CN112390525A - Optical fiber preform, preparation method thereof and optical fiber - Google Patents
Optical fiber preform, preparation method thereof and optical fiber Download PDFInfo
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- CN112390525A CN112390525A CN202011289065.4A CN202011289065A CN112390525A CN 112390525 A CN112390525 A CN 112390525A CN 202011289065 A CN202011289065 A CN 202011289065A CN 112390525 A CN112390525 A CN 112390525A
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
- C03B37/018—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
- C03B37/01807—Reactant delivery systems, e.g. reactant deposition burners
- C03B37/01815—Reactant deposition burners or deposition heating means
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
- C03B37/018—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
- C03B37/01853—Thermal after-treatment of preforms, e.g. dehydrating, consolidating, sintering
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- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P40/00—Technologies relating to the processing of minerals
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Abstract
The invention relates to an optical fiber preform, a preparation method thereof and an optical fiber, wherein the preparation method comprises the following steps: providing a reaction tube, installing the reaction tube on chemical vapor deposition equipment, and enabling the reaction tube to be in a rotating state; introducing silicon tetrachloride and oxygen into the reaction tube, adjusting the temperature of a heating source to 1500 +/-30 ℃, heating the reaction tube, moving the heating source forward at a speed of 100-130 mm/min, and repeating the step for multiple times; continuously introducing the silicon tetrachloride and the oxygen into the reaction tube, adjusting the temperature of the heating source to 1600 +/-30 ℃, moving the heating source forward at a speed of 100-130 mm/min, and repeating the step for multiple times, wherein silicon dioxide generated by the reaction of the silicon tetrachloride and the oxygen is gradually deposited to form a loose layer on the inner wall of the reaction tube; doping rare earth element ions and aluminum ions into the loose layer through liquid phase doping; and melting and shrinking the reaction tube to obtain the optical fiber preform.
Description
Technical Field
The invention relates to the technical field of optical fiber preparation, in particular to an optical fiber preform, a preparation method thereof and an optical fiber.
Background
The conventional optical fiber design with small core diameter and Large numerical aperture is not suitable for high-power output application, but has high rare earth doping concentration, and meanwhile, the Large Mode Area (LMA) optical fiber with relatively Large core diameter and relatively small numerical aperture can improve the output power and the beam quality, so that the LMA ytterbium-doped double-clad optical fiber becomes a hot spot developed by the current active optical fiber. However, the existing LMA ytterbium-doped double-clad fiber is relatively complex in preparation process and is not beneficial to industrial production.
Disclosure of Invention
Therefore, it is necessary to provide an optical fiber preform, a preparation method thereof and an optical fiber, aiming at the problems that the existing LMA ytterbium-doped double-clad optical fiber preparation process is complex and is not beneficial to industrial production.
A method for preparing an optical fiber preform, comprising the steps of:
providing a reaction tube, installing the reaction tube on chemical vapor deposition equipment, and enabling the reaction tube to be in a rotating state;
introducing silicon tetrachloride and oxygen into the reaction tube, adjusting the temperature of a heating source to 1500 +/-30 ℃, heating the reaction tube, moving the heating source forward at a speed of 100-130 mm/min, and repeating the step for multiple times;
continuously introducing the silicon tetrachloride and the oxygen into the reaction tube, adjusting the temperature of the heating source to 1600 +/-30 ℃, moving the heating source forward at a speed of 100-130 mm/min, and gradually depositing silicon dioxide generated by the reaction of the silicon tetrachloride and the oxygen to form a loose layer on the inner wall of the reaction tube;
doping rare earth element ions and aluminum ions into the loose layer through liquid phase doping;
and melting and shrinking the reaction tube to obtain the optical fiber preform.
