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

Abstract

The invention relates to a laser array pointing error correction system based on a light intensity gradient potential well, and belongs to the technical field of laser. According to the method, a self-adaptive optical fiber collimator array, an extended target, a target area optical imaging lens, a spectroscope, a light intensity gradient potential well modulation sheet, a photoelectric detector, a control platform, a high-voltage amplifier and an imaging camera connected to the spectroscope are arranged. A laser array is emitted by a self-adaptive optical fiber collimator array and is transmitted to an extended target to form a light spot pattern, the light spot pattern is imaged by a target area optical imaging lens at a transmitting end, an imaging light beam is imaged on a light sensing surface of a photoelectric detector after passing through a light intensity gradient potential well modulation sheet, and a light source is formed. A photoelectric conversion signal of the photoelectric detector is transmitted to the control platform, a control voltage signal is generated after calculation of an optimization control algorithm, the control voltage signal acts on the self-adaptive optical fiber collimator array, pointing error closed-loop correction of emitted light beams is achieved, and finally light beam synthesis is achieved at a specific position of an expansion target.

Description

Technical Field

[0001] The invention belongs to the field of laser technology, and in particular relates to a laser array pointing error correction system based on light intensity gradient potential well. Background Art

[0002] Fiber laser array coherent synthesis technology is a specific form of optical phased array technology. It uses a fiber collimator array to construct a densely arranged distributed optical aperture, and achieves coherent synthesis on the target by manipulating the piston and tilt phase of the output laser array. Among them, the adaptive fiber collimator is a commonly used piezoelectric actuator for manipulating the pointing of fiber laser beams. Driven by the demand for larger calibers and higher powers, fiber laser array coherent synthesis technology is developing towards multiple units. At this time, the pointing error between array beams becomes an important factor affecting the beam synthesis effect.

[0003] Currently, the commonly used method for correcting laser array pointing errors is to use image sensors (such as CCD cameras, CMOS cameras) to collect spot image information, and then calculate performance indicators for algorithm iteration to 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 photodetectors instead of image sensors (such as CCD cameras, CMOS cameras) enables the application system to have a higher working speed and lower cost. However, photodetectors can only obtain light intensity information, but cannot obtain the position information of the light spot. Generally, when the light spot pattern is at different positions on the extended target, the light intensity value of the image of the light spot pattern detected by the photodetector remains constant, and there is no corresponding relationship between the light intensity voltage conversion signal obtained by the photodetector and the position of the light spot pattern on the extended target, resulting in the use of the photodetector method. The method cannot implement active control of the position of the light spot pattern on the extended target, and cannot solve the technical problem of array beam pointing error correction for the extended target; and the technical solution of the photodetector method cannot meet the needs of various forms of beam synthesis, special light field generation, etc. Summary of the invention

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The laser array pointing error correction system based on light intensity gradient potential well comprises: an adaptive fiber collimator array, an extended target, a target area optical imaging lens, 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, which are connected in sequence; the laser array is emitted through 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 target area optical imaging lens located at the same end of the adaptive fiber collimator array, and the imaging light beam is divided into two paths by a spectroscope, one of which is converged on the target surface of the imaging camera. , used to observe the beam synthesis effect. The other imaging beam passes through the light intensity gradient potential well modulator and is imaged on the photosensitive surface of the photodetector. The photodetector is used to realize the linear transformation of optical signal to electrical signal, and the imaging beam imaged on the photosensitive surface of the photodetector is photoelectrically converted. The photoelectrically converted signal is transmitted to the control platform, and the control platform generates a control voltage signal after calculation. The control voltage signal is amplified by the high-voltage amplifier and 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.

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

[0008] The present invention uses an optical hardware such as a light intensity gradient potential well modulator to replace traditional camera imaging, does not require complex software operations, and reduces the complexity and development cost of the application system. At the same time, various types of light intensity gradient potential wells can be flexibly designed to meet the needs of cutting-edge technology research on light field control such as various forms of beam synthesis and special light field generation. The present invention overcomes the difficulty that the array beam pointing error correction for the extended target cannot be achieved by relying solely on light intensity information. The light intensity gradient potential well modulator is placed in front of the photosensitive surface of the photodetector, so that the light intensity gradient potential well modulator and the photodetector jointly construct a light intensity gradient potential well based on transmittance, establish a mapping relationship between the light intensity information of the photodetector and the light spot position information, and realize that when the image of the light spot pattern falls on different positions of the light intensity gradient potential well, the light intensity voltage conversion signal of the photodetector is different, so as to achieve high-speed and high-quality beam synthesis on the extended target. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0010] Figure 2 Schematic diagram of the structure and working principle of the light intensity gradient potential well in the present invention;

[0011] Figure 3It is an effect diagram of the real image of the light spot pattern after the real image of the light spot pattern in the present invention passes through the light intensity gradient potential well modulator from different positions, and the real image of the light spot pattern after being modulated;

