A temperature resistant optical fiber having a ceramifiable coating and methods and systems for making the same

Abstract

The present application relates to a kind of temperature-resistant optical fiber with ceramic coating and its preparation method and system, comprising the following steps: coating silane coupling agent coating on bare optical fiber, form chemical grafting transition layer after curing, obtain first optical fiber;Flexible bonding coating is coated on first optical fiber, form flexible bonding pre-cured layer after curing, obtain second optical fiber;Flexible bonding coating includes first ceramic precursor polymer and flexible adjusting component;Rigid protective coating is coated on second optical fiber, form rigid protective pre-cured layer after curing, obtain first temperature-resistant optical fiber with polymer state coating;Rigid protective coating includes second ceramic precursor polymer and modified reinforcing filler;First temperature-resistant optical fiber can be treated by offline heat to form ceramic state coating, obtain second temperature-resistant optical fiber.The present application can obtain first temperature-resistant optical fiber with temperature resistance not more than 350 DEG C and second temperature-resistant optical fiber with temperature resistance above 600 DEG C, can effectively take into account coating processability and high temperature serviceability.

Description

Technical Field

[0001] This invention relates to the field of optical fibers, and more specifically to a heat-resistant optical fiber with a ceramicizable coating, and its preparation method and system. Background Technology

[0002] Fiber Bragg grating (FBG) sensors, especially grating arrays based on draw-trumping technology, have shown great potential in large-scale structural health monitoring (such as bridges, tunnels, and highways) due to their ability to achieve long-distance, high-density quasi-distributed measurements. However, when extending their monitoring range to high-temperature core areas such as aero-engines, gas turbines, and chemical reactors, a fundamental limitation is encountered: the fiber optic protective coating cannot simultaneously meet the requirements of "processability" and "high-temperature resistance" across a wide temperature range.

[0003] Currently, the coatings used for optical fibers in high-temperature environments mainly include organic polymer coatings, metal coatings, and direct ceramic coatings.

[0004] (1) Organic polymer coatings: such as polyimide, are currently the main coating choice for commercial high-temperature resistant optical fibers. Its advantages are that the process is mature and it is easy to coat and cure online during the fiber drawing process. However, its temperature resistance limit is usually 300-350℃. If it is exposed to temperatures above this for a long time, thermal oxidation, decomposition or carbonization will occur, leading to coating failure, fiber embrittlement and signal attenuation;

[0005] (2) Metal coatings: such as gold and aluminum, although they have high melting points, their preparation often relies on complex and expensive processes such as chemical vapor deposition and magnetron sputtering. More importantly, the difference in thermal expansion coefficients between metal materials and quartz optical fibers is significant, which will generate huge thermal stress during thermal cycling, making it very easy for the coating to crack or peel off from the fiber substrate, resulting in poor interface reliability;

[0006] (3) Direct ceramic coating: Oxide ceramic (such as Al2O3, SiO2) coatings prepared by sol-gel method, etc., have high theoretical temperature resistance, but their ceramic transformation process usually requires long-term high-temperature heat treatment, which is incompatible with the high-speed continuous optical fiber drawing process. More importantly, during this long ceramicization process, the coating will undergo significant non-uniform shrinkage and accumulate huge thermal stress, which is very easy to cause cracks or even peeling due to the mismatch between the thermal expansion and contraction behavior of the optical fiber substrate, making it difficult to form a complete, dense and firmly bonded protective layer.

[0007] Therefore, there is an urgent need to provide a coating material system and process in which the coating can exhibit a polymer "processable state" at room temperature or low temperature, so as to achieve efficient and continuous production using mature optical fiber coating technology; while in the high temperature environment of final use, it can transform into a ceramic-like "service-resistant state" to provide long-lasting protection. Summary of the Invention

[0008] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a heat-resistant optical fiber with a ceramicizable coating, as well as its preparation method and system, thereby solving the technical problem that it is difficult to balance the coating processability and high-temperature service performance of heat-resistant optical fibers in the prior art.

[0009] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows:

[0010] In a first aspect, the present invention provides a method for preparing a heat-resistant optical fiber with a ceramicizable coating, comprising the following steps: S1, coating a bare optical fiber with a silane coupling agent coating, and then grafting and curing it to form a chemical grafting transition layer to obtain a first optical fiber; S2, coating a flexible bonding coating on the first optical fiber, and then hydrosilylation and curing it to form a flexible bonding pre-cured layer to obtain a second optical fiber; the flexible bonding coating comprises a first ceramic precursor polymer and a flexible adjustment component; S3, coating a rigid protective coating on the second optical fiber, and then curing it to form a rigid protective pre-cured layer to obtain a first heat-resistant optical fiber with a polymeric coating; the rigid protective coating comprises a second ceramic precursor polymer and a modified reinforcing filler; and / or, further comprising: S4, subjecting the first heat-resistant optical fiber to offline heat treatment to form a ceramic coating to obtain a second heat-resistant optical fiber.

