All-solid-state triple-clad zinc fluoride-based glass optical fiber and method for manufacturing the same

Abstract

The application relates to the technical field of special optical material preparation, in particular to a full-solid-state three-clad zinc fluoride-based glass optical fiber and a preparation method thereof. The optical fiber comprises, from inside to outside, an optical fiber core layer, an optical fiber inner clad layer, an optical fiber middle clad layer and an outer clad layer; the optical fiber core layer, the optical fiber inner clad layer and the optical fiber middle clad layer are all zinc fluoride-based glass and have the same component types; the refractive index of the optical fiber core layer is greater than that of the optical fiber inner clad layer; the materials of the optical fiber core layer, the optical fiber inner clad layer and the optical fiber middle clad layer all comprise the following components: ZnF2, BaF2, GaF3, SrF2, LiF, YF3, LaF3, PbF2, NaF and 0-12 mol% of rare earth fluoride; and the material of the outer clad layer is polytetrafluoroethylene. The prepared optical fiber has the advantages of high transmittance, low phonon energy, small loss, stable structure, high mechanical strength, simple preparation process, good repeatability, suitability for mass production and application in the fields of communication and the like.

Description

Technical Field

[0001] This invention relates to the field of special optical material preparation technology, and in particular to an all-solid-state triple-clad zinc fluoride-based glass optical fiber and its preparation method. Background Technology

[0002] Fiber lasers utilize rare-earth-doped optical fibers as the gain medium, allowing for active regions several kilometers long and thus providing extremely high optical gain for high-power laser output. Compared to solid-state or gas lasers of comparable power, fiber lasers offer superior beam quality, high optical-to-optical conversion efficiency, excellent heat dissipation, compact structure, and high reliability. Currently, the output wavelength of fiber lasers is continuously expanding from the near-infrared to the mid-infrared band, demonstrating their significant research importance and value, attracting widespread attention from researchers both domestically and internationally. Compared to single-clad fibers, multi-clad fibers utilize clad pumping, enabling them to withstand higher thermal loads and reduce quantum defects, thereby achieving higher-power laser output. Compared to other fluoride glasses, zinc fluoride-based glasses exhibit lower phonon energy, a wider mid-infrared transmission window, and excellent physical and chemical stability. Therefore, rare-earth ion-doped zinc fluoride-based glass fibers are currently the most promising mid-infrared optical fibers. Unlike traditional optical fiber cladding that uses low-refractive-index resin, triple-clad optical fiber structures made of all-solid-state glass are more stable, have a wider transmission window, and do not require the outer cladding to be removed during fiber cleaving.

[0003] However, existing double-clad zinc fluoride-based optical fibers mostly use low-refractive-index resin to coat single-clad fibers as the outer cladding of double-clad fibers. This results in narrow intrinsic absorption bands and transmission windows, and low transmittance in the mid-infrared band, limiting the pump wavelength. Furthermore, the resin coating needs to be removed before fiber cleaving. Meanwhile, the gain fibers currently used to generate mid-infrared lasers are mostly double-clad zirconium fluoride-based glass fibers, which have high phonon energies, making it difficult to achieve laser output at wavelengths above 3.8 μm.

[0004] All-solid-state triple-clad fiber expands the pump wavelength selection, offers greater structural stability, and retains its double-clad structure even after end-face dicing, resulting in excellent coupling. The coating requirements during fiber drawing are lower. High-efficiency lasers can still be obtained even with high background loss and short fiber lengths. Therefore, developing a zinc fluoride-based glass with excellent infrared transmission properties is of great significance for promoting the development of long-wavelength, high-power fiber lasers. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides an all-solid-state triple-clad zinc fluoride-based glass optical fiber and its preparation method.

