CN113708206A - Laser array piston phase control method and system based on interference fringes - Google Patents
Laser array piston phase control method and system based on interference fringes Download PDFInfo
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Abstract
The invention provides a method and a system for controlling the phase of a laser array piston based on interference fringes, which are used for collecting part of a laser array and contracting the laser array; detecting interference fringe images of the shrunk laser array and the reference beams by using a high-speed camera, measuring and obtaining piston phase errors of each unit beam and the reference beams in the laser array at the high-speed camera according to the interference fringe images, and obtaining time domain distribution of the piston phase errors of each unit beam and the reference beams in the laser array within a period of time; and controlling the piston phase of each unit beam in the laser array according to the time domain distribution of the piston phase errors of each unit beam and the reference beam in the laser array within a period of time. The invention can more accurately control the piston phase of each path of unit beam, thereby improving the synthesis efficiency of the synthesis system and solving the defect of low synthesis effect caused by low sampling frequency in the traditional method.
Description
Technical Field
The invention relates to the technical field of intense laser, in particular to a laser array piston phase control method and system based on interference fringes.
Background
The fiber laser has the advantages of compact structure, good beam quality, convenient heat management and the like, and is widely applied to important fields of industrial processing, material forming, high-energy laser system construction and the like. Along with the continuous improvement of the output power of the single-path fiber laser, the further improvement of the fiber laser power and the brightness is restricted by the effects of the brightness of the pumping source, the nonlinear effect, the unstable thermotropic mode and the like. At present, coherent synthesis and spectral synthesis are two main technical means for breaking through the limitation of single-path optical fiber laser brightness improvement.
For a coherent combining system, in order to improve the system brightness, closed-loop phase control is required to effectively compensate the dynamic phase noise of the system, so that each path of fiber laser can stably interfere on a target plane. In order to compensate for the dynamic phase noise of the system, real-time closed-loop control of the phase noise of the array must be performed by a phase closed-loop control system.
In recent years, with rapid development of hardware performance of high-speed cameras and software performance of image processing techniques, light field information extraction and phase control based on two-dimensional light intensity information have become a new trend. However, the existing control system only performs the next frame phase control according to the data extracted from each frame of image, and the piston phase noise changes from moment to moment, so that the two values are not completely the same. In an actual system, the operating frame rate of the high-speed camera and the characteristic frequency of the phase noise are in the same order of magnitude, so in terms of a control strategy, a more efficient control strategy is required to ensure the accuracy of each phase control, so as to ensure that the whole system can obtain laser output with higher brightness when the phase is subjected to closed-loop control. Generally, how to realize real-time and accurate piston phase control according to a high-speed camera detection signal with a sampling rate equivalent to a noise frequency becomes a key for improving the phase control precision. The invention provides a method and a system for controlling the phase of a laser array piston with higher precision based on two-dimensional light field information through optimization of a controller control strategy level according to time domain change of a high-speed camera detection signal.
Disclosure of Invention
In order to solve the problem that the control effect is reduced due to the low sampling rate of the piston phase based on interference fringe control, the invention provides a method and a system for controlling the piston phase of a laser array based on the interference fringe, which are a method and a system for performing high-efficiency piston phase time sequence control on the interference fringe by adopting a high-speed camera, and can improve the light spot energy concentration ratio in a closed-loop control stage on the premise that the high-speed camera has the same operation frame rate, thereby improving the brightness of synthesized laser and further improving the synthesis efficiency of coherent synthesis.
In order to achieve the technical purpose, the invention adopts the following specific technical scheme:
the invention provides a laser array piston phase control method based on interference fringes, which comprises the following steps:
dividing seed laser into two parts, inputting one part into a laser array coherent synthesis unit for generating a laser array, and taking the other part as a reference beam;
collecting a part of laser arrays generated by the laser array coherent synthesis unit and performing beam shrinking on the laser arrays;
detecting interference fringe images of the shrunk laser array and the reference beams by using a high-speed camera, measuring and obtaining piston phase errors of each unit beam and the reference beams in the laser array at the high-speed camera according to the interference fringe images, and obtaining time domain distribution of the piston phase errors of each unit beam and the reference beams in the laser array within a period of time;
and controlling the piston phase of each unit beam in the laser array according to the time domain distribution of the piston phase errors of each unit beam and the reference beam in the laser array within a period of time.