[0011] Secondly, the present invention provides a heat-resistant optical fiber prepared by the above-described preparation method.

[0012] Thirdly, the present invention provides a fabrication system for the aforementioned heat-resistant optical fiber, comprising an online pre-curing unit and an optional offline ceramicizing unit; the online pre-curing unit comprises a drawing module and a multi-stage coating and curing module arranged sequentially; the drawing module is used to obtain bare optical fiber; the multi-stage coating and curing module is used to sequentially coat and pre-cur a chemical grafting transition layer, a flexible bonding pre-curing layer and a rigid protective pre-curing layer on the bare optical fiber to obtain a first heat-resistant optical fiber; the offline ceramicizing unit is used to perform heat treatment on the first heat-resistant optical fiber to obtain a second heat-resistant optical fiber.

[0013] Compared with the prior art, the beneficial effects of the present invention include:

[0014] This invention involves coating a bare optical fiber with a chemical grafting transition layer, a flexible bonding pre-cured layer, and a rigid protective pre-cured layer, sequentially forming a gradient structure coating with increasing modulus from the inside out, resulting in a first heat-resistant optical fiber with a temperature resistance not exceeding 350℃. Simultaneously, the first heat-resistant optical fiber can be heat-treated to ceramicize the gradient structure coating, thereby obtaining a second heat-resistant optical fiber with a temperature resistance exceeding 600℃. The gradient structure is retained and strengthened during the transformation of the coating from a polymeric state to a ceramic state, and the transformed ceramic coating maintains a continuous gradient in composition and performance. Furthermore, the coating process of this invention can be directly combined with online optical fiber production processes, facilitating efficient and continuous production using mature optical fiber coating technologies. Therefore, the protective coating of this invention's heat-resistant optical fiber exhibits optimal performance under different temperature conditions: an easily processable polymeric state at room temperature and a durable ceramic state at high temperatures, effectively balancing coating processability and high-temperature serviceability, thus benefiting applications in a wide temperature range and extreme environments. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the preparation system of the present invention;

[0016] Figure 2 This is a schematic diagram of the structure of the first heat-resistant optical fiber in this invention;

[0017] The components are as follows: 1-Online pre-curing unit; 11-Wire drawing module; 1101-Preform feeding device; 1102-High temperature wire drawing furnace; 1103-First wire diameter gauge; 1104-Raster writing platform; 1105-Second wire diameter gauge; 12-Multi-stage coating and curing module; 1201-Coating device; 1202-Curing furnace; 13-Fiber optic take-up module; 14-Controller; 2-Offline ceramicization unit; 3-Bare optical fiber;

[0018] Figure 3 The images show the surface morphology of the coating on the first heat-resistant optical fiber in Example 1 of the present invention, and the surface morphology of the coating on the second heat-resistant optical fiber in Examples 1-2 and Comparative Examples 1-3 after cyclic thermal shock. Among them, (a) the coating on the first heat-resistant optical fiber in Example 1, (b) the coating on the second heat-resistant optical fiber in Example 1 after thermal shock, (c) the coating on the second heat-resistant optical fiber in Example 2 after thermal shock, (d) the coating on the second heat-resistant optical fiber in Comparative Example 1 after thermal shock, (e) the coating on the second heat-resistant optical fiber in Comparative Example 2 after thermal shock, and (f) the coating on the second heat-resistant optical fiber in Comparative Example 3 after thermal shock.

[0019] Figure 4 A schematic diagram of the flexibility of the polymer-state first heat-resistant optical fiber in Example 1. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] Currently, the coatings for optical fibers in high-temperature environments mainly include organic polymer coatings, metallic coatings, and direct ceramic coatings. Among them, organic polymer coatings are easy to apply and cure online during the fiber drawing process, but they have a low upper temperature limit, usually between 300 and 350°C. Long-term exposure to temperatures above this level will cause thermal oxidation, decomposition, or carbonization, leading to coating failure, fiber embrittlement, and signal attenuation. Metallic coatings usually require complex and expensive processes such as chemical vapor deposition and magnetron sputtering, and the significant difference in thermal expansion coefficients between metallic coatings and silica optical fibers makes them prone to detachment, resulting in poor interface reliability. Direct ceramic coatings often require long-term high-temperature heat treatment, which is incompatible with the high-speed continuous fiber drawing manufacturing process, and they also suffer from weak interface bonding.

