Method for reducing end surface temperature in wire drawing process of hollow-core optical fiber preform

Abstract

The invention designs a method for reducing the temperature of an end surface in a wire drawing process of a hollow-core optical fiber preform. According to the method, high-reflectivity optical films are plated on the end face, the inner wall and the outer wall of an outer sleeve and the outer wall of a capillary tube on the outermost layer to realize photo-thermal blocking, so that the temperature of the end face of the hollow-core optical fiber preform in the wire drawing process is greatly reduced, and the hollow-core optical fiber preform is kept in a low-temperature state of 30 DEG C or below. Under the temperature condition, the sealant for sealing can keep the optimal performance, and degradation or failure of the sealant caused by high temperature is avoided. In addition, the method also supports that an air control device is directly arranged at the tail end of the preform, so that the complex process of opening a hole in the side wall is omitted, and the preparation efficiency of the hollow-core optical fiber can be greatly improved.

Description

Technical Field

[0001] This invention relates to the field of hollow optical fiber fabrication technology, and specifically to a method for reducing the end-face temperature during the drawing process of hollow optical fiber preforms. Background Technology

[0002] Hollow-core optical fiber, due to its light-guiding properties in air, possesses advantages such as low loss, low nonlinearity, and low latency, demonstrating great potential in various AI computing-driven applications. The hollow-core optical fiber preform, as the base material for drawing hollow-core optical fiber, needs to be fixed at the top of the drawing tower during the fiber drawing process. After softening at temperatures above 2000°C, it is drawn into fiber filaments of hundreds of micrometers using traction force. This process requires extremely high control over the internal gas environment of the preform, and the sealing reliability between the preform and the gas control device is one of the key aspects. Commonly used sealants are prone to failure or expansion under high-temperature environments. Because the thermal expansion coefficients of high-purity quartz and sealants differ significantly, seal failure is easily caused. This not only leads to internal pressure imbalance and microstructure collapse but may also result in the release of organic contaminants from the sealant, forming scattering centers within the optical fiber and severely affecting fiber quality.

[0003] Currently, due to the excessively high end-face temperature during the drawing process of hollow optical fiber preforms, it is generally difficult to install a gas control device at the end. The traditional approach is to create a hole approximately 20cm from the end of the outer sheath wall, through which the gas control device is connected, and the end of the preform is sealed by oxyhydrogen flame burning. This method is easily implemented when the outer sheath wall is thin, but as the length of a single drawing increases, a thicker outer sheath is inevitably required. At this point, the difficulty and risk of creating a hole in the side wall increase significantly, and cracking of the outer sheath frequently occurs; for example, when the wall thickness reaches 3 mm, the tube body is prone to cracking. Summary of the Invention

[0004] The present invention aims to solve the technical problems commonly found in the above-mentioned engineering processes and provides a method for reducing the end face temperature during the drawing process of hollow optical fiber preforms. By coating the end face, inner and outer walls, and outermost layer of the multi-nested capillary tube with a high reflectivity film, photothermal blocking is achieved, keeping the end face temperature of the preform below 30°C during the drawing process. Furthermore, a gas control device can be directly installed on the end face of the preform, eliminating the need for the preform sidewall opening process, which can effectively improve the drawing efficiency and finished product quality of hollow optical fibers.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] S1. Surface cleaning of the outer sheath and multi-layered nested capillaries used to prepare hollow optical fiber preforms; S2. Coat the cleaned pipe surface with an optical film layer that has high reflectivity to visible light and infrared bands; S3. Use film layer testing equipment to inspect the quality of the film layer; S4. The coated capillary tubes are stacked into the outer tube and fixed by local heating with an oxyhydrogen flame or laser.

[0007] Furthermore, the cleaning process uses isopropanol as the main solvent and is usually supplemented by blowing with dry high-purity air, nitrogen, or argon.

[0008] Furthermore, the multi-layered nested capillary includes a non-nested single-layer capillary, a single-nested capillary, and a double-nested capillary.

[0009] Furthermore, the coating process includes physical vapor deposition, chemical vapor deposition, and solution / sol-gel methods, with magnetron sputtering, electron beam evaporation, or sol-gel methods being preferred.

