Multi-wavelength self-selecting spectral synthesis system based on superluminescent source

Abstract

A kind of multi-channel wavelength self-selection spectrum synthesis system based on superfluorescent source.The superfluorescent source is divided into N paths by beam splitter as the seed light of N synthesis arms, and converges to the diffraction grating with corresponding angle after passing through focusing system. For each individual synthesis arm, only the light of specific wavelength corresponding to its end cap position can return to the original path after being reflected by 0° plane mirror, recouple into each synthesis arm, re-inject into the fiber main amplifier after pre-amplifier, and realize wavelength self-selection in the main amplifier through gain competition process. The present application has the advantages of wavelength self-selection, simple and compact structure, strong expansion of synthesis channel number, etc. The superfluorescent source is both the seed source and can protect the fiber laser system from self-oscillation damage and improve safety when the system is disturbed by environment and loses feedback light. The wavelength of synthesized light is selected by the system itself, which can effectively overcome the phenomenon of synthesized beam pointing drift caused by seed wavelength drift, end cap mechanical jitter and other factors.

Description

Technical Field

[0001] This invention mainly relates to the field of fiber laser spectral synthesis, and in particular to a fiber laser spectral synthesis system suitable for high power and high brightness, and capable of wavelength self-selection. Background Technology

[0002] Fiber lasers possess advantages such as compact structure, high beam quality, high conversion efficiency, and convenient thermal management. Currently, the output power of single-fiber lasers has exceeded 20 kilowatts. However, further increases in the output power of single-fiber lasers are limited by factors such as the nonlinear effects of the medium, fiber end-face damage, and mode instability. Therefore, combining multiple laser beams through coherent or incoherent methods is an effective means to extend their power. Spectral combining is an incoherent combining technique that does not require the phase of the sub-beams, can achieve common-aperture combining, and can achieve near-diffraction-limited beam quality, making it a good choice for achieving high-power, high-brightness output in fiber lasers. Spectral combining is the inverse process of dispersion, using dispersive elements to project sub-beams of different wavelengths incident at different angles out at the same angle. Depending on the dispersive elements used, it can be divided into combining techniques based on prisms, dichroic plates, volume Bragg gratings, and diffraction gratings. The spectral synthesis scheme using multilayer dielectric reflective diffraction gratings has excellent characteristics such as strong dispersion capability, high efficiency, and high damage threshold, and has become the mainstream scheme in spectral synthesis technology.

[0003] The spectral synthesis technique based on multilayer dielectric reflective diffraction gratings has the following bottleneck problems:

[0004] (1) Each sub-beam of the spectral synthesis system requires a specific wavelength. Wavelength deviation will affect the consistency of the synthesized light direction. Therefore, the wavelength of each sub-beam needs to be precisely adjusted, which reduces the reliability and stability of the system to some extent.

[0005] (2) During the actual operation of the system, key components such as fiber end caps and reflectors are affected by environmental mechanical vibration and thermal distortion, which can cause the sub-beam pointing to deviate. This requires online wavelength adjustment for pointing compensation, which further reduces the stability of the system.

[0006] (3) For spectral synthesis systems with external cavity oscillation structures, the self-organization threshold is high. In the initial stage of free operation, or when the space optical system is disturbed by the environment and the system loses feedback light, the amplifier is prone to self-excited oscillation, causing irreversible optical damage.

[0007] The above factors can affect the efficiency and quality of the synthesized beam of the spectral synthesis system, and there are potential safety risks associated with the spectral synthesis system. Therefore, there is an urgent need to develop a highly reliable spectral synthesis system with autonomous online adjustment of sub-beam wavelengths. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a low-cost, compact, highly scalable array system with wavelengths that can be automatically selected by the system, thereby improving the environmental stability and safety of the spectral synthesis system.

[0009] The technical solution of the present invention is as follows:

