A complex variable diameter optical fiber, its fabrication method and application

Abstract

This invention relates to the field of optical fiber fabrication technology, specifically disclosing a complex variable-diameter optical fiber, its fabrication method, and its applications. This invention achieves fiber diameter expansion and taper by etching and heat-treating specific locations on the optical fiber preform, forming multiple non-uniform diameter regions. Combined with annealing and drawing processes, it successfully fabricates a complex variable-diameter optical fiber. The fabrication method for complex variable-diameter optical fibers provided by this invention is simple, significantly improving the yield rate. It effectively solves the problems of existing technologies that require modification of the drawing tower conditions during the fabrication of complex variable-diameter optical fibers, resulting in complex operations and low yield rates.

Description

Technical Field

[0001] This invention relates to the field of optical fiber fabrication technology, and specifically discloses a complex variable diameter optical fiber, its fabrication method, and its applications. Background Technology

[0002] In recent years, high-power fiber lasers have made rapid progress, but the continuous improvement of their power has become increasingly difficult due to the effects of stimulated Raman scattering (SRS) and transverse mode instability. To address this issue, researchers have proposed various solutions, such as bending and coiling active fibers; applying gradient temperature or gradient stress to active fibers; and using variable-diameter fibers (e.g., tapered or spindle fibers). Among these, using variable-diameter fibers can achieve higher output power than conventional fibers with equivalent core diameter while maintaining comparable beam quality. Existing research has demonstrated that the stimulated Brillouin scattering gain coefficient of variable-diameter fibers is higher than that of conventional single-mode fibers, making them widely applicable in high-precision fiber sensing, ultra-narrow linewidth fiber lasers, and other fields. Therefore, research on the fabrication of variable-diameter fibers is of great significance.

[0003] However, current methods for achieving variable-diameter optical fibers involve altering drawing conditions, such as variable-speed rod feeding and variable-speed drawing. This process requires complex manual intervention and is difficult to implement for complex diameter variations, such as multi-point taper and multi-point expansion regions. Furthermore, the yield of complex variable-diameter optical fibers is low. Therefore, developing a simple method for fabricating complex variable-diameter optical fibers is of significant importance for further improving the power of high-power fiber lasers. Summary of the Invention

[0004] To address the problems of complex variable-diameter fiber fabrication processes requiring modification of the drawing tower conditions, which are complex and result in low yields, this invention provides a method and application for fabricating complex variable-diameter fibers. This invention achieves fiber diameter expansion and taper by etching and heat-treating specific locations on the fiber preform, forming multiple non-uniform diameter regions. Combined with annealing and drawing processes, complex variable-diameter fibers are successfully fabricated. The fabrication method provided by this invention is simple and significantly improves the yield of complex variable-diameter fibers.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] The first aspect of this invention provides a method for fabricating complex variable-diameter optical fibers, comprising the following steps:

[0007] Step 1: Weld extension preforms to both ends of the optical fiber preform, perform point etching on the optical fiber preform using inorganic acid, polish the etched points, and then heat treat the polished points at 1600-2000℃. At the same time as heat treatment, stretch or compress the extension preform along the axial direction to obtain the optical fiber preform with reduced diameter.

[0008] Step 2: Anneal, wash, dry, and draw the fiber preform after diameter reduction to obtain complex diameter-reduced optical fiber.

[0009] Preferably, the inorganic acid is a mixed acid solution of hydrofluoric acid, concentrated hydrochloric acid, and concentrated nitric acid.

[0010] Compared to existing technologies, this invention first fuses extension preforms to both ends of the optical fiber preform. Then, it etches specific points on the optical fiber preform using inorganic acid, followed by high-temperature softening of the etched points through heat treatment. Simultaneously, axial force is applied to the extension preform during softening, causing the softened areas to be stretched or compressed axially, forming non-uniform diameter regions that are expanded or tapered. The inventors discovered that the reduced-diameter optical fiber preform is prone to uneven internal stress, which can easily lead to fiber breakage during subsequent fiber drawing. Therefore, this invention performs an overall annealing treatment on the reduced-diameter optical fiber preform to eliminate this uneven internal stress. After eliminating the internal stress of the preform through annealing, complex reduced-diameter optical fibers can be obtained through a simple fiber drawing operation. The method for fabricating complex variable-diameter optical fibers provided by this invention can achieve multi-point diameter variation and obtain complex variable-diameter optical fibers with multiple non-uniform diameter regions according to different needs. This method does not require human intervention or changes to the drawing tower drawing conditions, which greatly reduces the drawing difficulty and improves the yield of complex variable-diameter optical fibers.

