High-power and large-energy super-continuum spectrum fiber laser

Abstract

The invention discloses a super-continuum spectrum fiber laser, which adopts two optimized technical paths to respectively realize high average power and high monopulse energy output. According to the first scheme, a high-repetition-frequency pulse seed source is adopted, continuous or high-repetition-frequency pumping amplification is carried out through an ultra-large mode field active optical fiber amplifier, and high-average-power laser is obtained. According to the second scheme, a low-repetition-frequency and high-pulse-energy seed source is adopted, synchronous pulse pumping amplification is carried out through an ultra-large-mode-field active optical fiber amplifier, and high-single-pulse-energy laser is obtained. According to the two schemes, an amplified light beam is coupled to a high-nonlinearity multimode optical fiber, the optical fiber has parabolic gradient refractive index distribution, the light beam quality is optimized while wide spectrum broadening is achieved through the nonlinear space self-cleaning effect, and finally high-brightness and wide-spectrum super-continuum light is output. The system has an all-fiber structure, has high-power / large-energy bearing capacity and excellent light beam quality, and is suitable for the fields of spectral analysis, biological imaging, laser processing and the like.

Description

Technical Field

[0001] This invention relates to the field of fiber laser technology, and more specifically to a supercontinuum fiber laser. Background Technology

[0002] Supercontinuum fiber optic sources, due to their ultra-wideband and continuous spectral characteristics, have wide applications in precision measurement, spectroscopy, lidar, and biomedical imaging. However, different application scenarios place different demands on the performance of the light source: high average power is required in applications such as high-speed frequency sweeping and material processing to improve the signal-to-noise ratio and processing efficiency; while high single-pulse energy is required in applications such as time-resolved spectroscopy and long-range detection to ensure the working distance and detection sensitivity. Most existing supercontinuum light sources are based on highly nonlinear photonic crystal fibers, which broaden the input pulse to form a wide spectrum output through strong nonlinear effects. However, photonic crystal fiber (PCF) solutions have significant limitations in applications that pursue high power and high energy: their microstructure fiber core diameter is small, making it difficult to effectively couple and transmit laser pulses with high average power or high single-pulse energy; at the same time, the strong nonlinearity and thermal effects inside the fiber are prone to damage, resulting in a low laser damage threshold for the system. In addition, PCF end faces are fragile and have large splice losses, which is not conducive to achieving fiber-based integration, leading to complex structures and insufficient reliability. Therefore, although PCF exhibits excellent nonlinear characteristics in laboratory research, its application in engineering systems such as high-power and high-energy systems is significantly limited.

[0003] On the other hand, rare-earth-doped active fibers are currently the core medium for high-power fiber amplification and high-energy pulse amplification. They provide gain through stimulated emission of rare-earth ions, achieving high average power output in the hundreds of watts or even kilowatts under continuous or high repetition frequency operation; and in low repetition frequency pulse operation, they can achieve large single-pulse energy output in the millijoules or even higher range. To further enhance energy carrying capacity, researchers have proposed using ultra-large mode field fibers, significantly reducing the light intensity per unit area by increasing the core diameter, thereby increasing the laser damage threshold of the fiber and allowing for higher power or higher energy pump inputs. However, even with a large mode field structure, traditional rare-earth-doped fibers still face severe mode field degradation problems in the final stage amplification: because higher-order modes are easily excited, the output beam often exhibits mode aliasing and spatial non-uniform distribution, making it difficult to directly obtain high brightness and high beam quality output. Especially when pursuing high single-pulse energy, high peak power is more likely to excite nonlinear effects and exacerbate mode instability, placing more stringent requirements on amplifier design.

[0004] In existing technologies, CN113659412B uses highly nonlinear multimode fiber to achieve broad spectral broadening from visible to near-infrared, but its amplification link uses conventional large-mode-field fiber, limiting its power carrying capacity. CN103199415B uses photonic crystal fiber combined with polarization control to achieve stable output, but the fiber core diameter is small, making it difficult to carry high power or high energy. CN104201545A achieves broad spectral coverage through dual-band fiber laser cascade and PCF, but the mode distribution of the high-power amplification link is not optimized. CN105759531B uses large-mode-field rare-earth-doped fiber to amplify power, but the final stage is still prone to exciting higher-order modes, leading to a decrease in beam quality.

[0005] Based on the above analysis, current technological advancements in pursuing high performance in supercontinuum fibers have fallen into a dilemma: solutions with sufficient load-carrying capacity suffer from poor beam quality, while solutions with good beam quality have weak load-carrying capacity. Furthermore, it is worth noting that the nonlinear spatial self-cleaning effect has also been reported in ordinary step-index multimode fibers, but its energy transfer efficiency is low, the required nonlinear threshold is high, and it often competes with or even inhibits the broadband generation process, making it difficult to efficiently and synergistically achieve beam purification and spectral broadening while carrying high-power / high-energy lasers. Therefore, existing technologies have failed to provide an all-fiber solution that can fundamentally and synergistically resolve the contradiction between high load-carrying capacity, high quality, and broadband output. Therefore, there is an urgent need for an innovative technological approach that can combine the high load-carrying capacity of ultra-large mode field fibers with a novel fiber structure that can simultaneously achieve beam purification and nonlinear broadening, in order to break through this performance bottleneck. Summary of the Invention

[0006] To address the systemic contradiction in existing technologies where high-performance photonic crystal fibers have insufficient load-carrying capacity while high-load-capacity, large-mode-field fibers have poor output beam quality, this invention provides two parallel, specifically optimized technical solutions to meet the differentiated high-end demands for high average power and high single-pulse energy supercontinuum output, respectively.

[0007] The core innovation of this invention lies in the following: By constructing a master oscillation power amplifier (MOPA) structure using a series of ultra-large mode field active fibers with progressively larger core diameters, and employing targeted high-repetition-rate continuous / pulse pumping or low-repetition-rate synchronous pulse pumping strategies, high average power or high single-pulse energy laser output is first achieved, fundamentally improving the system's power and energy carrying capacity threshold. Building upon this, a highly nonlinear multimode fiber with a parabolic graded refractive index distribution is creatively introduced as a broadening and shaping medium. This fiber utilizes its unique waveguide structure and nonlinear spatial self-cleaning effect to spontaneously and efficiently transfer higher-order mode energy to the fundamental mode while carrying high-power / high-energy lasers. This allows for simultaneous beam purification and optimization during the broadband nonlinear broadening process, ultimately outputting a supercontinuum spectrum with high brightness and a near-Gaussian spatial distribution.

