CN114859566A - Multi-path laser splicing and synthesizing system based on automatic light path alignment and pointing accurate control - Google Patents
Multi-path laser splicing and synthesizing system based on automatic light path alignment and pointing accurate control Download PDFInfo
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Abstract
The invention discloses a multi-path laser splicing and synthesizing system based on automatic light path alignment and pointing accurate control, which comprises a laser group (1), a beam expanding and collimating system (2), a reflector group (3), a composite sensor (4), a control computer (5), a high-voltage amplifier (6), a block inclined mirror (7), a spectroscope (8), a diaphragm (9), a calibration light source (10) and a beam combiner (11). The invention combines the optimization algorithm with the micro-lens array method, reduces the difficulty of light path adjustment, improves the anti-interference capability of the synthesis system, realizes the automatic alignment of the light path and the stable closed loop with sudden large pointing error, and provides technical support for the laser splicing synthesis system to be better applied to a motion platform.
Description
Technical Field
The invention relates to the field of optical systems and light beam control, in particular to the technical field of light path alignment and pointing control methods in multi-path laser splicing and synthesizing, and particularly relates to a multi-path laser splicing and synthesizing system based on automatic light path alignment and pointing accurate control.
Background
With the technical development of laser application fields such as precision laser processing, laser communication, biophotonic research and the like, the requirements on the power and the beam quality of an output laser beam are higher and higher. Due to the influence of factors such as the thermal effect and the nonlinear effect of a gain medium, a single laser cannot meet part of application requirements in the aspects of power and beam quality. In order to solve the problem, researchers develop a new method and provide a light beam synthesis method. As a light beam synthesis method, multi-path laser splicing synthesis is successfully applied to various fields such as laser processing, space laser communication and the like.
The basic principle of splicing synthesis is to make multiple paths of laser light closely arranged and output in the same direction by a light beam control method, and the splicing synthesis can be divided into incoherent synthesis and coherent synthesis according to whether phase locking exists or not. The incoherent synthesis is to splice multiple laser sources together, to make the output direction of each laser identical by pointing control, and finally to converge each laser to the same far-field position. Coherent synthesis is to splice multiple coherent light sources together tightly, to make each laser in the same direction by pointing control, and then to ensure the phase of each laser beam to be consistent by phase-locked control, and finally to realize far-field coherent superposition. In both incoherent and coherent combining systems, optical path alignment and precise pointing control are one of the key technologies.
In recent years, the laser splicing synthesis technology is rapidly developed, and the main results are as follows: sprangl et al, US navy research laboratory, 2008, reported 4-path Fiber laser (total power 6.2kW), and the results OF incoherent synthesis experiments after 1.2km OF Atmospheric transmission showed a transmission efficiency OF 94% (Phillip Sprangle, Antonio Ting, Joseph Penano, et al, incorporated Combining and Atmospheric Propagation OF High-power Fiber Lasers for direct-Energy Applications [ J ]. IEEE JOURNAL OF QUANTUM ELECTRICS, 2009,45(2): 138-148); U.S. Noger corporation realized 7-slab solid-state Laser coherent synthesis in 2009, with a power output of 105kW also being the highest power currently obtained by coherent synthesis (S.J. McNaught, C.P. Asman, H.Injeyan, et al.100-kW coherent Combined Nd: YAG MOPA Laser Array [ C ]. in Frontiers in Optics, OSA Technical Digest (CD), Optical society of America,2009: paper FThD 2); in 2012, the university of defense science and technology adopts the SPGD algorithm to realize a fiber laser coherent synthesis experiment with 9 paths and 1.8kW power output (X.Wang, J.leng, P.ZHou, et al.1.8-kW simultaneous spectra and coherent combining of three-tone-channel all-fiber amplifier array [ J ]. Appl.Phys.B,2012,107: 785-790); in 2014, the national institute of engineering and physics, color macro, and the like, reported the experimental results of coherent synthesis of four-way hectowatt-level laths by solid laser, wherein the quality BQ of the synthesized light beam is less than 1.3, and the peak light intensity is improved by 2.8 times (the research of the experimental study of coherent synthesis of four-way hectowatt-level laths by laser [ J ] the annual science and technology of the national institute of engineering and physics, 2014,165-166); in 2014, the advanced research and planning department of the united states department of defense reports the latest progress of the 'saint sword' (escape) plan, a 21-unit fiber laser phased array is taken as a transmitting device, and a delay SPGD optimization algorithm based on TIL control is adopted, so that coherent synthesis of the laser array is realized at seven kilometers (V.Coffey, New Advances in feedback applications: high-energy lasers, optics & Photonics New, 2014,1047-6938/14/10/28/8); in 2019, the university of national defense science and technology reports a 60-path large-array-element fiber laser coherent synthesis result, and the stripe contrast after synthesis is about 97% (Seawa, Hades, and the like, 60-path large-array-element fiber laser high-efficiency coherent synthesis [ J ]. infrared and laser engineering, 2019,48 (1)).
