Miniature bending-resistant low-loss high-temperature-resistant optical fiber and preparation method thereof

Abstract

The invention discloses a miniature bending-resistant low-loss high-temperature-resistant optical fiber and a preparation method thereof. The optical fiber comprises a fiber core, an inner cladding layer, a sunken layer, a first outer cladding layer, a second outer cladding layer, an inner coating layer and an outer coating layer, the relative refractive index difference delta 1 of the fiber core ranges from 0.30% to 0.89%, the relative refractive index difference delta 2 of the inner cladding ranges from-0.002% to-0.08%, the relative refractive index difference delta 3 of the sunken layer ranges from-0.3% to-0.015%, the relative refractive index difference delta 4 of the first outer cladding ranges from-0.1% to 0.02%, and the second outer cladding is a pure silicon dioxide glass layer. The optical fiber has high bending resistance, high temperature resistance and hydrogen loss resistance, and can solve the problems of narrow wiring space, stress concentration after aging and hydrogen loss increase of the traditional optical fiber in high temperature and other environments.

Description

Technical Field

[0001] The invention belongs to the technical field of communication optical fibers, and particularly relates to a miniature anti-bending, low-loss, and high-temperature resistant optical fiber and a preparation method thereof. Background Art

[0002] With the development of current information technology, optical fiber transmission technology has been widely used in the fields of communication and sensing. The low loss and low delay characteristics of optical fiber make it more and more common in deep sea, mining, oil well detection and other fields. By adjusting the coating material of conventional single-mode optical fiber accordingly, optical fiber products for use in special environments can be obtained; for example, by modifying acrylic resin materials or using polyimide polymer materials to replace conventional acrylic resin materials, optical fibers that can work normally at 150°C or even 300°C can be obtained. With this performance, it can be applied to some environmental detection fields under oil and gas wells. There are already relevant patents that have detailed descriptions and application examples in this regard. However, as the application of this type of optical cable in oil and gas wells becomes more popular, the detection conditions faced are also more complicated. The conventional use of terrestrial communication optical fiber, by improving the process route of the coating layer, can no longer meet the repeated use of optical fiber in a narrow, high temperature, and hydrogen-rich environment. The main problems it faces include stress fatigue caused by repeated use of optical cables, which reduces the transmission performance of optical fibers, and the rich H2S gas in the environment also leads to increased hydrogen loss of optical fibers, increased transmission loss, and space utilization of optical fibers in composite cables. Summary of the invention

[0003] In order to solve the above technical problems, the purpose of the present invention is to provide a miniature bending-resistant, low-loss, high-temperature-resistant optical fiber and a preparation method thereof. The optical fiber has the properties of high bending resistance, high temperature resistance, and hydrogen loss resistance, and can solve the problems of small wiring space, stress concentration after aging, and increased hydrogen loss encountered by traditional optical fibers in high-temperature environments.

[0004] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0005] A micro-bending-resistant, low-loss, high-temperature-resistant optical fiber, characterized in that it comprises a core, an inner cladding, a depressed layer, a first outer cladding, a second outer cladding, an inner coating and an outer coating; the relative refractive index difference Δ1 of the core is 0.30%-0.89%, the relative refractive index difference Δ2 of the inner cladding is -0.002% to -0.08%, the relative refractive index difference Δ3 of the depressed layer is -0.3% to -0.015%, the relative refractive index difference Δ4 of the first outer cladding is -0.1% to 0.02%, and the second outer cladding is a pure silica glass layer; the relationship between the radius R1 of the core layer, the radius R2 of the inner cladding, the radius R3 of the depressed layer, and the radius R4 of the first outer cladding satisfies the following: R1=2.75~3.5μm, R2 / R1=1.5~3, R3 / R1=3.5~4.5, R4 / R1=5~7.5.

[0006] Furthermore, the fiber core is germanium-doped silica.

[0007] Furthermore, the inner cladding is a CF4-doped silica glass layer.

[0008] Furthermore, the recessed layer is a fluorine-doped silica glass layer.

