A fiber grating and fabry-perot resonant cavity combined temperature and pressure flow sensor

Abstract

The application provides a fiber grating and F-P resonant cavity combined temperature and pressure flow sensor, which comprises four fiber gratings arranged in a triangular pyramid in a sleeve, and a F-P resonant cavity is further prepared on the fiber end at the center position. The application measures the change of the center wavelength of the fiber grating on the fiber caused by the same frequency change of the outside temperature, and then calculates the outside temperature; when the F-P resonant cavity at the center position of the fiber is subjected to the outside pressure, the diaphragm is compressed into the cavity, and the outside pressure value can be calculated by measuring the cavity length change; the spatial arrangement of the fibers at different positions on the sensor can measure the temperature change and the heat flow in different directions. The sensor has the advantages of simultaneously measuring multiple parameters, resisting electromagnetic interference, high sensitivity, compact structure and the like.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensor technology, and in particular to a temperature, pressure and current sensor that combines a fiber optic grating and a Fabry-Perot resonator. Background Technology

[0002] The measurement of temperature, heat flux, and pressure under extreme environments is of great concern in various fields such as aerospace, shipbuilding, marine engineering, energy exploration, and petrochemicals. Particularly in the field of advanced engines, with the continuous development and increasing demand for next-generation aero engines, combustion chamber components are evolving towards higher temperatures and higher heat capacities. During engine operation, a series of abnormal factors, such as surge, inlet distortion, poor nozzle atomization, and interference between engine components, can lead to combustion instability. Combustion instability can cause vibration and fatigue in the thin-walled structure of the engine combustion chamber, shortening its service life and even causing in-flight engine failure, resulting in serious accidents. Therefore, real-time monitoring of the temperature, heat flux, and pressure parameters of key engine components is crucial for improving engine reliability, enhancing engine stability control, increasing operational safety, and extending service life. In these tests, conventional pressure measurement methods are often affected by extreme high-temperature environments, potentially causing measurement deviations or sensor malfunctions. To address this challenge, fiber optic sensors have emerged as a promising solution due to their high-temperature resistance and electromagnetic interference immunity. While fiber optic sensors perform exceptionally well in high-temperature environments with current technology, most still only achieve single-parameter measurements, such as patents CN115628826A and CN115790923A. Simultaneous monitoring of multiple parameters, including temperature, pressure, and heat flux, remains a challenge. Therefore, the research and application of multi-parameter sensors hold immense potential, providing more comprehensive and accurate monitoring solutions for engineering applications in high-temperature environments. Summary of the Invention

[0003] The purpose of this invention is to provide a temperature, pressure, and flow sensor that combines a fiber optic grating and a Fabry-Perot resonator. This sensor offers advantages such as simultaneous measurement capability, resistance to electromagnetic interference, high sensitivity, compact structure, and integration using homogeneous materials. It meets the requirements for simultaneous measurement of temperature, heat flow, and pressure in complex and harsh environments, exhibiting ingenious structure, reliable function, and significant application prospects.

[0004] To solve the above-mentioned technical problems, the present invention provides a temperature, pressure and current sensor composed of fiber optic grating and Fabry-Perot resonator. The sensor includes a second optical fiber, a third optical fiber and a fourth optical fiber arranged in a triangle and sleeved in a sleeve, wherein the first optical fiber is located at the center of the triangle.

[0005] The first optical fiber is inscribed with a high-temperature resistant first fiber grating, and a Fabry-Perot resonant cavity is fabricated at its end; the second, third, and fourth optical fibers are respectively inscribed with a high-temperature resistant second fiber grating, a third fiber grating, and a fourth fiber grating.

[0006] In a preferred embodiment: the grating region length of the first fiber grating, the second fiber grating, the third fiber grating, and the fourth fiber grating is <1mm, and the grating Bragg wavelength is in the range of 1500nm-1600nm.

[0007] In a preferred embodiment: the first fiber grating to the second fiber grating, the third fiber grating, and the fourth fiber grating form a triangular pyramid structure in spatial position, with the first fiber grating located at the vertex of the triangular pyramid, and the second, third, and fourth fiber gratings located at the three vertices of the base triangle of the triangular pyramid, respectively.

[0008] In a preferred embodiment: the Fabry-Perot resonant cavity is a sealed cavity formed by fusing a section of hollow optical fiber at the tail end of the first optical fiber using arc discharge technology, and then fusing the hollow optical fiber with a matching optical fiber.

