Optical fibers and methods for manufacturing the same

Abstract

The present invention provides an optical fiber that can be used in high-temperature environments and a method for manufacturing the same. [Solution] The optical fiber 100 comprises a core 102, a cladding 104 covering the outer circumference of the core 102, a CNT coating 106 made of carbon nanotubes (CNTs) covering the outer circumference of the cladding 104, and a metal coating 108 made of metal covering the outer circumference of the CNT coating 106. The manufacturing method of the optical fiber 100 comprises the steps of forming the CNT coating 106 by winding a CNT film around a bare fiber portion consisting of the core 102 and the cladding 104 using a winding machine, and forming the metal coating 108 around the CNT coating 106 by electroplating.

Description

Technical Field

[0004] , ,

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[0001] The present invention relates to an optical fiber and a method for manufacturing the same.

Background Art

[0002] An optical fiber includes a core through which light propagates, a cladding that covers the outer periphery of the core, and a coating that covers the outer periphery of the cladding. By providing the coating, the optical fiber can be protected from mechanical damage and the external environment, enhancing the resistance of the optical fiber and extending its lifespan. Conventionally, as materials for the coating of optical fibers, for example, acrylate, polyimide, or a metal (e.g., gold / nickel) has been used (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The acrylate coating softens and loses its mechanical properties when the temperature exceeds 125°C. The polyimide coating oxidizes and becomes brittle when the temperature exceeds 300°C. The gold / nickel coating roughens the surface of a bare fiber made of silica glass and is formed by electroless plating. However, roughening the surface reduces the strength, and at temperatures above 400°C, due to the large difference in the thermal expansion coefficients of gold / nickel and the bare fiber, the coating peels off and the optical fiber is prone to breakage. Thus, in a high-temperature environment, there is a problem that the coating protection function is lost, significantly degrading the mechanical performance.

[0005] This invention has been made in view of the above problems, and aims to provide an optical fiber that can be used in high-temperature environments and a method for manufacturing the same. [Means for solving the problem]

[0006] The optical fiber according to the present invention comprises a core, a cladding covering the outer periphery of the core, and a carbon nanotube coating made of carbon nanotubes covering the outer periphery of the cladding.

[0007] The optical fiber manufacturing method according to the present invention comprises the step of winding a carbon nanotube film around a bare fiber portion consisting of a core and a cladding covering the outer circumference of the core using a winding machine to form a carbon nanotube coating. [Effects of the Invention]

[0008] According to the present invention, by providing a carbon nanotube coating to the optical fiber, the heat resistance of the optical fiber can be increased, making it usable even in high-temperature environments. [Brief explanation of the drawing]

[0009] [Figure 1A] This is a schematic diagram showing the structure of an optical fiber according to this embodiment. [Figure 1B] Figure 1A is a schematic diagram illustrating the grating region within an optical fiber. [Figure 2] This is a schematic diagram illustrating the process of removing the resin coating from an existing optical fiber to obtain a bare fiber portion. [Figure 3] This is a schematic diagram illustrating the process of cleaning the surface of the bare fiber section. [Figure 4A] This is a schematic diagram illustrating a system for wrapping a carbon nanotube (CNT) film around a bare fiber. [Figure 4B] This is a schematic diagram illustrating the extraction of CNT film from a CNT forest. [Figure 5]This is a schematic diagram illustrating the process of forming a metal coating around a CNT coating using electrolytic plating. [Figure 6] This graph shows the tensile strength of CNT-coated fibers with different numbers of layers at different temperatures. [Figure 7] This graph shows the tensile strength at different temperatures for bare fibers, resin-coated fibers, and CNT-coated fibers with different numbers of layers. [Figure 8] This graph shows the tensile strength of CNT-coated fibers at different temperatures with different winding angles. [Figure 9] This graph shows the tensile strength at different temperatures for bare fibers, resin-coated fibers, and CNT-coated fibers with different winding angles. [Figure 10] This graph shows the tensile strength of bare fiber, resin-coated fiber, CNT-coated fiber, and CNT-gold coated fiber at different temperatures. [Figure 11] This graph shows the tensile strength of various CNT-metal coated fibers at different temperatures. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will now be described with reference to the drawings. In the following embodiments, the same or similar components are denoted by the same reference numerals throughout the drawings. The drawings are schematic, and the relationship between planar dimensions and thickness, and the ratio of the thicknesses of each component, differ from those in reality. Furthermore, it goes without saying that there are parts where the dimensional relationships and ratios differ between drawings.

[0011] <Configuration of optical fibers> As shown in FIG. 1A, the optical fiber 100 of the present embodiment includes a core 102 made of silica glass, a cladding 104 made of silica glass that covers the outer periphery of the core 102 and has a refractive index lower than that of the core 102, a CNT coating 106 made of carbon nanotubes (CNT) that covers the outer periphery of the cladding 104, and a metal coating 108 made of metal that covers the outer periphery of the CNT coating 106. Examples of the material of the metal coating 108 include gold (Au), nickel (Ni), invar, platinum (Pt), copper (Cu), palladium (Pd), etc. The metal coating 108 is made of any one or two or more of these metals.

