Tapered optical fiber and optical fiber ring laser-based strain sensing system and method

Abstract

The invention discloses a strain sensing system and method based on a tapered optical fiber and an optical fiber ring laser. The system comprises a laser light source, an optical fiber amplifier, an optical isolator, a polarization controller, the tapered optical fiber, an optical fiber coupler and a spectrum analyzer. The tapering optical fiber is arranged at a strain measurement position; the output of the optical fiber coupler is provided with a first light splitting light path and a second light splitting light path; the optical fiber amplifier, the optical isolator, the polarization controller, the tapered optical fiber and the first light splitting optical path form a resonant cavity, after laser passes through the optical fiber coupler, one part of light enters the resonant cavity through the first light splitting optical path, and the other part of light enters the spectrum analyzer through the second light splitting optical path. The system realizes high-sensitivity and high-resolution monitoring of strain sensing, has excellent stability, and is suitable for various scenes of high-precision strain measurement.

Description

Technical Field

[0001] The present invention relates to the field of strain monitoring, and in particular to a strain sensing system and method based on a tapered optical fiber and an optical fiber ring laser. Background Art

[0002] Strain monitoring technology is a core means to ensure engineering safety and structural health, and is widely used in many key areas. In civil engineering, large structures such as bridges, dams, and high-rise buildings can warn of material fatigue, foundation settlement or overload risks by real-time monitoring of strain changes, thereby avoiding collapse accidents. The aerospace field relies on strain sensors to monitor the deformation of key parts such as aircraft wings and engines to ensure flight safety and optimize lightweight design. The energy and power industry monitors the strain state of wind turbine blades and transmission cables to assess equipment life and prevent fracture risks. In transportation facilities, high-speed rail tracks, undersea tunnels, etc. achieve precise operation and maintenance and disaster prevention and control through long-term strain data analysis. In addition, stress distribution monitoring of mechanical equipment in industrial manufacturing can optimize production processes and reduce downtime losses. With the advancement of smart cities and digital transformation, strain monitoring technology has not only reduced maintenance costs through high-precision data collection and analysis, but has also become a key support for preventing catastrophic accidents and extending the life of facilities, and has irreplaceable value for public safety, economic sustainability, and industrial upgrading.

[0003] Fiber optic sensing technology has a significant advantage in strain detection due to its unique performance: its characteristics based on optical signal transmission give it strong resistance to electromagnetic interference and can work stably in complex environments such as high voltage and strong radiation; at the same time, fiber optic sensors can achieve high-precision detection of micro-strain, far exceeding traditional electrical or mechanical sensors. A single optical fiber can support distributed continuous monitoring within a few kilometers, breaking through the limitations of the density and coverage of traditional point sensors. The fiber optic material itself is corrosion-resistant, fatigue-resistant and does not require power supply, which greatly improves the reliability of long-term buried monitoring. In addition, by analyzing multi-dimensional changes in optical signal wavelength, phase, etc., the technology can simultaneously obtain parameters such as strain, temperature, and vibration, significantly reducing the complexity of multi-system integration. These technical advantages make fiber optic sensing an innovative solution in the field of extreme environment and large-scale structural health monitoring.

[0004] The existing solution for applying optical fiber to strain sensing is basically a sensing system consisting of a broadband light source and multi-point distributed fiber grating sensors. However, this sensing system has problems such as high loss, low signal-to-noise ratio and excessive bandwidth. Summary of the invention

[0005] The object of the present invention is to provide a strain sensing system and method based on a tapered optical fiber and a fiber ring laser to achieve accurate monitoring of strain.

[0006] In order to solve the above technical problems, the present invention provides a strain sensing system based on a tapered optical fiber and a fiber ring laser, comprising a laser light source, an optical fiber amplifier, an optical isolator, a polarization controller, a tapered optical fiber, an optical fiber coupler, and a spectrum analyzer; the tapered optical fiber is arranged at a strain measurement position; the output of the optical fiber coupler has a first splitting optical path and a second splitting optical path; the optical fiber amplifier, the optical isolator, the polarization controller, the tapered optical fiber, and the first splitting optical path constitute a resonant cavity, and after the laser passes through the optical fiber coupler, a part of the light enters the resonant cavity through the first splitting optical path, and the other part of the light enters the spectrum analyzer through the second splitting optical path.