Further, in the present invention, for any unit beam in the laser array, the voltage applied to both ends of the phase modulator corresponding to the unit beam at the current k time is generated according to the following control strategy, so as to control the piston phase thereof:
for any unit light beam in the laser array, Δ u (k) is a change amount of a voltage applied to two ends of a phase modulator in a laser array coherent combining unit corresponding to the unit light beam at the time k relative to the time k-1, u (k-1) is a voltage applied to two ends of a phase modulator in a laser array coherent combining unit corresponding to the unit light beam at the time k-1, and u (k) is a voltage applied to two ends of a phase modulator in a laser array coherent combining unit corresponding to the unit light beam at the time k; kPAs a proportional parameter, KiAs integral parameter, KdAnd e (k) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k, e (k-1) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k-1, and e (k-2) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k-2.
Furthermore, the seed laser in the invention is from a seed laser, the laser output by the seed laser is subjected to power amplification by a preamplifier, and then is divided into two parts by a 1 × 2 fiber beam splitter, one part is input into a laser array coherent combining unit for generating a laser array, and the other part is used as a reference beam.
Furthermore, the laser array coherent combination unit in the invention includes a collimator array composed of a 1 × N fiber beam splitter, N phase modulators, N main amplifiers and N collimators, seed laser input to the laser array coherent combination unit is divided equally into N unit beams by the 1 × N fiber beam splitter, each unit beam corresponds to one transmission path, each transmission path is provided with a phase modulator, a main amplifier and a collimator in sequence, and each unit beam is output by collimation of the collimator in the collimator array after being subjected to phase modulation and power amplification by the phase modulator and the main amplifier in sequence.
Further, in the invention, the sampling mirror collects the laser array to the optical beam reducer to obtain the laser array after the beam is reduced.
Furthermore, in the invention, the contracted laser array is incident to the half-transmitting and half-reflecting mirror, the reference beam is incident to the half-transmitting and half-reflecting mirror after passing through the reference light amplifier and the reference light collimating lens, and is incident to the high-speed camera after being transmitted and reflected by the half-transmitting and half-reflecting mirror respectively.
Further, the present invention provides an interference fringe based laser array piston phase control system, comprising:
the seed laser generating unit is used for generating seed laser and dividing the seed laser into two parts, one part is input into the laser array coherent combining unit and used for generating a laser array, and the other part is used as a reference beam;
the laser array coherent combination unit comprises a collimator array consisting of a 1 XN optical fiber beam splitter, N phase modulators, N main amplifiers and N collimators, wherein seed laser input into the laser array coherent combination unit is divided into N paths of unit beams through the 1 XN optical fiber beam splitter, each path of unit beam corresponds to one path of transmission path, the phase modulators, the main amplifiers and the collimators are arranged in each path of transmission path in sequence, and each path of unit beam is subjected to phase modulation and power amplification through the phase modulators and the main amplifiers in sequence and then is output by collimation through the collimators in the collimator array;
the laser array sampling unit comprises a sampling mirror and an optical beam reducer, and the sampling mirror collects the laser array to the optical beam reducer to obtain a laser array after beam reduction;
the image acquisition unit is used for detecting an interference fringe image of the shrunk laser array and the reference beam by using a high-speed camera;
the interference fringe resolving module obtains the piston phase errors of the unit beams and the reference beams in the laser array at the high-speed camera according to the interference fringe image measurement, and obtains the time domain distribution of the piston phase errors of the unit beams and the reference beams in the laser array within a period of time;
and the phase control unit is used for controlling the piston phase of each unit beam in the laser array according to the time domain distribution of the piston phase errors of each unit beam and the reference beam in the laser array within a period of time.
Further, in the system for controlling piston phase of laser array based on interference fringe provided by the present invention, for any unit beam in the laser array, the phase control unit generates the voltage applied to two ends of the phase modulator corresponding to the unit beam at the current k time according to the following control strategy, so as to control the piston phase of the phase modulator:
for any unit light beam in the laser array, Δ u (k) is a change amount of a voltage applied to two ends of a phase modulator in a laser array coherent combining unit corresponding to the unit light beam at the time k relative to the time k-1, u (k-1) is a voltage applied to two ends of a phase modulator in a laser array coherent combining unit corresponding to the unit light beam at the time k-1, and u (k) is a voltage applied to two ends of a phase modulator in a laser array coherent combining unit corresponding to the unit light beam at the time k; kPAs a proportional parameter, KiAs integral parameter, KdFor differential parameters, e (k) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k, e (k-1) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k-1, and e (k-2) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k-2The phase error is plugged.
