Optical path difference real-time measurement and control device and method for fiber laser coherent synthesis system

Abstract

An optical path difference real-time measurement and control device and method of a fiber laser coherent synthesis system, comprising a fiber laser coherent synthesis system and a dynamic optical path difference control module; a phase modulator, a high-speed optical fiber delay line, a wavelength division multiplexer, an amplifier and an optical fiber collimator are arranged on the transmission light path of each sublaser in the fiber laser coherent synthesis system; the high-speed optical fiber delay line is used for real-time compensation of the dynamic optical path difference, the high-speed optical fiber delay line corresponding to each sublaser and the wavelength division multiplexer are connected with the dynamic optical path difference control module, the dynamic optical path difference control module emits probe laser, the end face of the optical fiber collimator corresponding to each sublaser can reflect the probe laser, the probe laser reflected from the end face of the optical fiber collimator corresponding to each sublaser is detected, corresponding optical path calculation is carried out and real-time compensation is carried out. The present application can improve the coherence between each sublaser of the fiber laser coherent synthesis when operating at high output power.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical coherence synthesis, and particularly relates to an optical path difference real-time measurement and control device and method of a fiber laser coherent synthesis system. BACKGROUND

[0002] The output power of a fiber laser is limited by thermal effects, nonlinear effects and mode instability. In order to further improve the output power of the fiber laser, coherent synthesis of multiple fiber lasers is one of the effective methods. In a high-power fiber laser coherent synthesis system, narrow-linewidth lasers are often selected as subunits, and fiber lasers with a wider linewidth are beneficial to increasing the optical power threshold of Brillouin scattering and thus increasing the output of a single fiber laser. However, as the linewidth of a single fiber laser increases, the coherence length decreases, thereby making the coherence between the output lasers of the fiber amplifiers poor or even incoherent.

[0003] In order to ensure that the optical path differences of the output lasers of the fiber amplifiers are within the coherence length, the optical path differences between the fiber amplifiers need to be compensated. The traditional optical path difference compensation method has two steps. First, a picosecond pulse light source is simultaneously injected into each amplifier link, and the approximate optical path difference range is determined by measuring the time at which the output reaches a photodetector, and then coarse compensation is achieved by compensating the passive fiber length. Then, a fiber delay line is used to finely compensate the output laser so that the interference amplitude of each sub-laser is maximized.

[0004] The above-mentioned traditional optical path difference compensation method can achieve static compensation of the optical path differences of a high-power narrow-linewidth fiber laser array. However, when the output power of the fiber laser increases, the optical path in the fiber laser changes in real time due to thermal effects and other factors, which makes the coherence between the sub-beams poor, and further real-time measurement and compensation are needed. SUMMARY

[0005] In view of the technical problems existing in the prior art, the present application provides an optical path difference real-time measurement and control device and method of a fiber laser coherent synthesis system.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows:

[0007] On the one hand, the present application provides an optical path difference real-time measurement and control device of a fiber laser coherent synthesis system, comprising a fiber laser coherent synthesis system and a dynamic optical path difference control module.

[0008] A phase modulator, a high-speed fiber delay line, a wavelength division multiplexer, an amplifier and a fiber collimator are arranged on the transmission optical path of N sub-lasers in the fiber laser coherent synthesis system, wherein N is greater than or equal to 2.

[0009] The high-speed optical fiber delay line is used for real-time compensation of dynamic optical path difference, a dynamic optical path difference control module is connected between the high-speed optical fiber delay line corresponding to each sublaser and the wavelength division multiplexer, the dynamic optical path difference control module issues probe laser, the end face of the optical fiber collimator corresponding to each sublaser can reflect the probe laser, and the corresponding optical path is calculated and compensated in real time by detecting the probe laser reflected from the end face of the optical fiber collimator corresponding to each sublaser.

[0010] Further, the laser coherent synthesis system comprises one seed laser, one first 1xN beam splitter, N phase modulators, N high-speed optical fiber delay lines, N wavelength division multiplexers, N amplifiers, N optical fiber collimators and one closed-loop phase control module.

[0011] The seed laser is used for outputting seed laser with a wavelength of .

[0012] The first 1xN beam splitter is used for splitting the seed laser into N sublasers.

