A low-temperature resistant, ultra-low-loss, large effective area optical fiber and its fabrication method

Abstract

This invention relates to a low-temperature resistant, ultra-low-loss, large effective area optical fiber and its fabrication method. The fiber comprises a core layer and a cladding layer. The core layer has a radius R1 of 5–6.5 μm and a relative refractive index difference Δn1 of 0–0.1%. The cladding layer, from the inside out, comprises a first inner cladding layer, a second inner cladding layer, and an outer cladding layer. The first inner cladding layer has a radius R2 of 9–14 μm and a relative refractive index difference Δn2 of -0.23–-0.18%. The second inner cladding layer has a radius R3 of 20–40 μm and a relative refractive index difference Δn3 of -0.32–-0.24%, with Δn2–Δn3 ≥ 0. The outer cladding layer has a radius R4 of 62.5 μm and a relative refractive index difference Δn4 of -0.18–-0.12%. The outer cladding layer is coated with a resin coating layer, which includes an inner coating layer and an outer coating layer. The inner coating layer is a low-glass transition resin coating layer, and the outer coating layer is a whisker resin coating layer. This invention achieves ultra-low loss transmission in low-temperature environments by optimizing the optical fiber structure and coating materials.

Description

Technical Field

[0001] This invention relates to a low-temperature resistant, ultra-low-loss, large effective area optical fiber and its fabrication method, belonging to the field of optical communication transmission technology. Background Technology

[0002] With the rapid development of global information and communication, deep space exploration, polar scientific research, quantum information, and superconducting power, ultra-long-distance optical transmission and extreme environment optical interconnection place dual extreme demands on the transmission performance and environmental adaptability of optical fibers. Ultra-low loss optical fiber, as the core transmission medium for long-distance, high-capacity optical communication systems, can reduce transmission loss in the 1550nm band to below 0.17 dB / km through high-purity raw materials, precise structural design, and optimized fabrication processes. This significantly extends repeaterless transmission distances and reduces system power consumption, making it a key support for backbone networks, submarine communications, and high-end sensing. Meanwhile, large-scale applications in low-temperature extreme environments (-40℃ to -70℃, and even deep cryogenic zones) continue to emerge: communication networks in polar and high-latitude regions, external optical paths for spacecraft, cryogenic interconnection for superconducting quantum computing, and fiber optic sensing and data transmission in high-altitude power grids all require optical fibers to maintain stable ultra-low loss characteristics and mechanical reliability at low temperatures. However, existing conventional ultra-low loss optical fibers generally suffer from performance degradation in low-temperature environments, making it difficult to simultaneously meet the dual requirements of low-temperature resistance and ultra-low loss.

[0003] For ultra-low attenuation effective area optical fibers used for long-distance transmission, their large mode field diameter makes them increasingly sensitive to low-temperature environments, resulting in a significant increase in low-temperature-related losses. Low temperatures cause uneven thermal shrinkage and internal stress accumulation in the quartz matrix, increasing Rayleigh scattering loss and waveguide defect loss. Simultaneously, the traditional acrylate coating hardens, becomes embrittled, and undergoes abrupt modulus changes at low temperatures, creating a mismatch with the shrinkage rate of the fiber glass layer, leading to a sharp increase in microbending loss and compromising ultra-low loss characteristics. In summary, developing an optical fiber with both excellent low-temperature resistance and stable ultra-low loss characteristics, along with a commercially viable fabrication method, for extremely cold and cryogenic applications has become a pressing technical challenge in the optical fiber field. Summary of the Invention

[0004] The following are definitions and explanations of some terms used in this invention: ppm: parts per million by weight.

[0005] Starting from the axis at the very center of the optical fiber, the layer closest to the axis is defined as the core layer, based on the change in refractive index, while the outermost layer of the optical fiber is defined as the cladding.

[0006] The relative refractive index difference Δni between the layers of an optical fiber is defined by the following equation:

[0007] Where ni is the refractive index of the fiber core, and nc is the refractive index of pure silicon dioxide.

[0008] The effective area Aeff of the optical fiber

[0009] Where E is the electric field related to propagation, and R is the distance between the axis and the point where the electric field is distributed.

