Two-parameter optical fiber sensor based on FP-WGM composite microcavity and preparation method thereof

Abstract

The invention provides a two-parameter optical fiber sensor based on an FP-WGM composite microcavity and a preparation method of the two-parameter optical fiber sensor, and relates to the technical field of optical fiber sensing. The two-parameter optical fiber sensor comprises a circulator, a composite microcavity column, a left conical optical fiber and a right conical 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 which are connected in series and welded; the circulator transmits an optical signal to the composite microcavity column, the optical signal excites FPI interference in the composite microcavity column, generated FPI reflected light is directionally transmitted to the left conical optical fiber through the circulator, WGM resonance is excited through coupling of the left conical optical fiber and the composite microcavity column, and then an FPI-WGM composite optical signal is received through the right conical optical fiber. The device can be used for measuring the environment temperature and the liquid concentration at the same time and eliminating cross interference of the temperature on concentration measurement.

Description

Technical Field

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

[0002] Due to advantages such as high sensitivity, anti-electromagnetic interference, and compact structure, optical fiber sensors are widely used in fields such as biomedicine and environmental monitoring. The Whispering Gallery Mode (WGM) microcavity sensor can achieve high-precision detection of liquid concentration by virtue of its ultra-high quality factor, i.e., Q value, and tiny mode volume. However, traditional WGM sensors are susceptible to temperature changes when measuring liquid concentration, resulting in cross-sensitivity problems. In the prior art, additional temperature compensation devices such as fiber Bragg gratings FBG or external temperature probes usually need to be introduced, but such methods increase the system complexity and manufacturing cost, and it is difficult to achieve miniaturized integration.

[0003] Regarding the above problems, solutions for temperature compensation have been proposed in recent years through material modification (such as a negative thermo-optic coefficient coating) or composite structures (such as the combination of FBG and WGM), but these solutions still have the following problems:

[0004] 1. Material modification has strict requirements for manufacturing processes, and it is difficult to precisely control the coating thickness or microcavity size;

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

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

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

[0008] Aiming at the deficiencies of the above prior art, based on the Fabry–Pérot interferometer (FPI) and the Whispering Gallery Mode WGM, the present invention proposes a dual-parameter optical fiber sensor based on an FP-WGM composite microcavity and a preparation method thereof, aiming to be able to measure the ambient temperature and liquid concentration simultaneously and eliminate the cross-interference of temperature on concentration measurement.

[0009] In the first aspect of the present invention, a dual-parameter optical fiber sensor based on an FP-WGM composite microcavity is proposed. The dual-parameter optical fiber sensor includes: a circulator, a composite microcavity column, a left tapered optical fiber, and a right tapered optical fiber; wherein the composite microcavity column includes: a front-end single-mode optical fiber C, a hollow optical fiber B, and a rear-end single-mode optical fiber A connected in series by fusion splicing.

[0010] The circulator transmits the 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 fiber by the circulator, and the coupling of the left tapered fiber and the composite microcavity column excites the WGM resonance. Then the right tapered fiber receives the FPI-WGM composite optical signal.

[0011] Further, the circulator is coupled to the composite microcavity column by fiber fusion splicing; the circulator is connected to the left tapered fiber through a fiber adapter and a jumper wire.

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

[0013] Further, the left tapered fiber and the right tapered fiber have the same size, including: the waist diameter of the taper is 1.8 μm, the waist length range of the taper is 1000 - 2000 μm, and the overall length range of the taper region is 5000 - 6000 μm.

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

[0015] Among them, the reflection interface M1 and the reflection interface M2 form the first FP cavity; the reflection interface M2 and the reflection interface M3 form the second FP cavity; the reflection interface M1 and the reflection interface M3 form the third FP cavity; and it is required that the difference between the free spectral range FSR1 of the first FP cavity and the free spectral range FSR3 of the third FP cavity is less than 12% of FSR1 to generate a superimposed interference spectrum.

