Multi-refractive-index nested hollow-core anti-resonance optical fiber and preparation method thereof

Abstract

The invention discloses a multi-refractive-index nested hollow-core anti-resonance optical fiber and a preparation method thereof, and relates to the technical field of optical communication. The hollow-core anti-resonance optical fiber sequentially comprises an air core, a plurality of first-stage cladding tubes, a plurality of second-stage cladding tubes, a plurality of third-stage cladding tubes and a peripheral cladding tube from inside to outside. Wherein the first-stage cladding tube and the peripheral cladding tube are fixed in an internally tangent manner, the second-stage cladding tube and the first-stage cladding tube are fixed in an internally tangent manner, and the third-stage cladding tube and the second-stage cladding tube are fixed in an internally tangent manner. The design of the optical fiber breaks through the limitation of a traditional uniform-refractive-index hollow-core anti-resonance optical fiber, the cladding tube is composed of a high-refractive-index material and a low-refractive-index material, and effective regulation and control of light wave transmission are achieved. According to the hollow-core optical fiber, the ultra-low loss level can be maintained even under the bending condition while the ultra-low loss is maintained, the preparation process is simple and convenient, reduction of the production cost and improvement of the production efficiency are facilitated, and the hollow-core optical fiber has good industrial application prospects.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a multi-refractive index nested hollow core anti-resonant optical fiber and a preparation method thereof. Background Art

[0002] The rapid growth of the Internet has caused people to worry about the "capacity crisis" of data transmission. When facing massive data transmission, the performance of traditional solid-core optical fiber is limited due to problems such as dispersion effect and Kerr nonlinearity. This has prompted people to explore more advanced optical fiber technology to meet the growing demand for data transmission.

[0003] In recent years, the advent of hollow-core antiresonant fibers has attracted widespread attention in the field of optical fiber technology. Hollow-core antiresonant fibers effectively control light leakage by providing additional design freedom, such as the adjustment of the core and cladding tube shapes. At the same time, its broadband light transmission characteristics make hollow-core antiresonant fibers a hot topic in the current research field.

[0004] Chinese patent CN110208901A discloses a hollow core anti-resonant optical fiber, which includes a core, an inner cladding tube and an outer cladding tube. The core is filled with low-refractive-index air, and the inner cladding tube adopts a structure of alternating high- and low-refractive-index light-guiding materials. This patent only uses a single-layer cladding tube, and the gap between the cladding tubes is too large, the transmission loss is too large, and the transmission effect is poor.

[0005] Chinese patent CN116840966A provides an elliptical core hollow core anti-resonant optical fiber, which realizes low-loss light guidance in the 1.3-1.8μm band by designing a mixed structure of circular arc cladding tube and rectangular cladding tube in the optical fiber cladding. The patent cladding tube structure design is complex, the manufacturing process is difficult, the practicality is not strong, and the reliability is poor.

[0006] US Patent US2019026844W proposes a single-layer solid arched hollow-core anti-resonant fiber designed and manufactured from infrared soft glass, allowing energy to be transmitted in the infrared band. By controlling the thickness and spacing of the arched cladding tube, the loss is controlled to less than 1dB / m to the maximum extent. The patent has only one resonant layer, which is much different from the nested hollow-core anti-resonant fiber in terms of loss.

[0007] In summary, traditional solid core optical fibers cannot solve the scientific problems of nonlinearity and thermal damage well, while hollow core photonic crystal fibers are limited by high scattering loss and narrow bandwidth. Therefore, hollow core antiresonant optical fibers have become a major research hotspot. However, some patents for hollow core antiresonant optical fibers only use a single-layer cladding tube, which has poor loss effect; the cladding tube structure design is complex, the practicality is not high, and the reliability is poor. In order to solve the above problems, the present invention proposes a multi-refractive index nested hollow core antiresonant optical fiber and a preparation method thereof. Summary of the invention

[0008] The purpose of the present invention is to provide a multi-refractive index nested hollow core antiresonant optical fiber and a preparation method thereof to solve the problems raised in the background technology:

[0009] Traditional solid-core optical fibers cannot solve the scientific problems of nonlinearity and thermal damage well, while hollow-core photonic crystal fibers are limited by high scattering losses and narrow bandwidth. Some patents for hollow-core antiresonant optical fibers only use a single-layer cladding tube, which has poor loss effect; the cladding tube structure design is complex, not practical, and has poor reliability.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] A multi-refractive index nested hollow core anti-resonant optical fiber comprises, from the inside to the outside, an air core, a plurality of first-stage cladding tubes, a plurality of second-stage cladding tubes, a plurality of third-stage cladding tubes and a peripheral cladding tube; wherein the first-stage cladding tube is fixedly inscribed with the peripheral cladding tube, the second-stage cladding tube is fixedly inscribed with the first-stage cladding tube, the third-stage cladding tube is fixedly inscribed with the second-stage cladding tube, and the material of each cladding tube is quartz glass / multi-component glass / polymer.

[0012] Preferably, the first-stage cladding tube, the second-stage cladding tube and the third-stage cladding tube are all in a negative curvature shape, and there are no contact nodes between the first-stage cladding tubes.

[0013] Preferably, each of the second-level cladding tubes comprises two third-level cladding tubes, the two third-level cladding tubes are centrally symmetrically distributed in the second-level cladding tube, and the centers of the two third-level cladding tubes and the center of the second-level cladding tube are both kept in a straight line.

[0014] Preferably, the radius range of the air core is 9.25-22.75 μm, the radius range of the first-level cladding tube is 12.26-30.15 μm, the radius range of the second-level cladding tube is 9.81-24.12 μm, and the radius range of the third-level cladding tube is 5.21-12.81 μm, wherein the radius of the first-level cladding tube is greater than the radius of the second-level cladding tube, and the radius of the second-level cladding tube is greater than the radius of the third-level cladding tube.

[0015] Preferably, the first-stage cladding tube, the second-stage cladding tube and the third-stage cladding tube are designed to be an inner layer and an outer layer, the thickness of the inner layer is in the range of 0.21 to 0.34 μm, and the thickness of the outer layer is in the range of 0.22 to 0.35 μm.

[0016] Preferably, the outer layer is a high refractive index layer, and its high refractive index ranges from 1.4399 to 1.4580, and the inner layer is a low refractive index layer, and its low refractive index ranges from 1.4256 to 1.4398.

[0017] Preferably, the anti-resonance wavelength range of the hollow-core anti-resonance optical fiber is 1200-1600 nm, and the anti-resonance wavelength range is adjusted according to the thickness of the cladding tube.

[0018] A method for preparing a multi-refractive index nested hollow core antiresonant optical fiber, the method adopting a stacking drawing method, comprising the following steps:

[0019] S1: Select the sleeve and cladding tube with customized optical fiber ratio and arrange them into a preform, and then use a special mold to position the cladding tube to form a preform;

[0020] S2: Control the temperature range of the wire drawing furnace to 2000-2250°C, the feed rate range to 3.50-4.50 mm / min, finely draw the preform to form an intermediate, control the casing pressure range to 10-50 Pa, and the pressure range in the cladding tube to 2900-3100 Pa;

[0021] S3: The intermediate formed in S2 is subjected to secondary drawing, the temperature range of the drawing furnace is controlled to be 2000-2050°C, the feed speed range is 2.50-3.50 mm / min, the intermediate is finely drawn to form an optical fiber, the pressure range of the sleeve is controlled to be 15500-16500 Pa, and the pressure range in the cladding tube is 32000-33000 Pa.

[0022] Compared with the prior art, the present invention provides a multi-refractive index nested hollow core antiresonant optical fiber and a preparation method thereof, which has the following beneficial effects:

[0023] The present invention comprises an air core, a first-level cladding tube, a second-level cladding tube, a third-level cladding tube and a peripheral cladding tube to form a hollow core antiresonant optical fiber. The three-level cladding tubes are nested and each level of cladding tube adopts a multi-refractive index structure distribution to reduce transmission loss, improve material damage threshold, and increase application reliability. It not only achieves the goal of binding light of a specific wavelength in the air core for transmission, improves nonlinear damage, reduces transmission loss, but also solves the problems of high scattering loss and narrow bandwidth. The shape of the cladding tubes is circular, without a complex composite structure, strong in practicality, and suitable for mass production. The present invention is suitable for low-loss transmission and has good anti-bending properties, and has broad application prospects in long-distance energy transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the cross-sectional structure of the multi-refractive index nested hollow-core antiresonant optical fiber mentioned in Examples 1-3 of the present invention;