[0022] To address the aforementioned shortcomings, the inventors attempted to design a coating material system and process. This coating can exhibit a polymer-like "processable state" at room temperature or low temperatures, enabling efficient and continuous production using mature optical fiber coating processes. Simultaneously, in the high-temperature environment of final use, it can transform into a ceramic-like "service-resistant state" to provide durable protection. The inventors discovered that polymer-derived ceramic coating technology can offer a new solution to the above problems. This type of material initially exists as a polymer solution, which can be easily coated onto the optical fiber surface and thermally cured to form a polymer coating, exhibiting good process compatibility. Subsequently, this coating can be transformed into corresponding ceramics such as SiC, Si3N4, or SiCN through controlled pyrolysis at medium to high temperatures (e.g., 500–900°C), thereby achieving excellent high-temperature stability. However, how to perfectly combine this material characteristic with the continuous manufacturing process of optical fibers, and ensure that the coating possesses reliable mechanical properties and interfacial adhesion in both states, remains a key technical problem to be solved.

[0023] Based on this, the present invention provides a high-temperature resistant optical fiber with a ceramizable coating, and its preparation method and system. This high-temperature resistant optical fiber is a novel high-temperature resistant optical fiber based on a "ceramizable" material system. Its protective coating is entirely composed of ceramizable ceramic precursor polymer materials, giving the coating the ability to transform from a "processable polymer" to a "high-performance ceramic," thereby flexibly providing different levels of protection performance according to the temperature requirements of the final application environment. The method of the present invention is efficient and continuous, and creatively combines "online forming" with "offline conversion," achieving a leapfrog improvement in product performance while ensuring process feasibility.

[0024] In a first aspect, the present invention provides a method for preparing a heat-resistant optical fiber with a ceramizable coating, comprising the following steps:

[0025] S1, a silane coupling agent coating is applied online to the bare optical fiber, and a chemical grafting transition layer is formed by grafting and curing to obtain the first optical fiber;

[0026] S2, a flexible bonding coating is applied online to the first optical fiber, and then cured by hydrosilylation to form a flexible bonding pre-cured layer, thus obtaining the second optical fiber; the flexible bonding coating includes a first ceramic precursor polymer and a flexible adjustment component;

[0027] S3, a rigid protective coating is applied online to the second optical fiber and cured to form a rigid protective pre-cured layer, resulting in a first heat-resistant optical fiber with a polymer coating; the rigid protective coating includes a second ceramic precursor polymer and modified reinforcing filler;

[0028] And / or, also includes:

[0029] S4, the first heat-resistant optical fiber is subjected to offline heat treatment to form a ceramic coating, thus obtaining the second heat-resistant optical fiber.

[0030] See Figure 1 This invention involves online coating of a bare optical fiber with a chemical grafting transition layer, a flexible bonding pre-cured layer, and a rigid protective pre-cured layer, forming a gradient structure coating with increasing modulus from the inside out, resulting in a first heat-resistant optical fiber with a temperature resistance not exceeding 350°C. Optionally, the first heat-resistant optical fiber can be heat-treated to ceramicize the gradient structure coating, thereby obtaining a second heat-resistant optical fiber with a temperature resistance above 600°C. The gradient structure is retained and strengthened during the transformation of the coating from a polymeric state to a ceramic state, and the transformed ceramic coating maintains a continuous gradient in composition and performance. Furthermore, the coating process of this invention can be directly combined with online optical fiber production processes, facilitating efficient and continuous production using mature optical fiber coating technologies.

[0031] Among them, the chemical grafting transition layer is derived from the condensation product formed by the reaction of silane coupling agent and silanol on the surface of optical fiber; the flexible bonding pre-cured layer mainly plays the role of flexible stress buffering and is derived from the thermal cross-linking network formed by the first ceramic precursor polymer and the flexible adjustment component; the rigid protective pre-cured layer is derived from the thermal cross-linking composite network formed by the second ceramic precursor polymer and the modified reinforcing filler.

[0032] The protective coating of the high-temperature resistant optical fiber of the present invention is composed of a ceramic precursor polymer material, which has two stable states: the polymeric coating is a thermosetting polymer, which gives the optical fiber good flexibility and processability, and is suitable for conventional manufacturing and medium temperature (≤350℃) environment; the coating is transformed into an inorganic ceramic phase after heat treatment, which gives the optical fiber excellent high temperature resistance (≥600℃) and resistance to environmental corrosion.

[0033] It should be noted that the offline heat treatment in step S4 of the present invention is optional. When the application environment temperature of the optical fiber is not higher than 350°C, the first heat-resistant optical fiber with polymer coating obtained in step S3 can be used directly. When the application environment temperature of the optical fiber is above 600°C, the second heat-resistant optical fiber with ceramic coating obtained in steps S1-S4 can be used directly.

