A laser array pointing error correction system based on light intensity gradient potential well

Abstract

The present application relates to a kind of laser array pointing error correction system based on light intensity gradient potential well, belong to laser technology field, the method includes setting adaptive fiber collimator array, extended target, target area optical imaging lens, beam splitter, light intensity gradient potential well modulating piece, photoelectric detector, control platform, high voltage amplifier and imaging camera connected to beam splitter.Laser array is emitted via adaptive fiber collimator array, is transmitted to the light spot pattern formed on extended target, the light spot pattern is imaged by target area optical imaging lens of emission end, after imaging beam passes through light intensity gradient potential well modulating piece, image on the photosensitive surface of photoelectric detector, the photoelectric conversion signal of photoelectric detector is transmitted to control platform, control voltage signal is generated after being calculated by optimization control algorithm, act on adaptive fiber collimator array, realize the pointing error closed-loop correction of emission beam, finally realize beam synthesis in the specific position of extended target.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser, and particularly relates to a laser array pointing error correction system based on an optical intensity gradient potential well. BACKGROUND

[0002] The fiber laser array coherent synthesis technology is a specific form of the optical phased array technology, dense distribution of distributed optical apertures is constructed by using a fiber collimator array, and coherent synthesis on a target is realized by controlling piston and tilt phases of an outgoing laser array. The adaptive fiber collimator is a commonly used piezoelectric actuator for controlling the pointing of a fiber laser beam. Under the traction of application requirements of larger aperture and higher power, the fiber laser array coherent synthesis technology is developing towards very large number of units, at this time, the pointing error between array beams becomes an important factor affecting the beam synthesis effect.

[0003] The commonly used laser array pointing error correction method at present is to use an image sensor (such as a CCD camera and a CMOS camera) to collect spot image information, calculate performance indicators for algorithm iteration, and then implement subsequent closed-loop correction.

[0004] In the traditional image sensor imaging method, the software operation is complex, the system complexity is high, and the development cost is high. Using a photoelectric detector instead of an image sensor (such as a CCD camera and a CMOS camera) makes the application system have higher working speed and lower cost, but the photoelectric detector can only obtain light intensity information and cannot obtain position information of a spot. Generally, when a spot pattern is at different positions on an extended target, the light intensity value of the image of the spot pattern detected by the photoelectric detector is constant, and there is no corresponding relationship between the light intensity voltage conversion signal obtained by the photoelectric detector and the position of the spot pattern on the extended target, which leads to that the photoelectric detector method cannot implement active control of the position of the spot pattern on the extended target, and cannot solve the technical problem of array beam pointing error correction for the extended target. Moreover, the technical scheme of the photoelectric detector method cannot meet the needs of various forms of beam synthesis, special light field generation and the like. SUMMARY

[0005] To solve the above technical problems, the application adopts the following technical scheme:

[0006] The laser array pointing error correction system based on the light intensity gradient potential well comprises, in sequence, an adaptive optical fiber collimator array, an extended target, a target area optical imaging lens, a beam splitter, a light intensity gradient potential well modulation sheet, a photodetector, a control platform, a high-voltage amplifier, and an imaging camera connected to the beam splitter; the laser array is emitted via the adaptive optical fiber collimator array, transmitted to the extended target to form a light spot pattern, the light spot pattern is imaged by the target area optical imaging lens located at the same end of the adaptive optical fiber collimator array, the imaging light beam is split into two paths by the beam splitter, one of the imaging light beams is collected on the target surface of the imaging camera for observing the light beam synthesis effect, and the other imaging light beam is imaged on the photosensitive surface of the photodetector after passing through the light intensity gradient potential well modulation sheet; the photodetector is used to realize linear conversion of the optical signal to the electrical signal, the imaging light beam imaged on the photosensitive surface of the photodetector is optoelectronically converted, the optoelectronically converted signal is transmitted to the control platform, a control voltage signal is generated after calculation by the control platform, the control voltage signal is amplified by the high-voltage amplifier, and then acts on the adaptive optical fiber collimator array to generate a specified tilted wavefront, thereby realizing closed-loop correction of the laser beam pointing error and laser beam synthesis at a specific position of the extended target.

