CN108462024B - System for inhibiting thermal induced mode instability in high-brightness narrow-linewidth ytterbium-doped optical fiber amplifier - Google Patents
System for inhibiting thermal induced mode instability in high-brightness narrow-linewidth ytterbium-doped optical fiber amplifier Download PDFInfo
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- H01S3/131—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the active medium, e.g. by controlling the processes or apparatus for excitation
- H01S3/1312—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the active medium, e.g. by controlling the processes or apparatus for excitation by controlling the optical pumping
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Abstract
A system for suppressing thermal induced mode instability in a high brightness narrow linewidth ytterbium doped fiber amplifier includes a waveguide having a center wavelength lambda 1 Is a narrow linewidth fiber laser seed source with a center wavelength lambda 2 The optical fiber laser comprises an optical fiber laser, an all-fiber high-power wavelength division multiplexer, an ytterbium-doped main amplifier, an optical fiber end cap, a collimator, a dichroic mirror, a power receiver I, a high-reflection mirror, a power receiver II, a beam splitter, a photoelectric signal acquisition display module and a beam quality monitoring module; simultaneously injecting a beam of ytterbium-doped fiber amplifier with center wavelength lambda in narrow linewidth 2 Is a short-wavelength laser beam with a central wavelength lambda 1 Long wavelength laser of narrow linewidth of lambda 2 <λ 1 . By forming gain competition in the gain fiber, effective suppression of the thermally induced mode instability effect and effective output of single-wavelength narrow-linewidth laser are realized.
Description
Technical Field
The invention belongs to the technical field of strong lasers, and particularly relates to a system for inhibiting thermal induced mode instability of a high-brightness narrow-linewidth ytterbium-doped optical fiber amplifier.
Background
The high-brightness narrow-linewidth fiber laser has wide application requirements in various application fields such as coherent synthesis, spectrum synthesis, nonlinear frequency conversion, earth science, atomic molecular physics and the like. However, with the continuous increase of power, sudden mode distortion, i.e., thermally induced mode instability, occurs in the narrow linewidth fiber amplifier due to the presence of heat. Since 2010 heat-induced mode instability phenomenon was first reported, the phenomenon is widely focused by a plurality of domestic and foreign units as an important factor for limiting the further brightness improvement of the current fiber laser.
The research results show that: when the output power of the fiber laser exceeds a certain threshold power, the output laser modes can be dynamically coupled and hopped from a basic mode to a high-order mode, and the output brightness of the system is seriously affected along with the rapid reduction of the quality of the light beam. In addition, after the mode instability occurs, the output time-domain characteristics of the laser light may fluctuate significantly. Further research results show that the mode instability threshold is related to various factors such as optical fiber structure, signal/pump wavelength, photodarkening and the like.
At present, it is basically agreed that the physical mechanism of occurrence of thermally induced mode instability is internationally that the fundamental mode and the higher-order modes interfere in the optical fiber, causing the inverted population distributed longitudinally along the gain fiber to exhibit a periodic distribution. The periodic distribution of the inverted population causes the formation of an index modulated grating in the fiber by the Kramers-Kronig effect. When there is a phase shift in the index grating interfering with the optical field, energy will be coupled between the fundamental and higher order modes. With respect to the generation of phase shifts, the prevailing explanation is that there is a frequency shift between the fundamental mode and the higher order modes, thus causing the modulated grating to shift in phase.
Based on the generation mechanism, a plurality of research institutions at home and abroad have proposed a plurality of technical schemes for inhibiting the instability of the thermotropic mode, and the technical schemes mainly comprise: control of higher order mode excitation to eliminate modulated index gratings, reduce the quantum deficit of the fiber laser amplifier, enhance the gain saturation effect of the fiber laser amplifier by changing the signal/pump wavelength, increase the relative loss of higher order modes (reduce the interaction of higher order modes and fundamental modes), etc.
However, despite the various approaches to suppression described above, the effect of thermally induced mode instability remains one of the key factors limiting current high brightness narrow linewidth fiber amplifiers. Therefore, starting from the design of the optical fiber amplifier system, based on the physical mechanism generated by the unstable thermal induced mode, the pursuit and tracing propose a new method for inhibiting the new method, which has important scientific significance and practical needs for promoting the further brightness improvement of the narrow-linewidth optical fiber amplifier.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention provides a system for inhibiting the thermal mode instability of a high-brightness narrow-linewidth ytterbium-doped optical fiber amplifier based on the dependency relationship between a mode instability threshold and signal light wavelength and the difference of absorption and emission sections of signal light with different wavelengths, which adopts dual-wavelength injection in the narrow-linewidth ytterbium-doped optical fiber amplifier, relies on gain competition to simultaneously realize single-wavelength effective amplification and thermal mode instability effect inhibition, provides a high-performance optical fiber light source design scheme with reliable performance and compact structure for the fields of coherent synthesis, spectrum synthesis, nonlinear frequency conversion and the like, and promotes the overall performance improvement of high-power narrow-linewidth optical fiber laser and the further development of application fields.