[0010] A multi-wavelength self-selective spectral synthesis system based on a superfluorescent source includes: a superfluorescent source, a 1xN beam splitter, N synthesis arms, a multilayer dielectric reflective diffraction grating, a focusing system, a 45° plane mirror, a pinhole aperture, and a 0° plane mirror. Each synthesis arm includes a 2x1 beam combiner, a fiber main amplifier, a fiber preamplifier, a circulator, and a fiber tail output device. The circulator includes ports ①②③. The superfluorescent source is split into N paths by the beam splitter as seed light for synthesis. After amplification, the seed light enters through port ① of the circulator and exits through port ②, then outputs spatial light through the fiber tail output device. The N output lights are sequentially arranged parallel to the dispersion surface of the grating in space. The N output lights are emitted in parallel and converge at different angles after passing through the focusing system, achieving common-aperture synthesis output. Due to the dispersion effect of the grating, the diffracted light of each freely oscillating laser beam will diverge within the dispersion plane after passing through the grating. The main power of the synthesized light is reflected by the 45° mirror as the output beam, and a small amount of transmitted light is incident on the 0° mirror as feedback light. According to Fermat's principle, for each individual synthesizing arm, only light of a specific wavelength can be reflected by the 0° plane mirror and return along the original path. After secondary diffraction by the grating, it is recoupled into each synthesizing arm, which is called the backfeedback light. The backfeedback light enters from port ② of the circulator and exits from port ③. After passing through the first-stage fiber preamplifier, it is re-injected into the fiber main amplifier along with the seed light through a 2x1 combiner. In the fiber main amplifier, the feedback light amplified by the fiber preamplifier competes for gain with the superfluorescent source, selecting the mode with the lowest loss to start oscillation, thus realizing wavelength self-selection for each synthesizing arm. The linewidth of the mode that oscillates after system screening is jointly determined by the aperture diameter, the focal length of the focusing system, and the numerical aperture of the fiber optic output device. This linewidth can be designed and adjusted by the user to meet the requirements of near-diffraction-limited output with high beam quality. When the synthesized sub-beam drifts due to thermal distortion or mechanical vibration of components in the system, resulting in a decrease in the synthesizing effect, the system can automatically tune the selected wavelength and achieve error cancellation through adaptive feedback.

[0011] The superfluorescent source has a flat spectral line shape in the synthesis band and a power stability of ≤2%.

[0012] The 1xN beam splitter operates in wavelengths that cover the laser gain band, with a splitting ratio of 1 / N, and the input light is uniformly divided into N output beams.

[0013] The fiber optic preamplifier and fiber optic main amplifier can be either monopole amplifiers or multi-stage amplifiers;

[0014] The focusing system can be selected as a transmission or reflection type, a coaxial or off-axis system, depending on the specific embodiment, and the operating wavelength covers the laser gain band;

[0015] The isolation between port ② and port ① of the circulator is ≥50dB, and the operating bandwidth covers the laser gain band;

[0016] The 45° plane mirror reflects wavelengths that cover the laser gain band. It is coated with a high-reflectivity film on the front and an anti-reflection film on the back. The reflectivity and transmittance can be designed according to different specific embodiments.

[0017] The 0° plane mirror reflects wavelengths that cover the laser gain band. It is coated with a high-reflectivity film on the front and an anti-reflection film on the back. The reflectivity and transmittance can be designed according to different specific embodiments.

[0018] The pinhole aperture is coaxial with the composite beam, and its diameter is smaller than that of the composite beam.

[0019] Compared with the prior art, the advantages of the present invention are as follows:

[0020] 1. The all-fiber multi-wavelength self-selective spectral synthesis system based on superfluorescent source of the present invention uses superfluorescent source as self-organizing seed source for each channel, which can avoid amplifier self-excitation oscillation when operating at high power; compared with the traditional external cavity oscillator spectral synthesis system, it greatly reduces its self-organization threshold and has higher safety.

[0021] 2. The all-fiber multi-wavelength self-selective spectral synthesis system based on superfluorescence source of the present invention has the synthesis wavelength of each channel automatically selected by the system without human intervention or adjustment; the system has a built-in feedback loop, which can realize real-time wavelength tuning, eliminate the problem of reduced synthesis effect caused by thermal distortion or mechanical vibration of components in the system, and has high stability.

[0022] 3. The all-fiber multi-wavelength self-selective spectral synthesis system based on a superfluorescent source of the present invention can adjust the linewidth of each selected oscillation mode by changing the size of the pinhole aperture, the focal length of the focusing system, and the numerical aperture of the fiber tail output device; the center wavelength interval of each synthesis arm can be changed by changing the spacing between adjacent fiber tail output devices, providing sufficient space for design and use to meet the requirements of grating spectral synthesis for the linewidth and beam quality of each beam, resulting in good beam quality and good temporal stability of the synthesized beam.

[0023] 4. The all-fiber multi-wavelength self-selective spectral synthesis system based on superfluorescent source of the present invention has a focusing system that can be freely designed by the designer as a transmission or reflection type, a coaxial or off-axis system. It has a simple and compact structure, strong expandability of the number of synthesis paths, is easy to equip and debug, and has a wide range of applications. Users can freely select the number of synthesis paths and beam quality according to their needs. Attached Figure Description

[0024] Figure 1 This is a schematic diagram illustrating the principle of one embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram illustrating the principle of the coaxial transmission focusing system used in an embodiment of the present invention;

[0026] Figure label:

[0027] 1 Fiber laser superfluorescence source; 2 1×N beam splitter; 3 combining arm; 4 2×1 beam combiner; 5 fiber main amplifier; 6 circulator; 7 fiber end cap; 8 focusing system; 9 multilayer dielectric reflective diffraction grating; 10 45° plane mirror; 11 pinhole aperture; 12 0° plane mirror; 13 fiber preamplifier. Detailed Implementation

