Feedback type multi-wavelength fiber laser shaping and amplifying system

Abstract

The invention belongs to the technical field of laser application, and discloses a feedback type multi-wavelength optical fiber laser shaping and amplifying system which comprises a laser light source, an optical fiber frequency doubling device and a laser shaping and amplifying mechanism. The laser shaping and amplifying mechanism comprises a laser shaping and amplifying branch or more than two laser shaping and amplifying branches which are arranged in sequence; the laser shaping and amplifying branch comprises a feedback type laser shaping device and an optical fiber gain amplifying device; the optical fiber frequency doubling device is used for carrying out selective frequency conversion on fundamental frequency laser output by the laser light source; the feedback laser shaping device is used for carrying out waveform shaping on target wavelength laser; and the optical fiber gain amplification device is used for performing gain amplification on the shaped target wavelength laser. The device has the advantages of being simple in structure and high in expansibility, is suitable for being used in an optical fiber laser application system, and is used for modulating laser frequency, improving multi-wavelength laser waveforms and improving multi-wavelength laser output energy.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser applications, and relates to multi-wavelength laser frequency doubling, shaping, and amplification technologies, and particularly relates to a feedback multi-wavelength fiber laser shaping and amplification system. Background Art

[0002] With the further development of modern information application technologies, it has become an irresistible trend for future intelligent optoelectronic devices to be applied in multiple wavelengths, multiple elements, multiple functions, and multiple platforms. In particular, multi-wavelength and multi-function composite systems have become the focus of current development, and dual-wavelength and even multi-wavelength laser light sources with high power and high beam quality have become a realistic requirement for technological development. For example, dual-wavelength and even multi-wavelength lasers can be applied in important fields such as optical communication, optical computing, fine laser spectroscopy, laser color printing, interference rainbow holography, photodynamic medicine, environmental monitoring, lidar, laser remote sensing, and optoelectronic countermeasures.

[0003] In the field of traditional fiber lasers, high-quality, high-power, multi-wavelength fiber lasers have achieved great development. However, the optical path structure of the system is relatively complex, and the implementation steps are relatively cumbersome, which greatly limits the development in the research and development process of current and future multi-functional small integrated and integrated system products. In particular, in current fiber lasers, frequency doubling, amplification, and waveform shaping of lasers are more limited to single-wavelength lasers, and it is often difficult to perform the above-mentioned processing on multi-wavelength lasers through the same system. In other words, to obtain dual-wavelength or multi-wavelength lasers composed of fundamental-frequency lasers and frequency-doubled lasers with higher power and better waveforms, the usual method is to perform frequency doubling, amplification, and shaping on single-wavelength lasers, and then perform beam combining of single-wavelength laser beams. The disadvantage of this is that each single-wavelength laser itself has an independent optical path structure, plus the subsequent multi-source laser beam combining optical path structure, resulting in a relatively complex and large optical path structure for the final multi-wavelength laser, a large number of components, and a high cost, which is not conducive to the small and lightweight design of the system itself and subsequent system applications. Summary of the Invention

[0004] The purpose of the present invention aims to solve the problems in traditional fiber optical path systems, such as the difficulty in simultaneously realizing frequency conversion, distortion waveform optimization and shaping, and power amplification of multi-wavelength lasers. A feedback multi-wavelength fiber laser shaping and amplification system is provided, which can simultaneously perform fiber laser frequency up-conversion, Gaussian shaping of fiber laser waveforms, and amplification of fiber laser power or energy for multi-wavelength lasers to obtain high-power and high-quality laser output of multi-wavelength fiber lasers. The present invention provides a new idea for realizing the optimization, shaping, and amplification of multi-wavelength lasers, and provides basic technical support for the development of future multi-wavelength laser application technologies.

[0005] To achieve the above object, the present invention changes the traditional method for realizing multi-wavelength fiber lasers. For the first time, an optical path structure integrating flexible multi-stage frequency doubling, multi-stage gain amplification, multi-wavelength feedback waveform shaping, and multi-wavelength filtering is designed and integrated, so as to achieve the effects of simultaneous frequency doubling of multi-wavelength fiber lasers, simultaneous waveform shaping of multi-wavelength fiber lasers, simultaneous power amplification of multi-wavelength fiber lasers, and simultaneous filtering of multi-wavelength fiber lasers.

[0006] The present invention provides a feedback multi-wavelength fiber laser shaping and amplifying system, which includes a laser light source, a fiber frequency doubling device, and a laser shaping and amplifying mechanism; the laser shaping and amplifying mechanism includes one laser shaping and amplifying branch or two or more sequentially arranged laser shaping and amplifying branches; each laser shaping and amplifying branch has the same structure and includes a feedback laser shaping device and a fiber gain amplifying device; The laser light source is used to provide fundamental frequency lasers of more than one wavelength; The fiber frequency doubling device is used for selectively frequency converting the fundamental frequency laser output by the laser light source; the fiber frequency doubling device includes an optical fiber beam splitter, frequency doubling fiber optical paths and fundamental frequency fiber optical paths in two optical output directions behind the optical fiber beam splitter, and an optical fiber combiner; the frequency doubling fiber optical path includes multi-stage frequency doubling crystal fibers and a multi-wavelength fiber filter A; the multi-stage frequency doubling crystal fibers are used for frequency doubling the fundamental frequency laser, and the multi-stage frequency doubling crystal fibers are composed of one frequency doubling crystal fiber jumper or two or more frequency doubling crystal fiber jumpers connected in series, and each frequency doubling crystal fiber jumper corresponds to a laser of one wavelength; the frequency doubled laser after frequency doubling is filtered by the multi-wavelength fiber filter A and then transmitted to the optical fiber combiner; the fundamental frequency laser from the laser light source is directly transmitted to the optical fiber combiner through the fundamental frequency fiber optical path; the fundamental frequency laser and the frequency doubled laser input into the optical fiber combiner form a target wavelength laser; The feedback laser shaping device is used for shaping the waveform of the target wavelength laser; The fiber gain amplifying device is used for gain amplifying the shaped target wavelength laser.

[0007] When the laser shaping and amplifying mechanism includes two or more groups of laser shaping and amplifying branches, the target wavelength laser output by the previous laser shaping and amplifying branch is used as the input of the next laser shaping and amplifying branch, and the last laser shaping and amplifying branch outputs the final target wavelength laser.

[0008] In an implementable manner, the laser light source is a single-wavelength fiber laser or a multi-wavelength fiber laser; when the laser light source is a single-wavelength fiber laser, the wavelength of the output fundamental frequency laser is 1064 nm, 1550 nm, or 2 μm; when the laser light source is a multi-wavelength fiber laser, the wavelength of the output fundamental frequency laser is any two or three of 1064 nm, 1550 nm, and 2 μm.

[0009] In one realizable manner, the fiber frequency doubling device is used to perform selective frequency conversion on the laser output by the laser light source.

[0010] Furthermore, the fiber beam splitter is a 50:50 fiber beam splitter.

