CN110729628A - Piston phase control system and method - Google Patents

Abstract

The invention discloses a piston phase control system and method. The method comprises the following steps: a seed laser is phase-modulated, amplified and collimated and then emitted; after the emitted laser array is split, a part of the laser is transmitted to a target surface through atmospheric turbulence and scattered and converged. It is detected to form a first feedback signal to control the collimator to correct the tilt aberration caused by atmospheric turbulence; after the outgoing laser array is split, another part of the laser is spatially phase-modulated to simulate atmospheric turbulence, and after focusing, it is detected to form a second feedback The signal is used to control the phase modulator to correct the piston phase difference caused by the amplification process; the second-stage piston phase control device is connected between the first detector and the spatial phase modulation device array. The problem in the prior art that when the laser transmission distance is long, the control rate of the piston phase is difficult to meet the requirements of a large number of laser arrays is solved, the piston phase control rate can meet the requirements of a large number of laser arrays, and the laser transmission distance is not limited.

Description

A piston phase control system and method

technical field

The invention relates to the technical field of optical coherent synthesis, in particular to a graded piston phase control system.

Background technique

Laser arrays can be widely used in fields such as laser communication, lidar and directed energy technology. The laser coherent array based on the master oscillator power amplifier (English name Master Oscillator Power Amplifier, MOPA for short) can realize the synthetic aperture emission, increase the system emission aperture, and reduce the laser transmission divergence angle. Using the target-based loop, it is also possible to compensate for atmospheric turbulence through tilt phase and piston phase control (see Patent 1: CN104037606B, see Reference 1: T Weyrauch, et al. Deep turbulence effects mitigation with coherent combining of 21laser beams over 7km [ J]. Optics Letters, 2016, 41(4):840-843).

FIG. 1 is a schematic block diagram of the structure of a target-in-loop laser coherent array in the prior art. The system mainly includes a seed laser 101, a laser beam splitter 102, a plurality of phase modulators 103, a plurality of laser amplifiers 104, a plurality of adaptive laser collimators 105, a receiving telescope 106, a photodetector 107, and a tilt control circuit 108 and piston phase control circuit 113. After the laser light emitted by the seed laser 101 is split by the laser beam splitter 102 , each laser beam enters the phase modulator 103 respectively. Each phase modulator 103 is optically connected to each corresponding laser amplifier 104, respectively. Each laser amplifier 104 is optically connected to the adaptive laser collimator 105, respectively. The laser light emitted by each adaptive laser collimator 105 reaches the target surface 116 after being transmitted through the atmospheric turbulence 115 . The receiving telescope 106 receives the scattered light scattered by the target, and the scattered light is incident on the photodetector 107 . The photodetector 107 converts the detected optical signal into an electrical signal, and transmits it to the tilt control circuit 108 and the piston phase control circuit 113 . The tilt control circuit 108 runs a control algorithm, generates an output signal according to the input signal as a feedback signal, and controls each adaptive laser collimator 105 to correct the tilt difference caused by the atmospheric turbulence 115 . The piston phase control circuit 113 runs a control algorithm, generates an output signal according to the input signal as a feedback signal, and controls each phase modulator 103 to correct the piston phase difference caused by the laser amplifier 104 and atmospheric turbulence 115 . By correcting the tilt aberration and piston aberration, the laser array can achieve coherent synthesis at the target, so that the laser energy at the target can be maximized.

However, since the scattered light of the far-field target is used as the feedback signal, after changing the control parameters such as the phase and tilt of the laser array, the new laser array needs to travel a certain distance to reach the target, and then wait for the scattered laser signal to return to the laser emission position. , to obtain the feedback signal, and finally correct the control parameters according to the change of the feedback signal. Therefore, the single iteration time of the adaptive control is greater than the round trip time of the laser between the reflection and the target. The frequency of the piston phase noise in the laser amplifier 104 is usually high, and when the laser transmission distance is long, the control rate of the piston phase is difficult to meet the requirements of a large number of laser arrays.