[0007] According to the above solution, the optical fiber amplifier is an erbium-doped optical fiber amplifier.

[0008] According to the above scheme, the preparation process of the tapered optical fiber includes: A1. Select single-mode optical fiber that meets the requirements; A2. Set the taper machine parameters according to the transmission characteristics and tensile strength of the single-mode optical fiber; A3. Monitor the shape change of the optical fiber during the taper drawing process to ensure that the taper area meets the requirements; A4. Test the tapered optical fiber formed by taper drawing; A5. Adjust the taper machine parameters according to the test results to optimize the taper process; A6. Repeat steps A3 to A5 until a tapered optical fiber that meets the requirements is obtained, and then solidify the tapered optical fiber.

[0009] According to the above scheme, the splitting ratio of the first splitting optical path and the second splitting optical path is 9:1.

[0010] According to the above scheme, the analysis process of the spectrum analyzer includes: B1. spectrally decompose the received optical signal to obtain a spectrum diagram; B2. Identify the wavelength value where the shift occurs according to the wavelength change in the spectrum; B3. The change in the measured strain is obtained based on the degree of wavelength shift of the shifted wavelength value.

[0011] The present invention also provides a strain sensing method based on a tapered optical fiber and an optical fiber ring laser, comprising: B1. spectrally decompose the received optical signal to obtain a spectrum diagram; B2. Identify the wavelength value where the shift occurs according to the wavelength change in the spectrum; B3. Obtaining the change in the measured strain according to the degree of wavelength shift of the shifted wavelength value; Steps B1 to B3 are performed by a spectrum analyzer, which is located in the strain sensing system; the strain sensing system includes a laser light source, a fiber amplifier, an optical isolator, a polarization controller, a tapered fiber, a fiber coupler, and a spectrum analyzer; the tapered fiber is arranged at the strain measurement position; the output of the fiber coupler has a first split light path and a second split light path; the fiber amplifier, the optical isolator, the polarization controller, the tapered fiber, and the first split light path constitute a resonant cavity, and after the laser passes through the fiber coupler, a part of the light enters the resonant cavity through the first split light path, and the other part of the light enters the spectrum analyzer through the second split light path.

[0012] According to the above solution, the optical fiber amplifier is an erbium-doped optical fiber amplifier.

[0013] According to the above scheme, the preparation process of the tapered optical fiber includes: A1. Select single-mode optical fiber that meets the requirements; A2. Set the taper machine parameters according to the transmission characteristics and tensile strength of the single-mode optical fiber; A3. Monitor the shape change of the optical fiber during the taper drawing process to ensure that the taper area meets the requirements; A4. Test the tapered optical fiber formed by taper drawing; A5. Adjust the taper machine parameters according to the test results to optimize the taper process; A6. Repeat steps A3 to A5 until a tapered optical fiber that meets the requirements is obtained, and then solidify the tapered optical fiber.

[0014] According to the above scheme, the splitting ratio of the first splitting optical path and the second splitting optical path is 9:1.

[0015] Beneficial Effects The strain sensing system of the present invention adopts a tapered optical fiber and utilizes the micron-level diameter of the tapered optical fiber to enhance the interaction between the evanescent field and the environment in the cone-region mode, thereby significantly improving the sensing sensitivity. The optical fiber is used to build a ring-shaped resonant cavity to form a fiber ring laser. Thanks to the high signal-to-noise ratio, narrow spectral bandwidth and high quality factor of the fiber ring laser, the system can more accurately identify and measure tiny wavelength changes, thereby achieving high-resolution and high-sensitivity strain measurement.