[0006] The primary objective of this invention is to provide an all-solid-state triple-clad zinc fluoride-based glass optical fiber, comprising, from the inside out, an optical fiber core, an inner cladding, a middle cladding, and an outer cladding. The fiber core, inner cladding, and middle cladding are all zinc fluoride-based glass with the same composition; the refractive index of the fiber core is greater than that of the inner cladding. The materials of the fiber core, inner cladding, and middle cladding all contain the following molar percentage components: ZnF 241~43mol% BaF2 14~16 mol% GaF3 10~12 mol% SrF 25.5~6.5 mol% LiF 4.5~5.5 mol% YF 30.5~2.5 mol% LaF 30.5~2.5 mol% PbF20~14mol% NaF 0~14mol% Rare earth fluorides 0~12 mol% The sum of the molar percentages of all components is 100%; The outer cladding material is polytetrafluoroethylene.

[0007] Preferably, the rare earth fluoride is selected from at least one of HoF3, ErF3, PrF3, YbF3, TmF3, and DyF3.

[0008] Preferably, the contents of NaF and PbF2 satisfy the following: 11mol%≤PbF2+NaF≤14mol%.

[0009] Preferably, the fiber core, fiber inner cladding, and fiber middle cladding contain 11 mol% GaF3, 6 mol% SrF2, and 5 mol% LiF.

[0010] Preferably, the diameter of the all-solid triple-clad zinc fluoride-based glass fiber is 220~270μm.

[0011] The second objective of this invention is to provide a method for preparing an all-solid-state triple-clad zinc fluoride-based glass optical fiber, which specifically includes the following steps: S1. Weigh each raw material according to the ratio of fiber core, fiber inner cladding, and fiber middle cladding, grind and mix them, then add 18-22% of the total mass of ammonium bifluoride, heat to purify and remove impurities. S2. Add 18-22% of ammonium bifluoride to the raw materials of the inner cladding and core of the optical fiber, respectively, melt them at 800-900℃, and then pour them into a preheated mold to form a zinc fluoride-based preform. After polishing, pre-stretch it into a glass rod. S3. Melt the cladding material of the optical fiber and spin-cast it into a hollow cladding glass tube; S4. The glass rod prepared in step S2 is coaxially inserted into the middle cladding glass tube prepared in step S3, and the whole thing is placed into a polytetrafluoroethylene sleeve. After vacuuming, it is heated and drawn into an optical fiber.

[0012] Preferably, in step S1, the purity of each raw material is not less than 99.99%; 20% of the total mass of the raw materials is added as ammonium bifluoride; the heating and purification is carried out in an electric furnace at 350~450℃ for 1~3 hours.

[0013] Preferably, step S2 specifically includes the following steps: S21. The anhydrous raw materials of the fiber core and the fiber inner cladding are mixed separately to form a batch; 20% of the total mass of ammonium bifluoride is added, and then the mixed raw materials are placed in a crucible; the crucible is placed in a resistance heating furnace, and the mixed raw materials are kept at 800~900℃ for 0.5~2 hours in an argon atmosphere to obtain molten core glass and molten inner cladding glass, respectively. S22. Pour the inner cladding glass melt and the core glass melt into a mold preheated at 220~250℃ and anneal at that temperature for 2~4 hours to obtain a zinc fluoride-based preform; polish the zinc fluoride-based preform and pre-draw it into a glass rod.

[0014] Preferably, step S3 specifically includes: placing the purified optical fiber cladding material in a platinum crucible, heating it to 800~900℃ and holding it at that temperature for 0.5~2 hours to obtain molten cladding glass, pouring it into a mold preheated to 220~230℃, and rotating it at a speed of 2800~3500 rpm to form a hollow cladding glass tube.

[0015] Preferably, in step S4, a vacuum pump is used to evacuate and remove interlayer air, so that the glass rod and glass tube are tightly bonded together; after heating to 360~370℃, it is drawn into an optical fiber.

[0016] Compared with the prior art, the present invention can achieve the following beneficial effects: (1) The preparation process is highly repeatable, easy to operate, and low in cost. The fiber produced has a minimum loss of less than 0.2dB and is ready for mass production.