SUMMARY OF THE INVENTION

The invention provides a piston phase control system and method for overcoming the high frequency of piston phase noise in laser amplifiers in the prior art. When the laser transmission distance is long, the control rate of the piston phase is difficult to meet the requirements of a large number of laser arrays and other defects, reducing the single iteration time of the feedback signal, the piston phase control rate meets the requirements of a large number of laser arrays, and the laser transmission distance is not limited.

In order to achieve the above object, the present invention provides a piston phase control system, which includes a seed laser, a laser beam splitter, a phase modulator array, a laser amplifier array, an adaptive laser collimator array, and an adaptive laser collimator array connected in sequence. The outgoing laser light of each collimator in the collimator array reaches the target surface after being transmitted by atmospheric turbulence. On the scattered light path of the target target surface, the target scattered light is received by the telescope and then incident on the first detector. The first detector is tilted The control circuit is connected with each collimator; it also includes:

The beam splitter is arranged on the optical path between the outgoing laser of each collimator and the atmospheric turbulence, and is used to split the outgoing laser energy of the collimator. After splitting, part of the laser energy is transmitted to the target surface, and the other part of the laser energy is incident. onto the spatial phase modulation device array;

The spatial phase modulation device array is used to change the piston phase of the outgoing laser light;

a focusing device for focusing the outgoing laser that changes the phase of the piston;

The second detector, the input end receives the focused laser, and the output end is connected to the phase modulator array via the first-stage piston phase control device.

In order to achieve the above object, the present invention also provides a piston phase control method, comprising the following steps:

The seed laser is emitted after phase modulation, amplification and collimation;

After the outgoing laser array is split, a part of the laser light is transmitted to the target surface through atmospheric turbulence, and after scattering and convergence, it is detected and extracted to form a first feedback signal to control the collimator to correct the tilt aberration caused by atmospheric turbulence;

After the outgoing laser array is split, another part of the laser is spatially phase-modulated, focused, and then detected to form a second feedback signal to control the phase modulator to correct the piston aberration caused by the amplification process;

The first feedback signal is also used to control the spatial phase modulator to correct the piston phase difference caused by the simulated atmospheric turbulence in the spatial phase modulation process.

The piston phase control system and method provided by the present invention perform light splitting on the optical path of the laser array incident on the atmospheric turbulent flow, split a part of the laser light through the spatial phase modulation array for phase modulation and focus, and then be collected by the second detector, and convert the optical signal into electrical signals. The signal is then output and calculated by the first-stage piston phase control device to obtain the phase difference of the amplifier array piston and form a phase modulation signal accordingly, which is fed back to the phase modulator array to correct the piston phase noise in the laser amplifier, that is, the first-stage piston phase control. The device obtains the evaluation function from the output end of the laser array. Since the evaluation function can be obtained from the near field, there is no need to obtain the evaluation function from the target, and the feedback rate of the phase modulation signal is high, so it has the advantage of high control rate; another part of the light is incident on the original path Atmospheric turbulence reaches the target and is scattered by the target and returns to the telescope. The scattered light is output by the telescope and collected by the first detector. After converting the optical signal, the tilt control circuit calculates and obtains the tilt difference caused by atmospheric turbulence for correction. The piston phase difference caused by the turbulent flow can be calculated by obtaining the signal from the output end of the first detector through the secondary piston phase control device as an evaluation function, and the piston phase difference caused by the atmospheric turbulence can be obtained, and then the phase modulation signal is formed, which is fed back to the spatial phase modulation device. array to correct for piston phase noise caused by atmospheric turbulence. Compared with the prior art, the one-stage piston phase control device of the present solution has a faster control rate due to the feedback signal obtained from the near field, so as to correct the piston phase difference caused by the amplifier, and the rate of the piston phase difference caused by the atmospheric turbulence is slower. , the spatial phase modulation device array is controlled by the secondary piston phase control device to perform secondary correction of the piston phase difference caused by atmospheric turbulence, which satisfies the accuracy of phase correction on the one hand, and improves the control rate on the other hand. , it will not affect the control rate of the piston phase, so as to meet the requirements of a large number of laser arrays.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can also be obtained according to the structures shown in these drawings without creative efforts.