[0009] Furthermore, the first outer cladding layer is a CF4-doped silica glass layer.

[0010] Furthermore, the inner coating is a polyacrylic acid resin coating, and the outer coating is a high temperature resistant acrylic resin coating.

[0011] Furthermore, the density of the high temperature resistant polyacrylic resin coating used in the outer coating is 1.132 g / m 3 , the elastic modulus of the coating is between 650 and 950 MPa, and the modulus of the inner coating is 0.1-0.95 MPa.

[0012] Furthermore, the diameter of the second outer cladding is 110 μm, and the outer diameter of the outer coating is 195±15 μm.

[0013] The present invention further provides a method for preparing a micro-bending-resistant, low-loss, high-temperature-resistant optical fiber, comprising the following steps:

[0014] (1) Inert protective gas is introduced into the drawing furnace, and the optical fiber preform is melted and drawn through the drawing furnace to obtain a bare optical fiber;

[0015] (2) After the bare optical fiber is drawn out from the lower furnace port of the drawing furnace, it is annealed in a segmented annealing furnace, and the temperature of the segmented annealing furnace is set to a gradient type;

[0016] (3) The bare optical fiber is coated with polyacrylic acid resin twice and then cured to obtain a finished optical fiber.

[0017] Furthermore, the segmented annealing furnace has three zones, and the temperatures thereof are 950-1100°C, 850-950°C and 650-850°C respectively.

[0018] Beneficial effects of the present invention:

[0019] The optical fiber of the present invention has excellent bending resistance. Under the waveguide structure design and the specific coating structure design, in the bending test of R18mm*1000 turns, its macrobending loss reaches 0.005-0.015dB. In the cabling process, the macrobending loss in the tube caused by the large excess length can be overcome, and the stress sensitivity caused by repeated use can be suppressed.

[0020] The present invention adopts an optical fiber with an outer diameter of 180 to 210 μm, which can greatly solve the problem of the space capacity of optoelectronic composite cables in the current detection field. Compared with an optical fiber with a specification of 245 μm, it saves 30% of space, and the optical fiber cladding diameter is adjusted to 110 μm, which can reserve sufficient coating space for the inner coating and the outer coating.

[0021] The additional attenuation of the optical fiber of the present invention at 150-200°C can reach less than 5‰, and its transmission attenuation is less than 0.32dB / km in the 1310nm window and less than 0.18dB / km in the 1550nm window.

[0022] The tensile Weibull strength distribution of the optical fiber of the present invention can reach 4200-5000 MPa at 15% tensile strength, and can reach 4600-5500 MPa at 50% tensile strength.

[0023] The preparation method of the optical fiber of the present invention can better ensure the release of internal stress of the optical fiber and the self-healing of microcracks through gradient progressive annealing, and can further improve the attenuation performance of the optical fiber, which can be reduced to 4‰-7‰ compared with the attenuation of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a refractive index profile structure distribution diagram of the micro-bending-resistant, low-loss, and high-temperature-resistant optical fiber of the present invention.

[0025] Figure 2 It is a schematic diagram of the radial cross-sectional structure of the micro-bending-resistant, low-loss, and high-temperature-resistant optical fiber of the present invention.

[0026] Figure 3 It is the attenuation change curve of the micro anti-bending, low-loss and high-temperature resistant optical fiber of the present invention at 175°C. DETAILED DESCRIPTION

[0027] The technical solutions in the present invention will be described clearly and completely below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] like Figure 1 and Figure 2 As shown, a micro-bending-resistant, low-loss, and high-temperature-resistant optical fiber comprises a core, an inner cladding, a depressed layer, a first outer cladding, a second outer cladding, an inner coating, and an outer coating; the radius R1 of the core is 2.75-3.5 μm, the relative refractive index difference Δ1 is 0.30%-0.89%, the relative refractive index difference Δ2 of the inner cladding is -0.002%-0.08%, the relative refractive index difference Δ3 of the depressed layer is -0.3%-0.015%, the relative refractive index difference Δ4 of the first outer cladding is -0.1%-0.02%, and the second outer cladding is a pure silica glass layer; the relationship between the radius R1 of the core layer, the radius R2 of the inner cladding, the radius R3 of the depressed layer, and the radius R4 of the first outer cladding satisfies the following: R1=2.75-3.5 μm, R2 / R1=1.5-3, R3 / R1=3.5-4.5, and R4 / R1=5-7.5. The diameter of the second outer cladding is 110 μm, and the outer diameter of the outer coating is 195±15 μm.

