A flexible multi-core optical fiber and a preparation method thereof

Abstract

The present invention discloses a flexible multi-core optical fiber and a preparation method thereof. The flexible multi-core optical fiber includes a cladding and a plurality of flexible optical fiber cores disposed inside the cladding. The plurality of flexible optical fiber cores are fixed to the inner wall of the cladding in a surrounding manner through a fixing material, and a filling material is filled between adjacent two flexible optical fiber cores. The cladding is a flexible hollow slender cylindrical structure, and the flexible optical fiber core is a solid slender cylindrical structure. Compared with the traditional preparation method of multi-core optical fibers, the preparation method proposed by the present invention is more economical and reliable, and multi-core flexible optical fibers with different structures, different compositions and different core numbers can be prepared by flexible use of the method. The flexible multi-core optical fiber prepared by the present invention has strong stretchability and flexibility, the refractive indexes of its cladding and core materials can be adjusted, and other specific recognition substances or sensing substances can be directly doped, and these advantages enable it to work in some scenarios with special requirements.

Description

Technical Field

[0001] The present invention relates to the field of multi-core optical fiber preparation applications, and particularly to a flexible multi-core optical fiber and a preparation method thereof. Background Art

[0002] With the continuous development of optical fiber technology, various new types of optical fiber structures have emerged. To solve the two major problems of reducing the manufacturing cost of optical fiber cables and developing high-density large-core-count optical fiber cables, in 1979, researchers proposed the concept of multi-core optical fiber, and subsequently, multi-core optical fiber has been widely studied and applied. Ordinary optical fiber is composed of a core region and a cladding region surrounding it, but multi-core optical fiber has multiple cores in a common cladding region. Due to the different degrees of proximity of the cores, there are two functions. One is that the core spacing is large, that is, a structure in which almost no optical coupling occurs between each core. This kind of optical fiber can increase the integration density per unit area of the transmission optical path. In optical communication, ribbon optical fiber cables with multiple cores can be made. The other is to make the distance between the cores close, which can produce optical wave coupling effects. Using this principle, multi-core sensors or optical loop devices can be developed.

[0003] Although traditional multi-core optical fiber with quartz as the core and cladding materials has been widely used in various fields, there are also certain problems and disadvantages. Since multi-core optical fiber is made of silica material, the optical fiber is brittle and easily broken, and usually needs to be armored. A support material with relatively high mechanical strength is wrapped outside the optical fiber as an outer armor to compensate for the mechanical properties of the multi-core optical fiber. Although armoring increases the mechanical properties of the multi-core optical fiber, it increases the preparation cost of the multi-core optical fiber and greatly reduces the flexibility of use of the multi-core optical fiber. Traditional quartz optical fiber has poor biocompatibility. If it is required to perform sensing detection and other scenarios inside or on the surface of a living body, when using traditional quartz optical fiber, it is easy to break and may cause rejection reactions in the living body. And the existing traditional quartz optical fiber has poor stretchability and flexibility, it is very difficult to achieve bending with a small radius, and the waveguide is not stretchable, which also limits its application range. Summary of the Invention

[0004] The purpose of the present invention is to provide a flexible multi-core optical fiber and a preparation method thereof, and to provide a low-cost, stretchable flexible multi-core optical fiber preparation method that can select a variety of available materials and whose core and cladding material sizes and refractive indices can be adjusted. The flexible multi-core optical fiber prepared by this preparation method has biocompatibility and can be naturally degraded. And the refractive index of its cladding and core materials can be adjusted, and other specific recognition substances or sensing substances can be directly doped. The existing traditional quartz optical fiber has a Young's modulus of 1 to 10 GPa at room temperature, while this flexible multi-core optical fiber has strong stretchability and a Young's modulus lower than 900 MPa at room temperature.

[0005] To achieve the above object, the present invention provides a flexible multi-core optical fiber, which includes a cladding and a plurality of flexible optical fiber cores disposed inside the cladding. The plurality of flexible optical fiber cores are fixed to the inner wall of the cladding in a surrounding manner by a fixing material, and a filling material is filled between adjacent two flexible optical fiber cores. The cladding is a flexible hollow slender cylindrical structure, and the flexible optical fiber core is a solid slender cylindrical structure.

[0006] A method for preparing a flexible multi-core optical fiber includes the following steps:

[0007] S1: Fill the core material into a hollow slender cylindrical core mold, perform a curing treatment on the core material. After the core material is cured, use a core mold treatment liquid to dissolve or corrode the outer core mold to prepare a flexible optical fiber core.

[0008] S2: Repeat the process of S1 to prepare any number of flexible optical fiber cores.

