A 2.3 μm fiber laser pumped by a 980 nm laser

Abstract

This invention discloses a 2.3 μm fiber laser based on 980 nm laser pumping, relating to the field of mid-infrared fiber laser technology. This fiber laser utilizes fluorotellurate glass fiber co-doped with thulium and erbium ions as the gain medium. It absorbs the 980 nm pump light energy by introducing erbium ion doping, and then achieves Tm through the energy transfer process between erbium and thulium ions. 3+ of 3 H4- 3 The population inversion of the H5 energy level ultimately yields laser output in the 2.3 μm band. This invention utilizes a high-power 980 nm laser as the pump source and a thulium-erbium co-doped fluorotellurate glass fiber prepared by the rod-tube method as the gain medium. By writing fiber gratings with appropriate reflectivity at both ends of the fiber, a resonant cavity with a reflection wavelength of 2.3 μm is constructed, enabling the development of a high-power 2.3 μm laser that can operate stably for a long time.

Description

Technical Field

[0001] This invention belongs to the field of mid-infrared fiber laser technology, specifically relating to a 2.3 μm fiber laser based on 980 nm laser pumping. Background Technology

[0002] The 2.3 μm band laser covers the characteristic absorption lines of various gases and exhibits high absorption sensitivity to toxic and harmful gases such as CO, HF, and CH4. Therefore, it has broad application prospects in fields such as industrial exhaust gas monitoring, mine safety inspection, and environmental pollutant tracing. This band of laser light also falls within a relatively safe range for human tissue and can be used in laser medicine, biological detection, and other scenarios. Furthermore, this band is located within the low absorption window of the atmosphere, making it valuable for applications in atmospheric remote sensing, long-range laser ranging, free-space optical communication, and specialized optoelectronic countermeasures.

[0003] Thulium-doped fiber lasers are one of the important means to achieve laser output in the 2.3 μm band. Existing 2.3 μm thulium-doped fiber lasers typically use 793 nm, 1064 nm, or 1400 nm wavelengths as pump sources. While these pumping schemes can achieve 2.3 μm laser output, they still have certain limitations in terms of high-power device supply, system cost, and ease of engineering integration, which hinders the further promotion of 2.3 μm high-power fiber laser technology.

[0004] In contrast, 980 nm high-power semiconductor lasers are technologically mature, have a wide range of device sources, lower costs, and a high degree of engineering sophistication, and have been widely used in various fiber laser systems. However, thulium ions cannot directly absorb 980 nm pump light energy to obtain 2.3 μm laser output. Therefore, how to utilize 980 nm pumping to establish an energy transfer and inversion mechanism suitable for 2.3 μm output, and further achieve synergistic optimization of device structural parameters and cavity parameters, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the problems in existing 2.3 μm thulium-doped fiber lasers, which typically rely on specific pump sources such as 793 nm, 1064 nm, or 1400 nm, resulting in high costs and limited engineering implementation of high-power pump devices, and the difficulty in directly establishing efficient population inversion at the 2.3 μm transition of thulium ions under 980 nm pumping conditions and the lack of corresponding structural parameter optimization methods, this invention provides a 2.3 μm fiber laser based on 980 nm laser pumping.

[0006] This invention employs a fluorotellurate glass fiber co-doped with thulium and erbium ions as the gain medium. Erbium ions absorb the 980 nm pump light, and through energy transfer from erbium to thulium ions, population inversion is established between the upper and lower energy levels corresponding to the 2.3 μm laser transition in thulium ions, thereby achieving 2.3 μm laser output. Simultaneously, this invention further establishes a joint model relating erbium ion absorption, erbium-to-thulium energy transfer, stimulated emission of thulium ions, resonant cavity threshold conditions, and intracavity optical power transmission under the 980 nm pump condition. An analytical expression for the 2.3 μm output power is obtained under steady-state approximation conditions, and based on this, the gain fiber structural parameters and resonant cavity parameters are jointly optimized to achieve high output power and long-term stable operation.