There are three main ways of directional control used in analyzing the splicing synthesis system reported at present. The first mode has no automatic closed-loop control loop, each path of laser far field is coincided by manual adjustment, the precision of the mode is low, the practicability is weak, and the mode is only suitable for laboratory principle verification experiments under certain low-power conditions. The second mode adopts optimization methods such as random parallel gradient descent algorithm (SPGD) and the like, takes a certain parameter of a synthesized far field as an optimization object, completes multi-path laser pointing control and realizes coaxial output of synthesized laser. This approach is simple in construction and low in system cost, but has two significant drawbacks: firstly, the system control bandwidth is reduced along with the increase of the number of synthesis paths, and the requirement of the splicing synthesis on the directional control bandwidth developing towards a large-scale and super-large-scale direction is difficult to meet; secondly, the control stability is poor, and the situation of falling into a local extreme value is easy to occur. In the third mode, a single independent camera is used for detecting the optical axis of each laser, and then the pointing direction of the laser corresponding to each camera is controlled through a controller. The method needs the number of cameras equal to the number of the synthetic laser paths, has high system cost and is difficult to apply to a large-scale and super-large-scale splicing and synthesizing system.
The invention patent (application number CN102608764A) of the photoelectric technology research of the Chinese academy of sciences provides a pointing regulation and control method for realizing the detection of the optical axis of a synthesized sub laser beam and the real-time closed-loop control by matching a micro-lens array with a single camera. The system has simple structure, good control stability and easy expansion. However, the requirement on optical path adjustment is high, each path of sub-laser far-field light spot needs to be adjusted to a sub-aperture range, and the operation in a large-scale splicing synthesis system is difficult. In addition, the motion platform is difficult to avoid the situations of external impact, sudden strong vibration and the like, and the pointing detection dynamic range of the method is small, so that sub-laser far-field light spots are easy to exceed the sub-aperture range, and the closed loop is disordered or cannot be closed. In order to reduce the difficulty of light path adjustment and improve the anti-interference capability of the system, the invention provides a multi-path laser splicing and synthesizing system with automatic light path alignment and accurate pointing control, which combines an optimization algorithm with a micro-lens array method to realize the stable closed loop of the automatic light path alignment and the sudden large pointing error and provide technical support for the laser splicing and synthesizing system to be better applied to a motion platform.
Disclosure of Invention
The technical problems to be solved by the invention are as follows: (1) automatically adjusting a large quasi-static alignment deviation in laser splicing synthesis; (2) accurately controlling optical axis jitter within a certain frequency range; (3) stable closed-loop control of sudden large pointing errors caused by external impact and other factors.