Further, in the laser array piston phase control system based on interference fringes provided by the invention, the seed laser generating unit comprises a seed laser, a preamplifier and a 1 × 2 fiber beam splitter, laser output by the seed laser is subjected to power amplification by the preamplifier, and then is divided into two parts by the 1 × 2 fiber beam splitter, wherein one part is input into the laser array coherent combining unit for generating the laser array, and the other part is used as a reference beam.
Furthermore, in the system for controlling the piston phase of the laser array based on the interference fringes, the image acquisition unit comprises a reference light amplifier, a reference light collimating lens, a half-mirror and a high-speed camera, wherein the laser array after being shrunk is incident to the half-mirror, a reference beam is incident to the half-mirror after passing through the reference light amplifier and the reference light collimating lens, and is incident to the high-speed camera after being transmitted and reflected by the half-mirror respectively, and the high-speed camera detects the interference fringe image of the laser array after being shrunk and the reference beam.
Compared with the prior art, the invention has the beneficial effects that:
the invention can more accurately control the piston phase of each unit beam in the laser array coherent combination unit, thereby improving the combination efficiency of the combination system, solving the defect of low combination effect caused by low sampling frequency in the traditional piston phase control system based on interference fringes, and providing a more efficient control system for the practical application system.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.
FIG. 1 is a schematic structural diagram of an embodiment of the present invention;
fig. 2 is a schematic diagram of the effect of piston phase drift on fringes in the present invention, where (a) is an interference fringe image corresponding to a piston phase error phi of 0; (b) the interference fringe image is corresponding to the piston phase error phi pi/2; (c) the method comprises the following steps of (1) obtaining an interference fringe image corresponding to a piston phase error phi pi; (d) the interference fringe image is corresponding to the piston phase error phi of 3 pi/2;
FIG. 3 is a flow chart of the interference fringe solution module according to the present invention;
FIG. 4 is a control schematic diagram of a phase control unit according to an embodiment of the present invention;
FIG. 5 is a control flow diagram according to an embodiment of the present invention;
fig. 6 is a comparison diagram of control effects in an embodiment of the present invention, where (a) represents a control effect diagram corresponding to a laser array piston phase control system that performs closed-loop control using a conventional interference fringe phase-locking method, and (b) represents a control effect diagram corresponding to a laser array piston phase control system that performs closed-loop control using a time-domain phase control method proposed by the present application.
Reference numbers in fig. 1:
1. a seed laser; 2. a preamplifier; 3. a 1 × 2 fiber splitter; 4. a 1 XN fiber optic splitter; 5. a phase modulator; 6. a main amplifier; 7. an array of collimators; 8. a sampling mirror; 9. an optical beam reducer; 10. a reference optical amplifier; 11. a reference light collimating lens; 12. a semi-transparent semi-reflective mirror; 13. a high-speed camera; 14. an interference fringe resolving module; 15. a phase control unit.
Detailed Description
In order to make the technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
An embodiment of the present invention provides a method for controlling a phase of a laser array piston based on interference fringes, including:
dividing seed laser into two parts, inputting one part into a laser array coherent synthesis unit for generating a laser array, and taking the other part as a reference beam;
collecting a part of laser arrays generated by the laser array coherent synthesis unit and performing beam shrinking on the laser arrays;
detecting interference fringe images of the shrunk laser array and the reference beams by using a high-speed camera, measuring and obtaining piston phase errors of each unit beam and the reference beams in the laser array at the high-speed camera according to the interference fringe images, and obtaining time domain distribution of the piston phase errors of each unit beam and the reference beams in the laser array within a period of time;
and controlling the piston phase of each unit beam in the laser array according to the time domain distribution of the piston phase errors of each unit beam and the reference beam in the laser array within a period of time.
The time domain distribution of the position information can be obtained by analyzing and calculating the position information of the interference fringes of the fiber laser array and the reference beam after the high-speed camera detects the beam, and the time domain distribution of the piston phase error of each unit beam and the reference beam in the laser array within a period of time is obtained according to the linear corresponding relation between the position information and the piston phase. The time domain distribution characteristic of the parameter is analyzed, a control strategy aiming at the piston phase is designed, and the control efficiency of the controller is improved to the maximum extent.