[0034] In some embodiments, in step S1, the bare optical fiber is a bare optical fiber formed by melting and drawing a quartz preform and then grating it.

[0035] In some embodiments, in step S1, the silane coupling agent coating comprises, by mass percentage, 2.0–4.0 wt% γ-aminopropyltriethoxysilane, 96–98 wt% anhydrous ethanol, and 0.1–0.5 wt% glacial acetic acid. γ-aminopropyltriethoxysilane is the main functional substance for achieving chemical grafting; its hydrolysis products bond with the silanol groups on the optical fiber surface, while simultaneously providing amino groups for external bonding. Insufficient γ-aminopropyltriethoxysilane will not form a complete grafted layer, while excessive γ-aminopropyltriethoxysilane will easily lead to adsorption, thus reducing interfacial strength. Glacial acetic acid acts as an aid in promoting the hydrolysis of γ-aminopropyltriethoxysilane; insufficient acetic acid will result in incomplete hydrolysis, while excessive acetic acid will negatively impact subsequent coating application.

[0036] In some embodiments, in step S2, the flexible adhesive coating comprises 70–90 wt% of a first ceramic precursor polymer and 10–30 wt% of a flexible modifier component by weight percentage.

[0037] In some embodiments, in step S2, the first ceramic precursor polymer comprises vinyl polysilazane with an average molecular weight of about 1500.

[0038] In some embodiments, in step S2, the flexible adjustment component includes hydroxyl-terminated polydimethylsiloxane with a molecular weight of approximately 4000.

[0039] In some embodiments, in step S2, the coating pressure is 0.05 MPa to 0.2 MPa.

[0040] In some embodiments, in step S3, the rigid protective coating comprises, by mass percentage, 90–97 wt% of a second ceramic precursor polymer and 3–10 wt% of modified reinforcing filler.

[0041] In some embodiments, in step S3, the second ceramic precursor polymer includes at least one selected from perhydropolysilazane, methylpolysilazane, and phenylpolysilazane. This invention provides high hardness and high ceramic yield for rigid protective pre-cured layers using a second ceramic precursor polymer.

[0042] In some embodiments, in step S3, the modified reinforcing filler is prepared by mixing hydrophilic fumed silica and hexamethyldisilazane. Hexamethyldisilazane is used as a surface treatment agent for the reinforcing filler (fumed silica). Too little hexamethyldisilazane can easily lead to filler agglomeration, while too much can easily affect the coating performance.

[0043] Furthermore, the mass ratio of hydrophilic fumed silica to hexamethyldisilazane is 5:(1-2).

[0044] In some embodiments, in step S3, the coating pressure is 0.01 MPa to 0.1 MPa.

[0045] In some embodiments, the total thickness of the polymeric coating is 25–60 μm, and the flexible adhesive pre-cured layer accounts for 40–50% of the total thickness. This invention requires controlling the thickness of the polymeric coating. If the coating is too thin, its protective effect on the optical fiber is limited; if the coating is too thick, the shrinkage stress during high-temperature ceramization is too high, making the coating prone to cracking.

[0046] In some embodiments, the curing temperature is 150–350°C, and the curing time for a single layer does not exceed 30 seconds. By controlling the curing temperature and time, the polymer coating of the present invention can be continuously thermally cured online on a drawing tower, achieving rapid coating shaping and continuous production.

[0047] In some embodiments, the offline heat treatment conditions in step S4 include: holding at 500–900°C for 90–150 minutes in a protective atmosphere. After heat treatment, the coating is ceramicized, and the resulting heat-resistant optical fiber can withstand a high-temperature environment of not less than 600°C for a long time. After undergoing at least 10 thermal shock cycles from 600°C to room temperature, the ceramic coating can still maintain its structural integrity without cracking or peeling.

[0048] Furthermore, the heating rate for offline heat treatment is 2–4 °C / min; the cooling regime for offline heat treatment includes: after holding at a certain temperature, cooling to 100–150 °C at a rate of 2–4 °C / min, and then cooling to room temperature in the furnace. This invention employs a slow cooling method to avoid peeling of the ceramic coating after drastic cooling, which would affect performance.

[0049] Secondly, the present invention provides a heat-resistant optical fiber prepared by the above-described preparation method.