[0010] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a low-temperature resistant, ultra-low loss, large effective area optical fiber and its preparation method. By optimizing the optical fiber structure and coating materials, ultra-low loss transmission in low-temperature environments can be achieved.

[0011] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows: It includes a core layer and a cladding layer, characterized in that the core layer has a radius R1 of 5–6.5 μm and a relative refractive index difference Δn1 of 0–0.1%; the cladding layer, from the inside to the outside, includes a first inner cladding layer, a second inner cladding layer, and an outer cladding layer; the first inner cladding layer has a radius R2 of 9–14 μm and a relative refractive index difference Δn2 of -0.23–-0.18%; the second inner cladding layer has a radius R3 of 20–40 μm and a relative refractive index difference Δn3 of -0.32–-0.24%, and Δn2–Δn3 ≥ 0; the outer cladding layer has a radius R4 of 62.5 μm and a relative refractive index difference Δn4 of -0.18–-0.12%; and the outer cladding layer is covered with a resin coating layer, the resin coating layer including an inner coating layer and an outer coating layer; the inner coating layer is a low glass transition resin coating layer, and the outer coating layer is a whisker resin coating layer.

[0012] According to the above scheme, the core layer is a silica glass layer co-doped with germanium and fluorine and doped with alkali metals, wherein the Ge content is 20,000~30,000 ppm, the F content is 2,000~6,000 ppm, and the average content of alkali metals is 1,500~3,000 ppm.

[0013] According to the above scheme, the whisker resin coating layer is formed by coating with whisker resin paint. The whisker resin paint is an acrylic resin mixed with whisker material. The content of the whisker material is 0.1~1wt%, the diameter is 0.1~0.3μm, and the length is 0.5~1.5μm.

[0014] According to the above scheme, the whisker material is potassium hexatitanate whisker (K2Ti6O). 13 ( ), calcium sulfate whiskers, calcium carbonate whiskers, zinc oxide whiskers, or one or more of these.

[0015] According to the above scheme, the low glass transition resin coating layer is formed by coating with a low glass transition resin coating, wherein the low glass transition resin coating is a resin coating with a low glass transition temperature (Tg) < -45℃.

[0016] According to the above scheme, the modulus of the inner coating layer is ≤0.5MPa, and the modulus of the outer coating layer is ≥1000 MPa.

[0017] According to the above scheme, the loss of the optical fiber at a wavelength of 1550nm is equal to or less than 0.155dB / km; under preferred conditions, it is equal to or less than 0.153dB / km, and under more preferred conditions, it is equal to or less than 0.148dB / km.

[0018] According to the above scheme, the effective area of ​​the optical fiber at a wavelength of 1550nm is 110~150μm. 2 .

[0019] According to the above scheme, the cable cutoff wavelength of the optical fiber is equal to or less than 1530nm.

[0020] According to the above scheme, the optical fiber operates in a temperature range of -80℃ to 80℃. Under the condition of -80℃ to 80℃, the additional attenuation value of the optical fiber at wavelengths of 1550nm, 1625nm, and 1310nm is less than 0.05dB / kmn.

[0021] According to the above scheme, the additional attenuation of the optical fiber at 1550nm under long-term low temperature of -60℃ for 30 days is ≤0.015dB / km, preferably ≤0.005dB / km.

[0022] According to the above scheme, the additional attenuation of the optical fiber at 1550nm under long-term low temperature of -80℃ for 30 days is ≤0.025dB / km, preferably ≤0.01dB / km.

[0023] The technical solution for the preparation method of the above-mentioned doped alkali metal optical fiber of the present invention is as follows: First, a core rod with an inner cladding layer is prepared: a fluorine-doped quartz tube is used, and the core layer is deposited using an in-tube deposition method. The relative refractive index difference Δn1 of the core layer is 0–0.1%. After deposition, the quartz tube is subjected to alkali metal doping of the core layer using a heating diffusion method. Then, the alkali metal-doped quartz liner is melted and condensed into a solid core rod. The average alkali metal content of the core layer is 1500–3000 ppm. Fabrication of optical fiber preforms: Using a preform containing an inner cladding as a target, an outer cladding is deposited through an OVD process to form an F-doped outer cladding. The relative refractive index difference of the outer cladding is Δn4, which is -0.18% to -0.12%. After deposition, the preform is sintered to form a complete optical fiber preform. Fiber drawing: The fiber preform is clamped into a drawing furnace and drawn to obtain a bare glass fiber. After the bare fiber is semi-cooled, inner and outer coating layers are applied successively. Both inner and outer coating layers are treated with ultraviolet light. The inner coating layer is a low glass transition resin coating layer and the outer coating layer is a whisker resin coating layer. After coating with the resin coating layer, the fiber preparation is completed.