In order to achieve the technical purpose, the technical scheme of the invention is as follows:
a system for inhibiting thermal induced mode instability of high-brightness narrow-linewidth ytterbium-doped optical fiber amplifier is characterized in that a beam of optical fiber amplifier with central wavelength lambda is injected simultaneously 2 Is a short-wavelength laser beam with a central wavelength lambda 1 Long wavelength laser of narrow linewidth of lambda 2 <λ 1 The method comprises the steps of carrying out a first treatment on the surface of the By forming gain competition in the gain fiber, effective suppression of the thermally induced mode instability effect and effective output of single-wavelength narrow-linewidth laser are realized.
The system comprises a center wavelength lambda 1 Is a narrow linewidth fiber laser seed source with a center wavelength lambda 2 The optical fiber laser comprises an optical fiber laser, an all-fiber high-power wavelength division multiplexer, an ytterbium-doped main amplifier, an optical fiber end cap, a collimator, a dichroic mirror, a power receiver I, a high-reflection mirror, a power receiver II, a beam splitter, a photoelectric signal acquisition display module and a beam quality monitoring module;
the center wavelength is lambda 1 Laser beam emitted from narrow linewidth optical fiber laser seed source and having center wavelength lambda 2 The laser beam emitted by the optical fiber laser is synthesized into a beam of dual-wavelength laser by the optical fiber high-power wavelength division multiplexer and then is output, the dual-wavelength laser is injected into the ytterbium-doped main amplifier to perform gain competition and power amplification, and the laser output after the power amplification of the ytterbium-doped main amplifier is transmitted to the collimator through the optical fiber end cap to be collimated and then is output to the free space. After the collimated output beam passes through the dichroic mirror, the gain competition residual center wavelength is lambda 2 Is injected into the power receiver I with the wavelength lambda 1 Is reflected to be incident to the high-reflection mirror; the laser reflected by the high-reflection mirror is received by the power receiver II, and the laser transmitted by the high-reflection mirror is divided into two beams after passing through the beam splitter, wherein the laser transmitted by the beam splitter is incident to the photoelectric signal acquisition display module, and the laser reflected by the beam splitter is incident to the beam quality monitoring module.
In the invention, the following components are added: the optical fiber also comprises a cascade ytterbium-doped optical fiber preamplifier, and the central wavelength is lambda 1 Laser beams emitted by a narrow linewidth fiber laser seed source are preamplified by a cascade ytterbium-doped fiber preamplifier, and the laser beams after preamplification and the laser beams with the center wavelength lambda are amplified by a cascade ytterbium-doped fiber preamplifier 2 The laser beam emitted by the optical fiber laser is synthesized into a beam of dual-wavelength laser by the optical fiber high-power wavelength division multiplexer and then output. The number of stages of the pre-amplification of the cascade ytterbium-doped fiber pre-amplifier is determined by the expected amplification factor. In general, for a hundred milliwatt single stage fiber preamplifier, the amplification is about 30-50 times, for a tens of milliwatt preamplifier, the amplification is possible>100 times.
In the invention, the central wavelength is lambda 1 The implementation mode of the narrow linewidth fiber laser seed source is not limited, and can be single-frequency seed applied phase modulation productionThe laser source can be a raw narrow-linewidth laser source, a narrow-band filtering super-fluorescent light source, a direct narrow-linewidth oscillator and a narrow-band filtering random fiber laser, or can be a laser source which is formed by coupling and outputting a narrow-linewidth semiconductor laser or a narrow-linewidth solid laser through a fiber. Center wavelength lambda 1 The specific value of (2) is not limited, and is generally any wavelength in the range of 1060nm to 1090 nm.
The center wavelength of the invention is lambda 2 The implementation mode of the fiber laser is not limited, and the fiber laser can be a direct high-power oscillator, a super-fluorescent light source, a random fiber laser and the like, and can also be a multi-stage cascade main oscillation power amplification system. The central wavelength is lambda 2 The line width of the optical fiber laser is not limited, and the optical fiber laser can be a narrow line width optical fiber laser or a wide spectrum optical fiber laser.