[0007] This invention is achieved through the following technical solution: A 2.3 μm fiber laser pumped by a 980 nm laser, characterized in that the fiber laser comprises: The system comprises a 980 nm laser pump source, an optical isolator, a gain fiber, and a first fiber Bragg grating and a second fiber Bragg grating respectively disposed at both ends of the gain fiber. The pump light output from the 980 nm laser pump source is coupled into the gain fiber after passing through the optical isolator. The gain fiber is a fluorotellurate glass fiber co-doped with thulium and erbium ions. After absorbing the 980 nm pump light, the erbium ions transfer energy to the thulium ions, thereby enhancing the energy transfer efficiency of the thulium ions. 3 H4 energy level and 3 Population inversion is established between the H5 energy levels, thereby generating 2.3 μm band laser output; the center reflection wavelengths of the first and second fiber Bragg gratings are both located in the 2.3 μm band, and together with the gain fiber, they form a 2.3 μm fiber laser resonant cavity, wherein: the first fiber Bragg grating is a high-reflectivity grating, and the second fiber Bragg grating is an output coupling grating; at least one end face of the gain fiber is a beveled end face to suppress parasitic oscillations formed by end face reflection; The core diameter d, fiber length L, and thulium ion doping concentration N of the gain fiber are... Tm Erbium ion doping concentration N Er The reflectivity R1 of the first fiber Bragg grating and the reflectivity R2 of the second fiber Bragg grating are configured to satisfy the following output power relationship: , Where: R1 is the reflectivity of the first fiber Bragg grating in the 2.3 μm band; R2 is the reflectivity of the second fiber Bragg grating in the 2.3 μm band; Add a loss factor to the dimensionless resonant cavity; The pump light wavelength, and =980 nm; The center wavelength of the output laser is located in the 2.3 μm band; The pump light power coupled into the gain fiber; The absorption cross section of erbium ions against 980 nm pump light; The erbium ion doping concentration in the gain fiber; denoted as the mode field overlap factor between the pump light and the doped region; L is the length of the gain fiber; d is the core diameter of the gain fiber; h is Planck's constant; and c is the speed of light in vacuum. The overlap factor between the 2.3 μm laser mode field and the doped region is given. The stimulated emission cross section of thulium ions in the 2.3 μm band; This represents the upper energy level lifetime corresponding to the laser transition of thulium ions in the 2.3 μm band; The linear background loss coefficient of the gain fiber in the 2.3 μm band is given. The efficiency of energy transfer from erbium ions to thulium ions; P out This refers to the output power.

[0008] Preferably, the core glass composition of the gain fiber is composed of TeO2, BaF2, Y2O3, Tm2O3, and Er2O3, with the following molar percentages: TeO2: 70%, BaF2: 20%, Y2O3: 9.6%, Tm2O3: 0.2%, Er2O3: 0.2%; the cladding composition of the fiber is composed of TeO2, BaF2, and Y2O3, with the following molar percentages: TeO2: 67%, BaF2: 23%, Y2O3: 10%.

[0009] Preferably, the gain fiber is prepared by a combination of rod-tube method, extrusion method or double crucible method and drawing process.

[0010] Preferably, the parameters satisfy: the reflectivity of the first fiber Bragg grating is 90%, the reflectivity of the second fiber Bragg grating is 10%, the core diameter of the gain fiber is 8 μm, the length of the gain fiber is 3 m, and the thulium ion doping concentration is... and the erbium ion doping concentration These correspond to 0.2% molar percentage of Tm2O3 and 0.2% molar percentage of Er2O3, respectively.