For any unit beam in the laser array, generating a voltage applied to two ends of a phase modulator corresponding to the unit beam at the current k moment according to the following control strategy so as to control the piston phase of the unit beam:
for any unit beam in the laser array, Δ u (k) is the change amount of the voltage applied to the two ends of the phase modulator in the laser array coherent combining unit corresponding to the unit beam at the time k relative to the time k-1, u (k-1) is the voltage applied to the two ends of the phase modulator in the laser array coherent combining unit corresponding to the unit beam at the time k-1, and u (k) is the voltage applied to the two ends of the phase modulator in the laser array coherent combining unit corresponding to the unit beam at the time kVoltage of (d); kPAs a proportional parameter, KiAs integral parameter, KdAnd e (k) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k, e (k-1) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k-1, and e (k-2) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k-2.
The invention is to change the control signal of the phase modulator applied according to the real-time stripe position from the original direct loading into the time domain distribution in a period of time according to the stripe position to calculate the control quantity of the phase modulator. Therefore, in the process of resolving the time domain signals, parameters in the control strategy can be adjusted according to the distribution characteristics of the time domain signals, and therefore the synthesis efficiency of the system in the closed loop process is improved.
Referring to fig. 1, in an embodiment of the present invention, a laser array piston phase control system based on interference fringes is first built, including:
the seed laser generating unit comprises a seed laser 1, a preamplifier 2 and a 1 x 2 optical fiber beam splitter 3, wherein laser output by the seed laser 1 is subjected to power amplification through the preamplifier 2 and then is divided into two parts by the 1 x 2 optical fiber beam splitter 3, one part is input into the laser array coherent combining unit to generate a laser array, and the other part is used as a reference beam.
The laser array coherent combining unit comprises a collimator array 7 consisting of a 1 xN optical fiber beam splitter 4, N phase modulators 5, N main amplifiers 6 and N collimators, seed lasers input into the laser array coherent combining unit are divided into N paths of unit beams through the 1 xN optical fiber beam splitter 4, each path of unit beam corresponds to one path of transmission path, the phase modulators 5, the main amplifiers 6 and the collimators are arranged in each path of transmission path in sequence, and each path of unit beam is subjected to phase modulation and power amplification through the phase modulators 5 and the main amplifiers 6 in sequence and then is collimated and output through the collimators in the collimator array 7;
the laser array sampling unit comprises a sampling mirror 8 and an optical beam reducer 9, and the sampling mirror 8 collects a laser array to the optical beam reducer 9 to obtain a laser array after beam reduction;
the image acquisition unit comprises a reference light amplifier 10, a reference light collimating lens 11, a half mirror 12 and a high-speed camera 13, wherein the shrunk laser array is incident to the half mirror 12, a reference beam is incident to the half mirror 12 after passing through the reference light amplifier 10 and the reference light collimating lens 11, is incident to the high-speed camera 13 after being transmitted and reflected by the half mirror 12 respectively, and the high-speed camera 3 detects an interference fringe image of the shrunk laser array and the reference beam;
the interference fringe resolving module 14 obtains the piston phase errors of the unit beams and the reference beams in the laser array at the high-speed camera according to the interference fringe image measurement, and obtains the time domain distribution of the piston phase errors of the unit beams and the reference beams in the laser array within a period of time;
and the phase control unit 15 is used for controlling the piston phase of each unit beam in the laser array according to the time domain distribution of the piston phase errors of each unit beam and the reference beam in the laser array in a period of time.
In the embodiment shown in fig. 1, a coherent combining system of a MOPA (Master Oscillator Power-Amplifier) structure is built based on a fiber laser array, and a sampling mirror is used to collect a part of a laser array to an optical beam reducer, so as to obtain a reduced laser array, so as to match the target surface size of a high-speed camera.
In the embodiment shown in fig. 1, the reference beam passes through a reference light amplifier 10 and a reference light collimating lens 11 and then enters a half mirror 12. The power and the inclination angle of the reference beam are adjusted by the reference beam through the reference light amplifier 10 and the reference light collimating lens 11, so that stable and clear interference fringes are obtained on the target surface of the high-speed camera, the fringe position of the interference fringes moves in space along with the change of the piston phase of the fiber laser array unit, and the high-speed camera 13 is responsible for converting fringe data into an electric signal from an optical signal and transmitting the electric signal to the interference fringe resolving module.
