Dual-parameter optical fiber sensor based on FP-WGM composite microcavity and its preparation method

Abstract

The present invention provides a dual-parameter optical fiber sensor based on an FP-WGM composite microcavity and a preparation method thereof, relating to the field of optical fiber sensing technology. The dual-parameter optical fiber sensor comprises: a circulator, a composite microcavity column, a left tapered optical fiber, and a right tapered optical fiber; wherein the composite microcavity column comprises: a front-end single-mode optical fiber C, a hollow-core optical fiber B, and a rear-end single-mode optical fiber A fused in series; the circulator transmits an optical signal to the composite microcavity column, and the optical signal excites FPI interference in the composite microcavity column. The generated FPI reflected light is directionally transmitted to the left tapered optical fiber through the circulator, and WGM resonance is excited by coupling between the left tapered optical fiber and the composite microcavity column, and then the FPI-WGM composite optical signal is received by the right tapered optical fiber. The present invention can be used to simultaneously measure ambient temperature and liquid concentration, and eliminate the cross-interference of temperature on concentration measurement.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to a dual-parameter optical fiber sensor based on an FP-WGM composite microcavity and a preparation method thereof. Background Art

[0002] Fiber optic sensors are widely used in biomedicine, environmental monitoring and other fields due to their high sensitivity, resistance to electromagnetic interference and compact structure. Whispering Gallery Mode (WGM) microcavity sensors can achieve high-precision detection of liquid concentration due to their ultra-high quality factor (Q value) and tiny mode volume. However, traditional WGM sensors are susceptible to temperature changes when measuring liquid concentration, leading to cross-sensitivity problems. In existing technologies, additional temperature compensation devices such as fiber Bragg gratings (FBGs) or external temperature probes are usually required. However, such methods increase system complexity and manufacturing costs and are difficult to achieve miniaturized integration.

[0003] In recent years, solutions to the above problems have been proposed, such as material modification (such as negative thermo-optical coefficient coating) or composite structures (such as the combination of FBG and WGM) for temperature compensation. However, these solutions still have the following problems:

[0004] 1. Material modification has stringent requirements on the manufacturing process, and the coating thickness or microcavity size is difficult to accurately control;

[0005] 2. Composite structures (such as FBG and WGM in series) require multi-optical path design, making signal demodulation complex and unstable.

[0006] 3. Although existing FPI sensors are sensitive to temperature, they cannot be directly used for simultaneous multi-parameter measurement.

[0007] Therefore, there is an urgent need for a dual-parameter optical fiber sensor that has a simple structure, low cost, and can eliminate temperature interference as much as possible. Summary of the Invention

[0008] In response to the above-mentioned shortcomings of the existing technology, the present invention proposes a dual-parameter fiber optic sensor based on a Fabry–Pérot interferometer (FPI) and a whispering gallery mode (WGM) and a preparation method thereof, aiming to simultaneously measure ambient temperature and liquid concentration and eliminate the cross-interference of temperature on concentration measurement.

[0009] The first aspect of the present invention proposes a dual-parameter optical fiber sensor based on an FP-WGM composite microcavity, which comprises: a circulator, a composite microcavity column, a left-tapered optical fiber, and a right-tapered optical fiber; wherein the composite microcavity column comprises: a front-end single-mode optical fiber C, a hollow optical fiber B, and a rear-end single-mode optical fiber A, which are fused in series;

[0010] The circulator transmits the optical signal to the composite microcavity column, where the optical signal excites FPI interference. The generated FPI reflected light is directionally transmitted to the left tapered optical fiber through the circulator, and excites WGM resonance through the coupling between the left tapered optical fiber and the composite microcavity column. The FPI-WGM composite optical signal is then received by the right tapered optical fiber.

[0011] Furthermore, the circulator is connected to the composite microcavity column through optical fiber fusion coupling; the circulator is connected to the left tapered optical fiber through an optical fiber adapter and a jumper.

[0012] Furthermore, the length range of the front-end single-mode optical fiber C is 230-240 μm; the length range of the hollow-core optical fiber B is 280-310 μm; the length range of the rear-end single-mode optical fiber A is 300-350 μm; and the diameter of the composite microcavity column is 125 μm.

