Glass optical fiber preform and preparation method thereof

Abstract

The invention relates to a glass optical fiber preform and a preparation method thereof, and belongs to the technical field of glass optical fibers. The preform is composed of a core layer and a cladding layer, the core layer is mainly composed of ZrF4, AlF3, BaF2, LaF3, Er < 3 + > doped rare earth fluoride, K2SiF6 and Bi2O3, and the doping concentration of Er < 3 + > is high; and the cladding layer is composed of ZrF4, AlF3, PbF2, InF3 and NaF. A specific mass ratio of Bi2O3 to LaF3 in the core layer and a specific mass ratio of InF3 to PbF2 in the cladding layer are kept. The preparation method comprises a core layer preparation step and a cladding layer coating step, the core layer is formed by adopting a step-by-step melting and down-drawing method, the cladding layer is realized by adopting a plasma enhanced chemical vapor deposition method, SiCl4 / GeF4 mixed gas is introduced in the process, and InF3 steam is synchronously introduced to form a refractive index gradient. In the preparation process, deposition parameters such as the gas molar ratio, the carrier gas volume ratio and the GeF4 flow are also optimized. The glass optical fiber preform has excellent rare earth ion doping efficiency and optical performance stability, and is suitable for the field of optical fiber communication and sensing.

Description

Technical Field

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

[0002] In the field of optical fiber communication technology, as the core material for optical fiber manufacturing, the performance of glass optical fiber preforms directly affects the transmission efficiency and stability of optical fibers. Traditional glass optical fiber preforms mostly use quartz-based materials. However, in the mid-infrared band, the transmission loss of quartz-based optical fibers is relatively large, which limits their application in specific fields. Therefore, fluoride glass optical fiber preforms have attracted much attention due to their characteristics of low phonon energy and wide infrared transmission window.

[0003] There are still many deficiencies in the composition and preparation process of existing fluoride glass optical fiber preforms. On the one hand, the doping concentration and solubility of rare earth ions in the core layer are limited, which restricts the gain efficiency of optical fiber amplifiers and lasers. On the other hand, the control of the composition and refractive index distribution of the cladding is not precise enough, making it difficult to achieve an ideal gradient refractive index distribution, which in turn affects the mode field diameter and transmission bandwidth of the optical fiber.

[0004] In the preparation process, traditional methods often have problems such as complex processes, high costs, and difficulty in large-scale production. For example, during the melting and forming process of the core layer, defects such as crystallization and bubbles are likely to occur, affecting the optical properties of the preform. The deposition process of the cladding is also often difficult to precisely control, resulting in problems such as interface defects and uneven refractive index distribution.

[0005] In view of the above problems, the present invention provides a glass optical fiber preform and a preparation method thereof. By optimizing the composition design of the core layer and the cladding, the doping concentration and solubility of rare earth ions are increased, and at the same time, an accurate gradient refractive index distribution is achieved. In the preparation process, melting and deposition technologies are used to ensure the optical properties and mechanical strength of the preform, providing strong support for the development of optical fiber communication technology. Summary of the Invention

[0006] The purpose of the present invention is to provide a glass optical fiber preform and a preparation method thereof, which have the characteristic of low transmission loss.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A glass optical fiber preform, the preform is composed of a core layer and a cladding, and the specific composition of the core layer is as follows, by mass percentage: ZrF4 55-58%, AlF3 15-20%, BaF2 10-15%, LaF3 5-8%, Er 3+ Doped rare earth fluoride 3-5%, K2SiF6 2-4%, Bi2O3 0.5-0.8%;

[0009] Among them, the doping concentration of Er in the core layer 3+ is (1.5 - 2.5)×10 20 ions / cm 3 ;

[0010] The specific components of the cladding are as follows. By mass percentage, ZrF4 is 40 - 50%, AlF3 is 20 - 25%, PbF2 is 10 - 15%, InF3 is 8 - 12%, and NaF is 7 - 13%;

[0011] Furthermore, the rare earth fluoride is one of cerium fluoride and lanthanum fluoride.

[0012] Furthermore, the mass ratio of Bi2O3 to LaF3 in the core layer is 1:10.

[0013] Furthermore, the mass ratio of InF3 to PbF2 in the cladding is 1:1.25.

