Ultra-wideband spectrum generation device and method

Abstract

The application provides an ultra-wideband spectrum generating device and an ultra-wideband spectrum generating method, and relates to the fields of nonlinear optics and ultrafast laser technology. 3+ The application adopts a neodymium-doped phosphate glass optical fiber (N31 type matrix + high-concentration Nd 3+ doping) as a gain medium, provides a femtosecond pulse sequence in a specific wavelength range through a pump light source, couples the femtosecond pulse sequence into the optical fiber through an optical adjustment and coupling system, cooperates with the nonlinear frequency conversion of the stimulated Raman cascade effect and the neodymium ion energy level transition of the matrix, synchronously generates short-wave side deep ultraviolet to visible light radiation and long-wave side near-infrared to mid-infrared radiation, and finally realizes the ultra-wideband coherent spectrum output of 200-2400 nm across the frequency multiplication range, thereby breaking the spectrum coverage limit of the traditional single physical mechanism.

Description

Technical Field

[0001] This invention relates to the fields of nonlinear optics and ultrafast laser technology, and more specifically, to an ultrawideband spectrum generator and an ultrawideband spectrum generation method. Background Technology

[0002] Supercontinuum light sources, due to their extremely wide spectral coverage, high spatial coherence, and high brightness, have immense application value in fields such as biomedical imaging, environmental monitoring, and nonlinear optical detection. In particular, coherent light sources capable of simultaneously covering the deep ultraviolet to mid-infrared bands possess significant engineering value for detecting electronic transition information and molecular fingerprint characteristics. Generating supercontinuum in optical fibers primarily relies on the interaction between dispersion and third-order nonlinear effects, including self-phase modulation, four-wave mixing, stimulated Raman scattering, and soliton dynamics. However, achieving simultaneous coverage of these two extreme spectral regions on a single optical fiber platform remains a significant challenge, as most optical materials are limited by short-wavelength absorption edges or insufficient long-wavelength transmittance.

[0003] In the field of short-wavelength broadening research, traditional silica media, while performing well in the visible light band, face extremely high intrinsic absorption and photodarkening effects in the deep ultraviolet region. To forcibly extend into the ultraviolet range despite material limitations, early researchers such as Stark et al. (SP Stark, JC Travers, and P. St. J. Russell 2012 Optics Letters 37(5): 770-772) employed a silica tapered structure. The logic behind this approach is to drastically alter the waveguide dispersion of the medium through extreme physical deformation, thereby using a phase-matching mechanism to forcibly couple some energy to the ultraviolet dispersive wave. However, since the matrix material remains silica, this simple structural modification cannot fundamentally eliminate the high loss and photodamage problems in the deep ultraviolet band. To completely bypass the absorption bottleneck of solid materials, Sabbah et al. (M Sabbah, R Mears, K Harrington, WJ Wadsworth, JM Stone, TABirks and JC Travers 2025 Journal of Physics: Photonics 7(2): 025019) subsequently converted the waveguide mechanism into an inflatable hollow anti-resonant structure, transferring the nonlinear interaction between light and matter to the gas cavity, successfully achieving spectral output covering 260 nm to 750 nm. However, although such inflatable systems can reach the deep ultraviolet, their extension capability at the long-wave infrared end is fundamentally limited by the nonlinear mechanism of the gas and the waveguide characteristics of the cavity.

[0004] In the field of mid-infrared broadening, soft glass optical fibers have attracted widespread attention due to their low phonon energy and wide infrared transparency window. Ren et al. (G Ren, L Yang, C Yao, X Wang, L Pu, K Li, L Zhang and P Li 2025 Photonics 12(4): 297) achieved ultra-flat mid-infrared supercontinuum generation in tapered fluorotellurate optical fibers. In addition, Jiang et al. (X Jiang, NY Joly, MA Finger, F Babic, GKL Wong, JC Travers and PSJ Russell 2015 Nature Photonics 9(2): 133-139) successfully demonstrated an ultra-broad spectrum covering 200 nm to 2500 nm using microstructured optical fibers made of fluoride materials. Although fluoride optical fibers exhibit excellent cross-band capabilities, their poor chemical stability, susceptibility to deliquescence, material toxicity, and complex fabrication process limit their long-term application in harsh environments.

[0005] In contrast, phosphate glasses possess a wider spectral window, a stronger Raman response than silica, and excellent physicochemical stability. In particular, introducing active rare-earth ions such as neodymium into the phosphate matrix provides a unique physical dimension for extending the spectrum to shorter wavelengths. Neodymium ions possess a rich electronic energy level structure, and under high transient field intensity excitation by ultrafast pulses, they can generate abundant upconversion radiation in the visible light band through mechanisms such as excited-state absorption and energy transfer upconversion. This frequency conversion process based on the energy level transitions of active ions can synergistically enhance the polarizability nonlinear effects of the matrix material (such as third harmonic generation and sum-frequency processes) in both the time and frequency domains, thereby effectively compensating for the insufficient broadening efficiency of traditional nonlinear effects in the deep ultraviolet region while maintaining the robustness of the medium.

[0006] In early research on phosphate glass fibers, Strutynski et al. (C Strutynski, V Couderc, T Mansuryan, G Santarelli, P Thomas, S Danto and T Cardinal 2022 Frontiers of Optoelectronics 15(1): 4) only achieved limited broadening from about 400 nm to 1600 nm, failing to fully explore its potential in the deep ultraviolet and mid-infrared ends. Current research mostly focuses on adjusting the dispersive modes through complex structural designs, while neglecting the role of excitation conditions in regulating nonlinear paths. In fact, the generation of supercontinuum involves the competition and synergy of various nonlinear effects, including self-phase modulation and stimulated Raman scattering. Under different pump pulse widths, the relative contributions of these two nonlinear processes change fundamentally: when the pump pulse width is much shorter than the Raman response time (on the order of 0-100 fs), self-phase modulation dominates, spectral broadening is predominantly symmetrical, and energy is difficult to transfer efficiently to longer wavelengths; when the pump pulse width is comparable to the Raman response time, the contribution of stimulated Raman scattering is significantly enhanced, enabling efficient energy transfer to the infrared direction through multiphonon cascade effects. Therefore, how to utilize robust oxide glass fibers to balance instantaneous electronic nonlinearity and delayed Raman response through optimized excitation mechanisms, thereby achieving an ultrawide spectral conversion from deep ultraviolet to mid-infrared in a single, simple fiber structure, has become a highly challenging research direction in this field. Summary of the Invention

[0007] To overcome the shortcomings of existing supercontinuum light sources, such as severe deep ultraviolet absorption, limited mid-infrared broadening, and poor stability of microstructured optical fibers, this invention provides an ultra-wideband spectrum generation device and method to solve the problems of difficulty in simultaneously covering the 200nm to 2400nm band and high power damage on a single platform.