[0009] S3: Fill the cladding material into a hollow slender cylindrical cladding mold and stand it vertically. Part of the cladding material will adhere to the inner wall of the cladding mold, and the rest will flow out from the opening of the cladding mold. Through the curing treatment of the cladding material, the flexible optical fiber cladding material is cured.

[0010] S4: Control the cladding thickness by repeating the process of filling the cladding material in S3. After the prepared cladding material hollow tube is cured, dissolve or corrode the cladding mold to obtain the prepared cladding.

[0011] S5: Place the prepared flexible optical fiber core on the inner wall of the cladding, fill the fixing material into the gap between the flexible optical fiber core and the cladding, and perform a curing treatment after appropriately processing the fixing material.

[0012] S6: Fill the filling material into the gap of the flexible optical fiber core prepared in S5. After the curing treatment, the flexible multi-core optical fiber is finally prepared.

[0013] Preferably, the core material, the cladding material, the fixing material, and the filling material are each one of a mixed adhesive main agent - mixed adhesive secondary agent, gelatin - aqueous solution, polydimethylsiloxane - curing glue mixed solution, acrylamide - N,N - methylenebisacrylamide mixed solution, polyethylene glycol diacrylate - 2 - hydroxy - 2 - methylpropiophenone mixed solution.

[0014] Preferably, a refractive index modulation solution is doped in the core material, the cladding material, the fixing material, and the filling material, and the refractive index modulation solution is one or more of metal ion salts, sugars, and glycerol.

[0015] Preferably, when the core material, cladding material, fixing material, and filling material are one of the mixed adhesive main agent - mixed adhesive secondary agent, gelatin - aqueous solution, the curing treatment method becomes solid by standing still. When the core material, cladding material, fixing material, and filling material are a polydimethylsiloxane - curing glue mixed solution, the curing treatment method becomes solid by high - temperature treatment. When the core material, cladding material, fixing material, and filling material are one of the acrylamide - N,N’ - methylenebisacrylamide mixed solution, polyethylene glycol diacrylate - 2 - hydroxy - 2 - methylpropiophenone mixed solution, the curing treatment method becomes solid by ultraviolet irradiation.

[0016] Preferably, the materials of the core mold and the cladding mold are one or several of acrylonitrile - butadiene - styrene alcohol copolymer, polyethylene terephthalate, polyvinyl chloride, polyethylene, polypropylene, polystyrene, glass, fused silica, and plexiglass.

[0017] Preferably, the core mold treatment liquid and the cladding mold treatment liquid are one or several of acetone, chloroform, cyclohexanone, dimethylformamide, sodium hydroxide, hydrofluoric acid, concentrated phosphoric acid, chloroform, dichloroethane, ethanol, and toluene.

[0018] Preferably, the filling material includes one of air, the same as the fixing material, the same as the cladding material, and other flexible materials.

[0019] Therefore, the multi - core flexible optical fiber prepared by the method of the present invention has the following beneficial effects: 1. In the present invention, flexible materials are used to prepare optical fibers. Due to the excellent mechanical properties of flexible materials, compared with ordinary optical fibers, it has better bending characteristics and tensile characteristics, is easy to bend, and is not easy to break. It can be applied to some environments where traditional multi - core optical fibers are difficult to work, such as being more adaptable to the flexible and complex deformation conditions of the human body, so it is very suitable for wearable devices. 2. The process of preparing multi - core optical fibers in the present invention has high flexibility. Flexible optical fiber cores with various structures can be prepared. When preparing, different numbers of flexible optical fiber cores can be filled into the optical fiber according to needs, so as to make multi - core optical fibers with different core numbers. Different - core - number multi - core optical fibers can be prepared according to the different requirements between high optical fiber strength and high light - guiding density. And the thickness of the material can be adjusted to prepare various solid or hollow multi - core flexible optical fibers. 3. The refractive indices of the cladding and core materials of the flexible multi - core optical fiber prepared by the present invention are adjustable, and other specific recognition substances or sensing substances can be directly doped.

[0020] The following further describes the present invention in detail through the drawings and embodiments. Description of the Drawings

[0021] Figure 1 It is a schematic diagram of the preparation process of the flexible optical fiber core;

[0022] Figure 2 Schematic diagram of the preparation process for the cladding of a flexible optical fiber;

[0023] Figure 3 Schematic diagram of the preparation process for a flexible multi-core optical fiber;

[0024] Figure 4 Schematic diagram of an embodiment of a flexible dual-core optical fiber;

[0025] Figure 5 Schematic diagram of an embodiment of a flexible triple-core optical fiber;

[0026] Figure 6 Schematic diagram of an embodiment of a flexible quadruple-core optical fiber; Description of the Drawings

[0028] 1. Core mold; 2. Flexible optical fiber core; 3. Cladding; 4. Fixing material; 5. Filling material; 6. Cladding mold. Detailed Embodiments

[0029] The present invention will be further described below with reference to the drawings and embodiments.