[0011] A design method for the aforementioned 2.3 μm fiber laser pumped by a 980 nm laser, characterized by comprising the following steps: S1: Establish a multi-level rate equation model for erbium ion absorption of pump light, energy transfer from erbium ions to thulium ions, and 2.3 μm transition of thulium ions under 980 nm pump conditions; S2: By combining the multi-level rate equation model with the total particle number conservation relationship, the laser resonator threshold condition, and the intracavity optical power transmission equation under steady-state conditions, the 2.3 μm output power P is obtained. out The parsing expression; S3: Solve for the extrema of the analytical expression to determine the core diameter d, length L, and thulium ion doping concentration N of the gain fiber that maximizes the 2.3 μm output power. Tm Erbium ion doping concentration N Er The parameter combination of the high-reflectivity grating R1 and the reflectivity of the output coupling grating R2; S4: Based on the parameter combination determined in step S3, select thulium- and erbium-doped fluorotellurate glass fiber as the gain medium, and form a first fiber Bragg grating and a second fiber Bragg grating with a central reflection wavelength in the 2.3 μm band at both ends to construct a laser resonant cavity. S5: Pump the gain fiber with a 980 nm laser to obtain a 2.3 μm laser output.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention uses a 980 nm laser as the pump source, not simply replacing another pump source. Instead, it establishes a joint model of 980 nm pump absorption, Er→Tm energy transfer, Tm ion stimulated emission, resonant cavity threshold and intracavity power transfer, and reduces it to an analytical expression of 2.3 μm output power, thus realizing 2.3 μm laser output under 980 nm pump conditions. Therefore, it solves the problem that 980 nm pump is difficult to directly adapt to 2.3 μm band thulium-doped laser output.

[0013] (2) This invention utilizes fluorotellurate glass as the matrix for co-doped gain fiber. Through the expression for the 2.3μm output power, the original device design process, which relied on trial and error based on experience, is transformed into a parameter design process that can be quantitatively analyzed and optimized for extreme values. This significantly improves design efficiency and the specificity of parameter selection. The formula not only describes the relationship between output power and pump power, but also introduces multiple core structural parameters such as the core diameter of the gain fiber, fiber length, thulium ion doping concentration, erbium ion doping concentration, and output coupling grating reflectivity. This allows the formula to reflect the coupling relationship between 980 nm pump absorption efficiency, energy transfer efficiency, mode overlap, resonant cavity loss, and output coupling, achieving multi-parameter synergistic optimization rather than optimizing a single parameter in isolation. In this invention, the 980nm pump scheme and the output power expression have a synergistic effect. The 980nm pump absorption term, energy transfer efficiency term, and resonant cavity loss term are all incorporated into the same expression, allowing the absorption path, energy transfer path, and output coupling path related to the 980 nm pump to be optimized simultaneously. This truly transforms the engineering advantages of the 980 nm pump into the performance advantages of the 2.3μm laser output.

[0014] (3) The design method of the present invention can directly guide the design of 2.3μm fiber lasers with different core diameters, lengths, Tm / Er doping ratios and output coupling conditions. It has good scalability and engineering reuse value, and is suitable for device development, parameter screening and mass production design. While realizing 980 nm pumped 2.3 μm mid-infrared laser output, the present invention introduces analytical model constraints, so that the device structure, energy transfer path and parameter optimization path form a closed loop. This not only improves the problem of traditional design relying on experience and scattered parameter selection, but also improves repeatability and verifiability. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be construed as limiting the scope of protection of the present invention; for those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of a 2.3 μm fiber laser based on thulium-erbium co-doped fluorine telluride glass fiber pumped by a 980 nm laser in an embodiment of the present invention; In the figure: pump source 1, isolator 2, fiber Bragg grating 3 (including a first fiber Bragg grating and a second fiber Bragg grating), thulium-erbium co-doped fluorine telluride glass fiber 4, spectrometer 5, optical power meter 6; Figure 2 Tm in the embodiments of the present invention3+ / Er 3+ Schematic diagram of the energy level structure of the co-doped system; Figure 3 This is a 2.3 μm band laser spectrum output from a thulium-erbium co-doped fluorotellurate glass fiber with a core diameter of 8 μm and a length of 3 m under 980 nm laser pumping, as described in this embodiment of the invention.

[0017] Figure 4 The graph shows the relationship between the 2.3 μm laser output power and the 980 nm pump power in an embodiment of the present invention. The glass composition of the thulium-erbium co-doped fluorotellurate glass fiber is: TeO2: 70 mol%, BaF2: 20 mol%, Y2O3: 9.6 mol%, Tm2O3: 0.2 mol%, Er2O3: 0.2 mol%, with a core diameter of 8 μm and a length of 3 m. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Where there is no conflict, the technical features in the following embodiments can be combined with each other. Equivalent substitutions or modifications made by those skilled in the art without departing from the concept of the present invention should all fall within the scope of protection of the present invention.

