1.6-2.1 [mu] m full-band single-frequency Tm < 3 + > doped germanosilicate composite fiber laser

Abstract

The invention provides a 1.6-2.1 [mu] m full-band single-frequency Tm < 3 + >-doped germanosilicate composite fiber laser, which comprises a fiber short linear cavity (2) which forms a distributed Bragg reflection cavity through a Tm < 3 + >-doped germanosilicate composite fiber, a broadband fiber bragg grating and a narrowband fiber bragg grating, or the Tm < 3 + >-doped germanosilicate composite optical fiber inscribes the phase shift grating to form a distributed feedback cavity, Tm2O3 with the concentration smaller than or equal to 0.5 mol% and GeO2 with the concentration larger than or equal to 20 mol% are doped into one area of a fiber core of the Tm < 3 + >-doped germanosilicate composite optical fiber at the same time, and Tm2O3 with the concentration larger than or equal to 1 mol% and GeO2 with the concentration smaller than or equal to 10 mol% are doped into the other area of the fiber core of the Tm < 3 + >-doped germanosilicate composite optical fiber at the same time. According to the optical fiber laser, a full-wave-band single-frequency laser with the working wavelength covering 1.6-2.1 microns, the power larger than 100 mW and the line width smaller than 2 kHz can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of lasers, and particularly to a single-frequency Tm-doped germanosilicate composite fiber laser with a wide operating wavelength range (1.6 - 2.1 μm band). 3+ Background Art

[0002] Single-frequency fiber lasers have the advantages of narrow linewidth, low noise, good beam quality, and compact structure, and have important application values in the fields of military defense, scientific research, coherent optical communication, lidar, laser medicine, etc. Currently, with the continuous increase in the demand for communication capacity, the use of traditional communication bands is approaching saturation. If the narrow-linewidth laser in the L band (1565 - 1625 nm) for communication is further extended to the 1.7 - 2.0 μm band, the capacity and bandwidth of the communication system can be greatly improved. In addition, fiber lasers operating in the 1.6 - 1.7 μm band have a high absorption rate for organic materials, making them have unique application prospects in some fields of transparent material processing. Moreover, due to the high absorption of water for 2.0 μm band lasers, 2.0 μm band fiber lasers can precisely cut human tissues while reducing thermal damage to surrounding tissues, and perform excellently in the field of medical applications.

[0003] Based on different structures such as long linear cavities, short linear cavities, and ring cavities, Tm-doped 3+ or Tm 3+ / Ho 3+ co-doped single-frequency fiber lasers can achieve an operating wavelength range covering 1.72 - 2.05 μm band. However, the cavity lengths of long linear cavities and ring cavities are relatively long, lacking an effective frequency discrimination mechanism, and are prone to mode hopping and mode competition. It is difficult for the laser to operate stably for a long time in a certain specific longitudinal mode (single frequency). For example, Zhang et al. used a 5 m long Tm-doped 3+ quartz fiber to construct a ring cavity and achieved single-frequency laser with an operating wavelength of 2050 nm and a power of 215 mW [Optics Letters, 2022, 47: 3964]; Shi et al. used a 4.6 m long Tm 3+ / Ho 3+ co-doped quartz fiber to construct a long linear cavity and achieved single-frequency laser with an operating wavelength of 2050 nm and a power of 1.2 W [Optics Letters, 2023, 48: 6144]. In contrast, short linear cavities (the cavity length is generally on the centimeter scale) are widely used due to their advantages of simple structure, not easy to mode-hop, and stable operation. For example, Cen et al. used Tm 3+ ​Highly doped germanate fiber is used to construct a distributed Bragg reflection (DBR) type short linear cavity, and single-frequency laser with a working wavelength of 1727 nm and a power of 12.4 mW is achieved [IEEE Photonics Technology Letters, 2021, 33: 350]; Walasik et al. inscribed a phase-shifted grating on a Tm-doped 3+ quartz fiber with a length of 8 cm to construct a distributed feedback (DFB) type short linear cavity, and single-frequency laser with a working wavelength of 2051 nm and a power of 65 mW is achieved [Journal of Lightwave Technology, 2021, 39:5096]. Due to technical bottlenecks such as small emission cross-sections (low gain) at both ends of the emission spectrum of the gain fiber, strong amplified spontaneous emission ASE, and parasitic oscillations, the currently publicly reported (single-module) single-frequency fiber lasers cannot cover bands such as 1.6 - 1.7 μm and 2.1 μm, and the lasers have technical problems such as low conversion efficiency, poor optical signal-to-noise ratio, and easy self-excitation.

[0004] Related research patents include: (1) In 2023, Shandong University disclosed a Tm 3+ / Ho 3+ :YAG-SiO2 special fiber, a 2 μm single-frequency fiber laser based on this fiber and its preparation method [Publication number: CN116482797A]. By increasing the doping concentration of Ho 3+ to improve the absorption of the gain fiber to pump light and the gain at the 2 μm band, single-frequency laser output at the 2 μm band is achieved. However, the laser required by this patent does not have the characteristic of covering the entire 1.6 - 2.1 μm working band; (2) In 2018, South China University of Technology disclosed a highly gain Tm 3+ / Ho 3+ co-doped multi-component germanate glass single-mode fiber and its preparation method [Publication number: CN109180010B]. By doping high concentrations of Tm 3+ and Ho 3+ , the gain at 2.05 μm is as high as 3.5 dB / cm. However, the gain fiber required by this patent does not have the characteristic of single-frequency laser output, nor does it have the characteristic of covering the entire 1.6 - 2.1 μm working band. Summary of the Invention

[0005] Based on this, it is necessary to provide a single-frequency fiber laser with a wide working wavelength range covering the entire 1.6 - 2.1 μm band to address the above technical problems. The technical problems to be solved are: to overcome the technical disadvantages of existing single-frequency fiber lasers such as narrow working wavelength range, low conversion efficiency, poor optical signal-to-noise ratio, and easy self-excitation.

