Hollow core anti-resonant optical fiber and its preparation method and sensing system

Abstract

The application discloses a kind of hollow core anti-resonant optical fiber and its preparation method and sensing system, it is related to optical fiber technical field, its technical solution main point is: including: air core;Quartz anti-resonant cladding microstructure, including a plurality of circumferentially arranged anti-resonant elements, a plurality of anti-resonant elements are enclosed and define air core, quartz anti-resonant cladding microstructure is used to limit optical field transmission in air core;Platinum alloy functional layer, it is coated on the outer surface of quartz anti-resonant cladding microstructure.The application improves the mechanical strength and extreme environment tolerance of optical fiber by platinum alloy functional layer, realizes the firm combination of quartz anti-resonant cladding microstructure and platinum alloy functional layer using integrated forming process, and with platinum alloy functional layer and air core as electrical temperature measurement and optical strain measurement channel respectively, realize distributed temperature and strain synchronous measurement, with the advantages of excellent mechanical performance, strong environmental adaptability, multiple functions.

Description

Technical Field

[0001] This invention relates to the field of optical fiber technology, and more specifically, to a hollow-core anti-resonant optical fiber, its fabrication method, and a sensing system thereof. Background Technology

[0002] Hollow-core antiresonant fibers, due to their excellent optical properties such as low loss, low nonlinearity, and high damage threshold, have broad application prospects in optical communication, high-power laser transmission, and sensing. Existing hollow-core antiresonant fibers are typically made of quartz glass with an air core and a cladding employing a periodic microstructure design. Light is confined within the hollow core through an antiresonance effect. These fibers are generally fabricated using a "stack-drawing" method, and after drawing, a polymer coating (such as acrylate) is applied to provide basic mechanical protection.

[0003] However, existing hollow-core antiresonant optical fibers have several drawbacks. At the structural level, while the quartz antiresonant cladding employs a thin-walled microstructure to achieve excellent optical performance, external protection relies solely on a polymer coating. This results in low intrinsic mechanical strength, sensitivity to external forces, and susceptibility to structural collapse or breakage. Furthermore, the polymer coating has a low temperature resistance limit, making it prone to failure under extreme environments such as high temperature, high pressure, corrosion, and radiation, failing to provide effective protection for the fiber body. At the manufacturing process level, the polymer coating is typically applied post-coating, resulting in only physical adhesion between the coating and the quartz glass. This leads to low bonding strength, making it susceptible to peeling under thermal cycling or mechanical stress. Moreover, the post-coating process struggles to guarantee the uniformity and density of the coating thickness. At the system application level, existing optical fibers serve only as passive optical transmission media. Temperature measurement requires external sensors or complex distributed fiber optic sensing technologies, resulting in complex and costly systems that struggle to achieve simultaneous monitoring of multiple parameters such as temperature and strain.

[0004] The root cause of the above defects is that existing technologies treat optical transmission, mechanical protection, environmental tolerance and functional integration as separate functions implemented by different components or systems, and fail to carry out integrated innovation from the structural design, manufacturing process and system application of the optical fiber itself.

[0005] Therefore, a new solution is needed to address this problem. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a hollow anti-resonant optical fiber, its preparation method and sensing system, which has the advantages of excellent mechanical properties, strong environmental adaptability and diverse functions.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a hollow-core anti-resonant optical fiber, comprising:

[0008] Air core;

[0009] A quartz anti-resonant cladding microstructure includes a plurality of anti-resonant elements arranged circumferentially, the plurality of anti-resonant elements surrounding and defining the air core, the quartz anti-resonant cladding microstructure being used to confine the optical field for transmission within the air core;

[0010] A platinum alloy functional layer is coated on the outer surface of the quartz anti-resonant cladding microstructure, and the platinum alloy functional layer is a continuous metal conductor layer.

[0011] Preferably, the material of the platinum alloy functional layer is a platinum-based alloy, which includes platinum as well as rhodium and / or iridium.

[0012] Preferably, the rhodium and / or iridium account for 5%-20% of the weight of the platinum-based alloy.