[0008] This synergistic design of "ultra-high load capacity amplification" and "self-cleaning stretching and shaping" constitutes the fundamental innovation of this invention, breaking through the technical bottleneck of the difficulty in achieving both "high load capacity" and "high quality" in traditional solutions, and providing a brand-new technical path for realizing a fully fiber-optic, highly reliable, and high-performance supercontinuum laser system.

[0009] First technical solution: A high-power supercontinuum fiber laser The invention includes: a high repetition rate (PRR) pulse seed source, a large mode field (VMD) active fiber amplifier, a highly nonlinear multimode fiber, and a laser output head. The output of the PPR seed source is connected to the input of the VMD active fiber amplifier, the output of the VMD active fiber amplifier is connected to the input of the highly nonlinear multimode fiber, and the output of the highly nonlinear multimode fiber is connected to the laser output head. The VMD active fiber amplifier is an amplification device with VMD active fiber as the core gain medium. In a preferred embodiment of the invention, it adopts a master oscillation power amplifier (MOPA) structure, which is composed of cascaded multi-stage amplification units, used to efficiently and stably amplify the energy of the PPR seed pulse, providing a drive for the subsequent generation of a high average power supercontinuum.

[0010] Furthermore, the high repetition rate pulse seed source is used to output a pulsed laser signal with high average power. It can be any of various fiber output lasers, such as a pulse-modulated continuous laser or a high repetition rate fiber laser with a repetition rate higher than 1MHz. In addition, an optical isolator is connected in series at the output end to protect the laser.

[0011] Furthermore, in the aforementioned ultra-large mode field active fiber amplifier, the active fiber used for power amplification or energy enhancement in the final stage amplification unit has a normalized frequency V-parameter of not less than 4.7 at the operating wavelength, and is mainly configured for continuous pumping or high repetition rate pulse pumping to achieve high average power output. To carry higher average power and maintain good beam quality, the V-parameter of the active fiber can be designed to be 10, 20, or higher, depending on the power enhancement requirements, to support a larger mode field area, thereby reducing power density and improving the system's thermal management and damage threshold.

[0012] Second technical solution: A high-energy supercontinuum fiber laser comprising: a low repetition rate, a high pulse energy seed source, an ultra-large mode field active fiber amplifier, and a highly nonlinear... The system includes a multimode fiber and a laser output head. The output of the low-repetition-rate, high-pulse-energy seed source is connected to the input of the ultra-large mode field active fiber amplifier (UMP), the output of the UMP is connected to the input of the highly nonlinear multimode fiber, and the output of the highly nonlinear multimode fiber is connected to the laser output head. This UMP is an amplification device using ultra-large mode field active fiber as the core gain medium. In a preferred embodiment, the amplifier employs a master oscillator power amplifier (MOPA) structure, composed of cascaded multi-stage amplification units, to efficiently and stably amplify the energy of the low-repetition-rate, high-energy seed pulse, providing drive for the subsequent generation of a high-single-pulse-energy supercontinuum.

[0013] Furthermore, the low repetition frequency, high pulse energy seed source is used to output a pulsed laser signal with high peak power. It can be any of various fiber output lasers, such as a solid-state laser or a low repetition frequency, high energy pulsed fiber laser with a repetition frequency between 1 Hz and 100 kHz. In addition, an optical isolator can be connected in series at the output end to protect the laser.

[0014] Furthermore, in the aforementioned ultra-large mode field active fiber amplifier, the active fiber used for power amplification or energy enhancement in the final stage amplification unit has a normalized frequency V-parameter of not less than 4.7 at the operating wavelength and is primarily configured for pulse pumping to achieve high single-pulse energy output. To support higher single-pulse energy and the resulting high peak power, the V-parameter of the active fiber can be designed to be 10, 20, or higher, depending on the energy enhancement requirements, to support a larger mode field area, thereby effectively suppressing nonlinear effects and increasing the damage threshold of pulse energy.

[0015] General characteristics of key components in the system Furthermore, the active optical fiber used in the ultra-large mode field active optical fiber amplifier can be ytterbium-doped, thulium-doped, erbium-doped or other rare earth element-doped optical fiber, or chromium-doped, titanium-doped or other transition metal element-doped optical fiber, or co-doped optical fiber of two or more rare earth elements or rare earth and transition metal elements.

[0016] Furthermore, the output end of the ultra-large mode field active fiber amplifier and the input end of the highly nonlinear multimode fiber are coupled and matched efficiently through a fusion splicing tapered process.

[0017] General characteristics, working principle and design method of the aforementioned highly nonlinear multimode optical fiber As mentioned earlier, both technical solutions couple the amplified laser to a highly nonlinear multimode fiber, which is the core component for realizing beam optimization and supercontinuum generation.

[0018] Furthermore, the core function of the highly nonlinear multimode fiber lies in beam shaping and nonlinear spectral broadening of the input high-power / high-energy beam. Its ultimate goal is to enable the output laser to simultaneously possess near-Gaussian spatial quality and a continuous spectrum covering a wide wavelength range. Therefore, after processing by the highly nonlinear multimode fiber, the supercontinuous light output by the laser output head achieves improvements in both beam quality and spectral width compared to the laser input into the fiber. Specifically, it exhibits a smaller beam quality M² factor and a wider spectral width.

[0019] Furthermore, the highly nonlinear multimode fiber possesses a parabolic or approximately parabolic graded refractive index (GRIN) distribution. Its radial refractive index n(r) is formed by the distribution of refractive index modulating elements in the fiber core and can be characterized as follows:

[0020] In the formula, n0 is the maximum refractive index at the center of the fiber core. R is the relative refractive index difference, r is the core radius, r is the radial coordinate, and α is the refractive index distribution coefficient. α is preferably between 1.8 and 2.2 to form a parabolic or approximately parabolic structure.

[0021] Furthermore, the unique waveguide structure of this graded-index multimode fiber synchronizes the phase velocities of different transmission modes, thereby stimulating a nonlinear spatial self-cleaning effect. When a high-power laser pulse is input, the nonlinear Kerr effect and mode coupling within the fiber work together to drive the energy transfer of higher-order modes to the fundamental mode, ultimately forming a near-Gaussian distributed steady-state beam at the output end. This process completes the beam optimization.