[0050] Thirdly, the present invention provides a system for fabricating the aforementioned heat-resistant optical fiber, see [link to documentation]. Figure 1 The system includes an online pre-curing unit 1 and an optional offline ceramicizing unit 2. The online pre-curing unit 1 includes a drawing module 11, a multi-stage coating and curing module 12, and an optical fiber take-up module 13 arranged sequentially. The drawing module is used to obtain bare optical fibers 3. The multi-stage coating and curing module 12 is used to coat and pre-cur the bare optical fibers 3 sequentially with a chemical grafting transition layer, a flexible bonding pre-curing layer, and a rigid protective pre-curing layer to obtain a first heat-resistant optical fiber. The optical fiber take-up module 13 is used to wind up the first heat-resistant optical fiber. The offline ceramicizing unit 2 is used to perform heat treatment on the first heat-resistant optical fiber to obtain a second heat-resistant optical fiber.

[0051] In some embodiments, the wire drawing module 11 includes a preform feeding device 1101, a high-temperature wire drawing furnace 1102, a first wire diameter gauge 1103, and a grating writing platform 1104 arranged sequentially.

[0052] In some embodiments, the multi-stage coating and curing module 12 includes three sets of coating devices 1201 and a curing oven 1202. The first coating device coats a silane coupling agent coating onto the bare optical fiber 3, and after heating in the first curing oven, forms a chemical grafting transition layer. The second coating device further coats a flexible adhesive coating onto the chemical grafting transition layer, and after heating in the second curing oven, forms a flexible adhesive pre-cured layer. The third coating device further coats a rigid protective coating onto the flexible adhesive pre-cured layer, and after heating in the third curing oven, forms a rigid protective pre-cured layer. The second and third curing ovens can be purged with a protective gas, such as nitrogen, as needed.

[0053] A second wire diameter meter 1105 is installed between the third curing oven and the optical fiber take-up module 13.

[0054] It is understood that the present invention sets a wire diameter meter between the high-temperature wire drawing furnace 1102 and the grating writing platform 1104, between the third curing furnace and the fiber take-up module 13, in order to detect and control the diameter of the optical fiber.

[0055] The preform feeding device 1101, grating writing platform 1104, multi-stage coating and curing module 12 and optical fiber take-up module 13 of the present invention are all connected to controller 14 to realize the monitoring and adjustment of wire drawing diameter, wire drawing speed, curing temperature, etc.

[0056] See Figure 2 The first heat-resistant optical fiber of the present invention includes a polymeric coating 4 disposed on a bare optical fiber 3. The polymeric coating 4 includes a chemical grafting transition layer 41, a flexible bonding pre-cured layer 42, and a rigid protective pre-cured layer 43. The flexible bonding pre-cured layer 42 forms a flexible toughening phase 4201 by adding a flexible adjustment component, and the rigid protective pre-cured layer 43 forms a rigid reinforcing phase 4301 by adding a modified reinforcing filler.

[0057] The essential characteristic of the optical fiber of this invention lies in the fact that its surface composite coating is prepared using a ceramic precursor polymer material that can be ceramized throughout the entire system. This positioning is the core of this invention, as it clarifies the intrinsic properties and performance potential of the coating material.

[0058] It should be noted that the coating in this invention is designed as a functionally graded structure, specifically including:

[0059] (1) Innermost layer (chemical grafting transition layer): It is a condensation product formed by the reaction of silane coupling agent and silanol on the surface of optical fiber, providing an interface with extremely strong chemical bonding;

[0060] (2) Intermediate layer (flexible adhesive pre-cured layer): It is derived from the first ceramic precursor polymer and the flexible adjustment component. It has a low modulus and is used to absorb and buffer thermal stress.

[0061] (3) Outermost layer (rigid protective pre-cured layer): It is derived from the second ceramic precursor polymer and modified reinforcing filler, with high modulus, providing mechanical strength and environmental protection;

[0062] (4) After the intermediate layer and the outermost layer are simultaneously ceramicized at high temperature, they are combined into a whole, but their gradient characteristics are preserved or even optimized, thus exhibiting excellent interface stability and mechanical integrity under extreme high temperature (such as above 600℃) and thermal cycling conditions.

[0063] Therefore, the heat-resistant optical fiber provided by this invention has two stable states, resulting in two products: a first heat-resistant optical fiber with a polymer coating and a second heat-resistant optical fiber with a ceramic coating. The coating on the surface of the first heat-resistant optical fiber has a three-layer structure and has been formed through an online process, but has not yet undergone high-temperature ceramicization treatment, and is in a high-performance polymer pre-cured state; the optical fiber in this state already possesses excellent mechanical properties and good medium-temperature (≤350℃) tolerance, and can be directly used in applications with relatively low requirements. The first heat-resistant optical fiber is the basis for finally obtaining the ceramicized second heat-resistant optical fiber, and also reflects the process flexibility of this invention.

