A sapphire optical fiber micro-cavity high-temperature-resistant pressure sensor and a preparation method thereof

Abstract

The application discloses a sapphire optical fiber micro-cavity high-temperature-resistant pressure sensor and a preparation method thereof. The preparation method comprises processing of a homogenous and different-diameter sapphire optical fiber end face, in particular, a femtosecond laser dry etching processing method for a large-diameter sapphire optical fiber end face, and a sapphire optical fiber inner groove end face processing method based on a CO2 laser heating technology. The application also discloses a homogenous and different-diameter sapphire optical fiber fusion method based on an arc discharge technology, so that a complete micro-cavity is formed between a fusion point and a ground end face. The micro-cavity can form a Fabry-Perot interference cavity, and when the cavity is affected by temperature and pressure, the cavity length will change accordingly. The pressure or temperature of an external environment can be calculated by measuring the change of the cavity length. The sapphire optical fiber micro-cavity high-temperature-resistant pressure sensor prepared by the technical scheme has high melting point, high hardness, and electromagnetic interference resistance.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensor technology, specifically relating to a sapphire fiber micro-cavity high-temperature pressure sensor and its fabrication method. Background Technology

[0002] High-temperature pressure sensors are widely used in aerospace, energy exploration, and marine engineering. These sensors enable real-time pressure monitoring of critical components in high-temperature and high-pressure environments such as aerospace engines, oil well drilling rigs, and large boilers. This allows for effective assessment of component performance under harsh conditions, providing technical reference for subsequent component optimization design. Taking aerospace as an example, with the development of next-generation aerospace vehicles, engine combustion chamber components are increasingly operating at higher temperatures. The main components of typical turbine engines or rocket engines already operate at temperatures exceeding 1200℃, with pressure variations ranging from 0.01 to 4 MPa. Real-time monitoring of the pressure in critical engine components such as pipes, chambers, and combustion chambers effectively ensures the long-term normal operation and mode switching of the engine and its systems. However, the complex structure, limited internal space, and harsh high-temperature environment of engines place extremely stringent requirements on sensor development.

[0003] Existing pressure sensors are mainly traditional electrical sensors. However, they are prone to piezoresistive degradation and ohmic contact failure in high-temperature environments, which limits their maximum operating temperature to no more than 600°C. In addition, these sensors require electromagnetic shielding protection in strong electromagnetic fields.

[0004] Fiber optic sensing technology, developed in the 1970s, has rapidly gained attention due to its advantages such as resistance to electromagnetic interference, corrosion resistance, miniaturization, and ease of networking. Fiber optic FP pressure sensors are an important branch of fiber optic sensors. They measure pressure by modulating the interference information of the FP cavity through external pressure, and then demodulating this interference information. Conventional fiber optic FP pressure sensors primarily use ordinary fused silica fiber. These sensors have low temperature tolerance and are mostly open-cavity sensors, making it difficult to quickly and accurately measure pressure under various environmental conditions. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a sapphire fiber micro-cavity high-temperature pressure sensor and its preparation method, which solves the problems of poor temperature resistance of quartz fiber material and low accuracy of open cavity sensors in the above-mentioned background art.

[0006] One of the technical solutions adopted by this invention to solve its technical problem is: a method for fabricating a high-temperature resistant pressure sensor with a sapphire fiber micro-cavity, comprising the following steps:

[0007] 1) Prepare the end faces of two sapphire optical fibers with different diameters, and etch a cylindrical groove on the end face of the large-diameter sapphire optical fiber.

[0008] 2) Insert the end face of the small-diameter sapphire fiber into the cylindrical groove of the large-diameter sapphire fiber, ensuring that there is a gap between the end face of the small-diameter sapphire fiber and the bottom of the cylindrical groove; use homogeneous sapphire fiber arc discharge technology to fuse two sapphire fibers of different diameters together, so that the end face of the small-diameter sapphire fiber and the inner wall and bottom of the cylindrical groove form a closed cavity.

[0009] 3) Cut the sapphire fiber on any side of the closed cavity to obtain a sapphire fiber miniature cavity high-temperature pressure sensor.

[0010] In a preferred embodiment of the present invention, in step 1), the end face of a large-diameter sapphire optical fiber is ground to obtain a flat end face, a cylindrical groove is obtained by femtosecond laser dry etching, and then the groove is irradiated by CO2 laser to obtain an end face with an optical-grade roughness.

