A model-based adaptive multi-aperture fiber coupling control system and method

Abstract

The present invention relates to the field of optical engineering technology, and in particular to a model-based adaptive multi-aperture fiber coupling control system and method, a fiber coupler array, an optical fiber, a photodetector, a controller and a high-voltage amplifier, wherein a plurality of optical fibers and photodetectors are provided, and the fiber coupler array is composed of a plurality of fiber couplers, wherein the output ends of the plurality of fiber couplers are respectively connected to the input ends of the plurality of photodetectors through a plurality of optical fibers, the output ends of the plurality of photodetectors are respectively connected to the input ends of the controller, the output ends of the controller are respectively connected to the input ends of the high-voltage amplifier, and the output ends of the high-voltage amplifier are respectively connected to the plurality of fiber couplers. The present invention provides an adaptive multi-aperture fiber coupling control system and method with fast system convergence speed, high fiber coupling efficiency, strong robustness for fiber coupling applications under different turbulence intensities, and high stability.

Description

Technical Field

[0001] The present invention relates to the field of optical engineering technology, and in particular to a model-based adaptive multi-aperture optical fiber coupling control system and method. Background Art

[0002] Adaptive optics technology can improve imaging quality or system performance, and has been applied to astronomical observation, laser communication, microscopic imaging and other fields. Free space optical communication (FSOC-Free Space Optical Communications) is a new type of communication method that has emerged in recent years. It has significant advantages such as fast transmission rate, strong information carrying capacity and excellent confidentiality. As one of the core components in the free space optical communication system, the fiber coupler is used to realize signal coupling and distribution between optical fibers. After coupling and distribution, the laser signal enters the optical fiber receiving end. The overall performance of the optical fiber receiving end, including the fiber coupler, represents the performance of the laser communication system. However, in actual free space optical communication applications, due to the presence of atmospheric turbulence on the laser transmission path, the fiber coupling efficiency is greatly reduced, far from the theoretical fiber coupling efficiency value. Therefore, how to suppress or reduce the influence of atmospheric turbulence on the laser signal coupling efficiency and improve the coupling efficiency of the optical fiber receiving end is a recent research hotspot and goal in the field of space laser communication applications.

[0003] At present, the stochastic parallel gradient descent algorithm (SPGD-Stochastic ParallelGradient Descent JOSA, 1998, 15 (10): 2745-2758) is often used at the optical fiber receiving end to control the optical fiber coupler array to improve the optical fiber coupling efficiency. However, due to the dynamic change of atmospheric turbulence, the slow convergence speed of the SPGD algorithm is difficult to meet practical applications. In order to further improve the performance of laser communication systems, it is necessary to study a control method with faster convergence speed so that the adaptive optical fiber coupler can quickly find the optimal control parameters to improve the optical fiber coupling efficiency. Summary of the invention

[0004] The purpose of the present invention is to provide a model-based adaptive multi-aperture fiber coupling control system and method to solve the technical problems existing in the above-mentioned background technology.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A model-based adaptive multi-aperture fiber-optic coupling control system comprises: a fiber-optic coupler array, an optical fiber, a photodetector, a controller and a high-voltage amplifier, wherein a plurality of optical fibers and photodetectors are provided, and the fiber-optic coupler array is composed of a plurality of fiber-optic couplers, wherein the output ends of the plurality of fiber-optic couplers are respectively connected to the input ends of the plurality of photodetectors through a plurality of optical fibers, the output ends of the plurality of photodetectors are respectively connected to the input ends of the controller, the output ends of the controller are respectively connected to the input ends of the high-voltage amplifier, and the output ends of the high-voltage amplifier are respectively connected to the fiber-optic couplers.

[0007] Furthermore, the fiber coupler comprises: a receiving aperture, a sub-aperture, a coupling lens and a rear focal plane, wherein a plurality of sub-apertures are provided, and the receiving aperture, the plurality of sub-apertures, the coupling lens and the rear focal plane are arranged in sequence, one end of the optical fiber is connected to the rear focal plane, the distorted wavefront is incident on the receiving aperture of the fiber coupler, and then is divided into sub-beams by the sub-aperture of the fiber coupler, the sub-beams of the plurality of sub-apertures are focused by the coupling lens and form a focusing spot on the rear focal plane, and part of the incident light is coupled into the optical fiber at the rear focal plane; the coupled light beam is transmitted into a corresponding photodetector through the optical fiber, converted into a corresponding electrical signal, and sent to a controller; the control algorithm in the controller calculates a corresponding control signal and transmits it to a high-voltage amplifier, the control signal is amplified by the high-voltage amplifier and transmitted to the fiber coupler, a surface shape opposite to the distorted wavefront is generated by the fiber coupler, and superimposed with the distorted wavefront to complete the correction of the distorted wavefront, thereby controlling the fiber end face to find the maximum coupling efficiency point at the respective rear focal planes.