[0013] Preferably, a transition layer is provided between the platinum alloy functional layer and the quartz anti-resonance cladding microstructure, and the transition layer is a chromium layer, a titanium layer, a chromium nitride layer, or a titanium nitride layer.

[0014] Preferably, the quartz anti-resonant cladding microstructure further includes a quartz outer tube, and a plurality of the anti-resonant elements are disposed within the quartz outer tube.

[0015] A method for fabricating a hollow-core anti-resonant optical fiber, comprising the following steps:

[0016] S1. Provide a hollow anti-resonant optical fiber preform, the hollow anti-resonant optical fiber preform includes a quartz outer tube and a plurality of anti-resonant elements disposed in the quartz outer tube, the plurality of anti-resonant elements are arranged circumferentially and surround to form an air fiber core.

[0017] S2. Pre-treat the outer surface of the hollow anti-resonant optical fiber preform;

[0018] S3. Deposit a platinum alloy functional layer on the outer surface of the pretreated hollow anti-resonant optical fiber preform to obtain a metallized preform.

[0019] S4. The metallized preform is installed on the optical fiber drawing tower for drawing. During the drawing process, the temperature field of the drawing furnace is controlled to soften the quartz material in the metallized preform and simultaneously put the platinum alloy functional layer in a plastic rheological state, so as to achieve synchronous deformation and bonding of quartz and platinum alloy, and obtain the hollow anti-resonant optical fiber.

[0020] Preferably, the method further includes step S5, which involves online annealing of the hollow anti-resonant optical fiber obtained in step S4 to eliminate internal stress.

[0021] Preferably, in step S3, before depositing the platinum alloy functional layer, a transition layer is first deposited on the outer surface of the hollow anti-resonant optical fiber preform. The transition layer is a chromium layer, a titanium layer, a chromium nitride layer, or a titanium nitride layer.

[0022] A sensing system includes any of the hollow anti-resonant optical fibers described above, and further includes an electrical demodulation module, an optical demodulation module, and a data fusion unit;

[0023] The platinum alloy functional layer of the hollow anti-resonant optical fiber serves as a distributed temperature sensing function, used to measure the temperature distribution along the optical fiber through an electrical demodulation module.

[0024] The air core of the hollow anti-resonant optical fiber serves as a distributed strain sensing function, used to measure the strain and / or vibration distribution along the optical fiber through an optical demodulation module.

[0025] The data fusion unit is electrically connected to the electrical demodulation module and the optical demodulation module, respectively, and is used to receive temperature signals and strain signals, and to use the temperature signals to perform temperature compensation on the strain signals in order to obtain real strain information.

[0026] Preferably, the data fusion unit is an industrial control computer or an industrial computer.

[0027] Compared with existing technologies, the advantages of the hollow-core anti-resonant optical fiber, its fabrication method, and the sensing system disclosed in this invention are:

[0028] 1. By coating the outer surface of the quartz anti-resonant cladding microstructure with a platinum alloy functional layer, the mechanical strength and fatigue resistance of the optical fiber are effectively improved. At the same time, by utilizing the high melting point, chemical inertness and radiation resistance of the platinum-based alloy, the optical fiber can work stably for a long time under extreme environments such as high temperature, high pressure, corrosion and radiation, overcoming the defects of traditional polymer coatings that are prone to failure.

[0029] 2. By drawing the metallized preform into wire, the quartz material is softened and the platinum alloy functional layer is simultaneously in a plastic rheological state, achieving synchronous deformation and bonding of the two, forming a hollow anti-resonant optical fiber with a strong bond and uniform thickness. This solves the problem of low coating strength and easy peeling in the post-coating process, and realizes the integrated molding process of "metallized preform + synchronous drawing".

[0030] 3. By using a platinum alloy functional layer as an electrical temperature measurement channel and an air fiber core as an optical strain measurement channel, a single hollow anti-resonant optical fiber can simultaneously possess two independent sensing functions: distributed temperature measurement and strain measurement. This eliminates the need for additional temperature sensors or complex distributed optical fiber sensing systems. Furthermore, by using a data fusion unit to perform temperature compensation on the strain signal using the temperature signal, the accuracy of strain measurement is improved, and the system complexity is simplified. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the structure of the hollow anti-resonant optical fiber according to an embodiment of this application;

[0033] Figure 2 This is a flowchart illustrating the fabrication method of a hollow anti-resonant optical fiber according to an embodiment of this application;

[0034] Figure 3 This is a system block diagram of the sensing system according to an embodiment of this application.