[0006] The present invention is based on a short linear cavity constructed with a thulium-doped germanosilicate composite fiber having a centimeter-scale length and high-gain broadband. 3+ The fiber short linear cavity is composed of a thulium-doped germanosilicate composite fiber and a pair of uniform fiber gratings to form a DBR cavity, or a phase-shifted grating is inscribed on the thulium-doped germanosilicate composite fiber to form a DFB cavity (optional). 3+ The core of the thulium-doped germanosilicate composite fiber is formed by "structural compounding" of regional doping and bandwidth regulation, and different concentrations of Tm and germanium (Ge) elements that adjust the coordination field environment of the glass matrix are doped in each region. 3+ In one region of the core, Tm2O3 with a concentration ≤ 0.5 mol% and GeO2 with a concentration ≥ 20 mol% are simultaneously doped, and in another region of the core, Tm2O3 with a concentration ≥ 1 mol% and GeO2 with a concentration ≤ 10 mol% are simultaneously doped. 3+ By using the high doping of Tm in the short-length composite fiber and regulating and optimizing its emission wavelength range, the laser can efficiently lasing and stably operate in the single longitudinal mode (single frequency) within the wavelength range of 1.6 - 2.1 μm, and a full-band single-frequency laser with a working wavelength covering 1.6 - 2.1 μm, a power greater than 100 mW, and a linewidth less than 2 kHz can be obtained. 3+ To achieve the above object, the specific technical solution adopted by the present invention is as follows: 3+

[0007] A 1.6 - 2.1 μm full-band single-frequency thulium-doped germanosilicate composite fiber laser, comprising: a fiber short linear cavity (2), and the fiber short linear cavity (2) forms a distributed Bragg reflection cavity through a thulium-doped germanosilicate composite fiber, a broadband fiber grating, and a narrowband fiber grating, or a phase-shifted grating is inscribed on the thulium-doped germanosilicate composite fiber to form a distributed feedback cavity.

[0008]

[0009] 3+ In one region of the core of the thulium-doped germanosilicate composite fiber, Tm2O3 with a concentration ≤ 0.5 mol% and GeO2 with a concentration ≥ 20 mol% are simultaneously doped, and in another region, Tm2O3 with a concentration ≥ 1 mol% and GeO2 with a concentration ≤ 10 mol% are simultaneously doped. 3+ Further, the 3 dB bandwidth range of the broadband fiber grating in the distributed Bragg reflection cavity is 1 ± 0.5 nm, the broadband fiber grating has high transmittance for the pump laser wavelength, the transmittance is greater than 95%, and high reflectance for the signal laser wavelength, the reflectance is greater than 95%; the 3 dB bandwidth range of the narrowband fiber grating is 0.1 ± 0.05 nm, and the narrowband fiber grating partially reflects the signal laser wavelength, and the reflectance range at its central wavelength is 10 - 90%. 3+ 3+ ​​​​​

[0010] Furthermore, the distributed feedback cavity is to inscribe a π-phase shift grating at the middle position of the Tm-doped 3+ germanosilicate composite optical fiber. The transmission window linewidth of the central wavelength of the π-phase shift grating is less than 0.02 nm, and the reflectivity at its central wavelength is greater than 80%; the π-phase shift grating has high transmittance for the pump laser wavelength, and the transmittance is greater than 95%.

[0011] Furthermore, the doping structure of the core region of the Tm-doped 3+ germanosilicate composite optical fiber in the short fiber linear cavity (2) is symmetric semi-circular, bow-shaped, taiji arc-shaped, bow arc-shaped or 120° sector-shaped; the core diameter of the Tm-doped 3+ germanosilicate composite optical fiber ranges from 4 to 30 μm, the numerical aperture ranges from 0.06 to 0.3, and the usable length is from 0.1 to 10.0 cm.

[0012] Furthermore, the cladding of the Tm-doped 3+ germanosilicate composite optical fiber in the short fiber linear cavity (2) is made of germanosilicate, germanate, silicate or quartz glass matrix, and the cladding diameter ranges from 80 to 250 μm.

[0013] Furthermore, the preparation steps of the Tm-doped 3+ germanosilicate composite optical fiber in the short fiber linear cavity (2) include:

[0014] 1) Prepare core glass by the melting-quenching method. Weigh the core glass raw materials according to the molar percentages of each oxide composition. The molar components include 40 - 85 mol% SiO2, 5 - 35 mol% GeO2, 0.3 - 3 mol% Tm2O3, and a combination of 0 - 25 mol% of BaO, Al2O3, and PbO, and it satisfies that within one core glass raw material, Tm2O3 with a concentration ≤ 0.5 mol% and GeO2 with a concentration ≥ 20 mol% are simultaneously doped, and within another core glass raw material, Tm2O3 with a concentration ≥ 1 mol% and GeO2 with a concentration ≤ 10 mol% are simultaneously doped;

[0015] 2) Subject each core glass raw material to stirring, melting, water removal, and clarification processes respectively, and then through casting, forming, and annealing processes to obtain core glass;

[0016] 3) Process each core glass through mechanical cold processing and polishing processes to make core rods and composite them together, then sleeve them into a cladding glass tube to assemble an optical fiber preform;

[0017] 4) Place the optical fiber preform in a drawing tower for heating, evacuate during the drawing process, and draw it into a Tm-doped 3+ germanosilicate composite optical fiber.