1 is a schematic block diagram of the structure of a target-in-loop laser coherent array in the prior art;

FIG. 2 is a schematic block diagram of the structure of a target-in-loop laser coherent array for hierarchical piston phase control provided by an embodiment of the present invention.

Description of reference numbers:

Seed laser 201, laser beam splitter 202, phase modulator 203, laser amplifier 204, adaptive laser collimator 205, receiving telescope 206, photodetector 207, tilt control circuit 208, beam splitter 209, spatial phase modulation device 210 , convex lens 211 , aperture diaphragm 212 , primary piston phase control circuit 213 , secondary piston phase control circuit 214 , atmospheric turbulence 215 , and target surface 216 .

The realization, functional characteristics and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relationship between various components under a certain posture (as shown in the accompanying drawings). The relative positional relationship, the movement situation, etc., if the specific posture changes, the directional indication also changes accordingly.

In addition, descriptions such as "first", "second", etc. in the present invention are only for descriptive purposes, and should not be construed as indicating or implying their relative importance or implicitly indicating the number of indicated technical features. Thus, a feature delimited with "first", "second" may expressly or implicitly include at least one of that feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise expressly and specifically defined.

In the present invention, unless otherwise expressly specified and limited, the terms "connected", "fixed" and the like should be understood in a broad sense, for example, "fixed" may be a fixed connection, a detachable connection, or an integrated; It can be a mechanical connection, an electrical connection, a physical connection or a wireless communication connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction between the two elements. unless otherwise expressly qualified. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but must be based on the realization by those of ordinary skill in the art. When the combination of technical solutions is contradictory or cannot be realized, it should be considered that the combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

Example 1

As shown in FIG. 2 , this embodiment provides a piston phase control system, which mainly includes: a seed laser 201 , a laser beam splitter 202 , N phase modulators 203 , N laser amplifiers 204 , and N self-adaptive laser beams. Straight device 205, receiving telescope 206, two photodetectors 207 (the first photodetector connected to the receiving telescope 206 is the first photodetector, and the one connected to the aperture diaphragm 212 is the second photodetector), tilt control circuit 208, beam splitter 209 , N spatial phase modulation devices 210 , a convex lens 211 , a small aperture diaphragm 212 , a first-stage piston phase control circuit 213 and a second-stage piston phase control circuit 214 .

The spatial phase modulation device 210 is used to simulate atmospheric turbulence through the adjustment of the secondary piston phase control circuit 214. The primary piston phase control circuit 213 obtains the evaluation function from the output end of the collimated laser array. In order to improve the accuracy of the phase control, The secondary piston phase control circuit 214 here implements applying a control signal to the primary piston phase control circuit 213 to compensate for the phase difference caused by the spatial phase modulation device 210 simulating atmospheric turbulence.

The seed laser 201 is divided into N laser beams through a laser beam splitter 202 , and each laser beam passes through a phase modulator 203 , a laser amplifier 204 and an adaptive laser collimator 205 in sequence.

The beam splitter 209 is a high-reflection mirror or a low-reflection mirror, and may be a single beam splitter or a beam splitter array composed of multiple beam splitters. After more than 99% of the laser energy passes through the spectroscope 209, it is transmitted through the atmospheric turbulence 215 and reaches the target surface 216; after less than 1% of the laser energy passes through the spectroscope 209, N lasers are incident on N spatial phase modulation devices 210 respectively. . N phase modulators 203, laser amplifiers 204, adaptive laser collimators 205, and spatial phase modulation devices 210 are arrayed to form a corresponding array. The array layout can refer to the shape of a rectangular lattice, a regular polygon lattice or a circular lattice. .

The spatial phase modulation device 210 can be a liquid crystal, an electro-optic crystal, or other active devices, which can generate different optical paths according to different applied signals, and can change the phase of the piston of the outgoing laser light.