[0017] (2) Ammonium fluoride is used to purify the raw materials twice, effectively removing oxides and hydroxyl impurities and significantly reducing the background loss of optical fibers.

[0018] (3) The optical fiber of the present invention can be adapted to single or co-doped with various rare earth ions. The solubility of rare earth can be improved by adjusting the composition to meet the application requirements of high-power fiber laser.

[0019] (4) The prepared all-solid triple-clad zinc fluoride-based glass fiber has a stable structure and high mechanical strength, and can realize high-power and high-efficiency laser output of mid-infrared long wavelength, which has good application prospects in communication, sensing and other fields.

[0020] (5) The prepared zinc fluoride-based glass material has low phonon energy, high purity, strong resistance to deliquescence, wide infrared transmission window, high transmittance, and lower pump transmission loss. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the fabrication process of an all-solid-state triple-clad zinc fluoride-based glass optical fiber according to an embodiment of the present invention.

[0022] Figure 2 This is a physical image of a zinc fluoride-based preform provided according to an embodiment of the present invention.

[0023] Figure 3 This is a physical image of a cladding glass tube provided according to an embodiment of the present invention.

[0024] Figure 4 This is a physical image of an all-solid-state triple-clad zinc fluoride-based glass optical fiber provided according to an embodiment of the present invention.

[0025] Figure 5 This is a cross-sectional view of an all-solid-state triple-clad zinc fluoride-based glass optical fiber provided according to an embodiment of the present invention.

[0026] Figure 6 This is a Raman spectrum of a bismuth fluoride-based glass sample provided according to an embodiment of the present invention.

[0027] Figure 7 This is a transmission spectrum test diagram of bismuth fluoride-based glass optical fiber provided according to an embodiment of the present invention. Detailed Implementation

[0028] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0030] This invention provides an all-solid-state triple-clad zinc fluoride-based glass optical fiber with a diameter of 220~270μm; comprising, from the inside out, an optical fiber core, an inner cladding, a middle cladding, and an outer cladding; The fiber core, inner cladding, and middle cladding are all zinc fluoride-based glass with the same composition but different molar contents. The refractive index of the fiber core is greater than that of the inner cladding. The diameter of the fiber core is 7~20μm, and the diameter of the inner cladding is 70~100μm. The materials of the fiber core, inner cladding, and middle cladding all contain the following molar percentage components: ZnF 241~43mol% BaF2 14~16 mol% GaF3 10~12 mol% SrF 25.5~6.5 mol% LiF 4.5~5.5 mol% YF 30.5~2.5 mol% LaF 30.5~2.5 mol% PbF20~14mol% NaF 0~14mol% Rare earth fluorides 0~12 mol% The sum of the molar percentages of all components is 100%; Preferably, the composition is GaF 311 mol%, SrF 26 mol%, LiF 5 mol%; Preferably, the contents of NaF and PbF2 satisfy: 11 mol% ≤ PbF2 + NaF ≤ 14 mol% The purity of each component is 99.99% or higher to reduce the loss of the drawn optical fiber; The rare earth fluoride is selected from at least one of HoF3, ErF3, PrF3, YbF3, TmF3, and DyF3; in some embodiments, the doped rare earth fluoride is two (denoted as MF and NF). The outer cladding material is polytetrafluoroethylene (Teflon). The fiber optic loss is less than 0.2 dB.

