A preparation device and method for multi-glass cladding optical fiber

Abstract

The present invention discloses a preparation device and method for multi-glass cladding optical fiber, that is, firstly preparing and processing the required preform rod, and then depositing a layer of required F-doped (or other glass components) glass cladding on the glass cladding optical fiber with a special shape online to obtain the required multi-glass cladding optical fiber.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber cable preparation, and more specifically, relates to a preparation device and method for multi-glass cladding optical fiber. Background Art

[0002] Fiber laser is a laser that uses optical fiber as a laser gain medium. By doping different rare earth ions in the optical fiber quartz matrix, laser outputs of different wavelengths are obtained. Fiber lasers are widely used in industrial processing, medical treatment, military, and communications due to their advantages such as high beam quality, large specific surface area, good heat dissipation, high conversion efficiency, small size, compact structure, and easy maintenance. Thanks to the invention of double-clad fiber pumping technology, by injecting multi-mode pump light into the glass cladding, it is converted into a laser with a better mode and higher power at a specific wavelength in a low NA and small-sized rare earth-doped core (usually a core size of 10μm or 20μm). In order to obtain higher laser conversion efficiency, its quartz cladding often uses a non-circular cross-section to destroy its symmetry, so that more pump light is injected into the core, which is then absorbed by the core and converted into the required laser output. In double-clad optical fiber, pure quartz glass is used as the inner cladding and fluorine-doped acrylic resin coating is used as the outer cladding. Since the fluorine-doped acrylic resin coating has an ultra-low refractive index (refractive index is about 1.3), the pump light injected into the inner cladding is totally reflected at the interface between the inner cladding and the outer cladding. However, the interface is not a complete mirror, and part of the pump light will propagate in the fluorine-doped acrylic resin in the form of evanescent waves. After a long period of laser radiation, excessive temperature, laser radiation, and the intrusion of water vapor will cause the low-refractive index coating to age. Especially in high-power fiber lasers, as the transmission power continues to increase, the power density in the fiber core also gradually increases, which inevitably requires the input of more pump light. The coating is impacted by the high-power density pump light, and the aging rate will accelerate. When the low-refractive index coating ages, its absolute refractive index will increase, the adhesion to the glass cladding will decrease, and peeling and microcracks will occur, which will affect the gain performance of the optical fiber. In severe cases, light leakage will occur, causing the optical fiber to burn, and even damage other components of the fiber laser, including the combiner, pump source, isolator, etc.

[0003] By adding a layer of low-folding quartz cladding with a circular cross-section shape outside the irregular quartz cladding, the problem of large differences in fiber parameters caused by fluctuations in the wire diameter and tension of the non-circular preform can be solved, while reducing pump light leakage and extending the service life of the fiber. The existing method for preparing triple-clad rare-earth-doped optical fiber or triple-clad passive optical fiber is to first prepare a core rod, then polish it into the required quadrilateral, D-shape, hexagon, octagon, etc., and then melt it with an F-doped tube into a solid preform rod, and finally process it into a circular preform rod. This process is very complicated and time-consuming, especially when preparing triple-clad rare-earth-doped optical fiber, it is very easy to cause a sharp increase in core loss and an extremely low yield rate. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the present invention provides a method for preparing a multi-glass cladding optical fiber. The specific method and steps are as follows:

[0005] (1) Prepare the required doped core rod on MCVD or PCVD;

[0006] (2) grinding the doped core rod in (1) into a preform rod of a desired size and shape (referred to as preform rod A), which may be any irregular shape such as a quadrilateral, D-shape, hexagon, octagon, etc.;

[0007] (3) The preform rod in (2) is cleaned and dried, and then drawn into a bare optical fiber of the required size (referred to as bare optical fiber B) on a drawing tower. The core layer of the preform rod is the core of the optical fiber, and the cladding layer of the preform rod is the first glass cladding layer of the optical fiber.

[0008] (4) The bare optical fiber in (3) is passed through a molten F-doped glass liquid. At this time, the surface of the bare optical fiber will be coated with F-doped glass. After passing through a special mold and cooling, a layer of F-doped glass (referred to as bare optical fiber C) is formed on the surface of the bare optical fiber B. This cladding is the second glass cladding of the optical fiber. The shape and thickness of this cladding can be arbitrarily adjusted by the mold.

[0009] (5) The desired triple-clad (or multi-clad) optical fiber can be obtained by annealing, cooling, and coating the optical fiber in (4) with an organic coating.

[0010] In order to achieve the above-mentioned object, according to another aspect of the present invention, a method and device for preparing a second glass cladding (or multiple glass cladding) optical fiber are provided, wherein the device comprises a bare optical fiber B preheating device, an F-doped glass melting device, a bare optical fiber C preforming device, and a bare optical fiber C cooling annealing device.