[0013] The N optical fiber collimators are arranged in an array into an optical fiber collimator array and are used for collimating and outputting the combined beams of the sublasers.

[0014] The closed-loop phase control module collects a small amount of power of the collimated and outputted combined beams and inputs the laser into the closed-loop phase control module, and the closed-loop phase control module is used for realizing phase control of the sublasers and coherent synthesis.

[0015] Further, a large-range optical fiber delay line is arranged on the transmission path of each sublaser in the laser coherent synthesis system, and the large-range optical fiber delay line is used for compensating the static optical path difference of the sublasers.

[0016] Further, the dynamic optical path difference control module comprises a probe laser with a wavelength of , a Mach-Zehnder modulator, a second 1xN beam splitter, N three-port optical circulators, N high-speed photodetectors and an optical path controller.

[0017] The probe laser is connected with a Mach-Zehnder modulator in an optical path, and the Mach-Zehnder modulator is connected with a first port of a second 1×N beam splitter in an optical path; an i+1th port of the second 1×N beam splitter is connected with a first port of an i-th three-port optical circulator in an optical path, a second port of the i-th three-port optical circulator is connected with an i-th wavelength division multiplexer in an optical path, and a third port of the i-th three-port optical circulator is connected with an i-th high-speed photodetector in an optical path, i=1, 2, …, N; the laser input from the first port of the three-port optical circulator can only be output from the second port of the three-port optical circulator, and the laser input from the second port of the three-port optical circulator can only be output from the third port of the three-port optical circulator.

[0018] The i-th high-speed photodetector is used for detecting the light intensity of the probe light with a wavelength of returned from the end surface of the fiber collimator on the transmission optical path of the i-th sub-laser and converting the light intensity into an electrical signal; the output end of the i-th high-speed photodetector is electrically connected with an i-th input end of an optical path controller; a first output end of the optical path controller is electrically connected with the Mach-Zehnder modulator for applying modulation, and the Mach-Zehnder modulator is used for amplitude modulation of the probe laser; an i+1th output end of the optical path controller is electrically connected with an i-th high-speed fiber delay line, the optical path controller demodulates the absolute optical path values of each sub-laser in real time and calculates the optical path changes of each sub-laser, so as to obtain the delay increments of each sub-laser, and realize real-time control of the optical path difference of each sub-laser.

[0019] Further, the closed-loop phase control module comprises a sampling mirror, a focusing lens, a photodetector and a phase controller; the laser output by the fiber collimator array is incident on the sampling mirror, a small part of the power of the laser output by the fiber collimator array is focused by the focusing lens and then incident on the photodetector; the photodetector converts the light intensity signal into an electrical signal, the output end of the photodetector is electrically connected with the input end of the phase controller, and each output end of the phase controller is electrically connected with the electrical input end of the phase modulator on the transmission optical path of each sub-laser, and the phase controller is used for compensating the phase error existing in the system to realize the phase consistency of each sub-laser.

[0020] Further, the sampling mirror is a high-reflective mirror, the laser output by the fiber collimator array is incident on the high-reflective mirror, most of the power of the laser is reflected by the high-reflective mirror to the free space, and the rest of the small part of the power of the laser is transmitted by the high-reflective mirror to the focusing lens.

[0021] Further, the sampling mirror is a high-transmissive mirror, the laser output by the fiber collimator array is incident on the high-transmissive mirror, most of the power of the laser is transmitted by the high-transmissive mirror to the free space, and the rest of the small part of the power of the laser is reflected by the high-transmissive mirror to the focusing lens.

[0022] In one aspect, the application provides a method for real-time measurement and control of optical path difference of a fiber laser coherent synthesis system, i.e., the real-time measurement and control of optical path difference of the fiber laser coherent synthesis system is realized based on the optical path difference real-time measurement and control device of any of the above fiber laser coherent synthesis systems.