[0018] Further, it includes: an end cap (1), a short fiber linear cavity (2), a wavelength division multiplexer (3), a pump source (4), and an isolator (5). One end of the end cap (1) and both ends of the short fiber linear cavity (2) are sequentially connected to the common end of the wavelength division multiplexer (3); the pump end of the wavelength division multiplexer (3) is connected to the pigtail of the pump source (4); the signal end of the wavelength division multiplexer (3) is connected to the input end of the isolator (5); the output end of the isolator (5) serves as the output port of the laser.

[0019] Further, one end face of a section of single-mode fiber of the end cap (1) is ground into an 8 - 15° bevel angle and an antireflection film is coated. The transmittance of the antireflection film for the signal laser wavelength is greater than 95%.

[0020] Further, the wavelength division multiplexer (3) is a fused biconical taper type or a crystalline optical device. The pigtail types of the signal end, the common end, and the pump end are all single-mode fibers; the power that the wavelength division multiplexer (3) can withstand is greater than 1 W.

[0021] Further, the pump source (4) is a single transverse mode fiber laser with pigtail coupled output, a semiconductor laser, or other solid-state lasers; the pump power of the pump source (4) is greater than 100 mW; the pump wavelength range of the pump source (4) is 780 - 820 nm, or 1500 - 2000 nm.

[0022] Compared with the prior art, the technical effect of the present invention is that: a short linear cavity is constructed by using a centimeter-length, high-gain broadband Tm-doped 3+ germanosilicate composite fiber. The short fiber linear cavity consists of a Tm-doped 3+ germanosilicate composite fiber and a pair of uniform fiber gratings (front and rear cavity mirrors) to form a DBR cavity, or a phase shift grating (cavity mirror) is inscribed on the Tm-doped 3+ germanosilicate composite fiber to form a DFB cavity (optional). Under the continuous excitation of the pump light, the luminescent ions Tm in the fiber core 3+ undergo population inversion to generate stimulated emission signal light. Under the feedback of cavity mirrors in different wavelength bands, it oscillates back and forth in the cavity multiple times, strengthens, and undergoes a continuous stimulated emission process; since the cavity length of the resonant cavity is only on the order of centimeters, the longitudinal mode interval in the cavity can reach GHz. When the 3 dB reflection spectrum or the transmission window linewidth of the output cavity mirror is as narrow as dozens of pm or a few pm, it can be realized that only one single longitudinal mode operates in the cavity, and continuous output of single-frequency laser is achieved through the output cavity mirror; that is, by using the high-doping Tm of the short-length composite fiber 3+, and regulating and optimizing its emission wavelength range so that the laser can efficiently lasing and operate stably in a single longitudinal mode within the wavelength range of 1.6 - 2.1 μm. A single-frequency fiber laser with a full coverage of the working wavelength range of 1.6 - 2.1 μm, high conversion efficiency, and high optical signal-to-noise ratio can be obtained.

[0023] Compared with the existing Tm-doped 3+ fiber lasers, the advantages of the present invention are as follows:

[0024] (1) The Tm-doped 3+ germanosilicate composite fiber used in the laser of the present invention can reduce the clustering effect of Tm 3 + by doping Ge element, that is, improve the solubility (doping concentration) of the glass matrix to Tm 3+ to obtain high-gain performance. Using a high-gain fiber to construct a short linear cavity can avoid the mode-hopping phenomenon, thus ensuring the stable single-longitudinal-mode (single-frequency) operation of the laser and high conversion efficiency;

[0025] (2) The Tm-doped 3+ germanosilicate composite fiber used in the laser of the present invention can regulate the coordination field environment of the glass matrix by doping Ge element, thereby regulating the emission peak spectrum of Tm 3+ and shifting the emission wavelength of the gain fiber to blue, that is, a certain region of the core with a high Ge doping concentration has both high gain and large bandwidth at the short wavelength band of 1.6 - 1.7 μm, which is beneficial to efficiently lasing the signal laser at the short wavelength band of 1.6 - 1.7 μm; and by adjusting the concentration ratio of Ge element and Tm 3+ , regulating the spectral characteristics to weaken the reabsorption of the short-wavelength signal laser by the gain fiber, further improving the conversion efficiency of the laser;

[0026] (3) The Tm-doped 3+ germanosilicate composite fiber used in the laser of the present invention has high gain at the long wavelength band of 2.1 μm by doping a high concentration of Tm 3+ and a low concentration of Ge element in a certain region of the core. The high-gain performance is beneficial to efficiently lasing the signal laser at the long wavelength band of 2.1 μm.

[0027] In addition, the laser of the present invention is based on a co-band pump source with a pump wavelength range of 1500 - 2000 nm, having a low quantum deficit effect; adopting a single-mode core pumping method, increasing the utilization efficiency of the pump light, reducing the reabsorption of the signal laser and the thermal effect of the system, and improving the stability and reliability of the laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic structural diagram of the DBR cavity.

[0029] In the figure: 2 - fiber short linear cavity, 21 - Tm-doped 3+ germanosilicate composite fiber, 22 - broadband fiber grating, 23 - narrowband fiber grating.