[0028] The present invention will be further described below with reference to embodiments and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0029] Please refer to Figure 1 , Figure 1 This is a schematic diagram of an embodiment of the all-fiber multi-wavelength self-selective spectral synthesis system based on a superfluorescent source according to the present invention. As shown in the figure, the present invention includes a superfluorescent source 1, a 1xN beam splitter 2, a synthesizing arm 3, an off-axis mirror focusing system 8, a multilayer dielectric reflective diffraction grating 9, a 45° plane mirror 10, a pinhole aperture 11, and a 0° plane mirror 12; wherein each synthesizing arm includes a 2x1 beam combiner 4, a fiber main amplifier 5, a circulator 6, a fiber output cap 7, and a fiber preamplifier 13.

[0030] The superfluorescent source 1 is split into N beams of the same power and spectrum by a 1×N beam splitter, and each beam is connected to a N combining arm 3. In the combining arm 3, the incident light is input through one end of a 2×1 beam combiner 4, enters through port ① of the circulator 6 after passing through the fiber main amplifier 5, and outputs through port ②. The N fiber end caps 7 are arranged in parallel in space and are parallel to the dispersion plane of the multilayer dielectric reflective diffraction grating 9. The spacing between the fiber end caps 7 can be ≤2mm. The fiber end caps 7 should be located within the front focal plane of the off-axis mirror focusing system 8. The N seed beams emitted are collimated and emitted into the multilayer dielectric reflective diffraction grating 9 after passing through the off-axis mirror focusing system 8. The multilayer dielectric reflective diffraction grating 9 should be located within the back focal plane of the off-axis reflective self-focusing imaging system 8. Due to the dispersion effect of the multilayer dielectric reflective diffraction grating 9, the emitted light will be dispersed within the dispersion plane and spread out in space. The degree of spread out is determined by the angular dispersion rate of the multilayer dielectric reflective diffraction grating 9, which is 1 rad / μm in this embodiment. The main power of the emitted light is reflected by the 45° plane mirror 10 (reflectivity 80%) and used as the output beam of the synthesis system. A small amount of transmitted light (20%) is filtered by the pinhole aperture 11 to obtain a narrowband spectrum, and then reflected by the 0° plane mirror 12 (reflectivity ≥99.9%) as the system feedback signal.

[0031] After being diffracted by the multilayer dielectric reflective diffraction grating 9, the feedback light is reflected at the Littrow angle and recoupled into the fiber end cap 7 after passing through the off-axis mirror focusing system. The coupling efficiency between the feedback light and the fiber end cap 7 can be adjusted by adjusting the deflection angle of the 0° mirror 11. The feedback light coupled into the fiber end cap 7 enters through port ② of the circulator 6 and exits through port ③. After being amplified by the fiber preamplifier 13, it is injected into the fiber amplifier 5 together with the superfluorescent source.

[0032] In specific application examples, to ensure that the feedback light wins the gain competition in fiber amplifier 5 and thus obtains a stable oscillating beam output, the selection of the reflectivity R of the 45° plane mirror, the amplification factor β1 of fiber amplifier 5, and the amplification factor β2 of preamplifier 13 should meet the following criteria:

[0033] β1·(1-A) 2 ·B 2 ·C 2 ·Dβ2·(1-R) 2 >1

[0034] Where A is the insertion loss of the circulator 6, B is the coupling efficiency of the fiber end cap 7, C is the diffraction efficiency of the multilayer dielectric reflective diffraction grating 9, and D is the percentage of feedback optical power. Let A = 20%, B = 98%, C = 97%, and D = 10%. -3 If β1 = 50 and β2 = 1000, then a typical value for the reflectivity R of a 45° plane mirror can be 80%.

[0035] In specific application examples, the aperture of the 11-inch pinhole aperture can satisfy the following relationship:

[0036]

[0037] Where d is the diameter of the pinhole stop 11, L is the distance between the pinhole stop 11 and the diffraction grating 9, Δλ is the linewidth of the synthesized sub-beam, and D θ The dispersion of the 9-axis diffraction grating.

[0038] In a specific embodiment, the superfluorescent source has a flat spectral line shape in the wavelength range of 1040nm to 1090nm, power stability ≤2%, and continuous output power ≥1W;

[0039] In a specific embodiment, the bandwidth of the 1xN beam splitter covers 1040nm to 1090nm;

[0040] In a specific embodiment, the circulator is non-polarization dependent, with an insertion loss ≤1dB, an isolation of port ② to port ① ≥50dB, and an operating bandwidth covering 1040nm~1090nm;

[0041] In a specific embodiment, the diffraction grating has a line density of 960 lines / mm and a diffraction efficiency of ≥97% in the wavelength range of 1040nm to 1090nm.