[0012] The optical fiber 100 is an optical fiber ultrasonic sensor for inspecting a structure in a high-temperature environment. As shown in FIG. 1B, a grating region 110 having a periodic refractive index modulation of the core 102 is provided in the core 102. The grating region 110 is a region where the refractive index in the axial direction (light propagation direction) of the core 102 is periodically modulated, and the phase of the refractive index modulation is shifted by a half cycle at the center of the grating region 110. With such a configuration, the optical fiber 100 functions as a regenerated phase-shifted fiber-optic Bragg grating sensor.

[0013] <Manufacturing method of optical fiber> Next, a manufacturing method of the optical fiber 100 will be described with reference to FIGS. 2 to 5.

[0014] First, a standard optical fiber 200, which is an existing optical fiber, is prepared. The standard optical fiber 200 includes a core 102, a cladding 104, and a coating made of resin or metal that covers the outer periphery of the cladding 104. Hereinafter, the case where the coating of the standard optical fiber 200 is made of a UV-curable resin will be described as an example.

[0015] As shown in FIG. 2, a part of the standard optical fiber 200 is immersed in concentrated sulfuric acid at room temperature for 30 minutes. As a result, the resin coating of the immersed part dissolves and peels off, obtaining a bare fiber part composed of the core 102 and the cladding 104.

[0016] Next, as shown in FIG. 3, the surface of the bare fiber part 300 is washed with acetone to remove residues (resin and sulfuric acid).

[0017] Next, using the winding machine 400 shown in FIG. 4A, while rotating the standard optical fiber 200 around the axis with a motor, a CNT film is wound around the bare fiber part 300 to form a CNT coating 106. Specifically, as shown in FIG. 4B, a CNT forest, which is a CNT array in which a large number of CNTs are vertically grown on a silicon substrate, is prepared, and a CNT film with a predetermined width is pulled out from the CNT forest using tweezers. Here, the CNTs are bonded by van der Waals forces and form a CNT film due to the tension.

[0018] Here, as shown in FIG. 4A, the CNT film is wound around the bare fiber part 300 so as to be oblique with respect to the axial direction of the bare fiber part 300. Specifically, the CNT film is pulled out from the CNT forest 401 on the moving stage 410, and while moving the moving stage 410 in the horizontal direction (the axial direction of the bare fiber part 300), the CNT film is wound from one end 301 to the other end 302 of the bare fiber part 300 at a winding angle θ1 to form the first layer of the CNT coating. Next, the CNT film is pulled out from the CNT forest 402 on the moving stage 420, and while moving the moving stage 420 in the horizontal direction, the CNT film is wound from the other end 302 to the one end 301 of the bare fiber part 300 at a winding angle θ2 to form the second layer of the CNT coating.

[0019] The winding angles θ1 and θ2 are the angles between the axial direction of the standard optical fiber 200 and the CNT film. For example, a multilayer CNT coating 106 can be formed by alternately winding CNT films from two CNT forests 401 and 402 onto the bare fiber portion 300 such that θ1 = +45° in the first layer, θ2 = -45° in the second layer, θ1 = +45° in the third layer, and θ2 = -45° in the fourth layer.

[0020] In Figure 4A, the sponge is provided to facilitate the rotation of the standard optical fiber 200. Furthermore, by spraying ethanol when winding the CNT film around the bare fiber section 300, a dense CNT coating 106 can be formed. In this way, the CNT film drawn from the CNT forests 401 and 402 can be easily wound around the bare fiber section 300 using the winding machine 400.

[0021] While carbon nanotubes (CNTs) are thermally stable up to 2000°C in a vacuum, they oxidize above 540°C in air. Therefore, to shield against oxygen and improve heat resistance, a metal coating 108 is formed around the CNT coating 106. Since the CNT coating 106 is conductive, the metal coating 108 can be formed by electroplating.

[0022] As shown in Figure 5, a platinum mesh is connected to the anode and the CNT coating 106 is connected to the cathode and immersed in the plating solution. When coating the CNT coating 106 with gold, the CNT coating 106 connected to the cathode is immersed in the gold plating solution and an electric current is passed through it, causing gold ions in the gold plating solution to move from the anode onto the CNT coating 106 and deposit, thereby forming the gold coating.

[0023] Figures 2 and 3 show the process of partially removing the coating from an existing standard optical fiber 200 to obtain a bare fiber portion 300. However, if an optical fiber product having a bare fiber portion 300 is prepared in advance, the above-described coating removal process becomes unnecessary.

[0024] Next, the results of tensile tests on CNT-coated fibers and CNT-metal coated fibers (Examples 1-4) will be described with reference to Figures 6-11. [Examples]

[0025] Figures 6 and 7 show the tensile strength of fibers coated with 1 to 4 layers of CNTs (without metal coating) after heating at 25°C (room temperature), 300°C, 500°C, and 700°C for 1 hour. For comparison, Figure 7 also shows the tensile strength of bare fibers and resin-coated fibers in addition to the CNT-coated fibers.