The high-power wavelength division multiplexer of the invention has the advantages of no limitation in implementation mode, diaphragm type wavelength division multiplexer and fusion tapered wavelength division multiplexer, and has the function of setting the central wavelength as lambda 1 Is lambda in the central wavelength and the fiber laser 2 The optical fiber laser beam is combined into one laser output.
The ytterbium-doped main amplifier comprises a pumping source, a high-power signal-pumping beam combiner, a doped optical fiber, a cladding light filter and the like. The wavelength of the pump source can be selected from 976nm, 915nm, 960nm, etc., the high power signal-pump beam combiner is generally of (6+1) x 1 structure considering the high power output of several kilowatts, the doped fiber can be selected from the various, the fiber core diameter is generally >20 μm, and the cladding thickness is generally >200 μm. The cladding light filter has the function of filtering residual pump light and cladding light into free space, preventing the cladding light from damaging an output device and ensuring high-beam quality output.
The optical fiber end cap is a laser transmission and emission device manufactured by adopting an optical fiber and a fused quartz head through fused tapering, so that the laser power density of an output end face can be effectively reduced, and optical discharge is prevented.
The collimator is used for laser beam collimation, can realize laser collimation emission by one or a plurality of lens combinations, has various material selections of the lens, can be fused quartz, znSe, caF2 and the like, has various film plating modes of the lens anti-reflection film, and can be single-layer film plating or multi-layer film plating.
The dichroic mirror is used for setting the residual center wavelength to be lambda 2 Is separated from the main laser with the central wavelength lambda 1 to finally obtain the pure laser with the central wavelength lambda 1 The constituent materials of the narrow linewidth laser are not limited, and may be fused silica, K9, etc., specifically selected according to the irradiation laser power density. The reflection-transmission wavelength range is determined by the output laser band range.
The implementation modes of the power receiver I and the power receiver II are not limited, and can be a traditional power meter, a conical waste light collector and the like.
The high-reflection mirror realizes that the center wavelength is lambda 1 High reflectivity of narrow linewidth laser light, its reflectivity is generally>99 percent; the constituent materials of the high-reflection mirror are not limited, and are fused quartz, K9 and the like, and specifically selected according to the irradiation laser power density.
The beam splitter has various implementation modes, and can be a white piece (reflectivity is 4%), a wedge-shaped mirror, a beam splitter with a fixed beam splitting ratio and the like, and the beam splitter can be made of materials such as fused quartz, K9, znSe, caF2 and the like without limitation.
The photoelectric signal acquisition display module converts an optical signal into an electric signal after receiving incident laser, and displays a time domain signal and a frequency domain signal of the incident laser on a terminal so as to observe time domain fluctuation caused by a thermal mode instability effect and determine a threshold value of the occurrence of the thermal mode instability effect in real time. The module is typically composed of a photodetector and an oscilloscope.
The beam quality monitoring module is used for monitoring and measuring the beam quality of incident laser and observing the beam quality change after the occurrence of the unstable effect of the thermally induced mode in the power increasing process.
The principle of the invention for realizing the suppression of the thermal mode instability effect is as follows:
the current research results about the dependence relationship between the mode instability threshold and the central wavelength of the signal light show that: for the conventional large-mode-field double-cladding ytterbium-doped optical fiber, when the central wavelength is tuned from the vicinity of 1030nm to the vicinity of 1090nm, as the central wavelength is tuned to a long band, the number of inverted particles at the upper energy level is continuously increased due to the fact that the emission cross section of signal light is reduced in a near-exponential manner, the gain saturation effect is continuously weakened from strong, and the mode instability threshold value is reduced in an exponential manner. The above-described results indicate that the thermal mode instability threshold can be significantly increased when the narrow linewidth optical fiber amplifier is operated near the short wavelength band only for the thermal mode instability effect. However, it is extremely difficult to boost the power around 1030nm to several kw due to the influence of spontaneous radiation effect. In order to realize power output of several kilowatts, the central wavelength of the optical fiber amplifier is generally selected in the wavelength range of 1060nm to 1090 nm. The laser amplification in the wave band can effectively inhibit the influence of spontaneous radiation on the output power, but the thermal mode instability effect becomes a main limiting factor for improving the brightness.
