A microsphere feedback-based mid-infrared narrow linewidth fiber laser and a method for laser output thereof

Abstract

This invention discloses a mid-infrared narrow-linewidth fiber laser based on microsphere feedback and a method for laser output, relating to the field of mid-infrared laser technology. The mid-infrared narrow-linewidth fiber laser includes Er... 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass optical fiber, pump light source, multilayer dielectric film and passive fluorotellurate glass microspheres, Er 3+ / Yb 3+ The co-doped low-hydroxyl fluorotellurate glass fiber has a tapered region, and passive fluorotellurate glass microspheres achieve wavelength-selective feedback of the whispering-gallery mode through evanescent field coupling. This invention can output a narrow linewidth laser of 2.7 μm, which is extended to the 3-5 μm band through stimulated Raman scattering. This invention has advantages such as narrow linewidth, high stability, precise coupling, and good integration, and is suitable for applications such as environmental monitoring, biomedicine, and high-precision spectroscopic detection.

Description

Technical Field

[0001] This invention relates to the field of laser fabrication technology, and more specifically, to a mid-infrared narrow-linewidth fiber laser based on microsphere feedback and a method for laser output. Background Technology

[0002] Mid-infrared (3-5 μm) narrow-linewidth lasers have broad application prospects in environmental monitoring, biomedicine, and quantum technology. Their MHz-level linewidths enable the detection of gases such as CH4 and N2O at the part-in-a-billion (ppb) level, with precise resolution of absorption spectra. In biomedicine, their wavelength matches the characteristic absorption of molecules, making them suitable for non-invasive blood glucose detection, cancer diagnosis, and tissue spectral imaging. Simultaneously, their low phase noise and high stability make them suitable for high-precision interferometry and quantum technologies such as optical clocks. Therefore, this laser has become an international research hotspot and is considered a core light source for next-generation precision detection and quantum technology. Among current mainstream mid-infrared light sources, quantum cascade lasers are limited by linewidth and temperature drift, while optical parametric oscillators are large and consume high power. In contrast, fiber lasers offer high integration, low power consumption, and good beam quality, and are considered one of the key technologies for overcoming the bottleneck of mid-infrared lasers. Existing research has achieved mid-infrared output through active optical fibers, but due to the lack of narrow-linewidth mirrors or gratings, the linewidths are mostly above GHz and the wavelengths are discrete. In passive fiber lasers, a 3.77μm laser has been obtained by pumping a two-stage Raman shift using a self-developed ~3μm laser. Compared with near-infrared (e.g., 1.55μm) pump, this reduces multi-stage losses and improves efficiency. However, the pump source itself has a wide linewidth (>GHz), making it difficult to achieve a narrow linewidth output. Simultaneously, this type of laser also faces the problem of a shortage of mid-infrared narrow-linewidth optical components and commercially available narrow-linewidth ~3μm pump sources. Although techniques such as four-wave mixing, supercontinuum, and Kerr frequency combs can produce broadband output, they are mostly multi-wavelength or supercontinuum, unable to provide stable single-frequency narrow-linewidth lasers. To overcome the limitations of mid-infrared narrow-linewidth fiber lasers in narrow-band components such as mirrors or gratings, this invention introduces a high quality factor (…). Q This invention utilizes a Whispering Gallery Mode (WGM) optical resonator to achieve narrow linewidth laser output. In this invention, the microsphere not only serves as a narrowband frequency selection unit but also functions as an output mirror of the resonator; this structure facilitates narrow linewidth output and compact integration. The WGM microcavity provides extremely narrow mode selection through Rayleigh scattering-induced mode coupling, enabling single-frequency or narrow linewidth output. At low thresholds, it can trigger nonlinear processes such as stimulated Raman scattering, stimulated Brillouin scattering, and Kerr frequency combing, providing possibilities for mid-infrared wavelength extension. Employing fiber taper coupling achieves both efficient evanescent field coupling and high... Q It maintains its value while seamlessly integrating with existing fiber optic systems, providing a compact and efficient solution for all-fiber, narrow-linewidth mid-infrared lasers. Summary of the Invention

[0003] To overcome the shortcomings of the prior art, this invention provides a mid-infrared narrow-linewidth fiber laser based on microsphere feedback and a method for its laser output. This method utilizes fiber taper evanescent wave coupling to enhance the high-performance of the microsphere resonant cavity. Q Value feedback is introduced into the fiber laser system to achieve high-power, narrow-linewidth mid-infrared laser output, solving the problems of difficulty in balancing power and linewidth and poor system stability in existing technologies.

[0004] The first objective of this invention is to provide a mid-infrared narrow-linewidth fiber laser based on microsphere feedback, comprising: Er 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass fiber: used to generate 2.7μm laser light, and the Er 3+ / Yb 3+ The co-doped low-hydroxyl fluorotellurate glass fiber has a tapered region. Pump light source: set in the Er 3+ / Yb 3+ One end of a co-doped low-hydroxyl fluorotellurate glass optical fiber; Multilayer dielectric film: disposed in the Er 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass fiber is placed near the incident end of the pump light source to achieve high transmission of pump light and high reflection of laser wavelength. Passive fluorotellurate glass microspheres: placed in the conical region and interacting with the Er through an evanescent field. 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass fiber coupling is used to provide wavelength-selective feedback for whispering-gallery modes; Spectrometer: located in the Er 3+ / Yb 3+ The output end of a co-doped low-hydroxyl fluorotellurate glass optical fiber; Wherein, Er 3+ / Yb 3+ In co-doped low-hydroxyl fluorotellurate glass optical fibers, Er 3+ The doping concentration is 0.5-2.0 mol%, Yb 3+ The doping concentration is 2.0-5.0 mol%, OH - The content is less than 10 ppm.