The above-described method for preparing an optical fiber preform requires multiple depositions to produce a loose layer in order to obtain a sufficiently large core diameter. In the deposition process, the reaction temperature in the initial stage and the later stage of deposition is accurately controlled, so that the loose layer has enough thickness, the layers are not separated, and different layers have viscosity and are not easy to fall off. The silicon dioxide loose layer with consistent density is formed by adopting the method, and high-concentration rare earth element ions can be doped in the loose layer only by carrying out liquid phase doping operation once subsequently. Compared with the method of alternately carrying out the deposition reaction and the liquid phase doping operation, the preparation method of the invention can greatly shorten the reaction time, improve the production efficiency, reduce the manual operation times and be beneficial to industrial production.
In one embodiment, the step of doping rare earth element ions and aluminum ions in the bulk layer by liquid phase doping comprises:
adding anhydrous rare earth element chloride with the mole percentage of 1% and anhydrous aluminum chloride with the mole percentage of 2% into the substrate solution to prepare a doping solution;
and placing the reaction tube in the doping solution, wherein the end part of the reaction tube is connected with a peristaltic pump, and the peristaltic pump pumps the doping solution into the reaction tube, so that the rare earth element ions and the aluminum ions in the doping solution are immersed in the loose layer.
In one embodiment, the step of doping the rare earth element ions and the aluminum ions into the bulk layer by liquid phase doping further comprises:
and adjusting the temperature of a heating source to 1500 +/-20 ℃, heating the reaction tube, and moving the heating source forward at a speed of 25-40 mm/min to pre-sinter the loose layer.
In one embodiment, the silicon tetrachloride and the oxygen are continuously introduced into the reaction tube, the temperature of the heating source is adjusted to 1500 ± 30 ℃, the heating source is moved forward at a speed of 100-130 mm/min, and the step is repeated for a plurality of times: the number of repetitions is greater than or equal to 2.
In one embodiment, before introducing silicon tetrachloride and oxygen into the reaction tube, the method further comprises the following steps:
and carrying out high-temperature corrosion on the inner wall of the reaction tube by adopting sulfur hexafluoride to remove surface impurities, and introducing oxygen to polish the inner surface of the reaction tube.
In one embodiment, the step of collapsing the reaction tube to obtain the optical fiber preform further comprises:
and oxidizing the rare earth element ions and the aluminum ions in the loose layer to generate rare earth oxides and aluminum oxide, and dehydrating and drying the loose layer.
In one embodiment, the step of performing dehydration drying treatment on the loose layer specifically includes:
and introducing mixed gas of chlorine, oxygen and helium into the reaction tube, and raising the temperature of the reaction tube to 1000-1200 ℃.
An optical fiber preform is prepared by the preparation method.
An optical fiber is prepared by drawing and coating the optical fiber preform.
Drawings
FIG. 1 is a schematic diagram of the deposition of a bulk layer during the fabrication of an optical fiber preform;
FIG. 2 is a schematic cross-sectional view of an optical fiber according to an embodiment;
FIG. 3 is a schematic diagram of relative refractive indices of optical fibers according to an embodiment;
FIG. 4 is an absorption spectrum of an optical fiber according to an embodiment.
The following detailed description of the invention will be further described in conjunction with the above-identified drawing figures.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.
The invention provides an optical fiber, which has a double-cladding structure. The optical fiber comprises a fiber core, an inner cladding and an outer cladding in sequence from inside to outside. The fiber core is formed by silica doped with rare earth elements, is a laser oscillation channel and is in a single mode for relevant wavelength. The inner cladding is composed of silica with larger transverse dimension than the fiber core and smaller refractive index than the fiber core, is a channel of pump light, and is multimode to the wavelength of the pump light. The outer cladding is composed of a material having a lower index of refraction than the inner cladding. The pumping light enters the inner cladding with larger size, is internally reflected in the inner cladding, passes through the fiber core for multiple times, is absorbed by the doped rare earth element ions, is converted into laser with another wavelength, and is output from the tail end of the optical fiber. Generally, the optical fiber further includes a protective layer made of hard plastic, which functions to protect the outer cladding, inner cladding, and core.