[0010] Furthermore, the high reflectivity film includes a metal film and / or a dielectric multilayer film; the material of the metal film is selected from at least one of gold, silver, copper, aluminum, chromium, platinum, magnesium and their alloys, and the thickness is 30-500 nm; the dielectric multilayer film is composed of one or more of titanium dioxide, tantalum pentoxide and silicon nitride, and each dielectric film layer has an optical thickness of 1 / 4 of the center wavelength of the target band.

[0011] Furthermore, the coating area includes the outer wall, inner wall, end face of the outer sleeve, and the outer side of the multi-layered nested capillary tubes; the coating length of the outer sleeve is 10-30% of the total length of the tube, preferably 10-30 cm; the coating of the multi-layered nested capillary tubes exposed on the outer sleeve is not less than 5 cm, and is appropriately adjusted according to the actual tube length, coating length, and coating area.

[0012] Furthermore, the film detection equipment includes an eddy current thickness gauge, an elliptic polarimeter, a spectrometer, an optical film thickness gauge, a scanning electron microscope, a transmission electron microscope, and an interferometer.

[0013] Furthermore, the film layer testing indicators include film layer thickness, uniformity, density, surface roughness, and transmittance, absorptivity, reflectivity, thermal conductivity, and thermal emissivity in the infrared and visible light bands.

[0014] Furthermore, the fixing method is achieved by locally micro-melting and rapidly solidifying high-purity quartz, which may cause some damage to the pipe during the process.

[0015] The beneficial effects of this invention are: Compared with the prior art, the present invention has the following advantages: (1) By coating a high reflectivity film layer, the present invention effectively blocks light and heat radiation during the fiber drawing process, keeping the temperature of the end face of the hollow fiber preform below 30°C, thus ensuring the normal use of the sealant.

[0016] (2) The method proposed in this invention can support the direct installation of a gas control device at the end of the preform without the need for side wall openings, thus avoiding the processing risks caused by the increase in pipe wall thickness.

[0017] (3) Simplify the processing flow, improve the efficiency of hollow fiber preparation, and make the installation of the gas control device not limited by the wall thickness of the outer tube. It can use a preform with a larger wall thickness to draw a longer distance of hollow fiber. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the coating area at the tail end of the preform in Example 1. The image only shows the last 50cm of the preform. The black area is the area with a high reflectivity coating, and the white area is the area without a coating. Figure 2 This is a schematic diagram of the air control device installed at the tail end of the preform in Example 1; Wherein: 1-Coated outer wall of the outer tube; 2-Uncoated outer wall of the outer tube; 3-Coated end face of the outer tube; 4-Coated outer wall of the capillary tube; 5-Coated inner wall of the outer tube; 6-Uncoated outer tube; 7-Coated outer tube; 8, 11-Sealing ring; 9-Metal threaded ring; 10-Metal part; 12-Metal threaded ring for inserting gas conduit. Detailed Implementation

[0020] To more clearly describe the technical solutions and advantages of the present invention, the present invention will be described in detail below with reference to the accompanying drawings. The present invention is not limited to this embodiment; other embodiments that conform to the spirit of the present invention may also fall within the scope of the present invention. The technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The components of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. It should be noted that similar reference numerals and letters in the following drawings indicate similar items; therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0021] Example A method for reducing the end face temperature during the drawing process of hollow optical fiber preforms includes the following steps: First, the outer sheath 1, 2 and the multi-layer nested capillary 3 used to prepare the hollow optical fiber are cleaned by wiping them with isopropyl alcohol soaked in lint-free paper, then wiping them with dry lint-free paper, and finally blowing them with compressed air.

[0022] Next, a 300 nm thick gold film was deposited on the outer tube and the tail end of the multi-layered nested capillary using magnetron sputtering. The deposition area includes the inner wall 5 of the outer tube, the end face 3 of the outer tube, the side wall 1 of the outer tube, and the outer wall 4 of the multi-layered nested capillary. The deposition area on the side wall 1 and inner wall 5 of the outer tube is 30 cm long, and the deposition area on the outer wall 4 of the multi-layered nested capillary is 8 cm long.