[0026] Figure 6 shows that the CNT-coated fiber maintains its mechanical strength up to 500°C. Furthermore, Figure 7 shows that at high temperatures (500°C and 700°C), the CNT-coated fiber has higher strength than the bare fiber and the resin-coated fiber, and that the strength is highest when the CNTs are in two layers. [Examples]

[0027] Figures 8 and 9 show the tensile strength of fibers coated with a single layer of CNTs at different winding angles (θ1 = 15°, 30°, 45°, 60°, 75°) after heating at 25°C (room temperature), 300°C, 500°C, and 700°C for 1 hour. For comparison, Figure 9 also shows the tensile strength of bare fibers and resin-coated fibers in addition to the CNT-coated fibers.

[0028] Figure 8 shows that the CNT-coated fiber maintains its mechanical strength up to 500°C. Furthermore, Figure 9 shows that the CNT-coated fiber at θ1 = 15°, 30°, 45°, and 60° has higher strength at high temperatures (500°C and 700°C) compared to the bare fiber and the resin-coated fiber, with the highest strength observed at θ1 = 30°. [Examples]

[0029] Figure 10 shows the tensile strengths obtained by tensile tests after heating uncoated bare fibers, UV-cured resin-coated fibers, CNT-coated fibers, and CNT-gold coated fibers at 25°C, 300°C, 500°C, 700°C, and 800°C for 1 hour. Here, the CNT-coated fibers and CNT-gold coated fibers have two layers of carbon nanotubes (CNTs) coated on them.

[0030] Figure 10 shows that the fiber coated only with CNTs exhibits the best strength after heating at 500°C. Furthermore, the CNT-gold coated fiber has lower strength than the other fibers, but after heating at 700°C it exhibits superior strength and maintains sufficient strength even after heating at 800°C. [Examples]

[0031] Figure 11 shows the tensile strength of various CNT-metal coated fibers after heating at 25°C, 300°C, 500°C, 700°C, and 800°C for 1 hour, as another example of the optical fiber 100 of this embodiment. Specifically, from left to right, the tensile strengths are shown for CNT-metal coatings of CNT / nickel / gold, CNT / gold / palladium / gold (outer gold thickness approximately 3 μm), CNT / gold (thickness 6 μm), and CNT / gold (thickness 10 μm).

[0032] Figure 11 shows that the fiber strength after heating to 700°C was highest for the CNT / gold / palladium / gold fiber, and that the strength increased with increasing gold coating thickness. Similarly, the fiber strength after heating to 800°C was highest for the CNT / gold / palladium / gold fiber, and that the strength increased with increasing gold coating thickness.

[0033] According to the optical fiber 100 of this embodiment, forming a CNT coating 106 around the bare fiber portion 300 not only enhances heat resistance but also improves hydrophobicity, preventing water erosion of the fiber surface. Furthermore, forming a metal coating 108 around the CNT coating 106 further enhances heat resistance, as well as corrosion resistance and ductility. Therefore, the optical fiber 100 can operate stably as an optical fiber ultrasonic sensor even in high-temperature environments.

[0034] The present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. [Explanation of symbols]

[0035] 100 optical fibers 102 cores 104 Clad 106 CNT coating 108 Metal coatings 110 Grating Area 200 standard optical fibers 300 Bare fiber section 400 Winding Machine 401, 402 CNT Forest

Claims

1. The core and A cladding covering the outer circumference of the core, A carbon nanotube coating consisting of carbon nanotubes covers the outer circumference of the cladding, Optical fiber equipped with

2. The optical fiber according to claim 1, further comprising a metal coating made of metal that covers the outer circumference of the carbon nanotube coating.

3. The optical fiber according to claim 2, wherein the metal coating consists of one or more of gold, nickel, Invar, platinum, copper, and palladium.

4. The optical fiber according to claim 1, wherein the core is provided with a grating region having periodic refractive index modulation of the core.

5. A method for manufacturing optical fibers, A method for manufacturing an optical fiber, comprising the step of winding a carbon nanotube film around a bare fiber portion consisting of a core and a cladding covering the outer circumference of the core using a winding machine to form a carbon nanotube coating.

6. The method for manufacturing an optical fiber according to claim 5, further comprising the step of forming a metal coating around the carbon nanotube coating by electroplating.

7. The method for manufacturing an optical fiber according to claim 5, further comprising the steps of preparing a standard optical fiber having the core, the cladding, and a coating made of resin or metal covering the outer circumference of the cladding, and obtaining the bare fiber portion by partially removing the coating of the standard optical fiber.

8. The method for manufacturing an optical fiber according to claim 5, wherein in the step of forming the carbon nanotube coating, the carbon nanotube film is wound so as to be oblique to the axial direction of the bare fiber portion.

9. The method for manufacturing an optical fiber according to claim 5, wherein in the step of forming the carbon nanotube coating, a plurality of layers of carbon nanotube film are wound around it.

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