[0025] Figure 2 Schematic diagram of the cross-sectional structure of the nested cladding tube with multiple refractive index distributions mentioned in Examples 1-3 of the present invention;

[0026] Figure 3 A schematic diagram of a curve showing a change in limiting loss versus wavelength of a multi-refractive index nested hollow-core antiresonant optical fiber mentioned in an embodiment of the present invention;

[0027] Figure 4 It is a schematic diagram of a curve showing the variation of the bending loss of the multi-refractive index nested hollow-core antiresonant optical fiber with the bending radius mentioned in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0029] The present invention comprises an air core, a first-level cladding tube, a second-level cladding tube, a third-level cladding tube and an outer cladding tube to form a hollow core antiresonant optical fiber. The three-level cladding tubes are nested and each level of cladding tube adopts a multi-refractive index structure distribution to reduce transmission loss, improve material damage threshold, and increase application reliability. It not only achieves the goal of confining light of a specific wavelength in the air core for transmission, improves nonlinear damage, reduces transmission loss, but also solves the problems of high scattering loss and narrow bandwidth. The shape of the cladding tubes is circular, without complex composite structures, strong in practicality, and suitable for mass production. The present invention is suitable for low-loss transmission and has good anti-bending properties, and has broad application prospects in long-distance energy transmission. Specifically, it includes the following contents.

[0030] See also Figure 1-4 The present invention discloses a multi-refractive index nested hollow core antiresonant optical fiber, which comprises, from the inside to the outside, an air core, a first-level cladding tube, a second-level cladding tube, a third-level cladding tube and a peripheral cladding tube; the first-level cladding tube is fixedly inscribed with the peripheral cladding tube, the second-level cladding tube is fixedly inscribed with the first-level cladding tube, and the third-level cladding tube is fixedly inscribed with the second-level cladding tube. The material of each cladding tube can be quartz glass, multi-component glass, or polymer.

[0031] The first-level cladding tube, the second-level cladding tube and the third-level cladding tube are all of negative curvature shape, and there are no contact nodes between the first-level cladding tubes. Each second-level cladding tube contains two third-level cladding tubes, and the two third-level cladding tubes are centrally symmetrically distributed in the second-level cladding tube, and the centers of the two third-level cladding tubes and the second-level cladding tube are kept in a straight line. The radius R_core of the air core ranges from 9.25 to 22.75μm, the radius r1 of the first-level cladding tube ranges from 12.26 to 30.15μm, the radius r2 of the second-level cladding tube ranges from 9.81 to 24.12μm, and the radius r3 of the third-level cladding tube ranges from 5.21 to 12.81μm, wherein the radius of the first-level cladding tube is greater than the radius of the second-level cladding tube, and the radius of the second-level cladding tube is greater than the radius of the third-level cladding tube. The first-stage cladding tube, the second-stage cladding tube and the third-stage cladding tube are divided into two layers, the outer layer thickness t1 ranges from 0.22 to 0.35μm, and the inner layer thickness t2 ranges from 0.21 to 0.34μm. Of course, the cladding tube can also be three-layer or four-layer, and the thickness can be the same or different. The outer layer is a high refractive index layer, and the outer layer high refractive index n1 ranges from 1.4399 to 1.4580, and the inner layer is a low refractive index layer, and the inner layer low refractive index n2 ranges from 1.4256 to 1.4398. The anti-resonance wavelength range is 1200-1600nm, and the loss is limited to less than 0.02dB / km in this anti-resonance region. For details, please refer to Figure 3 In the anti-resonant wavelength range of 1200-1600nm, the limiting loss is less than 0.02dB / km, i.e. 2.00×10 -5 dB / m. When the wavelength is 1.55μm, the bending loss is less than 0.05dB / km when the bending radius is greater than 3cm. Figure 4 When the bending radius is greater than 3 cm, the bending loss is less than 0.05 dB / km, i.e. 5.00 × 10 -5 dB / m.

