moment , respectively demodulate , to obtain the phase error signal and the polarization error signal of each split beam light, and control the operation of the phase modulator based on the phase error signal . Every , the phase modulator is controlled once, and at the same time, the polarization error signal is stored. When the control time is reached, the phase modulation is completed, and the phases of each split beam light are synchronized. Based on the polarization error signal , the polarization controller is controlled. Every , the polarization controller is controlled once until the polarization control is completed and the polarizations of each split beam light are the same. The specific duration of is determined according to user requirements. is one order of magnitude larger than

[0042] . By selecting different orders of magnitude, the control processes of phase synchronization and polarization identity do not interfere with each other, ensuring that the laser phase is already synchronized during polarization control. and the polarization error signal are determined as follows.

[0043] For phase control, each split beam light is applied with a modulation signal of a different modulation angular frequency. The radio frequency modulation angular frequency (i.e., the modulation angular frequency) of the th split beam light is , the phase modulation depth is , and the reference light (i.e., the 0th split beam light) is not modulated (i.e., = 0). According to the principle of light wave superposition, the synthesized light field of the first synthesized light after polarization and the first detection signal are: (1); In formula (1), is the moment; is the number of split beams; is the amplitude of the split beam in the main polarization direction; is the central angular frequency of the laser; is the phase of the split beam in the main polarization direction; is the phase modulation depth of the split beam; is the modulation angular frequency of the split beam; is the voltage conversion coefficient of the photodetector; is the detection area of the photodetector; are the vacuum permittivity, air refractive index, and speed of light, respectively; represents time averaging.

[0044] Multiply the first detection signal by the sine modulation signal of each split beam , and integrate within the integration time . Further, use the Bessel expansion formula of trigonometric functions and retain the first two orders for approximation to obtain the phase error signal of each split beam as: (2); In Equation (2), is the phase error signal corresponding to the split beam; is the integration time; is the modulation angular frequency of the split beam; is the time; is the first detection signal at time; is the voltage conversion coefficient of the photodetector; is the power of the split beam incident on the detection surface of the photodetector; is the first kind of Bessel function of order 1; is the phase modulation depth of the split beam; is the number of split beams; is the power of the split beam incident on the detection surface of the photodetector; is the first kind of Bessel function of order 0; is the phase modulation depth of the split beam; is the phase of the split beam in the main polarization direction; is the The phase of the split beam in the main polarization direction.

[0045] In the above formula (2), (for example 、 ) is the power of each split beam irradiated on the detection surface of the photodetector. , is the amplitude of each split beam in the main polarization direction. The phase error signal represents the average sinusoidal phase distance between the -th split beam and other split beams. After feedback control, the phase error signal of each path can be made to approach 0, thereby achieving phase synchronization between the split beams.

[0046] For polarization control, the second detection signal is , which is different from the first detection signal in that the phase of the reference light changes by 90° (the changed phase = the previous phase + 90°). Demodulation is performed similar to formulas (1) and (2), and only the phase of the 0-th split beam needs to be noted. When the phases of the split beams are synchronized ( - ≈ 0, ), , in formula (2), the terms from to are all 0, leaving only the term , and . Therefore, further approximation is made using the phase difference between the paths approximately equal to 0, and the polarization error signal is calculated as: (3); In formula (3), is the polarization error signal corresponding to the -th split beam; is the phase modulation depth of the -th split beam. If the phase modulation depths of the split beams are the same, then the at this time can be represented by ; is the power of the -th split beam irradiated on the detection surface of the photodetector. The 0-th split beam is the reference light.

[0047] Since the square root of the power of the -th split beam irradiated on the detection surface of the photodetector is proportional to the amplitude of this split beam, the amplitude of each split beam can be demodulated separately, and the polarization error signal of each path can be optimized to make its amplitude maximum, thereby completing multi-path polarization control and achieving the same polarization.

[0048] When performing simultaneous polarization and phase control, the polarization control should be at least one order of magnitude slower than the phase control to ensure that the phase is in a synchronous state during polarization control. Only in this case can the approximate formula for the polarization error signal hold.

[0049] At this time, in this embodiment, the first detection signal and the second detection signal output by the detection module are obtained. The first detection signal is demodulated to obtain the phase error signal corresponding to each split beam of light, and each phase modulator is controlled to work based on the phase error signal corresponding to each split beam of light to adjust the phase of each split beam of light. Then the second detection signal is demodulated to obtain the polarization error signal corresponding to each split beam of light, and each polarization controller is controlled to work based on the polarization error signal corresponding to each split beam of light to adjust the polarization of each split beam of light.