[0016] A second aspect of the present invention proposes a preparation method of a dual-parameter fiber optic sensor based on an FP-WGM composite microcavity, and this method includes the following processes:

[0017] Select a section of single-mode fiber as the rear-end single-mode fiber, splice the rear-end single-mode fiber with a section of hollow-core fiber to form a single-mode-hollow-core structure, and then use a fixed-length cutting system to cut the rear-end single-mode fiber of the single-mode-hollow-core structure into a fixed length;

[0018] Select another section of single-mode fiber as the front-end single-mode fiber, splice the hollow-core fiber of the single-mode-hollow-core structure with the front-end single-mode fiber, and require that the length of the hollow-core fiber after splicing is a preset fixed length to form a single-mode-hollow-core-single-mode structure;

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

[0020] Select a circulator and connect the circulator to the front single-mode optical fiber in the composite microcavity column through a jumper by fiber fusion splicing.

[0021] Select four identical single-mode optical fibers and divide them into two pairs of single-mode optical fibers. For any pair of single-mode optical fibers, place the pair of single-mode optical fibers in a fusion splicer according to the standard fiber fusion splicing procedure, and stretch the pair of single-mode optical fibers into a tapered optical fiber in the manual fusion splicing mode of the fusion splicer according to a preset program. Mark the two tapered optical fibers formed by stretching as the left tapered optical fiber and the right tapered optical fiber respectively.

[0022] Make a notch at a predetermined fusion splice point on the left side of the composite microcavity column, temporarily fix the tapered region of the left tapered optical fiber with a low-viscosity ultraviolet glue, and then use a fusion splicer to perform staged fusion tapering of the waist of the left tapered optical fiber and the notch point on the left side of the composite microcavity column; make a notch at a predetermined fusion splice point on the right side of the composite microcavity column, temporarily fix the tapered region of the right tapered optical fiber with a low-viscosity ultraviolet glue, and then use a fusion splicer to perform staged fusion tapering of the waist of the right tapered optical fiber and the notch point on the right side of the composite microcavity column.

[0023] Connect the circulator and the left tapered optical fiber through an optical fiber adapter to complete the preparation of a dual-parameter fiber optic sensor based on an FP-WGM composite microcavity.

[0024] The beneficial effects produced by adopting the above technical solution are as follows:

[0025] The present invention provides a fiber optic sensor combining the Vernier effect and WGM, namely a dual-parameter fiber optic sensor based on an FP-WGM composite microcavity. The dual-parameter fiber optic sensor realizes synchronous high-precision measurement of temperature and liquid concentration through a single optical path, and uses signal frequency domain separation technology to process the measurement data to eliminate the cross-sensitivity problem. The dual-parameter fiber optic sensor has the characteristics of compact structure, high sensitivity, good stability, anti-electromagnetic interference, etc., and is suitable for biomedical detection such as glucose concentration monitoring and liquid analysis in complex environments. Description of the Drawings

[0026] Figure 1 It is a schematic structural diagram of the composite microcavity column in this embodiment;

[0027] Figure 2 It is a schematic structural diagram of a dual-parameter fiber optic sensor based on an FP-WGM composite microcavity in this embodiment;

[0028] Figure 3Schematic diagram of resonance excitation and experimental testing of the composite microcavity column fiber optic sensor in this embodiment;

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

[0030] Figure 5 Spectral diagrams before and after Vernier coupling and its filtering in this embodiment;

[0031] Figure 6 Fitting curve graph of the concentration test experiment in this embodiment;

[0032] In the figure: 1 - Light source; 2 - Circulator; 3 - Composite microcavity column; 4 - Left tapered fiber; 5 - Right tapered fiber; 6 - Spectrometer. Specific embodiments

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

[0034] The specific embodiments of the present invention include sensor preparation, experimental system setup, signal processing algorithms, and performance testing methods. For detailed content, please refer to the following technical solutions. This sensor can be widely applied to biomedical liquid detection such as blood glucose monitoring, industrial process control, and environmental monitoring fields. 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 this dual-parameter fiber optic sensor is that a composite microcavity column and its end face are formed by fusing a section of hollow fiber with two sections of single-mode fiber, which can support both FPI interference and WGM resonance. Furthermore, dual-parameter separation is achieved through dual interference effects and signal demodulation technology for concentration testing and temperature testing.

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

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

[0037] The circulator 2 is connected to the compound microcavity column 3 by fiber fusion coupling; the circulator 2 is connected to the left tapered fiber 4 through a fiber optic adapter and a patch cord.