[0016] Furthermore, by optimizing the preparation process of the tapered optical fiber and the setting of system parameters, the sensor's response to stress changes is ensured to be predictable and consistent, thereby improving the monitoring stability and consistency of the sensing system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 is a structural diagram of a tapered single-mode optical fiber according to Embodiment 1 of the present invention; Figure 2 is a structural diagram of a sensor system according to a first embodiment of the present invention; Figure 3 is the transmission spectrum of the tapered optical fiber according to the first embodiment of the present invention; Figure 4 This is the output spectrum of the fiber ring laser according to the first embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the embodiments of the present disclosure clearer, the technical solution of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings of the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0019] Embodiment 1: Fiber Ring Laser (FRL) is a device that uses optical fiber to form a ring cavity to generate laser. Sensors made with FRL have high sensitivity and resolution, and a large dynamic range. They are widely used in measurements of temperature, refractive index, stress / strain, electric field / magnetic field, and air pressure. Their application areas include: structural health testing, environmental testing, medical and biomedical. The new generation of intelligent sensing technology is developing in the direction of high speed, high sensitivity, multi-parameters, and large dynamic range, in order to provide simpler, more efficient, and more accurate measurement solutions. FRL sensing technology has strong practicality and application value in the field of intelligent sensing due to its narrow linewidth, high signal-to-noise ratio and other characteristics.

[0020] See also Figure 1 In a tapered optical fiber (TOF), when the taper is non-adiabatic, not only the fundamental mode is excited , and several higher-order modes are excited, and most of the light energy is coupled to and (transmitted by single-mode fiber SMF The mode is excited in the cone region When the two modes propagate in the conical section, they interfere with each other and are then output from the single-mode fiber SMF at the other end. When the two modes propagate in the conical section, they interfere with each other, resulting in a series of transmission peaks and valleys over a wide wavelength range. According to the principle of interference, the phase difference between the two modes when they arrive at the other end is: (1) Where L is the distance between the two cone waists, is the effective refractive index difference between the two modes, and λ is the wavelength. For simplicity, without considering coupling and transmission losses, the interference intensity can be expressed as: (2) in, is the intensity of the two modes. From equation (1), we can see that the wavelength determines the phase difference. The interferometer length L and the effective refractive index difference ( ) can determine the periodicity of interference, and its expression is: (3) Since the radius of the TOF cone is small, the proportion of the excited high-order mode evanescent field is large and it is more easily affected by the external environment, so it has higher sensitivity.

[0021] Traditional point-type fiber optic sensors rely on broadband light sources to transmit external modulation information to the spectrometer for demodulation, and monitor environmental changes through wavelength changes. This method has problems such as large light intensity loss, low signal-to-noise ratio and excessive bandwidth, which seriously affect the performance of the sensor and reduce the actual application value of the system.

[0022] In contrast, FRL-based sensing technology provides a novel solution. This technology uses the wavelength shift caused by the external environment when the laser is transmitted in the optical fiber to obtain information about the change of physical quantities. Thanks to the high signal-to-noise ratio, narrow bandwidth and high Q factor of the laser spectrum, FRL technology can achieve higher resolution, sensitivity and a larger dynamic monitoring range compared to passive fiber Bragg grating spectral sensors.

[0023] The traditional fiber ring laser cavity sensing structure consists of a 980nm pump light source, a wavelength division multiplexer (WDM), a gain medium (doped fiber), an optical isolator (ISO), an optical coupler (OC), a sensing unit, and an optical spectrum analyzer (OSA). The pump light is generated by a 980nm semiconductor laser and injected into the fiber ring cavity through a wavelength division multiplexer. In the ring cavity, the pump light excites the gain medium, such as erbium-doped or ytterbium-doped fiber, triggering energy down-conversion and generating laser light. In order to ensure that the laser is transmitted in a single direction and prevent backscattered light from damaging the laser, an optical isolator is integrated in the ring cavity. The laser modulated by the filter (i.e., the sensing unit) is output through a 90:10 coupler and then sent to a spectrometer for analysis. Due to external factors such as temperature, refractive index, and strain, the interference pattern of the filter will change accordingly, resulting in a shift in the modulated laser output wavelength, which is the basic working principle of FRL sensing.