[0030] The present invention provides a flexible multi-core optical fiber, including a cladding 3 and a plurality of flexible optical fiber cores 2 disposed inside the cladding 3. The plurality of flexible optical fiber cores 2 are fixed to the inner wall of the cladding 3 in a surrounding manner through a fixing material 4, and a filling material 5 is filled between adjacent two flexible optical fiber cores 2. The cladding 3 is a flexible hollow slender cylindrical structure, and the flexible optical fiber core 2 is a solid slender cylindrical structure.

[0031] A method for preparing a flexible multi-core optical fiber, the steps of which include:

[0032] S1: Fill the core material into a hollow slender cylindrical core mold 1, perform a curing treatment on the core material. After the core material is cured, use a core mold treatment liquid to dissolve or corrode the outer core mold 1 to prepare the flexible optical fiber core 2.

[0033] The material of the core mold 1 includes one or more of acrylonitrile-butadiene-styrene alcohol copolymer, polyethylene terephthalate, polyvinyl chloride, polyethylene, polypropylene, polystyrene, glass, quartz glass, and plexiglass.

[0034] The core mold treatment liquid is a solution that can dissolve or corrode the corresponding material mold, including one or more of acetone, chloroform, cyclohexanone, dimethylformamide, sodium hydroxide, hydrofluoric acid, concentrated phosphoric acid, chloroform, dichloroethane, ethanol, and toluene.

[0035] The shape of the core mold 1 is a hollow slender cylinder, and its inner diameter ranges from 8 μm to 2000 μm. For example, the inner diameter can be 8 μm, 10 μm, 20 μm, 30 μm, 50 μm, 80 μm, 100 μm, 150 μm, 200 μm, 400 μm, 600 μm, 800 μm, 1000 μm, 1200 μm, 1400 μm, 1600 μm, 1800 μm, 2000 μm.

[0036] The shape of the core mold 1 is a hollow slender cylinder, and its length ranges from 1 cm to 100 cm. For example, it can be 1 cm, 2 cm, 5 cm, 8 cm, 10 cm, 13 cm, 15 cm, 20 cm, 25 cm, 30 cm, 35 cm, 40 cm, 45 cm, 50 cm, 55 cm, 60 cm, 65 cm, 70 cm, 75 cm, 80 cm, 85 cm, 90 cm, 95 cm, 100 cm.

[0037] Other refractive index modulation solutions can be doped into the core material to regulate the refractive index. The refractive index modulation solutions include one or more of metal ion salts, sugars, glycerol, etc. The refractive index of the core material ranges from 1.43 to 1.55. For example, it can be 1.430, 1.435, 1.440, 1.445, 1.450, 1.455, 1.460, 1.465, 1.470, 1.475, 1.480, 1.485, 1.490, 1.495, 1.500, 1.505, 1.510, 1.515, 1.520, 1.525, 1.530, 1.535, 1.540, 1.545, 1.550.

[0038] S2: Repeat the process of S1 to prepare any number of flexible optical fiber cores 2. Their diameters and lengths depend on the selected resin tube mold, and the refractive index depends on the poured core material. The refractive index of the prepared flexible core can be regulated by changing the concentration or doping compounds.

[0039] S3: Fill the hollow slender cylindrical cladding mold 6 with the cladding material and let it stand vertically. The material of the cladding mold 6 is the same as that of the core mold 1. Since the cladding material has a certain viscosity, a small part will stick to the inner wall of the cladding mold 6, and the rest will flow out from the opening of the cladding mold 6. Through the curing treatment of the cladding material, the flexible optical fiber cladding material is cured.

[0040] The shape of the cladding mold 6 is a hollow long cylinder, and its length should match the core length. Its inner diameter ranges from 0.1 mm to 30 mm. For example, it can be 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 1 mm, 2 mm, 5 mm, 8 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm.

[0041] Other refractive index modulation solutions can be doped into the cladding material to control the refractive index. The refractive index modulation solution includes one or more of metal ion salts, sugars, glycerol, etc., but it is necessary to satisfy the conditions that the refractive index of the core is greater than that of the cladding and total internal reflection. Its refractive index range includes 1.39 - 1.45. For example, it can be 1.390, 1.395, 1.400, 1.402, 1.405, 1.408, 1.410, 1.412, 1.415, 1.418, 1.420, 1.425, 1.430, 1.435, 1.440, 1.445, 1.450.

[0042] S4: Control the cladding thickness by repeating the process of pouring the cladding material in S3. The thickness can be changed according to different requirements. After the prepared hollow tube of the cladding material is cured, dissolve or corrode the cladding mold 6. The treatment liquid for the cladding mold is the same as that for the core mold.