[0032] The optical fiber preparation method adopts a stacking drawing method. In the first step, a sleeve and a cladding tube with a customized optical fiber ratio are selected and arranged to form a preform rod, and then the cladding tube is positioned using a special mold to form a preform rod. In the second step, the temperature range of the drawing furnace is controlled to be 2000-2250°C, the feed speed range is 3.50-4.50mm / min, the preform rod is finely drawn to form an intermediate, the sleeve pressure range is controlled to be 10-50Pa, and the pressure range in the cladding tube is 2900-3100Pa. In the third step, the intermediate is drawn again, the temperature range of the drawing furnace is controlled to be 2000-2050°C, the feed speed range is 2.50-3.50mm / min, the intermediate is finely drawn to form an optical fiber, the sleeve pressure range is controlled to be 15500-16500Pa, and the pressure range in the cladding tube is 32000-33000Pa.

[0033] A multi-refractive index nested hollow core antiresonant optical fiber and a preparation method thereof may be specifically referred to Examples 1-3.

[0034] Embodiment 1:

[0035] See also Figure 1-2 The present invention discloses a multi-refractive index nested hollow core antiresonant optical fiber, which comprises, from the inside to the outside, an air core, a first-level cladding tube, a second-level cladding tube, a third-level cladding tube and a peripheral cladding tube; the first-level cladding tube is internally fixed to the peripheral cladding tube, the second-level cladding tube is internally fixed to the first-level cladding tube, and the third-level cladding tube is internally fixed to the second-level cladding tube.

[0036] The first-level cladding tube, the second-level cladding tube and the third-level cladding tube are all of negative curvature shape, and there are no contact nodes between the first-level cladding tubes. Each second-level cladding tube contains two third-level cladding tubes, and the two third-level cladding tubes are centrally symmetrically distributed in the second-level cladding tube, and the centers of the two third-level cladding tubes and the second-level cladding tube are kept in a straight line. The radius R_core of the air core is 9.25μm, the radius r1 of the first-level cladding tube is 12.26μm, the radius r2 of the second-level cladding tube is 9.81μm, and the radius r3 of the third-level cladding tube is 5.21μm. The first-level cladding tube, the second-level cladding tube and the third-level cladding tube are divided into two layers, the outer layer thickness t1 is 0.22μm, and the inner layer thickness t2 is 0.34μm. The outer layer is a high refractive index layer, and the outer layer high refractive index n1 is 1.4580. The inner layer is a low refractive index layer, and the inner layer low refractive index n2 is 1.4398. The anti-resonance wavelength range is 1200-1600nm, and the limiting loss in this anti-resonance region is less than 0.02dB / km. When the wavelength is 1.55μm, the bending loss is less than 0.05dB / km when the bending radius is greater than 3cm.

[0037] The optical fiber preparation method adopts a stacking drawing method, which is as follows:

[0038] S1: Select a sleeve and cladding tube with a customized optical fiber ratio and arrange them into a preform rod, and then use a special mold to position the cladding tube to form a preform rod.

[0039] S2: The temperature of the wire drawing furnace is controlled to be 2000°C, the feed speed is 3.50 mm / min, the preform is finely drawn to form an intermediate, the casing pressure is controlled to be 10 Pa, and the pressure in the cladding tube is controlled to be 2900 Pa.

[0040] S3: The intermediate is then subjected to secondary drawing, the drawing furnace temperature is controlled at 2000°C, the feed rate is controlled at 2.50 mm / min, the intermediate is finely drawn to form an optical fiber, the casing pressure is controlled at 15500 Pa, and the pressure in the cladding tube is controlled at 32000 Pa.

[0041] Embodiment 2:

[0042] See also Figure 1-2 The present invention discloses a multi-refractive index nested hollow core antiresonant optical fiber, which comprises, from the inside to the outside, an air core, a first-level cladding tube, a second-level cladding tube, a third-level cladding tube and a peripheral cladding tube; the first-level cladding tube is internally fixed to the peripheral cladding tube, the second-level cladding tube is internally fixed to the first-level cladding tube, and the third-level cladding tube is internally fixed to the second-level cladding tube.