[0011] Preferably, the inorganic acid is a hydrofluoric acid solution, concentrated hydrochloric acid, and concentrated nitric acid in a volume ratio of 2:1-1.2:1.5-2; wherein the hydrofluoric acid solution contains 30%-40% hydrofluoric acid by mass.

[0012] Preferably, in step two, the annealing temperature is 900-1100℃ and the annealing time is 30-40h.

[0013] Annealing removes internal stress from the variable-diameter fiber preform, preventing uneven internal stress during subsequent fiber drawing and thus reducing the yield of complex variable-diameter fibers.

[0014] Preferably, in step two, the wire drawing speed is 20-30 m / min.

[0015] Preferably, the optical fiber preform is prepared by any one of chemical vapor deposition, plasma chemical vapor deposition, external vapor deposition, or axial vapor deposition.

[0016] Preferably, the optical fiber preform is either an active optical fiber preform or a passive optical fiber preform.

[0017] The fiber preform used in the method for fabricating complex variable-diameter optical fibers provided by this invention can be an active fiber preform or a passive fiber preform. This method can provide complex variable-diameter active optical fibers for high-power lasers and complex variable-diameter passive optical fibers for high-precision sensors, and can be widely used in the fields of fiber optic sensing and lasers.

[0018] More preferably, the active optical fiber preform is any one of erbium-doped optical fiber preform, thulium-doped optical fiber preform, ytterbium-doped optical fiber preform, holmium-doped optical fiber preform, or neodymium-doped optical fiber preform.

[0019] More preferably, the passive optical fiber preform is any one of a polarization-maintaining optical fiber preform, a single-mode optical fiber preform, a few-mode optical fiber preform, or a multi-core optical fiber preform.

[0020] Preferably, in step one, the heating method for the heat treatment is any one of oxyhydrogen flame heating, graphite furnace heating, or high-temperature plasma heating.

[0021] A second aspect of the present invention provides a complex variable-diameter optical fiber, which is prepared using the aforementioned method for preparing complex variable-diameter optical fibers.

[0022] A third aspect of the present invention provides an application of complex variable diameter in high-power lasers or high-precision sensors.

[0023] In summary, the method for fabricating complex variable-diameter optical fibers provided by this invention involves etching and softening specific locations on the optical fiber preform through heat treatment, followed by axial force applied to the preform to achieve fiber diameter expansion and taper formation, creating multiple non-uniform diameter regions. Combined with annealing and drawing operations, this method successfully fabricates complex variable-diameter optical fibers. This invention obtains complex variable-diameter optical fibers without requiring modification of the drawing conditions, simplifying the operation and significantly improving the yield of complex variable-diameter optical fibers by combining specific process parameters. This invention effectively solves the problem in existing technologies where the fabrication of complex variable-diameter optical fibers requires modification of the drawing tower conditions, resulting in complex operations and low yields. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] This embodiment provides a method for fabricating a complex variable-diameter optical fiber with three-point diameter variation, specifically including the following:

[0027] Step 1: Ytterbium-doped optical fiber preforms are prepared using chemical vapor deposition combined with high-temperature vapor phase doping. Extension preforms are fused to both ends of the optical fiber preforms. One-quarter of the pretreated optical fiber preform is etched using a hydrofluoric acid solution, concentrated hydrochloric acid, and concentrated nitric acid in a volume ratio of 2:1:2. After etching, the preforms are polished, and the etched areas are heat-treated using an oxyhydrogen flame at a temperature of 1750°C. Simultaneously, the extension preforms are axially compressed to obtain the first diameter variation region. The hydrofluoric acid solution contains 35% hydrofluoric acid by mass.

[0028] The pretreated optical fiber preform was etched at 2 / 4 of its length using a hydrofluoric acid solution, concentrated hydrochloric acid, and concentrated nitric acid in a volume ratio of 2:1:2. After etching, the preform was polished, and the second etched area was heat-treated with an oxyhydrogen flame at a temperature of 1820°C. Simultaneously, the preform was axially stretched to obtain the second diameter variation zone. The hydrofluoric acid solution contained 35% hydrofluoric acid by mass.

[0029] The pretreated optical fiber preform was etched at 3 / 4 of its length using a hydrofluoric acid solution, concentrated hydrochloric acid, and concentrated nitric acid in a volume ratio of 2:1:1.5. After etching, the preform was polished, and the third etched point was heat-treated with an oxyhydrogen flame at a temperature of 1800°C. Simultaneously, the preform was axially stretched to obtain a reduced-diameter optical fiber preform. The hydrofluoric acid solution contained 35% hydrofluoric acid by mass.