[0023] Compared with the prior art, the application can produce the following technical effects:

[0024] In view of the situation that, after the output power of the fiber laser coherent synthesis system is increased, the real-time change of the optical path in the fiber laser coherent synthesis system caused by thermal effects and other factors makes the coherence between the sub-beams poor, and further real-time measurement and compensation are needed, the application provides a device and a method for real-time measurement and control of optical path difference of a fiber laser coherent synthesis system, specifically, probe laser is injected into the transmission path of each sub-laser through a full-fiber structure, the end face of the fiber collimator corresponding to each sub-laser can reflect the probe laser, the probe laser reflected from the end face of the fiber collimator corresponding to each sub-laser is detected, the corresponding optical path is calculated and real-time compensation is performed, and the coherence between the sub-beams of the fiber laser coherent synthesis system during high-output power operation is improved. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of the drawings shown.

[0026] Figure 1 Fig. 1 is a structural schematic diagram of the optical path difference real-time measurement and control device of the fiber laser coherent synthesis system provided by an embodiment;

[0027] Figures in the drawings:

[0028] 1, seed laser; 2, preamplifier; 3, first 1xN beam splitter; 4, phase modulator; 5, large range fiber delay line; 6, high-speed fiber delay line; 7, wavelength division multiplexer; 8, amplifier; 9, fiber collimator; 10, sampling mirror; 11, focusing lens; 12, photodetector; 13, phase controller; 14, probe laser; 15, Mach-Zehnder modulator; 16, second 1xN beam splitter; 17, three-port optical circulator; 18, high-speed photodetector; 19, optical path controller. DETAILED DESCRIPTION

[0029] Clearly, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present application.

[0030] In an embodiment, a path difference real-time measurement and control device of a fiber laser coherent synthesis system is provided, comprising a fiber laser coherent synthesis system and a dynamic path difference control module.

[0031] A phase modulator, a high-speed fiber delay line, a wavelength division multiplexer, an amplifier and a fiber collimator are arranged on a transmission path of each of N sub-lasers in the fiber laser coherent synthesis system, wherein N≥2.

[0032] The high-speed fiber delay line is used for real-time compensation of the dynamic path difference, and a dynamic path difference control module is connected between the high-speed fiber delay line corresponding to each sub-laser and the wavelength division multiplexer. The dynamic path difference control module emits probe laser, the end face of the fiber collimator corresponding to each sub-laser can reflect the probe laser, and the probe laser reflected from the end face of the fiber collimator corresponding to each sub-laser is detected to calculate the corresponding path and compensate in real time.

[0033] Reference Figure 1 In an embodiment, a path difference real-time measurement and control device of a fiber laser coherent synthesis system is provided, comprising a fiber laser coherent synthesis system and a dynamic path difference control module. The fiber laser coherent synthesis system comprises a seed laser 1, a pre-amplifier 2, a first 1×N beam splitter 3, N phase modulators 4, N high-speed fiber delay lines 6, N wavelength division multiplexers 7, N amplifiers 8, N fiber collimators 9 and a closed-loop phase control module.

[0034] The seed laser 1 is connected with the input port of the pre-amplifier 2, and the output port of the pre-amplifier 2 is connected with the first port of the first 1×N beam splitter 3.

[0035] The seed laser 1 is used for outputting seed laser with a wavelength of The output wavelength of the seed laser 1 is , which is not generally selected as 1080nm, 1064nm, 1030nm, etc.

[0036] The seed laser 1 is connected with the pre-amplifier 2, and the pre-amplifier 2 is used for power amplification of the seed laser with a wavelength of outputted by the seed laser 1.

[0037] The first 1xN beam splitter 3 has N+1 ports. When the laser is input from the first port of the first 1xN beam splitter 3, the seed laser amplified by the pre-amplifier 2 will be divided into N paths of sub-laser by the first 1xN beam splitter 3, and output from the second port to the N+1 port of the first 1xN beam splitter 3 respectively.

[0038] The output laser i+1 port of the first 1xN beam splitter 3 is connected with the i-th phase modulator 4, i=1, 2, …, N.

[0039] The phase modulator 4 is used to change the piston phase of each path of laser. The i-th phase modulator 4 is connected with the i-th large range fiber delay line 5, the i-th high speed fiber delay line 6, the i-th wavelength division multiplexer 7, and the i-th amplifier 8 in sequence, i=1, 2, …, N.

[0040] The large range fiber delay line 5 is used to compensate the static optical path difference of each path of sub-laser. The high speed fiber delay line 6 is used to compensate the dynamic optical path difference of each path of sub-laser in real time.