[0043] The first-level cladding tube, the second-level cladding tube and the third-level cladding tube are all of negative curvature shape, and there are no contact nodes between the first-level cladding tubes. Each second-level cladding tube contains two third-level cladding tubes, and the two third-level cladding tubes are centrally symmetrically distributed in the second-level cladding tube, and the centers of the two third-level cladding tubes and the second-level cladding tube are kept in a straight line. The radius R_core of the air core is 22.75μm, the radius r1 of the first-level cladding tube is 30.15μm, the radius r2 of the second-level cladding tube is 24.12μm, and the radius r3 of the third-level cladding tube is 12.81μm. The first-level cladding tube, the second-level cladding tube and the third-level cladding tube are divided into two layers, the outer layer thickness t1 is 0.35μm, and the inner layer thickness t2 is 0.21μm. The outer layer is a high refractive index layer, and the outer layer high refractive index n1 is 1.4399. The inner layer is a low refractive index layer, and the inner layer low refractive index n2 is 1.4256. The anti-resonance wavelength is 1200-1600nm, and the limiting loss in this anti-resonance region is less than 0.02dB / km. When the wavelength is 1.55μm, the bending loss is less than 0.04dB / km when the bending radius is greater than 3cm.

[0044] The optical fiber preparation method adopts a stacking drawing method, which is as follows:

[0045] S1: Select a sleeve and cladding tube with a customized optical fiber ratio and arrange them into a preform rod, and then use a special mold to position the cladding tube to form a preform rod.

[0046] S2: The temperature of the wire drawing furnace is controlled to be 2250°C, the feed rate is 4.50 mm / min, the preform is finely drawn to form an intermediate, the casing pressure is controlled to be 50 Pa, and the pressure in the cladding tube is controlled to be 3100 Pa.

[0047] S3: The intermediate is then drawn for a second time, the temperature of the drawing furnace is controlled to be 2050°C, the feed rate is 3.50 mm / min, the intermediate is finely drawn to form an optical fiber, the casing pressure is controlled to be 16500 Pa, and the pressure in the cladding tube is controlled to be 33000 Pa.

[0048] Embodiment 3:

[0049] See also Figure 1-2 The present invention discloses a multi-refractive index nested hollow core antiresonant optical fiber, which comprises, from the inside to the outside, an air core, a first-level cladding tube, a second-level cladding tube, a third-level cladding tube and a peripheral cladding tube; the first-level cladding tube is internally fixed to the peripheral cladding tube, the second-level cladding tube is internally fixed to the first-level cladding tube, and the third-level cladding tube is internally fixed to the second-level cladding tube.

[0050] The first-level cladding tube, the second-level cladding tube and the third-level cladding tube are all of negative curvature shape, and there are no contact nodes between the first-level cladding tubes. Each second-level cladding tube contains two third-level cladding tubes, and the two third-level cladding tubes are centrally symmetrically distributed in the second-level cladding tube, and the centers of the two third-level cladding tubes and the second-level cladding tube are kept in a straight line. The radius R_core of the air core is 15.00μm, the radius r1 of the first-level cladding tube is 16.38μm, the radius r2 of the second-level cladding tube is 13.11μm, and the radius r3 of the third-level cladding tube is 5.57μm. The first-level cladding tube, the second-level cladding tube and the third-level cladding tube are divided into two layers, the outer layer thickness t1 is 0.25μm, and the inner layer thickness t2 is 0.25μm. The outer layer is a high refractive index layer, and the outer layer high refractive index n1 is 1.4440. The inner layer is a low refractive index layer, and the inner layer low refractive index n2 is 1.4256. The anti-resonance wavelength range is 1200-1600nm, and the limiting loss in this anti-resonance region is less than 0.02dB / km. The wavelength is 1.55μm, and when the bending radius is greater than 3cm, the bending loss is less than 0.05dB / km.

[0051] The optical fiber preparation method adopts a stacking drawing method, which is as follows:

[0052] S1: Select a sleeve and cladding tube with a customized optical fiber ratio and arrange them into a preform rod, and then use a special mold to position the cladding tube to form a preform rod.