[0013] Furthermore, the left tapered optical fiber and the right tapered optical fiber have the same dimensions, including: a tapered waist diameter of 1.8 μm, a tapered waist length ranging from 1000 to 2000 μm, and an overall tapered region length ranging from 5000 to 6000 μm.

[0014] Furthermore, there are three reflection interfaces M1, M2, and M3 in the composite microcavity column; wherein the reflection interface M1 is the fusion surface of the front single-mode optical fiber A and the hollow-core optical fiber B; the reflection interface M2 is the fusion surface of the hollow-core optical fiber B and the rear single-mode optical fiber C; and the reflection interface M3 is the top surface of the rear single-mode optical fiber C.

[0015] The reflective interface M1 and the reflective interface M2 constitute a first FP cavity; the reflective interface M2 and the reflective interface M3 constitute a second FP cavity; the reflective interface M1 and the reflective interface M3 constitute a third FP cavity; and the difference between the free spectral range FSR1 of the first FP cavity and the free spectral range FSR2 of the second FP cavity is required to be less than 12% of FSR1 to generate a superimposed interference spectrum.

[0016] The second aspect of the present invention proposes a method for preparing a dual-parameter optical fiber sensor based on an FP-WGM composite microcavity, which includes the following steps:

[0017] A single-mode fiber is selected as the back-end single-mode fiber, and the front-end single-mode fiber is fused with a hollow-core fiber to form a single-mode-hollow-core structure. The front-end single-mode fiber end of the single-mode-hollow-core structure is then cut into a fixed length using a fixed-length cutting system.

[0018] Select another section of single-mode fiber as the front-end single-mode fiber, and fuse the hollow-core fiber end of the single-mode-hollow-core structure with the front-end single-mode fiber. The length of the hollow-core fiber after the fusion is required to be a preset fixed length, forming a single-mode-hollow-core-single-mode structure.

[0019] Then, a fixed-length cutting system is used to cut the front single-mode optical fiber in the single-mode-hollow-core-single-mode structure into a fixed length to form a composite microcavity column;

[0020] A circulator is selected and connected to the front end single-mode optical fiber end of the composite microcavity column through a jumper and optical fiber fusion coupling;

[0021] Four identical single-mode optical fibers are selected and divided into two pairs. For each pair of single-mode optical fibers, the pair is placed in a fusion splicer according to the standard fiber fusion splicing process. The pair of single-mode optical fibers is then stretched into a tapered optical fiber using the fusion splicer's manual splicing mode according to a preset program. The two tapered optical fibers formed by stretching are labeled as the left tapered optical fiber and the right tapered optical fiber, respectively.

[0022] A predetermined fusion point is made on the left side of the composite microcavity column and a notch is made. A low-viscosity UV glue is used to temporarily fix the tapered area of ​​the left tapered optical fiber. A fusion splicer is then used to melt and taper the waist of the left tapered optical fiber and the notch on the left side of the composite microcavity column in stages. A predetermined fusion point is made on the right side of the composite microcavity column and a notch is made. A low-viscosity UV glue is used to temporarily fix the tapered area of ​​the right tapered optical fiber. A fusion splicer is then used to melt and taper the waist of the right tapered optical fiber and the notch on the right side of the composite microcavity column in stages.

[0023] The circulator was connected to the left tapered optical fiber through a fiber adapter to complete the preparation of the dual-parameter optical fiber sensor based on the FP-WGM composite microcavity.

[0024] The beneficial effects of adopting the above technical solution are:

[0025] This invention provides a dual-parameter fiber optic sensor based on an FP-WGM composite microcavity, combining the Vernier effect with WGM. This dual-parameter fiber optic sensor achieves simultaneous, high-precision measurement of temperature and liquid concentration through a single optical path. It utilizes signal frequency domain separation technology to process the measured data, eliminating cross-sensitivity issues. This dual-parameter fiber optic sensor boasts a compact structure, high sensitivity, excellent stability, and resistance to electromagnetic interference. It is suitable for biomedical testing, such as glucose concentration monitoring, and for liquid analysis in complex environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure of the composite microcavity column in this embodiment;

[0027] Figure 2 Schematic diagram of the structure of a dual-parameter optical fiber sensor based on the FP-WGM composite microcavity in this embodiment;

[0028] Figure 3Schematic diagram of the resonance excitation and experimental test of the composite micro-cavity column optical fiber sensor in this embodiment;