[0030] Figure 2 It is a schematic structural diagram of a DFB cavity.

[0031] In the figure: 2 - fiber short linear cavity, 21 - Tm-doped 3+ germanosilicate composite fiber, 24 - phase-shifted fiber grating.

[0032] Figure 3 For Tm-doped 3+ It is a schematic diagram of the doping structure of the core region of a germanosilicate composite fiber, where the shape of the core (211) is circular and is jointly composed of a region (01) doped with a low concentration of Tm2O3 and a high concentration of GeO2 and a region (02) doped with a high concentration of Tm2O3 and a low concentration of GeO2; (a) symmetric semi-circular, (b) bow-shaped, (c) Taiji arc-shaped, (d) bow arc-shaped, (e) 120° sector-shaped, (f) 90° sector-shaped, (g) inner triangle-shaped, (h) circular ring.

[0033] In the figure: 211 - core, 212 - cladding, 01 - region doped with a low concentration of Tm2O3 and a high concentration of GeO2, 02 - region doped with a high concentration of Tm2O3 and a low concentration of GeO2.

[0034] Figure 4 It is a schematic principle diagram of a 1.6 - 2.1 μm full-band single-frequency Tm-doped 3+ germanosilicate composite fiber laser in an embodiment of the present invention.

[0035] In the figure: 1 - end cap; 2 - fiber short linear cavity; 3 - wavelength division multiplexer; 4 - pump source; 5 - isolator.

[0036] Figure 5 It is the single-frequency fiber laser output spectrum diagram of the laser in an embodiment of the present invention at 1630 nm.

[0037] Figure 6 It is the single-frequency fiber laser output spectrum diagram of the laser in an embodiment of the present invention at 2097 nm. Specific embodiments

[0038] The following further elaborates on a 1.6 - 2.1 μm full-band single-frequency Tm-doped 3+ germanosilicate composite fiber laser of the present application with specific embodiments. The present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosed content of the present application more thorough and comprehensive.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terms used in the description of this application herein are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0040] In this application, among the technical features described in an open-ended manner, a closed technical solution composed of the listed features is included, as well as an open technical solution containing the listed features.

[0041] In this application, regarding numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0042] Regarding the percentage content involved in this application, unless otherwise specified, for solid-liquid mixtures and solid-solid mixtures, it refers to the mass percentage, and for liquid-liquid mixtures, it refers to the volume percentage.

[0043] Regarding the percentage concentration involved in this application, unless otherwise specified, it refers to the final concentration. The final concentration refers to the proportion of the added component in the system after adding the component.

[0044] Regarding the temperature parameters in this application, unless otherwise specified, both constant temperature treatment and treatment within a certain temperature range are allowed. The constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument.

[0045] This application provides a 1.6 - 2.1 μm all-band single-frequency Tm-doped 3+ germanosilicate composite fiber laser, comprising: a fiber short linear cavity, and the fiber short linear cavity forms a distributed Bragg reflection (DBR) cavity through a Tm-doped 3+ germanosilicate composite fiber and a pair of uniform fiber gratings (broadband fiber grating, narrowband fiber grating), or a distributed feedback (DFB) cavity is formed by inscribing a phase-shifted grating on the Tm-doped 3+ germanosilicate composite fiber, and in one region of the core of the Tm-doped 3+ germanosilicate composite fiber, Tm2O3 with a concentration ≤ 0.5 mol% and GeO2 with a concentration ≥ 20 mol% are simultaneously doped, and in another region, Tm2O3 with a concentration ≥ 1 mol% and GeO2 with a concentration ≤ 10 mol% are simultaneously doped.

[0046] Understandably, in the short fiber linear cavity, Tm-doped 3+ the core of the germanosilicate composite fiber is doped with different concentrations of Tm for luminescence in different regions 3+ and germanium (Ge) elements that adjust the coordination field environment to regulate and optimize the 3+ luminescence wavelength range are formed by "structural composite". The short fiber linear cavity has two different structures, and the schematic diagrams of the DBR cavity and DFB cavity structures are shown in Figure 1 and Figure 2 respectively.

[0047] Furthermore, in one region, Tm2O3 with a concentration of 0.3 - 0.5 mol% and GeO2 with a concentration of 20 - 35 mol% are simultaneously doped, and in another region, Tm2O3 with a concentration of 1 - 3 mol% and GeO2 with a concentration of 5 - 10 mol% are simultaneously doped. Specifically, the concentration of Tm2O3 includes but is not limited to: 0.3 mol%, 0.5 mol%, 0.8 mol%, 1 mol%, 1.3 mol%, 1.5 mol%, 1.8 mol%, 2 mol%, 1.3 mol%, 1.5 mol%, 1.8 mol%, 3 mol% or the range between any two of the foregoing; the concentration of GeO2 includes but is not limited to: 5 mol%, 8 mol%, 10 mol%, 12 mol%, 15 mol%, 17 mol%, 20 mol%, 22 mol%, 25 mol%, 27 mol%, 30 mol%, 32 mol%, 35 mol% or the range between any two of the foregoing.

[0048] Furthermore, in the distributed Bragg reflection (DBR) cavity, the 3 dB bandwidth range of the broadband fiber grating is 1 ± 0.5 nm. The broadband fiber grating has high transmittance for the pump laser wavelength, with a transmittance greater than 95%, and high reflectivity for the signal laser wavelength, with a reflectivity greater than 95%; the 3 dB bandwidth range of the narrowband fiber grating is 0.1 ± 0.05 nm. The narrowband fiber grating partially reflects the signal laser wavelength, and the reflectivity at its central wavelength ranges from 10% to 90%.

