Model-based adaptive multi-aperture optical fiber coupling control system and method

Abstract

The present invention relates to the technical field of optical engineering, and in particular to a model-based adaptive multi-aperture optical fiber coupling control system and method. The system comprises an optical fiber coupler array, optical fibers, photodetectors, a controller, and a high-voltage amplifier. A plurality of optical fibers and a plurality of photodetectors are provided; the optical fiber coupler array consists of a plurality of optical fiber couplers; output ends of the plurality of optical fiber couplers are respectively connected to input ends of the plurality of photodetectors by means of the plurality of optical fibers; output ends of the plurality of photodetectors are respectively connected to a plurality of input ends of the controller; a plurality of output ends of the controller are respectively connected to a plurality of input ends of the high-voltage amplifier; a plurality of output ends of the high-voltage amplifier are respectively connected to the plurality of optical fiber couplers. The present invention provides an adaptive multi-aperture optical fiber coupling control system and method having a high system convergence rate, high optical fiber coupling efficiency, strong robustness in optical fiber coupling applications under different turbulence intensities, and high stability.

Description

Model-based adaptive multi-aperture fiber coupling control system and method TECHNICAL FIELD

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

[0002] Adaptive optics technology can improve imaging quality or system performance, and has been applied to the fields of astronomical observation, laser communication, microscopic imaging, etc. Free space optical communication (FSOC) is a new type of communication method that has emerged in recent years, and has the advantages of fast transmission rate, strong information carrying capacity, and excellent confidentiality. The fiber coupler is one of the core components in the free space optical communication system, and is used to realize signal coupling and distribution between optical fibers. After the laser signal is coupled and distributed, it enters the optical fiber receiving end. The overall performance of the optical fiber receiving end including the fiber coupler represents the pros and cons of the performance of the laser communication system. However, in actual free space optical communication applications, due to the existence of atmospheric turbulence in 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 coupling efficiency of the laser signal and improve the coupling efficiency of the optical fiber receiving end is a hot spot and target in the field of space laser communication applications in recent years.

[0003] At present, the random parallel gradient descent algorithm (SPGD) is commonly used in the optical fiber receiving end to control the fiber coupler array in order to improve the fiber coupling efficiency. However, due to the dynamic changes of atmospheric turbulence, the slow convergence speed of the SPGD algorithm makes it difficult to meet the actual application. In order to further improve the performance of the laser communication system, it is necessary to study a control method with faster convergence speed, so that the adaptive fiber coupler can quickly find the optimal control parameters to improve the fiber coupling efficiency. SUMMARY

[0004] The present application aims to provide a model-based adaptive multi-aperture fiber coupling control system and method to solve the technical problems existing in the background art.

[0005] To achieve the above-mentioned purpose, the technical solution of the present application is as follows:

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

[0007] Further, the fiber coupler comprises: a receiving aperture, a sub-aperture, a coupling lens and a back focal plane, the sub-aperture is provided with a plurality of, the receiving aperture, the plurality of sub-apertures, the coupling lens and the back focal plane are sequentially arranged, one end of the optical fiber is connected at the back focal plane, the distorted wavefront is incident at 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 focused spots at the back focal plane, and part of the incident light is coupled into the optical fiber at the back 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 then transmitted to the fiber coupler, a surface shape opposite to the distorted wavefront is generated by the fiber coupler, and the distorted wavefront is superimposed, thereby completing the correction of the distorted wavefront, so that the fiber end face finds the maximum coupling efficiency point at the respective back focal plane.

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

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

[0010] Step one, initializing the parameters of the control algorithm in the controller, taking the fiber coupling efficiency as the objective function of the control algorithm;

[0011] Step two, preprocessing;

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

[0013] Step four, adding voltage disturbance of the X-direction basis function with a coefficient of a to the N sub-apertures in parallel, measuring and calculating the sum of the respective light intensities of the N sub-apertures; again adding voltage disturbance of the Y-direction basis function with a coefficient of a, measuring and calculating the sum of the respective light intensities of the N sub-apertures;

[0014] Step five, respectively subtracting the sum of the light intensities measured after the disturbance of the N sub-apertures from the sum of the light intensities corresponding to the distorted wavefront.