[0038] In this embodiment, a three-port circulator 2 is used and connected to other structures with patch cords, and the optical signal is directionally transmitted through each port in a fixed order. As Figure 3 shown, the optical signal emitted by the light source 1 enters a patch cord of the circulator 2 and excites FP interference in the compound microcavity column 3. The reflected light enters the tapered fiber through another patch cord of the circulator 2. That is, when FP interference occurs in the compound microcavity column 3, the light is reflected on the reflection surfaces in the three FP cavities in the compound microcavity column 3 to excite FP resonance. The reflected light is led out of the compound microcavity column 3 by the patch cord of the circulator 2 and enters the left tapered fiber 4. The coupling between the tapered fiber and the compound microcavity column 3 continues to excite WGM resonance. Finally, the composite optical signal carrying FPI and WGM information is collected by the right tapered fiber 5 and then transmitted to the spectrometer 6 for analysis.

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

[0040] The left tapered fiber 4 and the right tapered fiber 5 have the same dimensions, including: the waist diameter of the taper is 1.8 μm, the waist length range of the taper is 1000 - 2000 μm, and the overall length range of the taper region is 5000 - 6000 μm.

[0041] In this embodiment, when the refractive index of air is 1.0003 and the transmission loss coefficient On the premise that both the rear single-mode optical fiber C and the front single-mode optical fiber A use single-mode optical fibers with a refractive index of 1.4688, and the diameters of the rear single-mode optical fiber C, the hollow optical fiber B, and the front single-mode optical fiber A are approximately 125 μm. During the preparation of this embodiment, the length of the rear single-mode optical fiber C cut is 230.5 μm, the length of the hollow optical fiber B is 298.6 μm, and the length of the front single-mode optical fiber A is preferably in the range of 300 - 350 μm. There are no special conditions for fusion splicing, and the general conditions are an end face angle < 0.5°, a core offset < 0.5 μm, and a reserved overlap length of approximately 20 μm. The composite microcavity column fiber optic sensor consists of an FP cavity (Fabry–Pérot Cavity) formed by fusing and connecting two single-mode optical fibers and a hollow 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; among them, the reflection interface M1 is the fusion splicing surface of the front single-mode optical fiber A and the hollow optical fiber B; the reflection interface M2 is the fusion splicing surface of the hollow optical fiber B and the rear single-mode optical fiber C; the reflection interface M3 is the top surface of the rear single-mode optical fiber C.

[0043] Among them, the reflection interface M1 and the reflection interface M2 form the first FP cavity; the reflection interface M2 and the reflection interface M3 form the second FP cavity; the reflection interface M1 and the reflection interface M3 form the third FP cavity; and it is required that the difference between the free spectral range FSR1 of the first FP cavity and the free spectral range FSR3 of the third FP cavity is less than 12% of FSR1 to generate a superimposed interference spectrum.

[0044] After the left tapered optical fiber 4 is coupled with the composite microcavity column 3, WGM resonance is excited, and the optical signal is received by the right tapered optical fiber 5 and transmitted to the spectrometer.

[0045] When using the dual-parameter fiber optic sensor based on the FP-WGM composite microcavity proposed in this embodiment for synchronous high-precision measurement of temperature and liquid concentration, its working principle is as follows:

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

[0047] Concentration-sensitive mechanism: The wavelength shift of the WGM resonance is caused by the change in the refractive index of the external liquid, and its resonance peak position changes with temperature. As the temperature decreases, the WGM resonance peak shows an obvious blue shift phenomenon. For the dual-parameter fiber optic sensor in this embodiment, the concentration sensitivity of WGM is 52.95 pm / %, and the concentration sensitivity of FP is 2.2 pm / %.

[0048] Cross-interference cancellation: The collected composite spectrum is separated into a low-frequency FPI signal sensitive to temperature changes and a high-frequency WGM signal sensitive to concentration changes through the Fast Fourier Transform (FFT), and the two parameters are decoupled using the sensitivity matrix. The specific signal processing and demodulation methods are as follows:

[0049] Cutoff frequency FFT frequency-domain separation: Set the cutoff frequency to 0.79 nm -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, calculate the actual temperature by matrix inversion and concentration ; The sensitivity matrix equation is:

[0051]

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

[0053] In this embodiment, the composite microcavity column in the dual-parameter fiber optic sensor based on the FP-WGM composite microcavity is fabricated using fixed-length cutting and fusion splicing techniques.