[0005] The working process of the infrared narrow linewidth fiber laser in this invention is as follows: the pump source enters the Er through a multilayer dielectric film. 3+ / Yb 3+Co-doped low-hydroxyl fluorotellurate glass fiber is then coupled to a passive fluorotellurate glass microsphere via a tapered evanescent wave coupling. The high-field localization characteristics of the passive fluorotellurate glass microsphere's WGM (Wavelength Gaussian Mutual Spectroscopy) are utilized to achieve efficient feedback, resulting in a narrow-linewidth 2.7 μm laser output. This 2.7 μm laser serves as a secondary pump source to further excite high-energy lasers. Q The microspheres broaden the wavelength to 3-5 μm through stimulated Raman scattering.

[0006] Based on this, the present invention employs erbium-ytterbium co-doped low-hydroxyl fluorotellurate glass fiber with specific erbium and ytterbium ion doping concentrations and low hydroxyl content. Combined with a conical structure, multilayer dielectric film, and passive fluorotellurate glass microspheres, a complete laser resonance and feedback structure is formed, which can stably generate 2.7μm laser. Wavelength selective feedback is achieved by utilizing the whispering-gallery mode of the passive fluorotellurate glass microspheres, effectively reducing the internal loss of the fiber, ensuring efficient laser gain establishment, and improving the spectral purity of the laser output and the overall working stability of the system.

[0007] In one possible implementation, the passive fluorotellurate glass microspheres have a diameter of 50-200 μm and a quality factor of 1 × 10⁻⁶. 6 Up to 5×10 6 This invention, by limiting the diameter and quality factor range of passive fluorotellurate glass microspheres, can enhance the whispering-gallery mode resonance effect of passive fluorotellurate glass microspheres, improve the wavelength-selective feedback quality, significantly narrow the laser output linewidth, enhance laser monochromaticity and output stability, and make the operation of the mid-infrared narrow-linewidth fiber laser based on microsphere feedback more reliable.

[0008] In one possible implementation, the diameter of the conical region is 1-3 μm, and the coupling distance between the conical region and the surface of the passive fluorotellurate glass microsphere is 10-500 nm. By optimizing the diameter of the conical region and the coupling distance between the conical region and the surface of the passive fluorotellurate glass microsphere, this invention can improve the evanescent wave coupling efficiency of the light field through the conical region and the passive fluorotellurate glass microsphere, reduce light energy loss during the coupling process, ensure stable laser oscillation, and improve the overall laser output efficiency and quality.

[0009] In one possible implementation, the pump source is a 980nm laser diode pump source. By employing a 980nm laser diode pump source, it is possible to... 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass fiber achieves efficient matching, improves pump light absorption efficiency and energy conversion efficiency, provides stable and sufficient excitation conditions for laser generation, and ensures stable laser excitation and continuous output.

[0010] In one possible implementation, the multilayer dielectric film exhibits a reflectivity greater than 99.5% in the 2.7 μm wavelength band and a transmittance greater than 95% in the 980 nm wavelength band. By limiting the reflectivity and transmittance of the multilayer dielectric film in the corresponding wavelength bands, efficient transmission of pump light into Er can be achieved. 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass fiber achieves high-ratio reflection feedback of 2.7μm laser, improves laser resonance conditions, reduces laser oscillation threshold, and enhances laser output power and system operation stability.

[0011] In one possible implementation, a nano-displacement stage is also included for adjusting the relative position of the passive fluorotellurate glass microspheres to the conical region.

[0012] Compared with existing technologies, this invention, by adding a nano-displacement stage, can precisely adjust the relative position between the passive fluorotellurate glass microspheres and the cone region, ensuring a stable and controllable coupling state, improving the system's debugging accuracy and ease of operation, and ensuring that the laser output state remains stable.

[0013] In one possible implementation, the nanostage has a resolution of 10 nm, a stroke of ±2.5 mm, and an adjustment accuracy of 50 nm. This high-precision displacement adjustment system enables subwavelength-level coupling control, ensuring efficient and stable lasing. By limiting the resolution, stroke, and adjustment accuracy of the nanostage, high-precision subwavelength-level position control is achieved, meeting the requirements for fine coupling between the conical region and the passive fluorotellurate glass microspheres, and improving the long-term stability and reliability of the system.