[0030] Step 2: Anneal the fiber preform after diameter reduction at 1100℃ for 32 hours. Clean and dry the surface of the treated fiber preform, and then draw it in a drawing furnace at a uniform drawing speed of 25m / min. After cooling, a complex variable diameter fiber with three-point diameter reduction is obtained. The yield rate is 97.8%.

[0031] Example 2

[0032] This embodiment provides a method for fabricating a complex variable-diameter optical fiber with three-point diameter variation, specifically including the following:

[0033] Step 1: Ytterbium-doped fiber preforms are prepared using chemical vapor deposition combined with high-temperature vapor phase doping. Extension preforms are fused to both ends of the fiber preforms. One-fifth of the pretreated fiber preform is etched using a hydrofluoric acid solution, concentrated hydrochloric acid, and concentrated nitric acid in a volume ratio of 2:1:1.6. After etching, the preforms are polished, and the etched sites are heat-treated using high-temperature plasma heating at a temperature of 1680℃. Simultaneously, the extension preforms are axially compressed to obtain the first diameter variation region. The hydrofluoric acid solution contains 30% hydrofluoric acid by mass.

[0034] The pretreated optical fiber preform was etched at 2 / 4 of its length using a hydrofluoric acid solution with a volume ratio of 2:1.2:2, concentrated hydrochloric acid, and concentrated nitric acid. After etching, the preform was polished, and the second etched area was heat-treated using high-temperature plasma heating at 1760°C. Simultaneously, the preform was axially stretched to obtain the second diameter variation region. The hydrofluoric acid solution contained 30% hydrofluoric acid by mass.

[0035] The pretreated optical fiber preform was etched at 3 / 5 of its length using a hydrofluoric acid solution with a volume ratio of 2:1.1:1.8, concentrated hydrochloric acid, and concentrated nitric acid. After etching, the preform was polished, and the third etched point was heat-treated using high-temperature plasma heating at a temperature of 1940°C. Simultaneously, the preform was axially stretched to obtain a reduced-diameter optical fiber preform. The hydrofluoric acid solution contained 30% hydrofluoric acid by mass.

[0036] Step 2: Anneal the fiber preform after diameter reduction at 1050℃ for 38 hours. Clean and dry the surface of the treated fiber preform, and then draw it in a drawing furnace at a uniform drawing speed of 26m / min. After cooling, a complex variable diameter fiber with three-point diameter reduction is obtained. The yield rate is 96.9%.

[0037] Example 3

[0038] This embodiment provides a method for fabricating a complex variable-diameter optical fiber with four-point diameter variation, specifically including the following:

[0039] Step 1: Ytterbium-doped fiber preforms are prepared using chemical vapor deposition combined with high-temperature vapor phase doping. Extension preforms are fused to both ends of the fiber preforms. One-sixth of the pretreated fiber preform is etched using a hydrofluoric acid solution, concentrated hydrochloric acid, and concentrated nitric acid in a volume ratio of 2:1.1:1.5. After etching, the preforms are polished, and the etched areas are heat-treated in a graphite furnace at a temperature of 1750°C. Simultaneously, the extension preforms are axially compressed to obtain the first diameter variation region. The hydrofluoric acid solution contains 38% hydrofluoric acid by mass.

[0040] The pretreated optical fiber preform was etched at 2 / 6 of its length using a hydrofluoric acid solution with a volume ratio of 2:1:1.8, concentrated hydrochloric acid, and concentrated nitric acid. After etching, the preform was polished, and the second etched area was heat-treated in a graphite furnace at a temperature of 1820°C. Simultaneously, the preform was axially stretched to obtain the second diameter variation zone. The hydrofluoric acid solution contained 38% hydrofluoric acid by mass.

[0041] The pretreated optical fiber preform was etched at 3 / 6 of its length using a hydrofluoric acid solution with a volume ratio of 2:1.1:1.6, concentrated hydrochloric acid, and concentrated nitric acid. After etching, the preform was polished, and the third etched point was heat-treated in a graphite furnace at a temperature of 1960°C. Simultaneously, the preform was axially stretched to obtain a reduced-diameter optical fiber preform. The hydrofluoric acid solution contained 38% hydrofluoric acid by mass.