[0011] The basic principle of laser frequency doubling is that light with a frequency of ω passes through a frequency doubling medium to generate a frequency doubling effect. The output light contains a component of 2ω light, thereby obtaining a laser with a wavelength reduced by half. For example, a near-infrared laser of 1064 nm can obtain green light of 532 nm after passing through a KTP (potassium titanyl phosphate, KTiOPO4) frequency doubling medium. In the fiber optical path, this laser frequency doubling can be achieved through a frequency doubling crystal fiber.

[0012] The frequency doubling crystal fiber is an optical nonlinear fiber, mainly composed of a core and a cladding. Semiconductor nanocrystals or other high-nonlinearity media are mainly used as the fiber core, and its nonlinear effect is used to achieve frequency doubling and frequency conversion of optical signals. Common nonlinear crystal materials used for frequency doubling include KDP (potassium dihydrogen phosphate), BBO ( -barium borate), LBO (lithium triborate), and PPLN (periodically poled lithium niobate), etc. Compared with traditional nonlinear fibers, the frequency doubling crystal fiber has a higher nonlinear coefficient and lower loss, and can achieve more efficient optical signal conversion. The frequency doubling crystal fiber can be used in fields such as fiber frequency doubling and laser frequency conversion. Among them, fiber frequency doubling is the process of converting the fundamental frequency laser signal emitted by a laser into a high-frequency harmonic signal, and can be used in fields such as optical communication, optical sensing, and optical frequency standards. Laser frequency conversion is achieved by doubling the frequency of the input laser signal through a frequency doubling crystal fiber, and can be used in fields such as lidar, laser display, and laser medicine.

[0013] The frequency doubling crystal fiber includes a core A, a cladding A and a coating A that are sequentially coated outside the core A. The frequency doubling crystal fiber can be prepared by conventional methods already disclosed in the art or obtained by purchasing. The preparation method is, for example, prepared by the laser-heated pedestal drawing method.

[0014] Traditional fibers (such as silica fibers) usually cannot be directly used for frequency doubling due to the extremely weak second-order nonlinear effect caused by material symmetry. Therefore, in the fiber optical path to achieve frequency doubling, each frequency doubling fiber needs to be a polarization fiber or a photonic crystal fiber. Such fibers have the following characteristics: (a) Having a second-order nonlinear coefficient; this characteristic can be satisfied by material doping or periodic polarization to introduce an effective nonlinear response; (b) Satisfying the phase matching condition; this characteristic is mainly achieved by waveguide dispersion compensating material dispersion or by using the quasi-phase matching (QPM) technique (periodic polarization structure).

[0015] Based on the above analysis, for the 1064nm, 1550nm, and 2μm fundamental frequency lasers of the present invention, the frequency doubling crystal fiber is a frequency doubling crystal fiber based on KTP crystal, KDP crystal, BBO crystal, LBO crystal, or PPLN crystal; the core material is KTP crystal, KDP crystal, BBO crystal, LBO crystal, or PPLN crystal, and the frequency doubling of lasers with different wavelengths is achieved by adjusting the crystal orientation of the frequency doubling crystal; the cladding material uses the commonly used cladding materials for optical fibers in the art, such as quartz and silicate glass; the coating layer uses the conventional settings for optical fibers, such as being composed of acrylate, silicone rubber, and nylon. The diameter of the core A of the frequency doubling crystal fiber is designed to be 8μm - 30μm, the outer edge diameter of the cladding A is 125μm - 450μm, and the outer edge diameter of the coating layer A is 250μm - 650μm. By defining the core A material, core A diameter, cladding B diameter, etc. of the frequency doubling crystal fiber, the frequency doubling effect on the fundamental frequency laser can be improved.

[0016] To achieve effective frequency doubling of the frequency doubling optical fiber, in addition to selecting optical fiber materials that meet the requirements, it is also necessary to design the length of the frequency doubling crystal fiber. The calculation of the length of the frequency doubling crystal fiber is mainly carried out according to the following steps: (1) Through the dielectric constants ε ω and ε 2ω of the fundamental frequency laser or the frequency doubling laser in the medium, or through the law of refraction, the effective refractive indices of the fundamental frequency laser and the corresponding frequency doubling laser can be determined, which are n ω and n 2ω respectively, that is: , ; Among them, is the incident angle of the fundamental frequency laser or the frequency doubling laser on the surface of the medium, is the refraction angle of the fundamental frequency laser in the medium, is the refraction angle of the frequency doubling laser in the medium; (2) Calculate the phase mismatch ; is the wavelength of the fundamental frequency laser; When Δk≠0, the QPM technology needs to be adopted, and the polarization period is: ; (3) Calculate the length of the frequency doubling optical fiber; The most ideal phase matching is when Δk = 0, and the conversion efficiency is . The optimal length of the frequency doubling optical fiber is usually the accumulation of multiple polarization periods. For example, L = NΛ (N is the number of periods). The optimal length L of the frequency doubling crystal fiber is approximately: ; Among them,d eff is the effective nonlinear coefficient; I is the fundamental frequency laser intensity; η is the conversion efficiency, and ; P 2ω is the second harmonic generation laser power; P ω is the fundamental frequency laser power.

[0017] According to the calculation and statistical analysis of the effective lengths of second harmonic generation crystal fibers with different wavelengths, and fully considering the influence of the fiber length on the second harmonic generation effect, the effective length of the second harmonic generation crystal fiber designed by the present invention to meet the set requirements is 20 mm - 38 mm.

[0018] Therefore, the second harmonic generation crystal fiber jumper is composed of a second harmonic generation crystal fiber and fiber connectors A arranged at both ends of the second harmonic generation crystal fiber; adjacent two second harmonic generation crystal fiber jumpers are connected through a fiber coupler A. For the laser of which wavelength needs to be second harmonic generated, the corresponding second harmonic generation crystal fiber jumper is connected in series with the fiber coupler. In addition, each second harmonic generation crystal fiber jumper can transmit lasers with a wavelength range of 133 nm - 2 μm. For lasers with non - corresponding second harmonic generation wavelengths, except for having a certain power loss, no frequency conversion, or wavelength transformation, or gain amplification occurs.

[0019] Furthermore, a first fiber switch and a second fiber switch are respectively arranged on the second harmonic generation fiber optical path and the fundamental frequency fiber optical path; the first fiber switch is located before the multi - stage second harmonic generation crystal fiber; The first fiber switch and the second fiber switch are selectively turned on or off, and the fiber second harmonic generation device has three switch connection modes in total: (1) The first fiber switch and the second fiber switch are simultaneously turned on and connected; (2) The first fiber switch in the second harmonic generation fiber optical path is turned on and connected, and the second fiber switch in the fundamental frequency fiber optical path is turned off; (3) The first fiber switch in the second harmonic generation fiber optical path is turned off, and the second fiber switch in the fundamental frequency fiber optical path is turned on and connected.