[0014] In one possible implementation, a monitoring device is also included to determine the optimal coupling position between the conical region and the passive fluorotellurate glass microsphere. By adding a monitoring device, the optimal coupling position between the conical region and the passive fluorotellurate glass microsphere can be accurately determined based on changes in backscattered signal intensity, improving the accuracy and efficiency of coupling adjustment, simplifying the system debugging process, and ensuring efficient and stable laser lasing. The backscattered signal is the optical signal that, when light couples from the fiber conical region into the passive fluorotellurate glass microsphere, some of the light energy is backscattered back to the fiber conical region due to imperfect coupling between the passive fluorotellurate glass microsphere and the fiber interface, surface scattering of the passive fluorotellurate glass microsphere, WGM mode mismatch, and other reasons.

[0015] The second objective of this invention is to provide a method for achieving mid-infrared narrow-linewidth laser output based on microsphere feedback, comprising the following steps: Step S1: Provide 980nm pump light, which enters Er through a multilayer dielectric film. 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass optical fiber; Step S2: Precisely adjust the passive fluorotellurate glass microspheres and Er using a nano-displacement stage. 3+ / Yb 3+ The relative positions of the taper regions in the co-doped low-hydroxyl fluorotellurate glass fiber ensure that the coupling spacing is within the range of 10-500 nm. Step S3, the Er 3+ / Yb 3+ The 2.7 μm optical field generated in the co-doped low-hydroxyl fluorotellurate glass fiber is coupled to the passive fluorotellurate glass microsphere via the tapered region. The high Q value of the whispering-gallery mode of the passive fluorotellurate glass microsphere is used to provide wavelength selective feedback, thereby realizing 2.7 μm narrow linewidth laser output. Step S4: The passive fluorotellurate glass microspheres are further excited by 2.7μm laser light as pump light, and 3-5μm band laser output is obtained through stimulated Raman scattering effect.

[0016] Compared with existing technologies, this invention can stably achieve a narrow linewidth laser output of 2.7μm by sequentially executing pump light input, coupling position adjustment, laser resonant output, and stimulated Raman scattering band extension, and further obtain laser output in the 3-5μm band, thus broadening the application scenarios of lasers and meeting the needs of high-precision detection and application in the mid-infrared band. Attached Figure Description

[0017] Figure 1 This is a structural diagram of the mid-infrared narrow-linewidth fiber laser based on microsphere feedback according to the present invention; Figure 2 This is the 3-5μm stimulated Raman scattering spectrum of the mid-infrared narrow-linewidth fiber laser based on microsphere feedback according to the present invention.

[0018] Explanation of reference numerals in the attached figures: 1- 980nm laser diode pump source; 2- Multilayer dielectric film; 3- Er 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass optical fiber; 4-cone region; 5-passive fluorotellurate glass microspheres; 6-spectral analyzer. Detailed Implementation

[0019] 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.

[0020] 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.

[0021] 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.

[0022] like Figure 1 As shown, a specific embodiment of the present invention provides a mid-infrared narrow-linewidth fiber laser based on microsphere feedback, comprising: Er 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass fiber 3: used to generate 2.7μm laser light, and Er 3+ / Yb 3+ The co-doped low-hydroxyl fluorotellurate glass fiber 3 is provided with a tapered region 4, the diameter of which is 1-3 μm; 980nm laser diode-pumped light source 1: set in Er 3+ / Yb 3+ One end of the co-doped low-hydroxyl fluorotellurate glass optical fiber 3; Multilayer dielectric film 2: set in Er 3+ / Yb 3+ The co-doped low-hydroxyl fluorotellurate glass fiber 3 is located near the incident end of the 980nm laser diode pump source 1. The multilayer dielectric film 2 has a reflectivity greater than 99.5% in the 2.7μm band and a transmittance greater than 95% in the 980nm band. Passive fluorotellurate glass microspheres 5: placed in the cone region 4 and interacted with Er through an evanescent field. 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass fiber 3 is used for coupling to provide wavelength-selective feedback for whispering-gallery modes. The passive fluorotellurate glass microspheres 5 have a diameter of 50-200 μm and a quality factor of 1×10⁻⁶. 6 Up to 5×10 6The passive fluorotellurate glass microspheres with the above parameters can improve the evanescent wave coupling efficiency between the light field through the cone region and the passive fluorotellurate glass microspheres, reduce the loss of light energy during the coupling process, ensure stable laser oscillation, and improve the overall laser output efficiency and output quality. Furthermore, the coupling distance between the cone region 4 and the surface of the passive fluorotellurate glass microsphere 5 is 10-500 nm; Spectrum Analyzer 6: Set to Er 3+ / Yb 3+ The output end of co-doped low-hydroxyl fluorotellurate glass fiber 3; Among them, Er 3+ / Yb 3+ In co-doped low-hydroxyl fluorotellurate glass fiber 3, Er 3+ The doping concentration is 0.5-2.0 mol%, Yb 3+ The doping concentration is 2.0-5.0 mol%, OH - The content is less than 10 ppm.

[0023] In specific operation, a nano-displacement stage is also included: used to adjust the relative position of the passive fluorotellurate glass microspheres 5 and the cone region 4. More specifically, the nano-displacement stage has a resolution of 10 nm, a stroke of ±2.5 mm, and an adjustment accuracy of 50 nm.

[0024] In specific operations, a monitoring device may be further included to determine the optimal coupling position between the cone region 4 and the passive fluorotellurate glass microspheres 5.