[0011] In a preferred embodiment of the present invention, the femtosecond laser dry etching includes the following steps:

[0012] ① Place the large-diameter sapphire fiber after end-face treatment in the fiber clamp, and fix the fiber clamp on the three-dimensional stage of the femtosecond laser processing system so that the fiber end face is perpendicular to the laser beam.

[0013] ②Focus the objective lens on the end face of the optical fiber, design the program for the cylindrical groove to be engraved, start the equipment, and make the three-dimensional stage move according to the set program to engrave the cylindrical groove on the end face of the optical fiber.

[0014] In a preferred embodiment of the present invention, in step 1), a small-diameter sapphire optical fiber is ground and polished to obtain an end face with optical grade roughness.

[0015] In a preferred embodiment of the present invention, in step 2), the peripheral wall of the small-diameter sapphire fiber and the inner wall of the cylindrical groove are melted and nested and fixed by the homogenized sapphire fiber arc discharge technology.

[0016] In a preferred embodiment of the present invention, in step 3), the spliced ​​sapphire fiber is placed on a cutting platform, a blade is used to cut the large-diameter sapphire fiber on one side of the micro cavity, and a mechanical grinding method is used to grind the cut surface.

[0017] The second technical solution adopted by the present invention to solve its technical problem is: a high-temperature resistant pressure sensor with a micro-cavity made of sapphire fiber optic cable is provided, comprising two sapphire fibers of different diameters and a micro-cavity; wherein, a cylindrical groove is formed on the end face of the large-diameter sapphire fiber, and the small-diameter sapphire fiber is embedded in the cylindrical groove, with the peripheral wall of the embedded end fused to the inner wall of the cylindrical groove, and the embedding depth is such that a gap is left between the end face of the small-diameter sapphire fiber and the bottom of the cylindrical groove; the micro-cavity is a closed space formed by the end face of the small-diameter sapphire fiber, the inner wall of the cylindrical groove, and the bottom of the groove.

[0018] In a preferred embodiment of the present invention, the cylindrical groove of the large-diameter sapphire optical fiber and the end face of the small-diameter sapphire optical fiber have optical-grade roughness.

[0019] In a preferred embodiment of the present invention, the peripheral wall of the small-diameter sapphire optical fiber at the fusion splice point is melted and nested with the inner wall of the cylindrical groove.

[0020] In a preferred embodiment of the present invention, the sapphire optical fiber on any side of the micro cavity is cut off to become a wall of the micro cavity.

[0021] Compared with the prior art, this technical solution has the following advantages:

[0022] 1. This invention combines femtosecond laser dry etching and arc discharge technology to achieve homogeneous sapphire fiber fusion splicing. The preparation method has the advantages of high efficiency, convenience, ease of use and high repeatability.

[0023] 2. This invention constitutes a simple micro-cavity that can form a Fabry-Perot interferometer cavity. It has a closed structure that is simple and ingenious. It can accurately measure the pressure under various compositional environments when affected by temperature and pressure.

[0024] 3. This invention uses homogeneous sapphire fiber fusion splicing, which greatly improves the consistency of the sensor, makes the sensor more functionally stable, has higher temperature resistance, and has anti-electromagnetic interference capability. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the sensor structure for an example embodiment;

[0026] Figure 2 This is a schematic diagram of a femtosecond laser dry etching method as an example.

[0027] Figure 3 This is a schematic diagram of the morphology of the cylindrical groove on the end face of a large-diameter sapphire fiber in an embodiment. a-front view, b-right view;

[0028] Figure 4 This is a schematic diagram of the CO2 laser irradiation method in an embodiment;

[0029] Figure 5 This is a schematic diagram of the welding method in an embodiment;

[0030] Figure 6 This is a schematic diagram of the cut-off position in an embodiment;

[0031] Among them, 1-large diameter sapphire fiber, 2-small diameter sapphire fiber, 3-femtosecond laser platform, 4-fiber clamp, 5-laser (arrow indicates direction), 6-cylindrical groove, 7-CO2 laser, 8-reflector, 9-beam expander, 10-focusing lens, 11-micro cavity, 13-fusion splicer, 15-blade. Detailed Implementation

[0032] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the terms "large", "small", "upper", "lower", etc. are only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0033] Example

[0034] This embodiment describes a method for fabricating a high-temperature resistant pressure sensor with a sapphire fiber optic miniature cavity, comprising the following steps:

[0035] 1) Two types of sapphire fiber end faces with different diameters were prepared: a 125μm large-diameter sapphire fiber and a 75μm small-diameter sapphire fiber. The end faces of both fibers were ground using a fiber polishing machine, and the grinding process was monitored in real-time using a microscope. The large-diameter sapphire fiber end face only required rough and fine grinding. The grinding procedure included: grinding the large-diameter sapphire fiber with 30μm roughness diamond polishing paper to remove sharp parts of the fiber end face; then, further grinding the end face with 9μm roughness diamond polishing paper to obtain a relatively smooth end face; finally, grinding the end face again with 1μm roughness diamond polishing paper to obtain a smooth end face. The end face of small-diameter sapphire optical fibers requires rough grinding, fine grinding, and polishing. The grinding process includes: grinding the small-diameter sapphire optical fiber with diamond polishing paper with a roughness of 30μm to remove the sharp parts of the fiber end face; secondly, further grinding the end face with diamond polishing paper with a roughness of 9μm to obtain a relatively flat end face; thirdly, grinding the end face with diamond polishing paper with a roughness of 1μm to obtain a flat end face; finally, polishing the end face with ADS polishing paper to obtain an end face with optical grade roughness (in this embodiment, it means a surface roughness of less than 0.2μm).

[0036] Then, the end face of the large-diameter sapphire fiber is ground to obtain a flat end face. A cylindrical groove is obtained by femtosecond laser dry etching. The groove is then irradiated with CO2 laser to obtain an end face with an optical-grade roughness (surface roughness less than 0.2μm).

[0037] Specifically, femtosecond laser dry etching includes the following steps:

[0038] ① Place the large-diameter sapphire fiber after end-face treatment in the fiber clamp, and fix the fiber clamp on the three-dimensional stage of the femtosecond laser processing system so that the fiber end face is perpendicular to the laser beam.

[0039] ②Focus the objective lens on the fiber end face and design the program for the cylindrical groove to be etched. Start the equipment so that the three-dimensional stage moves from top to bottom according to the set program, and a cylindrical groove can be etched on the fiber end face. In this embodiment, the cylindrical groove prepared on the end face of a large-diameter sapphire fiber has a diameter of 78μm and a depth of 40μm.

[0040] Secondly, the CO2 laser irradiation steps are as follows:

[0041] The processed large-diameter sapphire fiber is placed in a dedicated fiber optic clamp. The clamp is moved so that the laser beam emitted by the CO2 laser, after passing through a reflector, beam expander, and focusing lens, illuminates the inner end face of the cylindrical groove on the large-diameter sapphire fiber end face. In this embodiment, a 10W CO2 laser with a frequency of 25kHz is used, and the irradiation time is set to 1 minute. The laser beam is focused onto the inside of the cylindrical groove using a focusing lens, irradiating its interior. High temperature is used to flatten the inner end face of the cylindrical groove, thereby obtaining an inner end face with optical-grade roughness (surface roughness less than 0.2μm).

[0042] 2) Welding:

[0043] The processed large-diameter and small-diameter sapphire fibers are placed in the fiber optic clamp of the fusion splicer. The relative positions of the two diameter sapphire fibers are adjusted using a stepper motor on the fusion splicer to align them on the same axis. The polished end face of the small-diameter sapphire fiber is inserted into the cylindrical groove of the large-diameter sapphire fiber to a certain depth. This insertion depth must allow for a gap between the polished end face of the small-diameter sapphire fiber and the bottom of the cylindrical groove of the large-diameter sapphire fiber. The appropriate discharge power, discharge magnitude, and advance distance are set, and arc discharge fusion is performed at the connection point. In this embodiment, the small-diameter sapphire fiber is inserted into the cylindrical groove by approximately 15 μm. Taking the Furukawa S178 fusion splicer as an example, the fusion splicer discharge parameters are set as follows: primary discharge power is 30, primary discharge time is 500 ms, secondary discharge power is 0, secondary discharge time is 0, and advance distance is 0; then, discharge is performed. Due to the presence of gaps and the use of small-diameter sapphire optical fibers, arc discharge can cause the inner wall of the cylindrical groove and the outer periphery of the small-diameter sapphire optical fiber to melt and become nested, thereby achieving the fusion splicing of homogeneous sapphire optical fibers.