[0008] The first aspect of the present invention provides an ultra-wideband spectral generator, comprising: Pump light source, used to provide femtosecond pulse sequences; An optical adjustment and coupling system is provided at the beam output end of the pump light source and includes a half-wave plate, a polarizing beam splitter, and a focusing lens arranged sequentially along the optical path. The input end face of the neodymium-doped phosphate glass fiber is located at the focal plane of the focusing lens; A spectral acquisition unit is located at the output end of the neodymium-doped phosphate glass optical fiber; The neodymium-doped phosphate glass fiber is a solid single-clad structure with a step refractive index distribution, consisting of a core region and a cladding region covering the core region; the core region uses N31 type phosphate glass as the matrix and is doped with Nd.3+ The Nd 3+ The doping concentration is 2.2 × 10⁻⁶. 20 -2.3×10 20 cm -3 The cladding region is made of phosphate glass. The pump light emitted by the pump source is guided and coupled to the core region of the neodymium-doped phosphate glass fiber by the half-wave plate, polarizing beam splitter and focusing lens in sequence. Stimulated Raman cascade and nonlinear frequency conversion effects are excited in the neodymium-doped phosphate glass fiber, and an ultra-wideband coherent spectrum spanning 200-2400 nm is output.

[0009] Compared with existing technologies, this invention uses neodymium-doped phosphate glass fiber (N31 type matrix + high concentration Nd) 3+ Using doped light as a gain medium, a femtosecond pulse sequence with a specific wavelength range is provided by a pump source. After being coupled into an optical fiber through an optical adjustment and coupling system, it synergistically excites the nonlinear frequency transformation of the stimulated Raman cascade effect in the matrix and the energy level transition of neodymium ions, and simultaneously generates deep ultraviolet to visible light radiation on the short-wavelength side and near-infrared to mid-infrared radiation on the long-wavelength side. Finally, it achieves ultrawide coherent spectrum output across octave bands of 200-2400nm, breaking through the spectral coverage limitation of traditional single physical mechanisms.

[0010] In one possible implementation, the center wavelength of the femtosecond pulse sequence output by the pump light source is 1028-1032 nm, the pulse width is 100-200 fs, and the repetition frequency is 0.1-10 MHz.

[0011] Compared with the prior art, the present invention ensures that the pump photon energy matches the high-frequency vibration mode of the phosphate matrix by limiting the center wavelength, pulse width and repetition frequency range of the pump light source output, and fully excites the strong stimulated Raman characteristic peaks of the phosphate matrix at multiple wavenumbers, providing a stable energy basis for multiphonon Raman cascade.

[0012] In one possible implementation, the center wavelength of the femtosecond pulse sequence output by the pump light source is 1030 nm, the pulse width is 160 fs, and the repetition frequency is 0.25 MHz.

[0013] Compared with the prior art, the present invention precisely sets the pulse width to a specific value that matches the Raman response time of phosphate glass, so that the pulse duration is sufficient to support the relaxation and activation of the phonon field inside the optical fiber. This guides energy into the stimulated Raman response path, drives the multiphonon Raman cascade effect to smoothly cross the zero-dispersion wavelength, and triggers soliton fission and soliton self-frequency shift after entering the anomalous dispersion region, thereby achieving a deep redshift of the spectrum to the mid-infrared band.

[0014] In one possible implementation, the diameter of the core region of the neodymium-doped phosphate glass fiber is 150-200 μm, and the diameter of the cladding region is 300-400 μm.

[0015] Compared with existing technologies, this invention significantly reduces the coupling difficulty of spatial light to the end face of neodymium phosphate glass fiber by setting a large core diameter geometric structure range, thereby improving coupling efficiency. At the same time, it effectively disperses the heat load at the end face by utilizing the increased mode field area, avoiding catastrophic end face damage that is prone to occur in small core diameter fibers under high power, and significantly improving the end face damage threshold of the fiber.

[0016] In one possible implementation, the diameter of the core region of the neodymium-doped phosphate glass fiber is 180 μm, and the diameter of the cladding region is 380 μm.

[0017] Based on this, the present invention precisely locks the zero-dispersion wavelength of neodymium phosphate glass fiber to around 1.30 μm by using a specific ratio of 180 μm core diameter to 380 μm cladding diameter. This ensures that the pump light in the normal dispersion region undergoes significant self-phase modulation and pulse compression before soliton fission occurs, thus creating the necessary ultra-high instantaneous field strength environment for subsequent triggering of deep ultraviolet nonlinear frequency conversion.

[0018] In one possible implementation, the neodymium-doped phosphate glass fiber is prepared by the following method: Step S1: High-purity neodymium-doped N31 type phosphate glass is used as the core region and phosphate glass is used as the cladding region, and then assembled into an extrusion mold; Step S2: Set an annular isolation ring inside the extrusion die so that the extrusion rod only acts on the core area and cladding area inside the annular isolation ring, while peeling off and removing the surface layer of the core area that contacts the inner wall of the extrusion die to obtain a preform. Step S3: The extruded preform is first annealed, and then heated in an inert atmosphere to be drawn into fibers to obtain the neodymium-doped phosphate glass optical fiber.

[0019] Compared with existing technologies, this invention prepares neodymium-doped phosphate glass optical fibers by introducing a "peeling and isolation extrusion method". A specially designed annular isolation ring is set in the extrusion mold, so that the extrusion rod applying pressure only acts on the core and cladding regions inside the annular isolation ring, while automatically peeling off the surface layer of the outer core region, which is in contact with the inner wall of the extrusion mold and has surface impurities and defects. This fundamentally eliminates physical defects such as bubbles, impurities and microcracks at the core-cladding interface, and significantly reduces the transmission loss of the optical fiber.