[0024] Among them, the quality factor Q is used to characterize the spectral quality of the optical fiber sensor. It is a normalized value and can be expressed as: (4) In the formula, K is a unit coefficient used to normalize the physical dimension, S represents the sensitivity of the sensor, V is the visibility of the spectrum, and FWHM (Full Width at Half Maximum) represents the 3dB bandwidth of the spectrum. It is easy to see from formula (1) that, under the condition of equal sensitivity, the quality factor of the sensor system using laser as the light source is 3 orders of magnitude higher than that of the broadband light source.

[0025] Another indicator for evaluating the comprehensive performance of the sensor is the limit of detection (LoD), which is expressed as: (5) Where R is the resolution of the sensor, which is determined by three factors: amplitude noise, thermal variation, and the spectral resolution of the system settings. The specific expression is: (6) The temperature-induced thermal changes are usually small and can be ignored, and the spectral resolution is equivalent for laser and broadband light sources. According to equations (4) and (6), it can be calculated that the sensor sensitivity does not change before and after FRL combination, but the detection sensitivity is greatly improved.

[0026] Based on the above characteristics, this embodiment combines a fiber ring laser with a tapered fiber to provide a strain sensing system based on a tapered fiber and a fiber ring laser. Figure 2 , including a laser light source, a fiber amplifier, an optical isolator, a polarization controller (PC, Polarization Control, used to control the polarization of light), a tapered fiber (equivalent to a filter modulated by the external environment, used to adjust the output mode of FRL), a fiber coupler, and a spectrum analyzer; the tapered fiber is set at the strain measurement position; the output of the fiber coupler has a first split light path and a second split light path; the fiber amplifier, the optical isolator, the polarization controller, the tapered fiber, and the first split light path constitute a resonant cavity. After the laser passes through the fiber coupler, part of the light enters the resonant cavity through the first split light path, and the other part of the light enters the spectrum analyzer through the second split light path (the selection of which needs to be able to provide high-resolution and high-sensitivity spectral analysis).

[0027] It should be understood that after completing the construction of the above-mentioned strain sensing system, the system needs to be debugged, including adjusting the gain of the fiber amplifier, adjusting the directionality of the optical isolator, and adjusting the polarization direction of the polarization controller to ensure the stable operation of the fiber ring laser and output a high-quality laser spectrum. Then, the performance of the constructed fiber ring laser needs to be tested, including key indicators such as laser stability, spectrum signal-to-noise ratio, and full width at half maximum (FWHM) to ensure that the fiber ring laser meets the technical requirements of strain measurement.

[0028] Furthermore, the optical fiber amplifier is an erbium-doped optical fiber amplifier.

[0029] It should be noted that the power of the pump source will affect the number of longitudinal modes and FWHM of the laser. Lower pump power may lead to incomplete mode competition, resulting in double peaks or multiple peaks; higher pump power may lead to excessive laser power, thus causing damage to devices such as Erbium-doped Optical Fiber Amplifier (EDFA) or OSA. Therefore, the power of the pump source should be controlled at an appropriate level to keep the output spectrum in single-mode output.

[0030] Furthermore, the preparation process of the tapered optical fiber includes: A1. Select single-mode optical fiber that meets the requirements; A2. Set the taper machine parameters according to the transmission characteristics and tensile strength of the single-mode optical fiber; A3. Monitor the shape change of the optical fiber during the taper drawing process to ensure that the taper area meets the requirements; A4. Test the tapered optical fiber formed by taper drawing; A5. Adjust the taper machine parameters according to the test results to optimize the taper process; A6. Repeat steps A3 to A5 until a tapered optical fiber that meets the requirements is obtained, and the tapered optical fiber is cured (to ensure its structural stability and long-term reliability).