The preparation process of the optical fiber is as follows: providing an optical fiber perform, grinding the optical fiber perform into an octagonal shape, then placing the optical fiber perform into an optical fiber drawing tower for drawing, and then performing coating treatment to form an outer cladding layer. In order to avoid the outer cladding, the inner cladding and the fiber core from being damaged, a plastic tube is sleeved on the outer cladding to be used as a protective layer. The performance of the optical fiber is mainly determined by various parameters of the optical fiber preform.
The invention provides a preparation method of an optical fiber preform for preparing a large mode field optical fiber, which comprises the following steps:
s100, providing a reaction tube, installing the reaction tube on a chemical vapor deposition (MCVD) device, and enabling the reaction tube to be in a rotating state.
The reaction tube is a carrier for performing chemical vapor deposition, and the corresponding size can be selected according to actual needs, and in one embodiment, the outer diameter of the reaction tube is 20mm, and the inner diameter is 16 mm.
In order to avoid the contamination of the optical fiber preform with impurities, step S100 is followed by step S110: and carrying out high-temperature corrosion on the inner wall of the reaction tube by adopting sulfur hexafluoride to remove surface impurities, and introducing oxygen to polish the inner surface of the reaction tube.
S200, referring to the figure 1, introducing silicon tetrachloride and oxygen into the reaction tube 200, adjusting the temperature of a heating source to 1500 +/-30 ℃, heating the reaction tube 200, moving the heating source forward at a speed of 100-130 mm/min, and repeating the steps for multiple times.
Specifically, oxygen flows through a bubbling bottle (not shown) containing a silicon tetrachloride solution, and silicon tetrachloride is loaded into the reaction tube 200. The gas flow direction in the reaction tube 200 is shown as a in figure 1, silicon tetrachloride and oxygen enter the reaction tube 200 from the left side, and the silicon tetrachloride and the oxygen react in the area shown as b in figure 1 at the temperature of 1500 +/-30 ℃ as follows:
SiCl4+O2→SiO2+Cl2↑
the silicon dioxide powder 101 generated by the reaction is deposited on the inner wall of the reaction tube 200, and the silicon dioxide powder 101 is accumulated to a certain thickness to form the loose layer 100.
A large number of experimental results show that the silicon tetrachloride in the reaction tube can fully react with oxygen to generate a uniform silicon dioxide loose layer by controlling the temperature within the range of 1500 +/-30 ℃. As the oxidation reaction proceeds, silica is gently attached to the inner wall of the reaction tube. In the temperature range, the silicon dioxide is not vitrified, and the silicon dioxide deposited in the reaction tube has a loose structure, so that liquid can permeate into the silicon dioxide loose layer when liquid phase doping is carried out subsequently.
In step S200: the number of repetitions is greater than or equal to 2.
S300, continuously introducing silicon tetrachloride and oxygen into the reaction tube, adjusting the temperature of the heating source to 1600 +/-30 ℃, moving the heating source forward at a speed of 100-130 mm/min, and gradually depositing silicon dioxide generated by the reaction of the silicon tetrachloride and the oxygen to form a loose layer on the inner wall of the reaction tube.
After the multiple layers are repeatedly deposited in the step S200, the thickness of the silicon dioxide loose layer is increased, the temperature close to the center of the reaction tube is reduced, and the temperature of the heating source is increased to 1600 +/-30 ℃ in the step S300, so that silicon dioxide with the same density as that in the step S200 is generated in the subsequent reaction, and the thickness of deposition and the uniformity of deposition are ensured. Moreover, experiments prove that the temperature is increased to 1600 +/-30 ℃ and the heating source is rapidly moved, so that the silicon dioxide with consistent density can be generated, and the non-uniformity of subsequent doping caused by sintering of the previously deposited silicon dioxide is avoided.
In one embodiment, step S300 is performed only once. In other embodiments, step S300 may be repeated multiple times.