[0020] The three switch connection modes respectively correspond to three output laser modes. When in the first connection mode, the fiber second harmonic generation device outputs by coupling: a mixed multi - wavelength output laser of the fundamental frequency laser output by the laser light source and the second harmonic generation laser converted by the multi - stage second harmonic generation crystal fiber; when in the second connection mode, the fiber second harmonic generation device outputs by coupling: the second harmonic generation laser converted by the multi - stage second harmonic generation crystal fiber; when in the third connection mode, the fiber second harmonic generation device outputs by coupling: the fundamental frequency laser output by the laser light source.

[0021] In an implementable manner, according to the requirements of laser waveform shaping and power amplification, the number of laser shaping and amplification branches in the multi-stage laser shaping and amplification mechanism is set. When the laser shaping and amplification mechanism includes one laser shaping and amplification branch, it is a first-stage laser shaping and amplification structure, which realizes two-time Gaussian shaping of the laser waveform, as well as one-time compensation and amplification of the laser power or energy. When the laser shaping and amplification mechanism includes N laser shaping and amplification branches, it realizes 2N-time Gaussian shaping of the laser waveform, as well as N-time compensation and amplification of the laser power or energy.

[0022] In an implementable manner, the feedback laser shaping device is used to perform Gaussian shaping on the input target-wavelength laser. The feedback laser shaping device includes an optical fiber circulator, a multi-wavelength optical fiber waveform shaper, and a Bragg optical fiber mirror. The laser input into the feedback laser shaping device enters the multi-wavelength optical fiber waveform shaper through the optical fiber circulator. The multi-wavelength optical fiber waveform shaper performs waveform shaping on the target-wavelength laser. The shaped target-wavelength laser is reflected by the Bragg optical fiber mirror and then undergoes a second waveform shaping by the multi-wavelength optical fiber waveform shaper. The target-wavelength laser after the second shaping is output through the optical fiber circulator.

[0023] Further, the optical fiber circulator includes port ①, port ②, and port ③. Port ① is the laser input end, port ② is docked with one end of the multi-wavelength optical fiber waveform shaper, and port ③ is the laser output end.

[0024] Further, the applicable wavelength range of the multi-wavelength optical fiber waveform shaper is 133 nm - 2 μm. It has multiple wavelength modulation channels inside, can simultaneously perform optimized modulation on the waveforms of lasers with multiple wavelengths, and is a two-way transmission device. No matter from which end the laser is input, the multi-wavelength optical fiber waveform shaper can perform Gaussian shaping on the laser, thereby achieving the purpose of improving the input laser waveform.

[0025] The laser waveform shaper mainly realizes precise control of the output waveform by regulating the time-domain or frequency-domain characteristics of the laser pulse. Its core principles include: Fourier transform principle, 4f system principle, phase and amplitude modulation principle, etc. The types of laser waveform shapers include: liquid crystal spatial light modulator, acousto-optic tunable filter, fiber-type shaper, etc.

[0026] Optical fiber waveform shapers typically include fiber acousto-optic modulators, electro-optic modulators, etc. On one hand, optical fiber waveform shapers can achieve the waveform shaping of fiber lasers through fiber nonlinear effects such as self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing, etc. For example, by using adiabatic soliton compression technology, soliton pulses can be generated and compressed in the optical fiber to obtain a high-quality optical pulse train. On the other hand, optical fiber waveform shapers can also achieve the purpose of waveform shaping of fiber lasers through dispersion characteristics; the principle is that based on the different propagation speeds of lasers with different wavelengths in the optical fiber, resulting in the broadening of their pulses, through reasonable design of the dispersion characteristics of the optical fiber, the broadening and compression of the pulses can be controlled, thereby achieving waveform shaping. For example, using dispersion compensation fiber (DCF) can offset the dispersion of conventional optical fiber, making the pulses remain compact and reducing distortion. By utilizing the nonlinear effects and dispersion effects of optical fiber, optical fiber waveform shapers can efficiently shape optical pulses within a wide wavelength range to meet the waveform shaping of multi-wavelength lasers.

[0027] The present invention uses a multi-wavelength optical fiber waveform shaper for waveform shaping of the laser. Generally, a multi-wavelength optical fiber waveform shaper is an optical device based on fiber grating technology, mainly used for precisely regulating the time-domain and frequency-domain characteristics of optical pulses; its main types include multi-phase shift multi-wavelength fiber gratings (MPS-MWFBG) and nonlinear effect assistance. The core of the multi-phase shift multi-wavelength fiber grating lies in the design of the multi-phase shift multi-wavelength fiber grating. By writing grating segments (i.e., Bragg gratings) with different periods on a single optical fiber and introducing controllable phase shifts between each segment, wavelength selection, amplitude adjustment, and phase matching of the input optical frequency beam can be achieved. Nonlinear effect matching refers to using nonlinear effects such as four-wave mixing (FWM) in some designs to suppress mode competition between multi-wavelengths and improve the stability and accuracy of the output waveform.

[0028] Specifically, the multi-wavelength optical fiber waveform shaper adopted in the present invention is a fiber acousto-optic modulator. This kind of fiber acousto-optic modulator is made of materials with high acousto-optic figure of merit and wide acoustic bandwidth (such as TeO2 is suitable for visible light / near-infrared, GaP is suitable for mid-infrared, etc.), and has designs such as multi-channel and wide frequency range. The present invention composes a feedback-type fiber laser shaping device with a fiber circulator, a fiber acousto-optic modulator, and a Bragg fiber mirror, which can achieve the waveform shaping of multi-wavelength lasers.

[0029] Furthermore, the applicable wavelength range of the Bragg fiber mirror is 133 nm - 2 μm, and the reflection efficiency is 99.9%.

[0030] In an implementable manner, the optical fiber gain amplifier compensates and amplifies the power or energy of the laser output by the feedback laser shaping device. The optical fiber gain amplifier comprises a wavelength division multiplexer, a multi-stage gain optical fiber and a multi-wavelength optical fiber filter B; the multi-stage gain optical fiber is composed of a gain optical fiber jumper or two or more gain optical fiber jumpers connected in series, each gain optical fiber jumper corresponds to a laser of a given wavelength band; each gain optical fiber jumper is configured with a corresponding pump source; the laser output by the pump source and the target wavelength laser are combined by the wavelength division multiplexer and then enter the multi-stage gain optical fiber to perform gain amplification on the target wavelength laser, and the target wavelength laser after gain amplification is filtered by the multi-wavelength optical fiber filter B.

[0031] The gain fiber can be a doped fiber or a photonic crystal fiber.

[0032] Doped fiber is a special fiber doped with trace rare earth elements, such as erbium (Er), ytterbium (Yb), praseodymium (Pr), thulium (Tm), etc., into the quartz glass matrix of conventional transmission fiber. It is also an active fiber. Pump light is the energy source that provides energy to the rare earth elements, so that the rare earth elements can achieve population inversion, which is one of the necessary conditions for light amplification. Wavelength division multiplexer (or optical coupler) is a device that combines signal light with pump light. Doped fiber is single-mode gain fiber or multi-mode gain fiber.

[0033] The following table shows the basic information of the four main doped optical fibers: erbium (Er), ytterbium (Yb), praseodymium (Pr), and thulium (Tm).