[0015] Step 6: Calculate and obtain the coupler drive signals corresponding to each of the N sub-apertures using the difference operation results; amplify the drive signals through a high-voltage amplifier and apply them to the drivers of the coupling lenses of each sub-aperture; the photodetector detects the corrected spot information, and calculates the system performance evaluation function for the current iteration based on the spot information;

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

[0017] Furthermore, the preprocessing in step two specifically involves defining a set of basis functions {Z} characterizing wavefront tilt aberration. x Z y Let X and Y be the tilts, respectively, and calculate Z. x and Z y Calculate the second-order moments of the gradients with respect to the x-components and y-components, and denote them as P; measure the influence function E of the coupling lens, and establish its cross-correlation matrix C with the basis functions. ze Calculate the autocorrelation coupling matrix C between the driver influence functions. e The driving signal v of the coupling lens is obtained using formula (1);

[0018] Where a is a variable scalar value.

[0019] Furthermore, step three specifically involves: taking the centroid corresponding to each sub-aperture as the center, extracting an image plane of size M*M, and calculating the sum of the light intensities I of each of the N sub-apertures. i0 , where i∈{1,...,N}.

[0020] Furthermore, step four specifically involves: applying a voltage perturbation of the X-direction basis function with coefficient a to N sub-apertures in parallel, the voltage magnitude being calculated according to formula (1); and taking an image plane of size M*M centered on the centroid of each sub-aperture, calculating the sum of the light intensities I of each of the image planes truncated by the N sub-apertures. ix ; Apply voltage perturbations of the Y-direction basis functions with coefficient a to N sub-apertures in parallel, and calculate the voltage magnitude according to formula (1); Take an image plane of size M*M centered on the centroid of each sub-aperture, and calculate the sum of the light intensities I of each of the image planes truncated by the N sub-apertures. iy .

[0021] Furthermore, step five specifically involves: measuring the light intensity (I) after perturbing the N sub-apertures respectively. ix ,I iy The light intensity I corresponding to the distorted wavefront i0 Performing the difference operation yields an N×2 dimensional vector Q:

[0022] Q i = {(I ix , I iy ) - I i0} i∈{1,...N} (2)。

[0023] Further, the calculation of the driving signal in step six is specifically: obtaining the coupling driving signal V i of each corresponding sub-aperture by using formula (3) as follows

[0024] Further, the termination condition in step seven includes a certain number of iterations or the overall fiber coupling efficiency is greater than a threshold value.

[0025] Compared with the prior art, the beneficial effects of the present application are:

[0026] 1. The model-based adaptive multi-aperture fiber coupling control method utilizes the mathematical relationship between the far-field spot and the wavefront aberration to establish a model, and compared with the existing blind optimization algorithm, the physical principle is fully utilized, and the reliability is high.

[0027] 2. The model established by utilizing the mathematical relationship between the far-field spot and the wavefront aberration is equivalent to that the fiber coupling control system has certain prior knowledge, the system is controlled based on the prior knowledge, so that the convergence speed of the system is greatly accelerated.

[0028] 3. The present technology has strong robustness for fiber coupling under different turbulence intensities, can greatly improve the coupling efficiency of the fiber receiving end, and enhance the signal quality. BRIEF DESCRIPTION OF DRAWINGS

[0029] Fig. 1 is a structural schematic diagram of the model-based adaptive multi-aperture fiber coupling control system in the present application;

[0030] Fig. 2 is a flow schematic diagram of the model-based adaptive multi-aperture fiber coupling control method in the present application;

[0031] Fig. 3 is a coupling efficiency comparison example of the model method and the SPGD method under the turbulence condition D / r0=7 and the sub-aperture of 19, wherein D is the telescope aperture, and r0 is the atmospheric coherence length. DETAILED DESCRIPTION

[0032] The present application will be further described in detail below in combination with the drawings and examples.