[0031] In some embodiments, the fiber core and inner cladding materials of the all-solid-state triple-clad zinc fluoride-based glass fiber are doped with two rare-earth fluorides (including a low doping ratio of 0-4% and a high doping ratio of 5-10%), and the specific content (mol%) of each component is shown in Table 1 below: Table 1. Multi-rare earth ion co-doped composition of zinc fluoride-based glass

[0032] In some embodiments, the fiber core and inner cladding materials of the all-solid-state triple-clad zinc fluoride-based glass fiber are doped with a rare earth fluoride (denoted as MF), and the specific content (mol%) of each component is shown in Table 2 below: Table 2. Zinc fluoride-based glass rare earth ion single-doped composition table

[0033] In some embodiments, the fiber core and inner cladding materials of the all-solid-state triple-clad zinc fluoride-based glass fiber are not doped with rare earth fluorides, and the specific content (mol%) of each component is shown in Table 3 below: Table 3. Composition of Zinc Fluoride-Based Glass Without Rare Earth Ion Doping

[0034] The preparation method of the above-mentioned all-solid-state triple-clad zinc fluoride-based glass optical fiber specifically includes the following steps: S1. Preparation and purification of raw materials: Weigh each compound raw material according to the preset molar ratio of the fiber core, fiber inner cladding and fiber middle cladding, grind and mix them evenly, then add 18~22% of the total mass of ammonium hydrogen fluoride, and heat in an electric furnace at 350~450℃ for 1~3 hours to remove impurities. Specifically, the raw materials are first weighed in a glove box with low water and low oxygen content, and then ground thoroughly in an agate mortar. Ammonium bifluoride of 20% of the total mass of the raw materials is added, and the mixture is heated in an electric furnace at 400°C for 2 hours to remove impurities such as oxides from the raw materials, improve the glass quality, and thus reduce the background loss of the optical fiber.

[0035] S2. Preform preparation and glass rod pre-drawing, specifically including: S21. The anhydrous components of the fiber core and the fiber cladding are mixed separately to form one batch each; 18-22% of the total mass of ammonium bifluoride is added (for example, if the total mass of the raw materials is 15 grams, then 3 grams of ammonium bifluoride is added), and then the mixed raw materials are placed in a crucible; the mixed raw materials are kept at 800-900°C under an argon atmosphere for 0.5-2 hours to obtain molten core glass and molten cladding glass, respectively. Specifically, add ammonium bifluoride at 20% of the total mass of the raw materials; place the crucible in a resistance heating furnace and keep the mixed raw materials at 850°C for 1 hour in an argon atmosphere; S22. The inner cladding glass melt and the core glass melt are poured sequentially into a mold preheated to 220~250℃ and annealed at that temperature for 2~4 hours to remove residual stress. This process is carried out in a glove box filled with dry nitrogen to reduce the influence of hydroxyl groups, resulting in a zinc fluoride-based preform. Figure 2The obtained zinc fluoride-based preforms with a diameter of 10-12 mm are polished and drawn into glass rods with a diameter of 3-5 mm. Specifically, the mold is preheated to 240℃; In some embodiments, after polishing the zinc fluoride-based preform, it is installed on an optical fiber drawing tower and drawn into a thin glass rod with a diameter of 3-3.5 mm and a length of 12 cm.

[0036] A 10cm cylindrical rod was cut from the aforementioned thin glass rod, and both ends were polished. The transmission spectrum of the glass was then measured. It was found that the glass exhibited good transmission performance in the 10μm range. Raman spectroscopy measurements were performed on some glass samples; all measured peaks appeared at approximately 500cm⁻¹. -1 The location indicates that the resulting glass has a relatively small phonon energy ( Figure 6 ).

[0037] S3. Preparation of the middle cladding glass tube: The purified optical fiber middle cladding material is placed in a platinum crucible and heated to 800~900℃ and held for 0.5~2 hours to obtain molten middle cladding glass. The molten glass is poured into a mold preheated to 220~230℃. By controlling the pouring temperature and pouring speed, the amount of air bubbles in the middle cladding glass tube can be significantly reduced, the optical fiber loss can be reduced, and the mechanical strength of the optical fiber can be improved. The tube is formed by rotating at a speed of 2800~3500 rpm to obtain a hollow middle cladding glass tube. The glass tube is annealed in a nitrogen atmosphere for no less than 3 hours to eliminate stress, resulting in a middle cladding glass tube with an inner diameter (diameter of the internal hollow region) of 3~5 mm and an outer diameter of 10~12 mm. Specifically, it is kept at 850℃ for 2 hours until completely melted; then poured into a brass mold preheated to 225℃ and shaped by rotating at 3000 rpm. See Figure 3 In some embodiments, the diameter of the hollow region inside the prepared middle-clad glass tube is about 3.5 mm, the outer diameter of the glass tube is 12 mm, and the length is 12 cm.