Based on the above consideration, ytterbium-doped fiber is used to obtain the optical fiber with the optical fiber in the vicinity of short wavelength (lambda 2 ) And the vicinity of a long wave (lambda) 1 ) The difference of the emission cross sections is absorbed, and gain competition is formed in the gain optical fiber, so that effective suppression of the thermal induced mode instability effect and effective output of single-wavelength narrow-linewidth laser can be finally realized. Specifically, a beam of a center wavelength lambda is injected simultaneously in the main amplifier 2 Is a short-wavelength laser beam with a central wavelength lambda 1 Long wavelength laser with narrow linewidth and center wavelength lambda 2 The short wavelength laser of (2) can effectively extract the reverse particle number in the front half part of the gain optical fiber of the main amplifier, enhance the gain saturation effect of the system and achieve the effect of inhibiting the unstable thermal induced mode. At the rear end of the gain fiber of the main amplifier, the center wavelength is lambda with the reduction of the pumping power 2 The gain of the short-band laser is gradually reduced, and finally the absorption and loss of the short-band laser are larger than the gain, and the power starts to be reduced. At the same time, the absorption center wavelength of the doped ions is lambda 2 After the short wavelength laser of (2), the population inversion is formed to have a center wavelength lambda 1 Provides gain for long wavelength lasers of (2). By reasonably setting the power ratio of the short wavelength laser and the long wavelength laser and the doped lightThe fiber length can be such that the center wavelength is lambda 2 Is substantially completely converted, and the final output laser of the narrow linewidth optical fiber amplifier contains most of the central wavelength lambda 1 Long wavelength narrow linewidth laser of (2) and a very small amount of lambda which is not completely converted 2 Short wavelength laser. In order to effectively suppress the influence of four-wave mixing on the amplification process, λ 1 And lambda (lambda) 2 The wavelength interval between them needs to be greater than 10nm. In addition, in addition to the gain of ytterbium ion itself, λ is realized for effective use of raman gain 2 To lambda 1 Fast conversion of lambda 1 And lambda (lambda) 2 The optimum value of the wavelength interval between should be the raman shift (typically 13.2THz for ytterbium doped fibers).
Compared with the prior art, the invention can produce the following technical effects:
1. according to the invention, the ytterbium-doped optical fiber absorbs the difference of emission sections near the short wave and near the long wave, and the gain competition is formed by injecting the dual-wavelength laser into the main optical fiber amplifier, so that the inverted particle number of the short-wavelength laser can be effectively extracted from the front half part of the gain optical fiber of the main optical fiber amplifier, the gain saturation effect of the system is enhanced, and the effective suppression of unstable modes is realized; at the rear end part of the gain fiber of the main amplifier, the particle number formed by the short-wave laser is reversed to provide gain for the long-wavelength laser, and finally, the narrow-linewidth fiber laser output with high brightness and long wavelength is realized.
2. The invention has universality: the method can be used for amplifying any wavelength from 1060nm to 1090nm in terms of the amplifying wavelength range. The wavelength range of the injected short-wave laser is flexible, and the short-wave laser can be any wavelength laser in the wave band of 1030 nm-1050 nm.
3. In the present invention, the center wavelength is lambda 1 The narrow-linewidth optical fiber laser seed source has various implementation modes, and can be a narrow-linewidth laser source, a narrow-band filtering super-fluorescent light source, a direct narrow-linewidth oscillator and a narrow-band filtering random optical fiber laser which are generated by single-frequency seed applied phase modulation, or can be a laser source which is output by a narrow-linewidth semiconductor laser or a narrow-linewidth solid laser through optical fiber coupling.
4. In the present invention, the wavelengthLambda is lambda 2 The short wave fiber laser has various implementation modes, can be a direct high-power oscillator, an ultra-fluorescent light source, a random fiber laser and the like, and can also be a multi-stage cascade main oscillation power amplification system. The central wavelength is lambda 2 The line width of the short-wave optical fiber laser is not limited, and the short-wave optical fiber laser can be a narrow-line-width optical fiber laser or a wide-spectrum optical fiber laser.
Drawings
Fig. 1 is a schematic diagram of a system structure according to the present invention.
