An infrared hollow optical fiber and its preparation method

Abstract

The present invention discloses an infrared hollow optical fiber and a preparation method thereof, relating to the technical field of optical fibers. In the present invention, polyethylene glycol with a relatively high degree of polymerization is used to assist in the precipitation of a metal film inside a quartz hollow base tube, increasing the effective area of the deposited metal, thereby reducing the height difference and roughness of the deposited film, making the obtained metal film more uniform, dense and smooth, and almost capable of achieving total reflection of light energy. Then, by coating a double-layer dielectric film on the metal film, while preventing metal oxidation, the transmission loss of the target wavelength is effectively reduced, and air is used as the transmission medium, so that the base tube reduces energy loss. The second dielectric film is obtained by immersing the tube base in polymethyl methacrylate and curing it. It not only improves the transmittance in the infrared region, but also forms a protective film outside the base tube, improving the mechanical properties of quartz, thereby reducing the loss rate of the base tube.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fibers, and specifically relates to an infrared hollow optical fiber and a preparation method thereof. Background Art

[0002] An optical fiber is short for an optical waveguide fiber, which is a dielectric waveguide operating in the optical waveband. It confines the electromagnetic wave energy in the form of light within its interface by using the total reflection principle and guides the light wave to advance along the axis direction of the optical fiber. According to different uses, it is divided into two categories: one is for transmitting optical signals, that is, communication optical fibers; the other is for transmitting energy, that is, energy transmission optical fibers.

[0003] With the development of laser technology, the application of infrared optical fibers has become more and more extensive, especially in the fields of communication engineering, industrial processing, military technology, and medical devices. In the infrared region, there are several very important lasers, such as the Er: laser at 2.94 μm, the CO laser at 5.3 μm, and the CO2 laser at 9 - 11 μm. Among them, the CO2 laser at 10.6 μm has the advantages of high conversion efficiency, large gain coefficient, and high output power. In addition to being widely used in industrial processing fields such as heat treatment, welding, and cutting of material surfaces, it also has broad application prospects in infrared technologies and scientific research fields such as automated operating systems, hazardous environments, mid-infrared spectral signal transmission, infrared imaging, and infrared radiation temperature measurement, especially in the medical and health fields, which is more important.

[0004] From the perspective of laser transmission performance, hollow optical fibers are more attractive than solid optical fibers. Hollow optical fibers can be divided into two categories in terms of structure: total reflection type and leaky type. The leaky type can greatly increase the reflection coefficient of the inner wall of the hollow optical fiber, overcome the loss caused by the large absorption rate k of the single-layer hollow, and theoretically can obtain smaller transmission loss than the single-layer structure, and this kind of optical fiber has better bending characteristics. Summary of the Invention

[0005] The purpose of the present invention is to provide an infrared hollow optical fiber and a preparation method thereof to solve the problems existing in the prior art.

[0006] To solve the above technical problems, the present invention provides the following technical solution: an infrared hollow optical fiber, the structure of the infrared hollow optical fiber from the inside to the outside is: double-layer dielectric film - metal film - quartz-based tube - protective film.

[0007] Further, the structure of the double-layer dielectric film is an silver iodide layer and a polymethyl methacrylate layer.

[0008] Further, the metal film is specifically a silver film.

[0009] Further, the protective film is specifically a polymethyl methacrylate film.

[0010] Further, a method for preparing an infrared hollow optical fiber includes the following preparation steps:

[0011] (1) Pretreat the quartz-based tube, then introduce a 2 wt% palladium chloride aqueous solution at a rate of 10 mL / min, activate for 25 min, introduce deionized water at a rate of 10 mL / min, and wash for 30 s to obtain a pretreated quartz-based tube;

[0012] (2) Add 20 wt% ammonia water to a 1.75 wt% silver nitrate aqueous solution at a rate of 1 - 3 mL / s, stir at 20 - 40 rpm for 5 - 15 min, and introduce both into the pretreated quartz-based tube at a rate of 5 mL / min for 20 - 50 min. Then wash with deionized water at a rate of 50 mL / min for 10 min, and then introduce nitrogen at a rate of 10 mL / min until the inside of the material is dry to obtain a silver film quartz-based tube;

[0013] (3) Mix iodine and cyclohexane at a mass ratio of 0.2:100, heat to 50°C, stir at 50 - 100 rpm for 1 - 2 h, introduce into the silver film quartz-based tube at a rate of 5 mL / min for 2 - 8 min, introduce nitrogen at a rate of 10 mL / min until the inside of the material is dry, then immerse in a 0.25 wt% polymethyl methacrylate - acetone solution, take out by the dip - coating method, and cure to obtain an infrared hollow optical fiber.