[0038] S4. Fiber Assembly and Drawing: After polishing, the glass rod obtained in S2 is coaxially inserted into the interclad glass tube obtained in S3, and then the entire assembly is placed inside a low-refractive-index polytetrafluoroethylene (PTFE) sleeve. The interlayer air of the assembled structure is expelled, and the fiber is heated to a softening temperature of 360~370℃. The drawing parameters (rod feed speed: 1.5 mm / min, traction speed: 3 m / min) are controlled to draw the fiber, resulting in a solid-state triple-clad zinc fluoride-based glass fiber with an outer diameter of 220~270 μm (e.g., ...). Figures 4-5 (as shown) Specifically, the assembly structure is placed in the fiber drawing tower, and a vacuum pump is used to evacuate and remove interlayer air, so that the glass rod and glass tube are tightly bonded; after heating to a softening temperature of 365°C, it is drawn.

[0039] The optical fiber drawing process uses the rod-tube method; see the flowchart below. Figure 1 The drawing equipment includes a feeding mechanism, heating device, air intake and exhaust device, diameter measuring system, coating and curing system, tension meter, traction system and winding system, all of which are controlled by a central computer system.

[0040] The all-solid-state triple-clad zinc fluoride-based glass fiber prepared above can be applied in high-power fiber lasers, effectively reducing the thermal load generated during fiber absorption of pump light and laser oscillation.

[0041] The key technical points and advantages of this invention are: the prepared zinc fluoride-based glass optical fiber has a transmission window as wide as 7 micrometers and a transmittance of over 90% (see...). Figure 7 This technology helps reduce transmission loss at specific pump wavelengths; it features low glass phonon energy, excellent physicochemical stability and deliquescence resistance; it employs a rare-earth doping system with high rare-earth ion solubility, allowing for doping amounts up to 12 mol%, suitable for single or co-doping with various rare-earth ions; it utilizes an all-solid-state glass structure with a low-refractive-index cladding, resulting in structural stability and high mechanical strength. After fiber end-face cutting, the cladding structure remains intact without stripping, leading to higher pump coupling efficiency; the fabrication process is highly repeatable, simple to operate, and low-cost, producing fibers with low background loss (minimum loss less than 0.2 dB), enabling mass production of low-loss fibers. These fibers can be used in mid-infrared high-power fiber lasers and have promising applications in communication, sensing, and other fields.

[0042] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0043] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A fully solid-state triple-clad zinc fluoride-based glass optical fiber, characterized in that: It includes, from the inside out, the fiber core, the inner cladding, the middle cladding, and the outer cladding; The fiber core, inner cladding, and middle cladding are all zinc fluoride-based glass with the same composition; the refractive index of the fiber core is greater than that of the inner cladding. The materials of the fiber core, inner cladding, and middle cladding all contain the following molar percentage components: ZnF 241~43mol% BaF2 14~16 mol% GaF3 10~12 mol% SrF 25.5~6.5 mol% LiF 4.5~5.5 mol% YF 30.5~2.5 mol% LaF 30.5~2.5 mol% PbF20~14mol% NaF 0~14mol% Rare earth fluorides 0~12 mol% The sum of the molar percentages of all components is 100%; The outer cladding material is polytetrafluoroethylene.