[0024] According to the above scheme, the alkali metal doped in the core layer is diffused to the core layer by heating an alkali metal source compound, wherein the alkali metal source compound is an alkali metal halide.

[0025] According to the above scheme, the low glass transition resin coating layer is coated with a low glass transition resin coating, wherein the low glass transition resin coating is a resin coating with a low glass transition temperature (Tg) < -45℃; the whisker resin coating layer is coated with a whisker resin coating, wherein the whisker resin coating is an acrylic resin mixed with whisker material, wherein the content of the whisker material is 0.1~1wt%, the diameter is 0.1~0.3μm, and the length is 0.5~1.5μm.

[0026] According to the above scheme, the whisker material is potassium hexatitanate whisker (K2Ti6O). 13 The whisker material is one or more of calcium sulfate whiskers, calcium carbonate whiskers, and zinc oxide whiskers; the whisker material is dried at a temperature of 190~210℃ for no less than 5~6 hours, and the water content of the whisker material after treatment is ≤0.3%. The whisker material preferably has a purity of ≥99.9% and is preferably in needle-like powder form.

[0027] According to the above scheme, the whisker resin coating is degassed before use, preferably by ultrasonic vibration for 2 to 3 hours to remove air bubbles introduced during the mixing process.

[0028] According to the above scheme, the wire drawing speed is 1000~2000m / min, and the UV curing time of the inner and outer coatings is less than 2s.

[0029] The beneficial effects of this invention are as follows: 1. Using a highly germanium-doped core layer facilitates alkali metal doping, thereby reducing the virtual temperature of the core layer. A lower virtual temperature indicates a lower degree of atomic disorder, resulting in lower Rayleigh scattering and thus reduced attenuation. Simultaneously, increasing the oxygen-silicon ratio during deposition effectively reduces the Cl content in the core layer, avoiding crystallization problems caused by excessive alkali metal doping in the core rod, which affects attenuation and increases costs. 2. Doping the coating layer with whisker materials utilizes their fibrous structure to form a mechanical framework in the resin, uniformly dispersing stress. Through toughening, shrinkage suppression, and interface strengthening, it inhibits coating brittleness, shrinkage, and debonding at low temperatures, reducing microbending loss at its source without introducing additional scattering. This effectively reduces the additional attenuation of the optical fiber caused by the low-temperature environment while ensuring ultra-low attenuation. The inner coating layer is a low-glass transition resin coating layer, which further improves the low-temperature resistance of the optical fiber. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the refractive index profile of the core layer and cladding layer according to an embodiment of the present invention.