[0022] Furthermore, during or after beam optimization, strong nonlinear effects continue to be triggered in the same fiber segment at high peak power densities, including self-phase modulation (SPM), stimulated Raman scattering (SRS), four-wave mixing (FWM), and intermodal nonlinear interactions. The superposition of these multiple nonlinear effects greatly broadens the pulse spectrum during propagation, ultimately forming a supercontinuum spectral output covering the visible to near-infrared bands. In a preferred embodiment, the -20 dB width of the spectrum can cover the band from 600 nm to 2300 nm.

[0023] Furthermore, to quantitatively guide fiber design for controllable beam optimization and spectral broadening, modeling and analysis can be performed based on the generalized multimode nonlinear Schrödinger equation (GMM-NLSE). By establishing a physical model of supercontinuum generation in graded-index fibers, the influence of key parameters such as mode area, fiber length, and input power was systematically analyzed. Numerical simulations revealed a clear optimal parameter range: the mode area of ​​the highly nonlinear multimode fiber should ideally be between 20 and 50 μm. 2 Within a certain range, the total fiber length exhibits a saturation threshold of approximately 3-30 meters; beyond this length, the contribution to spectral broadening decreases significantly. Input power should be increased as much as possible within the system's safe operating range to enhance nonlinear effects. This optimization scheme provides clear guidance for parameter selection in fiber design.

[0024] Furthermore, to obtain stable and efficient supercontinuum spectral output, the geometric and waveguide parameters of the highly nonlinear multimode fiber need to be appropriately matched with those of the preamplifier fiber. Its core diameter should preferably be slightly larger than the mode field diameter of the preamplifier fiber to achieve low-loss fusion coupling and efficient energy injection; simultaneously, its numerical aperture (NA) should be controlled between 0.1 and 0.3 to optimize mode coupling efficiency while ensuring sufficient nonlinear effects.

[0025] Based on the aforementioned matching principles and nonlinear effect requirements, in a preferred embodiment, the core diameter of the highly nonlinear multimode fiber can be selected as 30μm-100μm, and the numerical aperture (NA) is 0.1-0.3. This size range can effectively carry the pre-amplified optical energy and achieve low-loss coupling while ensuring sufficient nonlinear coefficients to produce efficient supercontinuum broadening.

[0026] Furthermore, to quantitatively guide the design of fiber length, three characteristic lengths can be introduced: nonlinear length... (Characterizing the intensity of nonlinear effects), beam self-cleaning length (Characterizing the transmission distance required for higher-order mode energy to transfer to the fundamental mode) and the supercontinuum broadening length (Characterizing the transmission distance required to generate the target width supercontinuum). Based on the estimation model. The total length of the optical fiber can be measured. Conduct engineering design and make reasonable parameter settings to achieve It was completed, and subsequently provided approximately The length is used for spectral broadening, thereby efficiently generating supercontinuum while ensuring the quality of the output beam (high fundamental mode ratio).

[0027] Furthermore, the highly nonlinear multimode fiber can be flexibly configured as a single-segment structure or a multi-segment cascaded structure. In the multi-segment cascaded structure, the two physical processes of beam optimization and spectral broadening can be optimized with emphasis in different fiber segments.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: By collaboratively innovating the design of "serialized ultra-large mode field active fiber amplifiers" and "large core diameter high nonlinear multimode fiber", the system-level output capability of high single pulse energy (millijoule level) / high average power (hundred watt level) and excellent beam spatial quality are unified, solving the fundamental problem of mutual constraint between the two in traditional solutions.

[0029] By constructing multi-stage amplifiers using a series of ultra-large mode field active fibers with progressively larger core diameters (e.g., using core diameters of approximately 30μm, 100μm, and 200μm in sequence), and combining this with optimized pumping strategies for high single-pulse energy (low repetition rate pulse pumping) or high average power (high repetition rate / continuous pumping), a reliable all-fiber solution is provided for safely and stably achieving high-performance laser output, overcoming the key limitation of traditional gain media having a low damage threshold due to excessively small core diameter.

[0030] The introduction of highly nonlinear multimode fiber with a large core diameter (50-100 μm) and a parabolic refractive index distribution can induce a strong nonlinear spatial self-cleaning effect. This effect enables the beam energy to spontaneously concentrate towards lower-order modes during the generation of an ultrawide continuous spectrum covering 600 nm to 2300 nm, resulting in an output beam spot distribution close to the Gaussian mode distribution, thus simultaneously achieving high brightness and wide spectral output characteristics.

[0031] The various optical fiber components of this invention can be integrated efficiently and with low loss through mature fusion splicing and tapered core expansion processes. Compared with traditional solutions that rely on special optical fibers such as photonic crystal fibers and have complex and fragile connection processes, this solution has significant advantages in terms of system packaging simplicity, connection reliability, long-term stability, and manufacturing cost, and is easier to engineer and apply in industry.

[0032] In summary, this invention provides a practical and high-performance technical path for achieving high-power or high-energy supercontinuum output through innovative architecture combination and parameter optimization. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the general principle structure of the supercontinuum fiber laser system proposed in this invention, showing the core component architecture that is followed by both high-power and high-energy technical solutions.

[0034] Figure 2 This is a schematic diagram of the specific implementation structure of Embodiment 1 (high-energy scheme) of the present invention, which shows an implementation method using three-stage MOPA amplification and a single-segment highly nonlinear multimode fiber.

[0035] The diagram is labeled as follows: 1. Laser seed source; 2. First semiconductor pumped laser; 3. First fiber isolator; 4. First combiner; 5. Small-sized active fiber; 6. Second fiber isolator; 7. Second semiconductor pumped laser; 8. Second combiner; 9. Medium-sized active fiber; 10. Third fiber isolator; 11. Third semiconductor pumped laser; 12. Third combiner; 13. Large-sized active fiber; 14. Highly nonlinear multimode fiber; 15. Laser output head.

[0036] Figure 3 This is a schematic diagram of the specific implementation structure of Embodiment 2 (high power scheme) of the present invention, which shows an implementation method using four-stage MOPA amplification and multi-segment cascaded highly nonlinear multimode fiber.

[0037] The diagram is labeled as follows: 1. Laser seed source; 2. First semiconductor pumped laser; 3. First fiber isolator; 4. First combiner; 5. Small-sized active fiber; 6. Second fiber isolator; 7. Second semiconductor pumped laser; 8. Second combiner; 9. Medium-sized active fiber; 10. Third fiber isolator; 11. Third semiconductor pumped laser; 12. Third combiner; 13. Large-sized active fiber; 16. Fourth fiber isolator; 17. Fourth semiconductor pumped laser; 18. Fourth combiner; 19. Ultra-large-sized active fiber; 14. Highly nonlinear multimode fiber; 15. Laser output head.