[0020] In one possible implementation, in step S2, the inner diameter of the annular isolation ring matches the diameter of the target core region of the neodymium-doped phosphate glass fiber, and the core glass surface layer stripped away is the peripheral defect layer that contacts the inner wall of the extrusion die.

[0021] In one possible implementation, the annealing parameters in step S3 are as follows: temperature is 400-550℃, holding time is 2-6h; and the heat treatment temperature is 520-650℃.

[0022] Compared with the prior art, the present invention completely eliminates the residual thermal stress inside the preform by annealing within a specific temperature range; and ensures that the intrinsic transmission loss of neodymium-doped phosphate glass fiber is maintained at an extremely low level in a specific band by heating and drawing the fiber in an inert atmosphere within a specific temperature range, thus maintaining excellent resistance to thermal softening.

[0023] A second objective of this invention is to provide a method for generating ultra-wideband spectra based on the aforementioned ultra-wideband spectrometer, comprising the following steps: Step A1: Adjust the pump light source to output a femtosecond pulse sequence within a preset center wavelength range, and set the pulse width to a duration sufficient to activate the stimulated Raman scattering path in the neodymium-doped phosphate glass fiber. Step A2: Adjust the incident light power through the optical adjustment and coupling system, and focus the pump light on the end face of the neodymium-doped phosphate glass fiber to control the incident peak power to a level sufficient to excite nonlinear effects; Step A3: After the pump light is coupled into the core region of the neodymium-doped phosphate glass fiber, the matrix nonlinearity effect of the neodymium-doped phosphate glass fiber and the energy level transition effect of neodymium ions are utilized to generate deep ultraviolet to visible light radiation on the short-wavelength side through the synergistic effect of frequency conversion and upconversion radiation, and to generate near-infrared to mid-infrared radiation on the long-wavelength side through stimulated Raman cascade and soliton frequency shift. Step A4: Collect ultra-wideband coherent spectral signals spanning a preset band range using the spectral acquisition unit.

[0024] By dynamically adjusting the pulse width to activate the stimulated Raman scattering path and combining it with peak power control, deep ultraviolet to visible radiation is generated on the short-wavelength side using third harmonic generation, sum-frequency effect, and the synergistic effect of excited-state absorption and upconversion radiation of neodymium ions. Near-infrared to mid-infrared radiation is generated on the long-wavelength side using multiphonon stimulated Raman cascade and soliton self-frequency shift. Without changing the physical structure of neodymium-doped phosphate glass fiber, the efficient generation of an ultrawide spectrum of 200-2400nm is achieved, with extremely high power processing capability. Attached Figure Description

[0025] Figure 1This is a cross-sectional image of the neodymium-doped phosphate glass optical fiber of the present invention; Figure 2 This is a schematic diagram of the ultra-wideband spectral generator of the present invention; Figure 3 The group velocity dispersion curve of the neodymium-doped phosphate glass fiber of the present invention is shown. Figure 4 The normalized spectrum of the 200-1100nm band under 160fs pulse width excitation in Embodiment 1 of the present invention. Figure 5 This is a normalized supercontinuum spectrum of the 600-2400nm band under high-power excitation with a pulse width of 160fs in Embodiment 1 of the present invention.

[0026] Explanation of reference numerals in the attached figures: 1. Core region; 2. Cladding region; 3. Pump source; 4. Half-wave plate; 5. Polarizing beam splitter; 6. Focusing lens; 7. Neodymium-doped phosphate glass fiber; 8. Spectrum acquisition unit. Detailed Implementation

[0027] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the claims of the present invention.

[0028] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0029] Unless otherwise defined, all terms, symbols, and other scientific terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In some instances, terms having a conventional meaning are defined herein for clarification or ease of reference, and such definitions should not be construed as indicating a significant difference from conventional understanding in the art. The technical methods described or referenced herein are generally well understood by those skilled in the art and employed by conventional methods. Unless otherwise stated, the use of commercially available kits, reagents, and instruments shall be performed according to the manufacturer's instructions and parameters.

[0030] like Figure 2As shown in the figure, this specific embodiment provides an ultra-wideband spectrum generator, including: Pump source 3, used to provide femtosecond pulse sequences; An optical adjustment and coupling system is set at the beam output end of the pump light source 3, and includes a half-wave plate 4, a polarizing beam splitter 5 and a focusing lens 6 arranged sequentially along the optical path; The neodymium-doped phosphate glass fiber 7 has its input end face placed at the focal plane of the focusing lens 6; The spectral acquisition unit 8 is located at the output end of the neodymium-doped phosphate glass fiber 7; like Figure 1 As shown in the cross-sectional image, the neodymium-doped phosphate glass fiber 7 is a solid single-clad structure with a step refractive index distribution, consisting of a core region 1 and a cladding region 2 covering the outside of the core region 1; the core region 1 uses N31 type phosphate glass as the matrix and is doped with Nd. 3+ Nd 3+ The doping concentration is 2.2 × 10⁻⁶. 20 -2.3×10 20 cm -3 The cladding region 2 is made of phosphate glass. The pump light emitted by the pump source 3 is guided and coupled to the core region 1 of the neodymium phosphate glass fiber 7 through the half-wave plate 4, the polarizing beam splitter 5 and the focusing lens 6 in sequence. The stimulated Raman cascade and nonlinear frequency conversion effect are excited in the neodymium phosphate glass fiber 7, and an ultra-wideband coherent spectrum spanning 200-2400 nm is output.

[0031] Under ultrafast pump light of 100-200 fs, neodymium-doped phosphate glass fiber 7 exhibits a strong nonlinear interaction with the excitation light through its unique phosphate glass matrix. Phosphate glass possesses an extremely high stimulated Raman scattering gain coefficient, with its peak gain typically several times that of silica glass. This device guides energy into the stimulated Raman response path by setting the pulse width sufficiently to support the relaxation and activation of the phonon field within the fiber. In this mode, the 1020-1060 nm pump light fully excites the multiphonon stimulated Raman cascade effect in the phosphate matrix. This cascade effect smoothly transfers energy across the zero-dispersion wavelength near 1.25-1.35 μm in the fiber. Upon entering the anomalous dispersion region, it further triggers soliton fission and a strong soliton self-frequency shift process, causing the spectrum to broaden to a depth of 2400 nm in the infrared end. Meanwhile, under the synergistic effect of third harmonic generation, sum-frequency nonlinearity, and neodymium ion upconversion luminescence, strong deep ultraviolet to visible light radiation is generated in the short-wavelength direction, ultimately achieving an ultrawide spectrum output spanning octave bands from 200 nm to 2400 nm.

