Wavelength adaptive feedback control system based on spectral beam combining

Abstract

A wavelength adaptive feedback control system based on spectral beam combining includes: N seed sources of different wavelengths, N fiber amplifier arrays, N fiber end caps, a focusing system, a beam combining diffraction grating, a sampling reflector, a plane reflector, a first dispersion diffraction grating, a second dispersion diffraction grating, an imaging lens, a linear array CMOS image sensor, and a data processing system. The dual grating system of the present invention implements the reverse dispersion of the combined beam through the dual grating, realizes real-time high-precision wavelength detection and online wavelength adaptive feedback, makes the wavelength work at the system design wavelength, solves the problem of pointing jitter and beam quality degradation caused by wavelength drift, and realizes high brightness output.

Description

Technical Field

[0001] The invention mainly relates to the field of optical fiber laser technology, in particular to a wavelength adaptive feedback control system based on spectral beam combining. Background Art

[0002] Fiber lasers have broad application prospects in industrial processing, national defense, scientific research, etc. due to their high efficiency, good beam quality, and convenient thermal management. With the development of technology, higher power and higher beam quality laser beams are needed. However, due to factors such as optical damage, thermal effects, and nonlinear effects, the output power of a single optical fiber is limited. The spectrum combining technology based on fiber lasers can achieve high beam quality common aperture beam output, which has great application potential.

[0003] At present, the commonly used spectral beam combining method is to make sub-beams of different wavelengths incident on the diffraction grating at a suitable angle through a reflector, so that they are emitted at the same angle to achieve high-power common aperture output of multiple lasers. In order to achieve high beam quality output in the spectral beam combining system, it is necessary that the wavelength of each laser beam is stable and does not drift over time, so that the diffraction angles of all diffracted beams are the same. However, in the actual operation of the system, the seed light has wavelength drift due to environmental disturbances and other problems; the key components of the spectral beam combining system, such as the fiber end cap and reflector, will also produce slight deformations due to environmental mechanical vibrations, thermal distortion, etc. These factors will cause the sub-beam pointing to shift, and then cause the output beam quality and pointing stability of the combined light to decrease. Through adaptive feedback control of the wavelength of the sub-beam, the output beam pointing of the sub-beam after diffraction by the beam combining diffraction grating can be compensated. Summary of the invention

[0004] In view of the problems of combined beam quality degradation and pointing jitter caused by seed wavelength drift and environmental disturbance in existing fiber laser beam combining systems, the present invention proposes a wavelength adaptive feedback control system based on spectral beam combining. The system deconstructs, detects and feedback controls the wavelength of the combined beam through a double grating dispersion system to achieve high-quality combined beam output.

[0005] The technical solution of the present invention is as follows:

[0006] A wavelength adaptive feedback control system based on spectral beam combining, characterized in that it includes: N seed sources of different wavelengths, N fiber amplifiers, N fiber end caps, a focusing system, a beam combining diffraction grating, a sampling reflector, a plane reflector, a first dispersion diffraction grating, a second dispersion diffraction grating, an imaging lens, a linear array CMOS image sensor, and a data processing system. The positional relationship of the above elements is as follows: the seed source, fiber amplifier, and fiber end cap are sequentially connected in series and arranged into a high-power fiber amplifier array in N rows and columns according to wavelength, and converge at different angles onto the beam combining diffraction grating after passing through the focusing system. The common aperture laser formed by beam combining is divided into transmission and reflection outputs through the sampling reflector, and a certain proportion of weak sampling light is reflected and output at 45 degrees;

[0007] The reflected sampling light is reflected at 45° by the plane reflector, enters a double grating system composed of a first dispersion diffraction grating and a second dispersion diffraction grating, outputs N sub-beams in parallel, and after being converged by the imaging lens, enters the linear array CMOS image sensor and is input into the data processing system. The data processing system locates the seed source that generates the drift Δλ by comparing the position list of each wavelength after the drift with the position list of the design wavelength. The data processing system assigns a value of -Δλ to the wavelength of the corresponding seed source, realizes online feedback adjustment, and corrects the wavelength of the sub-beam with the drifted wavelength. The combined light is output with a common aperture, wherein N is a positive integer greater than 3.

[0008] The wavelength range of the seed sources with different wavelengths is 1040nm-1090nm, and the line width is tens of GHz.

[0009] The beam combining diffraction grating, the first dispersion diffraction grating and the second dispersion diffraction grating are all polarization-independent multilayer dielectric reflective diffraction gratings, the line density of the beam combining diffraction grating, the first dispersion diffraction grating and the second dispersion diffraction grating is 960 lines per millimeter, and the first dispersion diffraction grating and the second dispersion diffraction grating are placed in parallel.

[0010] The focusing system can be selected according to the specific embodiment as a transmission type or a reflection type, a coaxial or off-axis system, and the operating wavelength covers the beam combining band.