The drawings include:
the center wavelength is lambda 1 The narrow linewidth optical fiber laser seed source 1-1, the cascade ytterbium-doped optical fiber preamplifier 1-2 and the center wavelength lambda 2 (λ 2 <λ 1 ) The optical fiber laser comprises an optical fiber laser 1-3, an all-fiber high-power wavelength division multiplexer 1-4, an ytterbium-doped main amplifier 1-5, an optical fiber end cap 1-6, a collimator 1-7, a dichroic mirror 1-8, a power receiver I1-9, a high-reflection mirror 1-10, a power receiver II 1-11, a beam splitter 1-12, a photoelectric signal acquisition display module 1-13 and a beam quality monitoring module 1-14.
Fig. 2 is a diagram showing an exemplary application of the present invention: the structure schematic diagram of the thermal induced mode instability suppression system of the 3 kW-level 1083nm narrow linewidth optical fiber amplifier is shown.
The drawings include: the optical fiber laser comprises a narrow linewidth fiber laser 2-1 with a central wavelength of 1083nm, a cascading ytterbium-doped fiber preamplifier 2-2 (comprising 2-21 and 2-22 cascading ytterbium-doped fiber preamplifiers), a fiber laser 2-3 with a central wavelength of 1033nm, an all-fiber high-power wavelength division multiplexer 2-4, a ytterbium-doped main amplifier 2-5, a fiber end cap 2-6, a collimator 2-7, a dichroic mirror 2-8, a power receiver I2-9, a high-reflection mirror 2-10, a power receiver II 2-11, a beam splitter 2-12, a photoelectric signal acquisition display module 2-13 and a beam quality monitoring module 2-14.
Wherein:
2-21 is a 200 mW-level preamplifier, and mainly comprises a 600 mW-level 976nm pump source 2-211, a 1W-level wavelength division multiplexer 2-212, a gain fiber with a fiber core cladding ratio of 6/125 μm 2-213, a 100 mW-level cladding light filter 2-214, a 200 mW-level fiber isolator 2-215 and a 200 mW-level band-pass filter 2-216;
the 2-22 is a 30W-level preamplifier, which mainly comprises a 60W-level 976nm pump source 2-221, (2+1) x 1 signal-pump beam combiner 2-222, a gain fiber 2-223 with a fiber core cladding ratio of 10/125 μm, a 10W-level cladding light filter 2-224, and a 30W-level fiber isolator 2-225;
the ytterbium-doped main amplifier 2-5 mainly comprises 6 700W 976nm pump sources 2-51, (6+1) x 1 high-power signal-pump beam combiners 2-52, doped optical fibers 2-53 and kilowatt-level cladding light filters 2-54.
Detailed Description
FIG. 1 is a schematic diagram of a system architecture of the present invention, comprising: the center wavelength is lambda 1 The narrow linewidth optical fiber laser seed source 1-1, the cascade ytterbium-doped optical fiber preamplifier 1-2 and the center wavelength lambda 2 (λ 2 <λ 1 ) The optical fiber laser comprises an optical fiber laser 1-3, an all-fiber high-power wavelength division multiplexer 1-4, an ytterbium-doped main amplifier 1-5, an optical fiber end cap 1-6, a collimator 1-7, a dichroic mirror 1-8, a power receiver I1-9, a high-reflection mirror 1-10, a power receiver II 1-11, a beam splitter 1-12, a photoelectric signal acquisition display module 1-13 and a beam quality monitoring module 1-14.
From the central wavelength lambda 1 The laser output by the narrow linewidth fiber laser seed source 1-1 is firstly injected into the cascade ytterbium-doped fiber preamplifier 1-2 for preamplification. The structure and the number of stages of the pre-amplifier are determined according to the power of the narrow linewidth fiber laser seed source 1-1 and the expected pre-amplification power index. If the output power of the narrow linewidth fiber laser seed source 1-1 can meet the requirement of subsequent amplification, the cascade ytterbium-doped fiber preamplifier 1-2 can be omitted. The pre-amplified light beam has a central wavelength lambda 2 (λ 2 <λ 1 ) The laser generated by the laser 1-3 is synthesized into a beam of dual wavelength laser by the all-fiber high-power wavelength division multiplexer 1-4, and then is injected into the ytterbium-doped main amplifier 1-5 for gain competition and power amplification. The laser amplified by the ytterbium-doped main amplifier 1-5 is output to a free space after passing through the optical fiber end cap 1-6 and the collimator 1-7. After the collimated output beam passes through the dichroic mirrors 1-8, the center wavelength of gain competition residual is lambda 2 Is injected into the power receiver I1-9 with a wavelength lambda 1 The laser of (2) is reflected and enters the high-reflection mirror 1-10; laser reflected by high reflection mirrorIs received by the power receivers II 1-11, and the transmitted laser light is split into two beams after passing through the beam splitters 1-12. The laser transmitted by the beam splitters 1-12 is incident to the photoelectric signal acquisition display modules 1-13 to observe time domain fluctuation caused by mode instability effect in real time and determine a threshold value of occurrence of thermally induced mode instability; the light beams reflected by the beam splitters 1-12 are incident on the beam quality monitoring modules 1-14 for observing the quality change of the light beams during the power boosting process, especially after the occurrence of the thermal mode instability.