[0031] It should be understood that the shape and size of the tapered fiber will affect the number of excited high-order modes and the proportion of the evanescent field, thereby affecting the period of inter-mode interference and the sensitivity of stress sensing. However, the tapered fiber is not made by controlling the parameters after tapering, such as the diameter of the taper area, but by controlling the specific process of the taper machine during the taper process and parameters such as the taper speed. In the specific process of taper fiber production, the parameters and processes of the taper machine need to be adjusted step by step to accurately pull out the ideal optical fiber, ensuring that the sensor's response to stress changes is predictable and consistent.

[0032] Furthermore, the splitting ratio between the first splitting optical path and the second splitting optical path is 9:1.

[0033] Furthermore, the analysis process of the spectrum analyzer includes: B1. spectrally decompose the received optical signal to obtain a spectrum diagram; B2. Identify the wavelength value where the shift occurs according to the wavelength change in the spectrum; B3. The change in the measured strain is obtained based on the degree of wavelength shift of the shifted wavelength value.

[0034] It should be understood that the tapered fiber ring laser may be sensitive to temperature, refractive index and stress changes at the same time. Changes in temperature, refractive index and stress may all lead to changes in the effective refractive index or length of the tapered mode of the tapered fiber. Under the combined influence of these factors, the spectrum of inter-mode interference may experience wavelength drift and intensity changes. Therefore, measures need to be taken to distinguish the cross-effects of these factors, or to compensate through algorithms. The specific compensation method has been maturely applied in the existing field of sensor technology. This part of the content does not belong to the innovation of the present invention, so it will not be repeated here.

[0035] In this embodiment, before performing strain measurement, the constructed strain sensing system should be calibrated, and the calibration steps include: C1. Apply a known strain to the tapered region of the tapered optical fiber (this can be achieved through mechanical devices or controlled temperature changes to ensure the accuracy of the measurement results), and obtain the spectral changes of the fiber ring laser output (including data on the change of the central wavelength with strain) through an optical spectrum analyzer; C2. (Based on the calculation formula described above) obtain the theoretical value of strain according to the spectral change (the change in the central wavelength); C3. Calibrate the strain sensing system according to the theoretical strain value and the known strain; C4. Repeat steps C1 to C3 until the deviation between the calibrated strain theoretical value and the known strain is within the set range.

[0036] To facilitate understanding of the technical solution, the working principle of the strain sensing system described in this embodiment is as follows: The light in ordinary optical fiber is transmitted in the core, so it is difficult to be affected by external environmental factors. By tapering the optical fiber and reducing its diameter, the interaction between the evanescent field in the optical fiber and the environment can be enhanced, so that it can be used to measure relevant parameters in the environment.

[0037] When the tapered fiber is fused between the two single-mode fibers, due to the core diameter mismatch between the tapered region and the single-mode fiber, part of the light transmitted from the single-mode fiber propagates in the core of the tapered region, and the other part propagates in the cladding of the tapered region. The fundamental mode in the single-mode fiber will excite high-order modes in the tapered region. Usually, low-order modes propagate in the core of the tapered region, and the evanescent field accounts for a small proportion, while high-order modes propagate in the cladding of the tapered region, and the evanescent field accounts for a large proportion. Therefore, high-order modes are greatly affected by the environment, thereby affecting the spectrum of inter-mode interference, which is manifested as wavelength drift.

[0038] When strain is applied to the cone region, the effective refractive index and coupling length of the mode change, causing the central wavelength to drift. According to the interference principle, the central wavelength of the mth order in the output spectrum can be expressed as: (7) After applying strain: (8) The relationship between the change in effective refractive index and coupling length and strain is: (9) (10) in, is the elastic-optical coefficient.