The interference fringe calculating module 14 is composed of a high-speed parallel processing circuit chip-FPGA, and is used for realizing real-time calculation of a high-speed image, calculating the interference fringe of each unit beam through the FPGA to obtain the piston phase error of each unit beam and a reference beam in the laser array at the high-speed camera, and transmitting the piston phase error to the phase control unit through data transmission.
The phase control unit 15 obtains the time domain distribution of the piston phase errors of each unit beam and the reference beam in the laser array in a period of time. The phase control unit receives phase time domain change information of each unit light beam, and performs closed-loop control on the piston phase of each unit light beam by analyzing the phase time domain signal of each unit light beam to realize coherent combination of the laser array. Specifically, the phase control unit records the piston phase error of the time domain distribution of each unit light beam and generates a multidimensional matrix. Taking a 7-channel fiber laser array as an example, the phase control unit will generate a 7 × N (N is the time domain length of the signal) matrix space for storing the piston phase error of the time domain distribution of each unit beam. When the phase control unit controls the piston phase of a certain unit light beam each time, fitting control is performed according to the evolution rule of the unit light beam phase on the time domain instead of the phase information of the unit light beam at the current moment.
For any unit beam in the laser array, generating a voltage applied to two ends of a phase modulator corresponding to the unit beam at the current k moment according to the following control strategy so as to control the piston phase of the unit beam:
for any unit light beam in the laser array, Δ u (k) is a change amount of a voltage applied to two ends of a phase modulator in a laser array coherent combining unit corresponding to the unit light beam at the time k relative to the time k-1, u (k-1) is a voltage applied to two ends of a phase modulator in a laser array coherent combining unit corresponding to the unit light beam at the time k-1, and u (k) is a voltage applied to two ends of a phase modulator in a laser array coherent combining unit corresponding to the unit light beam at the time k; kPIs prepared from radix GinsengNumber, KiAs integral parameter, KdAnd e (k) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k, e (k-1) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k-1, and e (k-2) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k-2.
In the above embodiment, each time the phase control is performed, the comprehensive control is performed by referring to the phase error signal of nearly three times, and based on the control strategy, the controller can control the phase of the piston more accurately to counteract the noise of the system.
In an embodiment of the present invention, a laser array piston phase control system based on interference fringes as shown in fig. 1 is built, and the high-speed camera 13 is responsible for measuring an interference fringe image of the laser array and the reference beam after shrinkage, so as to obtain a fringe image as shown in fig. 2. The images with different labels in fig. 2 correspond to interference fringe images with different phase noise value distributions, where (a) is the interference fringe image corresponding to the case where the piston phase error Φ is 0; (b) the interference fringe image is corresponding to the piston phase error phi pi/2; (c) the method comprises the following steps of (1) obtaining an interference fringe image corresponding to a piston phase error phi pi; (d) and the corresponding interference fringe image when the piston phase error phi is 3 pi/2.
The high-speed camera 13 converts the interference fringes in fig. 2 from optical signals into electrical signals and transmits the electrical signals to the interference fringe calculation module 14, and the interference fringe calculation module 14 is a high-speed image parallel processing system composed of a high-performance FPGA. The interference fringe calculating module 14 is responsible for calculating an interference fringe image transmitted by the high-speed camera for each frame, the processing flow is as shown in fig. 3, firstly, the image is divided according to the fiber laser array to obtain unit beam sub-images with the number equal to that of unit beams in the fiber laser array, and then, the fringe calculation is carried out on each unit beam sub-image to obtain the position coordinates of the fringes; the fringe position coordinates of each unit beam subimage are transmitted to the phase control unit 15 by the interference fringe resolving module 14, and the phase control unit 15 performs closed-loop control on the phase modulator according to the position coordinates to realize in-phase output of the fiber laser array.
The phase-locking control strategy in the phase control unit 15 is innovatively designed, the control schematic diagram of the phase control unit is shown in fig. 4, and the phase control unit 15 is an area framed by a dotted line in fig. 4 and is provided with two input ports and one output port. One input is a phase control quantity customized by a user, and in the field of coherent synthesis, the parameter is generally relative zero phase difference; the other input port is fringe position data calculated by an interference fringe calculating module; the output port controls the phase modulator to perform phase control. For any unit beam in the laser array, the phase control unit firstly converts the phase control quantity into fringe position data and makes a difference with fringe position data f (k) transmitted by the interference fringe resolving module, the relative fringe error between the unit beam and the reference beam measured by the high-speed camera at the time k, namely the piston phase error e (k) between the unit beam and the reference beam measured by the high-speed camera at the time k is obtained through the linear corresponding relation between fringe position information and piston phase, the error information is combined and calculated in a time domain signal mode, and the phase control quantity, namely the voltage u (k) applied to two ends of a phase modulator in the laser array coherent combining unit corresponding to the unit beam at the time k is obtained. The specific execution flow of the combined calculation is shown in fig. 5.