2. The all-solid-state triple-clad zinc fluoride-based glass optical fiber according to claim 1, characterized in that: The rare earth fluoride is selected from at least one of HoF3, ErF3, PrF3, YbF3, TmF3, and DyF3.

3. The all-solid-state triple-clad zinc fluoride-based glass optical fiber according to claim 1, characterized in that: The contents of NaF and PbF2 satisfy the following condition: 11 mol% ≤ PbF2 + NaF ≤ 14 mol.

4. The all-solid-state triple-clad zinc fluoride-based glass optical fiber according to claim 1, characterized in that: In the fiber core, fiber inner cladding, and fiber middle cladding, GaF3 is 11 mol%, SrF2 is 6 mol%, and LiF is 5 mol%.

5. The all-solid-state triple-clad zinc fluoride-based glass optical fiber according to claim 1, characterized in that: The diameter of the all-solid-state triple-clad zinc fluoride-based glass optical fiber is 220~270μm.

6. A method for preparing an all-solid-state triple-clad zinc fluoride-based glass optical fiber, used to prepare the all-solid-state triple-clad zinc fluoride-based glass optical fiber as described in claim 1, characterized in that: Specifically, the steps include the following: S1. Weigh each raw material according to the ratio of fiber core, fiber inner cladding, and fiber middle cladding, grind and mix them, then add 18-22% of the total mass of ammonium bifluoride, heat to purify and remove impurities. S2. Add 18-22% of ammonium bifluoride to the raw materials of the inner cladding and core of the optical fiber, respectively, melt them at 800-900℃, and then pour them into a preheated mold to form a zinc fluoride-based preform. After polishing, pre-stretch it into a glass rod. S3. Melt the cladding material of the optical fiber and spin-cast it into a hollow cladding glass tube; S4. The glass rod prepared in step S2 is coaxially inserted into the middle cladding glass tube prepared in step S3, and the whole thing is placed into a polytetrafluoroethylene sleeve. After vacuuming, it is heated and drawn into an optical fiber.

7. The method for preparing an all-solid-state triple-clad zinc fluoride-based glass optical fiber according to claim 6, characterized in that: In step S1, the purity of each raw material is not less than 99.99%; 20% of the total mass of the raw materials is added as ammonium bifluoride; the heating and purification is carried out in an electric furnace at 350~450℃ for 1~3 hours.

8. The method for preparing an all-solid-state triple-clad zinc fluoride-based glass optical fiber according to claim 6, characterized in that: Step S2 specifically includes the following steps: S21. The anhydrous raw materials of the fiber core and the fiber inner cladding are mixed separately to form a batch; 20% of the total mass of ammonium bifluoride is added, and then the mixed raw materials are placed in a crucible; the crucible is placed in a resistance heating furnace, and the mixed raw materials are kept at 800~900℃ for 0.5~2 hours in an argon atmosphere to obtain molten core glass and molten inner cladding glass, respectively. S22. Pour the inner cladding glass melt and the core glass melt into a mold preheated at 220~250℃ and anneal at that temperature for 2~4 hours to obtain a zinc fluoride-based preform; polish the zinc fluoride-based preform and pre-draw it into a glass rod.

9. The method for preparing an all-solid-state triple-clad zinc fluoride-based glass optical fiber according to claim 6, characterized in that: Step S3 specifically includes: placing the purified optical fiber cladding material in a platinum crucible, heating it to 800~900℃ and holding it at that temperature for 0.5~2 hours to obtain molten cladding glass, pouring it into a mold preheated to 220~230℃, and rotating it at a speed of 2800~3500 rpm to form a hollow cladding glass tube.

10. The method for preparing an all-solid-state triple-clad zinc fluoride-based glass optical fiber according to claim 6, characterized in that: In step S4, a vacuum pump is used to evacuate and remove interlayer air, so that the glass rod and glass tube are tightly bonded together; after heating to 360~370℃, it is drawn into an optical fiber.

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