[0050] Among them, demodulating the first detection signal to obtain the phase error signal corresponding to each split beam of light specifically includes: demodulating the first detection signal using the coherent radio frequency demodulation method to obtain the phase error signal corresponding to each split beam of light, and the calculation formula for the phase error signal is Equation (2).

[0051] Among them, demodulating the second detection signal to obtain the polarization error signal corresponding to each split beam of light specifically includes: demodulating the second detection signal using the coherent radio frequency demodulation method to obtain the polarization error signal corresponding to each split beam of light, and the calculation formula for the polarization error signal is Equation (3).

[0052] When controlling the phase modulator based on the phase error signal, the phase error signal can be multiplied by an appropriate feedback coefficient , and the phase of the split beam of light is updated. Then the phase of the th split beam of light becomes: , where is the updated phase of the th split beam of light, is the phase of the th split beam of light, is the feedback coefficient, is the th phase error signal corresponding to the split beam of light. A phase error signal is obtained every time interval , the phase modulator is controlled once, and the phase of the split beam of light is adjusted once.

[0053] At this time, in this embodiment, controlling each phase modulator to work based on the phase error signal corresponding to each split beam of light to adjust the phase of each split beam of light specifically includes: for each split beam of light, controlling the phase modulator corresponding to the split beam of light to work based on the phase error signal corresponding to the split beam of light, and adjusting the phase of the split beam of light to the updated phase.

[0054] The calculation formula for the updated phase is as follows: (4); In formula (4), is the updated phase of the th split beam; is the phase of the th split beam; is the feedback coefficient; is the th phase error signal corresponding to the split beam.

[0055] The control process of the phase modulator in this embodiment can also be implemented using other algorithms, such as the SPGD algorithm. Since the acquisition of the polarization error signal depends on the multi-dither method, modulation signals with different modulation angular frequencies must be applied to each split beam. Therefore, multi-channel phase active control is preferably also implemented using the multi-dither method (i.e., the method for solving the phase error signal and the method for controlling the phase given in this embodiment). At this time, there is no need to additionally set components for implementing multi-channel phase active control, nor to introduce additional algorithms, reducing the system complexity.

[0056] When controlling the polarization controller based on the polarization error signal, the SPGD algorithm can be used to optimize the polarization error signal (i.e., the of each split beam) to the maximum value, so that the polarization state of the split beam reaches the expected linear polarization direction. The SPGD algorithm contains N independent loops, which respectively control the polarization of N split beams. The <y th loop uses the th polarization error signal stored by the multi-dither method as the evaluation function, denoted as , that is, let = . When the polarization controller consists of 4 piezoelectric ceramics (this is the physical model of the polarization controller, composed of four piezoelectric ceramics, equivalent to four wave plates with adjustable phase delays), at this time, the change of the polarization state of each split beam requires simultaneous adjustment of 4 voltage signals. Taking a certain loop of the SPGD algorithm as an example, the steps are as follows (the time for executing one step is , ).

[0057] (1) Generate a set of random perturbation voltages , are the perturbation voltages for the 4 piezoelectric ceramics respectively. Positively perturb the current control voltage to obtain the evaluation function = ( + ).

[0058] (2) Using a set of randomly generated perturbation voltages in (1), negatively perturb the current control voltage to obtain the evaluation function after negative perturbation = ( - ).

[0059] (3) Calculate the change in the evaluation function after perturbation = ( - ) / ( + ), update the control voltage = + , where is the updated control voltage, is the gain coefficient of the SPGD algorithm, is the variance of a set of randomly generated perturbation voltages.

[0060] (4) Loop through (1)-(3) to continuously approach the maximum value of the evaluation function.

[0061] When all evaluation functions reach the maximum value, the polarization direction of the split beam is adjusted to the main polarization direction, and the polarization states of each path are consistent, and the polarization control is completed.

[0062] At this time, in this embodiment, based on the polarization error signals corresponding to each split beam, each polarization controller is controlled to work to adjust the polarization of each split beam. Specifically, for each split beam, using the polarization error signal corresponding to the split beam as the input, the SPGD algorithm is used to control the polarization controller corresponding to the split beam to work to adjust the polarization of the split beam.

[0063] The control process of the polarization controller in this embodiment can also be implemented using other algorithms. The polarization controller may not be equivalent to a structure of 4 piezoelectric ceramics, but the control principle is still to optimize according to the polarization error signals obtained by multi-dither method demodulation to make the signal amplitude the strongest (i.e., the amplitude of the main polarization direction of the split beam is the strongest). Since the multi-dither method is an active phase control algorithm based on phase modulation demodulation and is not directly related to laser amplitude / polarization, no research team has applied the multi-dither method to the polarization control process. In this embodiment, the multi-dither method is innovatively introduced into the polarization control, and the polarization error signals of each path of split beam can be calculated through one sampling and detection. Further, based on the polarization error signals, polarization control is performed, which can achieve the separation of multi-path control, and the control speed does not change with the number of paths, so as to achieve high-speed multi-path polarization active control under the condition of low system complexity.