[0025] This invention also provides a method for achieving mid-infrared narrow-linewidth laser output based on microsphere feedback, comprising the following steps: Step S1: Provide a 980nm laser diode pump source 1. The 980nm laser diode pump source 1 enters the Er through a multilayer dielectric film 2. 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass optical fiber 3; Step S2: Precisely adjust the passive fluorotellurate glass microspheres 5 and Er using a nano-displacement stage. 3+ / Yb 3+ The relative positions of the cone regions 4 of the co-doped low-hydroxyl fluorotellurate glass fiber 3 are such that the coupling spacing is in the range of 10-500nm. Specifically, a three-step adjustment method can be adopted: first, manually coarsely adjust the spacing to 10μm, then finely adjust it in 10nm steps, and finally precisely lock the position of the maximum value of the backscattered signal in 5nm steps. Step S3, Er 3+ / Yb 3+The 2.7 μm optical field generated in the co-doped low-hydroxyl fluorotellurate glass fiber 3 is coupled to the passive fluorotellurate glass microsphere 5 through the conical region. The high Q value of the whispering-gallery mode of the passive fluorotellurate glass microsphere 5 is used to provide wavelength selective feedback, thereby realizing 2.7 μm narrow linewidth laser output. Step S4: Use 2.7μm laser light as pump light to further excite passive fluorotellurate glass microspheres 5, and obtain 3-5μm band laser output through stimulated Raman scattering effect.

[0026] It is worth mentioning that the output linewidth (FWHM) of the 2.7μm laser of this invention is less than 0.1nm, and the output power is greater than 1mW. Compared with traditional fiber lasers, this invention achieves extremely narrow linewidth characteristics while maintaining high power output.

[0027] Furthermore, the 3-5μm laser generated by stimulated Raman scattering in this invention includes multi-level Stokes components, covering the 3.0-5.0μm wavelength band. The WGM resonant frequency is tuned by adjusting the size and refractive index of the passive fluorotellurate glass microspheres 5, achieving wavelength-tunable output.

[0028] This invention also provides a method for fabricating a mid-infrared narrow-linewidth fiber laser, comprising the following steps: A1. Preparation of Er 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass optical fiber 3; A2. Preparation of passive fluorotellurate glass microspheres 5; A3, Er 3+ / Yb 3+ A cone region 4 was fabricated from a co-doped low-hydroxyl fluorotellurate glass fiber 3; A4, in Er 3+ / Yb 3+ A multilayer dielectric film 2 is deposited on the incident end of a co-doped low-hydroxyl fluorotellurate glass optical fiber 3; The pump light emitted from the A5, 980nm laser diode pump source 1 enters Er through the multilayer dielectric film 2. 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass optical fiber 3; A6、Er 3+ / Yb 3+ The 2.7 μm optical field formed in the co-doped low-hydroxyl fluorotellurate glass fiber 3 is coupled to the passive fluorotellurate glass microsphere 5 via the conical region 4. The sound-gallery mode height of the passive fluorotellurate glass microsphere 5 is utilized. Q The value characteristics provide wavelength-selective feedback and serve as the output coupling unit of the resonant cavity to achieve narrow-linewidth lasing of 2.7μm laser; A7. Using a 2.7μm laser as a secondary pump source to further excite high... QThe passive fluorotellurate glass microspheres 5 broaden the wavelength to 3-5 μm through stimulated Raman scattering; A8. A nanometer displacement stage is used to finely adjust the relative position of the passive fluorotellurate glass microspheres 5 and the cone region 4, and a subwavelength-level coupling control is achieved in combination with a monitoring device. A9. Use a spectral analyzer to monitor laser output characteristics in real time and optimize system performance.

[0029] In practice, the passive fluorotellurate glass microspheres 5 are prepared by high-temperature melting method, with a surface roughness of less than 1 nm.

[0030] In practice, cone region 4 is prepared by the hydrogen-oxygen flame tapering method.