[0008] Furthermore, the optical fiber is a single-mode optical fiber.

[0009] A model-based adaptive multi-aperture optical fiber coupling control method, characterized in that it specifically includes the following steps:

[0010] Step 1: Initialize the parameters of the control algorithm in the controller, and use the fiber coupling efficiency as the objective function of the control algorithm;

[0011] Step 2: pre-processing;

[0012] Step 3, measuring and calculating the sum of the light intensities of the N sub-apertures;

[0013] Step 4: Add voltage perturbation of the X-direction basis function with coefficient a to the N sub-apertures in parallel, measure and calculate the sum of the light intensities of the N sub-apertures; add voltage perturbation of the Y-direction basis function with coefficient a again, measure and calculate the sum of the light intensities of the N sub-apertures;

[0014] Step 5, performing a difference operation on the sum of the light intensities measured after the N sub-apertures are disturbed and the sum of the light intensities corresponding to the distorted wavefront;

[0015] Step 6: Calculate and obtain the coupler driving signals corresponding to each of the N sub-apertures using the difference operation result; amplify the driving signals through a high-voltage amplifier and apply them to the driver of the coupling lens of each sub-aperture; use a photodetector to detect the corrected spot information, and calculate the system performance evaluation function of the current iteration based on the spot information;

[0016] Step 7: Use the corrected residual wavefront as the wavefront to be corrected, repeat steps 3 to 6, and complete the correction until the preset termination condition is reached.

[0017] Furthermore, the preprocessing in step 2 is specifically as follows: defining a set of basis functions {Z x ,Z y}, respectively recorded as the inclination in the X direction and the inclination in the Y direction, calculate the Z x and Z y The second-order moments of the gradient of the x component and the y component are calculated and inverted, which is recorded as P; the influence function E of the coupling lens is measured, and the cross-correlation matrix C between it and the basis function is established. ze , calculate the autocorrelation coupling matrix C between the driver influence functions e ; Use formula (1) to obtain the driving signal v of the coupling lens;

[0018]

[0019] Where a is a scalar value that can change.

[0020] Furthermore, the step three is specifically as follows: taking the centroid corresponding to each sub-aperture as the center, intercepting an image plane of size M*M, and calculating the sum of the light intensities of the N sub-apertures I i0 , where i∈{1,...,N}.

[0021] Furthermore, the step 4 is specifically as follows: adding voltage disturbance of the X-direction basis function with coefficient a to the N sub-apertures in parallel, and the voltage magnitude is calculated according to formula (1); intercepting an image plane of size M*M with the centroid of each sub-aperture as the center, and calculating the sum of the light intensities I of the portions of the image plane intercepted by the N sub-apertures ix ; Add voltage disturbance of Y-direction basis function with coefficient a to N sub-apertures in parallel, and the voltage magnitude is calculated according to formula (1); intercept an image plane of size M*M with the centroid of each sub-aperture as the center, and calculate the sum of the light intensities I of the portions of the image plane intercepted by the N sub-apertures iy .

[0022] Furthermore, the step 5 is specifically as follows: respectively measuring the light intensity (I ix ,I iy ) and the light intensity I corresponding to the distorted wavefront i0Perform the difference operation to obtain the N×2 dimensional vector Q:

[0023] Q i ={(I ix , I iy )-I i0} i∈{1,...N} (2).

[0024] Furthermore, the calculation of the driving signal in step 6 is specifically as follows: the coupler driving signal V corresponding to each of the N sub-apertures is obtained by using the following formula (3): i , where V is the N-dimensional control signal;

[0025]

[0026] Furthermore, the termination condition in step seven includes a certain number of iterations or the overall optical fiber coupling efficiency is greater than a threshold.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The model-based adaptive multi-aperture fiber coupling control method uses the mathematical relationship between the far-field spot and the wavefront aberration to establish a model. Compared with the existing blind optimization algorithm, it makes full use of physical principles and has high reliability.

[0029] 2. Using the mathematical relationship between the far-field spot and the wavefront aberration to establish a model is equivalent to having a certain prior knowledge of the fiber-coupled control system. Controlling the system based on the prior knowledge greatly accelerates the convergence speed of the system.