The convex lens 211 focuses the laser array passing through the spatial phase modulation device 210 . In other embodiments of the present invention, other optical devices can also be used to realize the convergence of the laser light, for example:

The diameter of the aperture diaphragm 212 is between 1.22λf/D and 2.44λf/D, where is the wavelength of the λ laser, f is the focal length of the convex lens 211, and D is the diameter of the laser array emitted by the adaptive laser collimator 205. Diameter of circumcircle. The aperture stop 212 is placed at the focal position of the convex lens 211, so that the central energy of the far-field light spot of the laser array passes through the aperture. After calculation, it can be seen that when the diameter of the aperture of the aperture diaphragm 212 is between 1.22λf/D and 2.44λf/D, the light intensity of the central spot formed after passing through the aperture diaphragm 212 can be beneficial to the evaluation of the formation after collection. function.

The photodetector 207 (the first detector) is located behind the small hole of the small hole diaphragm 212, and is used to detect the light intensity of the far-field central spot (relative to the target distance seed) after the laser array is focused by the convex lens 211. The laser is much closer and belongs to the near-field light; the light on the target scattering circuit belongs to the far-field light), and sends the electrical signal to the first-stage piston phase control circuit 213; another photodetector 207 (second detector) is located in the receiving telescope. The detection focal plane of 206 is used to detect the scattered light intensity (far-field light) scattered back after the laser array is emitted to the target surface 216 , and send electrical signals to the tilt control circuit 208 and the secondary piston phase control circuit 214 .

The tilt control circuit 208 runs a control algorithm to receive the electrical signal of the photodetector 207 (second detector) behind the telescope 206 as feedback to generate an output signal to control each adaptive laser collimator 205, and to The tilt aberration caused by atmospheric turbulence 215 is corrected.

The first-stage piston phase control circuit 213 runs a control algorithm, uses the electrical signal of the photodetector 207 behind the convex lens 211 as feedback, generates an output phase modulation signal, controls each phase modulator 203, and causes piston phase difference to the fiber amplifier. Real-time correction is performed to maintain a constant piston phase difference at the output end of the adaptive laser collimator 205 for each laser.

The two-stage piston phase control circuit 214 runs a control algorithm, and uses the electrical signal of the photodetector 207 behind the receiving telescope 206 as feedback to generate an output phase modulation signal, and controls each spatial phase modulation device 210 to make the receiving telescope 206 The received scattered light intensity is optimized, and the correction of the piston aberration caused by the atmospheric turbulence 215 is realized.

Compared with the prior art, the technical effect of the present invention:

The target of the hierarchical piston phase control of the present invention is a loop laser coherent array, and two-stage piston phase control is used to effectively correct the piston phase difference caused by the fiber amplifier and atmospheric turbulence. Among them, the first-stage piston phase control circuit 213 obtains the evaluation function from the output end of the laser array to correct the piston phase noise in the laser amplifier. Since there is no need to obtain the evaluation function from the target, it has the advantage of high control rate; the second-stage piston phase control Obtain the evaluation function from the target, use the spatial phase modulation device to simulate the piston phase difference caused by atmospheric turbulence, apply it to the laser array incident on the convex lens 211, and exert an influence on the control signal of the first-stage piston phase control circuit 213, and indirectly realize the Correction for Piston Aberration in Atmospheric Turbulence.

Embodiment 2

Based on the above-mentioned first embodiment, an embodiment of the present invention provides a piston phase control method, which includes the following steps:

S1, the seed laser is emitted after phase modulation, amplification and collimation;

S2, after the outgoing laser array is split, a part of the laser light is transmitted to the target surface through atmospheric turbulence, and the scattered light scattered by the target surface is collected and extracted by the detector to form a first feedback signal. The first feedback signal is input to the target surface. straightener to correct for the tilt difference caused by atmospheric turbulence;

The scattered light is collected by the telescope and output, and then detected by the photodetector to form an electrical signal, and the electrical signal is input to the tilt control circuit 208 to generate a first feedback signal to control the collimator to correct the tilt aberration caused by atmospheric turbulence;

S3, after the outgoing laser array is split, another part of the laser is spatially modulated to simulate atmospheric turbulence, and after focusing, a second feedback signal is formed after detection to control the phase modulator to correct the piston aberration caused by the amplification process;

S4, the first feedback signal is further used to control the spatial phase modulator to correct the piston phase difference caused by the simulated atmospheric turbulence in the spatial phase modulation process.