[0049] Furthermore, the distributed feedback (DFB) cavity is to engrave a π-phase shift grating at the middle position of the Tm-doped 3+ germanosilicate composite fiber. The line width of the transmission window at the central wavelength of the π-phase shift grating is less than 0.02 nm, and the reflectivity at its central wavelength is greater than 80%. Furthermore, the π-phase shift grating has high transmittance for the pump laser wavelength, with a transmittance greater than 95%.

[0050] Tm-doped 3+ the doping structure of the core region of the germanosilicate composite fiber can have different forms. Such as Figure 3As shown, in the present invention, the doped Tm 3+ Schematic diagram of the doping structure in the core region of the germanosilicate composite fiber doped with Tm. The shape of the core (211) is circular and is jointly composed of a region (01) doped with a low concentration of Tm2O3 and a high concentration of GeO2 and a region (02) doped with a high concentration of Tm2O3 and a low concentration of GeO2; (a) symmetric semi-circular, (b) bow-shaped, (c) taiji arc-shaped, (d) bow-shaped arc, (e) 120° sector, (f) 90° sector, (g) inner triangle, (h) ring. Further, the doped Tm 3+ The doping structure of the core region of the germanosilicate composite fiber doped with Tm is symmetric semi-circular, bow-shaped, taiji arc-shaped, bow-shaped arc or 120° sector.

[0051] Further, the doped Tm 3+ The diameter range of the core of the germanosilicate composite fiber doped with Tm is 4 - 30 μm, the numerical aperture range is 0.06 - 0.3, and the use length is 0.1 - 10.0 cm.

[0052] Further, the doped Tm 3+ The cladding of the germanosilicate composite fiber doped with Tm in the short linear cavity of the fiber is germanosilicate, germanate, silicate or quartz glass matrix. Without limitation, the cladding diameter range is 80 - 250 μm.

[0053] Further, the doped Tm 3+ The preparation steps of the germanosilicate composite fiber doped with Tm in the short linear cavity of the fiber include:

[0054] 1) Prepare the core glass by the melting - quenching method. Weigh the core glass raw materials according to the molar percentages of each oxide composition. The molar components include 40 - 85 mol% SiO2, 5 - 35 mol% GeO2, 0.3 - 3 mol% Tm2O3, and a combination of 0 - 25 mol% of BaO, Al2O3 and PbO, and it is ensured that within one core glass raw material, the concentration of Tm2O3 ≤ 0.5 mol% and the concentration of GeO2 ≥ 20 mol% are simultaneously doped, and within another core glass raw material, the concentration of Tm2O3 ≥ 1 mol% and the concentration of GeO2 ≤ 10 mol% are simultaneously doped; It can be understood that GeO2 is doped to adjust the coordination field environment of the glass matrix and optimize the local structure of Tm 3+ to increase the emission cross-section (gain) of Tm 3+ at the short wavelength band of 1.6 - 1.7 μm;

[0055] 2) Subject each core glass raw material to stirring, melting, water removal, and clarification processes respectively, and then through casting molding and annealing processes to obtain the core glass;

[0056] 3) The core glasses are processed by mechanical cold working and polishing processes to form core rods, which are then combined together and sleeved into a cladding glass tube to assemble an optical fiber preform;

[0057] 4) The optical fiber preform is placed in a drawing tower for heating, and vacuum is pumped during the drawing process to draw a Tm-doped 3+ germanosilicate composite optical fiber.

[0058] Without limitation, the stirring, melting, water removal, and clarification processes in step 2) can be carried out in a platinum crucible.

[0059] Furthermore, the 1.6 - 2.1 μm all-band single-frequency Tm-doped 3+ germanosilicate composite optical fiber laser, as Figure 4 shown, includes: an end cap 1, a short fiber linear cavity 2, a wavelength division multiplexer 3, a pump source 4, and an isolator 5. Among them, one end of the end cap 1 and both ends of the short fiber linear cavity 2 are sequentially connected to the common end of the wavelength division multiplexer 3; the pump end of the wavelength division multiplexer 3 is connected to the pigtail of the pump source 4; the signal end of the wavelength division multiplexer 3 is connected to the input end of the isolator 5; the output end of the isolator 5 serves as the output port of the laser.

[0060] Furthermore, the end cap 1 is the end face of a single-mode optical fiber ground into an 8 - 15° bevel angle and coated with an antireflection film, and the transmittance of the antireflection film for the signal laser wavelength is greater than 95%.

[0061] Furthermore, the wavelength division multiplexer 3 is a fused biconical taper type or crystalline optical device. Further, the pigtail types of the signal end, common end, and pump end are all single-mode optical fibers. Further, the power that the wavelength division multiplexer 3 can withstand is greater than 1 W.

[0062] Without limitation, the pump source 4 is a single transverse mode (single-mode) optical fiber laser, semiconductor laser, or other solid-state laser with pigtail-coupled output. Further, the pump power of the pump source 4 is greater than 100 mW. Further, the pump wavelength range of the pump source 4 is 780 - 820 nm, or 1500 - 2000 nm. It can be understood that the specific pump wavelength is selected according to the working wavelength of the single-frequency laser; the pumping method is single-wavelength pumping or multi-wavelength hybrid pumping, and the pumping direction is forward, backward, or bidirectional pumping.