[0043] S5: Place the prepared flexible optical fiber core 2 inside the inner wall of the cladding 3. Fill the fixing material 4 into the gap between the flexible optical fiber core 2 and the cladding 3. Since the fixing material 4 has a certain viscosity, part of it will stick to the wall of the cladding 3 and the flexible optical fiber core 2. After proper treatment and curing of the fixing material 4, various types of flexible multi-core optical fibers can be formed. When filling the fixing material 4 for fixing, the thickness of the fixing material can be controlled by the quantity and number of times of filling the material, or the gap can be filled up.

[0044] The number of flexible optical fiber cores 2 fixed inside the cladding 3 can be any quantity. The position where the flexible optical fiber core 2 is placed can be any position inside the hollow tube of the cladding.

[0045] S6: Pour the filling material 5 into the gap of the flexible optical fiber prepared in S5. After curing treatment, the flexible multi-core optical fiber is finally prepared. The filling material 5 can be one of air, the same as the fixing material, the same as the cladding material, and other flexible materials.

[0046] The core material, cladding material, fixing material, and filling material are each one of a mixed adhesive main agent - mixed adhesive secondary agent, gelatin - aqueous solution, polydimethylsiloxane - curing glue mixed solution, acrylamide - N,N'-methylenebisacrylamide mixed solution, and polyethylene glycol diacrylate - 2 - hydroxy - 2 - methylpropiophenone mixed solution. Since the compositions of the processing materials are different, the methods for curing the materials are also different. When the core material, cladding material, fixing material, and filling material are one of the mixed adhesive main agent - mixed adhesive secondary agent and gelatin - aqueous solution, the curing method is to become solid by standing still. When the core material, cladding material, fixing material, and filling material are the polydimethylsiloxane - curing glue mixed solution, the curing method is to become solid by high - temperature treatment. When the core material, cladding material, fixing material, and filling material are one of the acrylamide - N,N'-methylenebisacrylamide mixed solution and polyethylene glycol diacrylate - 2 - hydroxy - 2 - methylpropiophenone mixed solution, the curing method is to become solid by ultraviolet irradiation.

[0047] Example 1

[0048] This example provides a method for preparing a dual - core flexible optical fiber, and a schematic diagram of its finished product is as Figure 4 shown.

[0049] Cross - linker N,N - methylenebisacrylamide, photo - curing agent, and an aqueous solution of lithium bromide for adjusting the refractive index are added to an aqueous acrylamide solution to obtain a hydrogel precursor.

[0050] A resin tube is used as the core mold 1 and filled with the hydrogel precursor, and polyacrylamide is polymerized and cured under ultraviolet irradiation. Then, the outer resin tube is corroded with an acetone solution and rinsed clean with ethanol to prepare the flexible optical fiber core 2. The core material in this example is polyacrylamide after adjusting the refractive index, and its flow chart is as Figure 1 shown.

[0051] The shape of the used core mold 1 is a hollow long cylinder, its inner diameter is 1200 μm, and its length is 30 cm. The size of the prepared core matches this, and the refractive index after modulation is 1.460.

[0052] This process is repeated to prepare two flexible optical fiber cores with the same parameters.

[0053] Polydimethylsiloxane and a curing agent are mixed evenly in a mass ratio of 10:1, and then the evenly - mixed liquid is placed in a sealed box and the air in the sealed box is completely evacuated by a vacuum pump so that there are no bubbles in the mixed polydimethylsiloxane liquid. Then, the polydimethylsiloxane - curing agent mixed solution after removing bubbles is used as the core liquid.

[0054] Using a resin tube as the cladding mold 6, pour the polydimethylsiloxane core liquid into its inner wall. Place the mold vertically and let the core liquid flow out. Due to the viscous resistance, polydimethylsiloxane will adhere to the inner wall of the cladding mold 6. Heat it at 80 °C for 40 min until the polydimethylsiloxane cures, and then a layer of cladding 3 is obtained. By repeating this process multiple times, the thickness of the cladding can be controlled. The thickness is 0.6 mm. After the prepared polydimethylsiloxane hollow tube cures, corrode the outer resin tube with acetone solution and rinse it clean with ethanol to prepare the cladding 3. The flowchart is as shown in Figure 2 shown.

[0055] The shape of the used cladding mold 6 is a hollow long cylinder, with an inner diameter of 8 mm and a length of 30 cm. The outer diameter and length of the obtained cladding match the mold, and the refractive index is 1.400.

[0056] Place the prepared flexible optical fiber core 2 into the inner wall of the cladding 3, and pour in a new fixing material 4. In this embodiment, the fixing material is polydimethylsiloxane. Heat it at 80 °C for 40 min to fix it. The thickness of the polydimethylsiloxane can be changed by the amount and number of layers added, and it is 0.8 mm.