[0019] Example 1 This embodiment provides a thulium-erbium co-doped fluorotellurate glass optical fiber, which is an all-solid-state structure optical fiber. Its core glass composition consists of TeO2, BaF2, Y2O3, Tm2O3, and Er2O3, with the following molar percentages: TeO2: 70%, BaF2: 20%, Y2O3: 9.6%, Tm2O3: 0.2%, Er2O3: 0.2%. The cladding of the optical fiber is fluorotellurate glass, composed of TeO2, BaF2, and Y2O3, with the following molar percentages: TeO2: 67%, BaF2: 23%, and Y2O3: 10%.

[0020] Thulium-erbium co-doped fluorotellurate glass optical fibers are prepared by the following method, including the following steps: First, a preform is prepared using the adsorption method. The precise mass of each required chemical substance is weighed using a balance in a dry nitrogen-filled glove box. 30 g of the core and cladding mixture is weighed separately and placed in an agate mortar. The mixture is ground for 30-60 minutes to ensure homogeneity. The ground mixture is then placed in a corundum crucible. The corundum crucible is placed in a muffle furnace at 950°C for 120 minutes, after which the chemical substance changes from a powder to a liquid state. A copper mold is placed in another muffle furnace at 400°C for 2 hours. First, the molten glass from the cladding corundum crucible is poured into the mold, followed by the molten glass from the core corundum crucible. Due to thermal expansion and contraction, the molten glass at the interface between the core and cladding layers is drawn into the cladding, forming the glass preform. Maintain the muffle furnace temperature at 400℃ and anneal the glass preform in the mold for 3 hours to release stress within the glass. Turn off the muffle furnace and allow the glass inside to cool naturally to room temperature. Remove the preform. Polish the fiber optic preform using a polishing machine and sandpaper.

[0021] Secondly, optical fiber glass sleeves were prepared using a rotary casting method. The composition of the optical fiber glass sleeves was TeO2:65%, BaF2:25%, and Y2O3:10%. The mass of each component of the glass with different rare earth doping molar percentages was calculated, and then 90 g of raw material was weighed using a balance and placed in an agate mortar. The components were ground in the mortar for 30-60 minutes to ensure uniform mixing. The ground components were then placed in a corundum crucible. The corundum crucible was placed in a muffle furnace at a temperature of 950℃ for 120 minutes, after which the components changed from a powder state to a liquid state. A copper mold was placed in a rotary casting machine at a temperature of 400℃ for 2 hours. The molten glass in the crucible was poured into the mold, and the mold was rotated at high speed using the casting machine. Under the action of centrifugal force, the molten glass was thrown against the mold wall, forming a glass outer tube after solidification. Maintain the casting machine temperature at 400℃ and anneal the glass preform in the mold for 5 hours. Turn off the muffle furnace of the casting machine and allow the glass sleeve in the mold to cool naturally to room temperature. Remove the fiber optic glass sleeve. Polish the fiber optic glass sleeve using a polishing machine and sandpaper.

[0022] Furthermore, the fiber preform is first drawn using a drawing tower. By controlling the traction and lowering speed of the drawing tower, the outer diameter of the first fiber preform can be adjusted to match the inner diameter of the fiber optic glass sleeve. A suitable portion of the first fiber preform is then placed inside the fiber optic glass sleeve. A second drawing is performed on the first fiber preform and the fiber optic glass sleeve using the drawing tower. Under high-temperature evacuation, the softened preform and glass sleeve adhere together, ultimately forming a three-layer fiber structure; thus, a three-layer thulium-erbium co-doped fluorotellurate glass fiber is obtained.