[0023] Subsequently, the quality of the deposited film was inspected using film testing equipment. This included using a spectrometer with a supercontinuum light source to test the transmittance and reflectance of the film after coating; using a scanning electron microscope to test the film density; using an eddy current thickness gauge to test the film thickness; and using an interferometer to sample multiple points to test the film uniformity.

[0024] Finally, the multi-layered nested capillaries, after meeting the coating standards, are stacked into the outer tube and processed using a carbon dioxide laser processing platform to fix the multi-layered nested capillaries to the outer tube.

[0025] After the above treatment, the temperature at the coating end of the hollow fiber preform during the drawing process can be controlled below 30℃, ensuring good performance of the sealant. In this case, a gas control device can be directly installed in the coating area at the preform end to control the gas pressure of the microstructure. The gas control device consists of a metal screw ring 9, a metal screw ring 12 with an insertable gas conduit, a metal part 10, and sealing rings 8 and 11. The metal screw ring 12 with an insertable gas conduit is connected to the metal part 10 via threads; the built-in sealing rings 8 and 11 are compressed by tightening the metal screw ring 9 and the metal screw ring 12 with an insertable gas conduit, thereby generating radial expansion and achieving a reliable sealing effect. The metal part 10 has a pressure-dividing structure inside, and the seal of this structure is mainly ensured by sealant.

Claims

1. A method for reducing the end-face temperature during the drawing process of hollow optical fiber preforms, characterized in that, Includes the following steps: S1 performs surface cleaning treatment on the outer sheath and multi-layered nested capillaries used to prepare hollow optical fibers. S2 uses a coating process to coat the outer tube and the multi-layered nested capillary with an optical film layer that has high reflectivity to visible light and infrared bands. S3 uses a film inspection device to inspect the quality of the aforementioned optical film; S4 arranges multi-layered, nested capillaries coated with a film in a stacked structure inside the outer tube, and uses an oxyhydrogen flame or laser to locally melt and fix the high-purity quartz.

2. The method according to claim 1, characterized in that, The solvent used in the surface cleaning process is mainly isopropanol, and it is usually supplemented by dry high-purity air, nitrogen or argon for blowing.

3. The method according to claim 1, characterized in that, The multi-layered nested capillaries include unnested single-layer capillaries, single-nested capillaries, and double-nested capillaries.

4. The method according to claim 1, characterized in that, The coating process includes at least one of physical vapor deposition, chemical vapor deposition, and solution / sol-gel method; preferably magnetron sputtering, electron beam evaporation, or sol-gel method.

5. The method according to claim 1, characterized in that, The high reflectivity film package Includes metal films and / or dielectric multilayer films; the metal film is made of at least one of gold, silver, copper, aluminum, chromium, platinum, magnesium and their alloys, with a thickness of 30-500 nm; the dielectric multilayer film is composed of one or more of titanium dioxide, tantalum pentoxide and silicon nitride, and each dielectric film layer has an optical thickness of 1 / 4 of the center wavelength of the target band.

6. The method according to claim 1, characterized in that, The coating area includes the outer wall, inner wall, end face of the outer sleeve, and the outer side of the multi-layered nested capillary tubes; the coating length of the outer sleeve is 10-30% of the total length of the tube, preferably 10-30cm; the coating of the multi-layered nested capillary tubes exposed outside the outer sleeve is not less than 5cm, and is appropriately adjusted according to the actual tube length, coating length, and coating area.

7. The method according to claim 1, characterized in that, The film detection equipment includes an eddy current thickness gauge, an elliptic polarimeter, a spectrometer, an optical film thickness gauge, a scanning electron microscope, a transmission electron microscope, and an interferometer.

8. The method according to claim 7, characterized in that, The film layer testing indicators include film thickness, uniformity, density, surface roughness, as well as transmittance, absorptivity, reflectivity, thermal conductivity and thermal emissivity in the infrared and visible light bands.

9. The method according to claim 1, characterized in that, The aforementioned fixing method is achieved by locally micro-melting and rapidly solidifying high-purity quartz, a process that may cause some damage to the pipe.

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