[0057] Repeat the above process to fix both flexible optical fiber cores in the cladding 3. The shape is as shown in Figure 4 shown, and the flowchart is as shown in Figure 3 shown. Fill the gap between the cladding 3 and the flexible optical fiber core 2 with the new fixing material 4, polydimethylsiloxane. After heating at 80 °C for 40 min and fixing, a flexible dual-core optical fiber is obtained after curing.

[0058] Example 2

[0059] This embodiment provides a method for preparing a four-core flexible optical fiber. The schematic diagram of the finished product is as shown in Figure 6 shown.

[0060] Using a resin tube as the core mold 1, pour in the ultraviolet curable glue. After irradiating with ultraviolet light until the ultraviolet curable glue cures, then corrode the outer resin tube with acetone solution and rinse it clean with ethanol to obtain the prepared flexible optical fiber core 2. The flowchart is as shown in Figure 1 shown.

[0061] The shape of the used core mold 1 is a hollow long cylinder, with an inner diameter of 800 μm and a length of 20 cm. The size of the obtained core matches this, and after modulation, the refractive index is 1.480.

[0062] Repeat this process to prepare four flexible optical fiber cores 2 with the same parameters.

[0063] Mix polydimethylsiloxane and a curing agent evenly in a mass ratio of 10:1. Then place the evenly mixed liquid in a sealed box and use a vacuum pump to completely evacuate the air in the sealed box, so that there are no bubbles in the mixed polydimethylsiloxane liquid. Then use the polydimethylsiloxane-curing agent mixed solution without bubbles as the core liquid.

[0064] Use a resin tube as the cladding mold 6 and pour the polydimethylsiloxane core liquid into its inner wall. Place the mold vertically and let the core liquid flow out. Due to viscous resistance, polydimethylsiloxane will adhere to the inner wall of the cladding mold 6. Heat it at 80 °C for 40 min until the polydimethylsiloxane cures to obtain a layer of cladding 3. By repeating this process multiple times, the cladding thickness can be controlled. The thickness is 0.8 mm. After the prepared polydimethylsiloxane hollow tube cures, use an acetone solution to corrode the outer resin tube and rinse it clean with ethanol to prepare the cladding 3. Its flow chart is as Figure 2 shown.

[0065] The shape of the used cladding mold 6 is a hollow long cylinder, its inner diameter is 10 mm, and its length is 20 cm. The outer diameter and length of the obtained cladding match the mold, and the refractive index is 1.410.

[0066] Place the prepared flexible optical fiber core 2 into the inner wall of the cladding 3, and pour in a new fixing material 4. In this embodiment, the fixing material is polydimethylsiloxane. Heat it at 80 °C for 40 min to fix it. The thickness of the polydimethylsiloxane can be changed by the amount and number of layers added, and it is 0.8 mm.

[0067] Repeat the above process to fix four flexible optical fiber cores in the cladding. The shape is as Figure 6 shown. Pour in a filling material 5 of polydimethylsiloxane with a refractive index different from that of the cladding material and the fixing material, which is 1.400. After curing by heating at 80 °C for 40 min, a flexible four-core optical fiber is obtained.

[0068] Example 3

[0069] This embodiment provides a method for preparing a three-core flexible optical fiber. The schematic diagram of its finished product is as Figure 5 shown.

[0070] Use a resin tube as the core mold 1 and pour in gelatin. After the gelatin cures, use an acetone solution to corrode the outer resin tube and rinse it clean with ethanol to prepare the flexible optical fiber core 2. Its flow chart is as Figure 1 shown.

[0071] The shape of the used core mold 1 is a hollow long cylinder, its inner diameter is 1000 μm, and its length is 40 cm. The size of the obtained core matches this, and the refractive index after modulation is 1.470.

[0072] Repeat this process to prepare three flexible optical fiber cores 2 with the same parameters.

[0073] Mix polydimethylsiloxane and a curing agent in a mass ratio of 10:1 evenly. Then place the evenly mixed liquid in a closed box and use a vacuum pump to completely evacuate the air in the closed box, so that there are no bubbles in the mixed polydimethylsiloxane liquid. Then use the polydimethylsiloxane-curing agent mixed solution without bubbles as the core liquid.

[0074] Using a resin tube as the cladding mold 6, first place the three prepared flexible optical fiber cores around the inner wall of the mold. After the mold is set vertically, pour in the prepared polydimethylsiloxane core liquid. After heating at 80 °C for 40 min and the prepared polydimethylsiloxane is cured, corrode the outer resin tube with an acetone solution and rinse it clean with ethanol to prepare the cladding 3.