[0029] Figure 4 Flowchart of a preparation method of a dual-parameter optical fiber sensor based on an FP-WGM composite microcavity in this embodiment;

[0030] Figure 5 This is a graph of the vernier before and after coupling and its filtered spectrum in this embodiment;

[0031] Figure 6 Graph showing the fitted curve of the concentration test experiment in this embodiment;

[0032] In the figure: 1-light source; 2-circulator; 3-composite microcavity column; 4-left tapered optical fiber; 5-right tapered optical fiber; 6-spectrometer. DETAILED DESCRIPTION

[0033] For ease of understanding of the present application, the specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings and embodiments. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thoroughly and comprehensively understood.

[0034] The specific embodiments of the present invention include sensor preparation, experimental system construction, signal processing algorithm and performance testing method. For details, please refer to the technical solution and claims. The sensor can be widely used in biomedical liquid detection such as blood glucose monitoring, industrial process control and environmental monitoring. Specifically, in this embodiment, the dual-parameter fiber optic sensor based on the FP-WGM composite microcavity is a composite microcavity column fiber optic sensor. The core of the dual-parameter fiber optic sensor is to fuse a hollow optical fiber with two single-mode optical fibers to form a composite microcavity column and its end face, which can simultaneously support FPI interference and WGM resonance, and then realize dual-parameter separation through dual interference effect and signal demodulation technology to perform concentration testing and temperature testing.

[0035] A dual-parameter optical fiber sensor based on a FP-WGM composite microcavity in this embodiment, such as Figure 1-2 As shown, the dual-parameter optical fiber sensor includes: a circulator 2, a composite microcavity column 3, a left tapered optical fiber 4 and a right tapered optical fiber 5; wherein the composite microcavity column includes: a rear single-mode optical fiber C, a hollow optical fiber B and a front single-mode optical fiber A fused in series.

[0036] The circulator 2 transmits the optical signal to the composite microcavity column 3, and the optical signal excites FPI interference in the composite microcavity column 3. The generated FPI reflected light is directionally transmitted to the left tapered optical fiber 4 through the circulator 2, and excites WGM resonance through the coupling between the left tapered optical fiber 4 and the composite microcavity column 3. The FPI-WGM composite optical signal is then collected by the right tapered optical fiber 5.

[0037] The circulator 2 is connected to the composite microcavity column 3 through optical fiber fusion coupling; the circulator 2 is connected to the left tapered optical fiber 4 through an optical fiber adapter and a jumper.

[0038] In this embodiment, a three-port circulator 2 is used and connected to other structures with jumpers, and the optical signal is transmitted in a fixed order through each port to achieve directional transmission. Figure 3 As shown, the optical signal emitted by light source 1 enters a jumper wire of circulator 2 and excites FP interference in composite microcavity column 3. The reflected light then enters the tapered optical fiber through another jumper wire of circulator 2. Specifically, when FP interference occurs in composite microcavity column 3, the light reflects on the reflection surfaces within the three FP cavities in composite microcavity column 3, exciting FP resonance. The reflected light is then guided out of composite microcavity column 3 by the jumper wire of circulator 2 and enters the left tapered optical fiber 4. Through coupling between the tapered optical fiber and composite microcavity column 3, the composite optical signal carrying FPI and WGM information is finally collected by the right tapered optical fiber 5 and transmitted to the spectrometer 6 for analysis.

[0039] The length of the rear single-mode optical fiber C is in the range of 230-240 μm; the length of the hollow-core optical fiber B is in the range of 280-310 μm; the length of the front single-mode optical fiber A is in the range of 300-900 μm; and the diameter of the composite microcavity column is 125 μm.

[0040] The left tapered optical fiber 4 and the right tapered optical fiber 5 have the same dimensions, including: a tapered waist diameter of 1.8 μm, a tapered waist length ranging from 1000 to 2000 μm, and an overall tapered region length ranging from 5000 to 6000 μm.