[0064] The preparation method of this invention includes two core stages: (1) Online pre-curing coating preparation stage: On the optical fiber drawing tower, a continuous process of "coating one layer and curing one layer" is adopted to sequentially construct a chemical grafting transition layer, a flexible bonding pre-curing layer, and a rigid protective pre-curing layer on the surface of the bare optical fiber. This process is efficient, controllable, and compatible with existing optical fiber production lines. (2) Offline ceramicization treatment stage: The obtained pre-cured optical fiber is subjected to offline high-temperature heat treatment. In this process, by controlling the types and ratios of raw materials for the two coating layers, the two ceramic precursor polymers are simultaneously subjected to pyrolysis transformation to form a dense and firmly bonded gradient ceramic composite layer. This stage is the key to obtaining the final product with extreme high-temperature performance.

[0065] This invention creatively utilizes the "ceramization" property of coating materials, enabling the same coating system to possess two advantageous states: a polymer state that is easy to process and rapidly cures at room and medium temperatures, ensuring high compatibility with existing optical fiber drawing production lines and efficient continuous production; and a stable ceramic state that can be transformed entirely at extreme high temperatures, providing excellent resistance to high-temperature oxidation, thermal shock, and long-lasting protection. This fundamental characteristic solves the core contradiction of traditional coatings in balancing "process feasibility" and "high-temperature service performance." Based on this, the offline ceramicization stage of the gradient structure coating in this invention can be selected according to actual needs, offering flexibility. In both states (polymer and ceramic), it can effectively regulate stress distribution, strengthen interfacial bonding, and inhibit crack propagation, thereby significantly enhancing the mechanical integrity of the coating in the polymer state and its long-term environmental reliability in the ceramic state, achieving synergistic optimization from intrinsic material properties to macroscopic structural performance.

[0066] The invention will be further described in detail below through specific embodiments. The bare fiber fabrication steps include: drawing a quartz preform into a first bare fiber with a diameter of 125 μm in a drawing tower (furnace temperature 1950℃) at a drawing speed of approximately 12 m / min. Under tension control, the first bare fiber is immediately placed into an online grating platform. Using a 193 nm ArF excimer laser, the first bare fiber is subjected to single-pulse exposure through a phase mask, with a pulse energy of approximately 20 mJ and a repetition frequency of 2 Hz. A type I grating array with a reflectivity of approximately 0.05% and a grating spacing of 10 cm is continuously written onto the first bare fiber to obtain a second bare fiber. The bare fiber mentioned below refers to the second bare fiber after grating.

[0067] Example 1

[0068] A method for preparing a heat-resistant optical fiber with a ceramizable coating includes the following steps:

[0069] S1, mix 2.0 wt% γ-aminopropyltriethoxysilane, 97.8 wt% anhydrous ethanol and 0.2 wt% glacial acetic acid, and stir magnetically at room temperature for 60 minutes to obtain a silane coupling agent coating; coat the bare optical fiber surface with the silane coupling agent coating using a coating tool, then place it in a 1 m long curing oven and hold it in air at 200°C for about 5 seconds to complete the curing, forming a chemical grafting transition layer, and obtain the first optical fiber;

[0070] S2, mix 80.0 wt% vinyl polysilazane (average molecular weight ~1500) and 20 wt% hydroxyl-terminated polydimethylsiloxane (molecular weight ~4000), planetarily stir for 2 hours, and vacuum degas to obtain a flexible adhesive coating; use a pressure coater (pressure of 0.1 MPa) to coat the first optical fiber with the flexible adhesive coating, and set the wet film thickness to 25 μm; put it into a curing oven with high-purity nitrogen, and hold it at 250°C for about 5 seconds to form a flexible adhesive pre-cured layer through hydrosilylation curing, with a dry film thickness of about 20 μm, to obtain the second optical fiber;

[0071] S3, 5.0 wt% hydrophilic fumed silica and 1.5 wt% hexamethyldisilazane were treated in a high-speed mixer to hydrophobize the surface; then the treated filler was mixed with 93.5 wt% perhydropolysilazane, and a uniform rigid protective coating was obtained by high-speed shear emulsification and three-roll milling; the rigid protective coating was coated on the second optical fiber using a pressure coating cup (pressure of 0.05 MPa), with a wet film thickness of 30 μm. The fiber was then placed in a nitrogen atmosphere curing oven and cured at 300°C for about 5 seconds to form a rigid protective pre-cured layer with a dry film thickness of about 25 μm, resulting in a first heat-resistant optical fiber with a polymer coating (total coating thickness of about 45 μm); the first heat-resistant optical fiber was then retrieved onto a standard optical fiber reel via a traction wheel.