[0035] The numbers or letters in the attached diagram represent the names of the corresponding components:

[0036] 1. Air fiber core; 2. Quartz anti-resonant cladding microstructure; 3. Transition layer; 4. Platinum alloy functional layer; 5. Sensing unit; 6. Optical demodulation module; 7. Electrical demodulation module; 8. Data fusion unit; 9. Data analysis software; 10. Display. Detailed Implementation

[0037] The technical solution of the present invention will now be clearly and completely described through specific embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. 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.

[0038] Please see Figure 1 The embodiments of this application provide an air-core anti-resonant optical fiber, which, from the inside out, includes an air core 1, a quartz anti-resonant cladding microstructure 2, and a platinum alloy functional layer 4.

[0039] The quartz anti-resonant cladding microstructure 2 is made of ultra-high purity quartz glass and includes multiple anti-resonant elements arranged circumferentially. These anti-resonant elements can be single-layer quartz capillaries or nested structures, where one or more smaller quartz capillaries are nested within a slightly larger quartz capillary to further optimize the anti-resonance effect. The multiple anti-resonant elements together define the aforementioned air core 1, and the quartz anti-resonant cladding microstructure 2 is used to confine the light field within the air core 1 for transmission. A predetermined gap is maintained between adjacent anti-resonant elements, which is achieved by arranging the multiple anti-resonant elements circumferentially at a certain interval on the inner wall of a quartz outer tube. In another embodiment, this gap can also be achieved by fixing the multiple anti-resonant elements with connecting bridges or positioning spacers, similarly avoiding damage to the anti-resonance effect caused by contact between the tube walls of adjacent anti-resonant elements.

[0040] In this embodiment, a transition layer 3 is further provided between the platinum alloy functional layer 4 and the quartz anti-resonance cladding microstructure 2. The transition layer 3 is a chromium layer, a titanium layer, a chromium nitride layer, or a titanium nitride layer, with a thickness of 10 nanometers to 2 micrometers. The function of the transition layer 3 is to improve the adhesion between the quartz anti-resonance cladding microstructure 2 and the upper platinum alloy functional layer 4, and to buffer the difference in thermal expansion coefficients between the two, thereby reducing thermal stress.

[0041] It should be noted that the transition layer 3 is a preferred configuration. In other embodiments, depending on the material properties and surface treatment process of the platinum alloy functional layer 4 (e.g., by laser micro-melting or other surface treatment technologies), the transition layer 3 may be omitted, allowing the platinum alloy functional layer 4 to directly coat the outer surface of the quartz anti-resonance cladding microstructure 2, while still achieving the core function of the present invention.

[0042] The platinum alloy functional layer 4 is a continuous metallic conductor layer, tightly bonded to the transition layer 3 or directly bonded to the outer surface of the quartz anti-resonant cladding microstructure 2. The material of the platinum alloy functional layer 4 is a platinum-based alloy, including platinum and rhodium and / or iridium. The weight percentage of rhodium and / or iridium in the platinum-based alloy is 5%-20%, specifically 5%, 10%, or 15%. In this embodiment, the platinum-based alloy is a platinum-rhodium alloy composed of platinum and rhodium, wherein rhodium accounts for 10% of the weight percentage of the platinum-based alloy. The thickness of the platinum alloy functional layer 4 is 5 micrometers-100 micrometers, preferably 20 micrometers, 30 micrometers, or 50 micrometers. The platinum alloy functional layer 4 has multiple functions: First, utilizing the extremely high chemical inertness and density of platinum alloy, it provides an airtight enclosure for the quartz anti-resonant cladding microstructure 2 and its internal air core 1, isolating it from oxygen, hydrogen, water vapor, and corrosive media, effectively preventing hydrogen loss and chemical corrosion; Second, as a "metal armor," it enhances the mechanical strength of the hollow anti-resonant optical fiber, suppresses the initiation and propagation of microcracks on the surface of the quartz anti-resonant cladding microstructure 2, and effectively improves the tensile strength and fatigue resistance of the hollow anti-resonant optical fiber; At the same time, this layer is a continuous metallic conductor, and its resistance value has a stable and repeatable linear relationship with temperature (positive temperature coefficient). By measuring its resistance distribution along its length, distributed temperature measurement can be achieved.