[0032] In specific operation, the center wavelength of the femtosecond pulse sequence output by the pump light source 3 is 1028-1032nm, the pulse width is 100-200fs, and the repetition frequency is 0.1-10MHz.

[0033] More preferably, the center wavelength of the femtosecond pulse sequence output by the pump light source 3 is 1030 nm, the pulse width is 160 fs, and the repetition frequency is 0.25 MHz.

[0034] In specific operations, the diameter of the core region 1 of the neodymium-doped phosphate glass fiber 7 is 150-200 μm, and the diameter of the cladding region 2 is 300-400 μm.

[0035] More preferably, the diameter of the core region 1 of the neodymium-doped phosphate glass fiber 7 is 180 μm, and the diameter of the cladding region 2 is 380 μm.

[0036] Compared with existing technologies, this size ratio and design have the following advantages: Firstly, it significantly improves the energy injection efficiency and damage threshold under high-power pumping. The core region 1 at this ratio has a large transverse cross-section (180µm), which not only greatly reduces the coupling difficulty of spatial light to the fiber end face and significantly improves coupling efficiency, but more importantly, increases the end face damage threshold of the neodymium-doped phosphate glass fiber 7. When facing the megawatt-level peak power pumping required by this invention, the large core diameter design can effectively disperse the heat load at the end face, avoiding the catastrophic end face damage that easily occurs in small-core-diameter fibers under high power. By significantly increasing the absolute total power injected into the core region 1, the dilution of nonlinear density due to the larger effective mode field area is compensated, thereby obtaining a nonlinear interaction intensity sufficient to trigger ultra-wideband generation while maintaining fiber integrity.

[0037] Secondly, it achieves precise locking of dispersion characteristics and synergy with physical mechanisms. By employing neodymium-doped phosphate glass with a specific composition and a core diameter of 180µm, the zero-dispersion wavelength of the neodymium-doped phosphate glass fiber 7 is stabilized around 1.3µm. This ensures that the pump light with a center wavelength around 1030nm is in a deeper positive dispersion region. Under strong power injection (peak power up to 132.5MW), this dispersion configuration can induce significant self-phase modulation and pulse compression evolution of the initial pulse before soliton fission occurs. This pre-compression mechanism significantly enhances the pulse's peak intensity in the time domain, thus creating the necessary physical environment for triggering efficient deep-ultraviolet nonlinear frequency conversion within the fiber: it utilizes ultra-high instantaneous field strength to induce a third harmonic process with a center wavelength of approximately 344 nm, and promotes a cascaded sum-frequency effect between this high-energy shortwave signal and coherent components (such as 1130 nm and 580 nm frequency components) generated by four-wave mixing and Raman processes within the fiber. This allows for precise frequency broadening into the deep-ultraviolet band (such as 263 nm and 216 nm). This synergistic mechanism ensures that the device can achieve efficient redistribution of ultra-wideband energy using the unique nonlinear response of neodymium-doped phosphate fibers without relying on complex microstructures.

[0038] It is important to note that the large-core diameter (180µm) step-index fiber used in this invention is a multimode fiber. In actual experiments, by focusing the pump light tightly onto the central region of the fiber endface, the fundamental mode can be preferentially excited, allowing nonlinear interactions to occur primarily within the fundamental mode. Under these conditions, the dispersion and nonlinear characteristics of the fundamental mode dominate the spectral evolution process, including stimulated Raman cascades, soliton fission, and soliton self-frequency shifts. Simultaneously, the large-core diameter design provides a high-end surface damage threshold and low coupling loss, ensuring stable operation under high-power pumping.

[0039] It is worth mentioning that the neodymium-doped phosphate glass fiber 7 was prepared using the following method: Step S1: High-purity neodymium-doped N31 type phosphate glass is used as the core region 1 and phosphate glass is used as the cladding region 2, and then assembled into an extrusion mold; Step S2: Set an annular isolation ring inside the extrusion die so that the extrusion rod only acts on the core region 1 and cladding region 2 inside the annular isolation ring, while peeling off and removing the surface layer of the core region 1 that is in contact with the inner wall of the extrusion die to obtain a preform. Step S3: The extruded preform is first annealed, and then heated in an inert atmosphere to be drawn into fibers to obtain neodymium-doped phosphate glass optical fiber 7.

[0040] In specific operation, in step S2, the inner diameter of the annular isolation ring matches the diameter of the target core region 1 of the neodymium-doped phosphate glass fiber 7.

[0041] In specific operation, the parameters for annealing in step S3 are as follows: temperature is 400-550℃, holding time is 2-6h; and the temperature for heat treatment is 520-650℃.

[0042] The present invention also provides a method for generating ultra-wideband spectra based on an ultra-wideband spectrometer, comprising the following steps: Step A1: Adjust the pump light source 3 to output a femtosecond pulse sequence within a preset center wavelength range, and set the pulse width to be sufficient to activate the stimulated Raman scattering path in the neodymium-doped phosphate glass fiber 7. Step A2: Adjust the incident light power through the optical adjustment and coupling system, and focus the pump light on the end face of the neodymium-doped phosphate glass fiber 7 to control the incident peak power to a level sufficient to excite nonlinear effects; Step A3: After the pump light is coupled into the core region 1 of the neodymium-doped phosphate glass fiber 7, the deep ultraviolet to visible light radiation is generated on the short-wavelength side through the synergistic effect of frequency conversion and upconversion radiation, and on the long-wavelength side through stimulated Raman cascade and soliton frequency shift. Step A4: Collect ultra-wideband coherent spectral signals spanning a preset band range through the spectral acquisition unit 8.