[0031] In a specific embodiment of the present invention, a more specific method for fabricating a mid-infrared narrow-linewidth fiber laser is provided, comprising: B1. High-purity TeO2, ZnO, NaF, Er2O3, and Yb2O3 raw materials are mixed according to the specified ratio and melted in a high-temperature (approximately 900℃) melting furnace. The mixture is stirred thoroughly to ensure homogeneity of the components, and then drawn into Er2O3 under a controlled atmosphere. 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass fiber 3, controlling Er 3+ The doping concentration is 0.5-2.0 mol%, Yb 3+ The doping concentration is 2.0-5.0 mol%, OH - The content is less than 10 ppm; B2. Preparation of passive fluorotellurate glass microspheres 5: Fluorotellurate glass rods of the same composition are softened under high-temperature melting to form microspheres through surface tension. The diameter of the passive fluorotellurate glass microspheres 5 is controlled to be 50-200 μm, and the quality factor is 1×10⁻⁶. 6 Up to 5×10 6 ; B3. Conical region 4 is prepared by using standard single-mode fiber (SMF-28), heating and uniformly stretching it with an oxyhydrogen flame to prepare conical region 4 with a diameter of 1-3 μm. The diameter transition of conical region 4 is smooth, without breakage or defects. B4. Deposit a multilayer dielectric film 2, in Er 3+ / Yb 3+ A multilayer dielectric film 2 is deposited on the incident end face of the co-doped low-hydroxyl fluorotellurate glass fiber 3; preferably, ion beam sputtering can be used to alternately deposit 15 layers of SiO2 and ZnS materials, with the thickness of each layer designed according to λ / 4 optical thickness. The measured film system has a transmittance of greater than 95% at 980nm and a reflectance of greater than 99.5% at 2700nm. B5. System setup: 980nm laser diode pump source 1, multilayer dielectric film 2, Er 3+ / Yb 3+ 3. Co-doped low-hydroxyl fluorotellurate glass optical fiber; 4. Tapered region; 5. Passive fluorotellurate glass microspheres; 6. Spectrometer. Figure 1 Assemble the structure shown, and Er 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass fiber 3 is mounted on a nanoscale displacement stage, and passive fluorotellurate glass microspheres 5 are fixed on a precision optical platform; B6. Coupling Adjustment: Activate the 980nm laser diode pump source 1 and adjust the relative position of the conical region 4 and the passive fluorotellurate glass microspheres 5 using a nanometer displacement stage. Monitor the backscattered signal in real time using a monitoring device to find the optimal coupling position. When the backscattered signal reaches its maximum value, it indicates that the critical coupling state has been reached, and the displacement stage position is locked. B7. Laser output testing: A spectral analyzer 6 is used to monitor laser output characteristics in real time, measuring parameters such as laser output power, spectral shape, linewidth, and side-mode suppression ratio. Parameters such as coupling distance and pump power are optimized to achieve the best performance.

[0032] The preparation method of the passive fluorotellurate glass microspheres 5 includes the following steps: C1. The raw material of passive fluorotellurate glass microspheres 5 is melted to obtain passive fluorotellurate glass liquid. During the melting process, oxygen is continuously introduced while stirring. The oxygen flow rate is 2L / min and the melting temperature is 1090℃. The passive fluorotellurate glass liquid is transferred to an annealing furnace for cooling treatment to obtain passive fluorotellurate glass. The initial temperature of the annealing furnace is 405℃ and the annealing time is 11.5h. C2. The passive fluorotellurate glass obtained in step C1 is made into passive fluorotellurate glass powder, and then the powder is successively melted and cooled to prepare passive fluorotellurate glass microspheres 5. The above preparation steps have been maturely applied in the prior art, and will not be described again in this application.

[0033] It is worth mentioning that the stimulated Raman scattering theory calculations in this invention are as follows: Stimulated Raman scattering is a nonlinear optical process in which molecular vibrations in a medium are excited when the pump light intensity exceeds a threshold, resulting in coherent light output with a Stokes frequency shift. For fluorotellurate glass microspheres, the Raman frequency shift is mainly determined by the vibrational modes of the Te-O bonds.

[0034] The wavelength calculation formula, based on the law of conservation of energy, relates the wavenumber of Stokes light to the wavenumber of pump light as follows: ; in: Stokes wavenumber (cm) -1 ); Pump wavenumber (cm) -1 ); Raman frequency shift (cm) -1 ).

[0035] The relationship between wavelength and wavenumber is: .

[0036] Main Raman gain frequency shift range of fluorotellurate glass: (Corresponding to the strongest Raman gain peak).

[0037] Detailed calculation process: Pump light parameters: Pump wavelength Pump wavenumber .

[0038] First-order Stokes calculation: Low-frequency shifter ( ): ; .

[0039] High-frequency shifter ( ): ; .

[0040] First-order Stokes wavelength range: 3.329-3.567μm.

[0041] Second-order Stokes calculation: Low-frequency shifter ( ): ; .

[0042] High-frequency shifter ( ): ; .

[0043] Second-order Stokes wavelength range: 4.341-5.253μm; The visible first-order Stokes band is 3.329-3.567 μm, completely covering the 3-3.6 μm band; Secondary Stokes: 4.341-5.253 μm, covering 4.341-5.000 μm in the 3-5 μm band; Overall output range: 3.329-5μm, effectively covering the 3-5μm standard band; The 2.7μm pump light, through the stimulated Raman scattering effect of the passive fluorotellurate glass microspheres 5, can effectively generate laser output of 3.329-5.000μm, achieving full coverage within the 3-5μm target wavelength band, which meets the technical requirements of this invention.

[0044] The following description is based on specific embodiments.