[0042] The pretreated optical fiber preform was etched at 5 / 6 of its length using a hydrofluoric acid solution with a volume ratio of 2:1.1:2, concentrated hydrochloric acid, and concentrated nitric acid. After etching, the preform was polished, and the third etched point was heat-treated in a graphite furnace at a temperature of 1830°C. Simultaneously, the preform was axially compressed to obtain a reduced-diameter optical fiber preform. The hydrofluoric acid solution contained 38% hydrofluoric acid by mass.

[0043] Step 2: Anneal the fiber preform after diameter change at 900℃ for 40 hours. Clean and dry the surface of the treated fiber preform. Then, put it into a drawing furnace and draw it at a uniform speed of 20m / min. Cool it to obtain a complex variable diameter fiber with four-point diameter change. The yield rate is 96.7%.

[0044] Comparative Example 1

[0045] This comparative example provides a method for fabricating a complex variable-diameter optical fiber with three-point diameter variation. The difference from Example 1 is that the etching solution used is a pure hydrofluoric acid solution, while other operations and parameters remain unchanged. Specifically, it includes the following:

[0046] Step 1: Prepare ytterbium-doped fiber preforms using chemical vapor deposition combined with high-temperature vapor phase doping. Attach extension preforms to both ends of the fiber preforms. Etch 1 / 4 of the pretreated fiber preforms with hydrofluoric acid solution. Polish after etching. Heat-treat the etched areas with an oxyhydrogen flame at a temperature of 1750℃. Simultaneously, axially compress the extension preforms to obtain the first variable diameter region.

[0047] Two-quarters of the pretreated optical fiber preform is etched with hydrofluoric acid solution, polished after etching, and the second etched point is heat-treated with an oxyhydrogen flame at a temperature of 1820°C. At the same time, the extended preform is axially stretched to obtain the second variable diameter region.

[0048] The pretreated optical fiber preform is then etched at 3 / 4 of its length using hydrofluoric acid solution. After etching, it is polished and then heat-treated at the third etched point using an oxyhydrogen flame at a temperature of 1800°C. Simultaneously, the preform is axially stretched to obtain the optical fiber preform with a reduced diameter.

[0049] Step 2: Anneal the fiber preform after diameter reduction at 1100℃ for 32 hours. Clean and dry the surface of the treated fiber preform, and then draw it in a drawing furnace at a uniform drawing speed of 25m / min. After cooling, a complex variable diameter fiber with three-point diameter reduction is obtained. The yield rate is 52.1%.

[0050] Comparative Example 2

[0051] This comparative example provides a method for fabricating a complex variable-diameter optical fiber with three-point diameter variation. The difference from Example 1 is that no annealing treatment is performed on it, while other operations and parameters remain unchanged. Specifically, it includes the following:

[0052] Step 1: Ytterbium-doped optical fiber preforms are prepared using chemical vapor deposition combined with high-temperature vapor phase doping. Extension preforms are fused to both ends of the optical fiber preforms. One-quarter of the pretreated optical fiber preform is etched using a hydrofluoric acid solution, concentrated hydrochloric acid, and concentrated nitric acid in a volume ratio of 2:1:2. After etching, the preforms are polished, and the etched areas are heat-treated using an oxyhydrogen flame at a temperature of 1750°C. Simultaneously, the extension preforms are axially compressed to obtain the first diameter variation region. The hydrofluoric acid solution contains 35% hydrofluoric acid by mass.

[0053] The pretreated optical fiber preform was etched at 2 / 4 of its length using a hydrofluoric acid solution, concentrated hydrochloric acid, and concentrated nitric acid in a volume ratio of 2:1:2. After etching, the preform was polished, and the second etched area was heat-treated with an oxyhydrogen flame at a temperature of 1820°C. Simultaneously, the preform was axially stretched to obtain the second diameter variation zone. The hydrofluoric acid solution contained 35% hydrofluoric acid by mass.

[0054] The pretreated optical fiber preform was etched at 3 / 4 of its length using a hydrofluoric acid solution, concentrated hydrochloric acid, and concentrated nitric acid in a volume ratio of 2:1:1.5. After etching, the preform was polished, and the third etched point was heat-treated with an oxyhydrogen flame at a temperature of 1800°C. Simultaneously, the preform was axially stretched to obtain a reduced-diameter optical fiber preform. The hydrofluoric acid solution contained 35% hydrofluoric acid by mass.

[0055] Step 2: The surface of the modified optical fiber preform is cleaned and dried, then fed into a drawing furnace and drawn at a uniform speed of 25 m / min. After cooling, a complex modified optical fiber with three-point diameter variation is obtained; the yield rate is 42.38%.