[0023] In this embodiment, the core diameter of the obtained fiber can be prepared to be 8 μm, and one or both ends of the gain fiber can be further processed into beveled end faces to reduce end face backlighting and suppress parasitic oscillations. To verify that the fiber is suitable for 980 nm pumping 2.3 μm laser output, laser spectroscopy tests were performed on the prepared thulium-erbium co-doped fluorotellurate glass fiber. During the test, a 980 nm laser was used as the pump source to perform 2.3 μm band laser tests on a thulium-erbium co-doped fluorotellurate glass fiber with a core diameter of 8 μm and a length of 3 m. The pump light first passes through a 980 nm optical isolator, and then is coupled into the thulium-erbium co-doped fluorotellurate glass fiber through mechanical docking. Fiber Bragg gratings with a center reflection wavelength in the 2.3 μm band are etched at both ends of the fiber, with the input end grating having a reflectivity of 90% and the output end grating having a reflectivity of 10%, which are used to form a 2.3 μm fiber laser resonant cavity. The output signal light is received by a spectrometer, and its laser spectrum is as follows: Figure 3 As shown, this demonstrates that the thulium-erbium co-doped fluorotellurate glass fiber can achieve 2.3μm band laser output under 980 nm pump conditions.

[0024] This embodiment illustrates that the thulium-erbium co-doped fluorotellurate glass fiber can not only absorb 980 nm pump light, but also establish an effective inversion condition through the energy transfer process from erbium ions to thulium ions, which is a 2.3 μm laser transition, thereby forming the gain medium basis of the fiber laser of this invention.

[0025] Example 2 This embodiment provides a 2.3μm fiber laser pumped by a 980 nm laser, the structure of which is as follows: Figure 1 As shown. The fiber laser includes: a 980 nm laser pump source 1, an isolator 2, fiber Bragg gratings 3 inscribed at both ends of the gain fiber, a thulium-erbium co-doped fluorine telluride glass fiber 4, a spectrometer 5, and an optical power meter 6. The pump source 1 is a laser with a working wavelength of 980 nm. The pump light first passes through the isolator 2 and then couples into the thulium-erbium co-doped fluorine telluride glass fiber 4. The thulium-erbium co-doped fluorine telluride glass fiber 4 serves as the gain medium. It is an optical fiber prepared in Example 1, with a core diameter of 8 μm and a length of 3 m. The core contains T... m2 O3 and E r2 The molar percentages of O3 are 0.2% and 0.2%, respectively. Fiber Bragg gratings 3 with a center reflection wavelength in the 2.3 μm band are formed at both ends of the gain fiber, with the input grating reflectivity R1 being 90% and the output grating reflectivity R2 being 10%, thus forming a 2.3 μm laser resonant cavity.

[0026] In this embodiment, the 980 nm pump light is not directly at Tm 3+Instead of forming an efficient pump at the 2.3 μm transition, it is first generated by Er 3+ Absorption, and then through Er 3+ To Tm 3+ The energy transfer process achieves population inversion between the upper and lower energy levels of the thulium ion corresponding to the 2.3μm laser transition, thereby obtaining 2.3μm band laser output. To reduce the impact of end-face backlighting on the stability of the resonant cavity, at least one end face of the gain fiber is set as an angled end face to suppress parasitic oscillations and undesirable feedback.

[0027] To determine the optimal combination of structural parameters for this laser, this embodiment uses analytical expressions as the basis for optimization: the core diameter d of the gain fiber, the length L of the gain fiber, and the thulium ion doping concentration N. Tm Erbium ion doping concentration N Er The reflectivity of the first fiber Bragg grating and the reflectivity of the second fiber Bragg grating are configured to enable the 2.3μm output power P. out Achieve maximum output power P at 2.3μm out Under the steady-state approximation, the following analytical expression is satisfied: , Where: R1 is the reflectivity of the first fiber Bragg grating in the 2.3 μm band; R2 is the reflectivity of the second fiber Bragg grating in the 2.3 μm band; Add a loss factor to the dimensionless resonant cavity; The pump light wavelength, and =980 nm; The center wavelength of the output laser is located in the 2.3 μm band; The pump light power coupled into the gain fiber; The absorption cross section of erbium ions against 980 nm pump light; The erbium ion doping concentration in the gain fiber; denoted as the mode field overlap factor between the pump light and the doped region; L is the length of the gain fiber; d is the core diameter of the gain fiber; h is Planck's constant; and c is the speed of light in vacuum. The overlap factor between the 2.3 μm laser mode field and the doped region is given. The stimulated emission cross section of thulium ions in the 2.3 μm band; This represents the upper energy level lifetime corresponding to the laser transition of thulium ions in the 2.3 μm band; The linear background loss coefficient of the gain fiber in the 2.3 μm band is given. The efficiency of energy transfer from erbium ions to thulium ions; the efficiency of energy transfer from erbium ions to thulium ions. , The energy transfer coefficient from erbium ions to thulium ions is denoted as . The thulium ion doping concentration in the gain fiber is [missing information]. The lifetime of the upper energy level of the erbium ion is given.