The following describes a specific implementation of the present invention with reference to a typical application example, namely, a thermal mode instability suppression (a system structure schematic diagram is shown in fig. 2) of a 3 kW-level 1083nm narrow-linewidth optical fiber amplifier, and the application scope of the present invention is not limited to this typical example.
In fig. 2, laser light output from a narrow linewidth fiber laser seed source 2-1 having a center wavelength of 1083nm is first injected into a first-stage cascade ytterbium-doped fiber preamplifier 2-21 for preamplification. The laser pre-amplified by the first-stage cascade ytterbium-doped optical fiber pre-amplifier 2-21 is injected into the second-stage cascade ytterbium-doped optical fiber pre-amplifier 2-22 for further power improvement.
The light beam passing through the second-stage cascade ytterbium-doped optical fiber pre-amplifier 2-22 and the laser generated by the laser 2-3 with the center wavelength of 1033nm are synthesized into a beam of dual-wavelength laser through the all-fiber high-power wavelength division multiplexer 2-4, and then the dual-wavelength laser is injected into the ytterbium-doped main amplifier 2-5 for gain competition and power amplification. The ytterbium-doped main amplifier 2-5 consists of 6 700W 976nm pump sources 2-51, (6+1) x 1 high-power signal-pump beam combiners 2-52, doped optical fibers 2-53 and kilowatt-level cladding light filters 2-54; the pumping light generated by the 6 700W 976nm pumping sources 2-51 pumps the doped optical fibers 2-53 through the (6+1) multiplied by 1 high-power signal-pumping beam combiners 2-52, and the laser power is amplified to the order of 3 kW. The amplified laser is filtered by a kilowatt-level cladding light filter 2-54 to remove residual pump light and cladding light, and then is output to a free space through an optical fiber end cap 2-6 and a collimator 2-7; after the laser output by collimation passes through the dichroic mirror 2-8, the laser with the center wavelength of 1033nm remained by gain competition is injected into the power receiver I2-9, and the laser with the wavelength of 1083nm is reflected and injected into the high-reflection mirror 2-10; the 1083nm laser reflected by the high-reflection mirror 2-10 is received by the power receiver II 2-11, and the 1083nm laser transmitted by the high-reflection mirror 2-10 is split into two beams after passing through the beam splitter 2-12. The 1083nm laser transmitted by the beam splitter 2-12 is incident to the photoelectric signal acquisition display module 2-13 to observe time domain fluctuation caused by mode instability effect in real time and determine a threshold value of occurrence of thermally induced mode instability; the 1083nm laser reflected by the beam splitter 2-12 is incident to the beam quality monitoring module 2-14 for observing the beam quality change in the power boosting process.
Wherein: the first-stage cascade ytterbium-doped optical fiber preamplifier 2-21 is a 200 mW-stage preamplifier and consists of a 600 mW-stage 976nm pump source 2-211, a 1W-stage wavelength division multiplexer 2-212, a gain optical fiber with a fiber core cladding ratio of 6/125 mu m 2-213, a 100 mW-stage cladding light filter 2-214, a 200 mW-stage optical fiber isolator 2-215 and a 200 mW-stage band-pass filter 2-216. The pump light generated by the 600mW level 976nm pump source 2-211 is pumped to gain optical fiber 2-213 with the core-cladding ratio of 6/125 mu m through the 1W level wavelength division multiplexer 2-212, so that the power of the seed source is increased to 200mW level; the generated amplified laser is filtered by a 100 mW-level cladding light filter 2-214 to remove residual pump light and cladding light, and then is injected into a 200 mW-level optical fiber isolator 2-215 and a 200 mW-level band-pass filter 2-216. The 200 mW-level fiber isolator 2-215 is used to prevent return light in the subsequent amplification process from entering the preceding stage system to cause system damage. The 200 mW-level band-pass filter 2-216 is used for filtering amplified stray light outside the 1083nm signal light band range, and improves the 1083nm laser spectrum signal-to-noise ratio.