[0072] S4. The first heat-resistant fiber on the standard fiber optic tray is placed into a programmable temperature-controlled muffle furnace. High-purity nitrogen is continuously introduced into the furnace, and the temperature is raised from room temperature to 600°C at a rate of 3°C / min, and then held at 600°C for 90 minutes. Subsequently, the temperature is programmed to drop to 150°C at a rate of 3°C / min, the heating is turned off, and the fiber is cooled to room temperature with the furnace to obtain the second heat-resistant fiber. At this time, the total thickness of the ceramic gradient coating is about 25μm.

[0073] Example 2

[0074] Compared with Example 1, the only difference is that the dry film thickness of the flexible adhesive pre-cured layer is adjusted to 30 μm, and the dry film thickness of the rigid protective pre-cured layer is 30 μm; the other steps and conditions are the same as in Example 1.

[0075] Comparative Example 1

[0076] Compared with Example 1, the only difference is that the dry film thickness of the flexible adhesive pre-cured layer is adjusted to 5 μm and the dry film thickness of the rigid protective pre-cured layer is adjusted to 15 μm, so that the total coating thickness is 20 μm; other steps and conditions are the same as in Example 1.

[0077] Comparative Example 2

[0078] Compared with Example 1, the only difference is that the process of layer-by-layer coating and curing is adjusted to "wet-on-wet", that is, after sequentially coating the chemical grafting liquid, flexible layer liquid and rigid layer liquid (none of the three layers are cured separately), a concentrated curing is performed; other steps and conditions are the same as in Example 1.

[0079] Comparative Example 3

[0080] Compared with Example 1, the only difference is that the order of the flexible adhesive pre-cured layer and the rigid protective pre-cured layer is changed, and the rigid protective coating is applied first, followed by the flexible adhesive coating; the other steps and conditions are the same as in Example 1.

[0081] Comparative Example 4

[0082] Compared with Example 1, the only difference is that the offline ceramicization process is carried out at 450°C for 2 hours under a nitrogen atmosphere; the other steps and conditions are the same as in Example 1.

[0083] Performance testing

[0084] The first heat-resistant optical fiber (with a polymer coating) obtained in Example 1 without offline ceramic heat treatment was directly examined by optical microscopy, and the results are as follows: Figure 3 As shown in (a); the second heat-resistant optical fibers prepared in Examples 1-2 and Comparative Examples 1-3 were placed in a muffle furnace, heated from room temperature to 600°C, and then immediately placed back into room temperature environment. This cycle was repeated 10 times. The second heat-resistant optical fibers after the cyclic heat treatment were placed under an optical microscope to observe the surface morphology of the fiber coating. The results are as follows. Figure 3 As shown in (b)-(f).

[0085] like Figure 3 As shown in (a), the polymer coating that underwent the online pre-curing coating preparation stage in Example 1 remained intact, without any cracking or peeling, and exhibited good flexibility, such as... Figure 4 As shown, the coating remains intact even at large bending angles.

[0086] like Figure 3 As shown in (b) and (c), the second heat-resistant optical fiber after offline ceramicization treatment in Examples 1 and 2 maintained the integrity of the surface coating structure after 10 thermal shock cycles from 600°C to room temperature, without any breakage.

[0087] In Comparative Example 1, the second heat-resistant optical fiber suffered from an excessively thin ceramic coating and a low proportion of flexible adhesive pre-cured layer thickness. This resulted in incomplete stress release during thermal cycling, leading to shear fracture of the surface coating. Figure 3 As shown in (d).

[0088] In Comparative Example 2, the surface of the second heat-resistant optical fiber coating showed severe defects, such as... Figure 3 As shown in (e), the main reason is that changes in the coating and curing process lead to severe interdiffusion and mixing of the three coating layers, making it impossible to form the preset gradient composition and structure. After curing, the internal stress of the coating is uneven, directly presenting an uneven morphology, and obvious coating cracking will occur after multiple thermal cycles.

[0089] The regular fracture surface coating of Comparative Example 3 is mainly due to the reversed coating order of the flexible bonding pre-cured layer and the rigid protective pre-cured layer. The rigid layer near the bare fiber cannot effectively dissipate the chemical shrinkage stress of the coating, leading to axial tensile stress and subsequent fracture. Figure 3 As shown in (f).

[0090] In Comparative Example 4, the heat treatment temperature was lowered, which extended the heat treatment time. However, due to the excessively low ceramization temperature, the ceramization transformation of the coating was incomplete. In subsequent high-temperature tests, the coating continued to lose weight and generate shrinkage stress due to further pyrolysis of organic matter, resulting in fractures and cracks on the coating surface.

