Optical fiber strain sensing system and method

Abstract

The application provides a kind of optical fiber strain sensing system and method, including light source, coupler unit, delay optical fiber, resonant cavity, photoelectric detector and signal processing unit;Light source emits light signal;Coupler unit is split after receiving light signal;First split light successively passes through delay optical fiber and resonant cavity, and obtains first direction light;Second split light successively passes through resonant cavity and delay optical fiber, and obtains second direction light;First direction light and second direction light return coupler unit, and interference occurs after splitting in coupler unit, and interference signal with phase difference is obtained;Pre-set photoelectric detector detects interference signal, and outputs voltage signal;Signal processing unit collects and demodulates voltage signal, and obtains phase information of interference signal, carries out phase and strain signal calibration, and outputs vibration signal.The application can realize high-precision dynamic strain measurement with very simple device and optical path, and significantly reduces system cost and complexity.

Description

Technical Field

[0001] This invention relates to the technical field of fiber optic sensing, specifically to a fiber optic strain sensing system and method. More particularly, it preferably relates to a high-precision fiber optic strain sensing method and system. Background Technology

[0002] A resonant cavity is a structure that guides optical signals to be reflected multiple times within its cavity, thus generating resonance. It is of great significance in weak signal sensing. Currently, most widely used resonant cavity sensing systems are based on Fabry-Perot interferometers, fiber ring resonators, fiber Bragg gratings, and fiber lasers. Sensing information is obtained by measuring the shift in the resonant wavelength.

[0003] Chinese invention patent document CN114018171A discloses a high-resolution strain sensor based on a differential fiber optic resonator, comprising: a laser module, a PDH frequency locking module, a fiber optic resonator module, and a data processing module. The laser module generates laser light and adjusts its polarization direction and state to provide the laser light required for strain sensing. The fiber optic resonator module includes two fiber optic resonators, which are simultaneously frequency-locked with the laser in the laser module via the PDH frequency locking module to eliminate ambient background noise interference in a differential manner and perform strain sensing, generating a PDH error signal. The data processing module detects the transmission signals of the two fiber optic resonators and performs PDH error signal analysis.

[0004] Regarding the aforementioned technologies, the inventors believe that these systems require highly coherent light sources with linewidths in the kilohertz range. Such highly coherent light sources are very expensive, resulting in high costs for the sensing system and introducing parasitic noise from the laser. Complex modulation and demodulation techniques are required, along with additional circuitry and feedback devices, which greatly increases the complexity of the sensing system and limits the practical application of resonant cavity sensing systems. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the purpose of this invention is to provide an optical fiber strain sensing system and method.

[0006] According to the present invention, an optical fiber strain sensing system includes a light source, a coupler unit, a time-delay optical fiber, a resonant cavity, a preset photodetector, and a signal processing unit.

[0007] The light source emits light signals;

[0008] After receiving the optical signal, the coupler unit splits the beam to obtain a first split beam and a second split beam.

[0009] The first beam of light passes sequentially through a time-delay fiber and a resonant cavity to obtain light in the first direction;

[0010] The second beam of light passes sequentially through the resonant cavity and the delay fiber to obtain the second direction light;

[0011] The first directional light and the second directional light return to the coupler unit, and after interference at the coupler unit, they are split to obtain an interference signal with a phase difference;

[0012] The preset photodetector detects the interference signal and outputs a voltage signal;

[0013] The signal processing unit acquires and demodulates the voltage signal to obtain the phase information of the interference signal, calibrates the phase and strain signals, and outputs the vibration signal.

[0014] Preferably, the light source includes a broadband light source;

[0015] The coupler unit includes a 3*3 coupler unit;

[0016] The resonant cavity includes an optical fiber ring resonant cavity;

[0017] The preset photodetector includes a photoelectric balance detector;

[0018] The first directional light includes clockwise directional light (CW);

[0019] The second directional light includes counterclockwise directional light (CCW).