[0038] Figure 4 This is a diagram showing the beam optimization and spot change in Embodiment 1 of the present invention. Figure 4 (a) Initial input light spot, Figure 4 (b) Initial beam optimization of the beam spot, Figure 4 (c) The beam spot after basic beam optimization is completed. Figure 4 (d) The final output light spot; Figure 5 This is the output spectrum of Embodiment 1 of the present invention; Figure 6 This is a simulation diagram of the supercontinuous stretching capability of this invention in relation to mode area, fiber length, and input power; Figure 7 This is a simulated cross-sectional diagram of the supercontinuous stretching capability of this invention, relating to mode field area and fiber length. Figure 7(a) is a simulated cross-sectional view of the supercontinuous stretching capability in relation to the mode field area and fiber length. Figure 7 (b) is a simulated cross-sectional view of the supercontinuous stretching capability in relation to the mode field area and input power. Figure 7 (c) is a simulated cross-sectional view of the supercontinuous stretching capability in relation to fiber length and input power. Detailed Implementation

[0039] Design and theoretical models The designs in the following embodiments are based on an in-depth analysis of the physical processes of nonlinear spatial self-cleaning and supercontinuum spectrum generation in graded-index multimode fibers. This process is described by the generalized multimode nonlinear Schrödinger equation, and a design method for key parameters is established based on this equation.

[0040] 1. Generalized multimode nonlinear Schrödinger equation The evolution of the pulse in GRIN-MMF satisfies the generalized multimode nonlinear Schrödinger equation (GMM-NLSE), the core equation of which can be expressed as the evolution equation of the time envelope of mode p with propagation distance z:

[0041] : No. The amplitude of the complex electric field envelope of each mode is the propagation distance. and time The function.

[0042] Regarding the distance of transmission The partial differential operator.

[0043] Regarding time The partial differential operator.

[0044] Imaginary unit.

[0045] : No. Each mode at the center angular frequency The mismatch of the propagation constant at a given point relative to the reference value.

[0046] : No. The first-order dispersion (reciprocal of group velocity) of each mode is mismatched.

[0047] : Sum index of dispersion order.

[0048] : The highest order of dispersion expansion considered.

[0049] : No. The first mode Dispersion coefficient.

[0050] Nonlinear Kerr refractive index coefficient of optical fiber material, in m² / W.

[0051] : The center angular frequency of the input light pulse , The speed of light in a vacuum. The wavelength is the vacuum wavelength.

[0052] The speed of light in a vacuum.

[0053] Fractional contribution of the Raman effect to the total nonlinear polarization (0 ≤ ≤ 1).

[0054] : Nonlinear mode coupling coefficients corresponding to the Kerr effect, derived from the mode The field distribution is determined by the overlap integral.

[0055] : The nonlinear mode coupling coefficient corresponding to the Raman effect.

[0056] : Represents the first The amplitude of the complex electric field envelope of each mode.

[0057] : No. The complex conjugate of the complex electric field envelope amplitude of each mode.

[0058] The time delay integral variable of the Raman response.

[0059] Raman time-domain response function of the material In the formula, the first to third terms on the right side of the equation represent the dispersion operator at the central angular frequency ω0, which is expanded by a Taylor series. and These represent propagation constant mismatch and first-order dispersion (group velocity mismatch), respectively. Here, n is the higher-order dispersion coefficient; in the nonlinear part, n2 is the nonlinear refractive index, and ω0 is the central angular frequency. Contribution to the fraction of the Raman effect, Let be the Raman response function of the medium. and , respectively, are the nonlinear coupling coefficients between the Kerr effect and Raman effect modes, determined by the spatial overlap integral of the corresponding mode fields. This equation fully describes the energy transfer caused by nonlinear coupling between modes in a multimode system (such as intermodal four-wave mixing), and is the theoretical basis for understanding the nonlinear spatial self-cleaning effect.

[0060] 2. Characteristic lengths for beam self-cleaning and spectral broadening: To achieve engineering design, three key characteristic lengths are defined, and the total design length of the optical fiber is determined accordingly.

[0061] (1) Nonlinear length

[0062] Nonlinear length characterizes the scale at which nonlinear effects begin to take effect significantly:

[0063] : Non-linear length.

[0064] : Effective mode area of ​​optical fiber.

[0065] The working wavelength of light in a vacuum.

[0066] : The nonlinear Kerr refractive index coefficient of optical fiber materials.

[0067] Peak power of the optical pulse input into the optical fiber.

[0068] Among them, A eff The effective mode area is λ, and the operating wavelength is λ. n is the input peak power, and n2 is the nonlinear refractive index of the fiber material.

[0069] (2) Beam self-cleaning length

[0070] This length represents the distance required for efficient energy transfer from higher-order modes to the fundamental mode, thus achieving beam optimization. Its calculation must consider mode-field coupling efficiency and phase-matching conditions.

[0071] First, the effective overlap integral of the combination of the target low-order mode f and the participating background mode is defined as:

[0072] Target low-order model Effective nonlinear overlap integrals with all participating higher-order mode combinations.

[0073] : Summation index, representing other modes involved in nonlinear coupling (such as four-wave mixing).

[0074] Weighting coefficients, determined by the incident light in the mode The initial energy distribution (modal weights) on the surface is determined.

[0075] : Involves target pattern and pattern The specific nonlinear overlap integral value.

[0076] Where the coefficient Determined by the incident mode weights, For the nonlinear overlap integral involving modes f, n, p, q, the mode overlap factor (dimensionless) is given.

[0077] Mode overlap factor (dimensionless) measures the lateral efficiency of nonlinear coupling.

[0078] Effective nonlinear overlap integral The modulus.

[0079] : Effective mode area of ​​optical fiber.

[0080] Its value range is approximately 0 < η overlap 1. η overlap The larger the value, the more efficient the lateral coupling. Secondly, we define the phase matching efficiency factor S(Δβ) to characterize the degree of longitudinal phase matching: For those containing phase factors The coupling term has an effective accumulation amount within a single self-imaging cycle of .

[0081] Phase matching efficiency factor (dimensionless) measures the degree of longitudinal phase matching in nonlinear coupling.

[0082] : Self-imaging period length of GRIN multimode fiber.

[0083] The mismatch between the propagation constants of the modes involved in nonlinear interactions (such as four-wave mixing). .

[0084] :Singer function, .