[0034] Table 1 Basic information of typical doped optical fibers

[0035] For some special bands, such as 532nm and 775nm lasers, different photonic crystal fibers can be used for direct gain amplification. For example, the photonic crystal fiber Raman amplifier is a nonlinear laser device based on the stimulated Raman scattering effect of optical fiber, and its operating wavelength is mainly determined by the pump source: (1) When the pump light wavelength is about 602nm-632nm (Raman gain bandwidth is about 70nm-100nm), and the photonic crystal fiber has good transmission and interaction characteristics for the pump light and the 532nm laser, the 532nm laser can obtain Raman gain and achieve amplification; (2) When the pump light wavelength is about 845nm-945nm (Raman gain bandwidth is about 70nm-100nm), and the photonic crystal fiber has good transmission and interaction characteristics for the pump light and the 775nm laser, the 775nm laser can obtain Raman gain and achieve amplification.

[0036] In the present invention, the gain fiber is obtained by outsourcing. The gain fiber includes a core B, a cladding B and a coating B that are successively coated outside the core B. The diameter of the core B is 8μm - 30μm, the outer edge diameter of the cladding B is 125μm - 450μm, and the outer edge diameter of the coating B is 250μm - 650μm.

[0037] For doped fibers, when designing the effective length of the gain fiber, the fiber doping concentration, the pump absorption wavelength, the pump absorption efficiency, and the threshold conditions need to be considered. To ensure that the pump light is fully absorbed, the length of the gain fiber needs to satisfy: ; where, L abs is the length of the gain fiber; η abs is the pump absorption efficiency (the typical target value is 90% - 99%); In () is the logarithmic function with base 10; Γ p is the overlap factor (the range is 0 - 1, about 0.8 for single - mode fibers, about 0.02 for double - clad fibers); σ abs is the pump absorption cross - section (about 2.5×10 -24 m 2 for ytterbium - doped fibers, about 1.0×10 -24 m 2 )).

[0038] N dop is the doping concentration.

[0039] For photonic crystal fibers, the nonlinear effects in the photonic crystal fibers need to be considered. The gain fiber length γ (unit: W -1 •m -1 ), the input optical power P 0 (unit: W), and the required nonlinear phase shift φ NL can be used to calculate the gain fiber length L abs , and the formula is: .

[0040] Based on the analysis and consideration of doped gain fibers with different wavelengths, and fully considering the influence of the fiber length on the gain effect, in order to enable the gain fiber to achieve a better gain effect, through calculation and statistics, the effective length of the gain fiber designed in the present invention to meet the set requirements is 40 cm - 3 m.

[0041] Combined with the above analysis, the gain fiber jumper provided by the present invention is composed of a gain fiber and fiber connectors B arranged at both ends of the gain fiber. Adjacent two kinds of gain fiber jumpers are connected by a fiber coupler B. To amplify the laser of which wavelength, the corresponding gain fiber jumper is connected in series with the fiber coupler. In addition, each kind of gain fiber jumper can transmit the laser with a wavelength range of 133 nm - 2 μm. For the laser with a non-corresponding gain wavelength, except for a certain power loss, no frequency conversion, or wavelength transformation, or gain amplification, or waveform transformation occurs.

[0042] In an implementable manner, there are two multi-wavelength fiber filters. One is located in the frequency-doubled fiber optical path of the fiber frequency-doubling device, after multiple stages of frequency-doubled crystal fibers, and is used to lock the central wavelengths corresponding to all frequency-doubled crystal fibers and filter out the laser with other wavelengths except these central wavelengths. The other is located in the fiber gain amplification device, after multiple stages of gain fibers, and is used to lock the central wavelengths corresponding to all gain fibers and filter out the laser with other wavelengths except these central wavelengths.

[0043] A multi-wavelength fiber filter is an optical device that can simultaneously select or process multiple specific wavelength optical signals. Its principle is to design multiple narrow-band filtering channels within a wide wavelength range. Each narrow-band channel corresponds to a specified gain, and this gain corresponds to a specific laser wavelength. Therefore, each filtering channel can filter a specific wavelength laser, and through an integrated design of multiple narrow-band filtering channels, simultaneous filtering of multi-wavelength lasers can be achieved. Multi-wavelength fiber filters have important applications in the fields of optical communication, fiber lasers, spectral analysis, laser cutting, laser painting, etc. The multi-wavelength fiber filter mainly realizes multi-wavelength selection through physical structure design or optical effects, and its core mechanisms include: (a) Interference and diffraction: Utilize the interference effect of light (such as Fabry-Perot cavity) or the diffraction characteristics of gratings (such as fiber Bragg grating) to selectively transmit or reflect different wavelengths.

[0044] (b) Coupling modulation: The dual-core fiber filter realizes selective absorption or reflection of multiple wavelengths by adjusting the coupling strength between the two cores.

[0045] (c) Grating periodic structure: For example, a chirped moiré grating reflects a specific wavelength through a periodic concave-convex structure. When its period matches the target wavelength, multi-wavelength filtering can be achieved.

[0046] At present, the main types of multi-wavelength fiber filters include: twin-core fiber filters, fiber Bragg gratings (FBGs), chirped moiré grating filters, and thin-film filters (TFFs). Twin-core fiber filters are mainly based on the coupling effect of twin-core fibers. By adjusting the distance between the two cores or the external stress, the coupling strength is changed to achieve multi-wavelength selection. Fiber Bragg gratings (FBGs) form periodic refractive index changes in the fiber to reflect specific wavelengths. By designing a multi-segment grating structure, multi-wavelength filtering is achieved. Chirped moiré grating filters utilize the gradually varying period structure of chirped gratings to reflect optical signals of different wavelengths and achieve filtering over a wide wavelength range. In the specific embodiments of the present invention, a twin-core fiber filter is mainly used for multi-wavelength filtering.

[0047] All fiber devices are connected through transmission fibers. Except for the laser light source and the multi-wavelength fiber filter, all fiber devices and transmission fibers can transmit laser light with a wavelength range of 133 nm - 2 μm. The transmission fiber uses traditional quartz fiber; the core C diameter of the transmission fiber is designed to be 8 μm - 30 μm, the outer edge diameter of the cladding C is designed to be 125 μm - 450 μm, and the outer edge diameter of the coating C is designed to be 250 μm - 650 μm. That is to say, in the same system, the core diameters, cladding diameters, and coating diameters of the frequency doubling crystal fiber, the gain fiber, and the transmission fiber are all the same.

[0048] In the entire optical path, the laser energy output by the previous device is less than the laser energy threshold that the adjacent next device can withstand.