[0064] Based on the above principle, in this embodiment, a simulation of a 7-channel sub-aperture coherent combination system arranged in a hexagon is carried out. The initial polarization and phase of the light beam are random. The simulation results are as follows: Figure 2 As shown, the photodetector detects the central main lobe power of the far-field light spot. Figure 2 In (a) of Figure 2 , the optical aperture size of the reference light is the same as that of all the split beams, and it only coincides with the central split beam in the near field. Figure 2 In (b) of Figure 2 , the reference light is expanded and covers the aperture of the entire sub-aperture array, and it coincides with each split beam in the near field. It can be seen that both schemes can achieve polarization phase control and can quickly reach the maximum intensity (maximum combination efficiency), which proves the feasibility in the sub-aperture coherent combination system.

[0065] This embodiment requires two photodetectors to be used for phase and polarization control respectively. Through the coherent RF demodulation process of the multi-dither method, the phase error signal and polarization error signal (i.e., intensity information) of each split beam are obtained, which are further used as the input signals of each phase control loop and polarization control loop. The multi-channel polarization phase active control technology is expanded, and the application range of this technology is expanded. It can be used in the sub-aperture coherent combination system. Compared with the traditional polarization phase active control technology, it has the advantages of low system complexity and strong channel expansion ability, and adapts to the application requirements of large-scale sub-aperture coherent combination systems.

[0066] Embodiment 2.

[0067] This embodiment provides a multi-channel polarization phase active control method for a sub-aperture coherent combination system, which works based on the multi-channel polarization phase active control system of the sub-aperture coherent combination system described in Embodiment 1. As shown in Figure 3 , it includes the following steps. Figure 3 As shown, it includes the following steps.

[0068] S1: Obtain the first detection signal and the second detection signal output by the detection module.

[0069] S2: Demodulate the first detection signal to obtain the phase error signal corresponding to each split beam, and respectively control the operation of each phase modulator based on the phase error signal corresponding to each split beam to adjust the phase of each split beam.

[0070] S3: Demodulate the second detection signal to obtain the polarization error signal corresponding to each split beam, and respectively control the operation of each polarization controller based on the polarization error signal corresponding to each split beam to adjust the polarization of each split beam.

[0071] In S2, demodulating the first detection signal to obtain the phase error signal corresponding to each split beam specifically includes: demodulating the first detection signal by using the coherent RF demodulation method to obtain the phase error signal corresponding to each split beam.

[0072] In S3, demodulate the second detection signal to obtain the polarization error signal corresponding to each sub-beam of light, specifically including: demodulate the second detection signal by using the coherent radio frequency demodulation method to obtain the polarization error signal corresponding to each sub-beam of light.

[0073] In S2, the calculation formula for the phase error signal is: ; where is the phase error signal corresponding to the th sub-beam of light; is the integration time; is the th modulation angular frequency of the sub-beam of light; is the time; is the first detection signal at time is the voltage conversion coefficient of the photodetector; is the th power of the sub-beam of light irradiating on the detection surface of the photodetector; is the first-kind Bessel function of order 1; is the th phase modulation depth of the sub-beam of light; is the number of sub-beams of light; is the th power of the sub-beam of light irradiating on the detection surface of the photodetector; is the first-kind Bessel function of order 0; is the th phase modulation depth of the sub-beam of light; is the th phase of the sub-beam of light in the main polarization direction; is the th phase of the sub-beam of light in the main polarization direction.

[0074] In S3, the calculation formula for the polarization error signal is: ; where is the polarization error signal corresponding to the th sub-beam of light; is the th power of the sub-beam of light irradiating on the detection surface of the photodetector, and the 0th sub-beam of light is the reference light.

[0075] In S2, each phase modulator is controlled based on the phase error signal corresponding to each split beam of light to adjust the phase of each split beam of light. Specifically, for each split beam of light, the phase modulator corresponding to the split beam of light is controlled based on the phase error signal corresponding to the split beam of light, and the phase of the split beam of light is adjusted to the updated phase.

[0076] The calculation formula for the updated phase is: ; where is the updated phase of the split beam of light; is the phase of the split beam of light; is the feedback coefficient; is the phase error signal corresponding to the split beam of light.