[0029] Wherein, the core is germanium-doped silica; the inner cladding is a CF4-doped silica glass layer; the recessed layer is a fluorine-doped silica glass layer; and the first outer cladding is a CF4-doped silica glass layer.

[0030] The inner coating is a polyacrylic acid resin coating, and the outer coating is a high temperature resistant acrylic resin coating. The density of the high temperature resistant polyacrylic acid resin coating used in the outer coating is 1.132 g / m 3 The elastic modulus of the coating is between 650 and 950 MPa, and the modulus of the inner coating is 0.1-0.95 MPa. The refractive index of the cured outer coating is 1.52-1.54, the elongation at break is 23-25%, and the breaking strength is higher than 25 MPa. Under the size structure of the outer coating of 180-210 μm, the thickness ratio of the inner and outer coatings of the optical fiber is controlled in the range of 0.9-1.1.

[0031] The present invention further provides a method for preparing a micro-bending-resistant, low-loss, high-temperature-resistant optical fiber, comprising the following steps:

[0032] (1) Inert protective gas is introduced into the drawing furnace, and the optical fiber preform is melted and drawn through the drawing furnace to obtain a bare optical fiber;

[0033] (2) After the bare optical fiber is drawn out from the lower furnace port of the drawing furnace, it is annealed in a segmented annealing furnace, and the temperature of the segmented annealing furnace is set to a gradient type; the optical fiber drawing speed of this process is 350-600 m / min; the segmented annealing furnace has three zones, and the temperatures thereof are 950-1100°C, 850-950°C and 650-850°C respectively;

[0034] (3) The bare optical fiber is coated with polyacrylic acid resin twice, and then cured to obtain a finished optical fiber. During the coating process, the surface temperature of the optical fiber is controlled at 20-30°C, and a wet-to-dry two-step coating method or a wet-to-wet integrated coating process is adopted. The inner coating of the optical fiber adopts polyacrylic acid resin coating, and the outer coating adopts high-temperature resistant polyacrylic acid resin material. The curing process is UV-Led cold light source curing, and 5 groups of Led light sources are used for curing respectively. The power settings of the 5 groups of Led light sources are shown in Table 1.

[0035] Table 1

[0036] Group 1 Group 2 Group 3 Group 4 Group 5 75％ 75％ 70％ 65％ 50％

[0037] At a drawing speed of 300-450 m / min, the curing degree of the outer coating can reach 90%-97%. After curing, the optical fiber has the ability to work at 150℃-200℃. At the same time, the degree to which the optical fiber is affected by -OH and hydrogen ions in a H-rich environment is greatly reduced. Its typical attenuation performance at 175℃ is as follows: Figure 3 shown.

[0038] The optical fiber of the present invention has excellent bending resistance. Under the waveguide structure design and the specific coating structure design, in the bending test of R18mm*1000 turns, its macrobending loss reaches 0.005-0.015dB. In the cabling process, the macrobending loss in the tube caused by the large excess length can be overcome, and the stress sensitivity caused by repeated use can be suppressed.

[0039] The present invention adopts an optical fiber with an outer diameter of 180 to 210 μm, which can greatly solve the problem of the space capacity of optoelectronic composite cables in the current detection field. Compared with an optical fiber with a specification of 245 μm, it saves 30% of space, and the optical fiber cladding diameter is adjusted to 110 μm, which can reserve sufficient coating space for the inner coating and the outer coating.