[0020] Preferably, the broadband light source outputs continuous light, which is then input to a 3*3 coupler unit to obtain split beam light;

[0021] The split beam enters the delay fiber and resonant cavity to form clockwise CW and counterclockwise CCW beams; the clockwise CW and counterclockwise CCW beams return to the 3*3 coupler unit and interfere to output a signal with a preset phase difference;

[0022] The photoelectric balance detector detects signals with a preset phase difference and outputs a differential electrical signal U(t);

[0023] The signal processing unit receives the differential electrical signal U(t), and after the signal processing flow, outputs the strain information ε(t) applied to the sensing array.

[0024] Preferably, the broadband light source includes, but is not limited to, erbium-doped superfluorescent fiber optic light sources and LEDs.

[0025] Preferably, the 3x3 coupler unit includes coupler units using a 120-degree phase difference per port.

[0026] Preferably, the coupler unit includes, but is not limited to, a single-mode coupler and a polarization-maintaining coupler.

[0027] Preferably, the fiber optic ring resonator includes a first coupler, a second coupler, a first fiber segment, and a second fiber segment;

[0028] The first port of the first coupler is connected to the fourth port of the coupler unit via a time-delay optical fiber;

[0029] The third port of the first coupler is connected to the first port of the second coupler via a section of optical fiber;

[0030] The fourth port of the first coupler is connected to the second port of the second coupler via a fiber optic cable segment 2;

[0031] The third port of the second coupler is connected to the sixth port of the coupler unit;

[0032] The continuous optical signal emitted by the broadband light source is output to the second port of the coupler unit, and then emitted from the fourth and sixth ports of the coupler unit respectively;

[0033] A refractive index matching fluid is placed at the fifth port of the coupler unit;

[0034] The first and third ports of the coupler unit are connected to the photoelectric balance detector, respectively.

[0035] According to the present invention, an optical fiber strain sensing method is characterized by comprising the following steps:

[0036] Step S1: The light source emits a light signal;

[0037] After receiving the optical signal, the coupler unit splits the beam to obtain the first split beam and the second split beam.

[0038] The first beam of light passes sequentially through the time-delay fiber and the resonant cavity to obtain light in the first direction;

[0039] The second beam passes through the resonant cavity and the delay fiber in sequence to obtain the second direction beam;

[0040] The light from the first direction and the light from the second direction return to the coupler unit, where they interfere and are then split to obtain an interference signal with a phase difference.

[0041] A preset photodetector detects the interference signal and outputs a voltage signal;

[0042] Step S2: The signal processing unit acquires and demodulates the voltage signal to obtain the phase information of the interference signal, calibrates the phase and strain signals, and outputs the vibration signal.

[0043] Preferably, in step S1, a continuous low-coherence broadband light source is output to the input end of the coupler unit, and various sinusoidal strain signals are applied to a portion of the optical fiber in the second segment of the resonant cavity. The signal processing unit then begins to acquire signals.

[0044] Preferably, in step S2, the electrical signal U(t) generated by the photoelectric balance detector is acquired and integrated;

[0045] The integrated electrical signal is calibrated to obtain the strain to be measured;

[0046] The power spectral density of the strain to be measured is used to obtain the strain measurement accuracy.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] 1. This invention solves the problems of existing resonant cavity sensing systems, which require the use of high-coherence laser sources, which are expensive; require complex modulation and demodulation techniques and feedback circuit devices, making the system complex; and the system accuracy is limited by the laser linewidth.

[0049] 2. Compared with the prior art, the present invention can achieve high-precision dynamic strain measurement with very simple devices and optical paths, without the need for modulation and demodulation technology, which significantly reduces system cost and complexity;

[0050] 3. The accuracy of this invention can be improved by increasing the length of the delay fiber or improving the precision of the resonant cavity, thus solving the problem of the linewidth limitation of the laser demodulation resonant cavity system on the accuracy of the sensor. Attached Figure Description

[0051] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0052] Figure 1 This is a block diagram of a resonant cavity sensing system based on a broadband light source and a 3*3 coupler;

[0053] Figure 2 This is a flowchart of the demodulation method in an embodiment;

[0054] Figure 3 The power spectral density plots of the strain signals at different frequencies (100Hz, 1kHz and 5kHz) after demodulation are shown in the example.