The technical scheme adopted by the invention for realizing the technical aim is as follows: a multi-path laser splicing and synthesizing system based on automatic light path alignment and accurate pointing control comprises a laser group 1, a beam expanding and collimating system 2, a reflector group 3, a composite sensor 4, a control computer 5, a high-voltage amplifier 6, a blocking inclined mirror 7, a spectroscope 8, a diaphragm 9, a calibration light source 10 and a beam combiner 11. Laser output by a laser group 1 is expanded and shaped into a light beam size meeting design requirements by an expanded beam collimation system 2, then the position of each path of laser is adjusted by a reflector group 3 to meet the input position requirements of a beam combiner 11, each path of laser is adjusted by the beam combiner 11 to form an expected arrangement mode with high duty ratio, the spatial arrangement of sub-mirrors of a blocked tilting mirror 7 is consistent with that of a synthesized light beam, each tilting sub-mirror corresponds to one path of laser, and the synthesized light beam passes through the blocked tilting mirror 7 and a spectroscope 8 in sequence after the beam combiner and is finally emitted by the spectroscope 8. A small part of laser light penetrating through the beam splitter 8 enters the compound sensor 4, firstly passes through a main beam-reducing lens consisting of a lens I4001 and a lens II 4002, then is divided into two parts by the beam splitter 4003, the part of laser light reflected by the beam splitter 4003 sequentially passes through a reflecting mirror 4010 and a focusing lens 4009, enters a far-field detection camera 4008 positioned on a focal plane of the focusing lens 4009, so that far-field detection of a synthesized light beam is realized, and the synthesized far field is simultaneously used for automatic light path alignment control and synthesis effect evaluation. The laser transmitted by the beam splitter 4003 sequentially passes through a secondary beam-reducing lens consisting of a lens three 4004 and a lens four 4005 and a micro lens array 4006, enters a sub-light spot detection camera (4007) positioned on the focal plane of the micro lens array 4006, and the real-time measurement of the pointing direction of each path of sub-laser beams is completed.
Before the laser emits light, the composite sensor 4 needs to be calibrated by parallel light in advance, and the calibration process is as follows: the aperture of the light beam is adjusted by the parallel light output by the calibration light source 10 through the diaphragm to be consistent with the aperture of the synthesized light beam, and then the light beam is reflected by the spectroscope 8 to enter the composite sensor 4. The parallel light passes through a main beam-reducing lens composed of a first lens 4001 and a second lens 4002, and then is divided into two parts by a beam splitter 4003. The part of light reflected by the beam splitter 4003 sequentially passes through the reflecting mirror 4010 and the focusing lens 4009, enters the far-field detection camera 4008 positioned on the focal plane of the focusing lens 4009, forms a far-field light spot with a near diffraction limit on the far-field detection camera 4008, and records the centroid position of the far-field light spot as an automatic light path alignment reference. The light passing through the beam splitter 4003 sequentially passes through a secondary beam-reducing lens consisting of a lens three 4004 and a lens four 4005 and a micro lens array 4006, and is respectively converged to a sub-light spot detection camera 4007 positioned on the focal plane of the micro lens array 4006 to form a far-field sub-light spot array with a near diffraction limit, the number and the arrangement mode of the far-field sub-light spots correspond to the micro lens array one by one, and the centroid position of each sub-light spot is recorded and used as the direction correction reference of each path of laser light. And finishing the calibration of the composite sensor.
In the optical path adjusting stage, the pointing direction of each path of laser is adjusted manually to make the laser enter the visual field of the far-field detection camera 4008, but because the sub-aperture visual field range of the sub-spot detection camera 4007 is smaller, part of the far-field sub-spots can exceed the sub-aperture visual field range. In the formal working stage of the system, the computer 5 drives the block tilting mirror 7 to correct the alignment error of each path of laser through the high-voltage amplifier 6 according to a detection signal of the far-field detection camera 4008 and a calibration standard by using a control algorithm, so that each path of laser enters a sub-aperture field corresponding to the sub-spot detection camera 4007, and then is switched to a control loop of the sub-spot detection camera 4007, and the computer 5 drives the block tilting mirror 7 to correct the optical axis deviation of each path of laser through the high-voltage amplifier 6 according to the detection signal of the sub-spot detection camera 4007 and the calibration standard by using the control algorithm, so that the high-precision stable pointing control of the synthesized beam is realized.