[0043] Please see Figure 1 and Figure 2 The present invention also discloses a method for preparing a hollow anti-resonant optical fiber, which includes the following steps:

[0044] S1. A hollow anti-resonant optical fiber preform is provided, comprising a quartz outer tube and multiple anti-resonant elements disposed within the quartz outer tube. The multiple anti-resonant elements are arranged circumferentially and enclosed to form an air core 1. This hollow anti-resonant optical fiber preform can be prepared using a stacking-drawing method: first, multiple quartz capillaries are stacked and assembled within the quartz outer tube according to the designed structure; then, the assembled preform is sintered at high temperature to form a tight bond between the components; finally, the sintered primary preform is heated and stretched in an optical fiber drawing tower to obtain a hollow anti-resonant optical fiber preform of the required diameter.

[0045] S2. Pre-treatment of the outer surface of the hollow anti-resonant optical fiber preform includes ultrasonic cleaning and oxygen plasma treatment: ultrasonic cleaning removes surface oil and particles; oxygen plasma treatment can effectively remove organic pollutants and generate more silanol groups (-OH) on the surface of the quartz anti-resonant cladding microstructure 2, which greatly increases the surface energy and enhances the wettability and bonding force with the subsequent platinum alloy functional layer 4.

[0046] S3. A platinum alloy functional layer 4 is deposited on the outer surface of the pretreated hollow anti-resonant fiber preform to obtain a metallized preform. In this embodiment, a magnetron sputtering process is used to achieve this step. Specifically, the hollow anti-resonant fiber preform is placed in the vacuum chamber of a magnetron sputtering device, a platinum-rhodium alloy target is used as the cathode, argon gas is introduced, and argon ions are bombarded with the target material through glow discharge, sputtering the target material atoms and depositing them on the surface of the rotating hollow anti-resonant fiber preform to form a platinum alloy functional layer 4 (this thickness is the thickness on the metallized preform, which becomes thinner after drawing).

[0047] S4. Install the metallized preform on the optical fiber drawing tower for fiber drawing. During the drawing process, control the temperature field of the drawing furnace, maintaining the furnace temperature between 1900℃ and 2100℃ to soften the quartz material in the metallized preform (corresponding to a viscosity of 10). 6 Pa·s-10 7 (Pa·s). Simultaneously, utilizing the temperature gradient within the furnace, the platinum alloy functional layer 4, located on the outer layer of the hollow anti-resonant optical fiber, is placed in a plastic rheological state at 1250℃-1350℃. At this temperature, the platinum alloy functional layer 4 undergoes dynamic recrystallization, exhibiting excellent plastic deformation capability.

[0048] Under the tension of the traction rollers on the fiber drawing tower, the quartz anti-resonant cladding microstructure 2 and the platinum alloy functional layer 4 undergo coordinated plastic deformation and proportional diameter reduction, ultimately forming a firmly bonded, uniformly thick hollow anti-resonant optical fiber. The drawn platinum alloy functional layer 4 has a thickness of approximately 20-50 micrometers, a smooth surface, and is free of cracks and peeling.

[0049] S5. The hollow anti-resonant fiber obtained in step S4 is subjected to online annealing. That is, under the set temperature and tension, the hollow anti-resonant fiber is slowly passed through an annealing tube to eliminate the internal stress in the quartz anti-resonant cladding microstructure 2 and the platinum alloy functional layer 4, stabilize the crystal phase of the platinum alloy functional layer 4, and improve the long-term stability of the hollow anti-resonant fiber.