[0041] In this embodiment, the refractive index of air is 1.0003 and the transmission loss coefficient is Under the premise that both the back-end single-mode optical fiber C and the front-end single-mode optical fiber A use single-mode optical fibers with a refractive index of 1.4688, and the diameters of the back-end single-mode optical fiber C, the hollow-core optical fiber B, and the front-end single-mode optical fiber A are approximately 125 μm. In the preparation process of this embodiment, the length of the cut back-end single-mode optical fiber C is 230.5 μm, the length of the hollow-core optical fiber B is 298.6 μm, and the length of the front-end single-mode optical fiber A is preferably in the range of 300-350 μm. There are no special conditions for fusion splicing. The general conditions are that the end face angle is <0.5°, the core offset is <0.5 μm, and the reserved overlap length is approximately 20 μm. The composite microcavity column optical fiber sensor is an FP cavity (Fabry–Pérot Cavity) formed by fusion splicing two sections of single-mode optical fiber and a hollow-core optical fiber in series, and has three reflection interfaces.

[0042] There are three reflection interfaces M1, M2, and M3 in the composite microcavity column 3; the reflection interface M1 is the fusion surface of the front single-mode optical fiber A and the hollow optical fiber B; the reflection interface M2 is the fusion surface of the hollow optical fiber B and the rear single-mode optical fiber C; and the reflection interface M3 is the top surface of the rear single-mode optical fiber C.

[0043] The reflective interface M1 and the reflective interface M2 constitute a first FP cavity; the reflective interface M2 and the reflective interface M3 constitute a second FP cavity; the reflective interface M1 and the reflective interface M3 constitute a third FP cavity; and the difference between the free spectral range FSR1 of the first FP cavity and the free spectral range FSR2 of the second FP cavity is required to be less than 12% of FSR1 to generate a superimposed interference spectrum.

[0044] The left tapered optical fiber 4 is coupled with the composite microcavity column 3 to excite WGM resonance, and the right tapered optical fiber 5 receives and transmits the optical signal to the spectrometer.

[0045] When the dual-parameter optical fiber sensor based on the FP-WGM composite microcavity proposed in this embodiment is used to perform simultaneous high-precision measurements of temperature and liquid concentration, its operating principle is as follows:

[0046] Temperature-sensitive mechanism: The wavelength shift of the FPI interference spectrum is driven by both the thermo-optical effect and the thermal expansion effect. For the dual-parameter fiber optic sensor in this embodiment, the temperature sensitivity of the FPI is 13.75 pm / °C, and the temperature sensitivity of the WGM is 11.2 pm / °C.

[0047] Concentration Sensitivity Mechanism: The WGM resonant wavelength shift is caused by changes in the refractive index of the external liquid. Its resonant peak position varies with temperature, exhibiting a significant blue shift as the temperature decreases. For the dual-parameter fiber optic sensor in this embodiment, the WGM has a concentration sensitivity of 52.95 pm / %, while the FP has a concentration sensitivity of 2.2 pm / %.

[0048] Cross-interference elimination: Fast Fourier Transform (FFT) is used to separate the collected composite spectrum into a low-frequency FPI signal sensitive to temperature changes and a high-frequency WGM signal sensitive to concentration changes. The sensitivity matrix is ​​then used to decouple the two parameters. The specific signal processing and demodulation methods are as follows:

[0049] Cutoff frequency FFT frequency domain separation: Set the cutoff frequency to 0.79nm⁻¹, extract the FPI envelope by low-pass filtering the composite spectrum, and extract the WGM resonance peak by high-pass filtering.

[0050] Based on the sensitivity matrix equation, the actual temperature is calculated by matrix inversion and concentration ; The sensitivity matrix equation is:

[0051]

[0052] in Indicates the wavelength shift of FPI resonance caused by temperature and concentration changes; represents the wavelength shift of the WGM resonance; Indicates the actual temperature; Indicates actual concentration.

[0053] In this embodiment, the composite microcavity column in the dual-parameter optical fiber sensor based on the FP-WGM composite microcavity is manufactured by using a fixed-length cutting and fusion splicing technology.

[0054] A method for preparing a dual-parameter optical fiber sensor based on a FP-WGM composite microcavity in this embodiment is as follows: Figure 4 As shown, the preparation method includes the following steps:

[0055] A section of single-mode fiber is selected as the back-end single-mode fiber, and the front-end single-mode fiber is fused with a section of hollow-core fiber to form a single-mode-hollow-core structure. Then, a fixed-length cutting system is used to cut the front-end single-mode fiber end of the single-mode-hollow-core structure into a fixed length.