[0039] In order to further improve the detection limit, we can introduce a fiber ring laser. Through the erbium-doped fiber amplifier, optical isolator, polarization controller and optical coupler, a fiber ring cavity is formed with a tapered fiber. The oscillation is achieved under the effect of the gain spectrum of the erbium-doped fiber and the mode selection of the resonant cavity, and the laser single-mode output is achieved under mode competition. In the fiber ring laser, the tapered fiber is equivalent to an environment-related filter. When the environment changes, the mode selection also changes, which is manifested as a drift of the central wavelength. Therefore, it can be used for strain measurement. The introduction of the fiber ring laser significantly improves the signal-to-noise ratio of the sensor spectrum and greatly reduces the half-peak full width of the spectrum, thereby achieving high-resolution, high-sensitivity, and large dynamic range strain measurement.

[0040] Strain measurement, as the final application link of this embodiment, involves applying strain and demodulating the corresponding strain. First, a precisely controlled known strain is applied to the cone area of ​​TOF, which can be achieved through mechanical devices or temperature changes to ensure the accuracy of the measurement results. While the strain is applied, OSA is used to monitor the changes in the FRL output spectrum and record the data of the central wavelength changing with the strain. These data are the key to subsequent strain demodulation. Subsequently, the collected spectral data is analyzed in detail, the change in the central wavelength is calculated, and the wavelength change is converted into a strain value according to the formula provided in the technical solution. In order to improve the accuracy of the measurement, the system needs to be calibrated and the system is adjusted using known strain values ​​to ensure that the deviation between the measurement results and the actual values ​​is within an acceptable range. After the calibration is completed, it can be used in actual strain measurement. Apply unknown strain to the TOF cone area, analyze the wavelength drift in the spectrum, and demodulate the corresponding strain through the previously determined relationship between the wavelength drift and the strain, thereby realizing strain measurement.

[0041] The strain sensing system disclosed in this embodiment has at least the following technical effects: the tapered fiber structure, due to its micrometer-level diameter, enhances the interaction between the evanescent field and the environment in the cone mode, and has higher sensitivity than traditional point fiber sensing. Secondly, thanks to the advantages of the fiber ring laser such as high signal-to-noise ratio, narrow bandwidth, and high quality factor, higher-precision strain measurement can be achieved, and the narrower bandwidth can distinguish two spectral lines that are closer to each other, thereby greatly improving the detection limit of the sensor. In addition, by using a fiber ring laser for demodulation, very obvious peaks can be observed, which facilitates the measurement of wavelength drift, reduces the need for a flat broadband light source and a fine spectrometer, and thus reduces production costs.

[0042] See also Figure 3 , which shows the transmission spectrum of TOF and the output laser spectrum. It can be seen that the transmission spectrum of TOF is equivalent to a filter, which produces a single-mode output under the effect of the gain spectrum of the erbium-doped fiber, thus showing a peak in the spectrum. Figure 4 , which shows the wavelength drift change of FRL strain sensing. It can be seen that as the strain increases, the central wavelength gradually moves toward the long-wave direction.

[0043] Embodiment 2: The principles of this embodiment are basically the same as those of the first embodiment. On the basis of the first embodiment, this embodiment provides a strain sensing method based on a tapered optical fiber and a fiber ring laser, including: B1. spectrally decompose the received optical signal to obtain a spectrum diagram; B2. Identify the wavelength value where the shift occurs according to the wavelength change in the spectrum; B3. Obtaining the change in the measured strain according to the degree of wavelength shift of the shifted wavelength value; Steps B1 to B3 are performed by a spectrum analyzer, which is located in the strain sensing system; the strain sensing system includes a laser light source, a fiber amplifier, an optical isolator, a polarization controller, a tapered fiber, a fiber coupler, and a spectrum analyzer; the tapered fiber is arranged at the strain measurement position; the output of the fiber coupler has a first split light path and a second split light path; the fiber amplifier, the optical isolator, the polarization controller, the tapered fiber, and the first split light path constitute a resonant cavity, and after the laser passes through the fiber coupler, a part of the light enters the resonant cavity through the first split light path, and the other part of the light enters the spectrum analyzer through the second split light path.