[0063] For the experimental parameters not specified in the following specific embodiments, preferably refer to the guidance given in this application document, and it is also possible to refer to the experimental manuals in this field or other experimental methods known in this field, or refer to the experimental conditions recommended by the manufacturers.

[0064] The raw materials and reagents involved in the following specific embodiments can be obtained commercially, or those skilled in the art can prepare them according to known means.

[0065] Example 1:

[0066] In this example, the core region doping structure of the Tm-doped 3+ germanosilicate composite optical fiber is a symmetric semi-circle, which is composed of a region doped with low-concentration Tm 3+ and high-concentration Ge elements and a region doped with high-concentration Tm 3+ and low-concentration Ge elements. The doping in the core is symmetric left and right. The molar composition of one region in the core is 65 mol% SiO2 - 30 mol% GeO2 - 0.5 mol% Tm2O3 - 2.5 mol% BaO - 1 mol% Al2O3 - 1 mol% PbO, that is, low-concentration Tm2O3 and high-concentration GeO2 are simultaneously doped in the region, which are 0.5 mol% and 30 mol% respectively. The molar composition of another region in the core is 82 mol% SiO2 - 7 mol% GeO2 - 1.5 mol% Tm2O3 - 4.5 mol% BaO - 3 mol% Al2O3 - 2 mol% PbO, that is, high-concentration Tm2O3 and low-concentration GeO2 are simultaneously doped in the region, which are 1.5 mol% and 7 mol% respectively. The shape of the core is circular, and its cladding is a silicate glass matrix. Two melted core glasses are made into a core rod with a semi-circular structure and compounded together, then sleeved into a cladding glass tube to assemble an optical fiber preform, and drawn into a Tm-doped 3+ germanosilicate composite optical fiber. The core diameter of the obtained Tm-doped 3+ germanosilicate composite optical fiber is 9 μm, the numerical aperture is 0.2, the cladding diameter is 125 μm, and the use length of the Tm-doped 3+ germanosilicate composite optical fiber is 2.0 cm.

[0067] The fiber short linear cavity is composed of the Tm-doped 3+A DBR cavity is composed of a germanosilicate composite optical fiber and a pair of uniform fiber Bragg gratings. The center wavelength of the broadband fiber Bragg grating is 1630 nm, the 3-dB bandwidth is 0.92 nm, the reflectivity for the signal laser wavelength is 99.9%, and the transmittance for the pump laser wavelength of 1570 nm is 99.9%. The center wavelength of the narrowband fiber Bragg grating is 1630 nm, the 3-dB bandwidth is 0.12 nm, and the reflectivity for the signal laser wavelength is 80%. One end cap is the fiber end face of a section of single-mode fiber SMF-28e ground into an 8° bevel angle and coated with an antireflection film with a transmittance of 99% for the signal laser wavelength of 1630 nm. The wavelength division multiplexer is fabricated by the fused biconical taper process. The pigtails of the signal end, common end, and pump end are all single-mode fiber SMF-28e, and the power that the wavelength division multiplexer can withstand is 5 W. The pump source is a single transverse mode fiber laser with a pigtail coupled output. The operating wavelength of the pump source is 1570 nm, the power is 2 W, and the pumping direction is backward pumping.

[0068] In this embodiment, the 1570-nm pump light generated by the pump source is coupled into the core of the Tm-doped germanosilicate composite optical fiber through the wavelength division multiplexer. 3+ Under the continuous excitation of the pump light, the luminescent ions Tm in the core 3+ undergo population inversion, generating 1630-nm stimulated emission signal laser. Under the feedback of the broadband fiber Bragg grating and the narrowband fiber Bragg grating (front and rear cavity mirrors), the signal laser oscillates back and forth in the cavity multiple times, is strengthened, and undergoes a continuous stimulated emission process. In this embodiment, a 2-cm gain fiber is used, so that the cavity length of the resonant cavity is only on the centimeter scale, and the longitudinal mode interval in the cavity can reach GHz. When the 3-dB reflection spectrum of the narrowband fiber Bragg grating is narrowed to dozens of pm, it is possible to achieve single longitudinal mode (single frequency) operation in the cavity, and continuous output of single-frequency laser is realized through the narrowband fiber Bragg grating. In this example, the Tm-doped germanosilicate composite optical fiber adopts a symmetric semicircular region doping structure, with a high concentration of Ge element doped. The coordination field in the glass matrix changes, resulting in a blue shift of the emission wavelength of the gain fiber, having high gain at the short wavelength of 1630 nm, and being able to achieve efficient and stable 1630-nm single-frequency laser output. Moreover, the 1570-nm single-mode core pumping has low quantum deficit and high energy conversion efficiency for the 1630-nm signal laser, and can efficiently generate the signal laser. Finally, a single-frequency laser with a working wavelength of 1630 nm, a power of 200 mW, a line width of 1.5 kHz, and an optical signal-to-noise ratio of 60 dB is obtained. Its output spectrogram is as 3+ shown. Figure 5 shown.