[0050] As a preferred embodiment, in step S3, before depositing the platinum alloy functional layer 4, a transition layer 3 is first deposited on the outer surface of the hollow anti-resonant optical fiber preform. The transition layer 3 is a chromium layer, a titanium layer, a chromium nitride layer, or a titanium nitride layer. The deposition of the transition layer 3 can be performed using the same magnetron sputtering equipment, with the corresponding target material as the cathode.

[0051] Please see Figure 1 and Figure 3The present invention also discloses a sensing system comprising any of the aforementioned hollow anti-resonant optical fibers, wherein the hollow anti-resonant optical fiber serves as a sensing unit 5, which has distributed temperature sensing and distributed strain sensing functions. The sensing system further includes an electrical demodulation module 7, an optical demodulation module 6, and a data fusion unit 8. The platinum alloy functional layer 4 of the hollow anti-resonant optical fiber serves as the distributed temperature sensing function, used to measure the temperature distribution along the optical fiber via the electrical demodulation module 7. The air core 1 of the hollow anti-resonant optical fiber serves as the distributed strain sensing function, used to measure the strain and / or vibration distribution along the optical fiber via the optical demodulation module 6. The data fusion unit 8 is electrically connected to both the electrical demodulation module 7 and the optical demodulation module 6, and is used to receive temperature signals and strain signals, and to perform temperature compensation on the strain signals using the temperature signals to obtain accurate strain information.

[0052] Specifically, the ends of the hollow anti-resonant optical fiber are processed to expose the platinum alloy functional layer 4. Then, metal leads are fixed to the exposed platinum alloy functional layer 4 using conductive silver paste or welding to form a reliable electrical interface. This electrical interface is electrically connected to the electrical demodulation module 7. The electrical demodulation module 7 injects an electrical signal into the platinum alloy functional layer 4 through this interface and measures its resistance distribution to calculate the temperature distribution along the hollow anti-resonant optical fiber. In this embodiment, the electrical demodulation module 7 is a distributed resistance meter based on frequency domain reflection technology. It injects a swept-frequency signal into the continuous loop formed by the platinum alloy functional layer 4 and calculates the resistance distribution along the fiber length by analyzing the frequency domain characteristics of the reflected signal. Since the resistance of platinum alloy exhibits a stable linear relationship with temperature (positive temperature coefficient), the electrical demodulation module 7 converts the resistance distribution into a distributed temperature curve according to a pre-calibrated resistance-temperature relationship.

[0053] The optical end face of the hollow-core antiresonant fiber is precision ground and polished to form a flat end face perpendicular to the axis. This end face is then connected to the output pigtail of the optical demodulation module 6 via a fiber optic connector or fusion splice, ensuring that the optical signal can be injected into the air fiber core 1 with low loss and that backscattered light is received. The optical demodulation module 6 emits probe light into the air fiber core 1 and receives the backscattered light to calculate the strain and / or vibration signal along the hollow-core antiresonant fiber. In this embodiment, the optical demodulation module 6 is a distributed fiber demodulator based on phase-sensitive optical time-domain reflectometry (Φ-OTDR) technology. It injects a narrow-linewidth pulsed laser into the air fiber core 1 through a circulator. As the laser propagates through the fiber core, the backscattered Rayleigh light generated at each point along the path returns along the original path and is received by a photodetector via the circulator. By analyzing the dynamic changes in the phase of the backscattered light, the optical demodulation module 6 can calculate the dynamic strain or vibration signal at each point along the path.

[0054] The data fusion unit 8 is an industrial control computer or industrial PC. It has built-in data analysis software 9 and a display 10 for showing temperature curves, strain spectra, etc. The data fusion unit 8 connects to the electrical demodulation module 7 and the optical demodulation module 6 via a data acquisition card or communication interface (such as Ethernet, RS485, USB, etc.) to acquire synchronized measurement data in real time. The data fusion unit 8 includes a spatial alignment module and a temperature compensation module: the spatial alignment module maps the optical and electrical measurement results to unified spatial coordinates and timestamps, ensuring accurate correspondence between temperature and strain data at the same location; the temperature compensation module uses the precise temperature data obtained by the electrical demodulation module 7 to remove spurious strain components caused by thermal expansion in the optical strain signal, thus obtaining the true mechanical strain. After temperature compensation, the temperature drift error of the strain measurement is reduced, and the measurement accuracy is significantly improved.