[0075] The shape of the used cladding mold 6 is a hollow long cylinder, with an inner diameter of 10 mm and a length of 40 cm. The outer diameter and length of the obtained cladding match the mold, and the refractive index is 1.400.

[0076] Then coat a layer of the same polydimethylsiloxane core liquid on the outer wall of the corroded optical fiber, with a thickness of 1 mm.

[0077] After heating at 80 °C for 40 min and the polydimethylsiloxane tube is cured, a three-core flexible optical fiber is obtained. The schematic diagram of its finished product is as Figure 5 shown.

[0078] Example 4

[0079] This example provides a method for preparing a two-core flexible optical fiber. The schematic diagram of its finished product is as Figure 4 shown.

[0080] Add a crosslinking agent N,N'-methylenebisacrylamide, a photoinitiator, and an aqueous lithium bromide solution for adjusting the refractive index to an aqueous acrylamide solution to obtain a hydrogel precursor.

[0081] Using a resin tube as the core mold 1, pour in the hydrogel precursor and polymerize and cure polyacrylamide under ultraviolet irradiation. Then corrode the outer resin tube with an acetone solution and rinse it clean with ethanol to prepare the flexible optical fiber core 2. In this example, the core material is polyacrylamide after adjusting the refractive index. Its flow chart is as Figure 1 shown.

[0082] The shape of the used core mold 1 is a hollow long cylinder, with an inner diameter of 1400 μm and a length of 50 cm. The size of the obtained core matches this, and the refractive index after modulation is 1.460.

[0083] Repeat this process to prepare two flexible optical fiber cores 2 with the same parameters.

[0084] Mix polydimethylsiloxane and a curing agent evenly at a mass ratio of 10:1. Then, place the evenly mixed liquid in a sealed box and use a vacuum pump to completely evacuate the air in the sealed box, so that there are no bubbles in the mixed polydimethylsiloxane liquid. After that, use the polydimethylsiloxane-curing agent mixed solution without bubbles as the core liquid.

[0085] Use a double-layer hollow cylindrical resin tube with coaxial different diameters as the cladding mold 6. Pour the polydimethylsiloxane core liquid into its inner wall, heat it at 80 °C for 40 min, and wait for the polydimethylsiloxane to cure to obtain a layer of cladding with a thickness of 1 mm. After the prepared polydimethylsiloxane hollow tube cures, corrode the resin tube and rinse the surface with ethanol to prepare the cladding 3. The flowchart is as Figure 2 shown.

[0086] The shape of the used cladding mold 6 is a hollow long cylinder, its inner diameter is 8 mm, and its length is 50 cm. The outer diameter and length of the prepared cladding match the mold, and the refractive index is 1.400.

[0087] Place the two prepared flexible optical fiber cores on both sides of the cladding 3, and the shape is as Figure 4 shown. Pour a new fixing material, polydimethylsiloxane, into the gap between the cladding 3 and the flexible optical fiber core 2, heat it at 80 °C for 40 min and then fix it. After curing, the flexible dual-core optical fiber is obtained.

[0088] Place the prepared flexible optical fiber core 2 into the inner wall of the cladding 3, and the shape is as Figure 4 shown. Pour a new fixing material 4. In this embodiment, the fixing material is polydimethylsiloxane. Heat it at 80 °C for 40 min to fix it. The thickness of the polydimethylsiloxane can be changed by the added quantity and number of layers, and it is 0.6 mm. After curing, the flexible dual-core optical fiber is obtained.

[0089] Example 5

[0090] This embodiment provides a method for preparing a dual-core flexible biocompatible optical fiber. The schematic diagram of the finished product is as Figure 4 shown.

[0091] Take two cylindrical hollow structure tubes of polystyrene with an inner diameter of 0.3 mm, a wall thickness of 0.1 mm, and a length of 250 mm as the core molds 1. Mix 8 g of gelatin, 12 g of water, and 5 g of sucrose, heat it to 80 °C and stir well to make the core precursor liquid. Seal one end opening of the two core molds 1, and while it is hot, inject the just-prepared core precursor liquid into the two flexible optical fiber core molds respectively.

[0092] Place the two core molds 1 filled with core precursor liquid in a cool place and let them stand still until they reach room temperature. After the temperature of the core precursor liquid drops, the gelatin inside attracts and intertwines with each other, thus forming a transparent and flexible solid structure.

[0093] Place the core mold 1 in an appropriate amount of toluene, corrode the core mold 1 by the sacrificial template method, take out the flexible optical fiber core 2, rinse the flexible optical fiber core 1 - 2 times with clean water, wipe the liquid on its surface clean, and place it in a dry place for standby.

[0094] Mix 16 g of polyethylene glycol diacrylate and 1 g of 2 - hydroxy - 2 - methylpropiophenone in 3 g of water to prepare a flexible optical fiber cladding precursor liquid.