[0009] In a preferred embodiment: the end face of the cooperating optical fiber is mechanically polished to obtain a pressure-sensitive diaphragm that senses changes in ambient pressure.

[0010] In a preferred embodiment: the sleeve is 10-25cm long and has an outer diameter of 2.3mm-2.5mm. The sleeve has a four-hole structure with an inner diameter of 0.2mm. The first, second, and third holes are arranged in a triangular pattern. The two ends of the sleeve that connect to the first, second, third, and fourth optical fibers are treated with laser heating, causing the inner wall of the sleeve to collapse due to heat and encapsulate the first, second, third, and fourth optical fibers.

[0011] In a preferred embodiment: the sleeve is made of the same material as the first optical fiber, the second optical fiber, the third optical fiber, and the fourth optical fiber.

[0012] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0013] This invention provides a composite temperature, pressure, and flow sensor combining a fiber optic grating and a Fabry-Perot resonator, which boasts advantages such as high testing capability, high sensitivity, compact structure, resistance to electromagnetic interference, and homogeneous material integration. The fiber optic sensor overcomes the shortcomings of ordinary electrical sensors, which struggle to operate normally in high-temperature environments. The sensitive structure cascades a fiber optic grating and a Fabry-Perot resonator, enabling simultaneous measurement of temperature, pressure, and heat flow. Through ingenious structural design, four high-temperature resistant fiber optic gratings are arranged in a triangular pyramidal pattern in space, allowing for efficient measurement of heat flow changes in different spatial directions, providing multi-directional heat flow measurement capabilities. The optical fiber and encapsulation sleeve are fixed together using laser welding, achieving homogeneous integration of the sensitive core and encapsulation material, thus resolving the thermal stress mismatch problem. Attached Figure Description

[0014] Figure 1 This is a front view of the optical fiber-based temperature, pressure, and flow sensor of the present invention.

[0015] Figure 2 This is a top view of the optical fiber-based temperature, pressure, and flow sensor of the present invention.

[0016] Figure 3 This is a schematic diagram of the spatial arrangement of the fiber optic grating for the temperature, pressure and current sensor based on optical fiber according to the present invention;

[0017] Figure 4 This is a schematic diagram showing the arrangement of the fiber grating and Fabry-Perot resonant cavity on the first optical fiber of the optical fiber-based temperature-pressure-current sensor of the present invention.

[0018] Figure 5 This is a flowchart illustrating the fabrication process of a Fabry-Perot resonant cavity.

[0019] Figure 6 The diagram shows the different states during the fabrication process of the Fabry-Perot resonator. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0021] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "top / bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed", "equipped", "sleeved / connected", "connected", etc., should be interpreted broadly. For example, "connection" can be a wall-mounted connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0023] In the description of this invention, it should be noted that the term "triangular pyramid" should include triangular pyramid structures of various sizes, and triangular pyramid structures of other sizes can also be used, which are simple substitutions in this embodiment.

[0024] refer to Figure 1-3 The temperature, pressure and current sensor of fiber optic grating and Fabry-Perot resonant cavity composite described in this embodiment includes a second optical fiber 2, a third optical fiber 3 and a fourth optical fiber 4 arranged in a triangle and sleeved in a sleeve 5 with a four-hole structure inside. The first optical fiber 1 is located at the center of the triangle.

[0025] The first optical fiber 1 is inscribed with a high-temperature resistant first fiber grating I, and a Fabry-Perot resonant cavity V is fabricated at its port position; the second optical fiber 2, the third optical fiber 3, and the fourth optical fiber 4 are respectively inscribed with a high-temperature resistant second fiber grating II, a third fiber grating III, and a fourth fiber grating IV.

[0026] Specifically, in this embodiment, the first optical fiber 1, the second optical fiber 2, the third optical fiber 3, and the fourth optical fiber 4 are made of quartz single-mode fiber, with a SiO2 material, a core diameter of 9μm-10μm, and a cladding diameter of 124μm-130μm; the optical fiber can also be other types of optical fiber. Correspondingly, the Bragg wavelength of the grating in the first fiber grating region is in the 1500nm-1600nm band, and the Bragg wavelengths of the gratings in the second, third, and fourth fiber grating regions are also in the 1500nm-1600nm range.