[0041] The wavelength division multiplexer 7 is used to combine two beams of light with different wavelengths into one beam, or separate one beam of light according to different wavelength components.

[0042] The amplifier 8 is used to amplify the power of the laser, and the amplifier 8 is a fiber amplifier.

[0043] The corresponding fiber collimator 9 of each path of sub-laser is connected with the corresponding fiber collimator 9 in sequence. The N fiber collimators 9 are arranged in an array to form a fiber collimator array, which is used to collimate and output the combined sub-laser.

[0044] The dynamic optical path difference control module includes a probe laser 14 with a wavelength of 1550 nm, a Mach-Zehnder modulator 15, a second 1xN beam splitter 16, N three-port optical circulators 17, N high speed photodetectors 18, and an optical path controller 19. The second 1xN beam splitter 16 has N+1 input ports. When the laser is input from the first port of the second 1xN beam splitter 16, the laser will be divided into N paths by the second 1xN beam splitter 16, and output from the second port to the N+1 port of the second 1xN beam splitter 16 respectively. The three-port optical circulator 17 has N, and the high speed photodetector 18 has N. The wavelength of the laser for detecting the optical path is 1550 nm. The selection of the wavelength should avoid the absorption and emission peaks of the gain fiber doped particles in the subsequent amplifier, and also ensure that it has a small loss when passing through the laser link. Without loss of generality, the wavelength of 1550 nm can be selected. For sensing wavelengths such as 1330 nm or 1550 nm.

[0045] The probe laser 14 is connected with the Mach-Zehnder modulator 15 in an optical path, the Mach-Zehnder modulator 15 is connected with the first port of the second 1×N beam splitter 16 in an optical path; the i+1th port of the second 1×N beam splitter 16 is connected with the first port of the i th three-port optical circulator 17 in an optical path, the second port of the i th three-port optical circulator 17 is connected with the i th wavelength division multiplexer 7 in an optical path, the third port of the i th three-port optical circulator 17 is connected with the i th high-speed photodetector 18 in an optical path, i = 1, 2, …, N; the laser input from the first port of the three-port optical circulator 17 can only be output from the second port of the three-port optical circulator 17, and the laser input from the second port of the three-port optical circulator 17 can only be output from the third port of the three-port optical circulator 17.

[0046] The i th high-speed photodetector 18 is used for detecting the light intensity of the probe light with a wavelength of returned from the end face of the fiber collimator 9 on the transmission optical path of the i th sub-laser and converting it into an electrical signal; the output end of the i th high-speed photodetector 18 is electrically connected with the i th input end of the optical path controller 19; the first output end of the optical path controller 19 is electrically connected with the Mach-Zehnder modulator 15 for applying modulation, and the Mach-Zehnder modulator 15 is used for amplitude modulation of the probe laser; the i+1th output end of the optical path controller 19 is electrically connected with the i th high-speed fiber delay line 6, the optical path controller 19 demodulates the absolute optical path value of each sub-laser in real time and calculates the optical path change of each sub-laser, thereby obtaining the delay increment of each sub-laser, and realizing real-time control of the optical path difference of each sub-laser.

[0047] The closed-loop phase control module collects a small part of the power of the laser output by the beam combining collimation, and uses the closed-loop phase control module to realize phase control of each sub-laser and then realize coherent synthesis. The closed-loop phase control module comprises a sampling mirror 10, a focusing lens 11, a photodetector 12 and a phase controller 13; the laser output by the beam combining collimation of the fiber collimator array is incident to the sampling mirror 10, a small part of the power of the laser output by the beam combining collimation is collected by the sampling mirror 10, focused by the focusing lens 11 and then incident to the photodetector 12 (preferably, a photodetector with a pinhole); the photodetector 12 converts the light intensity signal into an electrical signal, the output end of the photodetector 12 is electrically connected with the input end of the phase controller 13, and each output end of the phase controller 13 is electrically connected with the electrical input end of the phase modulator 4 on the transmission optical path of each sub-laser, and the phase controller 13 is used for compensating the phase error existing in the system to realize consistent phase of each sub-laser.