The calculation process of the combination control strategy of proportion, differentiation and integration in the discretization stripe data is relatively simple, in the calculation process, a control system is initialized firstly, specific values of the phase control quantity are given, and generally, in a coherent synthesis system, the phase control quantity is an integral multiple of 2 pi. In the system operation process, a time sequence signal is required to be obtained, so the variable k is used for representing the system cycle number to represent the system operation time length. When K is 1, the control system needs to initialize the system, including Kp、KdAnd KiAnd e (k-1) and e (k-2). After the initialization is completed, the system starts to receive the stripe position information calculated by the high-speed image calculation system, the system converts the stripe position information into phase information and then makes a difference with the set phase control quantity to calculate and obtain e (k); then theChanging a voltage value of the responsive phase modulator driver according to a control strategy formula; finally, transmitting the error quantity in a time sequence mode according to the transmission relation of the error quantity; and circulating the steps to realize the time sequence control of the piston phase.
The piston phase control quantity obtained by the calculation flow in fig. 5 is more consistent with the piston phase noise characteristic at the current moment, so that the residual error of the phase lock of the method is lower than that of the prior art in the closed-loop control stage. Fig. 6 shows the control performance of the conventional interference fringe phase-locking method and the interference fringe calculation method provided by the present invention in time domain control, and the control capabilities of the two control methods are represented by performing closed-loop correction on power frequency interference with a frequency of 50 Hz. Referring to fig. 6, (a) and (b) in fig. 6 respectively represent that the control system adopts the conventional interference fringe phase-locking method and the time domain phase control method proposed in the present application to perform closed-loop control, and the value ranges of the dotted lines (residuals) in the two pictures can be obviously seen: when the interference fringe calculation method provided by the invention is used for phase-locked control, the phase-locked residual error is lower.
Therefore, the piston phase time sequence control method and the piston phase time sequence control system of the interference fringes can reduce the phase-locked residual error in the closed-loop control stage in a coherent synthesis system, and realize laser beam combination with higher efficiency so as to obtain laser output with higher brightness.
In summary, although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention.
Claims (10)
1. The laser array piston phase control method based on the interference fringes is characterized by comprising the following steps:
dividing seed laser into two parts, inputting one part into a laser array coherent synthesis unit for generating a laser array, and taking the other part as a reference beam;
collecting a part of laser arrays generated by the laser array coherent synthesis unit and performing beam shrinking on the laser arrays;
detecting interference fringe images of the shrunk laser array and the reference beams by using a high-speed camera, measuring and obtaining piston phase errors of each unit beam and the reference beams in the laser array at the high-speed camera according to the interference fringe images, and obtaining time domain distribution of the piston phase errors of each unit beam and the reference beams in the laser array within a period of time;
and controlling the piston phase of each unit beam in the laser array according to the time domain distribution of the piston phase errors of each unit beam and the reference beam in the laser array within a period of time.
2. The method for controlling the piston phase of the laser array based on the interference fringes according to claim 1, wherein for any unit beam in the laser array, the phase control unit generates the voltage applied to two ends of the phase modulator corresponding to the unit beam at the current k time according to the following control strategy, so as to control the piston phase of the phase modulator:
for any unit light beam in the laser array, Δ u (k) is a change amount of a voltage applied to two ends of a phase modulator in a laser array coherent combining unit corresponding to the unit light beam at the time k relative to the time k-1, u (k-1) is a voltage applied to two ends of a phase modulator in a laser array coherent combining unit corresponding to the unit light beam at the time k-1, and u (k) is a voltage applied to two ends of a phase modulator in a laser array coherent combining unit corresponding to the unit light beam at the time k; kPAs a proportional parameter, KiAs integral parameter, KdAnd e (k) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k, e (k-1) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k-1, and e (k-2) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k-2.
3. The method of claim 1, wherein the method further comprises: the seed laser comes from a seed laser, the laser output by the seed laser is subjected to power amplification by a preamplifier, and then is divided into two parts by a 1 x 2 optical fiber beam splitter, one part is input into a laser array coherent synthesis unit for generating a laser array, and the other part is used as a reference beam.