[0007] The present application has the following beneficial effects:

[0008] The present application uses the light intensity gradient potential well modulation sheet as optical hardware to replace the traditional camera imaging, without the need for complex software operation, thereby reducing the complexity and development cost of the application system. Meanwhile, various types of light intensity gradient potential wells can be flexibly designed to meet the needs of research on various forms of light beam synthesis, special light field generation, and other light field regulation and control front technologies. The present application overcomes the problem that the array light beam pointing error correction cannot be realized for the extended target only by relying on the light intensity information, places the light intensity gradient potential well modulation sheet in front of the photosensitive surface of the photodetector, thereby constructing a light intensity gradient potential well based on transmittance by the light intensity gradient potential well modulation sheet and the photodetector, establishing a mapping relationship between the light intensity information and the light spot position information of the photodetector, realizing different effects of the light intensity voltage conversion signal of the photodetector when the image of the light spot pattern falls at different positions of the light intensity gradient potential well, and achieving high-speed and high-quality light beam synthesis on the extended target. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 FIG. 1 is a schematic diagram of the laser array pointing error correction system based on the light intensity gradient potential well of the present application;

[0010] Figure 2 FIG. 2 is a schematic diagram of the structure and working principle of the light intensity gradient potential well in the present application;

[0011] Figure 3Effect diagram of the real image of the light spot pattern after the real image of the light spot pattern passes through the light intensity gradient potential well modulation piece from different positions in the present application;

[0012] Figure 4 Light intensity transmittance distribution curve of the light intensity gradient potential well modulation piece;

[0013] Figure 5 Image of the target area formed by the target area imaging lens; wherein (a) is the distribution of the 7 light spot patterns on the extended target (or extended area) in the initial state; (b) is the distribution of the 7 light spot patterns after iteration of the optimized control algorithm without introducing the light intensity gradient potential well; (c) is the distribution of the 7 light spot patterns after iteration of the optimized control algorithm after introducing the light intensity gradient potential well;

[0014] Figure 6 Convergence curve of the normalized power-in-the-bucket after the light intensity gradient potential well modulation with the iteration of the optimized control algorithm. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solutions and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0016] Firstly, the concept of power-in-the-bucket (PIB) is introduced below.

[0017] In beam synthesis technology, power-in-the-bucket is usually used as a performance index of the optimized control algorithm, and its physical meaning is the sum of light intensity within a certain range (the range of the bucket), and the calculation formula is:

[0018] ;

[0019] Among them, represents the aperture function centered on the optical axis, which is called the bucket, is the far-field intensity distribution of the synthesized beam. The larger the value is, the more concentrated the synthesized beam is in the bucket, and the better the effect of beam synthesis is.

[0020] In the present application, the photosensitive surface of the photodetector corresponds to the imaging area of the extended target, and the entire photosensitive surface is selected as the range of the bucket. When the light intensity gradient potential well modulation sheet is not used, the image of the spot pattern moves on the photosensitive surface and does not cause a change in the sum of the light intensity on the photosensitive surface of the photodetector. When the light intensity gradient potential well modulation sheet is introduced, the photosensitive surface of the photodetector (the range of the bucket) is modulated, and when the image of the spot pattern moves on the photosensitive surface, it will cause a change in the sum of the light intensity on the photodetector.

[0021] If the light intensity transmittance of the light intensity gradient potential well is At this time, the formula for calculating the power in the modulated bucket is obtained as follows:

[0022] ;

[0023] This formula establishes a mapping relationship between the position information of the image of the spot pattern on the photodetector and the light intensity voltage conversion signal (corresponding to the power in the modulated bucket ) of the photodetector, and the corresponding mapping relationship can be changed by designing . Figure 2 The structure and working principle of the light intensity gradient potential well in the present application are shown in the schematic diagram.

[0024] The following examples take the output laser beam as a 7-laser array to illustrate the laser array pointing error correction system based on the light intensity gradient potential well of the present application.