[0014] A method for preparing a glass optical fiber preform, and the specific process of the preparation method is as follows

[0015] S5.1: Core layer preparation

[0016] a. Mix ZrF4, AlF3, BaF2 and LaF3, and melt them under argon protection at 900 - 950°C for 2 - 3 h, and introduce ultrasonic oscillation during melting;

[0017] b. Add the rare earth fluoride doped with Er 3+ , K2SiF6 and Bi2O3, raise the temperature to 1000 - 1050°C and keep it warm for 1 h, and make the melt melt uniformly by the rotating crucible method, with the rotation speed of 10 - 15 rpm;

[0018] c. Adopt the down-drawing method to draw and form at a rate of 1 - 3 mm / min, and control the die temperature gradient at 50 - 80°C / cm to obtain the core layer;

[0019] S5.2: Cladding coating

[0020] a. Mix the cladding raw materials ZrF4, AlF3, PbF2, InF3, and NaF according to the ratio, grind them to a particle size of ≤5 μm, and preheat them to 600 - 650°C in an argon atmosphere and keep them warm for 30 min;

[0021] b. Adopt the plasma-enhanced chemical vapor deposition method, use the core layer as the substrate, introduce a SiCl4 / GeF4 mixed gas, with the carrier gas being Ar / O2, the pressure being 200 - 300 Pa, the deposition temperature being 1100 - 1150°C, and control the deposition rate at 2 - 4 μm / min;

[0022] c. Synchronously introduce InF3 vapor, and adjust the flow rate of GeF4 to make the refractive index of the cladding decrease in a gradient from the inside out, with a gradient change rate of 0.003 - 0.005 / μm and a deposition thickness of 1.2 - 1.5 times the core diameter;

[0023] d. After the deposition is completed, anneal at 800 - 850 °C for 2 - 3 h, introduce NF3 gas during the annealing process, and cool to room temperature at a rate of 10 °C / min after annealing to obtain the glass fiber preform.

[0024] Furthermore, in the SiCl4 / GeF4 mixed gas in S5.2, the molar ratio of the two is 1:(0.3 - 0.5).

[0025] Furthermore, in the carrier gas Ar / O2 in S5.2, the volume ratio of the two is 9:1.

[0026] Furthermore, the flow rate of GeF4 in S5.2 is 50 - 100 ml / min.

[0027] Through the composition optimization of the core and cladding and the innovation of the preparation process, the present invention has significantly improved the rare earth ion doping efficiency, optical performance stability, and interface quality of the fluoride glass fiber preform. In the core design, based on the ZrF4 - AlF3 - BaF2 - LaF3 glass system, by introducing Er 3+ The synergistic effect of the doped rare earth fluoride and Bi2O3 / K2SiF6 significantly enhances the stability of the glass network and the solubility of rare earth ions; among them, a specific mass ratio (1:10) of Bi2O3 and LaF3 can form a stable [BiO3]-[LaF6] composite structure, effectively inhibiting the phase separation tendency of the fluoride glass. At the same time, the lone pair electron effect of Bi 3 + can broaden the infrared transmission window of the glass and improve the fluorescence quantum efficiency of Er 3+ at the 1550 nm band. In addition, the introduction of K2SiF6 promotes the uniform dispersion of Er 3+ in the form of [ErF6] 3- in the glass network gaps by providing free F- ions. Combining the dynamic mixing of ultrasonic oscillation and the rotating crucible method, the doping concentration of Er 3+ reaches (1.5 - 2.5)×10 20 ions / cm 3 , which is about 50% higher than that of traditional fluorozirconate glass, providing a material basis for high - gain fiber amplifiers.

[0028] In the cladding design, the ZrF4-AlF3-PbF2-InF3-NaF system is taken as the core. By controlling the mass ratio of InF3 to PbF2 to be 1:1.25, a covalent network structure of [PbF4]-[InF6] is formed. Its lower polarizability significantly reduces the cladding refractive index compared to the core layer, and the coefficient of thermal expansion matches that of the core layer, reducing the interfacial stress during the high-temperature wire drawing process. Using plasma-enhanced chemical vapor deposition technology, with a SiCl4 / GeF4 mixed gas as the precursor, the refractive index gradient of the cladding is dynamically controlled by adjusting the GeF4 flow rate, and combined with the synchronous doping of InF3 vapor, a continuous gradient decrease in the cladding refractive index from the inside out is achieved. This gradient distribution can effectively suppress the intermodal dispersion of multimode fibers. At the same time, GeO2 generated by the decomposition of GeF4 and SiO2 generated by SiCl4 can form a gradient-doped SiO2-GeO2 composite layer, which enhances the interfacial bonding strength between the cladding and the core layer and reduces the optical scattering loss.