Step S300 is followed by step S310: and adjusting the temperature of the heating source to 1500 +/-20 ℃, heating the reaction tube, and positively moving the heating source at the speed of 25-40 mm/min to pre-sinter the loose layer. The loose layer closest to the inner wall of the reaction tube is slightly sintered at low temperature to stick the tube wall, so that the loose layer is prevented from being attached unreliably to cause falling off in the liquid phase doping process, and the temperature is low so as not to cause the collapse of the inner part of the loose layer to cause the reduction of doping.
S400, doping rare earth element ions and aluminum ions into the loose layer through liquid phase doping.
The step S400 of doping rare earth element ions and aluminum ions into the bulk layer by liquid phase doping specifically includes steps S410 and S420.
S410, adding anhydrous rare earth element chloride with the mole percentage of 1% and anhydrous aluminum chloride with the mole percentage of 2% into the substrate solution to prepare a doping solution.
The base solution was anhydrous methanol. The rare earth element may be any one of ytterbium, erbium and thulium, and the absorption wavelength and the output wavelength of the optical fiber doped with different rare earth elements are different.
In this example, the rare earth element is ytterbium. The optical fiber has the advantages that the photon darkening effect can be effectively improved by introducing aluminum ions into the fiber core (namely the loose layer), the Al-O-Yb glass structure can be formed by doping the aluminum ions, the Yb-Yb structure can be effectively inhibited, the probability of forming a color center is reduced, meanwhile, the aluminum ions can effectively prevent ytterbium ions from forming clusters in quartz glass, the generation of crystallization is prevented, the concentration of the ytterbium ions in the loose layer is improved, and the gain performance of the optical fiber is effectively improved.
To produce a single mode fiber, the numerical aperture needs to be reduced as the mode field area increases. The invention ensures that ytterbium ions in the optical fiber have enough concentration and ion clustering can not occur by adjusting the proportion of ytterbium ions to the substrate solution and the proportion of aluminum ions to the substrate solution, and simultaneously ensures that the fiber core has smaller numerical aperture.
And S420, placing the reaction tube in the doping solution, wherein the end part of the reaction tube is connected with a peristaltic pump, and the peristaltic pump pumps the doping solution into the reaction tube so that the rare earth element ions and the aluminum ions in the doping solution are immersed in the loose layer.
S500, fusing and shrinking the reaction tube to obtain the optical fiber perform. Specifically, the temperature of the heating source is adjusted to 2200 ℃, the air pressure in the reaction tube is adjusted, and the reaction tube is repeatedly subjected to collapse treatment for many times, so that the solid optical fiber preform is finally obtained.
The above-described method for preparing an optical fiber preform requires multiple depositions to produce a loose layer in order to obtain a sufficiently large core diameter. In the deposition process, the reaction temperature in the initial stage and the later stage of deposition is accurately controlled, so that the loose layer has enough thickness, the layers are not separated, and different layers have viscosity and are not easy to fall off. Because the silicon dioxide with consistent density is formed in the multiple deposition processes, the rare earth element ions with high concentration can be doped in the loose layer only by carrying out liquid phase doping operation once subsequently. Compared with the method of alternately carrying out the deposition reaction and the liquid phase doping operation, the preparation method of the invention can greatly shorten the reaction time, improve the production efficiency, reduce the manual operation times and be beneficial to industrial production.
Step S500 is preceded by step S430: and oxidizing the rare earth element ions and the aluminum ions in the loose layer to generate rare earth oxides and aluminum oxide, and dehydrating and drying the loose layer.
Step S430 specifically includes: introducing a mixed gas of chlorine, oxygen and helium into the reaction tube, and raising the temperature of the reaction tube to 1000-1200 ℃.