[0056] In this embodiment, a fixed-length cutting system is used to cut the rear-end single-mode optical fiber into a single-mode-hollow-core structure of 300 μm.

[0057] Select another section of single-mode optical fiber as the front-end single-mode optical fiber, and fusion-splice the hollow-core optical fiber end of the single-mode-hollow-core structure with the front-end single-mode optical fiber. It is required that the length of the hollow-core optical fiber after fusion-splice is a preset fixed length, forming a single-mode-hollow-core-single-mode structure.

[0058] In this embodiment, the length of the hollow-core optical fiber after fusion splicing is 298.6 μm, and there is no requirement for the length of the front-end single-mode optical fiber.

[0059] Then, a fixed-length cutting system is used to cut the front single-mode optical fiber in the single-mode-hollow-core-single-mode structure into a fixed length to form a composite microcavity column.

[0060] In this embodiment, the length of the front-end single-mode optical fiber is cut to 230.5 μm, and the final composite microcavity column is obtained with a rear-end single-mode optical fiber length of 300 μm, a hollow-core optical fiber length of 298.6 μm, and a front-end single-mode optical fiber length of 230.5 μm, which is used as the core part of the sensor.

[0061] A circulator is selected and connected to the front single-mode optical fiber end of the composite microcavity column through a jumper through optical fiber fusion coupling.

[0062] Four identical single-mode optical fibers are selected and divided into two pairs of single-mode optical fibers. For any pair of single-mode optical fibers, the pair of single-mode optical fibers is placed in a fusion splicer according to the standard fiber fusion splicing process. The pair of single-mode optical fibers is stretched into a tapered optical fiber using the manual fusion splicing mode of the fusion splicer according to the preset program. The two tapered optical fibers formed by stretching are marked as the left tapered optical fiber and the right tapered optical fiber, respectively.

[0063] In this embodiment, the specific procedure for preparing the tapered optical fiber in the laboratory is shown in Table 1.

[0064] Table 1 Specific procedures for preparing fiber tapers in the laboratory:

[0065]

[0066] A predetermined fusion point is made on the left side of the composite microcavity column and a notch is made. A low-viscosity UV glue is used to temporarily fix the tapered area of ​​the left tapered optical fiber. Then, a fusion splicer is used to melt and taper the waist of the left tapered optical fiber and the notch point on the left side of the composite microcavity column in stages. A predetermined fusion point is made on the right side of the composite microcavity column and a notch is made. A low-viscosity UV glue is used to temporarily fix the tapered area of ​​the right tapered optical fiber. Then, a fusion splicer is used to melt and taper the waist of the right tapered optical fiber and the notch point on the right side of the composite microcavity column in stages.

[0067] In this embodiment, a cutter is used to make a notch at a predetermined fusion point on the side of the composite microcavity column, and the notch depth is required to be less than 10% of the diameter of the composite microcavity column, that is, 12.5 μm; a low-viscosity UV glue is used to temporarily fix the tapered area of ​​the tapered optical fiber; the composite microcavity column is fixed horizontally in the V-groove of the fusion splicer, with the notch point facing upward; the tapered optical fiber is clamped with a three-dimensional adjustment frame so that its waist is aligned with the notch point of the composite microcavity column, and the spacing is controlled between 100nm and 200nm; after the position of the composite microcavity column and the tapered optical fiber is corrected, 30% of the normal discharge intensity, that is, an intensity value of 30, is used to perform the first micro-discharge to make the tapered optical fiber stick to the composite microcavity column. If the position is correct, that is, there is no position offset after the first discharge, a second normal discharge is performed to melt the tapered optical fiber and the notch point of the composite microcavity column to couple the tapered fiber. In order to avoid the collapse of the optical fiber and ensure the cone waist diameter, it is slightly stretched outward during the fusion process, that is, an axial micro-tension is applied during the fusion process. The axial micro-tension requires a tension of no more than 0.005 Newtons and an action time of no longer than 1 second to prevent the cone waist diameter from shrinking.

[0068] The circulator was connected to the left tapered optical fiber through a fiber adapter to complete the preparation of the dual-parameter optical fiber sensor based on the FP-WGM composite microcavity.