[0014] Further, the pretreatment method in step (1) is as follows: Mix deionized water, ammonium hydroxide, and hydrogen peroxide at a mass ratio of 5:1:1 to obtain an alkaline solution; mix deionized water, hydrogen chloride, and hydrogen peroxide at a mass ratio of 5:1:1 to obtain an acidic solution; wash the quartz-based tube in the order of deionized water - alkaline solution - acidic solution - deionized water, with the flow rate of deionized water being 40 mL / min, and the flow rates of the alkaline and acidic solutions being 20 mL / min, rinse for 15 min each time, and dry at 100°C for 1 - 2 h.

[0015] Further, the reducing solution in step (2) is prepared by mixing a 10 wt% glucose aqueous solution, ethanol, polyethylene glycol 20000, and a 2 wt% sulfuric acid aqueous solution at a mass ratio of 100:10:5:7.

[0016] Further, the mass ratio of the 20 wt% ammonia water to the 1.75 wt% silver nitrate aqueous solution in step (2) is 1:8 - 12.

[0017] Further, the dip - coating speed in step (3) is 0.3 cm / s.

[0018] Further, it is characterized in that the curing temperature in step (3) is 50-70 °C and the time is 100-150 min.

[0019] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: The present invention uses polyethylene glycol to assist the precipitation of the metal film inside the quartz hollow substrate tube, that is, polyethylene glycol with a higher degree of polymerization is used. Through its active effect, the surface tension of the solvent adsorbed on the surface of the substrate tube is reduced, the effective area for depositing the metal is increased, and then the particle size of the precipitated metal particles is reduced, and the height difference and roughness of the deposited film are reduced, making the prepared metal film more uniform, dense and smooth. When light waves are incident on the inside of the substrate tube, almost all of the light energy can be reflected. Then, by coating a double-layer dielectric film on the metal film, while preventing the metal from oxidation, the transmission loss of the target wavelength is effectively reduced, and the bandgap characteristics of the multi-layer dielectric film are enhanced under the high reflection of the outer metal film, thereby reducing the additional loss during bending, enabling the light beam to be reflected thereon, and using air as the transmission medium, so that the substrate tube reduces the reflection loss during energy coupling, the scattering loss and absorption loss during light transmission. The second dielectric film is formed by immersing the tube substrate in polymethyl methacrylate. After curing, it not only improves the transmittance in the infrared region, but also forms a protective film outside the substrate tube, improving the mechanical properties of quartz, thereby reducing the loss rate of the substrate tube. Detailed implementation manners

[0020] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

[0021] In order to more clearly illustrate the method provided by the present invention, the following examples are used for detailed description. The test methods for each index of the infrared hollow optical fiber produced in the following examples are as follows:

[0022] Optical fiber performance: Take the same-sized examples and comparative examples, and use a CO2 laser to detect the straight-line loss power and the bending loss power with a bending angle of 90° by the truncation method, and the output power is 50 W.

[0023] Mechanical properties: Take the same-sized examples and comparative examples and refer to GB / T15972.31 to detect the tensile strength of the optical fiber.

[0024] Example 1

[0025] (1) Mix deionized water, ammonium hydroxide, and hydrogen peroxide in a mass ratio of 5:1:1 to obtain an alkaline solution; mix deionized water, hydrogen chloride, and hydrogen peroxide in a mass ratio of 5:1:1 to obtain an acidic solution; clean the quartz substrate tube in the order of deionized water - alkaline solution - acidic solution - deionized water, with the flow rate of deionized water being 40 mL / min, and the flow rates of the alkaline and acidic solutions being 20 mL / min. Rinse for 15 min each time and dry at 100 °C for 1 h; then introduce a 2 wt% palladium chloride aqueous solution at a flow rate of 10 mL / min and activate for 25 min, and then introduce deionized water at a flow rate of 10 mL / min and clean for 30 s to obtain a pretreated quartz substrate tube;