The mode of realizing the automatic alignment of the light path is as follows: in the calibration stage of the composite sensor, the calibration parallel light enters the composite sensor to form a far-field light spot in the far-field detection camera 4008, and the centroid coordinate of the far-field light spot is recorded as (x) d0 ,y d0 ). In the formal working stage of the system, the computer 5 acquires an image of the far-field detection camera 4008, and calculates the equivalent radius R of the image 0 The calculation formula is as follows:
where N and M are the total number of column and row pixels, x, of the image i And y i The coordinate value, I (x), corresponding to the ith column and the jth row of the image i ,y j ) The pixel of the ith column and the jth row corresponds to a gray value. With equivalent radius R 0 As a performance index, a control voltage is obtained by calculation through an optimization method such as a random parallel gradient descent (SPGD) algorithm and the like, and the voltage is amplified by a high-voltage amplifier 6 and then drives a blocking inclined mirror to correct alignment errors between laser beams and corresponding sub-apertures. In the process of automatic alignment of the optical path, the light energy received by each sub-aperture of the sub-spot detection camera 4007 is monitored in real time, when the sum of the gray values in all the sub-apertures corresponding to the synthetic laser is greater than a given threshold value, it is indicated that the laser beam and the corresponding sub-aperture are substantially aligned, the voltage value of the block tilting mirror driver at the moment is recorded, and the voltage value is switched to the control loop of the sub-spot detection camera 4007.
The mode for realizing the high-precision pointing control of the composite beam is as follows: in the calibration stage of the composite sensor, the calibration parallel light enters the composite sensor to form a sub-light spot array on the sub-light spot detection camera 4007, and the calibration centroid coordinate of the kth path of laser light is recorded as (p) k0 ,q k0 ) After the control loop is switched to the control loop of the sub-light spot detection camera 4007, the centroid coordinate of the kth path of laser in the s frame is obtained through calculation
Offset from the scaled centroid of
The control voltage in two directions is updated by adopting a classical PI control method as follows:
wherein a and b are control parameters which,
and
for the control voltage of the kth laser in both x and y directions at the s-th moment,
and
for the control voltage of the k laser in the x and y directions at the s +1 th time,
and
and the voltage is amplified by a high-voltage amplifier and then drives a blocking tilting mirror to correct the static and dynamic optical axis deviation of each path of laser, so that the real-time closed-loop control of the optical axis is realized.
Further, the laser group 1 includes all lasers that can be converted into a spatial beam, such as a fiber laser and a solid laser.
Further, the optical path alignment optimization method comprises a random parallel gradient descent algorithm (SPGD), a hill climbing method, a genetic algorithm and the like.
Further, the switching mode of the optical path alignment and the high-precision pointing control not only includes switching from the optical path alignment mode to the high-precision pointing control mode when the sum of the gray values in all the sub-apertures is greater than a given threshold value during system startup, but also includes switching from the high-precision pointing control mode to the optical path alignment mode when the sum of the gray values in some or all the sub-apertures is less than the given threshold value due to transient shock and the like during the high-precision pointing control mode, and switching back to the high-precision pointing control mode when the sum of the gray values in all the sub-apertures is greater than the given threshold value again.
Compared with the prior art, the invention has the following advantages:
1. the invention realizes the automatic alignment of larger quasi-static deviation, reduces the requirement on manual adjustment of the optical path, and improves the tolerance of the splicing synthesis system to the alignment deviation of the optical path;
2. the method combines an optimization algorithm with a micro-lens array method, realizes automatic alignment and accurate pointing control of the light path under the condition of not increasing the complexity of the system obviously, and provides a technical choice for the subsequent development of a splicing synthesis system towards large scale and super large scale;
3. according to the invention, flexible switching of two control loops is controlled through automatic light path alignment and pointing accuracy, so that stable closed loop can be realized for some emergency conditions such as external impact to a certain degree, short-time strong vibration and the like, the pointing control stability is improved, and the environment adaptability of a splicing synthesis system is expanded.