[0029] In terms of the preparation process, the core layer is formed by the step-by-step melting and down-drawing method. By adding different raw materials in stages under argon protection and combining the cavitation effect of ultrasonic oscillation on the melt, microcrystalline nuclei are effectively broken and bubbles are eliminated, raising the crystallization onset temperature of the glass to above 800 °C, significantly higher than the 600 - 700 °C of the traditional process. During the cladding deposition stage, through the synergistic effect of the oxidizing atmosphere of the carrier gas Ar / O2 and the NF3 annealing gas, In 3+ is oxidized to In 5+ , forming a stable [InF7] 2- structure. At the same time, the active F atoms generated by the decomposition of NF3 can repair the oxygen vacancy defects in the cladding glass, significantly reducing the transmission loss of the fiber preform.

[0030] Advantages of the present invention:

[0031] The fluoride glass fiber preform of the present invention has achieved significant improvements in many aspects through composition optimization and process innovation. In the core layer design, the introduction of specific proportions of Bi2O3, LaF3, and K2SiF6 enhances the stability of the glass network and increases the Er 3+ doping concentration, providing a material basis for high-gain fiber amplifiers. In the cladding design, the formation of the [PbF4]-[InF6] covalent network structure reduces the cladding refractive index, matches the coefficient of thermal expansion with the core layer, and reduces the interfacial stress. The application of plasma-enhanced chemical vapor deposition technology realizes a continuous gradient decrease in the cladding refractive index, effectively suppressing the intermodal dispersion, enhancing the interfacial bonding strength, and reducing the optical scattering loss. In the preparation process, the step-by-step melting and down-drawing method combined with ultrasonic oscillation raises the crystallization onset temperature; the synergistic effect of the Ar / O2 oxidizing atmosphere and the NF3 annealing gas repairs the oxygen vacancy defects, significantly reducing the transmission loss. Detailed Embodiments

[0032] To further illustrate the technical means and effects adopted by the present invention to achieve the intended invention purpose, the following will, in conjunction with the embodiments, elaborate in detail on the specific embodiments, structures, features and their effects of the present invention as follows.

[0033] Embodiment 1

[0034] A glass optical fiber preform, the preform is composed of a core layer and a cladding layer. The specific components of the core layer are as follows, by mass percentage: ZrF4 55%, AlF3 18%, BaF2 15%, LaF3 5%, Er 3+ Cerium fluoride doped with Er 3+ 3%, and the doping concentration of Er 20 is 2×10 3 ions / cm

[0035] K2SiF6 3.5%, Bi2O3 0.5%;

[0036] A method for preparing a glass optical fiber preform, the specific process of the preparation method is as follows,

[0037] S5.1: Core layer preparation

[0038] a. After mixing ZrF4, AlF3, BaF2 and LaF3, melt them at 900°C for 3 h under argon protection, and introduce ultrasonic oscillation during melting;

[0039] b. Add Er 3+ Cerium fluoride doped with, K2SiF6 and Bi2O3, raise the temperature to 1000°C and keep it warm for 1 h, and make the melt melt evenly by the rotating crucible method, with a rotation speed of 10 rpm;

[0040] c. Adopt the down-drawing method to draw and form at a rate of 2 mm / min, and control the mold temperature gradient at 70°C / cm to obtain the core layer;

[0041] S5.2: Cladding coating

[0042] a. Mix the cladding raw materials ZrF4, AlF3, PbF2, InF3, NaF according to the ratio, grind them to a particle size ≤ 5 μm, and preheat them to 600°C in an argon atmosphere and keep them warm for 30 min;

[0043] b. Using plasma-enhanced chemical vapor deposition method, with the core layer as the substrate, introducing a mixed gas of SiCl4 / GeF4. In the mixed gas, the molar ratio of the two is 1:0.4, the carrier gas is Ar / O2, the volume ratio of the two is 9:1, the pressure is 300 Pa, the deposition temperature is 1100 °C, and the deposition rate is controlled at 3 μm / min;

[0044] c. Synchronously introducing InF3 vapor, and making the refractive index of the cladding decrease in a gradient from inside to outside by adjusting the flow rate of GeF4. The flow rate of GeF4 is 50 ml / min, the gradient change rate is 0.003 μm, and the deposition thickness is 1.2 times the diameter of the core layer;

[0045] d. After the deposition is completed, annealing is carried out at 800 °C for 3 h. During the annealing process, NF3 gas is introduced, and after annealing, it is cooled to room temperature at a rate of 10 °C / min to obtain the glass fiber preform.