[0049] Compared with the prior art, the feedback multi-wavelength fiber laser shaping and amplification system provided by the present invention for the first time designs and integrates a fiber optical path structure that combines flexible multi-stage frequency doubling, multi-stage gain amplification, multi-wavelength feedback waveform shaping, and multi-wavelength filtering, thereby achieving simultaneous frequency doubling of multi-wavelength fiber lasers, simultaneous shaping of multi-wavelength fiber laser waveforms, simultaneous amplification of multi-wavelength fiber laser powers, and the effect of multi-wavelength fiber laser filtering; specifically manifested as: (1) The present invention simultaneously realizes the composite functions of selective frequency up-conversion of multi-wavelength fiber lasers, waveform modulation and shaping of multi-wavelength fiber lasers, gain amplification of multi-wavelength fiber lasers, and multi-wavelength fiber laser filtering through a set of fiber optical path structures, providing a new idea for realizing the shaping and amplification of multi-wavelength fundamental lasers, frequency-doubled lasers, or fundamental laser - frequency-doubled lasers; (2) The present invention solves the problem that the output laser peak power of the amplifier is limited due to the waveform distortion of the previous pulsed laser, which deviates far from the Gaussian type, through a feedback laser shaping device; it can effectively improve the single-pulse energy of the laser and enhance the laser application effect; (3) The present invention breaks through the bottleneck of the previous method of doubling the frequency of a single-wavelength laser separately and then achieving the output of multi-wavelength frequency-doubled laser through laser beam combination, making the way to obtain multi-wavelength frequency-doubled laser more concise; (4) The present invention breaks through the bottleneck of the previous single-wavelength fiber laser gain amplification, providing a new idea for the simultaneous gain of multi-wavelength fiber lasers; (5) The structure of the present invention is simple and easy to build; moreover, the number of frequency-doubling crystal fiber jumpers, gain fiber jumpers, etc. can be increased or decreased according to needs, and it has strong expandability and flexibility.

[0050] It should be noted here that the single wavelength or multi-wavelength mentioned in the present invention both refer to the central wavelength. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a feedback multi-wavelength fiber laser shaping and amplifying system provided by Embodiment 1 of the present invention; Figure 2 It is a schematic structural diagram of a single frequency-doubling crystal fiber jumper in Embodiment 1; Figure 3 It is a schematic connection diagram of two frequency-doubling crystal fiber jumpers in Embodiment 1; Figure 4 It is a schematic structural diagram of a single gain fiber jumper; Figure 5 It is a schematic connection diagram of four gain fiber jumpers; Figure 6 It is a feedback multi-wavelength fiber laser shaping and amplifying system provided by Embodiment 2 of the present invention; Figure 7 It is a feedback multi-wavelength fiber laser shaping and amplifying system provided by Embodiment 3 of the present invention; In the figure, 1 - laser light source; 2 - fiber frequency-doubling device; 21 - fiber beam splitter; 22 - fiber combiner; 23 - multi-stage frequency-doubling crystal fiber; 231 - frequency-doubling crystal fiber; 232 - fiber connector A; 233 - fiber coupler A; 24 - multi-wavelength fiber filter A; 25 - first fiber switch; 26 - second fiber switch; 3 - feedback laser shaping device; 31 - fiber circulator; 32 - multi-wavelength fiber waveform shaper; 33 - Bragg fiber mirror; 4 - fiber gain amplification device; 41 - wavelength division multiplexer; 42 - multi-stage gain fiber; 421 - gain fiber; 422 - fiber connector B; 423 - fiber coupler B; 43 - multi-wavelength fiber filter B; 44 - pump source. DETAILED DESCRIPTION OF THE INVENTION

[0052] To make the objectives, technical solutions and advantages of the present invention more clear, the technical solutions of the present invention will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other implementation manners obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope protected by the present invention.

[0053] Embodiment 1 This embodiment provides a feedback multi-wavelength fiber laser shaping and amplifying system, which includes a laser light source 1, a fiber frequency doubling device 2 and a laser shaping and amplifying mechanism; the laser shaping and amplifying mechanism includes a laser shaping and amplifying branch; this laser shaping and amplifying branch includes a feedback laser shaping device 3 and a fiber gain amplifying device 4.

[0054] In this embodiment, the laser light source 1 is used to provide fundamental frequency lasers of more than one wavelength. The laser light source 1 is a single-wavelength fiber laser or a multi-wavelength fiber laser. When the laser light source 1 is a single-wavelength fiber laser, the wavelength of the output fundamental frequency laser is 1064 nm, 1550 nm or 2 μm; when the laser light source 1 is a multi-wavelength fiber laser, the wavelength of the output fundamental frequency laser is any two or three of 1064 nm, 1550 nm, 2 μm.

[0055] In this embodiment, the fiber frequency doubling device 2 is used to perform selective frequency conversion on the fundamental frequency laser output by the laser light source. The fiber frequency doubling device 2 includes a fiber splitter 21, a frequency doubling fiber optical path and a fundamental frequency fiber optical path in two light output directions behind the fiber splitter 21, and a fiber combiner 22. The frequency doubling fiber optical path includes multiple stages of frequency doubling crystal fibers 23 and a multi-wavelength fiber filter A 24.

[0056] In this embodiment, the fiber splitter 21 used is a 50 / 50 fiber splitter.

[0057] In this embodiment, a first fiber switch 25 and a second fiber switch 26 are respectively arranged on the frequency doubling fiber optical path and the fundamental frequency fiber optical path; the first fiber switch 25 is located before the multiple stages of frequency doubling crystal fibers 23. The frequency doubling fiber optical path is used to perform frequency doubling processing on the fundamental frequency laser entering this optical path, and the fundamental frequency fiber optical path only determines whether to allow the fundamental frequency laser to pass through.

[0058] When the first fiber switch 25 and the second fiber switch 26 are both turned on, the fundamental frequency laser after passing through the fiber splitter 21 is divided into two paths, one of which enters the frequency doubling fiber optical path for frequency doubling processing, and the other enters the fundamental frequency fiber optical path; the frequency doubling laser output by the frequency doubling fiber optical path and the fundamental frequency laser output by the fundamental frequency fiber optical path are combined by the fiber combiner 22 and output as the target wavelength laser.

[0059] The multi-stage frequency doubling crystal optical fiber 23 is used for frequency doubling the fundamental frequency laser. The multi-stage frequency doubling crystal optical fiber 23 is composed of a frequency doubling crystal optical fiber jumper or two or more frequency doubling crystal optical fiber jumpers connected in series, and each frequency doubling crystal optical fiber jumper corresponds to a laser of a certain wavelength.

[0060] Figure 2 A structural schematic diagram of a frequency doubling crystal optical fiber jumper is given; the frequency doubling crystal optical fiber jumper includes a frequency doubling crystal optical fiber 231 and fiber connectors A 232 arranged at both ends of the frequency doubling crystal optical fiber.

[0061] Figure 3 A structural schematic diagram of a multi-stage frequency doubling crystal optical fiber formed by connecting two frequency doubling crystal optical fiber jumpers in series is given; each frequency doubling crystal optical fiber jumper is composed of a frequency doubling crystal optical fiber 231 and fiber connectors A 232 arranged at both ends of the frequency doubling crystal optical fiber. The two frequency doubling crystal optical fiber jumpers are connected through a fiber coupler A 233; during use, just insert the fiber connectors A 232 of the two frequency doubling crystal optical fiber jumpers into the fiber coupler A 233.