[0011] The front surface of the sampling plane mirror is coated with a high transmittance film with a laser transmittance of 99.9%, and the rear surface is coated with an anti-reflection film. The front surface of the plane reflector is coated with a high reflectance film with a laser reflectivity greater than 99.9%, and the rear surface is coated with an anti-reflection film. The working wavelength range of the two plane mirrors covers the beam combining band.

[0012] Compared with the prior art, the advantages of the present invention are:

[0013] The present invention is based on a spectral beam combining wavelength adaptive feedback control system. The combined light is dispersed onto a linear array CMOS image sensor through a double grating. The initial wavelength position and the combined wavelength position difference are determined by a data processing system, and the position difference is used to control the wavelengths of all seed lights, thereby achieving real-time wavelength tuning. The double grating system of the present invention implements inverse dispersion of the combined light through a double grating, thereby achieving real-time wavelength high-precision detection and online wavelength adaptive feedback, making the wavelength work at the system design wavelength, solving the problems of pointing jitter and beam quality degradation caused by wavelength drift, and achieving high-brightness output. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the wavelength adaptive feedback control system based on spectral beam combining of the present invention. DETAILED DESCRIPTION

[0015] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. The embodiments are only used to explain the present invention and should not be used to limit the protection scope of the present invention.

[0016] Please refer to Figure 1 , Figure 1 The schematic diagram of the principle of the wavelength adaptive feedback control system based on spectral beam combining of the present invention is shown in the figure. As can be seen from the figure, the wavelength adaptive feedback control system based on spectral beam combining of the present invention includes N seed sources 101 of different wavelengths, N fiber amplifiers 102, N fiber end caps 103, a focusing system 104, a beam combining diffraction grating 105, a sampling reflector 106, a plane reflector 107, a first dispersion diffraction grating 108, a second dispersion diffraction grating 109, an imaging lens 110, a linear array CMOS image sensor 111, and a data processing system 112. After the N seed sources 101 of different wavelengths pass through the N fiber amplifiers 102 and the N fiber end caps 103, they are converged to the beam combining diffraction grating 105 at different angles through the focusing system 104. The common aperture laser formed by beam combining is divided into transmission and reflection outputs through the sampling reflector 106. The main power is transmitted and output, and a certain proportion of weak sampling light is reflected and output at 45°.

[0017] The reflected sampling light is reflected at 45° by the plane reflector, enters a double grating system composed of a first dispersion diffraction grating and a second dispersion diffraction grating, outputs N sub-beams in parallel, and after being converged by the imaging lens, enters the linear array CMOS image sensor and is input into the data processing system. The data processing system locates the seed source that generates the drift Δλ by comparing the position list of each wavelength after the drift with the position list of the design wavelength. The data processing system assigns a value of -Δλ to the wavelength of the corresponding seed source, realizes online feedback adjustment, and corrects the wavelength of the sub-beam with the drifted wavelength. The combined light is output with a common aperture, wherein N is a positive integer greater than 3.

[0018] Example

[0019] The following is an example of combining a four-way fiber amplifier. The wavelengths of the four seed sources 1 are 1060nm, 1068nm, 1072nm, and 1080nm, respectively. First, the beam combining diffraction grating 105 is placed at the Littrow angle of the 1070nm wavelength laser. According to the grating equation 2dsinθ=mλ, it can be concluded that for a wavelength of 1070nm, the diffraction grating with a line density of 960 lines / mm has an incident angle of 30.9°. After the sub-beam is shaped by the fiber end cap 103, the divergence angle is 0.001NA (1mrad). The focal length of the focusing system 104 is 10 meters, so the diameter of the combined beam is 20mm. The first dispersion diffraction grating 108 and the second dispersion diffraction grating 109 are also placed in parallel at 30.9°, with a spacing of L. The spacing L satisfies the formula Assume x = 5 mm, λ n =1072nm,λ n+1 =1068nm,α=30.9°,cos 2 (β n+1 )=0.738, then L=1.120m.

[0020] The focal length of the imaging lens 110 is 75 mm, and the pixel size of the linear array CMOS image sensor 111 is 7.4 μm×7.4 μm. In the initial state of the system, the position list of the design wavelengths of each seed source is first obtained through the linear array CMOS image sensor 111. When the central wavelength of a certain sub-source drifts, assuming that the drift amount is Δλ=0.1 nm, the image on the linear array CMOS image sensor 111 through the imaging lens 110 has a lateral shift of Δx=8.4 μm, which exceeds the single pixel size (7.4 μm) and can be recognized by the linear array CMOS image sensor 111. The data processing system 112 can locate the seed source that produces the drift by comparing the position list of each wavelength after the drift with the position list of the design wavelength. The data processing system 112 assigns -Δλ to the wavelength of the corresponding seed source to achieve online feedback adjustment, and finally achieves the common aperture output of the synthetic beam.