[0077] In S3, each polarization controller is controlled based on the polarization error signal corresponding to each split beam of light to adjust the polarization of each split beam of light. Specifically, for each split beam of light, using the polarization error signal corresponding to the split beam of light as the input, the SPGD algorithm is used to control the polarization controller corresponding to the split beam of light to adjust the polarization of the split beam of light.

[0078] Embodiment 3.

[0079] In an exemplary embodiment, a computer device is provided. The computer device can be a server or a terminal, and its internal structure diagram can be as Figure 4 shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, abbreviated as I / O), and a communication interface. Among them, the processor, the memory, and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program, and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store data. The input / output interface of the computer device is used to exchange information between the processor and external devices. The communication interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, it implements a multi-channel polarization phase active control method for a sub-aperture coherent combination system.

[0080] Those skilled in the art can understand, Figure 4The structure shown is only a block diagram of some structures related to the solution of this application, and does not constitute a limitation on the computer device to which the solution of this application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine some components, or have a different component layout.

[0081] In an exemplary embodiment, a computer device is provided, including a memory and a processor. A computer program is stored in the memory, and when the processor executes the computer program, it implements the multi-channel polarization phase active control method of the sub-aperture coherent synthesis system in Embodiment 2.

[0082] Embodiment 4.

[0083] In an exemplary embodiment, a computer-readable storage medium is provided, storing a computer program, and when the computer program is executed by a processor, it implements the multi-channel polarization phase active control method of the sub-aperture coherent synthesis system in Embodiment 2.

[0084] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use, and processing of relevant data need to comply with relevant regulations.

[0085] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, 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, it should be considered as the scope recorded in this specification.

[0086] Specific examples are used in this article to elaborate on the principle and implementation manner of this application. The description of the above embodiments is only used to help understand the method and its core idea of this application; at the same time, for those of ordinary skill in the art, according to the idea of this application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation on this application.

Claims

1. A multi-channel polarization phase active control system for a split-aperture coherent synthesis system, characterized in that, Comprising: A detection module and a control module; The detection module is used to sample the coherently combined light output by the sub-aperture coherent combination system to obtain sampled light, perform two syntheses on the sampled light and the reference light to obtain a first combined light and a second combined light, and respectively detect the first combined light and the second combined light to obtain a first detection signal and a second detection signal; the reference light is a beam of light output by a beam splitter in the sub-aperture coherent combination system and collimated, the first combined light is the combined light obtained by combining the sampled light and the reference light, and the second combined light is the combined light obtained by combining the sampled light and the reference light with a 90-degree phase shift; The control module includes a control system, a plurality of phase modulators and a plurality of polarization controllers. The phase modulators and the polarization controllers correspond one-to-one to the other split beams output by the beam splitter except the reference light. The phase modulators are applied with modulation signals, and the modulation angular frequencies of the modulation signals applied to different phase modulators are different; The control system is used to demodulate the first detection signal to obtain a phase error signal corresponding to each split beam, and respectively control the operation of each phase modulator based on the phase error signal corresponding to each split beam to adjust the phase of each split beam, and then demodulate the second detection signal to obtain a polarization error signal corresponding to each split beam, and respectively control the operation of each polarization controller based on the polarization error signal corresponding to each split beam to adjust the polarization of each split beam.

2. The multi-channel polarization phase active control system of the sub-aperture coherent synthesis system according to claim 1, wherein The detection module includes a sampling mirror, a synthesizer, a first detector and a second detector; the sampling mirror is used to sample the coherently combined light output by the sub-aperture coherent combination system to obtain sampled light; the synthesizer is used to perform two syntheses on the sampled light and the reference light to obtain a first combined light and a second combined light; the first detector is used to detect the first combined light to obtain a first detection signal; The second detector is used to detect the second combined light to obtain a second detection signal.

3. The multi-channel polarization phase active control system of the sub-aperture coherent synthesis system according to claim 2, characterized in that The synthesizer is a 90° optical mixer; The first detector includes a first polarizer, a first focusing lens and a first photodetector. The first polarizer is used to convert the first combined light into a first combined polarized light. The first focusing lens is used to focus the first combined polarized light to obtain a first combined focused light. The first photodetector is used to perform photoelectric conversion on the first combined focused light to obtain a first detection signal; The second detector includes a second polarizer, a second focusing lens and a second photodetector. The second polarizer is used to convert the second combined light into a second combined polarized light. The second focusing lens is used to focus the second combined polarized light to obtain a second combined focused light. The second photodetector is used to perform photoelectric conversion on the second combined focused light to obtain a second detection signal.