Drawings
FIG. 1 is a schematic view of the overall structure of the present invention; wherein: 1 is a laser group, 2 is a beam expanding collimation system, 3 is a reflector group, 4 is a composite sensor, 5 is a control computer, 6 is a high-voltage amplifier, 7 is a blocking inclined mirror, 8 is a spectroscope, 9 is a diaphragm, 10 is a calibration light source, and 11 is a beam combiner;
FIG. 2 is a schematic view of the structure of the composite sensor used; wherein: 4001 is lens one, 4002 is lens two, 4003 is a spectroscope, 4004 is lens three, 4005 is lens four, 4006 is a microlens array, 4007 is a sub-spot detection camera, 4008 is a far-field detection camera, 4009 is a focusing lens, 4010 is a mirror;
FIG. 3 is a schematic diagram of the spatial arrangement of the composite beam;
FIG. 4 is a schematic view of arrangement of the block tilting mirror;
FIG. 5 is a schematic diagram showing the matching relationship between sub-laser beams and a microlens array;
FIG. 6 is a schematic view of a microlens array imaging mode;
fig. 7 is a schematic diagram of a far-field detection camera light spot and a sub-light spot detection camera light spot before closed-loop control, where fig. 7(a) is a schematic diagram of a far-field detection camera light spot before closed-loop control, and fig. 7(b) is a schematic diagram of a sub-light spot detection camera light spot before closed-loop control;
FIG. 8 is a light spot image of the far field detection camera and the sub-light spot detection camera before the light path alignment, after the light path alignment is switched to the pointing accurate control time and the accurate control stable closed loop; fig. 8(a1) and fig. 8(a2) are spot images of the far-field detection camera and the sub-spot detection camera before the optical path alignment, fig. 8(b1) and fig. 8(b2) are spot images of the far-field detection camera and the sub-spot detection camera switched from the optical path alignment to the point-oriented precise control time, and fig. 8(c1) and fig. 8(c2) are spot images of the far-field detection camera and the sub-spot detection camera after the precise control stabilizes the closed loop;
fig. 9 is a graph showing the variation of the synthesized far-field Strehl Ratio (SR) detected by the far-field detection camera.
Detailed Description
The invention is further described with reference to the following figures and detailed description.
As shown in fig. 1, the multi-channel laser splicing and synthesizing system based on the automatic light path alignment and pointing precise control of the present invention includes 9 sets of lasers 1, 9 sets of beam expanding and collimating systems 2, 9 sets of reflecting mirror sets 3, 1 set of composite sensor 4,1 control computer 5, 1 set of high- voltage amplifier 6, 1 set of blocking and tilting mirror 7, 1 block of beam splitter 8, 1 diaphragm 9, 1 set of calibration light source 10, and 1 set of beam combiner 11. The output lasers of the 9 sets of lasers are expanded and shaped into a square by the respective corresponding beam expanding and collimating systems, then the positions of the lasers are adjusted by the reflector group 3 to meet the requirement of the input position of the beam combiner 11, and the lasers are adjusted by the beam combiner 11 to form an expected arrangement mode with high duty ratio, as shown in fig. 3. The spatial arrangement of the sub-mirrors of the block tilting mirror 7 is as shown in fig. 4, which is consistent with the arrangement of the combined light beam, and each tilting sub-mirror corresponds to one of the laser beams. The synthesized light beam passes through the blocking inclined mirror 7 and the spectroscope 8 in sequence from the beam combiner and is finally emitted out by the spectroscope 8.
A small part of laser penetrating through the spectroscope 8 enters the composite sensor 4 to realize far-field detection of the synthesized light beam and high-precision detection of the pointing direction of the sub-laser beam, and the internal structure of the composite sensor is shown in fig. 2. The combined light beam firstly passes through a main beam-reducing lens consisting of a lens I4001 and a lens II 4002, then is divided into two parts by a beam splitter 4003, the part of laser light reflected by the beam splitter 4003 sequentially passes through a reflecting mirror 4010 and a focusing lens 4009, enters a far-field detection camera 4008 positioned on the focal plane of the focusing lens 4009, and the far-field detection of the combined light beam is realized, and the combined far field is simultaneously used as the automatic optical path alignment control and the evaluation of the combined effect. The laser light transmitted through the beam splitter 4003 sequentially passes through a secondary beam reduction lens consisting of a lens three 4004 and a lens four 4005 and a micro lens array 4006, enters a sub-light spot detection camera 4007 positioned on the focal plane of the micro lens array 4006, and completes real-time measurement of the pointing direction of each path of sub-laser beams, and the matching relation and the imaging mode of the sub-laser beams and the micro lens array are shown in fig. 5 and 6.