[0021] The present invention is based on a spectral beam combining wavelength adaptive feedback control system. The combined light is dispersed onto a linear array CMOS image sensor through a double grating. The data processing system is used to determine the initial wavelength position and the combined wavelength position difference, and the position difference is used to control the wavelengths of all seed lights. Real-time wavelength tuning can be achieved, eliminating the problem of combined light beam quality degradation and pointing jitter caused by seed source wavelength drift, thermal distortion or mechanical vibration of components in the system.

[0022] The above description is only a preferred embodiment of the present invention, and its description is relatively specific and detailed, but it cannot be used as a limitation on the scope of implementation of the present invention. For those skilled in the art, several modifications and modifications can be made without departing from the spirit and scope of the present invention, so the protection scope of the present invention shall be based on the scope defined by the claims.

Claims

1. A wavelength adaptive feedback control system based on spectral beam combining, comprising: N seed sources (101) of different wavelengths, N optical fiber amplifiers (102), N optical fiber end caps (103), a focusing system (104), a beam combining diffraction grating (105), a sampling reflector (106), and a plane reflector (107), characterized in that it also includes a first dispersion diffraction grating (108), a second dispersion diffraction grating (109), an imaging lens (110), a linear array CMOS image sensor (111), and a data processing system (112); The seed source (101), the optical fiber amplifier (102) and the optical fiber end cap (103) are sequentially connected in series and arranged according to wavelength to form a high-power optical fiber amplifier array with N rows and one column. After passing through the focusing system (104), they converge at different angles onto the diffraction grating (105) for beam combination. The common aperture laser beam formed by beam combination is divided into transmission output and reflection output through the sampling reflector (106): the main optical power is transmitted and a certain proportion of weak sampling light is reflected at 45° for output. The reflected sampling light is reflected at 45 degrees by the plane reflector (107) and enters a double grating system composed of a first dispersion diffraction grating (108) and a second dispersion diffraction grating (109), and outputs N sub-beams in parallel. After being converged by the imaging lens (110), the light enters the linear array CMOS image sensor (111) and is input into the data processing system (112). The data processing system (112) locates the seed source that generates the drift Δλ by comparing the position list of each wavelength after the drift with the position list of the design wavelength. The data processing system (112) assigns a value of -Δλ to the wavelength of the corresponding seed source (101), realizes online feedback adjustment, and corrects the wavelength of the sub-beam with the drifted wavelength. The combined light is output with a common aperture, wherein N is a positive integer greater than 3.

2. The wavelength adaptive feedback control system based on spectral beam combining according to claim 1 is characterized in that: The spacing L between the first dispersion diffraction grating (108) and the second dispersion diffraction grating (109) satisfies the following formula: In the formula, λ n and λ n+1 are the wavelengths of two seed sources of adjacent wavelengths, α is the incident angle of all seed sources incident on the first dispersion diffraction grating (108), β n+1 The wavelength is λ n+1 The seed source is the diffraction angle of the first dispersion diffraction grating (108); d is the line density of the first dispersion diffraction grating (108), which is the same as the line density of the second dispersion diffraction grating (109); and x is the spacing between the optical fiber end caps (103).

3. The wavelength adaptive feedback control system based on spectral beam combining according to claim 1 or 2, characterized in that The wavelength range of the seed sources (101) with different wavelengths is 1040nm-1090nm, and the line width is tens of GHz.

4. The wavelength adaptive feedback control system based on spectral beam combining according to claim 1 or 2, characterized in that The beam combining diffraction grating (105), the first dispersion diffraction grating (108) and the second dispersion diffraction grating (109) are all polarization-independent multilayer dielectric reflection diffraction gratings, and the line density of the beam combining diffraction grating (105), the first dispersion diffraction grating (108) and the second dispersion diffraction grating (109) is 960 lines per millimeter, and the first dispersion diffraction grating (108) and the second dispersion diffraction grating (109) are placed in parallel.

5. The wavelength adaptive feedback control system based on spectral beam combining according to claim 1 or 2, characterized in that The focusing system (104) is of transmission type or reflection type, and is a coaxial or off-axis system, and its operating wavelength covers the beam combining band.

6. The wavelength adaptive feedback control system based on spectral beam combining according to claim 1 or 2, characterized in that The front surface of the sampling reflector (106) is coated with a high-transmittance film with a laser transmittance of 99.9%, and the rear surface is coated with an anti-reflection film. The front surface of the plane reflector (107) is coated with a high-reflectivity film with a laser reflectance greater than 99.9%, and the rear surface is coated with an anti-reflection film. The operating wavelength range of the sampling reflector (106) and the plane reflector (107) covers the beam combining band.

Images