[0046] Example 2

[0047] A glass fiber preform, the preform is composed of a core layer and a cladding. The specific composition of the core layer is as follows, by mass percentage, ZrF4 58%, AlF3 16%, BaF2 10%, LaF3 8%, Er 3+ doped lanthanum fluoride 5%, Er 3+ doping concentration is 1.5×10 20 ions / cm 3 , K2SiF6 2.2%, Bi2O3 0.8%;

[0048] The specific composition of the cladding is as follows, by mass percentage, ZrF4 40%, AlF3 20%, PbF2 15%, InF3 12%, NaF 13%;

[0049] A method for preparing a glass fiber preform, the specific process of the preparation method is as follows,

[0050] S5.1: Core layer preparation

[0051] a. Mix ZrF4, AlF3, BaF2 and LaF3, and melt them at 950 °C for 2 h under argon protection. At the same time of melting, introduce ultrasonic oscillation;

[0052] b. Add Er 3+ doped cerium fluoride, K2SiF6 and Bi2O3, raise the temperature to 1050 °C and keep it warm for 1 h, and make the melt melt evenly by the rotating crucible method, and the rotation speed is 15 rpm;

[0053] c. Adopt the down-drawing method to draw and form at a rate of 1 mm / min, and control the die temperature gradient at 80 °C / cm to obtain the core layer;

[0054] S5.2: Cladding Coating

[0055] a. Mix the cladding raw materials ZrF4, AlF3, PbF2, InF3, and NaF according to the ratio, grind them until the particle size is ≤5 μm, preheat them to 650 °C in an argon atmosphere, and keep them warm for 30 min;

[0056] b. Using plasma-enhanced chemical vapor deposition method, with the core layer as the substrate, introduce the SiCl4 / GeF4 mixed gas. In the mixed gas, the molar ratio of the two is 1:0.3, the carrier gas is Ar / O2, the volume ratio of the two is 9:1, the pressure is 200 Pa, the deposition temperature is 1150 °C, and the deposition rate is controlled at 4 μm / min;

[0057] c. Synchronously introduce InF3 vapor, and adjust the GeF4 flow rate to make the cladding refractive index decrease gradually from the inside out. The flow rate of GeF4 is 100 ml / min, the gradient change rate is 0.005 μm, and the deposition thickness is 1.5 times the core layer diameter;

[0058] d. After the deposition is completed, anneal at 850 °C for 2 h. During the annealing process, introduce NF3 gas, and cool to room temperature at a rate of 10 °C / min after annealing to obtain the glass fiber preform.

[0059] Example Three

[0060] A glass fiber preform, the preform is composed of a core layer and a cladding layer. The specific composition of the core layer is as follows, by mass percentage, ZrF4 56%, AlF3 15%, BaF2 15%, LaF3 5%, Er 3+ doped cerium fluoride 5%, Er 3+ The doping concentration of is 2.5×10 20 ions / cm 3 、K2SiF6 3.5%, Bi2O3 0.5%;

[0061] The specific composition of the cladding layer is as follows, by mass percentage, ZrF4 40%, AlF3 20%, PbF2 15%, InF3 12%, NaF 13%;

[0062] A method for preparing a glass fiber preform, the specific process of the preparation method is as follows,

[0063] S5.1: Core Layer Preparation

[0064] a. Mix ZrF4, AlF3, BaF2 and LaF3, and melt them at 950 °C for 3 h under argon protection. Introduce ultrasonic oscillation while melting;

[0065] b. Add Er 3+Doped cerium fluoride, K2SiF6 and Bi2O3 are heated to 1000°C and held for 1 h. The melt is made uniform by the rotating crucible method at a rotation speed of 15 rpm.

[0066] c. The core layer is formed by pulling at a rate of 3 mm / min using the Czochralski method, and the temperature gradient of the mold is controlled at 50°C / cm.

[0067] S5.2: Cladding Coating

[0068] a. The cladding raw materials ZrF4, AlF3, PbF2, InF3, and NaF are mixed according to the ratio and ground to a particle size ≤ 5 μm, and preheated to 600°C in an argon atmosphere and held for 30 min.

[0069] b. Using plasma-enhanced chemical vapor deposition, with the core layer as the substrate, a SiCl4 / GeF4 mixed gas is introduced. In the mixed gas, the molar ratio of the two is 1:0.5, the carrier gas is Ar / O2, the volume ratio of the two is 9:1, the pressure is 200 Pa, the deposition temperature is 1150°C, and the deposition rate is controlled at 2 μm / min.