[0028] This invention establishes a multi-level dynamic model for a 980 nm pumped thulium-erbium co-doped fluorine tellurate glass fiber 2.3 μm laser. The model uses Tm... 3+ Multilevel systems and Er 3+ Based on a multi-level system, see [link / reference] Figure 2 Tm 3+ / Er 3+ A schematic diagram of the energy level structure of the co-doped system; considering the following processes: Er 3+ Absorption and stimulated emission of 980 nm pump light, Er 3 + Radiative transitions and multiphonon relaxation processes between excited states, Er 3+ To Tm 3+ Energy transfer process, Tm 3+ Stimulated absorption and stimulated emission processes between transition energy levels corresponding to 2.3 μm, Tm 3+ Spontaneous relaxation and cross-relaxation processes, as well as optical field propagation, background loss, and output coupling processes in the laser resonator.

[0029] The multi-level dynamical model satisfies the total particle number conservation relation, where Tm 3+ The sum of the particle number densities of each energy level equals Tm 3+ Total doping concentration, Er 3+ The sum of the particle number densities of each energy level equals Er. 3+ Total doping concentration. For continuous pump steady-state operation, the particle number density of each energy level is set to have a time derivative of zero. The steady-state condition and the particle number conservation relationship are solved simultaneously to obtain the steady-state population relationship related to pump power, energy transfer efficiency, and signal light transition gain.

[0030] In deriving the analytical expression from the multi-level rate equations, this invention employs the following approximation conditions: (1) The laser operates under continuous pump steady-state conditions, and the average changes in particle number density at each energy level and the signal power within the cavity over time are negligible; (2) The 980 nm pump absorption is mainly due to Er 3+ Done, Tm 3+ Direct absorption of 980 nm pump relative to Er 3+ Absorption can be ignored or incorporated into an equivalent small-scale treatment; (3) Er 3+ To Tm 3+ The energy transfer process is the establishment of Tm 3+The dominant channel for population inversion of 2.3 μm transition particles is neglected under the first-order approximation; (4) For 2.3 μm laser output, Tm 3+ The net gain between the upper and lower energy levels of the laser dominates the threshold behavior of the resonant cavity, and the influence of the other higher-order excited states far from the main transition on the steady-state output power is treated as a second-order small quantity in the analytical reduction; (5) The additional distributed loss in the resonant cavity is represented by the equivalent additional loss factor and the background loss coefficient; (6) The effective mode field cross-sectional area of ​​the gain fiber is approximated by the equivalent area corresponding to the fiber core diameter.

[0031] Based on experimental conditions, the core diameter d, gain fiber length L, and Tm were analyzed. 3+ Doping concentration N Tm Er 3+ Doping concentration N Er The reflectivity of the first fiber Bragg grating in the 2.3 μm band and the reflectivity of the second fiber Bragg grating in the 2.3 μm band were matched. After optimization, the selected parameter combination was: d=8μm, L=3m, R1=90%, R2=10%, and the molar percentages of Tm2O3 and Er2O3 were both 0.2%.

[0032] After setup, the 2.3 μm fiber laser was tested. During testing, the output signal light was received and monitored by a spectrum analyzer 5, and the output power was monitored by an optical power meter 6. Figure 3 As shown, a 2.3 μm wavelength laser spectrum output can be obtained under 980 nm laser pumping conditions. Figure 4 As shown, with the gradual increase of the 980 nm pump power coupled into the gain fiber, a 2.3 μm laser output can be achieved when the pump power increases to 0.6 W; furthermore, as the 980 nm pump power continues to increase, the 2.3 μm laser output power increases accordingly. When the 980 nm pump power increases to 30 W, the 2.3 μm laser output power can reach 5.4 W.