[0085] in For the propagation constant mismatch of the participating coupled modes, when When the value is close to an integer multiple of 2π, S≈1 (quasi-phase matching); otherwise, S will decrease significantly, and the value of S will be in the range of 0. <S≤1; R is the self-imaging period of the optical fiber (where R is the core radius and Δ is the relative refractive index difference). Define pattern overlap factor Characterize the transverse energy coupling efficiency between low-order and high-order modes, and define the phase-matching efficiency factor. Characterizing the longitudinal phase matching degree along the optical fiber propagation direction, the low-order mode energy is determined by the initial proportion. Increase to target percentage The required self-cleaning length is:

[0086] : Beam self-cleaning feature length.

[0087] : Non-linear length.

[0088] : Pattern overlap factor.

[0089] Phase matching efficiency factor.

[0090] Target low-order model The proportion (or energy value) of the initial energy of the fundamental mode to the total energy.

[0091] Target low-order model The proportion (or value) of the total energy to be achieved.

[0092] To ensure project controllability and process tolerance, a range coefficient κ can be introduced, which can range from 0.5 to 10, to obtain the design length range:

[0093] The length of optical fiber selected in actual engineering design.

[0094] The lower and upper limits of the range factor are used to define the tolerance range for the design length (e.g., ).

[0095] : Beam self-cleaning feature length.

[0096] (3) Supercontinuum broadening length

[0097] This length characterizes the additional nonlinear action distance required to generate the target width supercontinuum after beam optimization:

[0098] : Characteristic length of supercontinuum broadening.

[0099] : Non-linear length.

[0100] : Pattern overlap factor.

[0101] Phase matching efficiency factor.

[0102] The supercontinuum broadening factor (dimensionless) is an empirical or semi-empirical factor related to the target spectral width, fiber dispersion characteristics, and nonlinear coefficient.

[0103] in, The supercontinuum broadening factor reflects the contribution of nonlinear accumulation to spectral broadening. Its value is related to the target spectral width, fiber dispersion, and nonlinear coefficient.

[0104] (4) Total design length The total design length of the optical fiber is determined by the sum of the lengths of the two stages mentioned above:

[0105] Total design length of the optical fiber.

[0106] : Beam self-cleaning feature length.

[0107] : Characteristic length of supercontinuum broadening.

[0108] In a multi-segment cascaded fiber structure, the total length is the sum of the lengths of each segment.

[0109] 3. Parameter optimization design and evaluation function To evaluate the mode field area Aeff and the total fiber length Based on the combined effect of input power PP on the final spectral broadening capability, a broadening capability evaluation function W was constructed.

[0110] Considering the inverse relationship between the nonlinear coefficient and the modulus area (γ ∝ 1 / A) eff Based on the effects of fiber transmission loss, a function for evaluating fiber optic extension capability was constructed: W = tanh( )·exp(- α ) : Stretchability evaluation function (dimensionless), the larger the value, the better the overall stretchability.

[0111] : Hyperbolic tangent function, used to simulate the saturation characteristics of nonlinear effects.

[0112] : A proportionality coefficient related to fiber optic materials and wavelength. .

[0113] Peak power of the optical pulse input into the optical fiber.

[0114] Total design length of the optical fiber.

[0115] : Effective mode area of ​​optical fiber.

[0116] : Natural exponential function.

[0117] : The linear transmission loss coefficient of optical fiber (power loss per unit length, usually expressed in dB / m or 1 / m).

[0118] In the formula, This is a proportionality coefficient related to the nonlinear refractive index n2 of the optical fiber material and the operating wavelength λ. η =2 πn 2 / λ ; α The transmission loss coefficient of the optical fiber; the tanh() function describes the saturation characteristics of nonlinear effects; exp(- α The term describes the attenuation effect of transmission loss.

[0119] To make the technical solution of the present invention clearer, a detailed description will be provided below in conjunction with the accompanying drawings and specific embodiments. First, please refer to... Figure 1This invention demonstrates the basic principle architecture of the supercontinuum fiber laser system. As shown in the figure, the system mainly includes a pulse seed source, a large mode field active fiber amplifier, a highly nonlinear multimode fiber, and a laser output head. The pulse seed source can be selected as a high repetition rate pulse seed source (corresponding to a high-power scheme) or a low repetition rate, high pulse energy seed source (corresponding to a high-energy scheme), depending on the needs. After being amplified by the large mode field active fiber amplifier, the seed light is efficiently coupled into the highly nonlinear multimode fiber. Within the highly nonlinear multimode fiber, a nonlinear spatial self-cleaning effect occurs simultaneously to achieve beam optimization, and a strong nonlinear effect occurs to achieve spectral broadening. Finally, the laser output head outputs a high-brightness, broad-spectrum supercontinuum laser.

[0120] Based on the above general architecture, the present invention provides the following two preferred embodiments.

[0121] Example 1 like Figure 2 As shown, this embodiment provides a high-energy supercontinuum laser based on a single-segment highly nonlinear multimode fiber. The optical path of the laser along the laser transmission direction includes, in sequence: a laser seed source 1, a three-stage active fiber amplifier, a single-segment highly nonlinear multimode fiber 14, and a laser output head 15.

[0122] The three-stage active fiber amplifier employs a master oscillator power amplifier (MOPA) structure, which amplifies the energy of the seed pulse step by step to the level of hundreds of microjoules. The amplifier includes a primary amplification unit, a middle amplification unit, and a final amplification unit connected in series along the optical path, with its core gain media being a small-sized active fiber 5, a medium-sized active fiber 9, and a large-sized active fiber 13, respectively.

[0123] The primary amplification unit consists of a first semiconductor pump laser 2, a first fiber isolator 3, a first combiner 4, and a small-sized active fiber 5. The low-repetition-rate, high-pulse-energy nanosecond or sub-nanosecond pulsed seed light output from the laser seed source 1 passes through the first fiber isolator 3 and enters the signal input end of the first combiner 4. The pump light output from the first semiconductor pump laser 2 is injected into the pump input end of the first combiner 4. After the seed light and pump light are combined within the first combiner 4, they are coupled together into the small-sized active fiber 5 (core diameter 10 μm, cladding diameter approximately 50 μm, numerical aperture NA approximately 0.08). The first semiconductor pump laser 2, operating in pulse mode and synchronized with the seed light pulse, provides pulse pumping, resulting in preliminary amplification and power increase of the seed light signal.