[0062] The above-mentioned frequency doubling crystal optical fiber 231 includes a core A, a cladding A and a coating A that are sequentially coated outside the core A. The core material is KTP crystal, KDP crystal, BBO crystal, LBO crystal or PPLN crystal, and frequency doubling of lasers with different wavelengths is achieved by adjusting the crystal orientation of the frequency doubling crystal; the diameter of the core A is designed to be 8μm - 30μm, the outer edge diameter of the cladding A is 125μm - 450μm, and the outer edge diameter of the coating A is 250μm - 650μm; the effective length of the frequency doubling crystal optical fiber is 20mm - 38mm, and the frequency doubling crystal optical fiber can be obtained by the method for determining the length of the frequency doubling crystal optical fiber given above.

[0063] The frequency doubled laser after frequency doubling processing is transmitted to the fiber combiner 22 after being filtered by the multi-wavelength fiber filter A 24. The fundamental frequency laser from the laser light source 1 is directly transmitted to the fiber combiner 22 through the fundamental frequency fiber optical path. The fundamental frequency laser and the frequency doubled laser input into the fiber combiner 22 form a target wavelength laser and are output to the feedback type laser shaping device 3.

[0064] In this embodiment, the feedback type laser shaping device 3 is used for waveform shaping of the target wavelength laser. The feedback type laser shaping device 3 includes an optical fiber circulator 31, a multi-wavelength fiber waveform shaper 32 and a Bragg fiber mirror 33. The multi-wavelength fiber waveform shaper 32 uses an optical fiber acousto-optic modulator.

[0065] The target wavelength laser is input through port ① of the fiber optic circulator 31 and output from port ② of the fiber optic circulator 31 into the multi-wavelength fiber waveform shaper 32. The multi-wavelength fiber waveform shaper 32 shapes the waveform of the target wavelength laser. The shaped target wavelength laser is reflected by the Bragg fiber mirror 33 and then undergoes a second waveform shaping by the multi-wavelength fiber waveform shaper 32. The target wavelength laser after the second waveform shaping is input through port ② of the fiber optic circulator 31 and output from port ③ to the fiber optic gain amplifier 4.

[0066] The fiber optic gain amplifier 4 is used to amplify the gain of the shaped target wavelength laser. The fiber optic gain amplifier 4 includes a wavelength division multiplexer 41, a multi-stage gain fiber 42, and a multi-wavelength fiber filter B 43.

[0067] The multi-stage gain fiber 42 is composed of a gain fiber jumper or two or more gain fiber jumpers connected in series. Each gain fiber jumper corresponds to a laser in a given wavelength band.

[0068] Figure 4 A schematic structural diagram of a gain fiber jumper is given; the gain fiber jumper is composed of a gain fiber 421 and fiber connectors B 422 provided at both ends of the gain fiber.

[0069] Figure 5 A schematic structural diagram of a multi-stage gain fiber composed of four gain fiber jumpers is given. All four gain fiber jumpers are composed of a gain fiber 421 and fiber connectors B 422 provided at both ends of the gain fiber; adjacent two gain fiber jumpers are connected by a fiber coupler B 423; during use, just insert the fiber connectors B 422 of the two gain fiber jumpers into the fiber coupler B 423.

[0070] The above-mentioned gain fiber 421 is a doped fiber doped with rare earth elements or a photonic crystal fiber; if the gain fiber 421 is a doped fiber, the doping element is at least one of erbium, ytterbium, and thulium. Specifically, the doped fiber can be a single-mode gain fiber (such as doped fibers like EDFA, YDFZ, etc.), or a multi-mode gain fiber (such as a double-clad fiber amplifier doped with Yb 3+ and Er 3+ etc.).

[0071] The above-mentioned gain fiber 421 includes a core B, a cladding B and a coating B sequentially coated outside the core B. The diameter of the core B is 8μm - 30μm, the outer edge diameter of the cladding B is 125μm - 450μm, and the outer edge diameter of the coating B is 250μm - 650μm; the effective length of the gain fiber is 40cm - 3m. It can be obtained by the gain fiber length determination method given above.

[0072] Each gain fiber jumper configuration has a corresponding pump source 44. The laser output by the pump source 44 and the target wavelength laser are combined by a wavelength division multiplexer 41 and then enter a multi-stage gain fiber 42 to amplify the target wavelength laser. The amplified target wavelength laser is then filtered by a multi-wavelength fiber filter B 43 to obtain the final target wavelength laser.

[0073] Embodiment 2

[0074] This embodiment is a further improvement based on Embodiment 1.

[0075] The feedback multi-wavelength fiber laser shaping and amplifying system provided in this embodiment, as Figure 6 shown, includes a laser light source 1, a fiber frequency doubling device 2, and a laser shaping and amplifying mechanism; the laser shaping and amplifying mechanism includes two sequentially arranged laser shaping and amplifying branches with the same structure. Each laser shaping and amplifying branch includes a feedback laser shaping device 3 and a fiber gain amplifying device 4.

[0076] The structures of the above laser light source 1, fiber frequency doubling device 2, feedback laser shaping device 3, and fiber gain amplifying device 4 are the same as those in Embodiment 1.

[0077] The fundamental frequency laser output by the laser light source 1 is input into the fiber frequency doubling device 2. After passing through the fiber splitter 21, the fundamental frequency laser is divided into two paths. One path of the fundamental frequency laser enters the frequency doubling fiber optical path for frequency doubling processing, and the other path of the fundamental frequency laser enters the fundamental frequency fiber optical path; the frequency doubled laser output by the frequency doubling fiber optical path and the fundamental frequency laser output by the fundamental frequency fiber optical path are combined by a fiber combiner 22 and output as the target wavelength laser. The target wavelength laser output by the fiber frequency doubling device 2 is input into the first laser shaping and amplifying branch for primary waveform shaping and power amplification, and the target wavelength laser output by the first laser shaping and amplifying branch is input into the second laser shaping and amplifying branch for secondary waveform shaping and power amplification to obtain the final target wavelength laser.

[0078] Embodiment 3

[0079] This embodiment is a further improvement based on Embodiment 1 or Embodiment 2.

[0080] The feedback multi-wavelength fiber laser shaping and amplifying system provided in this embodiment, as Figure 7 shown, includes a laser light source 1, a fiber frequency doubling device 2, and a laser shaping and amplifying mechanism. The laser shaping and amplifying mechanism includes three sequentially arranged laser shaping and amplifying branches with the same structure. Each laser shaping and amplifying branch includes a feedback laser shaping device 3 and a fiber gain amplifying device 4.

[0081] The structures of the above laser light source 1, fiber frequency doubling device 2, feedback laser shaping device 3, and fiber gain amplifying device 4 are the same as those in Embodiment 1.