[0030] 3. This technology is highly robust for fiber coupling applications under different turbulence intensities, and can greatly improve the coupling efficiency at the fiber receiving end and enhance signal quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the structure of the model-based adaptive multi-aperture fiber coupling control system of the present invention;

[0032] Figure 2 It is a flow chart of the model-based adaptive multi-aperture optical fiber coupling control method of the present invention;

[0033] Figure 3 This is an example of the comparison of the coupling efficiency between the model method and the SPGD method when the turbulence condition D / r0=7 and the subaperture is 19, where D is the telescope aperture and r0 is the atmospheric coherence length. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

[0035] In practical applications, the number of subapertures is generally 3, 7, 19, 37, etc. The following takes the adaptive fiber coupler array when the number of subapertures is 19 as an example, and further describes the present invention in conjunction with the accompanying drawings. In this embodiment, Zernike polynomials are used as basis functions, but are not limited to Zernike polynomials in actual implementation. Fiber coupling efficiency is used as the objective function of the control algorithm. The smaller the aberration, the greater the system coupling efficiency. In actual implementation, the description of fiber coupling performance is not limited to coupling efficiency.

[0036] like Figure 1 As shown, a model-based adaptive multi-aperture fiber-optic coupling control system includes: a fiber-optic coupler array, an optical fiber, a photodetector, a controller and a high-voltage amplifier. A plurality of optical fibers and photodetectors are provided. The fiber-optic coupler array is composed of a plurality of fiber-optic couplers. The output ends of the plurality of fiber-optic couplers are respectively connected to the input ends of the plurality of photodetectors through a plurality of optical fibers. The output ends of the plurality of photodetectors are respectively connected to the input ends of the controller. The output ends of the controller are respectively connected to the input ends of the high-voltage amplifier. The output ends of the high-voltage amplifier are respectively connected to the fiber-optic couplers.

[0037] The optical fiber coupler includes: a receiving aperture, a sub-aperture, a coupling lens and a rear focal plane. There are several sub-apertures, and the receiving aperture, several sub-apertures, coupling lens and rear focal plane are arranged in sequence. One end of the optical fiber is connected to the rear focal plane. The distorted wavefront is incident on the receiving aperture of the optical fiber coupler, and then divided into sub-beams by the sub-aperture of the optical fiber coupler. The sub-beams of several sub-apertures are focused by the coupling lens and form a focusing spot on the rear focal plane. Part of the incident light is coupled into the optical fiber at the rear focal plane; the coupled light beam is transmitted into the corresponding photodetector through the optical fiber, converted into a corresponding electrical signal, and sent to the controller; the control algorithm in the controller calculates the corresponding control signal and transmits it to the high-voltage amplifier. The control signal is amplified by the high-voltage amplifier and transmitted to the optical fiber coupler. The optical fiber coupler generates a surface shape opposite to the distorted wavefront and superimposes it with the distorted wavefront to complete the correction of the distorted wavefront, thereby controlling the optical fiber end face to find the maximum coupling efficiency point in the respective rear focal planes.

[0038] like Figure 2 As shown, a model-based adaptive multi-aperture fiber coupling control method includes the following steps:

[0039] Step 1: Initialize the parameters of the control algorithm and use the fiber coupling efficiency as the objective function of the control algorithm.

[0040] Step 2: Preprocessing. This part includes the calculation of the gradient inverse matrix P, the measurement of the influence function E of the coupling lens, and the cross-correlation matrix C. ze And the autocorrelation coupling matrix C e Calculation.

[0041] According to the basis function {Z x ,Z y}Calculate Z x and Z y The gradient second-order moment of the x component and the y component is calculated respectively, and the inversion is obtained to obtain P. The influence function E of the coupling lens is measured, and the cross-correlation and autocorrelation coupling matrices C are calculated. ze and C e This information is calculated first and has nothing to do with the wavefront to be corrected.

[0042] Step 3: Take the center of mass of each sub-aperture as the center, intercept the image plane of size M*M, measure and calculate the sum of the light intensities of the 19 sub-apertures I i0 , where i∈{1,...,19}.

[0043] Step 4: Add the voltage perturbation of the X-direction basis function with coefficient a to the 19 sub-apertures in parallel, and the voltage magnitude is calculated according to formula (1). The deformation generated by the coupling lens is superimposed on the distorted wavefront. After being focused by the focusing lens, part of the light spot enters the single-mode fiber and is then detected by the photodetector. Measure and calculate the sum of the light intensities of the image planes intercepted by the 19 sub-apertures. ix Similarly, the voltage perturbation of the Y-direction basis function with coefficient a is added to the 19 sub-apertures in parallel, and the corresponding light intensity and I of each sub-aperture are obtained. iy .