[0012] Figure 4 is the light intensity transmittance distribution curve of the light intensity gradient potential well modulator;

[0013] Figure 5 is the image of the target area formed by the imaging lens of the target area; wherein, (a) is the distribution of the 7-beam spot pattern on the extended target (or extended area) in the initial state; (b) is the distribution of the 7-way spot pattern after iteration of the optimization control algorithm when the light intensity gradient potential well is not introduced; (c) is the distribution of the 7-way spot pattern after iteration of the optimization control algorithm after the light intensity gradient potential well is introduced;

[0014] Figure 6 It is the convergence curve of the power in the normalized bucket after light intensity gradient potential well modulation as the optimization control algorithm is iterated. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0016] The following first introduces the concept of Power-in-the-Bucket (PIB).

[0017] In beam synthesis technology, the power in the bucket is usually used as the performance indicator of the optimization control algorithm. Its physical meaning is the sum of the light intensities within a certain range (the range of the bucket), and the calculation formula is:

[0018] ;

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

[0020] In the present invention, 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 barrel. When the light intensity gradient potential well modulator is not used, the image of the spot pattern moves on the photosensitive surface, which does not cause a change in the sum of the light intensities on the photosensitive surface of the photodetector. When the light intensity gradient potential well modulator is introduced, the photosensitive surface of the photodetector (the range of the barrel) 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 intensities on the photodetector.

[0021] If the light intensity transmittance of the light intensity gradient potential well is , the calculation formula of the modulated barrel power is:

[0022] ;

[0023] This formula converts the position information of the image of the light spot pattern on the photodetector into the light intensity voltage conversion signal of the photodetector (corresponding to the power in the barrel after modulation). ) to establish a mapping relationship, you can design To change the corresponding mapping relationship. Figure 2 Schematic diagram of the structure and working principle of the light intensity gradient potential well in the present invention.

[0024] The following embodiment takes the output laser beam of a 7-beam laser array as an example to illustrate the laser array pointing error correction system based on light intensity gradient potential well of the present invention.

[0025] The schematic diagram of the present invention during specific implementation is as follows Figure 1As shown, the laser array pointing error correction system based on light intensity gradient potential well of the present invention comprises: an adaptive fiber collimator array, an extended target, a target area optical imaging lens, 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 output end of the spectroscope, which are connected in sequence; 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 target area optical imaging lens located at the same end of the adaptive fiber collimator array, and the imaging light beam is divided into two paths by the spectroscope, one of which is converged on the target surface of the imaging camera. The imaging camera is used to observe the beam synthesis effect. The other imaging beam passes through the light intensity gradient potential well modulator and is imaged on the photosensitive surface of the photodetector. The photodetector is used to realize the linear transformation of optical signal to electrical signal, and the imaging beam imaged on the photosensitive surface of the photodetector is photoelectrically converted. The photoelectrically converted signal is transmitted to the control platform, and the control platform generates a control voltage signal after calculation using the optimization control algorithm. The control voltage signal is amplified by the high-voltage amplifier and acts on the adaptive fiber collimator array to generate a specified tilted wavefront, realize closed-loop correction of the pointing error of the laser beam, and realize laser beam synthesis at a specific position of the extended target. The imaging camera is used to observe the beam pointing correction effect and the beam synthesis state. The image it collects does not participate in the iterative process of the optimization control algorithm.

[0026] Wherein, the photodetector is a photodiode, a phototransistor or a photomultiplier tube, and the working wavelength range of the photodetector covers the wavelength of the laser beam; the optimization control algorithm includes a random parallel gradient descent algorithm, a hill climbing method, a multi-jitter method, a single-jitter method, a genetic algorithm, a simulated annealing algorithm, a particle swarm algorithm, a neural network algorithm, and an evolutionary algorithm. The optimization control algorithm seeks optimization and generates a control signal according to the gradient information of the signal after the photoelectric conversion, and the control signal controls the adaptive fiber collimator array and then controls the direction of the laser array, so that the real image of the spot pattern of all laser beams falls into the center position of the light intensity gradient potential well; the adaptive fiber collimator can be replaced by a tilt mirror, a fast mirror, a galvanometer, a digital micro-mirror, a liquid crystal phased array or other pointing actuators; the maximum light intensity transmittance of the light intensity gradient potential well modulator can be not in the center, but in other selected positions, and the light intensity gradient potential well modulator and the photodetector construct a light intensity gradient potential well with an offset center, which is used for the laser array to synthesize the beam at other positions of the extended target.

[0027] The laser array emitted by the adaptive fiber collimator array of the present invention is a coherent composite light beam or an incoherent composite light beam, and the number of adaptive fiber collimator arrays is ≥1; the light intensity gradient potential well modulator has a gradual light intensity transmittance, the light intensity transmittance at the center position is the highest, and the light intensity transmittance gradually decreases radially 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 gradient transmittance surface of other shapes.