[0069] In this embodiment, an experimental system for resonant excitation of a dual-parameter fiber optic sensor based on an FP-WGM composite microcavity was constructed to detect the composite spectral characteristics of FPI and WGM, thereby verifying the effectiveness of the dual-parameter fiber optic sensor. The specific experimental process is as follows:

[0070] The experimental setup included a broadband ASE light source operating at 1520-1570 nm, a Yokogawa AQ6370D spectrometer with a resolution of 0.02 nm for spectral analysis, and a digital microscope for real-time monitoring of the coupling state between the microsphere and the tapered fiber. For the dual-parameter fiber sensor based on the FP-WGM composite microcavity, a three-port circulator with a 1550 nm wavelength, steel tube encapsulation, P-grade, 0.9 mm sleeve, and a fiber length of 1 mm was used. The patch cables used for the three ports were FAFA-SM-0901-0101, FUFU-SM-0901-0101, and FAFU-SM-0901-0101, respectively. It should be noted that the circulator and tapered fiber used in this embodiment can be replaced with other devices with equivalent functionality.

[0071] In this embodiment, if Figure 3 As shown, the optical signal emitted by the light source 1 is transmitted to the composite microcavity column of the dual-parameter optical fiber sensor through the spectrometer, i.e., the circulator 2. The spectrometer is connected to the composite microcavity column through optical fiber fusion coupling, and is connected to the tapered optical fiber and the light source through an optical fiber adapter. Its function is to simplify the optical path and ensure directional transmission of the optical signal.

[0072] The dual-parameter fiber sensor is coupled to a tapered fiber through fusion tapering. This involves bringing the two fibers to be connected into close contact, heating the fiber connection point with an arc, and then stretching the fibers to form a tapered region to couple the light field. WGM resonance is excited by coupling through a 1.8μm diameter tapered fiber, and the composite spectrum is recorded using a broadband light source and an optical spectrum analyzer (OSA). Figure 5 As shown, the abscissa of the composite spectrum is set to wavelength range, which in this experiment was 1400-1600 nm; the ordinate of the composite spectrum is set to contrast. Throughout the experiment, the total spectrum of FPI1, FPI2, FPI3, and the three reflectors, as well as the FPI spectral envelope shift and the coupled composite spectrum were recorded. Since the entire spectrum was recorded, some key data are provided below: FSR1 = 3.3 nm, FSR2 = 2.94 nm, FSR3 = 1.48 nm. The free spectral range of the interference spectrum envelope of the total reflectance spectrum of the three reflectors is 27.05 nm.

[0073] Temperature test: In the range of 10-50°C, the FPI envelope wavelength shift sensitivity is 13.75pm / °C, and the WGM resonance peak sensitivity is 11.2pm / °C;

[0074] Concentration test: When the concentration of NaCl solution changes from 0 to 3%, the WGM resonance peak sensitivity is 52.95pm / %, and the FPI sensitivity is 2.2pm / %. The concentration test fitting curve is as follows: Figure 6 As shown;

[0075] Stability test: During 55 minutes of continuous testing, the wavelength fluctuation was ≤18.32 pm, and the corresponding concentration error was ≤1.52%.

[0076] In summary, the dual-parameter fiber optic sensor based on the FP-WGM composite microcavity achieves simultaneous, high-precision measurement of temperature and liquid concentration through the FPI and WGM composite microcavity design. It also completely eliminates cross-sensitivity issues using FFT frequency-domain separation technology. This dual-parameter fiber optic sensor based on the FP-WGM composite microcavity offers advantages such as simple structure, low cost, high sensitivity (13.75 pm / °C for temperature and 52.95 pm / %) for concentration, and excellent stability (error ≤ 1.52%), providing an innovative solution for precise multi-parameter fiber optic sensing.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the present invention.

Claims

1. A dual-parameter optical fiber sensor based on FP-WGM composite microcavity, characterized in that: The dual-parameter optical fiber sensor comprises: a circulator, a composite microcavity column, a left tapered optical fiber and a right tapered optical fiber; wherein the composite microcavity column comprises: a front-end single-mode optical fiber C, a hollow-core optical fiber B and a rear-end single-mode optical fiber A fused in series; The length of the front-end single-mode optical fiber C is in the range of 230-240 μm; the length of the hollow-core optical fiber B is in the range of 280-310 μm; the length of the back-end single-mode optical fiber A is in the range of 300-350 μm; the diameter of the composite microcavity column is 125 μm; The circulator transmits the optical signal to the composite microcavity column, where the optical signal excites FPI interference. The generated FPI reflected light is directionally transmitted to the left tapered optical fiber through the circulator, and excites WGM resonance through the coupling between the left tapered optical fiber and the composite microcavity column. The FPI-WGM composite optical signal is then received by the right tapered optical fiber.