[0025] The schematic diagram of the present application in specific implementation is as follows Figure 1As shown, the laser array pointing error correction system based on the light intensity gradient potential well of the application comprises: an adaptive fiber collimator array, an extended target, a target area optical imaging lens, a beam splitter, a light intensity gradient potential well modulation sheet, a photodetector, a control platform, a high-voltage amplifier, and an imaging camera connected to the output end of the beam splitter; the laser array is emitted via the adaptive fiber collimator array, transmitted to the extended target to form a spot pattern, the spot pattern is imaged by the target area optical imaging lens located at the same end of the adaptive fiber collimator array, the imaging beam is split into two paths by the beam splitter, one of the imaging beams is collected on the target surface of the imaging camera for observing the beam synthesis effect, and the other imaging beam is imaged on the photosensitive surface of the photodetector after passing through the light intensity gradient potential well modulation sheet; the photodetector is used to realize linear conversion of optical signals to electrical signals, the imaging beam imaged on the photosensitive surface of the photodetector is photoelectrically converted, the photoelectrically converted signal is transmitted to the control platform, the control platform generates a control voltage signal after calculation using an optimization control algorithm, the control voltage signal is amplified by the high-voltage amplifier and then acts on the adaptive fiber collimator array to generate a specified tilted wavefront, thereby realizing closed-loop correction of the pointing error of the laser beam and achieving laser beam synthesis at a specific position of the extended target. The imaging camera is used to observe the pointing correction effect and the beam synthesis state, and the image collected by the imaging camera does not participate in the iteration process of the optimization control algorithm.

[0026] The photodetector is a photodiode, a phototriode, or a photomultiplier, and the working wavelength range of the photodetector covers the wavelength of the laser beam; the optimization control algorithm includes a stochastic parallel gradient descent algorithm, a hill climbing method, a multi-dithering method, a single-dithering method, a genetic algorithm, a simulated annealing algorithm, a particle swarm algorithm, a neural network algorithm, and an evolutionary algorithm. The optimization control algorithm performs optimization and generates a control signal according to the gradient information of the photoelectrically converted signal, the control signal controls the adaptive fiber collimator array to manipulate the pointing of the laser array, so that the real images of the spot patterns of all laser beams fall into the center position of the light intensity gradient potential well; the adaptive fiber collimator can be replaced by a tilting mirror, a fast mirror, a galvanometer, a digital micro-mirror, a liquid crystal phased array, or other pointing execution devices; the maximum light intensity transmission rate of the light intensity gradient potential well modulation sheet can not be at the center but at other selected positions, and the light intensity gradient potential well modulation sheet and the photodetector construct a biased center light intensity gradient potential well for laser array beam synthesis at other positions of the extended target.

[0027] The laser array emitted by the adaptive fiber collimator array of the present application is a coherent or incoherent combined light beam, and the number of adaptive fiber collimator arrays is greater than or equal to 1; the light intensity gradient potential well modulation sheet has a gradually changing light intensity transmittance, the light intensity transmittance at the center position is the highest, and the light intensity transmittance gradually decreases along the radial direction away from the center position; the surface distribution of the light intensity transmittance is a parabolic surface, a Gaussian surface, a conical surface, a customized gradient decreasing transmittance surface, or a gradually changing transmittance surface of other shapes.

[0028] The light intensity gradient potential well modulation sheet is placed in front of and completely covers the photosensitive surface of the photodetector, and the light intensity gradient potential well modulation sheet and the photodetector together construct a light intensity gradient potential well based on transmittance. The real image of the spot pattern falls at different positions of the light intensity gradient potential well, and the light intensity is different. When the image of the laser spot is closer to the center of the light intensity gradient potential well, the light intensity is greater; when the image of the laser spot is closer to the edge of the light intensity gradient potential well, the light intensity is smaller.

[0029] Figure 3 The effect diagram of the real image of the modulated spot pattern. As shown in Figure 3 , due to the light intensity gradient potential well modulation sheet having a light intensity transmittance distribution with high center transmittance and gradually decreasing radial transmittance, the real image of the modulated spot pattern has the characteristics of high light intensity at the center position and low light intensity near the edge.

