A spatial phase distortion compensation system and method based on genetic algorithm

Abstract

The present invention discloses a spatial phase distortion compensation system and method based on a genetic algorithm, wherein the system mainly includes a wavefront correction unit, a signal acquisition unit, and a signal processing unit. The heterodyne signal generated by the interference of the signal light beam compensated by the wavefront correction unit and the local oscillator light beam in the system is received by the signal acquisition unit. Subsequently, the signal processing unit calculates a new spatial phase compensation amount through a genetic algorithm based on the calculation result of the current fitness function value of the system, and sends it to the wavefront correction unit for real-time phase compensation. The system proposed in the present invention does not need to construct an accurate model, but only continuously approaches the optimal solution in an iterative form through an optimization algorithm, and has the advantages of low cost and simple structure. The method proposed in the present invention transforms the spatial phase distortion compensation problem into a combinatorial optimization problem that seeks optimization for the heterodyne signal-to-noise ratio of the system, and uses a genetic algorithm to iteratively calculate the optimal spatial phase compensation amount, thereby realizing fast and accurate compensation of spatial phase distortion.

Description

Technical Field

[0001] The invention belongs to the technical field of spatial phase distortion compensation, and in particular relates to a spatial phase distortion compensation system and method based on a genetic algorithm. Background Art

[0002] Coherent optical communication is a communication method that modulates the amplitude, frequency or phase of the optical carrier at the transmitting end and uses coherent detection technology to receive information at the receiving end. Coherent optical communication technology has flexible modulation methods, excellent spatial selectivity, high detection sensitivity and good background noise suppression capabilities, which makes coherent optical communication the main development direction of high-speed and long-distance space optical communication in the future. However, the most serious problem in practical applications is the impact of atmospheric turbulence on communication channels. Atmospheric turbulence is a random air movement, which refers to the random change of refractive index caused by random changes in local atmospheric temperature, pressure and other parameters. It mainly occurs at the junction of several airflow layers moving at different speeds. The atmospheric refractive index fluctuations caused by atmospheric turbulence will cause wavefront phase distortion in spatial coherent optical communication, causing the signal light field and the local oscillator light field wavefront mismatch, significantly reducing the signal-to-noise ratio of the coherent optical communication system.

[0003] Scholars at home and abroad have carried out a lot of research on spatial phase distortion compensation technology. At present, the two main spatial phase distortion compensation methods are adaptive optics method and array detection method.

[0004] Adaptive optics methods include traditional adaptive optics technology and adaptive optics technology without wavefront sensing. Traditional adaptive optics technology usually uses wavefront sensors to detect the wavefront distortion of the signal light field, and then compensates the wavefront distortion through a wavefront compensation system composed of deformable mirrors, see Christou JC et al.'s article Feature issue introduction: applications of adaptive optics. However, the scintillation phenomenon in complex environments will destroy the signal light wavefront, forming phase discontinuities, making wavefront detection very difficult. At the same time, adaptive optical systems usually require supporting automatic control and servo systems, which makes the structure of adaptive optical systems more complicated. Compared with conventional adaptive optics, the biggest feature of adaptive optics without wavefront sensing is that it does not use wavefront sensors to detect wavefront distortion, but directly controls the wavefront corrector to optimize the signal light through optimization algorithms, see Guo Y et al.'s literature Adaptive optics based on machine learning: a review. However, most of the optimization algorithms used in adaptive optics without wavefront sensing currently use traditional convolutional neural networks, which cannot achieve real-time compensation of wavefront distortion phase.

[0005] The basic idea of ​​the array detection method is to use an array detector to receive heterodyne signals, convert spatial phase distortion into phase difference between array heterodyne signals, and improve detection performance by compensating for the phase difference between heterodyne signals of each array, see the literature of Liu Y et al., Parallel array signal processing technology for spatial phase distortion correction in heterodyne detection. However, the array detector system has a complex structure, and the existing technical solutions have problems such as high time loss of phase calculation and difficulty in phase distortion compensation, which restrict the further development of the array detection method.

[0006] In summary, there is still a technical bottleneck in how to effectively solve the problem of reduced signal-to-noise ratio in coherent optical communication systems caused by spatial phase distortion. Therefore, designing a spatial phase distortion compensation method that takes into account both real-time performance and accuracy is a technical problem that urgently needs to be solved. Summary of the invention

[0007] In order to solve the above technical problems, the present invention proposes a spatial phase distortion compensation system and method based on genetic algorithm. The system uses optimization algorithm to solve complex combinatorial optimization problems, has the advantages of fast speed, small size, low cost and simple structure, and is conducive to realizing real-time dynamic compensation of spatial phase distortion.

[0008] The spatial phase distortion compensation system based on genetic algorithm proposed in the present invention mainly includes a wavefront correction unit, a signal acquisition unit, and a signal processing unit. The heterodyne signal generated by the interference of the signal beam compensated by the wavefront correction unit and the local oscillator beam in the system is first received by the signal acquisition unit. Subsequently, the signal processing unit calculates the new spatial phase compensation amount through the genetic algorithm based on the calculation result of the current fitness function value (heterodyne signal-to-noise ratio) of the system, and sends it to the wavefront correction unit for real-time phase compensation.