[0095] Take a quartz cylindrical hollow - structure tube with an inner diameter of 1 mm, a wall thickness of 0.2 mm, and a length of 200 mm as the cladding mold 6. Place this mold vertically and fix it on the experimental bench. Pour the cladding precursor liquid into the cladding mold 6 from above. The precursor liquid in the mold slowly flows down under the influence of gravity. Most of the precursor liquid drops from the bottom of the cladding mold 6, and a small part of the precursor liquid adheres to the cladding tube wall. This process can be repeated several times to ensure that the inner tube wall of the cladding mold 6 is covered with the precursor liquid.

[0096] Use ultraviolet light with a main wavelength of 360 nm and a light power of more than 10 mW / cm 2 above to irradiate the cladding mold 6. Since the cladding mold 6 is made of a transparent material, at this time the cladding precursor liquid is directly irradiated by ultraviolet light, thus triggering the cross - linking and curing of polyethylene glycol diacrylate to form a transparent and flexible solid structure. After irradiating for 15 minutes, turn off the ultraviolet lamp. At this time, the polyethylene glycol diacrylate has been completely cured, and the cladding 3 is prepared.

[0097] Put together the two prepared flexible optical fiber cores 2, and insert one end of the flexible optical fiber core bundle 10 mm into the cladding mold 6. Take a syringe filled with clean water, inject water from the place where the flexible optical fiber core bundle is inserted into the cladding mold 6, and bring the flexible optical fiber core bundle into the cladding mold 6 by virtue of the water flow. Separate the two flexible optical fiber cores 2 inside the flexible optical fiber core bundle. Since the flexible optical fiber core 2 is 50 mm longer than the flexible optical fiber cladding, at this time, by pulling about 25 mm of the part of each flexible optical fiber core that is longer than the optical fiber cladding at both ends, make the flexible optical fiber core taut. Keep the flexible optical fiber core 2 in a taut state, take appropriately heated hot melt adhesive and drop it at the contact place between the part of the multi - flexible optical fiber core that is longer than the optical fiber cladding and the cladding mold, and stick the flexible optical fiber core 2 to the outer end of the cladding mold 6, then the temporary fixation of the flexible optical fiber core 2, the cladding mold 6 and the flexible optical fiber cladding 3 can be realized.

[0098] Pour the cladding precursor liquid as the fixing material 4 into the cladding mold 6 from above. The precursor liquid in the mold slowly flows downward under the influence of gravity. Most of the precursor liquid drips from the bottom end of the cladding mold, and a small amount of the precursor liquid adheres to the cladding tube wall and the flexible optical fiber core. This process can be repeated several times to ensure that the tube wall inside the cladding mold 6 and the flexible optical fiber core 2 are covered with the precursor liquid.

[0099] Use ultraviolet light with a main wavelength of 360 nm and an optical power of more than 10 mW / cm 2 to irradiate the cladding mold 6. Since the cladding mold 6 is made of a transparent material, the cladding precursor liquid is directly irradiated by ultraviolet light at this time, thereby triggering the crosslinking and curing of polyethylene glycol diacrylate to form a transparent and flexible solid structure. After irradiating for 15 minutes, turn off the ultraviolet lamp. At this time, the polyethylene glycol diacrylate has been completely cured.

[0100] Cut off the cores of the flexible optical fiber that are longer than the cladding at both ends. Place the cladding mold 6 in an appropriate amount of 50% sodium hydroxide solution and heat the sodium hydroxide solution. Corrode the cladding mold 6 by the sacrificial template method. Take out the prepared dual-core flexible optical fiber, rinse the core of the dual-core flexible optical fiber with clean water 2-3 times, and wipe the liquid on its surface clean to obtain the dual-core flexible optical fiber, as Figure 4 shown.

[0101] The cladding and core of the dual-core flexible optical fiber prepared in this embodiment are all made of biocompatible materials, and will not cause symptoms such as allergies and inflammation when contacting biological tissues. It can be used in the fields of biosensing, optogenetic therapy, etc. The obtained dual-core flexible optical fiber has excellent mechanical properties and optical properties. The core structure and the cladding structure work together to transmit optical signals. The air holes inside it and the large core spacing make the leaked signals in the cladding lower, and the crosstalk is smaller when using this dual-core flexible optical fiber.

[0102] In the present invention, the raw materials and equipment used, unless otherwise specified, are all common raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are all conventional methods in the art.