[0044] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, and two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0045] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A strain sensing system based on tapered optical fiber and fiber ring laser, characterized in that: Including laser light source, fiber amplifier, optical isolator, polarization controller, tapered fiber, fiber coupler, spectrum analyzer; The tapered optical fiber is arranged at the strain measurement position; the output of the optical fiber coupler has a first split light path and a second split light path; the optical fiber amplifier, the optical isolator, the polarization controller, the tapered optical fiber, and the first split light path constitute a resonant cavity; after the laser passes through the optical fiber coupler, a part of the light enters the resonant cavity through the first split light path, and the other part of the light enters the spectrum analyzer through the second split light path.

2. The strain sensing system based on tapered optical fiber and fiber ring laser according to claim 1, characterized in that: The optical fiber amplifier is an erbium-doped optical fiber amplifier.

3. The strain sensing system based on tapered optical fiber and fiber ring laser according to claim 1, characterized in that: The preparation process of the tapered optical fiber includes: A1. Select single-mode optical fiber that meets the requirements; A2. Set the taper machine parameters according to the transmission characteristics and tensile strength of the single-mode optical fiber; A3. Monitor the shape change of the optical fiber during the taper drawing process to ensure that the taper area meets the requirements; A4. Test the tapered optical fiber formed by taper drawing; A5. Adjust the taper machine parameters according to the test results to optimize the taper process; A6. Repeat steps A3 to A5 until a tapered optical fiber that meets the requirements is obtained, and then solidify the tapered optical fiber.

4. The strain sensing system based on tapered optical fiber and fiber ring laser according to claim 1, characterized in that: The splitting ratio of the first splitting optical path and the second splitting optical path is 9:

1.

5. The strain sensing system based on tapered optical fiber and fiber ring laser according to claim 1, characterized in that: The analysis process of the spectrum analyzer includes: B1. spectrally decompose the received optical signal to obtain a spectrum diagram; B2. Identify the wavelength value where the shift occurs according to the wavelength change in the spectrum; B3. The change in the measured strain is obtained based on the degree of wavelength shift of the shifted wavelength value.

6. A strain sensing method based on tapered optical fiber and fiber ring laser, characterized in that: include: B1. spectrally decompose the received optical signal to obtain a spectrum diagram; B2. Identify the wavelength value where the shift occurs according to the wavelength change in the spectrum; B3. Obtaining the change in the measured strain according to the degree of wavelength shift of the shifted wavelength value; Steps B1 to B3 are performed by a spectrum analyzer, which is located in the strain sensing system; the strain sensing system includes a laser light source, a fiber amplifier, an optical isolator, a polarization controller, a tapered fiber, a fiber coupler, and a spectrum analyzer; The tapered optical fiber is arranged at the strain measurement position; the output of the optical fiber coupler has a first split light path and a second split light path; the optical fiber amplifier, the optical isolator, the polarization controller, the tapered optical fiber, and the first split light path constitute a resonant cavity; after the laser passes through the optical fiber coupler, a part of the light enters the resonant cavity through the first split light path, and the other part of the light enters the spectrum analyzer through the second split light path.

7. The strain sensing method based on tapered optical fiber and fiber ring laser according to claim 6, characterized in that: The optical fiber amplifier is an erbium-doped optical fiber amplifier.

8. The strain sensing method based on tapered optical fiber and fiber ring laser according to claim 6, characterized in that: The preparation process of the tapered optical fiber includes: A1. Select single-mode optical fiber that meets the requirements; A2. Set the taper machine parameters according to the transmission characteristics and tensile strength of the single-mode optical fiber; A3. Monitor the shape change of the optical fiber during the taper drawing process to ensure that the taper area meets the requirements; A4. Test the tapered optical fiber formed by taper drawing; A5. Adjust the taper machine parameters according to the test results to optimize the taper process; A6. Repeat steps A3 to A5 until a tapered optical fiber that meets the requirements is obtained, and then solidify the tapered optical fiber.

9. The strain sensing method based on tapered optical fiber and fiber ring laser according to claim 6, characterized in that: The splitting ratio of the first splitting optical path and the second splitting optical path is 9:1.

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