And after the liquid phase doping is finished, continuously and reversely clamping the reaction tube for drying for one hour, so that the methanol in the loose layer is slowly volatilized. Then the reaction tube is installed back to the MCVD equipment, mixed gas of chlorine, oxygen and helium is introduced, and the oxyhydrogen flame temperature is adjusted to 1050 ℃. The doped ytterbium trichloride and aluminum trichloride are oxidized into ytterbium trioxide and aluminum oxide, the melting point of the ytterbium trioxide and the aluminum oxide is higher than that of the ytterbium trichloride and the aluminum trichloride, and the doped concentration in the loose layer is not reduced due to gasification in the subsequent processing process. The hydroxyl ions in the loose layer react with the chlorine to produce water which is then carried away by the airflow, so that the water in the loose layer is removed.
Step S440 is further included after step S430: the temperature of the heating source was adjusted to 2000 ℃, so that the silica loose layer was vitrified.
Example 1
S100, providing a reaction tube, wherein the outer diameter of the reaction tube is 20mm, and the inner diameter of the reaction tube is 16 mm. The reaction tube is arranged on the chemical vapor deposition equipment and is in a rotating state.
S110: and carrying out high-temperature corrosion on the inner wall of the reaction tube by adopting sulfur hexafluoride to remove surface impurities, and introducing oxygen to polish the inner surface of the reaction tube by utilizing a heating source. After the treatment, the inner wall of the reaction tube is smooth and has no impurities, which is beneficial to reducing the loss of the optical fiber.
S200, introducing silicon tetrachloride and oxygen into the reaction tube, adjusting the temperature of the heating source to 1500 ℃, heating the reaction tube, moving the heating source forward at a speed of 120mm/min, repeating the step for 3 times, and keeping the air pressure at the tail end of the reaction tube at 50Pa to prevent air from entering the reaction tube.
S300, continuously introducing silicon tetrachloride and oxygen into the reaction tube, adjusting the temperature of the heating source to 1600 ℃, moving the heating source forward at the speed of 120mm/min, and repeating the step for 2 times, wherein silicon dioxide generated by the reaction of the silicon tetrachloride and the oxygen is gradually deposited to form a loose layer on the inner wall of the reaction tube.
Step S310: the temperature of the heating source was adjusted to 1500 ℃, the reaction tube was heated, and the heating source was moved forward at a speed of 30mm/min to pre-sinter the porous layer. The loose layer closest to the inner wall of the reaction tube is slightly sintered at low temperature to stick the tube wall, so that the loose layer is prevented from being attached unreliably to cause falling off in the liquid phase doping process, and the temperature is low so as not to cause the collapse of the inner part of the loose layer to cause the reduction of doping.
S400, doping rare earth element ions and aluminum ions into the loose layer through liquid phase doping.
Specifically, anhydrous ytterbium chloride with a molar percentage of 1% and anhydrous aluminum chloride with a molar percentage of 2% are added to anhydrous methanol to prepare a doping solution. After the loose layer is prepared, the reaction tube is disconnected from the tail part, the disconnected position is a horn-shaped opening, and after the reaction tube is placed and cooled, the reaction tube is clamped on a liquid phase doping workbench and vertically inserted into the prepared doping solution. The end part of the reaction tube is connected with a peristaltic pump, the peristaltic pump pumps the doping solution into the reaction tube for one hour, so that rare earth element ions and aluminum ions in the doping solution are slowly immersed into the loose layer.
And after doping is finished, continuously and reversely clamping the reaction tube for drying for one hour, so that the methanol in the loose layer is slowly volatilized. Then the reaction tube is installed back to the MCVD equipment, oxygen is introduced, the temperature of the heating source is adjusted to 1050 ℃, and the doped ytterbium trichloride and aluminum trichloride are oxidized into ytterbium trioxide and aluminum oxide.
And introducing a mixed gas of chlorine, oxygen and helium into the reaction tube, and dehydrating and drying the loose layer at 1000 ℃.
Oxygen was introduced into the reaction tube to vitrify the porous layer at 2000 ℃.
S500, fusing and shrinking the reaction tube to obtain the optical fiber perform.