[0033] The experimental results above demonstrate that the proposed solution, based on 980 nm laser pumping, thulium-erbium co-doped fluorotellurate glass fiber gain medium, and a 2.3 μm fiber Bragg grating resonator, can effectively achieve 2.3 μm mid-infrared laser output. Furthermore, optimizing the gain fiber parameters and resonator parameters using analytical expressions helps to coordinate the relationship between 980 nm pump absorption, Er→Tm energy transfer, intracavity loss, and output coupling, thereby improving device output performance and design efficiency. The experimental results obtained in this embodiment are consistent with the optimization trend given by the analytical expressions.

[0034] It should be noted that the core diameter, fiber length, Tm / Er doping concentration, input grating reflectivity, and grating reflectivity used in the above embodiments are merely example parameters in preferred embodiments and are not intended to limit the scope of protection of this invention. Those skilled in the art can adjust and optimize these parameters based on the theoretical model, analytical expressions, and specific application requirements, as long as 980 nm pumping and Er... 3+ Absorb and to Tm 3+ Energy transfer, in Tm 3+ The technical approach of establishing population inversion at the 2.3 μm laser transition and obtaining 2.3 μm laser output should all fall within the protection scope of this invention. Furthermore, the fiber fabrication methods, fiber end-face processing methods, coupling methods, fiber Bragg grating fabrication methods, and testing methods mentioned in the above embodiments can all be adapted to actual process conditions. As long as they do not deviate from the core concept of this invention, they will not affect the implementation of this invention.

[0035] This invention also provides a design method for a 2.3 μm fiber laser pumped by a 980 nm laser, comprising the following steps: S1: Establish a multi-level rate equation model for erbium ion absorption of pump light, energy transfer from erbium ions to thulium ions, and 2.3 μm transition of thulium ions under 980 nm pump conditions; S2: By combining the multi-level rate equation model under steady-state conditions with the total particle number conservation relationship, the laser resonator threshold condition, and the intracavity optical power transmission equation, the output power P at 2.3 μm is obtained. out The parsing expression; S3: Solve for the extrema of the analytical expression to determine the core diameter d, length L, and thulium ion doping concentration N of the gain fiber that maximizes the output power at 2.3 μm. Tm Erbium ion doping concentration N Er The parameter combination of the high-reflectivity grating R1 and the reflectivity of the output coupling grating R2; S4: Based on the parameter combination determined in step S3, select thulium- and erbium-doped fluorotellurate glass fiber as the gain medium, and form a first fiber Bragg grating and a second fiber Bragg grating with a central reflection wavelength in the 2.3 μm band at both ends to construct a laser resonant cavity. S5: Pump the gain fiber with a 980 nm laser to obtain a 2.3 μm laser output.

[0036] It is worth noting that the design method of this invention can directly guide the design of 2.3μm fiber lasers with different core diameters, lengths, Tm / Er doping ratios, and output coupling conditions. It has good scalability and engineering reuse value, and is suitable for device development, parameter screening, and mass production design. While realizing 980 nm pumped 2.3 μm mid-infrared laser output, this invention introduces analytical model constraints, which makes the device structure, energy transfer path, and parameter optimization path form a closed-loop unity. This not only improves the problems of traditional methods relying on experience and scattered parameter selection, but also improves repeatability and verifiability.