[0028] 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 on 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. When the image of the laser spot is closer to the edge of the intensity gradient potential well, the light intensity is smaller.

[0029] Figure 3 The figure is a rendering of the real image of the light spot pattern after the real image of the light spot pattern in the present invention passes through the light intensity gradient potential well modulator from different positions. Figure 3 As shown, since the light intensity gradient potential well modulator has a light intensity transmittance distribution with high central transmittance and gradually decreasing radial transmittance, the real image of the modulated light spot pattern shows the characteristics of strong light intensity at the center and weak light intensity near the edge.

[0030] In this embodiment, the laser wavelength is λ=1080 nm, the number of synthetic apertures is 7, the sub-aperture diameter is 55 mm, and the sub-beams are incoherent. Figure 4 It is the light intensity transmittance distribution curve of the light intensity gradient potential well modulator. Figure 5 is the image of the target area formed by the imaging lens of the target area. In the initial state, the distribution of the light spot pattern on the extended target (or extended area) is as follows: Figure 5 When the light intensity gradient potential well modulator is not introduced, a random parallel gradient descent algorithm with the light intensity voltage conversion signal of the photodetector as the performance indicator is used to implement the closed-loop control of the beam pointing error. The simulation results after the algorithm iteration are shown in Figure 5 As shown in (b), the pointing error between the laser arrays has not been corrected. The reason is that when the above method is executed, it is equivalent to using the range of the photodetector's photosensitive surface as the range of the power in the bucket. When the image of the spot pattern moves within the photosensitive surface, 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 modulator is introduced at the front end of the photodetector, the photodetector's photosensitive surface is modulated. The simulation results after the random parallel gradient descent algorithm iteration are shown in Figure 5 As shown in (c), the convergence curve of the power in the normalized bucket after light intensity gradient potential well modulation with the iteration of the optimization control algorithm is as follows Figure 6 As shown, the pointing errors between the laser arrays are corrected and incoherent synthesis is achieved at the center 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 After being amplified by a high-voltage amplifier, this group of voltage values ​​acts on a 7-unit adaptive fiber collimator array to change the direction of the laser array and obtain the total light intensity in the light intensity gradient potential well (i.e., the light intensity voltage conversion signal of the photodetector), which is recorded as the overall performance index J;

[0033] Step 2: The control platform randomly generates a set of small voltage disturbances with Bernoulli distribution. ;

[0034] Step 3: Control the platform to set the voltage value Acting on a 7-unit adaptive fiber collimator array to obtain the overall performance index at this time ;

[0035] Step 4: Control the platform to set the voltage value Acting on a 7-unit adaptive fiber collimator array to obtain the overall performance index at this time ;

[0036] Step 5: The control platform updates the voltage signal to ,in is the gain coefficient;

[0037] Step 6: Repeat steps 1 to 5 until the overall performance index J of the system converges to the optimal value and remains stable after multiple iterations. At this point, the pointing errors between the 7 laser arrays are corrected, and the laser arrays achieve incoherent synthesis at the center of the extended target (or extended area).

[0038] The method of the present invention described above takes a 7-beam laser array as an example. Laser arrays with other numbers can also use the method of the present invention to perform pointing error correction.

[0039] The present invention realizes closed-loop correction of pointing errors between 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 above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the equivalent forms of such scope and boundaries.

Claims

1. A laser array pointing error correction system based on light intensity gradient potential well, characterized in that: include: The adaptive fiber collimator array, the extended target, the target area optical imaging lens, the beam splitter, the light intensity gradient potential well modulator, the photodetector, the control platform, the high-voltage amplifier and the imaging camera connected to the beam splitter are connected in sequence; the laser array is emitted through 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 target area optical imaging lens located at the same end of the adaptive fiber collimator array, the imaging beam is divided 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 modulator; the photodetector is used to realize the linear transformation from the optical signal to the electrical signal, and 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, the control voltage signal is amplified by the high-voltage amplifier, and acts on the adaptive fiber collimator array to generate a specified tilt wavefront, so as to realize the closed-loop correction of the pointing error of the laser beam and realize the laser beam synthesis at the specific position of the extended target.

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 light 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 position is the highest and the light intensity transmittance gradually decreases away from the center position 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 photoelectric detector is a photodiode, a phototransistor or a photomultiplier tube, and the working wavelength range of the photoelectric detector 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 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 on 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. When the image of the laser spot is closer to the edge of the intensity gradient potential well, the light intensity is smaller.

8. 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.

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

10. The laser array pointing error correction system based on light intensity gradient potential well according to claim 8, characterized in that: The optimization control algorithm searches for 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 controls 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.

11. 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 micro-mirror, liquid crystal phased array or other pointing actuators.

12. 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 light intensity gradient potential well modulator is set not at the center but at other selected positions. The light intensity gradient potential well modulator and the photodetector construct a light 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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