[0043] Compared with the prior art, the present invention has the following advantages: 1. This invention breaks the dependence of ultra-wideband spectrum generation on complex physical waveguide structures. Existing technologies typically rely on altering the physical microstructure or geometric parameters of optical fibers (such as tapered diameter) to achieve specific dispersion modulation. Once fabricated, the spectral output characteristics are fixed by the physical structure. This invention utilizes the unique nonlinear response characteristics of neodymium-doped phosphate glass fibers to achieve efficient generation of octave band spectra from deep ultraviolet (200 nm) to mid-infrared (2400 nm) on a simple step-index fiber platform. This is achieved by effectively guiding the nonlinear evolution path of excited states (such as inducing multiphonon Raman cascades and soliton dynamics evolution), significantly improving the system's stability and ease of fabrication.

[0044] 2. Bidirectional synergistic broadening of the visible and infrared ends is achieved using Nd ion doping. Unlike existing technologies that use undoped optical fibers to generate supercontinuum, this invention introduces Nd ions into phosphate glass optical fibers. The excited-state absorption and upconversion fluorescence mechanisms of Nd ions synergistically generate strong visible light radiation, while the high Raman gain of the phosphate matrix achieves mid-infrared broadening. This dual spectral broadening mechanism of rare-earth ion upconversion and matrix nonlinearity is realized within the same optical fiber, resulting in spectral coverage exceeding that of a single nonlinear mechanism.

[0045] The following is a further verification based on specific embodiments.

[0046] Example 1

[0047] This embodiment provides an ultrawideband spectral generator based on excited-state modulation. The overall structure of the device mainly includes: Pump source 3: Located at the very front of the entire system's optical path. In this embodiment, a commercial ytterbium-doped femtosecond laser system is selected, with a center wavelength of 1030 nm, a pulse width of 160 fs, and a repetition frequency of 0.25 MHz. Half-wave plate 4 and polarizing beam splitter 5: are sequentially arranged downstream of the optical path of pump source 3. Together, they form a continuously adjustable power attenuation and polarization control unit, which is used to precisely adjust the power of the incident beam. Focusing lens 6: positioned after polarizing beam splitter 5, preferably with a focal length of [missing information]. f = 25mm plano-convex lens, used to focus spatial beams with high intensity; Neodymium-doped phosphate glass fiber 7: The input end is placed at the focal point of the focusing lens 6; Spectral acquisition unit 8: Located at the output end of neodymium-doped phosphate glass fiber 7, used to collect and analyze ultra-wideband spectral signals.

[0048] The neodymium-doped phosphate glass fiber 7, located at the focal point, is a solid single-clad structure with a step refractive index distribution. This neodymium-doped phosphate glass fiber 7 consists of a core region 1 and a cladding region 2. The diameter of the core region 1 is 180 µm, and the diameter of the cladding region 2 is 380 µm. The core region 1 uses N31 type phosphate glass as the matrix and is doped with Nd. 3+ Nd 3+ The doping concentration is 2.26 × 10⁻⁶. 20 cm -3 The cladding region 2 is made of phosphate glass; the physical length of the neodymium-doped phosphate glass optical fiber 7 is precisely cut and set to 40 cm. For example... Figure 3 As shown in the group velocity dispersion curve, the neodymium-doped phosphate glass fiber 7 exhibits normal dispersion at a pump wavelength of 1030 nm, and its zero-dispersion wavelength is precisely locked at around 1.30 µm.

[0049] The neodymium-doped phosphate glass fiber 7 in this embodiment is prepared using the "skin-removal and isolation extrusion method." This method overcomes the problem that physical defects such as bubbles, impurities, and microcracks easily form at the interface between the core region 1 and the cladding region 2 in traditional tube-rod methods or ordinary extrusion methods, leading to huge optical fiber transmission losses. The specific preparation process is as follows: Step S1: Glass grinding and mold assembly High-purity neodymium-doped N31 phosphate glass was used as the core glass, and undoped phosphate glass was used as the cladding glass. Both were cut and optically polished to match the dimensions of the extrusion die. The core glass was placed in the upper layer of the extrusion die cavity, and the cladding glass was placed in the lower layer. The assembly was then placed into the extrusion die.

[0050] Step S2: Peeling and extrusion molding assisted by annular isolation ring An annular isolation ring is set inside the extrusion die, the inner diameter of which matches the diameter of the core region 1 of the target optical fiber. When the extrusion rod applies pressure downwards, it only directly acts on the core glass inside the annular isolation ring and the cladding glass below it; the ring of core glass located outside the annular isolation ring and in direct contact with the inner wall of the extrusion die (i.e., the outer core region 1) is automatically peeled off and removed during the co-extrusion process because it is not subjected to axial pressure, and does not enter the preform body. The entire extrusion process is carried out under the protection of an inert gas (such as high-purity nitrogen or argon) to prevent glass oxidation.

[0051] Step S3, Annealing treatment The extruded preforms are transferred into an annealing furnace and held at 500°C for 4 hours to completely eliminate residual internal thermal stress. After annealing, they are cooled in the furnace.

[0052] Step S4: Precast rod cutting and inspection After annealing, the optical fiber preform is inspected for appearance and internal defects. Complete segments without bubbles, cracks, or interface delamination are cut and fixed on the clamping device of the drawing machine.

[0053] Step S5: Temperature-controlled drawing into fiber Under continuous inert gas protection, the heating zone temperature of the drawing furnace was precisely set to 600℃ based on the softening temperature characteristics of phosphate glass. By controlling the drawing tension and speed, the preform was drawn into a finished neodymium-doped phosphate glass optical fiber with the required core-cladding size.

[0054] The operation method of the ultra-wideband spectral generator based on excited-state modulation in this embodiment specifically includes the following steps: A1. Turn on the pump light source 3 with a center wavelength of 1030nm, and precisely adjust the pulse width to 160fs mode in the control program.

[0055] A2. The laser beam emitted by the pump source 3 passes through the half-wave plate 4 and the polarizing beam splitter 5 in sequence. By rotating the angle of the half-wave plate 4, the pump light power entering the subsequent system is linearly adjusted.