Before the laser emits light, the composite sensor 4 needs to be calibrated by parallel light in advance, and the calibration process is as follows: the aperture of the light beam is adjusted by the parallel light output by the calibration light source 10 through the diaphragm to be consistent with the aperture of the synthesized light beam, and then the light beam is reflected by the spectroscope 8 to enter the composite sensor 4. The parallel light passes through a main beam-reducing lens composed of a first lens 4001 and a second lens 4002, and then is divided into two parts by a beam splitter 4003. The part of light reflected by the beam splitter 4003 sequentially passes through the reflecting mirror 4010 and the focusing lens 4009, enters the far-field detection camera 4008 positioned on the focal plane of the focusing lens 4009, forms a far-field light spot with a near diffraction limit on the far-field detection camera 4008, and records the centroid position of the far-field light spot as an automatic light path alignment reference. The light passing through the beam splitter 4003 sequentially passes through a secondary beam-reducing lens consisting of a lens three 4004 and a lens four 4005 and a micro lens array 4006, and is respectively converged to a sub-light spot detection camera 4007 positioned on the focal plane of the micro lens array 4006 to form a far-field sub-light spot array with a near diffraction limit, the number and the arrangement mode of the far-field sub-light spots correspond to the micro lens array one by one, and the centroid position of each sub-light spot is recorded and used as the direction correction reference of each path of laser light.
In the optical path adjustment stage, the pointing direction of each laser beam is adjusted manually and roughly so that the laser beam enters the visual field of the far-field detection camera 4008, as shown in fig. 7(a), but because the sub-aperture visual field range of the sub-spot detection camera 4007 is small, part of the far-field sub-spots will exceed the sub-aperture visual field range, as shown in fig. 7 (b). Then, the automatic alignment and the accurate pointing control of the light path are sequentially carried out, and the specific implementation method and the steps are as follows:
1. scaled centroid of far field detection camera 4008The coordinates are (x) d0 ,y d0 ) The position of the calibration center of mass is shown as a cross in FIG. 7(a), and the calibration center of mass coordinate of the kth laser beam of the sub-spot detecting camera 4007 is recorded as (p) k0 ,q k0 ) The position of which is as the cross of fig. 7 (b);
2. at time t, the voltage applied to the block tilting mirror is
Randomly generating a set of small voltage disturbances with zero mean value and obeying Bernoulli distribution
3. Control signal of voltage
Acts on the blocking tilting mirror, wherein,
collecting an image of the far-field detection camera 4008 for the voltage applied to the blocking tilting mirror at the t-th moment, and calculating the equivalent radius R of the image 0 And is given to J + ，J + For the performance index of applying the positive disturbance voltage, the equivalent radius calculation formula is as follows:
where N and M are the total number of column and row pixels of the image, x i And y i The coordinate value, I (x), corresponding to the ith column and the jth row of the image i ,y j ) The pixel of the ith column and the jth row corresponds to a gray value;
4. control signal of voltage
Acting on the blocking mirror, collecting an image of the far field detection camera 4008, and calculating the equivalent radius R of the image 0 And is given to J - ，J - Performance indexes for applying negative disturbance voltage;
5. updating the control voltage signal to
Wherein gamma is the gain coefficient of the SPGD algorithm;
6. collecting an image of the sub-spot detection camera 4007, and calculating the gray value and I in the sub-aperture range k∑ If the sum of the gray values in all the sub-aperture ranges is larger than a given threshold value, entering the next step, otherwise, returning to the step 2 and entering the next iteration;
7. calculating the mass center coordinate of the kth path of laser light as
Offset from the scaled centroid of
8. The control voltage in two directions is updated by adopting a classical PI control method as follows:
wherein a and b are control parameters; wherein the content of the first and second substances,
and
for the control voltage of the kth laser in both x and y directions at the s-th moment,
and
for the control voltage of the k laser in the x and y directions at the s +1 th time,
and
mass center offset of the kth laser in the x direction and the y direction at the s moment;
9. and returning to the step 6, and entering the next control operation.
Spot images of the far-field detection camera 4008 and the sub-spot detection camera 4007 at three times before the optical path alignment, after the switching from the optical path alignment to the pointing precision control and the precision control stabilization closed loop are respectively shown in fig. 8(a1) (a2), fig. 8(b1) (b2), and fig. 8(c1) (c 2). The variation curve of the synthesized far-field Strehl Ratio (SR) detected by the far-field detection camera 4008 in the entire control process is shown in fig. 9.
The laser group 1 includes all lasers that can be converted into spatial beams, such as fiber lasers and solid state lasers.