[0011] The bare optical fiber B preheating device is used to heat the bare optical fiber B to the required temperature T1. In order to ensure the cleanliness of the bare optical fiber B and the subsequent preparation of the F-doped glass cladding, the bare optical fiber B is generally heated by constant temperature high-purity helium. This has two advantages: first, the high thermal conductivity of helium is used to make the optical fiber reach the temperature T1 quickly and evenly; second, the air on the surface of the bare optical fiber B is removed by helium to prevent the air from entering the F-doped glass melting device.

[0012] The above-mentioned bare optical fiber B preheating device can be made of high-purity aluminum oxide or high-purity quartz glass, and the shape can be cylindrical or rectangular;

[0013] The F-doped glass melting device is a closed high-temperature furnace used to melt the F-doped glass. It is located directly below the bare optical fiber B preheating device and fixed directly below the drawing furnace.

[0014] The F-doped glass mentioned above is a high-purity glass, which can be prepared by a sol-gel method or by a process such as PCVD;

[0015] The bare optical fiber C preforming device is used to form a bare optical fiber C with an F-doped cladding after the bare optical fiber B that has been doped with F glass passes through a mold, and is located directly below the F-doped glass melting device;

[0016] The bare optical fiber C cooling annealing device is used to rapidly cool the bare optical fiber C and maintain it at a certain temperature for annealing. Generally, constant temperature high-purity helium is used to cool the bare optical fiber C. It has two advantages: first, the high thermal conductivity of helium is used to make the optical fiber reach the annealing temperature quickly and evenly; second, the air on the surface of the bare optical fiber C is removed by helium to prevent the air from entering the F-doped glass melting device.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. By preparing a preform core rod and then subjecting it to an F-doped glass outsourcing treatment during wire drawing, the repetitive operations of polishing, melting, grinding and other processes on the core rod can be reduced, the complexity of the process can be reduced, and at the same time, crystallization or scrapping of the core rod caused by repeated heat treatment and mechanical processing can be avoided;

[0019] 2. Taking advantage of the temperature gradient during bare optical fiber drawing and the low melting point of F-doped glass, the F-doped glass cladding is deposited at a suitable temperature to ensure a high concentration of F doping and avoid F loss caused by high temperature.

[0020] 3. The F-doped glass cladding can be prepared into any shape by using a flexible and customized bare fiber C preforming device. In addition, the concentricity between the glass claddings can be ensured by the alignment of the drawing tower. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of a method and device for preparing a second glass cladding (or multiple glass cladding) optical fiber according to an embodiment of the present invention;

[0022] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0023] 1- Bare optical fiber 2- Bare optical fiber preheating device 3- F-doped glass melting device 4- High-purity SiF4 gas

[0024] 5- High-purity F-doped glass 6- Bare optical fiber preforming device 7- Bare optical fiber cooling annealing device. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] See also Figure 1 The present invention is to prepare a triple-clad ytterbium-doped optical fiber (34 / 460 / 530 microns), wherein the diameter of the ytterbium-doped core is 34 microns, and the NA is between 0.075-0.085; the first cladding of pure silica is a regular octagon, and the distance between the edges is 460 microns; the second cladding of F-doped glass is circular, with a diameter of 530 microns, the mass percentage of F concentration in the F-doped glass is greater than 2.5%, and the NA is greater than 0.23.

[0027] In this example, the ytterbium-doped core rod is first prepared by MCVD combined with the chelate high-temperature vapor phase method, and then the core rod is covered with pure quartz through a sleeve stretching process. Finally, a regular octagonal rare earth-doped preform is obtained by polishing, in which the diameter ratio of the pure quartz cladding layer to the rare earth-doped core layer is 460 / 34.

[0028] The above-mentioned regular octagonal preform rod is connected to an extension rod, corroded and cleaned, and drawn into a bare optical fiber 1 with an outer diameter of 460±2 microns at a high temperature of about 2000°C, and then the bare optical fiber 1 is passed through a bare optical fiber preheating device 2 to make the temperature of the bare optical fiber reach 1300-1500°C;

[0029] In this example, the bare optical fiber preheating device 2 is cylindrical and made of pure silica glass with a wall thickness of 5 mm. There is an 800-micron hole on the top for the entry channel of the bare optical fiber 1. 1-10 L / min of high-purity helium gas is introduced into the cylindrical tube. The temperature of the helium gas is 1300-1500°C. The helium gas enters the channel to purge the bare optical fiber 1 and remove the air on the surface of the optical fiber.