[0055] Figure label:

[0056] Broadband light source 1, First coupler 4, Signal processing unit 7

[0057] 3*3 Coupler 2 Second Coupler 5

[0058] Delayed fiber 3, balanced photodetector 6 Detailed Implementation

[0059] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0060] This invention discloses a high-precision fiber optic strain sensing system, such as... Figure 1 As shown, this is a resonant cavity sensing system based on a broadband white light source 1 and a 3*3 coupler 2, including: a broadband white light source, a 3*3 coupler unit, a time-delay fiber 3, a fiber ring resonant cavity, a photoelectric balanced detector (balanced photoelectric detector 6), and a signal processing unit 7. The 3*3 coupler (also called a splitter) enables optical signals transmitted in the optical fiber to couple in their coupling region, achieving equal power distribution across the three ports and a 120° phase difference distribution across the three ports. It can operate bidirectionally, meaning all ports can be used as inputs or outputs.

[0061] The optical signal emitted by the broadband light source 1 is split into two beams after passing through a 3*3 coupler unit. One beam (the first split beam) passes sequentially through the delay fiber 3, the resonant cavity, and back to the 3*3 coupler 2. The other beam (the second split beam) passes sequentially through the resonant cavity, the delay fiber 3, and back to the 3*3 coupler 2, forming clockwise (CW) and counterclockwise (CCW) beams, respectively. After the CW and CCW beams interfere at the 3*3 coupler 2, they are split into two beams again and output from two ports on the other side, finally reaching the photoelectric balance detector for detection. Since the CW and CCW beams arrive at the resonant cavity at different times, their phase difference is modulated by the vibration to be measured. The signal processing unit 7 collects the voltage signal output by the photoelectric detector, demodulates the phase information of the interference signal generated by the CW and CCW beams passing through the resonant cavity using signal demodulation technology, and after calibrating the phase and strain signals, the external vibration signal can be accurately output.

[0062] The continuous light output from broadband light source 1 is input to a 3*3 coupler unit. The output is split into two parts, which enter the delay fiber 3 and the resonant cavity respectively to form CW and CCW light, which then return to the 3*3 coupler 2 and interfere. The signal after interference is split into two beams with a certain phase difference at the output of the 3*3 coupler 2, which are detected by photoelectric balance detectors, and the output is a differential electrical signal U(t). The electrical signal U(t) enters the data processing unit, and after signal processing, the strain information ε(t) applied to the sensing array is output. t refers to time. U(t) refers to the voltage that changes with time.

[0063] The broadband light source used is not limited to low-cost light sources such as erbium-doped superfluorescent fiber optic light sources and LEDs.

[0064] The coupler unit used for demodulation is a 3x3 coupler unit with a 120-degree phase difference between each port. The 3x3 coupler unit used for demodulation is not limited to single-mode, polarization-maintaining, or other types of couplers.

[0065] The resonant cavity has two ports, which serve as both output and input ports. One port is connected to one port of a 3x3 coupler via a delay fiber 3, while the other port is directly connected to the other port of the 3x3 coupler.

[0066] The resonant cavity consists of two couplers as its basic structure. These couplers are not limited to single-mode, polarization-maintaining, or multi-mode couplers.

[0067] This invention utilizes broadband light as a light source and a resonant cavity sensing system with a 3*3 coupler 2 as a beam splitter and demodulator. While maintaining high strain resolution, it greatly reduces the cost and complexity of the sensing system.

[0068] The differential signal of the interference signals of the optical signals passing through the resonant cavity clockwise and counterclockwise after passing through the 3*3 coupler 2 is measured. The intensity change of the differential signal is used to detect the signal to be measured applied to the resonant cavity. The resonant cavity sensing system based on broadband light source 1 and 3*3 coupler 2 includes: broadband light, 3*3 coupler unit, time-delay fiber 3, resonant cavity, balanced photodetector 6, and signal processing unit 7. After passing through the 3*3 coupler unit, the broadband light splits into two directions: one direction passes sequentially through time-delay fiber 3 and resonant cavity; the other direction passes sequentially through resonant cavity and time-delay fiber 3. The returning light from the two directions interferes again through the 3*3 coupler unit and then enters the balanced photodetector 6. The two directions are clockwise (CW) and counterclockwise (CCW). The CW light and CCW light travel in different directions, travel the same optical path, reach the 3*3 coupler unit, and are detected by the balanced photodetector 6. Because of the presence of delay fiber 3 in the path, the CW light and CCW light arrive at the resonant cavity at different times, resulting in a delay τ.