[0082] The fundamental frequency laser output by the laser light source 1 is input into the fiber frequency doubling device 2. After passing through the fiber beam splitter 21, the fundamental frequency laser is divided into two paths. One path of the fundamental frequency laser enters the frequency doubling fiber optical path for frequency doubling processing, and the other path of the fundamental frequency laser enters the fundamental frequency fiber optical path; the frequency doubled laser output by the frequency doubling fiber optical path and the fundamental frequency laser output by the fundamental frequency fiber optical path are combined by the fiber combiner 22 and output as the target wavelength laser. The target wavelength laser output by the fiber frequency doubling device 2 is input into the first laser shaping and amplifying branch for primary waveform shaping and power amplification. The target wavelength laser output by the first laser shaping and amplifying branch is input into the second laser shaping and amplifying branch for secondary waveform shaping and power amplification. The target wavelength laser output by the second laser shaping and amplifying branch is input into the third laser shaping and amplifying branch for tertiary waveform shaping and power amplification to obtain the final target wavelength laser.

[0083] Application Example 1 Based on the feedback multi-wavelength fiber laser shaping and amplifying system provided in Embodiment 3, this application example performs simultaneous frequency doubling processing on 1064 nm and 1550 nm, combines with the fundamental frequency laser to form the target wavelength laser, and performs synchronous shaping and power amplification to obtain the final target wavelength laser.

[0084] Therefore, the laser light source 1 is a dual-wavelength fiber laser, which outputs fundamental frequency lasers with wavelengths of 1064 nm and 1550 nm respectively. The multi-stage frequency doubling crystal fiber 23 is composed of two frequency doubling crystal fiber jumpers for frequency doubling at wavelengths of 1064 nm and 1550 nm respectively, which are connected in series and coupled. In the frequency doubling crystal fiber jumper for frequency doubling at the 1064 nm wavelength, the core material of the frequency doubling crystal fiber is KTP crystal, and the effective length of the frequency doubling crystal fiber is 37 mm; in the frequency doubling crystal fiber jumper for frequency doubling at the 1550 nm wavelength, the core material of the frequency doubling crystal fiber is PPLN crystal, and the effective length of the frequency doubling crystal fiber is 20 mm. The multi-stage gain fiber 42 is composed of an EDFA gain fiber jumper (corresponding to the working band of 1550 nm), a YDFA gain fiber jumper (corresponding to the working band of 1030 - 1080 nm), a photonic crystal gain fiber jumper for 532 nm, and a photonic crystal gain fiber jumper for 775 nm; the effective length of the gain fiber in the EDFA gain fiber jumper is 1.2 m, the effective length of the gain fiber in the YDFA gain fiber jumper is 1.4 m, the effective length of the gain fiber in the photonic crystal gain fiber jumper for 532 nm is 80 cm, and the effective length of the gain fiber in the photonic crystal gain fiber jumper for 775 nm is 80 cm. In this application example, the core diameters, outer cladding edge diameters, and outer coating edge diameters of the frequency doubling crystal fiber, the gain fiber, and the transmission fiber are the same; specifically, the core A of the frequency doubling crystal fiber, the core B of the gain fiber, and the core C of the transmission fiber all have a diameter of 20 μm; the outer cladding edge diameters of the cladding A of the frequency doubling crystal fiber, the cladding B of the gain fiber, and the cladding C of the transmission fiber are all 400 μm; the outer coating edge diameters of the coating A of the frequency doubling crystal fiber, the coating B of the gain fiber, and the coating C of the transmission fiber are all 550 μm.

[0085] During operation, the 1064 nm and 1550 nm wavelength lasers output by the laser light source 1 are combined. At the same time, the first fiber optic switch 25 and the second fiber optic switch 26 are turned on. After the 1064 nm and 1550 nm wavelength hybrid laser passes through the 50 / 50 fiber optic splitter 21, it is divided into two paths for transmission. One path of the light beam is transmitted through the fundamental frequency fiber optic path, and the other path of the light beam is transmitted through the frequency-doubled fiber optic path. In the frequency-doubled fiber optic path, the 1064 nm and 1550 nm wavelength hybrid fundamental frequency laser after passing through the first fiber optic switch 25, after passing through the multi-stage frequency-doubled crystal fiber 23, the obtained frequency-doubled lasers of 532 nm and 775 nm are output by locking these two wavelengths through the multi-wavelength fiber optic filter A 24. And the laser after passing through the second fiber optic switch 26 in the fundamental frequency fiber optic path is still the 1064 nm and 1550 nm wavelength fundamental frequency laser. The frequency-doubled laser and the fundamental frequency laser pass through the fiber optic combiner 22 to obtain the target wavelength laser output containing the four wavelengths of 532 nm, 775 nm, 1064 nm and 1550 nm. These lasers enter the first laser shaping and amplification branch, are input from the ① port of the fiber optic circulator 31 therein, and are output from the ② port of the fiber optic circulator 31, and enter the multi-wavelength fiber optic waveform shaper 32. The multi-wavelength fiber optic waveform shaper 32 has waveform modulation channels for the four wavelengths of 532 nm, 775 nm, 1064 nm and 1550 nm, and can independently modulate the waveforms of these four wavelengths of lasers. The target wavelength laser after modulation output then enters the Bragg fiber optic mirror 33, and most of it is reflected by the Bragg fiber optic mirror 33 and transmitted back into the multi-wavelength fiber optic waveform shaper 32 in the reverse direction. The waveforms of the four wavelengths of 532 nm, 775 nm, 1064 nm and 1550 nm lasers after reflection are modulated and shaped again by the multi-wavelength fiber optic waveform shaper 32, making them closer to the Gaussian shape, and are input from the ② port of the fiber optic circulator 31 through the transmission fiber and output from the ③ port of the fiber optic circulator 31. The target wavelength laser after output is coupled with the pump source 44 laser corresponding to each gain fiber jumper in the multi-stage gain fiber through the wavelength division multiplexer 41 into the multi-stage gain fiber 42, increasing the power of these four wavelengths of lasers. Finally, these four target wavelength lasers are locked through the multi-wavelength fiber optic filter B, filtering out other stray light.

[0086] In the above manner, the four target wavelength lasers of 532 nm, 775 nm, 1064 nm and 1550 nm are subjected to secondary waveform shaping and power amplification through the second laser shaping and amplification branch, and then subjected to tertiary waveform shaping and power amplification through the third laser shaping and amplification branch, and then the four target wavelength lasers of 532 nm, 775 nm, 1064 nm and 1550 nm that have undergone a total of six times of waveform shaping and three times of energy / power amplification are obtained, and the deviation between the central wavelength and the target wavelength does not exceed 10 nm.

[0087] In summary, the feedback multi-wavelength fiber laser shaping and amplification system provided by the present invention has the following remarkable features: (1) Simultaneously achieving frequency modulation, waveform modulation and shaping, and power amplification of multi-wavelength lasers through a set of fiber optical path structures; (2) Improving the laser waveform; (3) Simultaneously achieving frequency modulation of multi-wavelength lasers; (4) Simultaneously achieving gain amplification of multi-wavelength lasers; (5) Simple structure and convenient setup; (6) Strong expandability and flexibility.