[0031] Figure 2 This is a schematic diagram showing the relationship between room temperature loss and alkali metal and core layer Ge content in an embodiment of the present invention. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0033] The device comprises a core layer and a cladding layer. The core layer has a radius R1 of 5–6.5 μm and a relative refractive index difference Δn1 of 0–0.1%. The cladding layer, from the inside out, comprises a first inner cladding layer, a second inner cladding layer, and an outer cladding layer. The first inner cladding layer has a radius R2 of 9–14 μm and a relative refractive index difference Δn2 of -0.23–-0.18%. The second inner cladding layer has a radius R3 of 20–40 μm and a relative refractive index difference Δn3 of -0.32–-0.24%, with Δn2–Δn3 ≥ 0. The outer cladding layer has a radius R4 of 62.5 μm and a relative refractive index difference Δn4 of -0.18–-0.12%. The core layer is co-doped with germanium, fluorine, and alkali metals. The core layer is doped with a high concentration of Ge via PCVD deposition, while the chlorine content remaining in the core layer is controlled by increasing the oxygen-silicon ratio, thereby increasing the doping concentration of alkali metals during subsequent melting and shrinkage. All cladding layers are fluorine-doped layers. The outer coating layer is a resin coating layer, which includes an inner coating layer and an outer coating layer. The inner coating layer is a low-glass transition resin coating layer, and the outer coating layer is a whisker resin coating layer. The whisker resin coating is an acrylic resin mixed with whisker materials. The main material of the outer coating layer is epoxy acrylate with added whisker materials, specifically potassium hexatite whiskers (K2Ti6O). 13The material comprises one or more of calcium sulfate whiskers, calcium carbonate whiskers, and zinc oxide whiskers. The whisker material is dried at 190-210°C for at least 5-6 hours, resulting in a moisture content ≤0.3%. The whisker material preferably has a purity of ≥99.9% and is preferably in needle-like powder form. The whisker resin coating is degassed before use, preferably by ultrasonic vibration for 2-3 hours to remove air bubbles introduced during mixing.

[0034] Table 1 lists the process parameters of the whisker material in the optical fiber coating layer of the present invention, and the whisker material content is A.

[0035] Table 1. Process parameters of whisker material in the optical fiber coating layer of the present invention

Claims

1. A low-temperature resistant, ultra-low-loss, large effective area optical fiber, comprising a core and a cladding, characterized in that... The core layer has a radius R1 of 5–6.5 μm and a relative refractive index difference Δn1 of 0–0.1%. The cladding layers, from the inside out, consist of a first inner cladding layer, a second inner cladding layer, and an outer cladding layer. The first inner cladding layer has a radius R2 of 9–14 μm and a relative refractive index difference Δn2 of -0.23–-0.18%. The second inner cladding layer has a radius R3 of 20–40 μm and a relative refractive index difference Δn3 of -0.32–-0.24%, and Δn2–Δn3 ≥ 0. The outer cladding layer has a radius R4 of 62.5 μm and a relative refractive index difference Δn4 of -0.18–-0.12%. The outer cladding layer is covered with a resin coating layer, which includes an inner coating layer and an outer coating layer. The inner coating layer is a low glass transition resin coating layer, and the outer coating layer is a whisker resin coating layer.

2. The low-temperature resistant, ultra-low-loss, large effective area optical fiber according to claim 1, characterized in that... The core layer is a silica glass layer co-doped with germanium and fluorine and doped with alkali metals, wherein the Ge content is 20,000~30,000 ppm, the F content is 2,000~6,000 ppm, and the average alkali metal content is 1,500~3,000 ppm.

3. The low-temperature resistant, ultra-low-loss, large effective area optical fiber according to claim 1 or 2, characterized in that... The whisker resin coating layer is formed by coating with whisker resin paint, which is an acrylic resin mixed with whisker material. The content of the whisker material is 0.1~1wt%, the diameter is 0.1~0.3μm, and the length is 0.5~1.5μm.

4. The low-temperature resistant, ultra-low-loss, large effective area optical fiber according to claim 3, characterized in that... The whisker material is one or more of potassium hexatitanate whiskers, calcium sulfate whiskers, calcium carbonate whiskers, and zinc oxide whiskers.

5. The low-temperature resistant, ultra-low-loss, large effective area optical fiber according to claim 1 or 2, characterized in that... The low glass transition resin coating layer is formed by coating with a low glass transition resin paint, wherein the low glass transition resin paint is a resin paint with a low glass transition temperature Tg < -45℃.

6. The low-temperature resistant, ultra-low-loss, large effective area optical fiber according to claim 1 or 2, characterized in that... The modulus of the inner coating layer is ≤0.5MPa, and the modulus of the outer coating layer is ≥1000 MPa.

7. The low-temperature resistant, ultra-low-loss, large effective area optical fiber according to claim 1 or 2, characterized in that... The optical fiber has a loss of 0.155 dB / km at a wavelength of 1550 nm.

8. The low-temperature resistant, ultra-low-loss, large effective area optical fiber according to claim 1 or 2, characterized in that... The optical fiber has an effective area of ​​110~150μm at a wavelength of 1550nm. 2 .