The second-stage cascade ytterbium-doped optical fiber preamplifier 2-22 is a 30W-stage preamplifier, and consists of a 60W-stage 976nm pump source 2-221, (2+1) x signal-pump beam combiner 2-222, a gain optical fiber 2-223 with a fiber core cladding ratio of 10/125 mu m, a 10W-stage cladding light filter 2-224 and a 30W-stage optical fiber isolator 2-225; the pump light generated by the 60W-level 976nm pump source 2-221 pumps the gain fiber 2-223 with the fiber core cladding ratio of 10/125 mu m through the (2+1) multiplied by 1 signal-pump beam combiner 2-222, and the laser power is amplified to 30W level. The generated 30W-level amplified laser is filtered by a 10W-level cladding light filter 2-224 to remove residual pump light and cladding light, and then is injected into a 30W-level optical fiber isolator 2-225; the 30W-stage fiber isolator 2-225 is used to prevent the return light from entering the preceding stage system during the subsequent amplification process from causing system damage.
When an actual system is built, the whole system can be optimized by reasonably proportioning the power proportion of 1083nm laser and 1033nm laser entering the ytterbium-doped main amplifier 2-5 and optimizing the length of the doped optical fiber 2-53 in the ytterbium-doped main amplifier 2-5, and finally, the short-wavelength laser with the central wavelength of 1033nm is basically and completely converted, so that the optimal thermal mode instability suppression effect is achieved.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A method for inhibiting thermal induced mode instability in a high-brightness narrow-linewidth ytterbium-doped optical fiber amplifier is characterized by comprising the following steps: simultaneously injecting a beam of ytterbium-doped fiber amplifier with center wavelength lambda in narrow linewidth 2 Is a short-wavelength laser beam with a central wavelength lambda 1 Long wavelength laser of narrow linewidth of lambda 2 <λ 1 The method comprises the steps of carrying out a first treatment on the surface of the The effective suppression of the thermal induced mode unstable effect and the effective output of the single-wavelength narrow linewidth laser are realized by forming gain competition in the gain optical fiber, wherein the central wavelength is lambda by reasonably proportioning 1 Is lambda from the center wavelength of the long wavelength laser 2 The ratio of the power of the short wavelength laser entering the ytterbium-doped main amplifier and the length of the doped fiber in the ytterbium-doped main amplifier are optimized so that the center wavelength is lambda 2 The short wavelength laser of (2) can effectively extract the reverse particle number in the front half part of the gain optical fiber of the main amplifier, so that the gain saturation effect of the system is enhanced, and the effect of inhibiting the unstable thermally induced mode is achieved; the rear end part of the gain fiber of the main amplifier has a center wavelength lambda with the reduction of pumping power 2 The gain of the short-wave band laser is gradually reduced, the absorption and loss of the short-wave band laser are finally larger than the gain, the power starts to be reduced, and at the same time, the absorption center wavelength of the doped ions is lambda 2 After a short wavelength laser of (2)Form a population inversion with a center wavelength lambda 1 Provides gain and achieves a high-brightness long-wavelength narrow linewidth fiber laser output.
2. A laser system utilizing the method for suppressing thermally induced mode instability in a high brightness narrow linewidth ytterbium doped fiber amplifier of claim 1, wherein: the system comprises a center wavelength lambda 1 Is a narrow linewidth fiber laser seed source with a center wavelength lambda 2 The optical fiber laser comprises an optical fiber laser, an all-fiber high-power wavelength division multiplexer, an ytterbium-doped main amplifier, an optical fiber end cap, a collimator, a dichroic mirror, a power receiver I, a high-reflection mirror, a power receiver II, a beam splitter, a photoelectric signal acquisition display module and a beam quality monitoring module;
the center wavelength is lambda 1 Laser beam emitted from narrow linewidth optical fiber laser seed source and having center wavelength lambda 2 The laser beam emitted by the optical fiber laser is synthesized into a beam of dual-wavelength laser through the optical fiber high-power wavelength division multiplexer and then is output, the dual-wavelength laser is injected into the ytterbium-doped main amplifier to perform gain competition and power amplification, and the laser output after the power amplification of the ytterbium-doped main amplifier is transmitted to the collimator through the optical fiber end cap to be collimated and then is output to the free space; after the collimated output beam passes through the dichroic mirror, the gain competition residual center wavelength is lambda 2 Is injected into the power receiver I with the wavelength lambda 1 Is reflected to be incident to the high-reflection mirror; the laser reflected by the high-reflection mirror is received by the power receiver II, and the laser transmitted by the high-reflection mirror is divided into two beams after passing through the beam splitter, wherein the laser transmitted by the beam splitter is incident to the photoelectric signal acquisition display module, and the laser reflected by the beam splitter is incident to the beam quality monitoring module.