[0026] (2) Mix a 10 wt% glucose aqueous solution, ethanol, polyethylene glycol 20000, and a 2 wt% sulfuric acid aqueous solution in a mass ratio of 100:10:5:7 to obtain a reducing solution; add a 20 wt% ammonia aqueous solution to a 1.75 wt% silver nitrate aqueous solution at a rate of 1 mL / s, stir at 20 rpm for 5 min, and introduce both into the pretreated quartz substrate tube at a flow rate of 5 mL / min for 20 min. Then rinse with deionized water at a flow rate of 50 mL / min for 10 min, and then introduce nitrogen at a flow rate of 10 mL / min until the interior of the material is dry to obtain a silver film quartz substrate tube; the mass ratio of the 20 wt% ammonia aqueous solution to the 1.75 wt% silver nitrate aqueous solution is 1:8;

[0027] (3) Mix iodine and cyclohexane in a mass ratio of 0.2:100, heat to 50 °C, stir at 50 rpm for 1 h, introduce into the silver film quartz substrate tube at a flow rate of 5 mL / min for 2 min, introduce nitrogen at a flow rate of 10 mL / min until the interior of the material is dry, then immerse in a 0.25 wt% polymethyl methacrylate - acetone solution and pull out at a rate of 0.3 cm / s, and cure at 50 °C for 100 min to obtain an infrared hollow optical fiber.

[0028] Example 2

[0029] (1) Mix deionized water, ammonium hydroxide, and hydrogen peroxide in a mass ratio of 5:1:1 to obtain an alkaline solution; mix deionized water, hydrogen chloride, and hydrogen peroxide in a mass ratio of 5:1:1 to obtain an acidic solution; clean the quartz substrate tube in the order of deionized water - alkaline solution - acidic solution - deionized water, with the flow rate of deionized water being 40 mL / min, and the flow rates of the alkaline and acidic solutions being 20 mL / min. Rinse for 15 min each time and dry at 100 °C for 1.5 h; then introduce a 2 wt% palladium chloride aqueous solution at a flow rate of 10 mL / min and activate for 25 min, and then introduce deionized water at a flow rate of 10 mL / min and clean for 30 s to obtain a pretreated quartz substrate tube;

[0030] (2) Mix a 10 wt% aqueous glucose solution, ethanol, polyethylene glycol 20000, and a 2 wt% aqueous sulfuric acid solution in a mass ratio of 100:10:5:7 to obtain a reducing solution; add a 20 wt% aqueous ammonia solution to a 1.75 wt% aqueous silver nitrate solution at a rate of 1 - 3 mL / s, stir at 30 rpm for 10 min, and then introduce both into a pretreated quartz substrate tube at a rate of 5 mL / min for 30 min. Subsequently, wash with deionized water at a rate of 50 mL / min for 10 min, and then introduce nitrogen at a rate of 10 mL / min until the inside of the material is dry to obtain a silver film quartz substrate tube; the mass ratio of the 20 wt% aqueous ammonia solution to the 1.75 wt% aqueous silver nitrate solution is 1:10;

[0031] (3) Mix iodine and cyclohexane in a mass ratio of 0.2:100, heat to 50 °C, stir at 75 rpm for 1.5 h, introduce into the silver film quartz substrate tube at a rate of 5 mL / min for 5 min, introduce nitrogen at a rate of 10 mL / min until the inside of the material is dry, then immerse in a 0.25 wt% polymethyl methacrylate - acetone solution, pull out at a rate of 0.3 cm / s, and cure at 60 °C for 125 min to obtain an infrared hollow optical fiber.