[0056] A3. The beam, after power adjustment, is spatially focused by focusing lens 6;

[0057] A4. A 40cm long neodymium-doped phosphate glass fiber 7 is placed on a precision three-dimensional adjustment platform. The platform is adjusted so that the input end face of the fiber is precisely positioned at the focal point of the focusing lens 6. By fine-tuning the end face position, the pump light is efficiently coupled into the fiber core region 1. Under this excitation state, the actual injected peak power reaches 1.325 × 10⁻⁶. 8 W (i.e., 132.5MW);

[0058] A5. At the fiber optic output end, the spectral acquisition unit 8 is used for segmented measurement and signal collection, and the vertical axis is uniformly normalized.

[0059] In the specific operation described above, when a 160 fs laser is injected into the neodymium-doped phosphate glass fiber 7 with an extremely high peak power of 132.5 MW, the nonlinear dynamic evolution mechanism inside the fiber is as follows: The 160 fs pulse width provided ample relaxation time for the phonon field inside the fiber, exciting significant stimulated Raman scattering and cascaded four-wave mixing effects. The results are as follows: Figure 4 and Figure 5 As shown. It should be noted that, Figure 4 and Figure 5 The characterization differences in the overlapping wavelength range of 600-1100nm are due to differences in testing equipment and dimensions. Figure 4 Data were collected using a marine optical spectrometer. The raw vertical axis represents detector counts, which characterizes relative light intensity. No power calibration was performed. Figure 5 Data were acquired using a Ganges spectrometer, with the original vertical axis representing the absolute power value (dBm). To facilitate a direct comparison of the spectral morphology of the two images and a joint characterization of the overall coverage characteristics of the supercontinuum, the two original spectra were normalized before being presented in the output image. Figure 4 and Figure 5 The vertical axis of the graph is labeled with normalized intensity (au). Normalization only changes the representation of the vertical axis dimensions and does not alter the relative morphology of the spectrum or the intensity relationships between bands. Based on this, under 160 fs excitation conditions, the detector of the marine optical spectrometer exhibits saturation in the 600-1100 nm band, leading to distortion of the relative intensity in this band. Therefore, the supercontinuum characteristics in the 600-1100 nm band and extending to the 2400 nm band are... Figure 5 For reference only; combined with normalized data. Figure 4 and Figure 5 This can fully characterize the supercontinuum coverage characteristics of Embodiment 1 of the present invention in the 200-2400 nm range.

[0060] Specifically, such as Figure 4As shown (the upper part is the spectral distribution image when the laser is input to the Nd: phosphate glass fiber 7 at 960 mW, and the lower part is the spectral distribution image when the laser is input to the Nd: phosphate glass fiber 7 at 200 mW), the spectral evolution in the 200-1100 nm band exhibits distinct regional characteristics. Near the 1030 nm pump wavelength, spectral broadening is mainly driven by significant self-phase modulation and strongly modulated by the intrinsic ground-state absorption bands of Nd: ions near 745 nm, 800 nm, and 870 nm, thus forming a characteristic transmission window. In the 300-450 nm region, the spectrum mainly originates from the third harmonic generation process of the 1032 nm pump light, with its calculated central peak located around 344 nm; while in the deep ultraviolet band of 200-300 nm, it is generated by the sum-frequency effect of the third harmonic signal and the infrared component (such as the peaks at 263 nm and 216 nm). In the 600-800nm ​​region, the spectral components mainly originate from cascaded four-wave mixing (such as the 802nm peak) and the sum-frequency process of the pump light and Raman components (such as the 605nm peak).

[0061] The more critical nonlinear evolution occurs in the infrared band. For example... Figure 5 As shown, when excited at a high power of 960mW, the spectrum in the 600-2400nm band exhibits an extremely broad and smooth banding. In this process, the system first generates frequency sidebands (such as nodes at 1087nm, 1179nm, and 1248nm) in the near-infrared region through cascaded four-wave mixing. Subsequently, these four-wave mixing sidebands further excite the high-frequency vibration modes unique to phosphate fiber networks. This is thanks to the phosphate matrix at 1180cm⁻¹. -1 1280cm -1 And 1474cm -1 The strong stimulated Raman characteristic peaks exhibited at this location, with high-energy sidebands (such as the 1248 nm component) undergoing significant Stokes shifts through these high-frequency phonon modes, form a strong multiphonon stimulated Raman cascade, producing strong Raman components near 1474-1489 nm. This mechanism of four-wave mixing and stimulated Raman cascade synergistically smoothly transfers energy to longer wavelengths, successfully crossing the zero-dispersion wavelength of approximately 1.30 µm. Once the energy enters the anomalous dispersion region, it immediately triggers significant soliton fission and continuous soliton self-shifting processes; combined with the high-level four-wave mixing effect in the deep infrared region (such as the 2022-2360 nm band), it ultimately extends the spectrum to 2.4 µm.

[0062] Ultimately, the device outputs a supercontinuum spanning an ultrawide frequency band from 200 nm to 2400 nm, covering not only the deep ultraviolet to visible light region but also extending deep into the mid-infrared molecular vibrational fingerprint region. Linear fitting of the input-output characteristics demonstrates that, under a 160 fs pumping mechanism, the device possesses extremely high power handling capabilities, with an average power conversion efficiency as high as 58.9%, providing a robust, efficient, and full-spectrum-covering high-quality light source for multimodal spectroscopy.

[0063] Example 2 This embodiment provides an ultrawideband spectral generator based on excited-state modulation. The overall structure of the device mainly includes: Pump source 3: Located at the very front of the entire system's optical path. In this embodiment, a commercial ytterbium-doped femtosecond laser system is selected, with a center wavelength of 1028 nm, operating in a 200 fs pulse mode and a repetition frequency of 0.1 MHz. Half-wave plate 4 and polarizing beam splitter 5: are sequentially arranged downstream of the optical path of pump source 3. Together, they form a continuously adjustable power attenuation and polarization control unit, which is used to precisely adjust the power of the incident beam. Focusing lens 6: Located after polarizing beam splitter 5, preferably a plano-convex lens with a focal length of f=25mm, used to focus the spatial beam with high intensity; Neodymium-doped phosphate glass fiber 7: The input end is placed at the focal point of the focusing lens 6; Spectral acquisition unit 8: Located at the output end of neodymium-doped phosphate glass fiber 7, used to collect and analyze ultra-wideband spectral signals.