[0069] Example 2:

[0070] In this embodiment, the Tm-doped 3+The doping structure of the core region of the germanosilicate composite fiber is a ring, which is composed of a region doped with low-concentration Tm 3+ and high-concentration Ge elements and a region doped with high-concentration Tm 3+ and low-concentration Ge elements. The molar composition of one region (inside the concentric circle) of the core is 62 mol% SiO2 - 32 mol% GeO2 - 0.5 mol% Tm2O3 - 2 mol% BaO - 1.5 mol% Al2O3 - 2 mol% PbO, that is, low-concentration Tm2O3 and high-concentration GeO2 are doped simultaneously in the region, which are 0.5 mol% and 32 mol% respectively. The molar composition of another region (outside the concentric circle) of the core is 75 mol% SiO2 - 5 mol% GeO2 - 1.3 mol% Tm2O3 - 7.5 mol% BaO - 5.2 mol% Al2O3 - 6 mol% PbO, that is, high-concentration Tm2O3 and low-concentration GeO2 are doped simultaneously in the region, which are 1.3 mol% and 5 mol% respectively. The shape of the core is circular, and its cladding is a silica glass matrix. Two pieces of melted core glass are made into a core rod with a circular and annular structure and compounded together, then sleeved into a cladding glass tube to assemble an optical fiber preform, and drawn into a Tm 3+ -doped germanosilicate composite fiber. The core diameter of the Tm 3+ -doped germanosilicate composite fiber is 8 μm, the numerical aperture is 0.22, the cladding diameter is 125 μm, and the use length of the Tm 3+ -doped germanosilicate composite fiber is 4 cm.

[0071] Among them, the fiber short linear cavity is composed of a π-phase shift grating inscribed on the Tm 3+ -doped germanosilicate composite fiber to form a DFB cavity. The line width of the transmission window at the central wavelength of 2097 nm of the π-phase shift grating is 0.01 nm, the reflectivity at the central wavelength is 90%, and the transmittance at the pump laser wavelength of 1610 nm is 99.9%. The end cap is the end face of one end of a single-mode fiber SM1950 ground into an 8° bevel angle and coated with an antireflection film with a transmittance of 99% for the signal laser wavelength of 2097 nm. The wavelength division multiplexer is made by the fused biconical taper process. The pigtails at the signal end and the common end are both SM1950, the pigtail at the pump end is a single-mode fiber SMF-28e, and the power that the wavelength division multiplexer can withstand is 10 W. The pump source is a single transverse mode fiber laser with a pigtail coupled output. The working wavelength of the pump source is 1610 nm, the power is 2 W, and the pumping direction is backward pumping.

[0072] In this embodiment, the 1610 nm pump light generated by the pump source is coupled into the core of the Tm 3+ -doped germanosilicate composite fiber through the wavelength division multiplexer. Under the continuous excitation of the pump light, the luminescent ions Tm in the core3+ Population inversion occurs, generating a stimulated emission signal laser at 2097 nm. Under the feedback of the π-phase shift grating (cavity mirror), the signal laser oscillates back and forth in the cavity multiple times, strengthens, and undergoes a continuous stimulated emission process. In this embodiment, a 4-cm gain fiber is used, making the cavity length of the resonant cavity only on the order of centimeters. The longitudinal mode spacing in the cavity can reach GHz. When the transmission window linewidth of the π-phase shift grating is as narrow as 10 pm, only one single longitudinal mode (single frequency) operation can be achieved in the cavity, and continuous output of single-frequency laser is realized through the phase shift grating. In this example, the Tm-doped 3+ germanosilicate composite fiber adopts a ring-shaped regional doping structure and is doped with a high concentration of Tm 3+ , which has high gain at the long wavelength of 2097 nm and can achieve efficient and stable single-frequency laser output at 2097 nm. Moreover, for the 2097-nm signal light, the 1610-nm single-mode core pumping has low quantum deficit and high energy conversion efficiency, and can efficiently generate the signal laser. Finally, a single-frequency laser with a working wavelength of 2097 nm, a power of 400 mW, a linewidth of 1.8 kHz, and an optical signal-to-noise ratio of 60 dB is obtained. Its output spectrogram is as shown in Figure 6 shown.

[0073] The system structure in the present invention is also applicable to different numbers of pump sources, output powers, pump wavelengths, pump modes, as well as other parameters such as different types of doped ions in the gain fiber, doping concentrations, regional doping methods, core diameters, and usage lengths. As described above, the above embodiments are only preferred embodiments of the present invention and are not used to limit its implementation scope.

[0074] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as these combinations of technical features do not conflict, they should be considered as within the scope described in this specification.

[0075] The above embodiments only represent several implementation manners of the present application, which are convenient for understanding the technical solutions of the present application specifically and in detail, but should not be construed as limiting the scope of patent protection of the application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several deformations and improvements can be made, and these all belong to the protection scope of the present application. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning, or limited experiments based on the technical solutions provided in the present application are all within the protection scope of the appended claims of the present application. Therefore, the protection scope of the patent of the present application should be subject to the content of the appended claims, and the specification can be used to explain the content of the claims.

Claims

1. A 1.6 - 2.1 μm all - band single - frequency Tm - doped 3+ germanosilicate composite fiber laser, characterized in that, Comprising: Fiber short linear cavity (2), the fiber short linear cavity (2) is doped with Tm 3+ Germanosilicate composite fiber and broadband fiber grating, narrowband fiber grating form a distributed Bragg reflection cavity, or Tm-doped 3+ Germanosilicate composite fiber inscribed with a phase-shifted grating forms a distributed feedback cavity, the Tm-doped 3+ Germanosilicate composite fiber is simultaneously doped with Tm2O3 with a concentration ≤ 0.5 mol% and GeO2 with a concentration ≥ 20 mol% in one region of the fiber core, and simultaneously doped with Tm2O3 with a concentration ≥ 1 mol% and GeO2 with a concentration ≤ 10 mol% in another region.