[0045] Example 1

[0046] This embodiment provides a mid-infrared narrow-linewidth fiber laser based on microsphere feedback, comprising: Er 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass fiber 3: used to generate 2.7μm laser light, and Er 3+ / Yb 3+ The co-doped low-hydroxyl fluorotellurate glass fiber 3 is provided with a tapered region 4, the diameter of which is 1 μm; 980nm laser diode-pumped light source 1: set in Er 3+ / Yb 3+ One end of the co-doped low-hydroxyl fluorotellurate glass optical fiber 3; Multilayer dielectric film 2: set in Er 3+ / Yb 3+ The co-doped low-hydroxyl fluorotellurate glass fiber 3 is located near the incident end of the 980nm laser diode pump source 1. The multilayer dielectric film 2 has a reflectivity greater than 99.5% in the 2.7μm band and a transmittance greater than 95% in the 980nm band. Passive fluorotellurate glass microspheres 5: placed in the cone region 4 and interacted with Er through an evanescent field. 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass fiber 3 is used for coupling to provide wavelength-selective feedback for whispering-gallery modes. The passive fluorotellurate glass microspheres 5 have a diameter of 50 μm and a quality factor of 1 × 10⁻⁶. 6 The passive fluorotellurate glass microspheres with the above parameters can improve the evanescent wave coupling efficiency between the light field through the cone region and the passive fluorotellurate glass microspheres, reduce the loss of light energy during the coupling process, ensure stable laser oscillation, and improve the overall laser output efficiency and output quality. Furthermore, the coupling distance between the cone region 4 and the surface of the passive fluorotellurate glass microsphere 5 is 10 nm; Spectrum Analyzer 6: Set to Er 3+ / Yb 3+ The output end of co-doped low-hydroxyl fluorotellurate glass fiber 3; Among them, Er 3+ / Yb 3+ In co-doped low-hydroxyl fluorotellurate glass fiber 3, Er 3+The doping concentration is 0.5 mol%, Yb 3+ The doping concentration is 5.0 mol%, OH - The content is less than 10 ppm.

[0047] In this embodiment, a nano-displacement stage is also included: used to adjust the relative position of the passive fluorotellurate glass microspheres 5 and the cone region 4. More specifically, the nano-displacement stage has a resolution of 10 nm, a stroke of ±2.5 mm, and an adjustment accuracy of 50 nm.

[0048] In this embodiment, a monitoring device is also included to determine the optimal coupling position between the cone region 4 and the passive fluorotellurate glass microspheres 5.

[0049] This embodiment also provides a method for achieving mid-infrared narrow-linewidth laser output based on microsphere feedback, including the following steps: Step S1: Provide a 980nm laser diode pump source 1. The 980nm laser diode pump source 1 enters the Er through a multilayer dielectric film 2. 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass optical fiber 3; Step S2: Precisely adjust the passive fluorotellurate glass microspheres 5 and Er using a nano-displacement stage. 3+ / Yb 3+ The relative positions of the cone region 4 of the co-doped low-hydroxyl fluorotellurate glass fiber 3 are such that the coupling spacing is within the range of 10nm. Specifically, a three-step adjustment method can be adopted: first, manually coarsely adjust the spacing to 10μm, then finely adjust it in 10nm steps, and finally precisely lock the position of the maximum value of the backscattered signal in 5nm steps. Step S3, Er 3+ / Yb 3+ The 2.7 μm optical field generated in the co-doped low-hydroxyl fluorotellurate glass fiber 3 is coupled to the passive fluorotellurate glass microsphere 5 through the conical region. The high Q value of the whispering-gallery mode of the passive fluorotellurate glass microsphere 5 is used to provide wavelength selective feedback, thereby realizing 2.7 μm narrow linewidth laser output. Step S4: Use 2.7μm laser light as pump light to further excite passive fluorotellurate glass microspheres 5, and obtain 3-5μm band laser output through stimulated Raman scattering effect.

[0050] Example 2

[0051] This embodiment provides a mid-infrared narrow-linewidth fiber laser based on microsphere feedback, comprising: Er 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass fiber 3: used to generate 2.7μm laser light, and Er 3+ / Yb 3+The co-doped low-hydroxyl fluorotellurate glass fiber 3 is provided with a tapered region 4, the diameter of which is 2μm; 980nm laser diode-pumped light source 1: set in Er 3+ / Yb 3+ One end of the co-doped low-hydroxyl fluorotellurate glass optical fiber 3; Multilayer dielectric film 2: set in Er 3+ / Yb 3+ The co-doped low-hydroxyl fluorotellurate glass fiber 3 is located near the incident end of the 980nm laser diode pump source 1. The multilayer dielectric film 2 has a reflectivity greater than 99.5% in the 2.7μm band and a transmittance greater than 95% in the 980nm band. Passive fluorotellurate glass microspheres 5: placed in the cone region 4 and interacted with Er through an evanescent field. 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass fiber 3 is used for coupling to provide wavelength-selective feedback for whispering-gallery modes. The passive fluorotellurate glass microspheres 5 have a diameter of 150 μm and a quality factor of 3 × 10⁻⁶. 6 The passive fluorotellurate glass microspheres with the above parameters can improve the evanescent wave coupling efficiency between the light field through the cone region and the passive fluorotellurate glass microspheres, reduce the loss of light energy during the coupling process, ensure stable laser oscillation, and improve the overall laser output efficiency and output quality. Furthermore, the coupling distance between the cone region 4 and the surface of the passive fluorotellurate glass microsphere 5 is 250 nm; Spectrum Analyzer 6: Set to Er 3+ / Yb 3+ The output end of co-doped low-hydroxyl fluorotellurate glass fiber 3; Among them, Er 3+ / Yb 3+ In co-doped low-hydroxyl fluorotellurate glass fiber 3, Er 3+ The doping concentration is 1.5 mol%, Yb 3+ The doping concentration is 4 mol%, OH - The content is less than 10 ppm.