[0033] In practical applications, the number of sub-apertures is generally 3, 7, 19, 37, etc. The adaptive fiber coupler array with 19 sub-apertures is taken as an example to further illustrate the present application in combination with the accompanying drawings. In the embodiment, the Zernike polynomial is taken as the base function, and the present application is not limited to the Zernike polynomial in practical implementation. The fiber coupling efficiency is taken as the target function of the control algorithm, and the smaller the aberration is, the greater the system coupling efficiency is. The fiber coupling performance is not limited to the coupling efficiency in practical implementation.

[0034] As shown in FIG. 1, a model-based adaptive multi-aperture fiber coupling control system includes a fiber coupler array, fibers, photodetectors, a controller, and a high-voltage amplifier. The fibers and the photodetectors are each provided with a plurality of fibers and photodetectors. The fiber coupler array is composed of a plurality of fiber couplers. The outputs of the plurality of fiber couplers are connected to the inputs of the plurality of photodetectors through a plurality of fibers. The outputs of the plurality of photodetectors are connected to the inputs of the controller. The outputs of the controller are connected to the inputs of the high-voltage amplifier. The outputs of the high-voltage amplifier are connected to the plurality of fiber couplers.

[0035] The fiber coupler includes a receiving aperture, sub-apertures, a coupling lens, and a back focal plane. The sub-apertures are provided with a plurality of sub-apertures. The receiving aperture, the plurality of sub-apertures, the coupling lens, and the back focal plane are sequentially arranged. One end of the fiber is connected to the back 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-apertures of the fiber coupler. The sub-beams of the plurality of sub-apertures are focused by the coupling lens and form focused spots on the back focal plane. Part of the incident light is coupled into the fiber at the back focal plane. The coupled light beams are transmitted into the corresponding photodetectors through the fiber, converted into corresponding electrical signals, and sent to the controller. The control algorithm in the controller calculates the corresponding control signals and transmits them to the high-voltage amplifier. The control signals are amplified by the high-voltage amplifier and transmitted to the fiber coupler. The 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, so that the fiber end face finds the maximum coupling efficiency point in the respective back focal plane.

[0036] As shown in FIG. 2, a model-based adaptive multi-aperture fiber coupling control method includes the following steps:

[0037] Step 1: initialize the parameters of the control algorithm, and take the fiber coupling efficiency as the target function of the control algorithm.

[0038] 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, the calculation of the cross-correlation matrix C ze , and the calculation of the autocorrelation coupling matrix C e .

[0039] According to the basis function {Z x ,Z y} calculate Z x and Z y The gradient second moment of x component, y component respectively, and inverse to get P. Measure the impact function E of coupling lens, calculate cross-correlation and autocorrelation coupling matrix C ze and C e This part of information is calculated in advance, and has nothing to do with the wavefront to be corrected.

[0040] Third step: take the centroid corresponding to each sub-aperture as the center, intercept the M*M size image plane, measure and calculate the sum of light intensity I i0 of each of the 19 sub-apertures, where i∈{1,...,19}.

[0041] Fourth step: add the voltage disturbance of X direction basis function with coefficient a to the 19 sub-apertures in parallel, and the voltage size is calculated according to formula (1). The deformation generated by the coupling lens is superimposed with the aberration wavefront, and after focusing through the focusing lens, part of the light spot enters the single-mode optical fiber, which is then detected by the photoelectric detector. Measure and calculate the sum of light intensity I ix of each of the 19 sub-apertures intercepted image plane; similarly, add the voltage disturbance of Y direction basis function with coefficient a to the 19 sub-apertures in parallel, and get the sum of light intensity I iy of each sub-aperture.

[0042] Fifth step: use formula (2) to calculate the difference Q between the light intensity (I ix ,I iy ) measured after disturbance of the 19 sub-apertures and the light intensity I i0 of the wavefront to be measured corresponding to each sub-aperture.

[0043] Sixth step: use formula (3) to get the driving signal V i of the 19 fiber couplers corresponding to the aberration wavefront. The driving signal is amplified by a high-voltage amplifier and applied to the driver of the coupling lens of each sub-aperture in parallel, generating a surface shape opposite to the wavefront to be measured, which is superimposed on the wavefront to be corrected, completing the control of the 19 fiber couplers. According to the information of the photoelectric detector, calculate the system performance evaluation function of the current iteration.