2. A 1.6 - 2.1 μm all - band single - frequency Tm - doped 3+ germanosilicate composite fiber laser according to claim 1, characterized in that In the distributed Bragg reflection cavity, the 3 dB bandwidth range of the broadband fiber grating is 1 ± 0.5 nm. The broadband fiber grating has high transmittance for the pump laser wavelength, with a transmittance greater than 95%, and high reflectivity for the signal laser wavelength, with a reflectivity greater than 95%. The 3 dB bandwidth range of the narrowband fiber grating is 0.1 ± 0.05 nm. The narrowband fiber grating partially reflects the signal laser wavelength, and the reflectivity at its central wavelength ranges from 10% to 90%.

3. A 1.6 - 2.1 μm all - band single - frequency Tm - doped 3+ germanosilicate composite fiber laser according to claim 1, characterized in that The distributed feedback cavity is formed by writing a π-phase shift grating at the middle position of the Tm-doped 3+ germanosilicate composite optical fiber. The line width of the transmission window at the center wavelength of the π-phase shift grating is less than 0.02 nm, and the reflectivity at its center wavelength is greater than 80%. The π-phase shift grating has a high transmittance for the pump laser wavelength, and the transmittance is greater than 95%.

4. A 1.6 - 2.1 μm all - band single - frequency Tm - doped 3+ germanosilicate composite fiber laser according to claim 1, characterized in that The core region doping structure of the Tm-doped germanosilicate composite optical fiber in the short linear optical fiber cavity (2) is symmetric semi-circular, bow-shaped, taiji arc-shaped, bow arc-shaped or 120° sector-shaped; the Tm-doped 3+ germanosilicate composite optical fiber has a core diameter ranging from 4 to 30 μm, a numerical aperture ranging from 0.06 to 0.3, and a use length of 0.1 to 10.0 cm. 3+ The core region doping structure of the Tm-doped germanosilicate composite optical fiber is symmetric semi-circular, bow-shaped, taiji arc-shaped, bow arc-shaped or 120° sector-shaped; the Tm-doped 5. A 1.6 - 2.1 μm all - band single - frequency Tm - doped 3+ germanosilicate composite fiber laser according to claim 1, characterized in that The Tm-doped 3+ The cladding of the germanosilicate composite optical fiber is made of germanosilicate, germanate, silicate or silica glass matrix, and the cladding diameter ranges from 80 to 250 μm.

6. A 1.6 - 2.1 μm all - band single - frequency Tm - doped 3+ germanosilicate composite fiber laser according to claim 1, characterized in that The Tm-doped 3+ The preparation steps of the germanosilicate composite optical fiber include: 1) The core glass is prepared by the melting - quenching method. The raw materials of the core glass are weighed according to the molar percentages of each oxide composition. The molar components include 40 - 85 mol% SiO2, 5 - 35 mol% GeO2, 0.3 - 3 mol% Tm2O3, and a combination of 0 - 25 mol% of BaO, Al2O3, and PbO, and it satisfies that within one core glass raw material, Tm2O3 with a concentration ≤ 0.5 mol% and GeO2 with a concentration ≥ 20 mol% are doped simultaneously, and within another core glass raw material, Tm2O3 with a concentration ≥ 1 mol% and GeO2 with a concentration ≤ 10 mol% are doped simultaneously. 2) Each core glass raw material undergoes stirring, melting, water removal, and clarification processes respectively, and then undergoes casting and annealing processes to obtain the core glass. 3) Each core glass is made into a core rod through mechanical cold processing and polishing processes and then compounded together, and is sleeved into a cladding glass tube to assemble an optical fiber preform. 4) Place the optical fiber preform in a drawing tower for heating, evacuate during the drawing process, and draw a Tm-doped 3+ germanosilicate composite optical fiber.

7. A 1.6 - 2.1 μm all - band single - frequency Tm - doped 3+ germanosilicate composite fiber laser according to any one of claims 1 - 6, characterized in that Comprising: A end cap (1), an optical fiber short linear cavity (2), a wavelength division multiplexer (3), a pump source (4), and an isolator (5). Among them, one end of the end cap (1), both ends of the optical fiber short linear cavity (2) are sequentially connected to the common end of the wavelength division multiplexer (3). The pump end of the wavelength division multiplexer (3) is connected to the pigtail of the pump source (4). The signal end of the wavelength division multiplexer (3) is connected to the input end of the isolator (5). The output end of the isolator (5) serves as the output port of the laser.

8. A 1.6 - 2.1 μm all - band single - frequency Tm - doped 3+ germanosilicate composite fiber laser according to claim 7, characterized in that The end cap (1) is the end face of a section of single - mode optical fiber ground into an 8 - 15° bevel angle and coated with an antireflection film. The transmittance of the antireflection film for the signal laser wavelength is greater than 95%.

9. A 1.6 - 2.1 μm all - band single - frequency Tm - doped 3+ germanosilicate composite fiber laser according to claim 7, characterized in that The wavelength division multiplexer (3) is a fused - tapered or crystalline optical device. The pigtail types of the signal end, common end, and pump end are all single - mode optical fibers. The power that the wavelength division multiplexer (3) can withstand is greater than 1 W.

10. A 1.6 - 2.1 μm all - band single - frequency Tm - doped germanosilicate composite fiber laser according to claim 7, characterized in that, 3+ The pump source (4) is a single - transverse - mode fiber laser with pigtail - coupled output, a semiconductor laser, or other solid - state lasers. The pump power of the pump source (4) is greater than 100 mW. The pump wavelength range of the pump source (4) is 780 - 820 nm, or 1500 - 2000 nm. ​

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