[0091] The specific embodiments and examples described above fully illustrate the effectiveness, flexibility, and superiority of the method described in this invention. By focusing on the fundamental material characteristic of "ceramicability" and supplementing it with innovative gradient structure design and a two-stage preparation process, this invention has successfully developed a series of temperature-resistant optical fibers that combine excellent performance with high flexibility. This invention not only provides a material solution for monitoring future high-end equipment but also takes into account the practical needs of current widespread industrial applications, demonstrating significant technological advancement and market adaptability.

[0092] Unlike existing technologies, the heat-resistant optical fiber produced by this invention belongs to the category of special optical fibers. The first heat-resistant optical fiber, at room and medium temperatures, has a polymer coating with good flexibility, adhesion, and processability, facilitating continuous online coating and rapid curing during fiber drawing. In extreme high-temperature environments, this coating can be transformed into a ceramic state through controlled heat treatment, forming a robust, dense, and high-temperature oxidation-resistant ceramic protective layer, thus obtaining a second heat-resistant optical fiber suitable for high-temperature environments. This invention, by selecting a specific ceramic precursor polymer system and combining it with an optimized gradient structure design, achieves a coating material system that simultaneously meets the conflicting requirements of "easy processing at low temperatures" and "durable service at high temperatures." The preparation method of this invention is simple, first continuously forming a polymer coating online, and then transforming it into a ceramic state through an optional heat treatment step, providing an innovative solution for the reliable application of optical fibers over a wide temperature range (from room temperature to above 600°C).

[0093] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A method of making a temperature resistant optical fiber having a ceramifiable coating, characterized in that, Includes the following steps: S1, a silane coupling agent coating is applied to the bare optical fiber, and a chemical grafting transition layer is formed by grafting and curing to obtain the first optical fiber; S2, a flexible bonding coating is coated on the first optical fiber, and then cured by hydrosilylation to form a flexible bonding pre-cured layer, thus obtaining a second optical fiber; the flexible bonding coating includes a first ceramic precursor polymer and a flexible adjustment component; the first ceramic precursor polymer includes vinyl polysilazane; the flexible adjustment component includes hydroxyl-terminated polydimethylsiloxane. S3, a rigid protective coating is coated on the second optical fiber and cured to form a rigid protective pre-cured layer, resulting in a first heat-resistant optical fiber with a polymeric coating; the rigid protective coating includes a second ceramic precursor polymer and a modified reinforcing filler; the second ceramic precursor polymer includes at least one of perhydropolysilazane, methylpolysilazane, and phenylpolysilazane; the modified reinforcing filler is made by mixing hydrophilic fumed silica and hexamethyldisilazane; the total thickness of the polymeric coating is 25-60 μm, and the flexible bonding pre-cured layer accounts for 40-50% of the total thickness.

2. The method for preparing a heat-resistant optical fiber with a ceramizable coating according to claim 1, characterized in that, In step S1, the bare optical fiber is a bare optical fiber formed by melting and drawing a quartz preform and then etching a grid.

3. The method for preparing a heat-resistant optical fiber with a ceramizable coating according to claim 1, characterized in that, In step S1, the silane coupling agent coating comprises, by mass percentage, 2.0–4.0 wt% γ-aminopropyltriethoxysilane, 96–98 wt% anhydrous ethanol, and 0.1–0.5 wt% glacial acetic acid.

4. The method for preparing a heat-resistant optical fiber with a ceramizable coating according to claim 1, characterized in that, In step S2, the flexible adhesive coating comprises 70-90 wt% of a first ceramic precursor polymer and 10-30 wt% of a flexible modifier component by mass percentage.

5. The method of claim 1, wherein the ceramicizable coating is formed by a process comprising: depositing a first layer of a first material on the optical fiber; and depositing a second layer of a second material on the first layer, wherein the first material and the second material are different. In step S3, the rigid protective coating comprises, by mass percentage, 90–97 wt% of a second ceramic precursor polymer and 3–10 wt% of modified reinforcing filler.

6. The method of claim 1, wherein the ceramicizable coating is formed by a process comprising: depositing a first layer of a first material on the optical fiber; and depositing a second layer of a second material on the first layer, wherein the first material and the second material are different. The curing temperature is 150-350℃, and the curing time for a single layer does not exceed 30 seconds.

7. The method for preparing a heat-resistant optical fiber with a ceramizable coating according to claim 1, characterized in that, Also includes: S4, the first heat-resistant optical fiber is subjected to offline heat treatment to form a ceramic coating, thus obtaining the second heat-resistant optical fiber.

8. The method for preparing a heat-resistant optical fiber with a ceramizable coating according to claim 7, characterized in that, In step S4, the conditions for the offline heat treatment include: holding at 500–900°C for 90–150 minutes in a protective atmosphere.

9. The heat-resistant optical fiber prepared by the preparation method according to any one of claims 1-8.

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