[0027] Furthermore, the first fiber grating I, along with the second, third, and fourth fiber gratings III and IV, form a triangular pyramid structure in space. The first fiber grating I is located at the vertex of the pyramid, while the second, third, and fourth fiber gratings IV are located at the three vertices of the base triangle of the pyramid. As a temperature-sensitive device, the fiber gratings, influenced by the thermal expansion and thermo-optic effects of the fiber material, cause the reflected center wavelength to change with temperature variations. By measuring this change in center wavelength, the external temperature can be calculated. The four fiber gratings are arranged in a triangular pyramidal spatial arrangement, allowing the temperature difference between any two gratings to be calculated based on the center wavelength drift, thus enabling the calculation of heat flux density. The heat flux changes in different directions between the different gratings can be calculated, thereby achieving multi-directional spatial heat flux monitoring.

[0028] Specifically, refer to Figure 4 In the first optical fiber 1, the high-temperature resistant first fiber grating I and the Fabry-Perot resonator V are connected in series, and the Fabry-Perot resonator V is located at the end of the first optical fiber 1 as a pressure-sensitive component.

[0029] It is important to emphasize the fabrication method of the Fabry-Perot resonator V, which can be found in the reference section. Figure 5 This fabrication method employs arc discharge technology to fuse a section of hollow fiber to the tail end of the first optical fiber 1. The hollow fiber is then fused with a matching fiber to form a sealed cavity. The end face of the fused first optical fiber 1 is mechanically polished to obtain a flat pressure-sensitive diaphragm. Under the action of the pressure-sensitive diaphragm, the spatial pressure value can be calculated by measuring the change in cavity length of the Fabry-Perot resonant cavity V, thereby achieving the measurement of external pressure.

[0030] refer to Figure 6 The specific fabrication steps for the Fabry-Perot resonator V are as follows:

[0031] Step 1: Use wire strippers to remove the coating layer from the surface of the first optical fiber 1 to be processed, and clean it with an alcohol swab. Then, place the cleaned first optical fiber 1 on a dedicated fiber optic cleaver to cut it, obtaining a flat fiber end face, and fix it inside the fiber optic fusion splicer 6. Place the hollow-core optical fiber 8 on the dedicated fiber optic cleaver to cut it, obtaining a flat fiber end face, and fix it at the other end of the fiber optic fusion splicer 6. (Reference) Figure 6 (a).

[0032] Step 2: Using the manual fusion splicing mode of the fiber optic fusion splicer 6, adjust the end-face positions of the first fiber 1 and the hollow fiber 8 to be fused. Set appropriate discharge parameters, discharge time, and advance distance, and discharge the electrode 7 to achieve end-face fusion of the corresponding fibers.

[0033] Step 3: Using a CCD vision fiber optic cleaving platform, the spliced ​​optical fiber is precisely positioned and its length is effectively measured before cleaving to obtain hollow optical fiber of the appropriate length. The dimensions of the Fabry-Perot cavity are directly determined by the cleaving length at this point.

[0034] Step 4: Clean the cut fiber end face using an ultrasonic cleaner and then place it back into the fiber optic fusion splicer. It is crucial here that the cleaning of the cut fiber end face ensures it is completely clean and does not affect subsequent optical properties.

[0035] Step 5: Place the quartz-coated fiber 9 into the fiber optic fusion splicer 6, adjust the corresponding splicing parameters, and repeat the operation in Step 3 to fuse the coated fiber 9 and the cleaned hollow fiber together. (Reference) Figure 6 (b)

[0036] Step 6: Adjust the corresponding cutting parameters and repeat the operation in Step 4 to obtain the appropriate design length of optical fiber as the pressure-sensing diaphragm. (Reference) Figure 6 (c)

[0037] Step 7: Due to the limitations of the fiber optic vision cutting platform, the pressure-sensitive diaphragm prepared in Step 6 is relatively thick. The diaphragm is then polished using abrasive paper of varying roughness. During the polishing process, a microscope is used to observe the polishing process in real time, and a spectral analyzer is used to monitor the signal. A thinner pressure-sensitive diaphragm is then prepared through this polishing process. (Reference) Figure 6 (d)

[0038] Specifically, the sleeve in this embodiment is made of quartz material to maintain homogeneity with the optical fiber. If other optical fiber materials are used, the sleeve material will change accordingly. For example, if the optical fiber is made of sapphire, the sleeve will also be made of sapphire.