[0055] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A hollow-core anti-resonant optical fiber, characterized in that, include: Air fiber core; A quartz anti-resonant cladding microstructure includes a plurality of anti-resonant elements arranged circumferentially, the plurality of anti-resonant elements surrounding and defining the air core, the quartz anti-resonant cladding microstructure being used to confine the optical field for transmission within the air core; A platinum alloy functional layer is coated on the outer surface of the quartz anti-resonant cladding microstructure, and the platinum alloy functional layer is a continuous metal conductor layer.

2. The hollow-core anti-resonant optical fiber according to claim 1, characterized in that: The material of the platinum alloy functional layer is a platinum-based alloy, which includes platinum as well as rhodium and / or iridium.

3. The hollow-core anti-resonant optical fiber according to claim 2, characterized in that: The rhodium and / or iridium constitute 5%-20% of the weight of the platinum-based alloy.

4. The hollow-core anti-resonant optical fiber according to claim 1, characterized in that: A transition layer is provided between the platinum alloy functional layer and the quartz anti-resonance cladding microstructure. The transition layer is a chromium layer, a titanium layer, a chromium nitride layer, or a titanium nitride layer.

5. The hollow-core anti-resonant optical fiber according to claim 1, characterized in that: The quartz anti-resonant cladding microstructure also includes a quartz outer tube, and a plurality of the anti-resonant elements are disposed inside the quartz outer tube.

6. A method for preparing a hollow-core anti-resonant optical fiber, used to prepare the hollow-core anti-resonant optical fiber as described in claim 5, characterized in that, Includes the following steps: S1. Provide a hollow anti-resonant optical fiber preform, the hollow anti-resonant optical fiber preform includes a quartz outer tube and a plurality of anti-resonant elements disposed in the quartz outer tube, the plurality of anti-resonant elements are arranged circumferentially and surround to form an air fiber core. S2. Pre-treat the outer surface of the hollow anti-resonant optical fiber preform; S3. Deposit a platinum alloy functional layer on the outer surface of the pretreated hollow anti-resonant optical fiber preform to obtain a metallized preform. S4. The metallized preform is installed on the optical fiber drawing tower for drawing. During the drawing process, the temperature field of the drawing furnace is controlled to soften the quartz material in the metallized preform and simultaneously put the platinum alloy functional layer in a plastic rheological state, so as to achieve synchronous deformation and bonding of quartz and platinum alloy, and obtain the hollow anti-resonant optical fiber.

7. The method for preparing hollow anti-resonant optical fiber according to claim 6, characterized in that: The method also includes step S5, which involves online annealing of the hollow anti-resonant optical fiber obtained in step S4 to eliminate internal stress.

8. The method for preparing hollow anti-resonant optical fiber according to claim 6, characterized in that: In step S3, before depositing the platinum alloy functional layer, a transition layer is first deposited on the outer surface of the hollow anti-resonant optical fiber preform. The transition layer is a chromium layer, a titanium layer, a chromium nitride layer, or a titanium nitride layer.

9. A sensing system comprising a hollow anti-resonant optical fiber as described in any one of claims 1 to 5, characterized in that: It also includes an electrical demodulation module, an optical demodulation module, and a data fusion unit; The platinum alloy functional layer of the hollow anti-resonant optical fiber serves as a distributed temperature sensing function, used to measure the temperature distribution along the optical fiber through an electrical demodulation module. The air core of the hollow anti-resonant optical fiber serves as a distributed strain sensing function, used to measure the strain and / or vibration distribution along the optical fiber through an optical demodulation module. The data fusion unit is electrically connected to the electrical demodulation module and the optical demodulation module, respectively, and is used to receive temperature signals and strain signals, and to use the temperature signals to perform temperature compensation on the strain signals in order to obtain real strain information.

10. The sensing system according to claim 9, characterized in that: The data fusion unit is an industrial control computer or industrial computer.

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