[0124] The intermediate amplification unit consists of a second fiber isolator 6, a second semiconductor pump laser 7, a second beam combiner 8, and a medium-sized active fiber 9. The primary amplified optical signal passes through the second fiber isolator 6 and enters the signal input of the second beam combiner 8. The pump light output from the second semiconductor pump laser 7 is injected into the pump input of the second beam combiner 8. The amplified optical signal and the pump light are combined within the second beam combiner 8 and then coupled together into the medium-sized active fiber 9 (core diameter 30 μm, cladding diameter approximately 120 μm, numerical aperture NA approximately 0.06–0.08). Pumped by the second semiconductor pump laser 7, which operates in pulse mode and is synchronized with the signal light pulse, intermediate power amplification is achieved. This stage effectively increases pulse energy while maintaining stable beam mode quality.

[0125] The final amplification unit consists of a third fiber isolator 10, a third semiconductor pump laser 11, a third combiner 12, and a large-size active fiber 13. The amplified optical signal passes through the third fiber isolator 10 and enters the signal input of the third combiner 12. The pump light output from the third semiconductor pump laser 11 is injected into the pump input of the third combiner 12. The amplified optical signal and the pump light are combined within the third combiner 12 and then coupled together into the large-size active fiber 13 (core diameter 100 μm, cladding diameter approximately 250 μm, numerical aperture NA approximately 0.06–0.1). The third semiconductor pump laser 11, which provides the pump for this unit, operates in pulsed mode, with its pulse synchronized with the signal light. Through this pulsed pumping method, the unit amplifies the pulse energy to the level of hundreds of microjoules, ultimately amplifying the pulse energy to over 100 µJ, ensuring effective control of nonlinear effects in the fiber while achieving high single-pulse energy output. After passing through the final amplification unit, the output end of the large-size active fiber 13 is fused to the input end of the subsequent single-segment highly nonlinear multimode fiber 14. This fusion splicing process aims to achieve mode field matching between the large-size active fiber 13 and the single-segment highly nonlinear multimode fiber 14. By optimizing the fusion parameters, a smooth mode field transition can be formed at the connection point, thereby minimizing the higher-order modes excited due to mode field mismatch and laying a good foundation for efficient nonlinear spatial self-cleaning effects in the subsequent single-segment highly nonlinear multimode fiber 14.

[0126] The single-segment highly nonlinear multimode fiber 14 has a core diameter of 50–100 μm, a cladding diameter of 200–500 μm, and a numerical aperture (NA) of 0.1–0.3, possessing a high damage threshold to withstand high single-pulse energy and high peak power. The beam propagation within the single-segment highly nonlinear multimode fiber 14 undergoes two stages sequentially: Beam optimization stage: Through nonlinear spatial self-cleaning effects such as multimode coupling within the fiber and energy redistribution between modes, higher-order mode energy is transferred to lower-order modes, significantly increasing the proportion of the fundamental mode. This results in the beam's lateral distribution approaching a Gaussian distribution after a certain transmission length, thus improving beam brightness. The beam spot evolution during this optimization process is as follows: Figure 4 As shown, from the initial multimode distribution ( Figure 4 a) Gradually purified to a near-Gaussian distribution ( Figure 4 d). The effect of beam optimization can be adjusted by selecting the fiber core diameter, NA value, and using tapered core expansion technology at the splice point, ultimately making the M² factor of the output beam significantly lower than that of the input beam.

[0127] Spectral broadening stage: Building upon beam optimization, and benefiting from the high peak power density, strong nonlinear effects continue to be triggered within the same fiber segment, including self-phase modulation, stimulated Raman scattering, and four-wave mixing. These effects work synergistically to rapidly broaden the spectrum of the input pulse, ultimately forming a spectrum as shown in the image. Figure 5 The example shown is a broadband supercontinuum output covering 600nm to 2300nm. The relationship between the stretching capability and mode area, fiber length, and input power can be illustrated by... Figure 6 and Figure 7 The simulation shown is used for system evaluation and optimization design.

[0128] To ensure stable transmission of high-energy pulses at the fiber end face and in the fusion splice area, if there are fusion splices inside a single segment of highly nonlinear multimode fiber 14, they must be finely processed using a combination of fusion splicing and tapered core expansion technology to achieve a smooth transition of the mode field, thereby effectively reducing the excitation of higher-order modes.

[0129] Finally, the spectrally broadened broadband beam is safely output through the laser output head 15. The output end face of the laser output head 15 can be designed with an angle and coated with a broadband anti-reflective coating to ensure the final output with high single-pulse energy, high stability, and broadband spectral characteristics.

[0130] This embodiment integrates the two physical processes of beam optimization and spectral broadening into the same fiber by cascading the three-stage active fiber amplification and a single-segment highly nonlinear multimode fiber, ultimately achieving supercontinuous light output with pulse energy exceeding 100 µJ, excellent beam quality, and a wide spectrum.

[0131] Example 2 like Figure 3 As shown, this embodiment provides a high-power supercontinuum laser based on multiple segments of highly nonlinear multimode fiber. The laser includes, in sequence along the optical path: a laser seed source 1, a four-stage active fiber amplifier, multiple cascaded segments of highly nonlinear multimode fiber 14, and a laser output head 15.

[0132] The four-stage active fiber amplifier adopts a master oscillator power amplifier (MOPA) structure, which includes a primary amplification unit, a middle amplification unit, a high-power enhancement unit and a final amplification unit, used to amplify the average power of the seed pulse step by step to the tens of watts level.

[0133] The primary amplification unit consists of a first semiconductor-pumped laser 2, a first fiber isolator 3, a first beam combiner 4, and a small-sized active fiber 5. The high-repetition-rate pulsed light signal output from the laser seed source 1 passes through the first fiber isolator 3 and enters the signal input end of the first beam combiner 4; the pump light output from the first semiconductor-pumped laser 2 is injected into the pump input end of the first beam combiner 4. The seed light and pump light are combined within the beam combiner 4 and then coupled together into the small-sized active fiber 5 (core diameter 10 μm, cladding diameter approximately 50 μm, numerical aperture NA approximately 0.08), achieving preliminary amplification of the seed signal.

[0134] The intermediate amplification unit consists of a second fiber isolator 6, a second semiconductor pump laser 7, a second beam combiner 8, and a medium-sized active fiber 9. The primary amplified optical signal passes through the second fiber isolator 6 and enters the signal input of the second beam combiner 8; the pump light output from the second semiconductor pump laser 7 is injected into the pump input of the beam combiner 8. The amplified optical signal and the pump light are combined within the beam combiner 8 and then coupled together into the medium-sized active fiber 9 (core diameter 30 μm, cladding diameter 120 μm, numerical aperture NA approximately 0.06–0.08). This stage effectively increases pulse power while maintaining stable beam mode quality.