[0042] In a specific embodiment, the focal length of the off-axis reflecting mirror focusing system is 2m;

[0043] In a specific embodiment, the fiber end cap fusion splice surface is coated with an anti-reflection film of 1040nm to 1090nm;

[0044] In a specific embodiment, the fiber laser main amplifier adopts a MOPA multi-stage amplification structure;

[0045] In a specific embodiment, the diffraction grating is a multilayer dielectric reflective diffraction grating with a size ≥100mm×100mm×15mm and a wavefront distortion ≤1 / 10λ.

[0046] In a specific embodiment, the 45° plane mirror has a wavelength range of 1040nm to 1090nm, a high-reflectivity film with a reflectivity of 80% on the front side, and an anti-reflective film with a transmittance of ≥99.9% on the back side.

[0047] In a specific embodiment, the 0° plane mirror has a wavelength range of 1040nm to 1090nm, and is coated with a high reflectivity film of ≥99.95% on both the front and back sides, and an antireflective film of ≥99.9% on the back side.

[0048] In a specific embodiment, the synthesized beam 1 / e2 20mm in diameter, pinhole aperture diameter 2mm;

[0049] In specific application examples, a sampling device can be added to the output end of the synthesized beam to monitor and analyze the beam spot morphology, temporal stability, and spectral line shape.

[0050] The above description is merely a preferred embodiment of the present invention, and while it is detailed and specific, it should not be construed as limiting the scope of the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A multi-wavelength self-selective spectral synthesis system based on a superfluorescent source, characterized in that, The system includes a superfluorescent source, a 1xN beam splitter, N combining arms, a focusing system, a diffraction grating, a 45° plane mirror, a pinhole aperture, and a 0° plane mirror. Each combining arm includes a 2x1 beam combiner, a fiber main amplifier, a fiber preamplifier, a circulator, and a fiber output cap. The superfluorescent source is split into N seed beams by the 1xN beam splitter. Each seed beam passes sequentially through the 2x1 beam combiner, the fiber main amplifier, and the circulator. A broadband beam is output from port ② of the circulator. After passing through the focusing system, the N broadband beams converge at different angles. The light is focused onto a diffraction grating for synthesis. After passing through the 45° mirror, the main power is reflected and output, while a small amount of transmitted light is incident on the 0° mirror. For each individual synthesizing arm, only the specific wavelength light corresponding to a specific end cap position can be reflected back through the 0° plane mirror and returned along the original path. This backfeedback light is then recoupled into the respective fiber end cap, passed through the fiber preamplifier, and re-injected into the fiber main amplifier via a 2x1 combiner. In the fiber main amplifier, wavelength self-selection and adaptive wavelength tuning are achieved through a gain competition process. The N-channel output light with self-selected wavelengths obtained at this time is focused onto the diffraction grating at the corresponding angle and achieves common aperture synthesis output; the main power of the synthesized light is reflected by the 45° mirror and used as the output beam. To ensure that the feedback light wins the gain competition in the fiber amplifier, thereby obtaining a stable oscillating beam output, the reflectivity R of the 45° plane mirror and the amplification of the fiber amplifier are crucial. Pre-amplification magnification of 13 The selection of [amount] should meet the following criteria: Where A is the circulator insertion loss, B is the coupling efficiency of the fiber end cap 7, C is the diffraction efficiency of the multilayer dielectric reflective diffraction grating, and D is the percentage of feedback light power.

2. The multi-wavelength self-selective spectral synthesis system based on a superfluorescent source according to claim 1, characterized in that, The 45° plane mirror reflects wavelengths covering the composite band, with a high-reflectivity coating on the front and an anti-reflection coating on the back.

3. The multi-wavelength self-selective spectral synthesis system based on a superfluorescent source according to claim 1, characterized in that, The 0° plane mirror and pinhole aperture serve as feedback elements. The wavelength range of the 0° plane mirror's reflective surface covers the combined wavelength band. The front side is coated with a high-reflectivity film, and the back side with an anti-reflection film. The optical axis of the pinhole aperture coincides with the combined beam, and its diameter is less than or equal to 1 / e of the combined beam. 2 diameter.

4. The multi-wavelength self-selective spectral synthesis system based on a superfluorescent source according to claim 1, characterized in that, The backward feedback light is recoupled to each synthesizing arm through port ② of the circulator, output from port ③ of the circulator, amplified by the fiber preamplifier, and then re-entered into the fiber main amplifier through a 2x1 combiner for amplification, thereby achieving wavelength self-selection for each synthesizing arm.

5. The multi-wavelength self-selective spectral synthesis system based on a superfluorescent source according to claim 1, characterized in that, The focusing system is an off-axis reflection system or a coaxial transmission system.

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