[0053] S2: The temperature of the wire drawing furnace is controlled to be 2150°C, the feed rate is 3.80 mm / min, the preform is finely drawn to form an intermediate, the casing pressure is controlled to be 25 Pa, and the pressure in the cladding tube is controlled to be 3150 Pa.

[0054] S3: The intermediate is then drawn for a second time, the temperature of the drawing furnace is controlled to be 2025°C, the feed rate is 2.80 mm / min, the intermediate is finely drawn to form an optical fiber, the casing pressure is controlled to be 16200 Pa, and the pressure in the cladding tube is controlled to be 32500 Pa.

[0055] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A multi-refractive index nested hollow core antiresonant optical fiber, characterized in that: The invention comprises, from the inside to the outside, an air core, a plurality of first-stage cladding tubes, a plurality of second-stage cladding tubes, a plurality of third-stage cladding tubes and a peripheral cladding tube; wherein the first-stage cladding tube is fixedly inscribed with the peripheral cladding tube, the second-stage cladding tube is fixedly inscribed with the first-stage cladding tube, the third-stage cladding tube is fixedly inscribed with the second-stage cladding tube, and the material of each cladding tube is quartz glass / multi-component glass / polymer.

2. The multi-refractive index nested hollow core antiresonant optical fiber according to claim 1, characterized in that: The first-level cladding tube, the second-level cladding tube and the third-level cladding tube are all in a negative curvature shape, and there are no contact nodes between the first-level cladding tubes.

3. The multi-refractive index nested hollow core antiresonant optical fiber according to claim 1, characterized in that: Each of the second-level cladding tubes includes two third-level cladding tubes, the two third-level cladding tubes are centrally symmetrically distributed in the second-level cladding tube, and the centers of the two third-level cladding tubes and the center of the second-level cladding tube are kept in a straight line.

4. The multi-refractive index nested hollow core antiresonant optical fiber according to claim 1, characterized in that: The radius range of the air core is 9.25-22.75 μm, the radius range of the first-level cladding tube is 12.26-30.15 μm, the radius range of the second-level cladding tube is 9.81-24.12 μm, and the radius range of the third-level cladding tube is 5.21-12.81 μm, wherein the radius of the first-level cladding tube is greater than the radius of the second-level cladding tube, and the radius of the second-level cladding tube is greater than the radius of the third-level cladding tube.

5. The multi-refractive index nested hollow core antiresonant optical fiber according to claim 1, characterized in that: The first-stage cladding tube, the second-stage cladding tube and the third-stage cladding tube are designed to be an inner layer and an outer layer. The thickness of the inner layer ranges from 0.21 to 0.34 μm, and the thickness of the outer layer ranges from 0.22 to 0.35 μm.

6. The multi-refractive index nested hollow core antiresonant optical fiber according to claim 5, characterized in that: The outer layer is a high refractive index layer, and the high refractive index thereof is in the range of 1.4399 to 1.4580. The inner layer is a low refractive index layer, and the low refractive index thereof is in the range of 1.4256 to 1.4398.

7. The multi-refractive index nested hollow core antiresonant optical fiber according to claim 1, characterized in that: The anti-resonance wavelength range of the hollow core anti-resonance optical fiber is 1200-1600 nm, and the anti-resonance wavelength range is adjusted according to the thickness of the cladding tube.

8. A method for preparing a multi-refractive index nested hollow core antiresonant optical fiber according to any one of claims 1 to 7, characterized in that: The preparation method adopts a stacking drawing method, comprising the following steps: S1: Select the sleeve and cladding tube with customized optical fiber ratio and arrange them into a preform, and then use a special mold to position the cladding tube to form a preform; S2: Control the temperature range of the wire drawing furnace to 2000-2250°C, the feed rate range to 3.50-4.50 mm / min, finely draw the preform to form an intermediate, control the casing pressure range to 10-50 Pa, and the pressure range in the cladding tube to 2900-3100 Pa; S3: The intermediate formed in S2 is subjected to secondary drawing, the temperature range of the drawing furnace is controlled to be 2000-2050°C, the feed speed range is 2.50-3.50 mm / min, the intermediate is finely drawn to form an optical fiber, the pressure range of the sleeve is controlled to be 15500-16500 Pa, and the pressure range in the cladding tube is 32000-33000 Pa.

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