[0056] Comparative Example 3

[0057] This comparative example provides a method for fabricating a complex variable-diameter optical fiber with three-point diameter variation. The difference from Example 1 is that the high-temperature treatment temperature used is 2100-2200℃, while other operations and parameters remain unchanged. Specifically, it includes the following:

[0058] Step 1: Ytterbium-doped fiber preforms are prepared using chemical vapor deposition combined with high-temperature vapor phase doping. Extension preforms are fused to both ends of the fiber preforms. One-quarter of the pretreated fiber preform is etched using a hydrofluoric acid solution, concentrated hydrochloric acid, and concentrated nitric acid in a volume ratio of 2:1:2. After etching, the preforms are polished, and the etched areas are heat-treated using an oxyhydrogen flame at a temperature of 2150°C. Simultaneously, the extension preforms are axially compressed to obtain the first diameter variation region. The hydrofluoric acid solution contains 35% hydrofluoric acid by mass.

[0059] The pretreated optical fiber preform was etched at 2 / 4 of its length using a hydrofluoric acid solution, concentrated hydrochloric acid, and concentrated nitric acid in a volume ratio of 2:1:2. After etching, the preform was polished, and the second etched area was heat-treated with an oxyhydrogen flame at a temperature of 2100°C. Simultaneously, the preform was axially stretched to obtain the second variable diameter region. The hydrofluoric acid solution contained 35% hydrofluoric acid by mass.

[0060] The pretreated optical fiber preform was etched at 3 / 4 of its length using a hydrofluoric acid solution, concentrated hydrochloric acid, and concentrated nitric acid in a volume ratio of 2:1:1.5. After etching, the preform was polished, and the third etched point was heat-treated with an oxyhydrogen flame at a temperature of 2200°C. Simultaneously, the preform was axially stretched to obtain a reduced-diameter optical fiber preform. The hydrofluoric acid solution contained 35% hydrofluoric acid by mass.

[0061] Step 2: Anneal the fiber preform after diameter reduction at 1100℃ for 32 hours. Clean and dry the surface of the treated fiber preform, and then draw it in a drawing furnace at a uniform drawing speed of 25m / min. After cooling, a complex variable diameter fiber with three-point diameter reduction is obtained. The yield rate is 23.67%.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fabricating complex variable-diameter optical fibers, characterized in that: Includes the following steps: Step 1: Weld extension preforms to both ends of the optical fiber preform, perform point etching on the optical fiber preform using inorganic acid, polish the etched points, and then heat treat the polished points at 1600-2000℃. At the same time as heat treatment, stretch or compress the extension preform along the axial direction to obtain the optical fiber preform with reduced diameter. Step 2: Anneal, wash, dry, and draw the modified optical fiber preform to obtain a complex modified optical fiber. The inorganic acid is a mixed acid solution of hydrofluoric acid, concentrated hydrochloric acid, and concentrated nitric acid; the inorganic acid is a hydrofluoric acid solution, concentrated hydrochloric acid, and concentrated nitric acid in a volume ratio of 2:1-1.2:1.5-2; and the hydrofluoric acid solution contains 30%-40% hydrofluoric acid by mass. In step two, the annealing temperature is 900-1100℃, and the annealing time is 30-40 hours. In step two, the wire drawing speed is 20-30 m / min.

2. The method for fabricating complex variable-diameter optical fibers as described in claim 1, characterized in that: The optical fiber preform is prepared using any one of the following methods: chemical vapor deposition, plasma chemical vapor deposition, external vapor deposition, or axial vapor deposition.

3. The method for fabricating complex variable-diameter optical fibers as described in claim 1, characterized in that: The optical fiber preform can be either an active optical fiber preform or a passive optical fiber preform.

4. The method for fabricating complex variable-diameter optical fibers as described in claim 3, characterized in that: The active optical fiber preform is any one of erbium-doped optical fiber preform, thulium-doped optical fiber preform, ytterbium-doped optical fiber preform, holmium-doped optical fiber preform, or neodymium-doped optical fiber preform; and / or The passive optical fiber preform is any one of polarization-maintaining optical fiber preform, single-mode optical fiber preform, few-mode optical fiber preform, or multi-core optical fiber preform.

5. The method for fabricating complex variable-diameter optical fibers as described in claim 1, characterized in that: In step one, the heating method for the heat treatment is any one of oxyhydrogen flame heating, graphite furnace heating, or high-temperature plasma heating.

6. A complex variable-diameter optical fiber, characterized in that: The complex variable diameter optical fiber is prepared using the fabrication method described in any one of claims 1-5.

7. The application of the complex variable-diameter optical fiber as described in claim 6 in high-power lasers or high-precision sensors.