Adjusting the temperature of the heating source to 2200 ℃, adjusting the air pressure in the tube, repeatedly collapsing the reaction tube for many times, and finally reversely collapsing to form the optical fiber preform.
And grinding the optical fiber preform into an octagon, and carrying out wire drawing and coating treatment to obtain the optical fiber. Referring to FIG. 2, the optical fiber includes a core 10, an inner cladding 20 and an outer cladding 30, the core 10 having a diameter of 22 μm, and the inner cladding 20 having a size of 130 μm. Note that fig. 2 does not show the outermost protective layer of the optical fiber.
And carrying out performance test on the optical fiber to obtain various parameters. Referring to FIG. 3, the relative refractive index of the core is about 0.0015, the numerical aperture is about 0.059, and the mode field diameter can reach 20 μm. Referring to FIG. 4, the absorption of 915nm light by the optical fiber can reach 5 db/m.
Example 2
S100, providing a reaction tube, wherein the outer diameter of the reaction tube is 20mm, and the inner diameter of the reaction tube is 16 mm. The reaction tube is arranged on the chemical vapor deposition equipment and is in a rotating state.
S110: and carrying out high-temperature corrosion on the inner wall of the reaction tube by adopting sulfur hexafluoride to remove surface impurities, and introducing oxygen to polish the inner surface of the reaction tube by utilizing a heating source. After the treatment, the inner wall of the reaction tube is smooth and has no impurities, which is beneficial to reducing the loss of the optical fiber.
S200, introducing silicon tetrachloride and oxygen into the reaction tube, adjusting the temperature of the heating source to 1470 ℃, heating the reaction tube, moving the heating source forward at the speed of 100mm/min, repeating the step for 3 times, and keeping the air pressure at the tail end of the reaction tube at 50Pa to prevent air from entering the reaction tube.
S300, continuously introducing silicon tetrachloride and oxygen into the reaction tube, adjusting the temperature of the heating source to 1570 ℃, moving the heating source forward at the speed of 100mm/min, and gradually depositing silicon dioxide generated by the reaction of the silicon tetrachloride and the oxygen to form a loose layer on the inner wall of the reaction tube.
Step S310: the temperature of the heating source was adjusted to 1480 ℃ and the reaction tube was heated, and the heating source was moved forward at a speed of 25mm/min to pre-sinter the porous layer. The loose layer closest to the inner wall of the reaction tube is slightly sintered at low temperature to stick the tube wall, so that the loose layer is prevented from being attached unreliably to cause falling off in the liquid phase doping process, and the temperature is low so as not to cause the collapse of the inner part of the loose layer to cause the reduction of doping.
S400, doping rare earth element ions and aluminum ions into the loose layer through liquid phase doping.
Specifically, anhydrous ytterbium chloride with a molar percentage of 1% and anhydrous aluminum chloride with a molar percentage of 2% are added to anhydrous methanol to prepare a doping solution. After the loose layer is prepared, the reaction tube is disconnected from the tail part, the disconnected position is a horn-shaped opening, and after the reaction tube is placed and cooled, the reaction tube is clamped on a liquid phase doping workbench and vertically inserted into the prepared doping solution. The end part of the reaction tube is connected with a peristaltic pump, the peristaltic pump pumps the doping solution into the reaction tube for one hour, so that rare earth element ions and aluminum ions in the doping solution are slowly immersed into the loose layer.
And after doping is finished, continuously and reversely clamping the reaction tube for drying for one hour, so that the methanol in the loose layer is slowly volatilized. Then the reaction tube is installed back to the MCVD equipment, oxygen is introduced, the temperature of the heating source is adjusted to 1050 ℃, and the doped ytterbium trichloride and aluminum trichloride are oxidized into ytterbium trioxide and aluminum oxide.
And introducing a mixed gas of chlorine, oxygen and helium into the reaction tube, and dehydrating and drying the loose layer at 1000 ℃.
Oxygen was introduced into the reaction tube to vitrify the porous layer at 2000 ℃.