[0135] The high-power enhancement unit consists of a third fiber isolator 10, a third semiconductor pump laser 11, a third combiner 12, and a large-size active fiber 13. The intermediate-stage amplified optical signal passes through the third fiber isolator 10 and enters the signal input of the third combiner 12; the pump light output from the third semiconductor pump laser 11 is injected into the pump input of the combiner 12. The amplified optical signal and the pump light are combined within the combiner 12 and then coupled together into the large-size active fiber 13 (core diameter 100 μm, cladding diameter 250 μm, numerical aperture NA approximately 0.06–0.08), achieving higher power amplification and preparing for the final stage enhancement.

[0136] The final amplification unit consists of a fourth fiber isolator 16, a fourth semiconductor pump laser 17, a fourth beam combiner 18, and a large-size active fiber 19. The high-power beam amplified by the high-power enhancement unit passes through the fourth fiber isolator 16 and enters the signal input of the fourth beam combiner 18; the pump light output from the fourth semiconductor pump laser 17 is injected into the pump input of the beam combiner 18. The beam and pump light are combined within the beam combiner 18 and then coupled together into the large-size active fiber 19 (core diameter 200 μm, cladding diameter 400 μm, numerical aperture NA approximately 0.1). This unit employs high-power continuous or high-repetition-rate pulse pumping, and its core function is to ultimately increase the average power of the laser to over 50 W to meet the core driving conditions required for generating a high-power supercontinuum.

[0137] In the high-power scheme of this embodiment, all semiconductor pump lasers (2, 7, 11, 18) that provide pumps for the four-stage active fiber amplifier operate in continuous output (CW) mode to provide stable gain for the system and ensure stable output of high average power. After the output of the final stage amplification unit, the output end of the ultra-large active fiber 19 is fused to the input end of the first segment of the subsequent multi-segment cascaded high nonlinear multimode fiber 14.

[0138] The multi-segment cascaded highly nonlinear multimode fiber 14 is composed of at least two segments of graded-index multimode fiber with high nonlinear coefficients, distinguishing it from the single-segment structure in Embodiment 1. Typical parameters for each fiber segment are: core diameter 50–100 μm, cladding diameter 200–500 μm, and numerical aperture (NA) 0.1–0.3. The beam propagation process in the multi-segment cascaded highly nonlinear multimode fiber 14 is designed as two functionally separated stages: Beam optimization stage: dominated by the first fiber segment. After the high-power beam is injected, multimode coupling and energy transfer occur through the nonlinear spatial self-cleaning effect excited within the fiber. The energy of higher-order modes converges to lower-order modes (especially the fundamental mode), thereby purifying the transverse mode distribution of the beam, making the output beam spot close to a Gaussian distribution, and significantly improving the beam quality factor M².

[0139] Spectral broadening stage: Dominated by the second (and subsequent) fiber segments. The mode-optimized beam enters the subsequent fibers. Here, due to improved beam quality and concentrated power density, a series of nonlinear effects can be excited more efficiently, including self-phase modulation (SPM), stimulated Raman scattering (SRS), and four-wave mixing (FWM). The synergistic effect of these effects leads to a significant broadening of the pulse spectrum, ultimately producing a supercontinuum output covering the 600 nm to 2300 nm wavelength range. The optimization relationship between the system's broadening performance and key parameters (mode area, fiber length, input power) can be based on, for example... Figure 6 and Figure 7The simulation analysis shown is used for precise design.

[0140] To ensure stable transmission of high-power beams at the fiber endfaces and fusion splice areas, the fusion splices between fiber segments within the multi-segment cascaded high-nonlinear multimode fiber 14 are connected using a fusion splicing combined with tapered core expansion process. This achieves a smooth transition of mode field area, thereby optimizing mode matching, reducing mode mismatch loss, and effectively suppressing the excitation of higher-order modes, ensuring beam stability during transmission. This fusion splicing combined with tapered core expansion process, through precise control of the fiber structure at the connection point, aims to achieve more ideal mode field matching and a smoother transition between cascaded fiber segments. Its core purpose is not only to reduce transmission loss but also to fundamentally suppress higher-order mode coupling caused by abrupt changes in mode field, thus ensuring that the beam enters each high-nonlinear fiber segment with an optimized mode distribution, providing a stable mode foundation for the continuous and efficient "mode purification" and "spectral broadening" processes throughout the entire link.

[0141] Finally, the broadband laser beam, after spectral broadening, is output from the laser output head 15. The output end face of the laser output head 15 can be polished at an angle (e.g., 8°) and coated with a broadband anti-reflection coating to further suppress backlighting, ensuring the long-term stability of the system and the high brightness and broadband characteristics of the output beam.

[0142] This embodiment achieves high average power amplification through a four-stage MOPA structure and employs multi-segment cascaded high nonlinear multimode fiber 14 to spatially separate and optimize the two key physical processes of "mode purification" and "spectral broadening," thereby simultaneously achieving excellent beam quality and ultrawide continuous spectrum output under high power conditions of over 50 W average power.

[0143] Example 3 This embodiment provides a design and simulation verification method for optimizing key parameters of a supercontinuum fiber laser system. Based on the aforementioned generalized multimode nonlinear Schrödinger equation (GMM-NLSE) and characteristic length theory, this method constructs and solves a broadening capability evaluation function. To achieve the control of the model area Total fiber optic length and peak input power The synergistic optimization of the three core parameters enables the pre-assessment and maximization of the system's spectral broadening capability during the engineering design phase.

[0144] The expansion capability evaluation function The expression is:

[0145] in, To match the nonlinear refractive index of optical fiber and operating wavelength The relevant proportionality coefficient, This is the fiber transmission loss coefficient. This function comprehensively quantifies nonlinear effects (derived from the hyperbolic tangent term). The description (which has saturation characteristics) and transmission loss (determined by the exponential decay term) are as follows: (Description) The combined effect on the final output spectral width.

[0146] The simulation and optimization process in this embodiment is as follows, and the results are obtained through... Figure 6 and Figure 7 Visual presentation: 1. Multi-parameter global scanning and visualization ( Figure 6 Within the set parameter space (e.g.) , , ), calculate the evaluation function The value of . Figure 6 The three-dimensional surface plot shown illustrates The complex relationship between the three parameters. The peak region on the surface corresponds to the region that optimizes the overall performance of the system. , and The parameter combinations provide direct guidance for initial design selection.