[0052] In this embodiment, a nano-displacement stage is also included: used to adjust the relative position of the passive fluorotellurate glass microspheres 5 and the cone region 4. More specifically, the nano-displacement stage has a resolution of 10 nm, a stroke of ±2.5 mm, and an adjustment accuracy of 50 nm.

[0053] In this embodiment, a monitoring device is also included to determine the optimal coupling position between the cone region 4 and the passive fluorotellurate glass microspheres 5.

[0054] This embodiment also provides a method for achieving mid-infrared narrow-linewidth laser output based on microsphere feedback, including the following steps: Step S1: Provide a 980nm laser diode pump source 1. The 980nm laser diode pump source 1 enters the Er through a multilayer dielectric film 2. 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass optical fiber 3; Step S2: Precisely adjust the passive fluorotellurate glass microspheres 5 and Er using a nano-displacement stage. 3+ / Yb 3+ The relative positions of the cone region 4 of the co-doped low-hydroxyl fluorotellurate glass fiber 3 are such that the coupling spacing is within the range of 250nm. Specifically, a three-step adjustment method can be adopted: first, manually coarsely adjust the spacing to 10μm, then finely adjust it in 10nm steps, and finally precisely lock the position of the maximum value of the backscattered signal in 5nm steps. Step S3, Er 3+ / Yb 3+ The 2.7 μm optical field generated in the co-doped low-hydroxyl fluorotellurate glass fiber 3 is coupled to the passive fluorotellurate glass microsphere 5 through the conical region. The high Q value of the whispering-gallery mode of the passive fluorotellurate glass microsphere 5 is used to provide wavelength selective feedback, thereby realizing 2.7 μm narrow linewidth laser output. Step S4: Use 2.7μm laser light as pump light to further excite passive fluorotellurate glass microspheres 5, and obtain 3-5μm band laser output through stimulated Raman scattering effect.

[0055] Example 3

[0056] This embodiment provides a mid-infrared narrow-linewidth fiber laser based on microsphere feedback, comprising: Er 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass fiber 3: used to generate 2.7μm laser light, and Er 3+ / Yb 3+ The co-doped low-hydroxyl fluorotellurate glass fiber 3 is provided with a tapered region 4, the diameter of which is 3 μm; 980nm laser diode-pumped light source 1: set in Er 3+ / Yb 3+ One end of the co-doped low-hydroxyl fluorotellurate glass optical fiber 3; Multilayer dielectric film 2: set in Er 3+ / Yb 3+ The co-doped low-hydroxyl fluorotellurate glass fiber 3 is located near the incident end of the 980nm laser diode pump source 1. The multilayer dielectric film 2 has a reflectivity greater than 99.5% in the 2.7μm band and a transmittance greater than 95% in the 980nm band. Passive fluorotellurate glass microspheres 5: placed in the cone region 4 and interacted with Er through an evanescent field. 3+ / Yb 3+Co-doped low-hydroxyl fluorotellurate glass fiber 3 is used for coupling to provide wavelength-selective feedback for whispering-gallery modes. The passive fluorotellurate glass microspheres 5 have a diameter of 200 μm and a quality factor of 5 × 10⁻⁶. 6 The passive fluorotellurate glass microspheres with the above parameters can improve the evanescent wave coupling efficiency between the light field through the cone region and the passive fluorotellurate glass microspheres, reduce the loss of light energy during the coupling process, ensure stable laser oscillation, and improve the overall laser output efficiency and output quality. Furthermore, the coupling distance between the cone region 4 and the surface of the passive fluorotellurate glass microsphere 5 is 500 nm; Spectrum Analyzer 6: Set to Er 3+ / Yb 3+ The output end of co-doped low-hydroxyl fluorotellurate glass fiber 3; Among them, Er 3+ / Yb 3+ In co-doped low-hydroxyl fluorotellurate glass fiber 3, Er 3+ The doping concentration is 2.0 mol%, Yb 3+ The doping concentration is 5.0 mol%, OH - The content is less than 10 ppm.

[0057] In this embodiment, a nano-displacement stage is also included: used to adjust the relative position of the passive fluorotellurate glass microspheres 5 and the cone region 4. More specifically, the nano-displacement stage has a resolution of 10 nm, a stroke of ±2.5 mm, and an adjustment accuracy of 50 nm.

[0058] In this embodiment, a monitoring device is also included to determine the optimal coupling position between the cone region 4 and the passive fluorotellurate glass microspheres 5.

[0059] This embodiment also provides a method for achieving mid-infrared narrow-linewidth laser output based on microsphere feedback, including the following steps: Step S1: Provide a 980nm laser diode pump source 1. The 980nm laser diode pump source 1 enters the Er through a multilayer dielectric film 2. 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass optical fiber 3; Step S2: Precisely adjust the passive fluorotellurate glass microspheres 5 and Er using a nano-displacement stage. 3+ / Yb 3+ The relative positions of the cone region 4 of the co-doped low-hydroxyl fluorotellurate glass fiber 3 are such that the coupling spacing is within the range of 500nm. Specifically, a three-step adjustment method can be adopted: first, manually coarsely adjust the spacing to 10μm, then finely adjust it in 10nm steps, and finally precisely lock the position of the maximum value of the backscattered signal in 5nm steps. Step S3, Er 3+ / Yb 3+The 2.7 μm optical field generated in the co-doped low-hydroxyl fluorotellurate glass fiber 3 is coupled to the passive fluorotellurate glass microsphere 5 through the conical region. The high Q value of the whispering-gallery mode of the passive fluorotellurate glass microsphere 5 is used to provide wavelength selective feedback, thereby realizing 2.7 μm narrow linewidth laser output. Step S4: Use 2.7μm laser light as pump light to further excite passive fluorotellurate glass microspheres 5, and obtain 3-5μm band laser output through stimulated Raman scattering effect.