S500, fusing and shrinking the reaction tube to obtain the optical fiber perform.
Adjusting the temperature of the heating source to 2200 ℃, adjusting the air pressure in the tube, repeatedly collapsing the reaction tube for many times, and finally reversely collapsing to form the optical fiber preform.
The optical fiber preform is ground into an octagon and drawn into an optical fiber with the core diameter ratio of 30/130, the relative refractive index of the core is about 0.0015, the numerical aperture is about 0.06, and the mode field diameter can reach 20 μm. The absorption rate of the optical fiber to the light with the 915nm wave band can reach 5 db/m.
Example 3
S100, providing a reaction tube, wherein the outer diameter of the reaction tube is 20mm, and the inner diameter of the reaction tube is 16 mm. The reaction tube is arranged on the chemical vapor deposition equipment and is in a rotating state.
S110: and carrying out high-temperature corrosion on the inner wall of the reaction tube by adopting sulfur hexafluoride to remove surface impurities, and introducing oxygen to polish the inner surface of the reaction tube by utilizing a heating source. After the treatment, the inner wall of the reaction tube is smooth and has no impurities, which is beneficial to reducing the loss of the optical fiber.
S200, introducing silicon tetrachloride and oxygen into the reaction tube, adjusting the temperature of the heating source to 1530 ℃, heating the reaction tube, moving the heating source forward at the speed of 130mm/min, and repeating the step for 3 times, wherein the air pressure at the tail end of the reaction tube is kept at 50Pa, so that air is prevented from entering the reaction tube.
S300, continuously introducing silicon tetrachloride and oxygen into the reaction tube, adjusting the temperature of the heating source to 1630 ℃, moving the heating source forward at a speed of 130mm/min, repeating the step for 2 times, and gradually depositing silicon dioxide generated by the reaction of the silicon tetrachloride and the oxygen to form a loose layer on the inner wall of the reaction tube.
Step S310: the temperature of the heating source was adjusted to 1520 deg.C, and the reaction tube was heated, and the heating source was moved forward at a speed of 40mm/min to pre-sinter the porous layer. The loose layer closest to the inner wall of the reaction tube is slightly sintered at low temperature to stick the tube wall, so that the loose layer is prevented from being attached unreliably to cause falling off in the liquid phase doping process, and the temperature is low so as not to cause the collapse of the inner part of the loose layer to cause the reduction of doping.
S400, doping rare earth element ions and aluminum ions into the loose layer through liquid phase doping.
Specifically, anhydrous ytterbium chloride with a molar percentage of 1% and anhydrous aluminum chloride with a molar percentage of 2% are added to anhydrous methanol to prepare a doping solution. After the loose layer is prepared, the reaction tube is disconnected from the tail part, the disconnected position is a horn-shaped opening, and after the reaction tube is placed and cooled, the reaction tube is clamped on a liquid phase doping workbench and vertically inserted into the prepared doping solution. The end part of the reaction tube is connected with a peristaltic pump, the peristaltic pump pumps the doping solution into the reaction tube for one hour, so that rare earth element ions and aluminum ions in the doping solution are slowly immersed into the loose layer.
And after doping is finished, continuously and reversely clamping the reaction tube for drying for one hour, so that the methanol in the loose layer is slowly volatilized. Then the reaction tube is installed back to the MCVD equipment, oxygen is introduced, the temperature of the heating source is adjusted to 1050 ℃, and the doped ytterbium trichloride and aluminum trichloride are oxidized into ytterbium trioxide and aluminum oxide.
And introducing a mixed gas of chlorine, oxygen and helium into the reaction tube, and dehydrating and drying the loose layer at 1000 ℃.
Oxygen was introduced into the reaction tube to vitrify the porous layer at 2000 ℃.
S500, fusing and shrinking the reaction tube to obtain the optical fiber perform.