[0147] 2. Two-parameter section analysis and trade-offs ( Figure 7 To reveal the inherent trade-off between any two parameters, a third parameter is fixed as a typical value to generate a two-dimensional contour map (section map).

[0148] Figure 7 (a) Demonstrates the effect at a fixed input power Under these conditions, expand capabilities With the area of ​​the mold field and fiber length The relationship is clear from the diagram; for a given power level, there exists an optimal... The combined region (usually represented by a narrow "ridge"), within this region Close to the maximum value. This guides designers: smaller. (Strong nonlinearity) requires a shorter matching length to avoid excessive loss; while a larger one... (For weak nonlinearity) a longer length is required to accumulate nonlinear phase shift, but the impact of increased loss must be weighed.

[0149] Figure 7 (b) Demonstrates the use of fixed fiber optic lengths Under the conditions, and and input power The relationship between the two is shown in the figure. This figure can be used to determine the minimum power threshold required to achieve the target stretching capability at a given fiber length, as well as the corresponding optimal mode area range.

[0150] Figure 7 (c) Demonstrates the use of a fixed mold field area Under the conditions, With fiber length and input power The diagram illustrates the relationship between the required power and the optimal fiber length for achieving the best performance after selecting a fiber type, thus avoiding insufficient power or wasted length.

[0151] When applying this method, designers first determine core constraints (such as maximum acceptable power, available fiber length range, and lower limit of mode field area corresponding to beam quality requirements) based on system objectives (such as high energy in Example 1 or high power in Example 2). Then, they utilize the simulation diagrams provided in this embodiment ( Figure 6 , Figure 7 Alternatively, a computational program based on the same model can be used to find the evaluation function under constraints. The maximum point is found, thus determining an optimal set of points. , and Design values. These optimized parameters can be directly used to guide the setting of the output characteristics of the active fiber amplifier, the selection of highly nonlinear multimode fiber, and the design of the total system length in Examples 1 and 2.

[0152] This embodiment closely integrates theoretical models, numerical simulations, and engineering design, providing a universal and quantitative method for parameter optimization. This method enables effective prediction and optimization of the performance generated by the supercontinuum before building the actual system, reducing trial-and-error costs, increasing the success rate of the design, and raising the performance ceiling. It is an important design tool supporting the achievement of optimal performance of the specific technical solutions described in Embodiments 1 and 2.

Claims

1. A supercontinuum fiber laser, characterized in that, include: Pulse seed source, ultra-large mode field active fiber amplifier, highly nonlinear multimode fiber, and laser output head; The output end of the pulse seed source is connected to the input end of the ultra-large mode field active fiber amplifier, the output end of the ultra-large mode field active fiber amplifier is connected to the input end of the highly nonlinear multimode fiber, and the output end of the highly nonlinear multimode fiber is connected to the laser output head. The ultra-large mode field active fiber amplifier amplifies the pulsed laser output from the pulse seed source, enabling the output laser to have high average power or high single pulse energy. The highly nonlinear multimode fiber has a parabolic or approximately parabolic gradient refractive index distribution and is used to receive the laser with high average power or high single pulse energy. The highly nonlinear multimode fiber utilizes the nonlinear spatial self-cleaning effect excited by the graded refractive index distribution to transfer the energy of higher-order modes in the laser to the fundamental mode, and uses the nonlinear effect in the fiber to broaden the laser spectrum, ultimately outputting supercontinuum light through the laser output head.

2. The supercontinuum fiber laser according to claim 1, characterized in that, The pulse seed source is a high repetition frequency pulse seed source, and the ultra-large mode field active fiber amplifier is continuously pumped or high repetition frequency pulse pumped.

3. The supercontinuum fiber laser according to claim 1, characterized in that, The pulse seed source is a low repetition frequency, high pulse energy pulse seed source, and the ultra-large mode field active fiber amplifier is synchronously pulse pumped.

4. The supercontinuum fiber laser according to any one of claims 1 to 3, characterized in that, The ultra-large mode field active fiber amplifier includes at least one final stage amplification unit, and the normalized frequency V parameter of the active fiber used in the final stage amplification unit is not less than 4.7 at the operating wavelength.

5. The supercontinuum fiber laser according to claim 1, characterized in that, The ultra-large mode field active fiber amplifier is a multi-stage master oscillator power amplifier (MOPA) structure.

6. The supercontinuum fiber laser according to claim 1, characterized in that, The active optical fiber used in the ultra-large mode field active optical fiber amplifier is selected from ytterbium-doped fiber, thulium-doped fiber, erbium-doped fiber, chromium-doped fiber, or titanium-doped fiber.

7. The supercontinuum fiber laser according to claim 1, characterized in that, The output end of the ultra-large mode field active fiber amplifier is connected to the input end of the highly nonlinear multimode fiber via a fusion splicing tapered process.

8. The supercontinuum fiber laser according to claim 1, characterized in that, The parabolic or approximately parabolic gradient refractive index distribution has a refractive index distribution coefficient α between 1.8 and 2.

2.

9. The supercontinuum fiber laser according to claim 1, characterized in that, The highly nonlinear multimode fiber is either a single-segment structure or a multi-segment cascaded structure.

10. The supercontinuum fiber laser according to claim 2, characterized in that, The high repetition rate pulse seed source is a pulse-modulated continuous laser or a high repetition rate fiber laser with a repetition rate higher than 1 MHz.

11. The supercontinuum fiber laser according to claim 3, characterized in that, The low repetition frequency, high pulse energy pulse seed source is a solid-state laser or a low repetition frequency, high energy pulse fiber laser with a repetition frequency between 1 Hz and 100 kHz.

12. The supercontinuum fiber laser according to claim 1, characterized in that, The core diameter of the highly nonlinear multimode fiber is 30 μm to 100 μm, and the numerical aperture is 0.1 to 0.

3.

13. The supercontinuum fiber laser according to claim 1, characterized in that, The supercontinuum output by the laser output head has a -20dB spectral width covering the 600nm to 2300nm band.

14. The supercontinuum fiber laser according to claim 1, characterized in that, The beam quality M² factor of the supercontinuum light output by the laser output head is less than 3.

15. The supercontinuum fiber laser according to claim 2, characterized in that, When the pulse seed source is a high repetition frequency pulse seed source, the average power of the supercontinuum output by the laser output head is greater than 50W.

16. The supercontinuum fiber laser according to claim 3, characterized in that, When the pulse seed source is a low repetition frequency, high pulse energy pulse seed source, the single pulse energy of the supercontinuum output by the laser output head is greater than 100 µJ.

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