[0054] A preparation method for a dual-parameter fiber optic sensor based on the FP-WGM composite microcavity in this embodiment, as Figure 4 shown, the preparation method includes the following processes:

[0055] Select a section of single-mode fiber as the rear single-mode fiber, fuse the rear single-mode fiber with a section of hollow fiber to form a single-mode-hollow structure, and then use a fixed-length cutting system to cut the rear single-mode fiber of the single-mode-hollow structure into a fixed length.

[0056] In this embodiment, a single-mode-hollow structure with a rear single-mode fiber cut to 300 μm is cut using a fixed-length cutting system.

[0057] Select another section of single-mode fiber as the front single-mode fiber, fuse the hollow fiber of the single-mode-hollow structure with the front single-mode fiber, and require that the length of the hollow fiber after fusion is a preset fixed length to form a single-mode-hollow-single-mode structure.

[0058] In this embodiment, the length of the hollow fiber after fusion is 298.6 μm, and the length of the front single-mode fiber is not required.

[0059] Then, use a fixed-length cutting system 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 cut front single-mode optical fiber is 230.5 μm, and finally a composite microcavity column with a rear single-mode optical fiber length of 300 μm, a hollow-core optical fiber length of 298.6 μm, and a front single-mode optical fiber length of 230.5 μm is obtained, which is used as the core part of the sensor.

[0061] Select a circulator and connect the circulator to the front single-mode optical fiber in the composite microcavity column through optical fiber fusion coupling by a jumper wire.

[0062] Select four identical single-mode optical fibers and divide them into two pairs of single-mode optical fibers. For any pair of single-mode optical fibers, place the pair of single-mode optical fibers in a fusion splicer according to the standard optical fiber fusion splicing procedure, and use the manual fusion splicing mode of the fusion splicer to stretch the pair of single-mode optical fibers into a tapered optical fiber according to a preset program. Mark the two tapered optical fibers formed by stretching 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 procedure for preparing the fiber taper in the laboratory:

[0065] Predetermine the fusion joint points on the left side of the composite microcavity column and make marks. Use a low-viscosity ultraviolet glue to temporarily fix the tapered area of the left tapered optical fiber, and then use a fusion splicer to perform staged melting and tapering of the waist of the left tapered optical fiber with the left-side marked point of the composite microcavity column; predetermine the fusion joint points on the right side of the composite microcavity column and make marks. Use a low-viscosity ultraviolet glue to temporarily fix the tapered area of the right tapered optical fiber, and then use a fusion splicer to perform staged melting and tapering of the waist of the right tapered optical fiber with the right-side marked point of the composite microcavity column.

[0066] In this embodiment, a notch is made with a cutting tool at a predetermined fusion point on the side of the composite microcavity column. The depth of the notch is required to be less than 10% of the diameter of the composite microcavity column, that is, 12.5 μm. The tapered region of the tapered optical fiber is temporarily fixed with a low-viscosity ultraviolet glue. The composite microcavity column is horizontally fixed in the V-groove of the fusion splicer, with the notch point facing up. The tapered optical fiber is clamped with a three-dimensional adjustment frame so that the waist of the taper is aligned with the notch point of the composite microcavity column, and the distance is controlled between 100 nm and 200 nm. After the position correction of the composite microcavity column and the tapered optical fiber, the first micro-discharge is carried out using 30% of the normal discharge intensity, that is, the intensity value 30, to stick the tapered optical fiber to the composite microcavity column. If the position is correct, that is, there is no deviation after the first discharge, the second normal discharge is carried out to melt and taper-couple the tapered optical fiber and the notch point of the composite microcavity column. To avoid fiber collapse and ensure the waist diameter of the taper, a slight outward stretch is applied during the fusion splicing process, that is, an axial micro-tension is applied during the fusion splicing process. The axial micro-tension requires that the tension is not higher than 0.005 N and the action time is not longer than 1 s to prevent the waist diameter of the taper from shrinking.

[0067] The circulator is connected to the left tapered optical fiber through a fiber optic adapter to complete the preparation of the dual-parameter fiber optic sensor based on the FP-WGM composite microcavity.