9. The low-temperature resistant, ultra-low-loss, large effective area optical fiber according to claim 1 or 2, characterized in that... The cable cutoff wavelength of the optical fiber is equal to or less than 1530nm.

10. The low-temperature resistant, ultra-low-loss, large effective area optical fiber according to claim 1 or 2, characterized in that... The optical fiber operates in a temperature range of -80℃ to 80℃. Under these conditions, the additional attenuation at wavelengths of 1550nm, 1625nm, and 1310nm is less than 0.05dB / kmn.

11. The low-temperature resistant, ultra-low-loss, large effective area optical fiber according to claim 1 or 2, characterized in that... The additional attenuation of the optical fiber at 1550nm under long-term low temperature of -60℃ for 30 days is ≤0.015dB / km.

12. The low-temperature resistant, ultra-low-loss, large effective area optical fiber according to claim 1 or 2, characterized in that... The additional attenuation of the optical fiber at 1550nm under long-term low temperature of -80℃ for 30 days is ≤0.025dB / km.

13. A method for fabricating any of the low-temperature resistant, ultra-low-loss, large effective area optical fibers according to claims 1-12, characterized in that... First, a core rod with an inner cladding layer is prepared: a fluorine-doped quartz tube is used, and the core layer is deposited using an in-tube deposition method. The relative refractive index difference Δn1 of the core layer is 0–0.1%. After deposition, the quartz tube is subjected to alkali metal doping of the core layer using a heating diffusion method. Then, the alkali metal-doped quartz liner is melted and condensed into a solid core rod. The average alkali metal content of the core layer is 1500–3000 ppm. Fabrication of optical fiber preforms: Using a preform containing an inner cladding as a target, an outer cladding is deposited through an OVD process to form an F-doped outer cladding. The relative refractive index difference of the outer cladding is Δn4, which is -0.18% to -0.12%. After deposition, the preform is sintered to form a complete optical fiber preform. Fiber drawing: The fiber preform is clamped into a drawing furnace and drawn to obtain a bare glass fiber. After the bare fiber is semi-cooled, inner and outer coating layers are applied successively. Both inner and outer coating layers are treated with ultraviolet light. The inner coating layer is a low glass transition resin coating layer and the outer coating layer is a whisker resin coating layer. After coating with the resin coating layer, the fiber preparation is completed.

14. The method for fabricating low-temperature resistant, ultra-low-loss, large effective area optical fiber according to claim 13, characterized in that... The core layer is doped with alkali metals through heating and diffusion to the core layer via an alkali metal source compound, wherein the alkali metal source compound is an alkali metal halide.

15. The method for fabricating a low-temperature resistant, ultra-low-loss, large effective area optical fiber according to claim 13 or 14, characterized in that... The low glass transition resin coating layer is formed by coating with a low glass transition resin coating material, wherein the low glass transition resin coating material is a resin coating material with a glass transition temperature Tg < -45℃; the whisker resin coating layer is formed by coating with a whisker resin coating material, wherein the whisker resin coating material is an acrylic resin mixed with whisker material, wherein the content of the whisker material is 0.1~1wt%, the diameter is 0.1~0.3μm, and the length is 0.5~1.5μm.

16. The method for fabricating low-temperature resistant, ultra-low-loss, large effective area optical fiber according to claim 15, characterized in that... The whisker material is one or more of potassium hexatitanate whiskers, calcium sulfate whiskers, calcium carbonate whiskers, and zinc oxide whiskers; the whisker material is dried at a temperature of 190~210℃ for no less than 5~6 hours, and the water content of the whisker material after treatment is ≤0.3%.

17. The method for fabricating a low-temperature resistant, ultra-low-loss, large effective area optical fiber according to claim 16, characterized in that... Before use, the whisker resin coating is degassed, preferably by ultrasonic vibration for 2-3 hours, to remove air bubbles introduced during the mixing process.

18. The method for fabricating low-temperature resistant, ultra-low-loss, large effective area optical fiber according to claim 13 or 14, characterized in that... The wire drawing speed is 1000~2000m / min, and the UV curing time of both the inner and outer coatings is less than 2s.

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