2. The dual-parameter optical fiber sensor based on the FP-WGM composite microcavity according to claim 1, characterized in that: The circulator is connected to the composite microcavity column through optical fiber fusion coupling; the circulator is connected to the left tapered optical fiber through an optical fiber adapter and a jumper.

3. The dual-parameter optical fiber sensor based on the FP-WGM composite microcavity according to claim 2, characterized in that: The left tapered optical fiber and the right tapered optical fiber have the same dimensions, including: a tapered waist diameter of 1.8 μm, a tapered waist length ranging from 1000 to 2000 μm, and an overall tapered region length ranging from 5000 to 6000 μm.

4. The dual-parameter optical fiber sensor based on the FP-WGM composite microcavity according to claim 3, characterized in that: There are three reflection interfaces M1, M2, and M3 in the composite microcavity column; the reflection interface M1 is the fusion surface of the front single-mode optical fiber A and the hollow-core optical fiber B; the reflection interface M2 is the fusion surface of the hollow-core optical fiber B and the rear single-mode optical fiber C; and the reflection interface M3 is the top surface of the rear single-mode optical fiber C. The reflective interface M1 and the reflective interface M2 constitute a first FP cavity; the reflective interface M2 and the reflective interface M3 constitute a second FP cavity; the reflective interface M1 and the reflective interface M3 constitute a third FP cavity; and the difference between the free spectral range FSR1 of the first FP cavity and the free spectral range FSR2 of the second FP cavity is required to be less than 12% of FSR1 to generate a superimposed interference spectrum.

5. The dual-parameter optical fiber sensor based on the FP-WGM composite microcavity according to claim 4, characterized in that: The preparation method of the dual-parameter optical fiber sensor based on the FP-WGM composite microcavity includes the following steps: A single-mode fiber is selected as the back-end single-mode fiber, and the front-end single-mode fiber is fused with a hollow-core fiber to form a single-mode-hollow-core structure. The front-end single-mode fiber end of the single-mode-hollow-core structure is then cut into a fixed length using a fixed-length cutting system. Select another section of single-mode fiber as the front-end single-mode fiber, and fuse the hollow-core fiber end of the single-mode-hollow-core structure with the front-end single-mode fiber. The length of the hollow-core fiber after the fusion is required to be a preset fixed length, forming a single-mode-hollow-core-single-mode structure. Then, a fixed-length cutting system is used to cut the front single-mode optical fiber in the single-mode-hollow-core-single-mode structure into a fixed length to form a composite microcavity column; A circulator is selected and connected to the front end single-mode optical fiber end of the composite microcavity column through a jumper and optical fiber fusion coupling; Four identical single-mode optical fibers are selected and divided into two pairs. For each pair of single-mode optical fibers, the pair is placed in a fusion splicer according to the standard fiber fusion splicing process. The pair of single-mode optical fibers is then stretched into a tapered optical fiber using the fusion splicer's manual splicing mode according to a preset program. The two tapered optical fibers formed by stretching are labeled as the left tapered optical fiber and the right tapered optical fiber, respectively. A predetermined fusion point is made on the left side of the composite microcavity column and a notch is made. A low-viscosity UV glue is used to temporarily fix the tapered area of ​​the left tapered optical fiber. A fusion splicer is then used to melt and taper the waist of the left tapered optical fiber and the notch on the left side of the composite microcavity column in stages. A predetermined fusion point is made on the right side of the composite microcavity column and a notch is made. A low-viscosity UV glue is used to temporarily fix the tapered area of ​​the right tapered optical fiber. A fusion splicer is then used to melt and taper the waist of the right tapered optical fiber and the notch on the right side of the composite microcavity column in stages. The circulator was connected to the left tapered optical fiber through a fiber adapter to complete the preparation of the dual-parameter optical fiber sensor based on the FP-WGM composite microcavity.

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