[0030] When the preheated bare optical fiber 1 enters the F-doped glass melting device 3, it will enter the melted F-doped glass solution 5 (temperature is 1300-1500°C), and the pure quartz glass surface of the bare optical fiber 1 will be covered with F-doped glass, and then pass through the bare optical fiber preforming device 6 to form an F-doped glass cladding;

[0031] In this example, the F-doped glass melting device 3 is a high-temperature furnace with a cylindrical interior, and the inner cavity is made of high-purity quartz glass, with an inner diameter of 200 mm and a height of 100 mm. It is cleaned before each use, and then a proper amount of high-purity F-doped glass is added therein, and then the air therein is evacuated. Then, the furnace temperature is raised to 1300-1500°C in the atmosphere of high-purity SiF4 gas 4. At this time, the bare optical fiber 1 will carry the molten F-doped glass cladding out through the bare optical fiber preforming device 6, and cool to form an F-doped glass cladding optical fiber. The bare optical fiber preforming device 6 is a funnel-shaped high-purity silica glass piece, and its outlet is cylindrical with an inner diameter of 600-1000 microns.

[0032] By measuring the fiber diameter and adjusting the temperature at the outlet of the bare fiber preforming device 6, the diameter of the F-doped cladding can be controlled between 530±3 μm, because a high concentration of F can be ensured in the atmosphere of high-purity SiF4 gas 4;

[0033] Then, the F-doped cladding optical fiber that has been preformed by the preforming device 6 is passed through a bare optical fiber cooling annealing device 7, which includes an annealing furnace and a helium cooling device for annealing the optical fiber and cooling the optical fiber to room temperature;

[0034] The optical fiber that has passed through the bare optical fiber cooling and annealing device 7 is subsequently coated with a coating to obtain the desired triple-cladding rare earth-doped optical fiber, wherein the pure silica cladding is the first cladding, the F-doped glass cladding is the second cladding, and the low refractive index coating is the third coating.

[0035] In addition, in this embodiment, the molten F-doped glass cladding is directly cooled to avoid the loss of F and the formation of bubbles at the octagonal interface caused by repeated high temperatures.

[0036] It is easy for those skilled in the art to understand that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation device for multi-glass cladding optical fiber, characterized in that: The device comprises a bare fiber preheating device, an F-doped glass melting device, a bare fiber preforming device, and a bare fiber cooling and annealing device, which are arranged in sequence from top to bottom. The bare fiber preheating device is used to heat the bare fiber to a required temperature T1. The F-doped glass melting device is a closed high-temperature furnace used to melt the F-doped glass, and is located directly below the bare fiber preheating device; the bare fiber preforming device is used to shape the bare fiber doped with F glass into a bare fiber doped with F cladding, and is located directly below the F-doped glass melting device; the bare fiber cooling and annealing device is used to rapidly cool the bare fiber and maintain it at a certain temperature for annealing; the bare fiber preheating device uses constant-temperature high-purity helium to heat the bare fiber.

2. The preparation device for multi-glass cladding optical fiber according to claim 1, characterized in that: The bare optical fiber preheating device is made of high-purity aluminum oxide or high-purity quartz glass and has a cylindrical or rectangular shape.

3. The preparation device for multi-glass cladding optical fiber according to claim 1, characterized in that: The F-doped glass is high-purity glass, which is prepared by a sol-gel method or a PCVD process.

4. The preparation device for multi-glass cladding optical fiber according to claim 1, characterized in that: The bare optical fiber cooling annealing device uses constant temperature high-purity helium to cool the bare optical fiber.

5. A method for preparing a multi-glass cladding optical fiber, using the preparation device according to any one of claims 1 to 4, characterized in that: Specifically, the method comprises the following steps: S1, preparing a required doped core rod on MCVD or PCVD; S2, grinding the doped core rod in S1 into a preform rod A of required size and shape; S3, cleaning and drying the preform rod A in S2, and then drawing the preform rod A into an optical fiber B of required size on a drawing tower, wherein the core layer of the preform rod is the core of the optical fiber, and the cladding of the preform rod is the first glass cladding of the optical fiber; S4, passing the optical fiber B in S3 through molten F-doped glass liquid, at which time the surface of the optical fiber B will be wrapped by the F-doped glass, and cooling to form an optical fiber C with a layer of F-doped glass on the surface of the optical fiber B, wherein the F-doped glass layer is the second glass cladding of the optical fiber; S5, annealing, cooling and coating the optical fiber C in S4 to obtain the required triple-cladding optical fiber.

6. The preparation method according to claim 5, characterized in that: In step S2, the shape of the preform rod A is a quadrilateral, a D-shape, a hexagon or an octagon.

7. The preparation method according to claim 5, characterized in that: In step S4, the shape and thickness of the F-doped glass layer can be arbitrarily adjusted by a mold.

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