[0060] like Figure 2 As shown, this spectrum illustrates the multi-level Stokes output of stimulated Raman scattering generated by passive fluorotellurate glass microspheres pumped by a 2.7 μm laser. The first-order Stokes component covers the 3.329–3.567 μm band, and the second-order Stokes component covers the 4.341–5.253 μm band. The overall output range is 3.329–5.000 μm, effectively achieving full coverage of the 3–5 μm mid-infrared target band. By adjusting the microsphere size and refractive index, the whispering-gallery mode resonant frequency can be tuned, achieving wavelength-tunable output to meet the application needs of various scenarios such as gas sensing and biomedical detection.

[0061] 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. A mid-infrared narrow-linewidth fiber laser based on microsphere feedback, characterized in that, include: Er 3+ / Yb 3+ Co-doped low-hydroxy tellurite fluoride glass optical fiber: for generating 2.7 μm laser, and the Er 3+ / Yb 3+ Co-doped low-hydroxy tellurite fluoride glass optical fiber is provided with a tapered zone; Pump light source: set in the Er 3+ / Yb 3+ One end of a co-doped low-hydroxyl fluorotellurate glass optical fiber; Multilayer dielectric film: disposed in the Er 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass fiber is placed near the incident end of the pump light source to achieve high transmission of pump light and high reflection of laser wavelength. Passive fluorotellurate glass microspheres: placed in the conical region and interacting with the Er through an evanescent field. 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass fiber coupling is used to provide wavelength-selective feedback for whispering-gallery modes; Spectrometer: located in the Er 3+ / Yb 3+ The output end of a co-doped low-hydroxyl fluorotellurate glass optical fiber; Wherein, Er 3+ / Yb 3+ In co-doped low-hydroxyl fluorotellurate glass optical fibers, Er 3+ The doping concentration is 0.5-2.0 mol%, Yb 3+ The doping concentration is 2.0-5.0 mol%, OH - The content is less than 10 ppm.

2. The mid-infrared narrow-linewidth fiber laser as described in claim 1, characterized in that, The passive fluorotellurate glass microspheres have a diameter of 50-200 μm and a quality factor of 1×10⁻⁶. 6 Up to 5×10 6 .

3. The mid-infrared narrow-linewidth fiber laser as described in claim 1, characterized in that, The diameter of the cone region is 1-3 μm, and the coupling distance between the cone region and the surface of the passive fluorotellurate glass microsphere is 10-500 nm.

4. The mid-infrared narrow-linewidth fiber laser as described in claim 1, characterized in that, The pump source is a 980nm laser diode pump source.

5. The mid-infrared narrow-linewidth fiber laser as described in claim 4, characterized in that, The multilayer dielectric film has a reflectivity greater than 99.5% in the 2.7μm band and a transmittance greater than 95% in the 980nm band.

6. The mid-infrared narrow-linewidth fiber laser as described in claim 1, characterized in that, It also includes a nano-displacement stage: used to adjust the relative position of the passive fluorotellurate glass microspheres and the conical region.

7. The mid-infrared narrow-linewidth fiber laser as described in claim 6, characterized in that, The nanostage has a resolution of 10 nm, a stroke of ±2.5 mm, and an adjustment accuracy of 50 nm.

8. The mid-infrared narrow-linewidth fiber laser as described in claim 6, characterized in that, It also includes a monitoring device for determining the optimal coupling position between the cone region and the passive fluorotellurate glass microspheres.

9. A method for achieving mid-infrared narrow-linewidth laser output based on microsphere feedback, characterized in that, Includes the following steps: Step S1: Provide 980nm pump light, which enters Er through a multilayer dielectric film. 3+ / Yb 3+ Co-doped low-hydroxyl fluorotellurate glass optical fiber; Step S2: Precisely adjust the passive fluorotellurate glass microspheres and Er using a nano-displacement stage. 3+ / Yb 3+ The relative positions of the taper regions in the co-doped low-hydroxyl fluorotellurate glass fiber ensure that the coupling spacing is within the range of 10-500 nm. Step S3, the Er 3+ / Yb 3+ The 2.7 μm optical field generated in the co-doped low-hydroxyl fluorotellurate glass fiber is coupled to the passive fluorotellurate glass microsphere via the tapered region. The high Q value of the whispering-gallery mode of the passive fluorotellurate glass microsphere is used to provide wavelength selective feedback, thereby realizing 2.7 μm narrow linewidth laser output. Step S4: The passive fluorotellurate glass microspheres are further excited by 2.7μm laser light as pump light, and 3-5μm band laser output is obtained through stimulated Raman scattering effect.

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