4. The method of any of claims 1 to 3, wherein: the laser array coherent combination unit comprises a collimator array consisting of a 1 xN optical fiber beam splitter, N phase modulators, N main amplifiers and N collimators, seed laser input into the laser array coherent combination unit is divided into N paths of unit beams through the 1 xN optical fiber beam splitter, each path of unit beam corresponds to one path of transmission path, the phase modulators, the main amplifiers and the collimators are arranged in the transmission paths in sequence, and each path of unit beam is subjected to phase modulation and power amplification through the phase modulators and the main amplifiers in sequence and then is output in a collimating mode through the collimators in the collimator array.
5. The method of claim 4, wherein the method further comprises: and collecting the laser array to an optical beam reducer by a sampling mirror to obtain the laser array after beam reduction.
6. The method of claim 4, wherein the method further comprises: the laser array after the contraction incides the half mirror, and reference beam incides the half mirror after reference light amplifier, reference light collimation lens, incides the half mirror, incides the high-speed camera after respectively passing through the half mirror transmission, reflection.
7. Laser array piston phase control system based on interference fringe, its characterized in that includes:
the seed laser generating unit is used for generating seed laser and dividing the seed laser into two parts, one part is input into the laser array coherent combining unit and used for generating a laser array, and the other part is used as a reference beam;
the laser array coherent combination unit comprises a collimator array consisting of a 1 XN optical fiber beam splitter, N phase modulators, N main amplifiers and N collimators, wherein seed laser input into the laser array coherent combination unit is divided into N paths of unit beams through the 1 XN optical fiber beam splitter, each path of unit beam corresponds to one path of transmission path, the phase modulators, the main amplifiers and the collimators are arranged in each path of transmission path in sequence, and each path of unit beam is subjected to phase modulation and power amplification through the phase modulators and the main amplifiers in sequence and then is output by collimation through the collimators in the collimator array;
the laser array sampling unit comprises a sampling mirror and an optical beam reducer, and the sampling mirror collects the laser array to the optical beam reducer to obtain a laser array after beam reduction;
the image acquisition unit is used for detecting an interference fringe image of the shrunk laser array and the reference beam by using a high-speed camera;
the interference fringe resolving module obtains the piston phase errors of the unit beams and the reference beams in the laser array at the high-speed camera according to the interference fringe image measurement, and obtains the time domain distribution of the piston phase errors of the unit beams and the reference beams in the laser array within a period of time;
and the phase control unit is used for controlling the piston phase of each unit beam in the laser array according to the time domain distribution of the piston phase errors of each unit beam and the reference beam in the laser array within a period of time.
8. The system of claim 7, wherein for any unit beam in the laser array, the applied voltage across the phase modulator corresponding to the unit beam at the current time k is generated according to the following control strategy, so as to control the piston phase of the unit beam at the current time k:
for any unit light beam in the laser array, Δ u (k) is a change amount of a voltage applied to two ends of a phase modulator in a laser array coherent combining unit corresponding to the unit light beam at the time k relative to the time k-1, u (k-1) is a voltage applied to two ends of a phase modulator in a laser array coherent combining unit corresponding to the unit light beam at the time k-1, and u (k) is a voltage applied to two ends of a phase modulator in a laser array coherent combining unit corresponding to the unit light beam at the time k; kPAs a proportional parameter, KiAs integral parameter, KdAnd e (k) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k, e (k-1) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k-1, and e (k-2) is the piston phase error of the unit beam and the reference beam measured by the high-speed camera at the time k-2.
9. The piston phase control system of the laser array based on the interference fringes as claimed in claim 7 or 8, wherein the seed laser generating unit comprises a seed laser, a preamplifier and a 1 x 2 fiber beam splitter, the laser output by the seed laser is power amplified by the preamplifier, and then is divided into two parts by the 1 x 2 fiber beam splitter, one part is input to the laser array coherent combining unit for generating the laser array, and the other part is used as a reference beam.
10. The system of claim 7 or 8, wherein the image capturing unit includes a reference light amplifier, a reference light collimating lens, a half mirror, and a high-speed camera, the retracted laser array is incident on the half mirror, the reference beam is incident on the half mirror after passing through the reference light amplifier and the reference light collimating lens, and is incident on the high-speed camera after being transmitted and reflected by the half mirror, respectively, and the high-speed camera detects the image of the interference fringes between the retracted laser array and the reference beam.
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