[0044] Seventh step: take the residual wavefront as the wavefront to be corrected, repeat the third-sixth step. 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 value, the closed-loop correction of the whole system is completed.

[0045] The above merely describes preferred embodiments of the present application, and is not intended to limit the present application in any form. Any modification, equivalent replacement, and improvement of the above embodiments made by any person skilled in the art, without departing from the technical solution of the present application, according to the technical essence of the present application, are still within the protection scope of the present application.

Claims

1. A model-based adaptive multi-aperture fiber coupling control method, characterized in that: Specifically, the following steps are included: Step 1: Initialize the parameters of the control algorithm within the controller, using fiber coupling efficiency as the objective function of the control algorithm; Step 2: Preprocessing; The preprocessing in step two specifically involves defining a set of basis functions {Z} to characterize wavefront tilt aberration. x Z y Let X and Y be the tilts, respectively, and calculate Z. x and Z y Calculate the second-order moments of the gradients with respect to the x-components and y-components, and denote them as P; measure the influence function E of the coupling lens, and establish its cross-correlation matrix C with the basis functions. ze Calculate the autocorrelation coupling matrix C between the driver influence functions. e The driving signal v of the coupling lens is obtained using formula (1); Where a is a variable scalar value; Step 3: Measure and calculate the sum of the light intensities of each of the N sub-apertures; Step three specifically involves: taking the centroid of each sub-aperture as the center, extracting an image plane of size M*M, and calculating the sum of the light intensities of each of the N sub-apertures, I. i0 where i∈{1,...,N}; Step 4: Apply voltage perturbations of the X-direction basis function with coefficient a to N sub-apertures in parallel, measure and calculate the sum of the light intensities of each of the N sub-apertures; apply voltage perturbations of the Y-direction basis function with coefficient a again, measure and calculate the sum of the light intensities of each of the N sub-apertures. Step four specifically involves: applying voltage perturbations of the X-direction basis function with coefficient a to N sub-apertures in parallel, the magnitude of which is calculated according to formula (1); taking the centroid of each sub-aperture as the center, extracting an image plane of size M*M, and calculating the sum of the light intensities I of each of the image planes extracted by the N sub-apertures. ix ; Apply voltage perturbations of the Y-direction basis functions with coefficient a to N sub-apertures in parallel, and calculate the voltage magnitude according to formula (1); Take an image plane of size M*M centered on the centroid of each sub-aperture, and calculate the sum of the light intensities I of each of the image planes truncated by the N sub-apertures. iy ; Step 5: Calculate the difference between the sum of the light intensities measured after perturbation of the N sub-apertures and the sum of the light intensities corresponding to the distorted wavefront. Step five specifically involves: measuring the light intensity (I) after perturbing the N sub-apertures respectively. ix ,I iy The light intensity I corresponding to the distorted wavefront i0 Performing the difference operation yields an N×2 dimensional vector Q: Q i ={(I ix ,I iy )-I i0 }i∈{1,...N} (2); Step 6: Calculate and obtain the coupler drive signals corresponding to each of the N sub-apertures using the difference operation results; amplify the drive signals through a high-voltage amplifier and apply them to the drivers of the coupling lenses of each sub-aperture; the photodetector detects the corrected spot information, and calculates the system performance evaluation function for the current iteration based on the spot information; The calculation of the driving signal in step six is ​​specifically as follows: the coupler driving signal V corresponding to each of the N sub-apertures is obtained using the following formula (3). i Here, V is an N-dimensional control signal; Step 7: Using the corrected residual wavefront as the wavefront to be corrected, repeat steps 3 to 6 until the preset termination condition is met to complete the correction.

2. The model-based adaptive multi-aperture fiber coupling control method according to claim 1, characterized in that: The termination conditions in step seven include a certain number of iterations or an overall fiber coupling efficiency greater than a threshold.

Images