[0044] 3) Place the spliced ​​sapphire fiber on the cutting platform and cut the sapphire fiber at any end of the splice point using a blade (15). In this embodiment, the large-diameter sapphire fiber was cut and the cut surface was polished by mechanical grinding so that the end face becomes a wall of the micro cavity and the wall thickness is made as thin as possible. Finally, a sapphire fiber micro cavity high-temperature pressure sensor was prepared.

[0045] The sapphire fiber microcavity high-temperature pressure sensor prepared in this embodiment uses a fusion method based on homogeneous sapphire fiber arc discharge technology to enclose the end face of a small-diameter sapphire fiber with the inner wall and bottom of a cylindrical groove to form a closed space. This closed space is the microcavity that can later form a Fabry-Perot interferometer. The structure is simple and ingenious. The homogeneous sapphire structure makes the sensor more functionally stable, and the sapphire material makes the sensor more temperature resistant.

[0046] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for fabricating a high-temperature resistant pressure sensor with a sapphire fiber microcavity, characterized in that: Includes the following steps: 1) Prepare the end faces of two different diameter sapphire optical fibers, and etch a cylindrical groove on the end face of the large diameter sapphire optical fiber; grind the end face of the large diameter sapphire optical fiber to obtain a flat end face, use femtosecond laser dry etching to obtain a cylindrical groove, and then irradiate the groove with CO2 laser to obtain an end face with an optical grade roughness. 2) Insert the end face of the small-diameter sapphire fiber into the cylindrical groove of the large-diameter sapphire fiber, ensuring that there is a gap between the end face of the small-diameter sapphire fiber and the bottom of the cylindrical groove; use homogeneous sapphire fiber arc discharge technology to fuse two sapphire fibers of different diameters together, so that the end face of the small-diameter sapphire fiber and the inner wall and bottom of the cylindrical groove form a closed cavity. 3) Cut the sapphire fiber on any side of the closed cavity to obtain a sapphire fiber miniature cavity high temperature pressure sensor.

2. The method for fabricating a sapphire fiber microcavity high-temperature pressure sensor according to claim 1, characterized in that: The femtosecond laser dry etching includes the following steps: ① Place the large-diameter sapphire fiber after end-face treatment in the fiber clamp, and fix the fiber clamp on the three-dimensional stage of the femtosecond laser processing system so that the fiber end face is perpendicular to the laser beam. ②Focus the objective lens on the end face of the optical fiber, design the program for the cylindrical groove to be engraved, start the equipment, and make the three-dimensional stage move according to the set program to engrave the cylindrical groove on the end face of the optical fiber.

3. The method for fabricating a high-temperature resistant pressure sensor with a sapphire fiber microcavity according to claim 1, characterized in that: In step 1), the small-diameter sapphire optical fiber is ground and polished to obtain an end face with optical-grade roughness.

4. The method for fabricating a sapphire fiber microcavity high-temperature pressure sensor according to claim 1, characterized in that: In step 2), the peripheral wall of the small-diameter sapphire fiber and the inner wall of the cylindrical groove are melted and nested and fixed using homogeneous sapphire fiber arc discharge technology.

5. The method for fabricating a high-temperature resistant pressure sensor with a sapphire fiber microcavity according to claim 1, characterized in that: In step 3), the spliced ​​sapphire fiber is placed on a cutting platform, and a blade is used to cut the sapphire fiber on one side of the micro cavity.

6. The method for fabricating a high-temperature resistant pressure sensor with a sapphire fiber microcavity according to claim 5, characterized in that: The cross-section was ground using mechanical grinding.

7. A sapphire fiber optic miniature cavity high-temperature pressure sensor prepared by the method according to any one of claims 1-6, characterized in that: The device includes two sapphire optical fibers of different diameters and a micro-cavity. The end face of the larger diameter sapphire optical fiber has a cylindrical groove. The smaller diameter sapphire optical fiber is embedded within the cylindrical groove, with its embedded end's peripheral wall fused to the inner wall of the groove. The embedding depth ensures a gap between the end face of the smaller diameter sapphire optical fiber and the bottom of the cylindrical groove. The micro-cavity is a closed space formed by the end face of the smaller diameter sapphire optical fiber, the inner wall of the cylindrical groove, and the bottom of the groove. At the fusion point, the peripheral wall of the smaller diameter sapphire optical fiber is fused to and nested within the inner wall of the cylindrical groove. The sapphire optical fiber on either side of the micro-cavity is cut off to become one wall of the micro-cavity.

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