[0048] Figure 1In the shown embodiment, the sampling mirror 10 is a high-transmission mirror, the laser output by the fiber collimator array is incident to the high-transmission mirror, and most of the power of the laser is transmitted to the free space through the high-transmission mirror, and the rest of the small power of the laser is reflected to the focusing lens through the high-transmission mirror.

[0049] It can be understood that the sampling mirror 10 can also be a high-reflection mirror, the laser output by the fiber collimator array is incident to the high-reflection mirror, and most of the power of the laser is reflected to the free space through the high-reflection mirror, and the rest of the small power of the laser is transmitted to the focusing lens through the high-reflection mirror.

[0050] One embodiment provides a method for real-time measurement and control of optical path difference of a fiber laser coherent combining system, based on the above-mentioned device for real-time measurement and control of optical path difference of a fiber laser coherent combining system, the optical path difference of each sub-laser light path is realized. Specifically, the following steps are included:

[0051] (i) The optical path controller 19 outputs a control signal to the Mach-Zehnder modulator 15, and the Mach-Zehnder modulator 15 amplitude-modulates the probe laser output by the probe laser 14;

[0052] The intensity of the modulated probe laser is:

[0053] (1)

[0054] In the formula, is the amplitude, is the modulation depth, is the angular frequency of the modulation signal, is the optical frequency, is the time;

[0055] At this time, it is considered that the change of the optical path is mainly caused by the thermal effect in the fiber amplifier, and the change of the optical path in other fibers is ignored.

[0056] (ii) The modulated probe laser is divided into N paths through the second 1×N beam splitter 16, the i-th path probe laser is input into the first port of the i-th three-port optical circulator 17 and then output from the second port of the i-th three-port optical circulator 17, and then enters the i-th sub-laser light path through the i-th wavelength division multiplexer 7. The reflected light reflected back at the end face of the i-th fiber collimator 9 in the i-th sub-laser light path returns to the second port of the i-th three-port optical circulator 17 and is output from the third port of the i-th three-port optical circulator 17, and is collected by the i-th high-speed photodetector 18. The light intensity signal collected by the i-th high-speed photodetector 18 is as follows:

[0057] (2)

[0058] In the formula,​ is the responsivity of the photoelectric detector, is the transmission delay, is the group velocity dispersion coefficient of the probe laser, is the optical path length of the ith sub-laser path.

[0059] (iii) input the light intensity signal collected by the ith high-speed photoelectric detector 18 into the optical path controller 19, the optical path controller 19 performs phase discrimination processing on the modulation signal input into the Mach-Zehnder modulator 15 and the light intensity signal collected by the high-speed photoelectric detector 18, obtains the phase difference, and obtains the optical path delay of the ith sub-laser path based on the phase difference.

[0060] Specifically, the modulation signal input into the Mach-Zehnder modulator 15 and the light intensity signal collected by the ith high-speed photoelectric detector 18 are subjected to phase discrimination processing, and the obtained phase difference is:

[0061] (3)

[0062] Since the phase discriminator output range is 0 to 2π, the phase needs to be unwrapped to obtain:

[0063] (4)

[0064] wherein, is a non-negative integer, is the measured phase value.

[0065] By combining formulas (3) and (4), the optical path delay of the ith sub-laser path can be obtained as:

[0066] (5)

[0067] wherein, .

[0068] By sweeping the modulation frequency, the unwrapped phase measured at different frequencies can be obtained. According to the phase and frequency curve, a straight line with an intercept of N1 and a slope of k can be fitted, and at this time can be expressed as , and then the delay of the ith sub-laser path is estimated according to formula (5).

[0069] (iv) according to the optical path delay of the ith sub-laser path at the current time and the previous time, the corresponding delay increment is calculated, and step (i) is returned to realize real-time measurement and control of the optical path difference of each sub-laser path.

[0070] In this way, the optical path controller records the delay of each sub-laser path and repeatedly measures it.

[0071] The details of the application are as follows.

[0072] The technical features of the above embodiments can be combined in any manner. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described, but it should be understood that any combination of the technical features is within the scope of the present disclosure as long as the combination does not result in contradictions.