[0064] The neodymium-doped phosphate glass fiber 7, located at the focal point, is a solid single-clad structure with a step refractive index distribution. This neodymium-doped phosphate glass fiber 7 consists of a core region 1 and a cladding region 2. The diameter of the core region 1 is 150 µm, and the diameter of the cladding region 2 is 300 µm. The core region 1 uses N31 type phosphate glass as the matrix and is doped with Nd. 3+ Nd 3+ The doping concentration is 2.2 × 10⁻⁶. 20 cm -3 The cladding region 2 is made of phosphate glass; the physical length of the neodymium-doped phosphate glass optical fiber 7 is precisely cut and set to 40 cm.

[0065] The neodymium-doped phosphate glass fiber 7 in this embodiment is prepared using the "skin-removal and isolation extrusion method." This method overcomes the problem that physical defects such as bubbles, impurities, and microcracks easily form at the interface between the core region 1 and the cladding region 2 in traditional tube-rod methods or ordinary extrusion methods, leading to huge optical fiber transmission losses. The specific preparation process is as follows: Step S1: Glass grinding and mold assembly High-purity neodymium-doped N31 phosphate glass was used as the core glass, and undoped phosphate glass was used as the cladding glass. Both were cut and optically polished to match the dimensions of the extrusion die. The core glass was placed in the upper layer of the extrusion die cavity, and the cladding glass was placed in the lower layer. The assembly was then placed into the extrusion die.

[0066] Step S2: Peeling and extrusion molding assisted by annular isolation ring An annular isolation ring is set inside the extrusion die, the inner diameter of which matches the diameter of the core region 1 of the target optical fiber. When the extrusion rod applies pressure downwards, it only directly acts on the core glass inside the annular isolation ring and the cladding glass below it; the ring of core glass located outside the annular isolation ring and in direct contact with the inner wall of the extrusion die (i.e., the outer core region 1) is automatically peeled off and removed during the co-extrusion process because it is not subjected to axial pressure, and does not enter the preform body. The entire extrusion process is carried out under the protection of an inert gas (such as high-purity nitrogen or argon) to prevent glass oxidation.

[0067] Step S3, Annealing treatment The extruded preforms are transferred into an annealing furnace and held at 400°C for 6 hours to completely eliminate residual internal thermal stress. After annealing, they are cooled in the furnace.

[0068] Step S4: Precast rod cutting and inspection After annealing, the optical fiber preform is inspected for appearance and internal defects. Complete segments without bubbles, cracks, or interface delamination are cut and fixed on the clamping device of the drawing machine.

[0069] Step S5: Temperature-controlled drawing into fiber Under continuous inert gas protection, the heating zone temperature of the drawing furnace was precisely set to 650℃ based on the softening temperature characteristics of phosphate glass. By controlling the drawing tension and speed, the preform was drawn into a finished neodymium-doped phosphate glass optical fiber with the required core-cladding size.

[0070] Example 3 This embodiment provides an ultrawideband spectral generator based on excited-state modulation. The overall structure of the device mainly includes: Pump source 3: Located at the very front of the entire system's optical path. In this embodiment, a commercial ytterbium-doped femtosecond laser system is selected, with a center wavelength of 1032nm, operating in a 100fs pulse mode and a repetition frequency of 10MHz. Half-wave plate 4 and polarizing beam splitter 5: are sequentially arranged downstream of the optical path of pump source 3. Together, they form a continuously adjustable power attenuation and polarization control unit, which is used to precisely adjust the power of the incident beam. Focusing lens 6: positioned after polarizing beam splitter 5, preferably with a focal length of [missing information]. fA plano-convex lens with a diameter of 25mm is used to focus spatial beams with high intensity. Neodymium-doped phosphate glass fiber 7: The input end is placed at the focal point of the focusing lens 6; Spectral acquisition unit 8: Located at the output end of neodymium-doped phosphate glass fiber 7, used to collect and analyze ultra-wideband spectral signals.

[0071] The neodymium-doped phosphate glass fiber 7, located at the focal point, is a solid single-clad structure with a step refractive index distribution. This neodymium-doped phosphate glass fiber 7 consists of a core region 1 and a cladding region 2. The diameter of the core region 1 is 200 µm, and the diameter of the cladding region 2 is 400 µm. The core region 1 uses N31 type phosphate glass as the matrix and is doped with Nd. 3+ Nd 3+ The doping concentration is 2.3 × 10⁻⁶. 20 cm -3 The cladding region 2 is made of phosphate glass; the physical length of the neodymium-doped phosphate glass optical fiber 7 is precisely cut and set to 40 cm.

[0072] The neodymium-doped phosphate glass fiber 7 in this embodiment is prepared using the "skin-removal and isolation extrusion method." This method overcomes the problem that physical defects such as bubbles, impurities, and microcracks easily form at the interface between the core region 1 and the cladding region 2 in traditional tube-rod methods or ordinary extrusion methods, leading to huge optical fiber transmission losses. The specific preparation process is as follows: Step S1: Glass grinding and mold assembly High-purity neodymium-doped N31 phosphate glass was used as the core glass, and undoped phosphate glass was used as the cladding glass. Both were cut and optically polished to match the dimensions of the extrusion die. The core glass was placed in the upper layer of the extrusion die cavity, and the cladding glass was placed in the lower layer. The assembly was then placed into the extrusion die.

[0073] Step S2: Peeling and extrusion molding assisted by annular isolation ring An annular isolation ring is set inside the extrusion die, the inner diameter of which matches the diameter of the target optical fiber core region 1. When the extrusion rod applies pressure downwards, it only directly acts on the core glass inside the annular isolation ring and the cladding glass below; the ring of core glass located outside the annular isolation ring, directly in contact with the inner wall of the extrusion die (i.e., the outer core region 1), is not subjected to axial pressure and is automatically peeled off and removed during the co-extrusion process, not entering the preform body. The radial thickness of the surface layer of the peeled-off core region 1 is 3 mm. The entire extrusion process is carried out under the protection of an inert gas (such as high-purity nitrogen or argon) to prevent glass oxidation.