[0103] Therefore, the present invention adopts the above-mentioned flexible multi-core optical fiber and its preparation method to provide a preparation method of a stretchable flexible multi-core optical fiber with low cost, capable of selecting a variety of available materials, and the core and cladding material sizes and refractive indexes can be regulated. It can be applied to implant in organisms for sensing detection or used as an optical fiber optical tweezer for particle capture, etc.; it can be made into any shape to adapt to a variety of scientific research and application scenarios, such as being used in smart wearable devices, capable of fully conforming to the movement of organisms to achieve real-time monitoring, etc.; it can be compatible with a variety of materials to realize functional devices, for example, injecting magnetic fluid, liquid crystal, or chemically depositing materials such as titanium dioxide, graphene / graphene oxide during the preparation process to achieve various functions such as magnetic field, electric field, brain-like computing, and photocatalysis.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions of the present invention or make equivalent replacements, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a flexible multi-core optical fiber, characterized in that, it includes the following steps: S1: Fill the core material into a hollow and slender cylindrical core mold (1), perform a curing treatment on the core material. After the core material is cured, use a core mold treatment liquid to dissolve or corrode the outer core mold to prepare a flexible optical fiber core (2); S2: Repeat the process of S1 to prepare any number of flexible optical fiber cores (2); S3: Fill the hollow and slender cylindrical cladding mold (6) with the cladding material and stand it vertically. Part of the cladding material will adhere to the inner wall of the cladding mold (6), and the rest will flow out from the opening of the cladding mold (6). Through the curing treatment of the cladding material, the flexible optical fiber cladding material is cured; S4: Control the cladding thickness by repeating the process of filling the cladding material in S3. After the prepared hollow tube of the cladding material is cured, dissolve or corrode the cladding mold to obtain the prepared cladding (3); S5: Place the prepared flexible optical fiber core (2) on the inner wall of the cladding (3), fill the fixing material (4) into the gap between the flexible optical fiber core (2) and the cladding (3), and perform a curing treatment after appropriately treating the fixing material (4); S6: Pour the filling material (5) into the gap of the flexible optical fiber core (2) prepared in S5. After the curing treatment, the flexible multi-core optical fiber is finally prepared.

2. The method for preparing a flexible multi-core optical fiber according to claim 1, characterized in that: The core material, cladding material, fixing material, and filling material are each one of a mixed adhesive main agent - mixed adhesive secondary agent, gelatin - aqueous solution, polydimethylsiloxane - curing glue mixed solution, acrylamide - N,N - methylenebisacrylamide mixed solution, polyethylene glycol diacrylate - 2 - hydroxy - 2 - methylpropiophenone mixed solution.

3. The method for preparing a flexible multi-core optical fiber according to claim 1, characterized in that: The core material, cladding material, fixing material, and filling material are doped with a refractive index modulation solution, and the refractive index modulation solution is one or more of metal ion salts, sugars, and glycerol.

4. The method for preparing a flexible multi-core optical fiber according to claim 1, characterized in that: When the core material, cladding material, fixing material, and filling material are one of a mixed adhesive main agent - mixed adhesive secondary agent, gelatin - aqueous solution, the curing treatment method is to become solid by standing; when the core material, cladding material, fixing material, and filling material are a polydimethylsiloxane - curing glue mixed solution, the curing treatment method is to become solid by high-temperature treatment; when the core material, cladding material, fixing material, and filling material are one of an acrylamide - N,N'-methylenebisacrylamide mixed solution, polyethylene glycol diacrylate - 2 - hydroxy - 2 - methylpropiophenone mixed solution, the curing treatment method is to become solid by ultraviolet irradiation.

5. The method for preparing a flexible multi-core optical fiber according to claim 1, characterized in that: The materials of the core mold (1) and the cladding mold (6) are one or more of acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate, polyvinyl chloride, polyethylene, polypropylene, polystyrene, glass, fused silica, and plexiglass.

6. A method for preparing a flexible multi-core optical fiber according to claim 1, characterized in that: The core mold treatment liquid and the cladding mold treatment liquid are each one or more of acetone, chloroform, cyclohexanone, dimethylformamide, sodium hydroxide, hydrofluoric acid, concentrated phosphoric acid, chloroform, dichloroethane, ethanol, and toluene.

7. A method for preparing a flexible multi-core optical fiber according to claim 1, characterized in that: The filling material (5) is air, the same as the fixing material or the same as the cladding material.

8. A flexible multi-core optical fiber prepared by the preparation method according to any one of claims 1-7, characterized in that: It includes a cladding (3) and a plurality of flexible optical fiber cores (2) arranged inside the cladding (3). The plurality of flexible optical fiber cores (2) are fixed to the inner wall of the cladding (3) in a surrounding manner through a fixing material (4). A filling material (5) is filled between adjacent flexible optical fiber cores (2). The cladding (3) is a flexible hollow slender cylindrical structure, and the flexible optical fiber core (2) is a solid slender cylindrical structure.

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