[0068] In this embodiment, an experimental system for resonance excitation of the dual-parameter fiber optic sensor based on the FP-WGM composite microcavity is built to detect the composite spectral characteristics of the FPI and WGM, so as to verify the effect of the dual-parameter fiber optic sensor. The specific experimental process is as follows:

[0069] The experimental setup includes: a broadband ASE light source in the range of 1520 - 1570 nm, a Yokogawa AQ6370D spectrometer with a resolution of 0.02 nm for spectral analysis, and a digital microscope is used to monitor the coupling state of the microsphere and the tapered optical fiber in real time. For the dual-parameter fiber optic sensor based on the FP-WGM composite microcavity, a three-port circulator with parameters of 1550 nm, steel tube packaging, P grade, 0.9 sleeve, and fiber length 1 is used, and the jumper models used for the three ports are FAFA-SM-0901-0101, FUFU-SM-0901-0101, and FAFU-SM-0901-0101 respectively. It should be noted that the circulator and the tapered optical fiber used in this embodiment can also be realized by using other devices with the same functions.

[0070] In this embodiment, as Figure 3 shown, the optical signal emitted by the light source 1 is transmitted into the composite microcavity column of the dual-parameter fiber optic sensor through the spectrometer, that is, the circulator 2. The spectrometer is connected to the composite microcavity column through fiber optic fusion splicing, and is connected to the tapered optical fiber and the light source through fiber optic adapters. Its function is to simplify the optical path and ensure the directional transmission of the optical signal.

[0071] The dual-parameter fiber optic sensor is coupled with the tapered fiber by fusion splicing, that is, the areas of the two fibers to be connected are brought into close contact, and the fiber connection point is heated by an electric arc. After melting, it is stretched to form a tapered region to couple the optical fields. The WGM resonance is excited by coupling through a tapered fiber with a diameter of 1.8 μm, and a broadband light source and an optical spectrum analyzer (OSA) are used to record the composite spectrum. As Figure 5 shown, the abscissa of the composite spectrum is set as the wavelength range, and the wavelength range in this experiment is 1400 - 1600 nm; the ordinate of the composite spectrum is set as the contrast ratio. During the whole experiment, the total spectra of FPI1, FPI2, FPI3 and the three reflecting surfaces, the spectral envelope offset of FPI, the composite spectrum after coupling, etc. are recorded. Since the whole spectrum is recorded, the following gives some key data: FSR1 = 3.3 nm, FSR2 = 2.94 nm, FSR3 = 1.48 nm, and the free spectral range of the interference spectral envelope of the total reflection spectrum of the three reflecting surfaces is 27.05 nm.

[0072] Temperature test: In the range of 10 - 50 °C, the wavelength offset sensitivity of the FPI envelope line is 13.75 pm / °C, and the sensitivity of the WGM resonance peak is 11.2 pm / °C;

[0073] Concentration test: When the concentration of the NaCl solution changes from 0 to 3%, the sensitivity of the WGM resonance peak is 52.95 pm / %, and the sensitivity of the FPI is 2.2 pm / %. The fitting curve of the concentration test is as Figure 6 shown;

[0074] Stability test: During the continuous test for 55 minutes, the wavelength fluctuation ≤ 18.32 pm, corresponding to a concentration error ≤ 1.52%.

[0075] In summary, the dual-parameter fiber optic sensor based on the FP-WGM composite microcavity realizes the synchronous high-precision measurement of temperature and liquid concentration through the design of the FPI and WGM composite microcavity, and uses the FFT frequency domain separation technology to completely eliminate the cross-sensitivity problem. The dual-parameter fiber optic sensor based on the FP-WGM composite microcavity has the advantages of simple structure, low cost, high sensitivity (temperature 13.75 pm / °C, concentration 52.95 pm / %), and excellent stability (error ≤ 1.52%), providing an innovative solution for multi-parameter fiber optic precise sensing.

[0076] 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 foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope defined by the claims of the present invention.

Claims

1. A dual-parameter fiber optic sensor based on an FP-WGM composite microcavity, characterized in that The dual-parameter fiber optic sensor includes: a circulator, a composite microcavity column, a left tapered fiber, and a right tapered fiber; wherein the composite microcavity column includes: a front single-mode fiber C, a hollow fiber B, and a rear single-mode fiber A connected in series by fusion splicing. The circulator transmits an optical signal to the composite microcavity column. The optical signal excites FPI interference within the composite microcavity column. The generated FPI reflected light is directionally transmitted by the circulator to the left tapered fiber, and the coupling between the left tapered fiber and the composite microcavity column excites WGM resonance. Then, the right tapered fiber receives the FPI-WGM composite optical signal.