[0073] The above embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the scope of the application. It should be pointed out that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these are within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

[0074] The above only describes the preferred embodiments of the present application, and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An optical path difference real-time measurement and control device of a fiber laser coherent combining system, characterized in that, The system comprises a fiber laser coherent synthesis system and a dynamic optical path difference control module. The N-path sub-laser transmission optical paths in the fiber laser coherent synthesis system are each provided with a phase modulator, a high-speed fiber delay line, a wavelength division multiplexer, an amplifier and a fiber collimator, wherein N>=2. The high-speed optical fiber delay line is used for real-time compensation of dynamic optical path difference, a dynamic optical path difference control module is connected between the high-speed optical fiber delay line corresponding to each sub-laser and the wavelength division multiplexer, the dynamic optical path difference control module issues a detection laser, the end face of the fiber collimator corresponding to each sub-laser can reflect the detection laser, the detection laser reflected from the end face of the fiber collimator corresponding to each sub-laser is detected, corresponding optical path calculation is performed and real-time compensation is performed, wherein the dynamic optical path difference control module comprises a detection laser with a wavelength of a Mach-Zehnder modulator, a second 1×N beam splitter, N three-port optical circulators, N high-speed photodetectors and an optical path controller, wherein the second 1×N beam splitter has N+1 input ports, when laser is input from the first port of the second 1×N beam splitter, the laser will be divided into N paths by the second 1×N beam splitter and output from the second port to the N+1 port of the second 1×N beam splitter respectively; the three-port optical circulators are N in number, and the high-speed photodetectors are N in number; the detection laser is connected with the Mach-Zehnder modulator in an optical path, the Mach-Zehnder modulator is connected with the first port of the second 1×N beam splitter in an optical path; the i+1 port of the second 1×N beam splitter is connected with the first port of the i three-port optical circulator in an optical path, the second port of the i three-port optical circulator is connected with the i wavelength division multiplexer in an optical path, the third port of the i three-port optical circulator is connected with the i high-speed photodetector in an optical path, i=1, 2, …, N. The laser input from the first port of the three-port optical circulator can only be output from the second port of the three-port optical circulator, and the laser input from the second port of the three-port optical circulator can only be output from the third port of the three-port optical circulator; the i-th high-speed photodetector is used for detecting the light intensity of the probe light with a wavelength of returned from the fiber collimator end face on the transmission light path of the i-th sub-laser and converting it into an electrical signal; the output end of the i-th high-speed photodetector is electrically connected with the i-th input end of the optical path controller; the first output end of the optical path controller is electrically connected with the Mach-Zehnder modulator for applying modulation, and the Mach-Zehnder modulator is used for amplitude modulation of the probe laser. An i+1 output end of the optical path controller is electrically connected with an i high-speed fiber delay line, the optical path controller demodulates absolute optical path values of each sub-laser in real time and calculates optical path changes of each sub-laser, thereby obtaining delay increments of each sub-laser, and realizing real-time control of optical path differences of each sub-laser.

2. The optical path difference real-time measurement and control device of the fiber laser coherent synthesis system according to claim 1, characterized in that, The laser coherent synthesis system comprises one seed laser, one first 1xN beam splitter, N phase modulators, N high-speed fiber delay lines, N wavelength division multiplexers, N amplifiers, N fiber collimators and one closed-loop phase control module. The seed laser is configured to output a seed laser having a wavelength of ​ The first 1xN beam splitter is used for splitting the seed laser into N sub-lasers. The N fiber collimators are arranged in an array into a fiber collimator array, and are used for collimating and outputting the sub-lasers. The closed-loop phase control module collects a small amount of power of the collimated and outputted laser, and inputs the laser into the closed-loop phase control module, and uses the closed-loop phase control module to realize phase control of each sub-laser and coherent synthesis.

3. The optical path difference real-time measuring and controlling device of the fiber laser coherent synthesis system according to claim 1 or 2, characterized in that, The N sub-laser transmission optical paths in the laser coherent synthesis system are each provided with a large-range fiber delay line, and the large-range fiber delay line is used for compensating static optical path differences of each sub-laser.