[0037] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0038] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0039] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A 2.3 μm fiber laser pumped by a 980 nm laser, characterized in that, The fiber laser includes: The system comprises a 980 nm laser pump source, an optical isolator, a gain fiber, and a first fiber Bragg grating and a second fiber Bragg grating respectively disposed at both ends of the gain fiber. The pump light output from the 980 nm laser pump source is coupled into the gain fiber after passing through the optical isolator. The gain fiber is a fluorotellurate glass fiber co-doped with thulium and erbium ions. After absorbing the 980 nm pump light, the erbium ions transfer energy to the thulium ions, thereby enhancing the energy transfer efficiency of the thulium ions. 3 H4 energy level and 3 Population inversion is established between the H5 energy levels, thereby generating 2.3 μm band laser output; the center reflection wavelengths of the first and second fiber Bragg gratings are both located in the 2.3 μm band, and together with the gain fiber, they form a 2.3 μm fiber laser resonant cavity, wherein: the first fiber Bragg grating is a high-reflectivity grating, and the second fiber Bragg grating is an output coupling grating; at least one end face of the gain fiber is a beveled end face to suppress parasitic oscillations formed by end face reflection; The core diameter d, fiber length L, and thulium ion doping concentration N of the gain fiber are... Tm Erbium ion doping concentration N Er The reflectivity R1 of the first fiber Bragg grating and the reflectivity R2 of the second fiber Bragg grating are configured to satisfy the following output power relationship: , Where: R1 is the reflectivity of the first fiber Bragg grating in the 2.3 μm band; R2 is the reflectivity of the second fiber Bragg grating in the 2.3 μm band; Add a loss factor to the dimensionless resonant cavity; The pump light wavelength, and =980 nm; The center wavelength of the output laser is located in the 2.3 μm band; The pump light power coupled into the gain fiber; The absorption cross section of erbium ions against 980 nm pump light; The erbium ion doping concentration in the gain fiber; denoted as the mode field overlap factor between the pump light and the doped region; L is the length of the gain fiber; d is the core diameter of the gain fiber; h is Planck's constant; and c is the speed of light in vacuum. The overlap factor between the 2.3 μm laser mode field and the doped region is given. The stimulated emission cross section of thulium ions in the 2.3 μm band; This represents the upper energy level lifetime corresponding to the laser transition of thulium ions in the 2.3 μm band; The linear background loss coefficient of the gain fiber in the 2.3 μm band is given. The efficiency of energy transfer from erbium ions to thulium ions; P out This refers to the output power.

2. The fiber laser as described in claim 1, characterized in that, The core glass of the gain fiber is composed of TeO2, BaF2, Y2O3, Tm2O3, and Er2O3, with the following molar percentages: TeO2: 70%, BaF2: 20%, Y2O3: 9.6%, Tm2O3: 0.2%, Er2O3: 0.2%; the cladding of the fiber is composed of TeO2, BaF2, and Y2O3, with the following molar percentages: TeO2: 67%, BaF2: 23%, Y2O3: 10%.

3. The fiber laser as described in claim 2, characterized in that, The gain fiber is prepared by combining the rod-tube method, extrusion method, or double crucible method with the drawing process.

4. The fiber laser as described in claim 2 or 3, characterized in that, The first fiber Bragg grating has a reflectivity of 90%, the second fiber Bragg grating has a reflectivity of 10%, the core diameter of the gain fiber is 8 μm, the length of the gain fiber is 3 m, and the thulium ion doping concentration is... and the erbium ion doping concentration These correspond to 0.2% molar percentage of Tm2O3 and 0.2% molar percentage of Er2O3, respectively.

5. A design method for a 2.3 μm fiber laser based on 980 nm laser pumping as described in claim 1, characterized in that, Includes the following steps: S1: Establish a multi-level rate equation model for erbium ion absorption of pump light, energy transfer from erbium ions to thulium ions, and 2.3 μm transition of thulium ions under 980 nm pump conditions; S2: By combining the multi-level rate equation model with the total particle number conservation relationship, the laser resonator threshold condition, and the intracavity optical power transmission equation under steady-state conditions, the 2.3 μm output power P is obtained. out The parsing expression; S3: Solve for the extrema of the analytical expression to determine the core diameter d, length L, and thulium ion doping concentration N of the gain fiber that maximizes the 2.3 μm output power. Tm Erbium ion doping concentration N Er The parameter combination of the high-reflectivity grating R1 and the reflectivity of the output coupling grating R2; S4: Based on the parameter combination determined in step S3, select thulium- and erbium-doped fluorotellurate glass fiber as the gain medium, and form a first fiber Bragg grating and a second fiber Bragg grating with a central reflection wavelength in the 2.3 μm band at both ends to construct a laser resonant cavity. S5: Pump the gain fiber with a 980 nm laser to obtain a 2.3 μm laser output.

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