[0088] Those of ordinary skill in the art will realize that the embodiments described herein are for helping the reader understand the principles of the present invention, and it should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific deformations and combinations that do not depart from the essence of the present invention based on the technical revelations disclosed in the present invention, and these deformations and combinations are still within the protection scope of the present invention.

Claims

1. A feedback multi-wavelength fiber laser shaping and amplification system, characterized in that: It comprises a laser light source (1), an optical fiber frequency doubling device (2) and a laser shaping and amplifying mechanism; the laser shaping and amplifying mechanism comprises one laser shaping and amplifying branch or two or more laser shaping and amplifying branches arranged in sequence; each laser shaping and amplifying branch has the same structure and comprises a feedback laser shaping device (3) and an optical fiber gain amplifying device (4); The laser light source (1) is used to provide a fundamental frequency laser with more than one wavelength; The optical fiber frequency doubling device (2) is used to selectively perform frequency conversion on the fundamental frequency laser output by the laser light source; the optical fiber frequency doubling device (2) comprises an optical fiber beam splitter (21), a frequency doubling optical fiber optical path and a fundamental frequency optical fiber optical path located in two light output directions after the optical fiber beam splitter (21), and an optical fiber combiner (22); the frequency doubling optical fiber optical path comprises a multi-stage frequency doubling crystal fiber (23) and a multi-wavelength optical fiber filter A (24); the multi-stage frequency doubling crystal fiber (23) is used to perform frequency doubling processing on the fundamental frequency laser, the multi-stage frequency doubling crystal fiber (23) is used to perform frequency doubling processing on the fundamental frequency laser, and the multi-stage frequency doubling crystal fiber (24) is used to perform frequency doubling processing on the fundamental frequency laser. The frequency-doubling crystal fiber (23) is composed of a frequency-doubling crystal fiber jumper or two or more frequency-doubling crystal fiber jumpers connected in series, each frequency-doubling crystal fiber jumper corresponds to a laser of a wavelength; the frequency-doubling laser after frequency doubling is filtered by a multi-wavelength optical fiber filter A (24) and then transmitted to the optical fiber combiner (22); the fundamental frequency laser from the laser light source (1) is directly transmitted to the optical fiber combiner (22) via the fundamental frequency optical fiber optical path; the fundamental frequency laser and the frequency-doubling laser input to the optical fiber combiner (22) constitute the target wavelength laser; The feedback laser shaping device (3) is used to perform waveform shaping on the target wavelength laser; The optical fiber gain amplification device (4) is used to perform gain amplification on the shaped target wavelength laser.

2. The feedback multi-wavelength fiber laser shaping and amplification system according to claim 1, characterized in that: The laser light source (1) is a single-wavelength fiber laser or a multi-wavelength fiber laser; when the laser light source (1) is a single-wavelength fiber laser, the wavelength of the output fundamental frequency laser is 1064nm, 1550nm or 2μm; when the laser light source is a multi-wavelength fiber laser, the wavelength of the output fundamental frequency laser is any two or three of 1064nm, 1550nm and 2μm.

3. The feedback multi-wavelength fiber laser shaping and amplification system according to claim 1, characterized in that: The frequency doubling crystal fiber jumper consists of a frequency doubling crystal fiber (231) and optical fiber connectors A (232) arranged at both ends of the frequency doubling crystal fiber; two adjacent frequency doubling crystal fiber jumpers are connected via an optical fiber coupler A (233).

4. The feedback multi-wavelength fiber laser shaping and amplification system according to claim 3, characterized in that: The frequency doubling crystal fiber (231) comprises a core A, a cladding A and a coating A which are sequentially coated outside the core A; the core material is KTP crystal, KDP crystal, BBO crystal, LBO crystal or PPLN crystal; the core A has a diameter of 8 μm-30 μm, the outer edge diameter of the cladding A is 125 μm-450 μm, and the outer edge diameter of the coating A is 250 μm-650 μm; and the effective length of the frequency doubling crystal fiber is 20 mm-38 mm.

5. The feedback multi-wavelength fiber laser shaping and amplification system according to claim 1, characterized in that: A first optical fiber switch (25) and a second optical fiber switch (26) are respectively arranged on the frequency doubling optical fiber path and the baseband optical fiber path; the first optical fiber switch (25) is located before the multi-stage frequency doubling crystal optical fiber (23).

6. The feedback multi-wavelength fiber laser shaping and amplification system according to claim 1, characterized in that: The feedback laser shaping device (3) comprises an optical fiber circulator (31), a multi-wavelength optical fiber waveform shaper (32) and a Bragg optical fiber reflector (33); the laser light input into the feedback laser shaping device (3) enters the multi-wavelength optical fiber waveform shaper (32) via the optical fiber circulator (31), the multi-wavelength optical fiber waveform shaper (32) performs waveform shaping on the target wavelength laser light, the shaped target wavelength laser light is reflected by the Bragg optical fiber reflector (33) and then undergoes a second waveform shaping by the multi-wavelength optical fiber waveform shaper (32), and the target wavelength laser light after the second waveform shaping is output via the optical fiber circulator (31).

7. The feedback multi-wavelength fiber laser shaping and amplification system according to claim 1, characterized in that: The optical fiber gain amplification device (4) comprises a wavelength division multiplexer (41), a multi-stage gain optical fiber (42) and a multi-wavelength optical fiber filter B (43); the multi-stage gain optical fiber (42) is composed of a gain optical fiber jumper or two or more gain optical fiber jumpers connected in series, each gain optical fiber jumper corresponds to a laser of a given wavelength band; each gain optical fiber jumper is configured with a corresponding pump source (44); the laser output by the pump source (44) and the target wavelength laser are combined through the wavelength division multiplexer (41) and then enter the multi-stage gain optical fiber (42), and the target wavelength laser is gain amplified. The target wavelength laser after gain amplification is then filtered by the multi-wavelength optical fiber filter B (43).

8. The feedback multi-wavelength fiber laser shaping and amplification system according to claim 7, characterized in that: The gain optical fiber jumper is composed of a gain optical fiber (421) and optical fiber connectors B (422) arranged at both ends of the gain optical fiber; two adjacent gain optical fiber jumpers are connected via an optical fiber coupler B (423).

9. The feedback multi-wavelength fiber laser shaping and amplification system according to claim 8, characterized in that: The gain optical fiber (421) is a doped optical fiber or a photonic crystal optical fiber doped with a rare earth element; if the gain optical fiber (421) is a doped optical fiber, the doping element is at least one of erbium, ytterbium and thulium.

10. The feedback multi-wavelength fiber laser shaping and amplification system according to claim 9, characterized in that: The gain optical fiber (421) is a single-mode gain optical fiber or a multi-mode gain optical fiber; the gain optical fiber (421) comprises a core B, a cladding B and a coating B which are sequentially coated outside the core B; the diameter of the core B is 8 μm-30 μm, the outer edge diameter of the cladding B is 125 μm-450 μm, and the outer edge diameter of the coating B is 250 μm-650 μm; the effective length of the gain optical fiber (421) is 40 cm-3 m.

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