It is collected by a part of the laser light split on the optical path before passing through atmospheric turbulent scattering, and the atmospheric turbulence is simulated by the spatial phase modulator, instead of collecting the laser light on the scattering circuit after reaching the target after passing through the atmospheric turbulence as the detection light signal. Obtain the evaluation function and use the near-field outgoing laser as the feedback signal. After changing the control parameters such as the phase and tilt of the laser array, the new laser array needs to travel a short distance to reach the collimator, and the laser signal returns to the laser emission position to obtain feedback signal, and finally correct the control parameters according to the change of the feedback signal. Therefore, the single iteration time of the adaptive control is less than the round trip time of the laser between the reflection and the target. The frequency of the phase noise of the piston in the laser amplifier is reduced. When the laser transmission distance is long, the control rate of the piston phase is not affected by it and remains fast, which meets the control rate required by a large number of laser arrays.

The above descriptions are only the preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Under the inventive concept of the present invention, the equivalent structural transformations made by the contents of the description and drawings of the present invention, or the direct/indirect application Other related technical fields are included in the scope of patent protection of the present invention.

Claims (6)

1. A piston phase control system comprises a seed laser, a laser beam splitter, a phase modulator array, a laser amplifier array and an adaptive stress light collimator array which are connected in sequence, wherein emergent laser of each collimator in the adaptive stress light collimator array reaches a target surface after being transmitted through atmospheric turbulence, and on a scattering light path of the target surface, the target scattering light is incident to a first detector after being received by a telescope, and the first detector is connected with each collimator through an inclination control circuit; it is characterized by also comprising:

the spectroscope is arranged on a light path between the emergent laser of each collimator and the atmospheric turbulence and is used for splitting the emergent laser energy of the collimator, one part of the split laser energy is transmitted to a target surface, and the other part of the split laser energy is incident on the spatial phase modulation device array;

the space phase modulation device array is used for changing the phase of a piston emitting laser;

the focusing device is used for focusing the emergent laser which changes the phase of the piston;

the input end of the second detector receives the focused laser, and the output end of the second detector is connected with the phase modulator array through the primary piston phase control device;

and the secondary piston phase control device is connected between the first detector and the space phase modulation device array.

2. The piston phase control system of claim 1 wherein said beam splitter comprises a high or low mirror; the reflectivity of the high reflection mirror is greater than or equal to 99%, or

The low reflection mirror has a transmittance of greater than or equal to 99%.

3. The piston phase control system of claim 1 wherein said beam splitter comprises a single beam splitter or an array of beam splitters, said array of beam splitters optically matching said array of adaptive stress light collimators, and said array of spatial phase modulation devices.

4. The piston phase control system of claim 1 wherein said focusing assembly comprises:

the convex lens is used for focusing the laser array passing through the spatial phase modulation device array;

a small aperture diaphragm; and the small hole is arranged at the focus position of the convex lens and is used for enabling the central energy of the far-field light spot of the laser array to pass through.

5. The piston phase control system of claim 4 wherein said aperture has a diameter of between 1.22 λ f/D and 2.44 λ f/D, where λ laser wavelength, f is the focal length of the convex lens, and D is the diameter of the circumscribed circle of the laser array exiting the adaptive stress optical collimator array.

6. A piston phase control method, comprising the steps of:

the seed laser is emitted after phase modulation, amplification and collimation;

after the outgoing laser array is subjected to light splitting, part of laser is transmitted to a target surface through atmospheric turbulence, and is detected and extracted after being scattered and converged so as to form a first feedback signal, so that a collimator is controlled to correct the inclination phase difference caused by the atmospheric turbulence;

after the outgoing laser array is subjected to light splitting, the other part of laser is subjected to space phase modulation and focusing and then is detected so as to form a second feedback signal for controlling the phase modulator to correct the piston phase difference caused in the amplification process;

the first feedback signal is also used for controlling the spatial phase modulator to correct the piston phase difference caused by simulating atmospheric turbulence in the spatial phase modulation process.

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