4. The multi-channel polarization phase active control system of the sub-aperture coherent synthesis system according to claim 1, characterized in that, The sub-aperture coherent combination system includes: a laser module and a beam combining module; The laser module includes a seed laser, a first laser amplifier, a beam splitter, multiple second laser amplifiers, multiple first collimators, and a second collimator. The seed laser is used to emit seed laser light. The first laser amplifier is used to amplify the seed laser light to obtain amplified laser light. The beam splitter is used to split the amplified laser light to obtain multiple split light beams and an output light beam. The second laser amplifiers and the first collimators correspond one-to-one to the split light beams. The second laser amplifier is used to amplify the split light beam to obtain amplified split light. The first collimator is used to collimate the amplified split light to obtain collimated split light. The second collimator is used to collimate the output light to obtain the reference light; The beam combining module is used to perform coherent combination on all the collimated split light beams.

5. The multi-channel polarization phase active control system of the sub-aperture coherent synthesis system according to claim 4, wherein The phase modulator and the polarization controller are located between the beam splitter and the second laser amplifier. The phase modulator is used to modulate the phase of the split light beam to obtain phase-modulated split light. The polarization controller is used to control the polarization of the phase-modulated split light to obtain polarization-controlled split light. After all the polarization-controlled split light beams are amplified by the second laser amplifier and collimated by the first collimator, they are combined by the beam combining module into the coherent combined light.

6. A multi-channel polarization phase active control method for a split-aperture coherent combination system, which works based on the multi-channel polarization phase active control system of the split-aperture coherent combination system according to any one of claims 1-5, characterized in that Including: Obtain a first detection signal and a second detection signal output by the detection module; Demodulate the first detection signal to obtain a phase error signal corresponding to each split light beam, and respectively control the operation of each phase modulator based on the phase error signal corresponding to each split light beam to adjust the phase of each split light beam; Demodulate the second detection signal to obtain a polarization error signal corresponding to each split light beam, and respectively control the operation of each polarization controller based on the polarization error signal corresponding to each split light beam to adjust the polarization of each split light beam.

7. The multi-channel polarization phase active control method for the sub-aperture coherent synthesis system according to claim 6, characterized in that, Demodulating the first detection signal to obtain a phase error signal corresponding to each split light beam specifically includes: demodulating the first detection signal by using a coherent radio frequency demodulation method to obtain a phase error signal corresponding to each split light beam; Demodulating the second detection signal to obtain a polarization error signal corresponding to each split light beam specifically includes: demodulating the second detection signal by using a coherent radio frequency demodulation method to obtain a polarization error signal corresponding to each split light beam.

8. The multi-channel polarization phase active control method for the sub-aperture coherent synthesis system according to claim 7, characterized in that The calculation formula for the phase error signal is: ； Among them, is the phase error signal corresponding to the split light beam; is the integration time; is the modulation angular frequency of the split light beam; is the time; is the first detection signal at time is the voltage conversion coefficient of the photodetector; is the power of the split light beam irradiating on the detection surface of the photodetector; is the first kind of Bessel function of order 1; is the phase modulation depth of the split light beam; is the number of split light beams; is the power of the split light beam irradiating on the detection surface of the photodetector; is the first kind of Bessel function of order 0; is the phase modulation depth of the split light beam; is the phase of the split light beam in the main polarization direction; is the phase of the split light beam in the main polarization direction; The calculation formula for the polarization error signal is: ； Among them, is the polarization error signal corresponding to the split beam of light; is the power of the split beam of light irradiating on the detection surface of the photodetector, and the 0th split beam of light is the reference light.

9. The multi-channel polarization phase active control method of the sub-aperture coherent synthesis system according to claim 6, characterized in that Respectively controlling the operation of each phase modulator based on the phase error signal corresponding to each split light beam to adjust the phase of each split light beam specifically includes: for each split light beam, controlling the operation of the phase modulator corresponding to the split light beam based on the phase error signal corresponding to the split light beam, and adjusting the phase of the split light beam to the updated phase; The calculation formula for the updated phase is: ； Among them, is the updated phase of the split beam; is the phase of the split beam; is the feedback coefficient; is the phase error signal corresponding to the split beam.

10. The multi-channel polarization phase active control method of the sub-aperture coherent synthesis system according to claim 6, characterized in that, Based on the polarization error signals corresponding to each split beam of light, control the operation of each polarization controller respectively to adjust the polarization of each split beam of light. Specifically, for each split beam of light, use the polarization error signal corresponding to the split beam of light as the input, and control the operation of the polarization controller corresponding to the split beam of light by using the SPGD algorithm to adjust the polarization of the split beam of light.

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