4. The optical path difference real-time measurement and control device of the fiber laser coherent synthesis system according to claim 2, characterized in that, The closed-loop phase control module comprises a sampling mirror, a focusing lens, a photoelectric detector and a phase controller; the collimated and outputted laser of the fiber collimator array is incident to the sampling mirror, a small amount of power of the collimated and outputted laser is focused by the focusing lens and then is incident to the photoelectric detector; the photoelectric detector converts the light intensity signal into an electric signal, an output end of the photoelectric detector is electrically connected with an input end of the phase controller, each output end of the phase controller is electrically connected with an electric input end of the phase modulator on the transmission optical path of each sub-laser, and the phase controller is used for compensating phase errors existing in the system and realizing phase consistency of each sub-laser.

5. The optical path difference real-time measurement and control device of the fiber laser coherent synthesis system according to claim 4, characterized in that, The sampling mirror is a high-reflectivity mirror, the collimated and outputted laser of the fiber collimator array is incident to the high-reflectivity mirror, a large amount of power of the laser is reflected to the free space by the high-reflectivity mirror, and the rest small amount of power of the laser is transmitted to the focusing lens by the high-reflectivity mirror.

6. The optical path difference real-time measurement and control device of the fiber laser coherent synthesis system according to claim 4, characterized in that, The sampling mirror is a high-transmittance mirror, the collimated and outputted laser of the fiber collimator array is incident to the high-transmittance mirror, a large amount of power of the laser is transmitted to the free space by the high-transmittance mirror, and the rest small amount of power of the laser is reflected to the focusing lens by the high-transmittance mirror.

7. An optical path difference real-time measurement and control method of a fiber laser coherent combining system, characterized in that, The optical path difference real-time measurement and control device based on the fiber laser coherent synthesis system of claim 1 realizes optical path difference real-time measurement and control of the fiber laser coherent synthesis system.

8. The method of claim 7, wherein the method further comprises: determining the optical path difference between the two optical paths based on the phase difference between the two optical paths. The laser coherent synthesis system comprises one seed laser, one first 1xN beam splitter, N phase modulators, N high-speed fiber delay lines, N wavelength division multiplexers, N amplifiers, N fiber collimators and one closed-loop phase control module. The seed laser is configured to output a seed laser having a wavelength of about 1550 nm. The first 1xN beam splitter is used for splitting the seed laser into N sub-lasers. The N fiber collimators are arranged in an array into a fiber collimator array for collimating and outputting each sublaser beam; The closed-loop phase control module collects a small part of the power of the collimated output laser beam, and uses the closed-loop phase control module to realize phase control of each sublaser beam and coherent combination.

9. The method of claim 8, wherein the method further comprises: determining the optical path difference between the two optical paths based on the phase difference between the two optical paths. A large-range fiber delay line is arranged on the transmission path of each of the N sublaser beams in the laser coherent combination system, and the large-range fiber delay line is used to compensate for the static optical path difference of each sublaser beam.

10. The method of claim 7, wherein the method further comprises: determining the optical path difference between the two optical paths of the two optical fibers; and adjusting the phase of the light source to compensate for the optical path difference. The method comprises the following steps: (1) the optical path controller outputs a control signal to the Mach-Zehnder modulator, and the Mach-Zehnder modulator amplitude-modulates the probe laser output by the probe laser; (2) the modulated probe laser is divided into N paths through the second 1×N beam splitter, the ith probe laser is input into the first port of the ith three-port optical circulator and then output from the second port of the ith three-port optical circulator, and then enters the ith sublaser path through the ith wavelength division multiplexer, the reflected light reflected back from the end face of the ith fiber collimator in the ith sublaser path returns to the second port of the ith three-port optical circulator and is output from the third port of the ith three-port optical circulator, and then is collected by the ith high-speed photodetector; (3) the light intensity signal collected by the ith high-speed photodetector is input into the optical path controller, the optical path controller performs phase discrimination on the modulation signal input into the Mach-Zehnder modulator and the light intensity signal collected by the high-speed photodetector, obtains a phase difference, and obtains the optical path delay of the ith sublaser path based on the phase difference; (4) according to the optical path delay of the ith sublaser path at the current time and the previous time, a corresponding delay increment is calculated, and the step (1) is returned, so as to realize real-time measurement and control of the optical path difference of each sublaser path.

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