[0074] Step S3, Annealing treatment The extruded preforms are transferred into an annealing furnace and held at 550°C for 2 hours to completely eliminate residual internal thermal stress. After annealing, they are cooled in the furnace.

[0075] Step S4: Precast rod cutting and inspection After annealing, the optical fiber preform is inspected for appearance and internal defects. Complete segments without bubbles, cracks, or interface delamination are cut and fixed on the clamping device of the drawing machine.

[0076] Step S5: Temperature-controlled drawing into fiber Under continuous inert gas protection, the heating zone temperature of the drawing furnace was precisely set to 520℃ based on the softening temperature characteristics of phosphate glass. By controlling the drawing tension and speed, the preform was drawn into a finished neodymium-doped phosphate glass optical fiber with the required core-cladding size.

[0077] As can be seen from the above results, the ultra-wideband spectral generation device and method provided by the present invention, by using an N31 type phosphate glass matrix and a high concentration of Nd... 3+ A solid single-clad fiber with doped step-index refractive index, combined with a femtosecond pump source with specific parameters, has successfully achieved ultrawideband coherent spectral output spanning the deep ultraviolet to mid-infrared bands without the need for complex microstructures. The core mechanism lies in two aspects: firstly, utilizing the high Raman gain of phosphate glass matched with the pump pulse width to drive multiphonon stimulated Raman cascades, soliton fission, and soliton self-frequency shifts, efficiently extending the spectrum into the mid-infrared region; secondly, leveraging the excited-state absorption and upconversion radiation of neodymium ions, along with third harmonic generation and sum-frequency nonlinear effects, to extend the spectrum into the deep ultraviolet region. Experimental results show that the device possesses extremely high power conversion efficiency, and the fiber prepared using the "peel-and-expose extrusion method" exhibits low transmission loss and strong resistance to optical damage. This invention breaks the traditional dependence of supercontinuum light sources on microstructured fibers or gas-filled hollow fibers, providing a novel coherent light source with a simple structure, stable performance, and full-spectrum coverage for fields such as multimodal spectroscopy, biomedical imaging, and environmental monitoring.

[0078] While the disclosure is as stated above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the protection scope of this invention.

Claims

1. An ultra-wideband spectral generator, characterized in that, include: Pump light source, used to provide femtosecond pulse sequences; An optical adjustment and coupling system is provided at the beam output end of the pump light source and includes a half-wave plate, a polarizing beam splitter, and a focusing lens arranged sequentially along the optical path. The input end face of the neodymium-doped phosphate glass fiber is located at the focal plane of the focusing lens; A spectral acquisition unit is located at the output end of the neodymium-doped phosphate glass optical fiber; The neodymium-doped phosphate glass fiber is a solid single-clad structure with a step refractive index distribution, consisting of a core region and a cladding region covering the core region; the core region uses N31 type phosphate glass as the matrix and is doped with Nd. 3+ The Nd 3+ The doping concentration is 2.2 × 10⁻⁶. 20 -2.3×10 20 cm -3 The cladding region is made of phosphate glass. The pump light emitted by the pump source is guided and coupled to the core region of the neodymium-doped phosphate glass fiber by the half-wave plate, polarizing beam splitter and focusing lens in sequence. Stimulated Raman cascade and nonlinear frequency conversion effects are excited in the neodymium-doped phosphate glass fiber, and an ultra-wideband coherent spectrum spanning 200-2400 nm is output. The center wavelength of the femtosecond pulse sequence output by the pump light source is 1028-1032nm, the pulse width is 100-200fs, and the repetition frequency is 0.1-10MHz. The diameter of the core region of the neodymium-doped phosphate glass fiber is 150-200 μm, and the diameter of the cladding region is 300-400 μm.

2. The ultra-wideband spectral generator as described in claim 1, characterized in that, The pump source outputs a femtosecond pulse sequence with a center wavelength of 1030 nm, a pulse width of 160 fs, and a repetition frequency of 0.25 MHz.

3. The ultra-wideband spectral generator as described in claim 1, characterized in that, The diameter of the core region of the neodymium-doped phosphate glass fiber is 180 μm, and the diameter of the cladding region is 380 μm.

4. The ultra-wideband spectral generator as described in claim 1, characterized in that, The neodymium-doped phosphate glass fiber is obtained by annealing the preform extruded by the extrusion die and then heating it in an inert atmosphere to draw it into fibers. The extrusion die is provided with an annular isolation ring, and the extrusion rod only acts inside the annular isolation ring to peel off and remove the surface layer of the fiber core area that is in contact with the inner wall of the extrusion die.

5. The ultra-wideband spectral generator as described in claim 4, characterized in that, The inner diameter of the annular isolation ring matches the diameter of the target core region of the neodymium-doped phosphate glass fiber, and the core glass surface layer stripped away is the outer defect layer that contacts the inner wall of the extrusion die.

6. The ultra-wideband spectral generator as described in claim 4, characterized in that, The parameters for annealing are as follows: temperature is 400-550℃, holding time is 2-6h; heat treatment temperature is 520-650℃.

7. A method for generating an ultra-wideband spectrum based on the ultra-wideband spectrum generating device according to any one of claims 1 to 6, characterized in that, Includes the following steps: Step A1: Adjust the pump light source to output a femtosecond pulse sequence within a preset center wavelength range, and set the pulse width to a duration sufficient to activate the stimulated Raman scattering path in the neodymium-doped phosphate glass fiber. Step A2: Adjust the incident light power through the optical adjustment and coupling system, and focus the pump light on the end face of the neodymium-doped phosphate glass fiber to control the incident peak power to a level sufficient to excite nonlinear effects; Step A3: After the pump light is coupled into the core region of the neodymium-doped phosphate glass fiber, the matrix nonlinearity effect of the neodymium-doped phosphate glass fiber and the energy level transition effect of neodymium ions are utilized to generate deep ultraviolet to visible light radiation on the short-wavelength side through the synergistic effect of frequency conversion and upconversion radiation, and to generate near-infrared to mid-infrared radiation on the long-wavelength side through stimulated Raman cascade and soliton frequency shift. Step A4: Collect ultra-wideband coherent spectral signals spanning a preset band range using the spectral acquisition unit.

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