[0044] Step 5: Use formula (2) to calculate the light intensity (I ix ,I iy ) and the light intensity I of the wavefront to be measured corresponding to each sub-aperture i0 The difference is Q.

[0045] Step 6: Use formula (3) to obtain the driving signal V of the 19 fiber couplers corresponding to the distorted wavefront i The driving signal is amplified by a high-voltage amplifier and applied in parallel to the driver of the coupling lens of each sub-aperture, generating a surface shape opposite to the wavefront to be measured, superimposed on the wavefront to be corrected, and completing the control of 19 fiber couplers. Based on the photodetector information, the system performance evaluation function of the current iteration is calculated.

[0046] Step 7: Use the residual wavefront as the wavefront to be corrected and repeat steps 3 to 6. When the preset termination condition is reached, such as a certain number of iterations or the overall fiber coupling efficiency is greater than a threshold, the closed-loop correction of the entire system is completed.

[0047] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, according to the technical essence of the present invention, any simple modification, equivalent replacement and improvement made to the above embodiment still falls within the protection scope of the technical solution of the present invention.

Claims

1. A model-based adaptive multi-aperture fiber coupling control method, characterized in that: The specific steps include: Step 1: Initialize the parameters of the control algorithm in the controller, and use the fiber coupling efficiency as the objective function of the control algorithm; Step 2: pre-processing; The preprocessing in step 2 is specifically as follows: defining a set of basis functions {Z x ,Z y }, respectively recorded as the inclination in the X direction and the inclination in the Y direction, calculate the Z x and Z y The second-order moments of the gradient of the x component and the y component are calculated and inverted, which is recorded as P; the influence function E of the coupling lens is measured, and the cross-correlation matrix C between it and the basis function is established. ze , calculate the autocorrelation coupling matrix C between the driver influence functions e ; Use formula (1) to obtain the driving signal v of the coupling lens; Where a is a scalar value that can change; Step 3: Measure and calculate the sum of the light intensities of the N sub-apertures; The step three is specifically as follows: taking the centroid corresponding to each sub-aperture as the center, intercepting an image plane of size M*M, and calculating the sum of the light intensities of the N sub-apertures I i0 , where i∈{1,...,N}; Step 4: Add voltage perturbation of the X-direction basis function with coefficient a to the N sub-apertures in parallel, measure and calculate the sum of the light intensities of the N sub-apertures; add voltage perturbation of the Y-direction basis function with coefficient a again, measure and calculate the sum of the light intensities of the N sub-apertures; The step 4 is specifically as follows: adding voltage disturbance of the X-direction basis function with coefficient a to the N sub-apertures in parallel, and the voltage magnitude is calculated according to formula (1); intercepting an image plane of size M*M with the centroid of each sub-aperture as the center, and calculating the sum of the light intensities I of the portions of the image plane intercepted by the N sub-apertures. ix ; Add voltage disturbance of Y-direction basis function with coefficient a to N sub-apertures in parallel, and the voltage magnitude is calculated according to formula (1); intercept an image plane of size M*M with the centroid of each sub-aperture as the center, and calculate the sum of the light intensities I of the portions of the image plane intercepted by the N sub-apertures iy ; Step 5, performing a difference operation on the sum of the light intensities measured after the N sub-apertures are disturbed and the sum of the light intensities corresponding to the distorted wavefront; The step 5 specifically comprises: respectively measuring the light intensity (I ix ,I iy ) and the light intensity I corresponding to the distorted wavefront i0 Perform the difference operation to obtain the N×2 dimensional vector Q: Q i ={(I ix ,I iy )-I i0 } i∈{1,...N} (2); Step 6: Calculate and obtain the coupler driving signals corresponding to each of the N sub-apertures using the difference operation result; amplify the driving signals through a high-voltage amplifier and apply them to the driver of the coupling lens of each sub-aperture; use a photodetector to detect the corrected spot information, and calculate the system performance evaluation function of the current iteration based on the spot information; The calculation of the driving signal in step 6 is specifically as follows: the coupler driving signal V corresponding to each of the N sub-apertures is obtained by using the following formula (3): i , where V is the N-dimensional control signal; Step 7: Use the corrected residual wavefront as the wavefront to be corrected, repeat steps 3 to 6, and complete the correction until the preset termination condition is reached.

2. The method of claim 1, wherein: The termination condition in step seven includes a certain number of iterations or the overall optical fiber coupling efficiency being greater than a threshold.

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