The optical path alignment optimization method can also be a hill climbing method, a genetic algorithm and the like.
Claims (4)
1. The utility model provides a multichannel laser concatenation synthesis system based on directional accurate control of light path automatic alignment which characterized in that: the system comprises a laser group (1), a beam expanding and collimating system (2), a reflector group (3), a composite sensor (4), a control computer (5), a high-voltage amplifier (6), a blocking inclined mirror (7), a spectroscope (8), a diaphragm (9), a calibration light source (10) and a beam combiner (11); the composite sensor (4) comprises a first lens (4001), a second lens (4002), a spectroscope (4003), a third lens (4004), a fourth lens (4005), a micro-lens array (4006), a sub-light spot detection camera (4007), a far-field detection camera (4008), a focusing lens (4009) and a reflecting mirror (4010);
laser output by a laser group (1) is expanded and shaped into a light beam size meeting design requirements by an expanded beam collimation system (2), then the position of each path of laser is adjusted by a reflector group (3) to meet the input position requirement of a beam combiner (11), each path of laser is adjusted by the beam combiner (11) to form an expected arrangement mode with high duty ratio, the spatial arrangement of sub-mirrors of a blocked inclined mirror (7) is consistent with that of a synthesized light beam, each inclined sub-mirror corresponds to one path of laser, the synthesized light beam passes through the blocked inclined mirror (7) and a spectroscope (8) in sequence after self-beam combiner, and is finally emitted by the spectroscope (8);
a small part of laser penetrating through the spectroscope (8) enters the composite sensor (4) to realize far-field detection of the synthesized light beam and high-precision detection of the pointing direction of the sub-laser beam; the synthetic light beam firstly passes through a main beam-shrinking lens consisting of a lens I (4001) and a lens II (4002), then is divided into two parts by a beam splitter (4003), the part of laser light reflected by the beam splitter (4003) sequentially passes through a reflecting mirror (4010) and a focusing lens (4009) and enters a far-field detection camera (4008) positioned on the focal plane of the focusing lens (4009) to realize the far-field detection of the synthetic light beam, and the synthetic far field is simultaneously used as the automatic light path alignment control and the synthetic effect evaluation; the laser passing through the spectroscope (4003) sequentially passes through a secondary beam-reducing lens consisting of a lens III (4004) and a lens IV (4005) and a micro lens array (4006) and enters a sub-light spot detection camera (4007) positioned on the focal plane of the micro lens array (4006), and the real-time measurement of the pointing direction of each path of sub-laser beams is completed;
before the laser emits light, the composite sensor (4) needs to be calibrated by parallel light in advance, and the calibration process is as follows: parallel light output by a calibration light source (10) passes through a diaphragm to adjust the aperture of the light beam to be consistent with the aperture of a synthesized light beam, then the light beam is reflected by a spectroscope (8) to enter a composite sensor (4), the parallel light passes through a primary beam shrinkage lens consisting of a lens I (4001) and a lens II (4002), then the parallel light is divided into two parts by the spectroscope (4003), the part of light reflected by the spectroscope (4003) sequentially passes through a reflecting mirror (4010) and a focusing lens (4009) to enter a far-field detection camera (4008) positioned on a focal plane of the focusing lens (4009), a far-field light spot with a near diffraction limit is formed on the far-field detection camera (4008), the centroid position of the far-field light spot is recorded, and the centroid position is used as an automatic light path alignment reference; the light transmitted by the spectroscope (4003) sequentially passes through a secondary beam-reducing lens consisting of a lens III (4004) and a lens IV (4005) and a micro lens array (4006), and is respectively converged to a sub-light spot detection camera (4007) positioned on the focal plane of the micro lens array (4006) to form a far-field sub-light spot array with a near diffraction limit, the number and the arrangement mode of the far-field sub-light spots are in one-to-one correspondence with the micro lens array, and the centroid position of each sub-light spot is recorded and used as the direction correction reference of each path of laser; at this point, the calibration of the composite sensor is finished;