[0070] c. InF3 vapor is introduced synchronously, and the refractive index of the cladding is made to decrease gradually from the inside out by adjusting the flow rate of GeF4. The flow rate of GeF4 is 50 ml / min, the gradient change rate is 0.003 μm, and the deposition thickness is 1.2 times the diameter of the core layer.

[0071] d. After deposition, annealing is carried out at 800°C for 3 h. NF3 gas is introduced during the annealing process, and after annealing, it is cooled to room temperature at a rate of 10°C / min to obtain the glass fiber preform.

[0072] The transmission loss of the examples is detected with reference to the standard ITU-T G.650, and the test results are summarized in the following table.

[0073]

[0074] The above is only a preferred embodiment of the present invention, and does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or variations equivalent to the equivalent embodiments within the scope of the technical solution of the present invention without departing from the technical solution of the present invention. However, any brief modifications, equivalent variations, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A glass optical fiber preform, characterized in that, The preform consists of a core layer and a cladding layer. The specific components of the core layer are as follows, by mass percentage: ZrF4 55-58%, AlF3 15-20%, BaF2 10-15%, LaF3 5-8%, Er 3+ Doped rare earth fluoride 3-5%, K2SiF6 2-4%, Bi2O3 0.5-0.8%; Among them, the doping concentration of Er in the core layer 3+ is (1.5 - 2.5)×10 20 ions / cm 3 ; The specific components of the cladding are as follows. By mass percentage, ZrF4 is 40 - 50%, AlF3 is 20 - 25%, PbF2 is 10 - 15%, InF3 is 8 - 12%, and NaF is 7 - 13%.

2. A glass optical fiber preform according to claim 1, wherein, The rare earth fluoride is one of cerium fluoride and lanthanum fluoride.

3. A glass optical fiber preform according to claim 1, characterized in that, In the core layer, the mass ratio of Bi2O3 to LaF3 is 1:

10.

4. A glass optical fiber preform according to claim 1, characterized in that, In the cladding, the mass ratio of InF3 to PbF2 is 1:1.

25.

5. A method for preparing an optical fiber preform according to any one of claims 1 to 4, characterized in that, The specific process of the preparation method is as follows. S5.1: Core layer preparation a. After mixing ZrF4, AlF3, BaF2, and LaF3, melt them under argon protection at 900 - 950 °C for 2 - 3 h, and introduce ultrasonic oscillation during melting. b. Add Er 3+ The doped rare earth fluoride, K2SiF6 and Bi2O3 are heated to 1000 - 1050 °C and kept warm for 1 h. The melt is made uniform by the rotary crucible method, and the rotation speed is 10 - 15 rpm; c. Use the down-drawing method to draw and form at a rate of 1 - 3 mm / min, and control the die temperature gradient at 50 - 80 °C / cm to obtain the core layer. S5.2: Cladding coating a. Mix the cladding raw materials ZrF4, AlF3, PbF2, InF3, and NaF according to the ratio, grind them to a particle size ≤ 5 μm, preheat them to 600 - 650 °C in an argon atmosphere, and keep them warm for 30 min. b. Use the plasma-enhanced chemical vapor deposition method, with the core layer as the substrate, introduce a SiCl4 / GeF4 mixed gas, the carrier gas is Ar / O2, the pressure is 200 - 300 Pa, the deposition temperature is 1100 - 1150 °C, and control the deposition rate at 2 - 4 μm / min. c. Synchronously introduce InF3 vapor, and adjust the flow rate of GeF4 to make the refractive index of the cladding decrease gradually from the inside to the outside, with a gradient change rate of 0.003 - 0.005 / μm, and the deposition thickness is 1.2 - 1.5 times the diameter of the core layer. d. After deposition, anneal at 800 - 850 °C for 2 - 3 h, introduce NF3 gas during the annealing process, and cool to room temperature at a rate of 10 °C / min to obtain the glass fiber preform.

6. The preparation method of a glass optical fiber preform according to claim 5, characterized in that, In the SiCl4 / GeF4 mixed gas in S5.2, the molar ratio of the two is 1:(0.3 - 0.5).

7. A method for preparing a glass optical fiber preform according to claim 5, characterized in that, In the carrier gas Ar / O2 in S5.2, the volume ratio of the two is 9:

1.

8. The manufacturing method of an optical fiber preform according to claim 5, characterized in that, In S5.2, the flow rate of GeF4 is 50 - 100 ml / min.

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