[0039] The sleeve 5, serving as an external component that combines protection and barrier fixation, has a length of 10-25cm and an outer diameter of 2.3mm-2.5mm. The sleeve has a four-hole structure with an inner diameter of 0.2mm. The first, second, and third holes corresponding to the second optical fiber 2, third optical fiber 3, and fourth optical fiber 4 are arranged in a triangular pattern inside the sleeve. The processed first optical fiber 1, second optical fiber 2, third optical fiber 3, and fourth optical fiber 4 are placed into the four holes of the sleeve 5. A CCD vision system is used for precise positioning of the optical fibers. After the first optical fiber 1, second optical fiber 2, third optical fiber 3, and fourth optical fiber 4 are adjusted to the correct positions, the sleeve 5 is heated using a laser. The heated inner wall of the sleeve 5 collapses, encasing the first optical fiber 1, second optical fiber 2, third optical fiber 3, and fourth optical fiber 4, achieving homogeneous integration of the sensitive core and the encapsulation material, thus solving the problem of thermal stress mismatch. To prevent stress from acting on the four fiber gratings, the welding position should be before the four fiber gratings. In particular, the welding point in the first fiber 1 should be between the high-temperature resistant first fiber grating I and the Fabry-Perot resonator V.

[0040] The above description is merely a preferred embodiment of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention by those skilled in the art within the scope of the technology disclosed in the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A temperature, pressure, and current sensor combining a fiber optic grating and a Fabry-Perot resonant cavity, characterized in that: The first optical fiber (1) is located at the center of the triangle and is connected in the sleeve (5) to the second optical fiber (2), the third optical fiber (3), and the fourth optical fiber (4). The first optical fiber (1) is inscribed with a high-temperature resistant first fiber grating (Ⅰ) and a Fabry-Perot resonant cavity (Ⅴ) is prepared at its end; the second optical fiber (2), the third optical fiber (3), and the fourth optical fiber (4) are respectively inscribed with a high-temperature resistant second fiber grating (Ⅱ), a third fiber grating (Ⅲ), and a fourth fiber grating (Ⅳ); The first fiber grating (Ⅰ) to the second fiber grating (Ⅱ), the third fiber grating (Ⅲ), and the fourth fiber grating (Ⅳ) form a triangular pyramid structure in space. The first fiber grating (Ⅰ) is located at the vertex of the triangular pyramid, and the second fiber grating (Ⅱ), the third fiber grating (Ⅲ), and the fourth fiber grating (Ⅳ) are located at the three vertices of the base triangle of the triangular pyramid, respectively.

2. The temperature, pressure, and current sensor combining a fiber optic grating and a Fabry-Perot resonator according to claim 1, characterized in that: The length of the grating region of the first fiber grating (Ⅰ), the second fiber grating (Ⅱ), the third fiber grating (Ⅲ), and the fourth fiber grating (Ⅳ) is <1mm, and the grating Bragg wavelength is in the range of 1500nm-1600nm.

3. The temperature, pressure, and current sensor combining a fiber optic grating and a Fabry-Perot resonator according to claim 1, characterized in that: The Fabry-Perot resonant cavity (V) is a sealed cavity formed by fusing a section of hollow fiber with an arc discharge technique at the tail end of the first optical fiber (1), and then fusing the hollow fiber with a matching optical fiber.

4. The temperature, pressure, and current sensor combining a fiber optic grating and a Fabry-Perot resonator according to claim 3, characterized in that: The end face of the optical fiber is mechanically polished to obtain a pressure-sensitive diaphragm that senses changes in environmental pressure.

5. The temperature, pressure, and current sensor combining a fiber optic grating and a Fabry-Perot resonator according to claim 1, characterized in that: The sleeve (5) is 10-25cm long and has an outer diameter of 2.3mm-2.5mm. The sleeve (5) has a four-hole structure with an inner diameter of 0.2mm. The first hole, the second hole, and the third hole are arranged in a triangular pattern. The two ends of the sleeve (5) connected to the first optical fiber (1), the second optical fiber (2), the third optical fiber (3), and the fourth optical fiber (4) are heated by laser, causing the inner wall of the sleeve (5) to collapse due to heat and wrap around the first optical fiber (1), the second optical fiber (2), the third optical fiber (3), and the fourth optical fiber (4).

6. The temperature, pressure, and current sensor combining a fiber optic grating and a Fabry-Perot resonator according to claim 5, characterized in that: The sleeve (5) is made of the same material as the first optical fiber (1), the second optical fiber (2), the third optical fiber (3), and the fourth optical fiber (4).

Images