the pointing direction of each path of laser is roughly adjusted manually to enable the laser to enter the visual field of a far-field detection camera (4008), but because the sub-aperture visual field range of a sub-spot detection camera (4007) is smaller, part of far-field sub-spots can exceed the sub-aperture visual field range, therefore, the computer (5) firstly utilizes the control algorithm to drive the block inclined mirror (7) to correct the alignment error of each path of laser through the high-voltage amplifier (6) according to the detection signal of the far-field detection camera (4008) and the calibration standard so that each path of laser enters the sub-aperture view field corresponding to the sub-spot detection camera (4007), then switching to a control loop of a sub-light spot detection camera (4007), and driving a blocking inclined mirror (7) by a computer (5) through a high-voltage amplifier (6) according to a detection signal of the sub-light spot detection camera (4007) and a calibration standard by using a control algorithm to correct the deviation of the optical axis of each path of laser, thereby realizing high-precision stable pointing control of the synthesized light beam;
the mode of realizing the automatic alignment of the light path is as follows: the calibrated parallel light enters the composite sensor to form a far-field light spot in a far-field detection camera (4008), and the coordinate of the calibration center of mass of the light spot is recorded as (x) d0 ,y d0 ) After the system starts to work, the computer (5) collects an image of the far-field detection camera (4008), and calculates the equivalent radius R of the image 0 The calculation formula is as follows:
where N and M are the total number of column and row pixels of the image, x i And y i The coordinate value, I (x), corresponding to the ith column and the jth row of the image i ,y j ) The pixel of the ith column and the jth row corresponds to a gray value; with equivalent radius R 0 As a performance index, calculating by using a random parallel gradient descent (SPGD) algorithm optimization method to obtain a control voltage, and amplifying the voltage by using a high-voltage amplifier (6) and then driving a blocking inclined mirror to correct alignment errors between laser beams and corresponding sub-apertures; in the automatic alignment process of the light path, monitoring the light energy received by each sub-aperture of the sub-spot detection camera (4007) in real time, when the sum of gray values in all sub-apertures corresponding to the synthetic laser is greater than a given threshold value, indicating that the laser beam is basically aligned with the corresponding sub-aperture, recording the voltage value of a block tilting mirror driver at the moment, and switching to a control loop of the sub-spot detection camera (4007);
the mode for realizing the high-precision pointing control of the composite beam is as follows: the calibrated parallel light enters the composite sensor to form a sub-light spot array on a sub-light spot detection camera (4007), and the calibration centroid coordinate of the kth path of laser is recorded as (p) k0 ,q k0 ) After the laser is switched to a control loop of a sub-spot detection camera (4007), the centroid coordinate of the kth path of laser at the s moment is calculated and obtained
Offset from the scaled centroid of
The control voltage in two directions is updated by adopting a classical PI control method as follows:
wherein a and b are control parameters which are,
and
for the control voltage of the kth laser in both x and y directions at the s-th moment,
and
the control voltage of the k path laser in the x and y directions at the s +1 th moment
And
for the mass center offset of the kth laser in the x and y directions at the s moment, the voltage is amplified by a high-voltage amplifier and then drives a block tilting mirror to correct the mass center offset of each laserAnd static and dynamic optical axis deviation is adopted, and real-time closed-loop control of the optical axis is realized.
2. The multi-path laser splicing and synthesizing system based on the automatic light path alignment and pointing precise control as claimed in claim 1, wherein: the laser group (1) comprises all lasers which can be converted into space beams, such as a fiber laser and a solid laser.
3. The multi-path laser splicing and synthesizing system based on the automatic light path alignment and pointing precise control as claimed in claim 1, wherein: the optical path alignment optimization method comprises a random parallel gradient descent algorithm (SPGD), a hill climbing method and a genetic algorithm.
4. The multi-path laser splicing and synthesizing system based on the automatic light path alignment and pointing precise control as claimed in claim 1, wherein: the switching mode of the light path alignment and the high-precision pointing control not only comprises the switching from the light path alignment mode to the high-precision pointing control mode when the gray value sum in all the sub-apertures is larger than a given threshold value during the system starting, but also comprises the switching from the high-precision pointing mode to the light path alignment mode when the gray value sum in part or all the sub-apertures is smaller than the given threshold value due to instant impact factors in the high-precision pointing control mode stage, and switching back to the high-precision pointing control mode when the gray value sum in all the sub-apertures is larger than the given threshold value again.
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