Adjusting the temperature of the heating source to 2200 ℃, adjusting the air pressure in the tube, repeatedly collapsing the reaction tube for many times, and finally reversely collapsing to form the optical fiber preform.
The optical fiber preform is ground into an octagon and drawn into an optical fiber with the core diameter ratio of 22/130, the relative refractive index of the core is about 0.0015, the numerical aperture is about 0.06, and the mode field diameter can reach 20 μm. The absorption rate of the optical fiber to the light with the 915nm wave band can reach 5 db/m.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above examples only show some embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (9)
1. A method for preparing an optical fiber preform, comprising the steps of:
providing a reaction tube, installing the reaction tube on chemical vapor deposition equipment, and enabling the reaction tube to be in a rotating state;
introducing silicon tetrachloride and oxygen into the reaction tube, adjusting the temperature of a heating source to 1500 +/-30 ℃, heating the reaction tube, moving the heating source forward at a speed of 100-130 mm/min, and repeating the step for multiple times;
continuously introducing the silicon tetrachloride and the oxygen into the reaction tube, adjusting the temperature of the heating source to 1600 +/-30 ℃, moving the heating source forward at a speed of 100-130 mm/min, and gradually depositing silicon dioxide generated by the reaction of the silicon tetrachloride and the oxygen to form a loose layer on the inner wall of the reaction tube;
doping rare earth element ions and aluminum ions into the loose layer through liquid phase doping;
and melting and shrinking the reaction tube to obtain the optical fiber preform.
2. The production method according to claim 1, wherein the step of doping rare earth element ions and aluminum ions in the bulk layer by liquid phase doping comprises:
adding anhydrous rare earth element chloride with the mole percentage of 1% and anhydrous aluminum chloride with the mole percentage of 2% into the substrate solution to prepare a doping solution;
and placing the reaction tube in the doping solution, wherein the end part of the reaction tube is connected with a peristaltic pump, and the peristaltic pump pumps the doping solution into the reaction tube, so that the rare earth element ions and the aluminum ions in the doping solution are immersed in the loose layer.
3. The method according to claim 1, wherein the step of doping rare earth element ions and aluminum ions in the bulk layer by liquid phase doping is preceded by:
and adjusting the temperature of a heating source to 1500 +/-20 ℃, heating the reaction tube, and moving the heating source forward at a speed of 25-40 mm/min to pre-sinter the loose layer.
4. The preparation method according to claim 1, wherein silicon tetrachloride and oxygen are introduced into the reaction tube, the temperature of a heating source is adjusted to 1500 ± 30 ℃, the reaction tube is heated, the heating source is moved forward at a speed of 100-130 mm/min, and the steps are repeated for a plurality of times: the number of repetitions is greater than or equal to 2.
5. The preparation method according to claim 1, further comprising the following steps before introducing silicon tetrachloride and oxygen into the reaction tube:
and carrying out high-temperature corrosion on the inner wall of the reaction tube by adopting sulfur hexafluoride to remove surface impurities, and introducing oxygen to polish the inner surface of the reaction tube.
6. The method of claim 1, wherein the step of collapsing the reaction tube to produce the optical fiber preform further comprises:
and oxidizing the rare earth element ions and the aluminum ions in the loose layer to generate rare earth oxides and aluminum oxide, and dehydrating and drying the loose layer.
7. The preparation method according to claim 6, wherein the step of subjecting the porous layer to dehydration drying treatment specifically comprises:
and introducing mixed gas of chlorine, oxygen and helium into the reaction tube, and raising the temperature of the reaction tube to 1000-1200 ℃.
8. An optical fiber preform, characterized by being produced by the production method according to any one of claims 1 to 7.
9. An optical fiber produced by drawing and coating the optical fiber preform of claim 8.
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| CN114735931A (en) * | 2022-06-09 | 2022-07-12 | 武汉长进激光技术有限公司 | Boron rod, polarization maintaining optical fiber containing boron rod, and preparation method and application of polarization maintaining optical fiber |
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