[0032] Example 3

[0033] (1) Mix deionized water, ammonium hydroxide, and hydrogen peroxide in a mass ratio of 5:1:1 to obtain an alkaline solution; mix deionized water, hydrogen chloride, and hydrogen peroxide in a mass ratio of 5:1:1 to obtain an acidic solution; wash the quartz substrate tube in the order of deionized water - alkaline solution - acidic solution - deionized water, with the flow rate of deionized water being 40 mL / min, and the flow rates of the alkaline and acidic solutions being 20 mL / min, each rinse for 15 min, and dry at 100 °C for 2 h; then introduce a 2 wt% aqueous palladium chloride solution at a rate of 10 mL / min for activation for 25 min, and introduce deionized water at a rate of 10 mL / min for cleaning for 30 s to obtain a pretreated quartz substrate tube;

[0034] (2) Mix a 10 wt% aqueous glucose solution, ethanol, polyethylene glycol 20000, and a 2 wt% aqueous sulfuric acid solution in a mass ratio of 100:10:5:7 to obtain a reducing solution; add a 20 wt% aqueous ammonia solution to a 1.75 wt% aqueous silver nitrate solution at a rate of 3 mL / s, stir at 40 rpm for 15 min, and then introduce both into the pretreated quartz substrate tube at a rate of 5 mL / min for 50 min. Subsequently, wash with deionized water at a rate of 50 mL / min for 10 min, and then introduce nitrogen at a rate of 10 mL / min until the inside of the material is dry to obtain a silver film quartz substrate tube; the mass ratio of the 20 wt% aqueous ammonia solution to the 1.75 wt% aqueous silver nitrate solution is 1:12;

[0035] (3) Mix iodine and cyclohexane at a mass ratio of 0.2:100, heat up to 50 °C, stir at 100 rpm for 2 h, introduce it into a silver film quartz tube at a rate of 5 mL / min for 8 min, introduce nitrogen at a rate of 10 mL / min until the inside of the material is dry, then immerse it in a 0.25 wt% polymethyl methacrylate-acetone solution, lift it out at a rate of 0.3 cm / s, and cure it at 70 °C for 150 min to obtain an infrared hollow optical fiber.

[0036] Comparative Example 1

[0037] The difference between Comparative Example 1 and Example 2 lies in step (2). Modify step (2) as follows: Mix a 10 wt% aqueous glucose solution, ethanol, and a 2 wt% aqueous sulfuric acid solution at a mass ratio of 100:10:7 to obtain a reducing solution; add a 20 wt% aqueous ammonia solution to a 1.75 wt% aqueous silver nitrate solution at a rate of 1 - 3 mL / s, stir at 30 rpm for 10 min, and introduce both into a pretreated quartz tube at a rate of 5 mL / min for 30 min. Then wash with deionized water at a rate of 50 mL / min for 10 min, and then introduce nitrogen at a rate of 10 mL / min until the inside of the material is dry to obtain a silver film quartz tube; the mass ratio of the 20 wt% aqueous ammonia solution to the 1.75 wt% aqueous silver nitrate solution is 1:10; the remaining steps are the same as in Example 2.

[0038] Comparative Example 2

[0039] The difference between Comparative Example 2 and Example 2 lies in step (3). Modify step (3) as follows: Immerse the silver film quartz tube in a 0.25 wt% polymethyl methacrylate-acetone solution, lift it out at a rate of 0.3 cm / s, and cure it at 60 °C for 125 min to obtain an infrared hollow optical fiber; the remaining steps are the same as in Example 2.

[0040] Comparative Example 3

[0041] The difference between Comparative Example 3 and Example 2 lies in step (3). Modify step (3) as follows: Mix iodine and cyclohexane at a mass ratio of 0.2:100, heat up to 50 °C, stir at 75 rpm for 1.5 h, introduce it into the silver film quartz tube at a rate of 5 mL / min for 5 min, introduce nitrogen at a rate of 10 mL / min until the inside of the material is dry to obtain an infrared hollow optical fiber; the remaining steps are the same as in Example 2.

[0042] Effect Example

[0043] The following Table 1 shows the performance analysis results of the infrared hollow optical fibers using Examples 1 - 3 and Comparative Examples 1 - 3 of the present invention.