[0030] In this embodiment, the laser wavelength is λ=1080nm, the number of synthetic apertures is 7, the diameter of each sub-aperture is 55mm, and the sub-beams are incoherent. Figure 4 The light intensity transmittance distribution curve of the light intensity gradient potential well modulation sheet. Figure 5 The image of the target area formed by the target area imaging lens. In the initial state, the spot pattern distribution on the extended target (or extended area) is shown in Figure 5 (a). When the light intensity gradient potential well modulation sheet is not introduced, the random parallel gradient descent algorithm using the light intensity voltage conversion signal of the photodetector as the performance index is used to implement the beam pointing error closed-loop control. The simulation result after the algorithm iteration is shown in Figure 5 (b), and the pointing error between the laser arrays is not corrected. The reason is that when the above method is executed, the range of the photodetector photosurface is equivalent to the range of the power in the bucket. When the image of the spot pattern moves in the photosurface, the total light intensity does not change, so the gradient information cannot be obtained, and the random parallel gradient descent algorithm cannot run. When the light intensity gradient potential well modulation sheet is introduced in front of the photodetector, the photodetector photosurface is modulated, and the simulation result after the random parallel gradient descent algorithm iteration is shown in Figure 5 (c). The convergence curve of the normalized power in the bucket after the light intensity gradient potential well modulation with the iteration of the optimization control algorithm is as followsFigure 6 As shown, the pointing error between the laser arrays is corrected, and the incoherent synthesis is achieved at the center position of the extended target (or extended area).

[0031] The control platform used in the embodiment is an FPGA hardware control platform. The execution steps of the optimization control algorithm are as follows:

[0032] Step 1: The control platform outputs a set of voltage values The set of voltage values is amplified by a high-voltage amplifier and then acts on the 7-unit adaptive optical fiber collimator array, so that the pointing of the laser array changes, and the total light intensity in the light intensity gradient potential well (i.e., the light intensity voltage conversion signal of the photodetector) is obtained, which is denoted as the overall performance index J.

[0033] Step 2: The control platform randomly generates a set of small voltage perturbations in Bernoulli distribution ;

[0034] Step 3: The control platform applies the voltage value to the 7-unit adaptive optical fiber collimator array to obtain the overall performance index ;

[0035] Step 4: The control platform applies the voltage value to the 7-unit adaptive optical fiber collimator array to obtain the overall performance index ;

[0036] Step 5: The control platform updates the voltage signal to , where is a gain coefficient.

[0037] Step 6: Steps 1 to 5 are repeated until the overall performance index J of the system converges to an optimal value and remains stable after multiple iterations. At this time, the pointing error between the 7-laser array is corrected, and the incoherent synthesis of the laser array is achieved at the center position of the extended target (or extended area).

[0038] The method of the present application described above with the 7-laser array as an example can also be used for pointing error correction of other numbers of laser arrays.

[0039] The present application realizes closed-loop correction of the pointing error between the laser arrays, and further realizes a method for beam synthesis on an extended target, which can be applied to the fields of laser processing, laser energy transmission, laser atmospheric transmission, and free-space laser communication.

[0040] It should be understood that the foregoing detailed description of the application, rather than limiting the application, is intended to explain and describe the current implementation of the application. Therefore, any modification, equivalent replacement or improvement made without departing from the spirit and scope of the application should be included in the protection scope of the application. In addition, the appended claims of the application are intended to cover all changes and modifications falling within the scope and boundary of the appended claims, or the equivalent form of such scope and boundary.