[0009] The system heterodyne signal-to-noise ratio is used as a fitness function, and a one-to-one correspondence between the spatial phase compensation amount combination and the fitness function is established, and the spatial phase distortion compensation problem is transformed into a combinatorial optimization problem based on the system heterodyne signal-to-noise ratio, and then the optimal spatial phase compensation amount combination is iteratively calculated using a genetic algorithm.

[0010] The genetic algorithm steps are divided into three steps:

[0011] In the first step, the signal processing unit randomly selects some individuals from all feasible solutions of the spatial phase distortion compensation combinatorial optimization problem to generate an initial population;

[0012] In the second step, the wavefront correction unit loads the phase adjustment value combination solution in the population respectively, and then determines whether the system fitness function value under the global optimal solution meets the set threshold or whether the number of iterations meets the iteration termination condition. If so, proceed to the next step. If not, use the genetic algorithm to generate a new generation of population and repeat the second step.

[0013] In the third step, the signal processing unit continuously outputs the global optimal phase adjustment combination solution to the system wavefront correction unit, and monitors the system signal-to-noise ratio in real time. When the system signal-to-noise ratio is lower than the set threshold, it jumps to the first step.

[0014] The spatial phase distortion compensation amount combination is to divide the signal light wavefront space area to be compensated into n×n independent spatial areas, and each independent area corresponds to a part of the spatial phase distortion. When the area of ​​the divided area is small enough, the phase distribution in each partial area can be considered to obey a uniform distribution. At this time, a set of determined spatial phase compensation amount combinations are applied to each of the n×n independent spatial areas. When the applied n×n independent spatial phase compensation amounts are equal to or approximately equal to the phase difference between the independent spatial regions, the compensation of the spatial phase distortion of the signal light field can be achieved.

[0015] The spatial phase distortion compensation amount combination After being applied to the signal light field, the heterodyne signal-to-noise ratio of the system can be written as

[0016]

[0017] Where IF is the intermediate frequency, γ is the detector quantum efficiency, P S is the heterodyne detection signal optical power, is Planck's constant, ν is the frequency of light, B IF is the IF signal bandwidth, Indicates the spatial phase difference between the local oscillator light and the signal light; Represents a set of determined combinations of spatial phase compensation amounts applied.

[0018] The above formula shows that different combinations of spatial phase compensation amounts correspond to different heterodyne signal-to-noise ratio results. There is a one-to-one correspondence between the spatial phase compensation amount combination and the heterodyne signal-to-noise ratio, that is, the higher the fit between the spatial phase compensation amount combination and the spatial phase distortion, the better the heterodyne signal-to-noise ratio.

[0019] The present invention performs real-time dynamic compensation for spatial phase distortion through a closed-loop control link of spatial phase distortion compensation based on a genetic algorithm. In the system, the heterodyne signal generated by the interference of the signal light beam compensated by the spatial light modulator of the wavefront correction unit and the local oscillator light beam is received by the detector of the signal acquisition unit, and then passes through the signal processing system after the intermediate frequency amplifier. The signal processing system calculates the new spatial phase compensation amount through a genetic algorithm based on the calculation result of the current fitness function, and sends it to the wavefront correction unit for real-time phase compensation. Therefore, the method proposed by the present invention can realize closed-loop compensation of spatial phase distortion.

[0020] The system proposed by the present invention does not need to construct an accurate mathematical model, but only simulates the natural evolution process of organisms to continuously approach the optimal solution of the optimization problem in an iterative form, and has the advantages of fast speed, small size, low cost and simple structure. The method proposed by the present invention transforms the spatial phase distortion compensation problem into a combinatorial optimization problem of optimizing the heterodyne signal-to-noise ratio of the system, and uses a genetic algorithm to iteratively calculate the optimal spatial phase compensation amount, so as to realize fast and accurate compensation of spatial phase distortion. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is an overall system block diagram of the present invention;

[0022] Figure 2 Generates a schematic diagram for the combined solution of spatial phase compensation quantities. DETAILED DESCRIPTION

[0023] In order to make the technical solution, advantages and purposes of the present invention clearer, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and a detailed implementation method and a detailed operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

[0024] like Figure 1-2 A spatial phase distortion compensation system based on genetic algorithm mainly includes a wavefront correction unit, a signal acquisition unit and a signal processing unit. The system actively compensates for the spatial phase distortion to improve the performance of the heterodyne detection system. The heterodyne signal generated by the interference of the signal beam compensated by the wavefront correction unit and the local oscillator beam in the system is received by the signal acquisition unit. Subsequently, the signal processing unit calculates the new spatial phase compensation amount through the genetic algorithm based on the calculation result of the current fitness function value (heterodyne signal-to-noise ratio) of the system, and sends it to the wavefront correction unit for real-time phase compensation.

[0025] A spatial phase distortion compensation method based on genetic algorithm uses the above system, takes the system heterodyne signal-to-noise ratio as the fitness function, establishes a one-to-one correspondence between the spatial phase compensation amount combination and the fitness function, transforms the spatial phase distortion compensation problem into a combinatorial optimization problem based on the system heterodyne signal-to-noise ratio, and then uses the genetic algorithm to iteratively calculate the optimal spatial phase compensation amount combination.