[0040] The additional attenuation of the optical fiber of the present invention at 150-200°C can reach less than 5‰, and its transmission attenuation is less than 0.32dB / km in the 1310nm window and less than 0.18dB / km in the 1550nm window.

[0041] The tensile Weibull strength distribution of the optical fiber of the present invention can reach 4200-5000 MPa at 15% tensile strength, and can reach 4600-5500 MPa at 50% tensile strength.

[0042] The preparation method of the optical fiber of the present invention can better ensure the release of internal stress of the optical fiber and the self-healing of microcracks through gradient progressive annealing, and can further improve the attenuation performance of the optical fiber, which can be reduced to 4‰-7‰ compared with the attenuation of the present invention.

[0043] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0044] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A micro-bending-resistant, low-loss, high-temperature-resistant optical fiber, characterized in that: The invention comprises a fiber core, an inner cladding, a depressed layer, a first outer cladding, a second outer cladding, an inner coating and an outer coating; the relative refractive index difference Δ1 of the fiber core is 0.30%-0.89%, the relative refractive index difference Δ2 of the inner cladding is -0.002%-0.08%, the relative refractive index difference Δ3 of the depressed layer is -0.3%-0.015%, the relative refractive index difference Δ4 of the first outer cladding is -0.1%-0.02%, and the second outer cladding is a pure silica glass layer; the relationship between the radius R1 of the core layer, the radius R2 of the inner cladding, the radius R3 of the depressed layer and the radius R4 of the first outer cladding satisfies the following: R1=2.75-3.5μm, R2 / R1=1.5-3, R3 / R1=3.5-4.5, R4 / R1=5-7.

5.

2. A micro-bending-resistant, low-loss, high-temperature-resistant optical fiber according to claim 1, characterized in that: The fiber core is germanium-doped silicon dioxide.

3. The micro-bending-resistant, low-loss, high-temperature-resistant optical fiber according to claim 1, characterized in that: The inner cladding is a CF4-doped silica glass layer.

4. The micro-bending-resistant, low-loss, high-temperature-resistant optical fiber according to claim 1, characterized in that: The recessed layer is a fluorine-doped silica glass layer.

5. The micro-bending-resistant, low-loss, high-temperature-resistant optical fiber according to claim 1, characterized in that: The first outer cladding layer is a CF4-doped silica glass layer.

6. The micro-bending-resistant, low-loss, high-temperature-resistant optical fiber according to claim 1, characterized in that: The inner coating is a polyacrylic acid resin coating, and the outer coating is a high temperature resistant acrylic resin coating.

7. The micro-bending-resistant, low-loss, high-temperature-resistant optical fiber according to claim 6, characterized in that: The density of the high temperature resistant polyacrylic resin coating used in the outer coating is 1.132 g / m 3 , the elastic modulus of the coating is between 650 and 950 MPa, and the modulus of the inner coating is 0.1-0.95 MPa.

8. The micro-bending-resistant, low-loss, high-temperature-resistant optical fiber according to claim 1, characterized in that: The diameter of the second outer cladding is 110 μm, and the outer diameter of the outer coating is 195±15 μm.

9. A method for preparing the micro-bending-resistant, low-loss, high-temperature-resistant optical fiber according to any one of claims 1 to 8, characterized in that: The steps include: (1) Inert protective gas is introduced into the drawing furnace, and the optical fiber preform is melted and drawn through the drawing furnace to obtain a bare optical fiber; (2) After the bare optical fiber is drawn out from the lower furnace port of the drawing furnace, it is annealed in a segmented annealing furnace, and the temperature of the segmented annealing furnace is set to a gradient type; (3) The bare optical fiber is coated with polyacrylic acid resin twice and then cured to obtain a finished optical fiber.

10. The method for preparing a micro-bending-resistant, low-loss, high-temperature-resistant optical fiber according to claim 9, characterized in that: The segmented annealing furnace has three zones, and the temperatures thereof are respectively 950-1100°C, 850-950°C and 650-850°C.

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