Claims

1. A laser array pointing error correction system based on light intensity gradient potential well, characterized in that: include: An adaptive fiber collimator array, an extended target, an optical imaging lens of a target area, a spectroscope, a light intensity gradient potential well modulator, a photodetector, a control platform, a high-voltage amplifier, and an imaging camera connected to the spectroscope are sequentially connected; the laser array is emitted via the adaptive fiber collimator array and transmitted to the extended target to form a light spot pattern, the light spot pattern is imaged by the optical imaging lens of the target area located at the same end of the adaptive fiber collimator array, and the imaging beam is divided into two paths by a spectroscope, one of which is converged on the target surface of the imaging camera for observing the beam synthesis effect, and the other imaging beam is imaged on the photosensitive surface of the photodetector after passing through the light intensity gradient potential well modulator; the photodetector is used to realize the linear conversion of optical signals to electrical signals, and the resultant light imaged on the photosensitive surface of the photodetector is converted into an image. The image beam is photoelectrically converted, and the signal after photoelectric conversion is transmitted to the control platform. After calculation by the control platform, a control voltage signal is generated. After being amplified by the high-voltage amplifier, the control voltage signal acts on the adaptive fiber collimator array to generate a specified tilted wavefront, thereby realizing closed-loop correction of the pointing error of the laser beam and realizing laser beam synthesis at a specific position of the extended target; the intensity gradient potential well modulator is placed in front of the photosensitive surface of the photodetector and completely covers the photosensitive surface. The intensity gradient potential well modulator and the photodetector jointly construct an intensity gradient potential well based on transmittance. The real image of the spot pattern falls at different positions of the intensity gradient potential well, and the light intensity is different. When the image of the laser spot is closer to the center of the intensity gradient potential well, the light intensity is greater, and when the image of the laser spot is closer to the edge of the intensity gradient potential well, the light intensity is smaller.

2. The laser array pointing error correction system based on light intensity gradient potential well according to claim 1, characterized in that: The laser array emitted by the adaptive fiber collimator array is a coherent composite beam, and the number of the adaptive fiber collimator array is ≥1.

3. The laser array pointing error correction system based on light intensity gradient potential well according to claim 1, characterized in that: The laser array emitted by the adaptive fiber collimator array is an incoherent composite beam, and the number of the adaptive fiber collimator array is ≥1.

4. The laser array pointing error correction system based on light intensity gradient potential well according to claim 1, characterized in that: The light intensity gradient potential well modulator has a gradually changing light intensity transmittance, wherein the light intensity transmittance at the center is the highest and the light intensity transmittance gradually decreases away from the center in the radial direction.

5. The laser array pointing error correction system based on light intensity gradient potential well according to claim 4, characterized in that: The surface distribution of the light intensity transmittance is a parabolic surface, a Gaussian surface, a conical surface, a customized gradient-decreasing transmittance surface, or a gradient transmittance surface of other shapes.

6. The laser array pointing error correction system based on light intensity gradient potential well according to claim 1, characterized in that: The photodetector is a photodiode, a phototransistor or a photomultiplier tube, and the operating wavelength range of the photodetector covers the wavelength of the laser beam.

7. The laser array pointing error correction system based on light intensity gradient potential well according to claim 1, characterized in that: The control platform generates voltage control signals after calculation using an optimized control algorithm.

8. The laser array pointing error correction system based on light intensity gradient potential well according to claim 7, characterized in that: The optimization control algorithm includes a random parallel gradient descent algorithm, a hill climbing method, a multi-dither method, a single-dither method, a genetic algorithm, a simulated annealing algorithm, a particle swarm algorithm, a neural network algorithm, and an evolutionary algorithm.

9. The laser array pointing error correction system based on light intensity gradient potential well according to claim 7, characterized in that: The optimization control algorithm seeks the best and generates a control signal based on the gradient information of the photoelectrically converted signal. The control signal controls the adaptive fiber collimator array and then manipulates the direction of the laser array so that the real images of the spot patterns of all laser beams fall into the center position of the light intensity gradient potential well.

10. The laser array pointing error correction system based on light intensity gradient potential well according to claim 1, characterized in that: Replace the adaptive fiber collimator with a tilt mirror, fast mirror, galvanometer, digital micromirror, liquid crystal phased array or other pointing actuators.

11. The laser array pointing error correction system based on light intensity gradient potential well according to claim 1, characterized in that: The maximum light intensity transmittance of the intensity gradient potential well modulator is set not at the center but at other selected positions. The intensity gradient potential well modulator and the photodetector construct an intensity gradient potential well with an offset center, which is used for beam synthesis of the laser array at other positions of the extended target.

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