[0026] The genetic algorithm steps are divided into three steps:

[0027] In the first step, the signal processing unit randomly selects some individuals from all feasible solutions of the spatial phase distortion compensation combinatorial optimization problem to generate an initial population;

[0028] In the second step, the wavefront correction unit loads the phase adjustment value combination solution in the population respectively, and then determines whether the system fitness function value under the global optimal solution meets the set threshold or whether the number of iterations meets the iteration termination condition. If so, proceed to the next step. If not, use the genetic algorithm to generate a new generation of population and repeat the second step.

[0029] In the third step, the signal processing unit continuously outputs the global optimal phase adjustment combination solution to the system wavefront correction unit, and monitors the system signal-to-noise ratio in real time. When the system signal-to-noise ratio is lower than the set threshold, it jumps to the first step.

[0030] The spatial phase distortion compensation combined optimization problem is to divide the signal light wavefront space area to be compensated into n×n independent space areas evenly, and each independent space area corresponds to a part of the spatial phase distortion, such as Figure 2 As shown. When the area of ​​the divided region is small enough, the phase distribution in each partial region can be considered to obey a uniform distribution. At this time, a set of determined spatial phase compensation combinations are applied to each of the n×n independent spatial regions. When the applied n×n independent spatial phase compensation amounts are equal to or approximately equal to the phase difference between the independent spatial regions, the compensation of the spatial phase distortion of the signal light field can be achieved.

[0031] The spatial phase distortion compensation amount combination After being applied to the signal light field, the heterodyne signal-to-noise ratio of the system can be expressed as

[0032]

[0033] Where IF is the intermediate frequency, γ is the detector quantum efficiency, P S is the heterodyne detection signal optical power, is Planck's constant, ν is the frequency of light, B IF is the IF signal bandwidth, Indicates the spatial phase difference between the local oscillator light and the signal light; Represents a set of determined combinations of spatial phase compensation amounts applied.

[0034] The above formula shows that different combinations of spatial phase compensation amounts correspond to different heterodyne signal-to-noise ratio results. There is a one-to-one correspondence between the spatial phase compensation amount combination and the heterodyne signal-to-noise ratio, that is, the higher the fit between the spatial phase compensation amount combination and the spatial phase distortion, the better the heterodyne signal-to-noise ratio.

[0035] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A spatial phase distortion compensation system based on genetic algorithm, characterized in that: It includes a wavefront correction unit, a signal acquisition unit and a signal processing unit. The heterodyne signal generated by the interference of the signal beam compensated by the wavefront correction unit and the local oscillator beam in the system is received by the signal acquisition unit. The signal processing unit calculates a new spatial phase compensation amount through a genetic algorithm based on the calculation result of the current fitness function value of the system, and sends it to the wavefront correction unit for real-time phase compensation. A method for compensating spatial phase distortion based on genetic algorithm, using the system, taking the system heterodyne signal-to-noise ratio as the fitness function, establishing a one-to-one correspondence between the spatial phase compensation amount combination and the fitness function, transforming the spatial phase distortion compensation problem into a combination optimization problem based on the system heterodyne signal-to-noise ratio, and then using the genetic algorithm to iteratively calculate the best spatial phase compensation amount combination; The genetic algorithm steps are divided into three steps: In the first step, the signal processing unit randomly selects some individuals from all feasible solutions of the spatial phase distortion compensation combinatorial optimization problem to generate an initial population; In the second step, the wavefront correction unit loads the phase adjustment value combination solution in the population respectively, and then determines whether the system fitness function value under the global optimal solution meets the set threshold or whether the number of iterations meets the iteration termination condition. If so, proceed to the next step. If not, use the genetic algorithm to generate a new generation of population and repeat the second step. In the third step, the signal processing unit continuously outputs the global optimal phase adjustment combination solution to the system wavefront correction unit, and monitors the system signal-to-noise ratio in real time. When the system signal-to-noise ratio is lower than the set threshold, it jumps to the first step. The spatial phase distortion compensation amount combination is to divide the signal light wavefront space area to be compensated into n×n independent spatial areas, each of which corresponds to a part of the spatial phase distortion; when the area of ​​the divided area is small enough, the phase distribution in each partial area can be considered to obey a uniform distribution; a set of determined spatial phase compensation amount combinations are applied to each of the n×n independent spatial areas. When the applied n×n independent spatial phase compensation amounts are equal to or approximately equal to the phase difference between the independent spatial regions, the compensation of the spatial phase distortion of the signal light field can be achieved; The spatial phase distortion compensation amount combination After being applied to the signal light field, the heterodyne signal-to-noise ratio of the system can be expressed as Where IF is the intermediate frequency, γ is the detector quantum efficiency, P S is the heterodyne detection signal optical power, is Planck's constant, ν is the frequency of light, B IF is the IF signal bandwidth, Indicates the spatial phase difference between the local oscillator light and the signal light; Represents a set of determined combinations of spatial phase compensation amounts applied.

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