[0044] Table 1

[0045] Linear loss power (W) Bending loss power (W) Tensile strength (g) Example 1 45.6 41.5 2150 Example 2 46.9 42.8 2200 Example 3 45.3 42.2 2175 Comparative Example 1 40.4 35.7 2140 Comparative Example 2 38.2 33.4 2000 Comparative Example 3 38.5 33.9 1000

[0046] From the comparison of the experimental data of the examples and the comparative examples in Table 1, it can be found that the present invention uses polyethylene glycol to assist in the precipitation of the metal film inside the quartz hollow substrate tube. That is, by using polyethylene glycol with a higher degree of polymerization, through its active effect, the surface tension of the solvent adsorbed on the surface of the substrate tube is reduced, the effective area of the deposited metal is increased, and then the particle size of the precipitated metal particles is reduced, and the height difference and roughness of the deposited film are reduced, making the prepared metal film more uniform, dense and smooth. When light waves are incident on the inside of the substrate tube, almost all of the light energy can be reflected. Then, by coating a double-layer dielectric film on the metal film, while preventing the oxidation of the metal, the transmission loss of the target wavelength is effectively reduced, and the bandgap characteristics of the multi-layer dielectric film are enhanced under the high reflection of the outer metal film, thereby reducing the additional loss during bending, enabling the light beam to be reflected on it, and using air as the transmission medium, so that the substrate tube reduces the reflection loss during energy coupling, the scattering loss and absorption loss during light transmission. Among them, the tube substrate is immersed in polymethyl methacrylate, and after curing, the second dielectric film is inside the tube substrate, improving the transmittance in the infrared region and forming a protective film outside the tube substrate to improve the mechanical properties of quartz, thereby reducing the loss rate of the tube substrate.

[0047] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be construed as limiting the claims concerned.

Claims

1. A method for preparing an infrared hollow-core optical fiber, characterized in that: The method comprises the following preparation steps: (1) Pre-treating the quartz substrate tube, then passing a 2 wt % palladium chloride aqueous solution at 10 mL / min, activating for 25 min, passing deionized water at 10 mL / min, washing for 30 s, and obtaining a pre-treated quartz substrate tube; (2) Add 20 wt % ammonia solution to 1.75 wt % silver nitrate solution at 1-3 mL / s, stir at 20-40 rpm for 5-15 min, pass the solution and the reducing solution into the pretreated quartz substrate tube at 5 mL / min for 20-50 min, then wash with deionized water at 50 mL / min for 10 min, and then pass nitrogen at 10 mL / min until the inside of the substance is dry, to obtain a silver film quartz substrate tube; (3) Mix iodine and cyclohexane in a mass ratio of 0.2:100, heat to 50°C, stir at 50-100 rpm for 1-2 h, pass 5 mL / min into the silver film quartz substrate tube for 2-8 min, pass nitrogen at 10 mL / min until the inside of the material is dry, then immerse in 0.25 wt% polymethyl methacrylate-acetone solution, take out by the pulling method, and solidify to obtain an infrared hollow optical fiber.

2. The method for preparing an infrared hollow optical fiber according to claim 1, characterized in that: The pretreatment method of step (1) is as follows: deionized water, ammonium hydroxide and hydrogen peroxide are mixed in a mass ratio of 5:1:1 to obtain an alkaline solution; deionized water, hydrogen chloride and hydrogen peroxide are mixed in a mass ratio of 5:1:1 to obtain an acid solution; the quartz substrate tube is cleaned in the order of deionized water-alkaline solution-acid solution-deionized water, the flow rate of deionized water is 40 mL / min, the flow rate of alkali and acid solution is 20 mL / min, each rinse is 15 minutes, and drying is carried out at 100°C for 1 to 2 hours.

3. The method for preparing an infrared hollow optical fiber according to claim 1, characterized in that: The reducing solution in step (2) is prepared by mixing 10 wt % glucose aqueous solution, ethanol, polyethylene glycol 20000, and 2 wt % sulfuric acid aqueous solution in a mass ratio of 100:10:5:

7.

4. The method for preparing an infrared hollow optical fiber according to claim 1, characterized in that: The mass ratio of the 20wt% ammonia solution to the 1.75wt% silver nitrate solution in step (2) is 1:8-12.

5. The method for preparing an infrared hollow optical fiber according to claim 1, characterized in that: The pulling speed in step (3) is 0.3 cm / s.

6. The method for preparing an infrared hollow optical fiber according to claim 1, characterized in that: The curing temperature in step (3) is 50-70°C and the curing time is 100-150 minutes.