2. The dual-parameter fiber optic sensor based on the FP-WGM compound microcavity according to claim 1, wherein The circulator is connected to the composite microcavity column by fiber fusion coupling; the circulator is connected to the left tapered fiber through a fiber adapter and a jumper wire.

3. The dual-parameter optical fiber sensor based on the FP-WGM composite microcavity according to claim 2, characterized in that, The length range of the front single-mode fiber C is 230 - 240 μm; the length range of the hollow fiber B is 280 - 310 μm; the length range of the rear single-mode fiber A is 300 - 350 μm; the diameter of the composite microcavity column is 125 μm.

4. The dual-parameter fiber optic sensor based on the FP-WGM compound microcavity according to claim 3, characterized in that, The left tapered fiber and the right tapered fiber have the same dimensions, including: a cone waist diameter of 1.8 μm, a cone waist length range of 1000 - 2000 μm, and a total cone region length range of 5000 - 6000 μm.

5. The dual-parameter fiber optic sensor based on the FP-WGM composite microcavity according to claim 4, characterized in that, There are three reflection interfaces M1, M2, and M3 in the composite microcavity column; wherein the reflection interface M1 is the fusion splicing surface between the front single-mode fiber A and the hollow fiber B; the reflection interface M2 is the fusion splicing surface between the hollow fiber B and the rear single-mode fiber C; the reflection interface M3 is the top surface of the rear single-mode fiber C. Wherein the reflection interface M1 and the reflection interface M2 form a first FP cavity; the reflection interface M2 and the reflection interface M3 form a second FP cavity; the reflection interface M1 and the reflection interface M3 form a third FP cavity; and it is required that the difference between the free spectral range FSR1 of the first FP cavity and the free spectral range FSR3 of the third FP cavity is less than 12% of FSR1 to generate a superimposed interference spectrum.

6. A preparation method of a dual-parameter fiber optic sensor based on an FP-WGM composite microcavity, which is used to prepare the dual-parameter fiber optic sensor based on an FP-WGM composite microcavity according to any one of claims 1-5, characterized in that, The preparation method includes the following process: Select a section of single-mode fiber as the rear single-mode fiber, fuse the rear single-mode fiber with a section of hollow fiber to form a single-mode - hollow structure, and then use a fixed-length cutting system to cut the rear single-mode fiber of the single-mode - hollow structure into a fixed length. Select another section of single-mode fiber as the front single-mode fiber, fuse the hollow fiber of the single-mode - hollow structure with the front single-mode fiber, and require the length of the hollow fiber to be a preset fixed length after fusion splicing to form a single-mode - hollow - single-mode structure. Then use a fixed-length cutting system to cut the front single-mode fiber in the single-mode - hollow - single-mode structure into a fixed length to form a composite microcavity column. Select a circulator and connect the circulator to the front single-mode fiber in the composite microcavity column by fiber fusion coupling through a jumper wire. Select four sections of the same single-mode fiber and divide them into two pairs of single-mode fibers. For any pair of single-mode fibers, place the pair of single-mode fibers in a fusion splicer according to the standard fiber fusion splicing specification process, and stretch the pair of single-mode fibers into a section of tapered fiber using the manual fusion splicing mode of the fusion splicer according to a preset program. Mark the two tapered fibers formed by stretching as the left tapered fiber and the right tapered fiber respectively. Predetermine the fusion points and make notches on the left side of the composite microcavity column, temporarily fix the tapered region of the left tapered optical fiber with a low-viscosity ultraviolet glue, and then use a fusion splicer to perform staged fusion tapering between the waist of the left tapered optical fiber and the notch point on the left side of the composite microcavity column; predetermine the fusion points and make notches on the right side of the composite microcavity column, temporarily fix the tapered region of the right tapered optical fiber with a low-viscosity ultraviolet glue, and then use a fusion splicer to perform staged fusion tapering between the waist of the right tapered optical fiber and the notch point on the right side of the composite microcavity column; Connect the circulator and the left tapered optical fiber through an optical fiber adapter to complete the preparation of the dual-parameter optical fiber sensor based on the FP-WGM composite microcavity.

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