3. The laser system of claim 2, wherein: the optical fiber also comprises a cascade ytterbium-doped optical fiber preamplifier, and the central wavelength is lambda 1 Laser beams emitted by a narrow linewidth fiber laser seed source are preamplified by a cascade ytterbium-doped fiber preamplifier, and the laser beams after preamplification and the laser beams with the center wavelength lambda are amplified by a cascade ytterbium-doped fiber preamplifier 2 Is a fiber laserThe laser beam is synthesized into a beam of dual wavelength laser by an optical fiber high-power wavelength division multiplexer and then output.
4. A laser system according to claim 3, characterized in that: the number of stages of the pre-amplification of the cascade ytterbium-doped fiber pre-amplifier is determined by expected amplification factors; the amplification factor is 30-50 times for a hundred milliwatt single-stage optical fiber pre-amplifier, and >100 times for a tens of milliwatt pre-amplifier.
5. The laser system of claim 2, 3 or 4, wherein: the central wavelength is lambda 1 The narrow-linewidth optical fiber laser seed source is a narrow-linewidth laser source, a narrow-band filtering super-fluorescent light source, a direct narrow-linewidth oscillator or a narrow-band filtering random optical fiber laser generated by single-frequency seed applied phase modulation, or is a laser source of a narrow-linewidth semiconductor laser or a narrow-linewidth solid laser which is output through optical fiber coupling; center wavelength lambda 1 Is any wavelength in the 1060nm to 1090nm band.
6. The laser system of claim 5, wherein: the central wavelength is lambda 2 The fiber laser of (2) is a direct high-power oscillator, a super-fluorescent light source or a random fiber laser; or a multi-stage cascade main oscillation power amplification system;
the central wavelength is lambda 2 The line width of the fiber laser is a narrow line width fiber laser or a wide spectrum fiber laser.
7. The laser system of claim 6, wherein: lambda (lambda) 1 And lambda (lambda) 2 The wavelength interval between them needs to be greater than 10nm.
8. The laser system of claim 6, wherein: lambda (lambda) 1 And lambda (lambda) 2 The optimal value of the wavelength interval between them is the raman shift amount.
9. The laser system of claim 6, wherein: the ytterbium-doped main amplifier comprises a pumping source, a high-power signal-pumping beam combiner, a doped optical fiber and a cladding light filter, wherein the wavelength of the pumping source is 976nm, 915nm or 960nm; the high-power signal-pump beam combiner is of a (6+1) x 1 structure; the fiber core diameter of the doped fiber is more than 20 mu m, and the thickness of the cladding is more than 200 mu m; the cladding light filter has the function of filtering residual pump light and cladding light into free space, preventing the cladding light from damaging an output device and ensuring high-beam quality output.
10. The laser system of claim 6, wherein: the high-power wavelength division multiplexer is a diaphragm type wavelength division multiplexer or a fused tapered type wavelength division multiplexer;
the optical fiber end cap is a laser transmission emitting device manufactured by adopting an optical fiber and a fused quartz head through fused tapering;
the center wavelength of the high-reflection mirror is lambda 1 High reflection of narrow linewidth laser light, its reflectivity>99％。
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| CN108879314B (en) * | 2018-09-06 | 2024-09-06 | 中国人民解放军国防科技大学 | High-power narrow linewidth long-wave fiber laser generation system |
| CN109813425B (en) * | 2019-03-18 | 2024-08-23 | 江苏镭创高科光电科技有限公司 | Light source light power detection device and laser light source |
| CN113097847A (en) * | 2021-04-30 | 2021-07-09 | 上海传输线研究所（中国电子科技集团公司第二十三研究所） | Novel narrow-linewidth high-power optical fiber laser generation device and method based on dispersion management |
| CN116053901A (en) * | 2021-10-28 | 2023-05-02 | 华为技术有限公司 | Amplifier and system |
| CN114300922B (en) * | 2021-12-31 | 2022-07-15 | 湖南大科激光有限公司 | Method for improving working stability of fiber laser |
| CN115528521A (en) * | 2022-09-07 | 2022-12-27 | 密尔医疗科技(深圳)有限公司 | Optical fiber laser |
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