[0069] τ=L / υ

[0070] Where L is the length of the delay fiber 3, and υ is the speed of light propagation in the fiber.

[0071] When strain ε(t) exists within the resonant cavity, due to the time delay τ, the cavity length changes relative to when the CCW light arrives at the resonant cavity. Therefore, the differential signal of the interference light generated by the CW light and CCW light is no longer zero. By detecting the intensity change of the differential signal, the vibration signal ε(t) can be recovered.

[0072] Erbium-doped superfluorescent fiber optic light sources are preferred for broadband applications. The resonant cavity unit includes, but is not limited to, an optical fiber ring cavity. The signal processing unit 7 is used to demodulate the electrical signal output from the balanced photodetector 6 to obtain the vibration signal to be measured.

[0073] This invention relates to a resonant fiber optic sensing system based on a broadband light source 1 and a 3*3 coupler 2, such as... Figure 1As shown, a resonant cavity sensing system based on a broadband light source 1 and a 3*3 coupler 2 for implementing the above method is disclosed. The system includes: a broadband light source 1, a 3*3 coupler 2, a first coupler 4, a second coupler 5, a delay fiber 3, a balanced photodetector 6, and a signal processing unit 7. The first coupler 4, the second coupler 5, and fiber segments L1 and L2 (fiber segment 1 and fiber segment 2) form a fiber ring resonant cavity structure. The d-port (fourth port) of the first coupler 4 is connected to the b-port (second port) of the second coupler 5 via fiber segment L2. The light is split into two parts at the second coupler 5. One part exits from the a-port (first port) of the second coupler 5 and connects to the c-port (third port) of the first coupler 4 via fiber segment L1, forming a fiber ring resonant cavity. The other part exits from the c-port of the second coupler and then reaches the 3*3 coupler. The continuous light signal emitted by the broadband light source 1 is output to port b of the 3*3 coupler 2, and then exits from port d (fourth port) and port f (sixth port) of the 3*3 coupler 2 respectively. The refractive index matching fluid is placed in port e (fifth port) of the 3*3 coupler 2, and this port is not used. Port b (second port) of the first coupler 4 and port d (fourth port) of the second coupler 5 are either idle or filled with refractive index matching fluid. The optical signal emitted from port d of the 3*3 coupler 2 first passes through the delay fiber 3, introducing a certain time delay τ, and then enters the resonant cavity structure through port a of the first coupler 4. After multiple rotations within the cavity, it finally exits from port c of the second coupler 5 to port f of the 3*3 coupler 2, forming a clockwise transmitted optical signal (CW). The optical signal emitted from port f of the 3*3 coupler 2 first enters the resonant cavity structure through port c of the second coupler 5. After multiple rotations within the cavity, it finally exits from port a of the first coupler 4, passes through the delay fiber 3 to introduce a certain time delay τ, and reaches port d of the 3*3 coupler 2, forming a counterclockwise transmitted optical signal (CCW). The clockwise and counterclockwise optical signals interfere at the 3*3 coupler 2 and then exit from ports a and c of the 3*3 coupler 2 respectively, forming two optical signals with a certain phase difference, which finally enter the photoelectric balance detector simultaneously. The data processing unit (signal processing unit 7) acquires the input voltage signal of the photoelectric balanced detector and demodulates it. For non-50:50 2*2 couplers, the output port has a different splitting ratio depending on the corresponding input port. Due to the splitting ratio of the couplers, the 1% output port of the first coupler is connected to the 1% output port of the second coupler to ensure the successful establishment of the resonant cavity.

[0074] In this embodiment, the phase difference between the same-end output ports of the 3*3 coupler 2, i.e., between ports a, b, and c, is 120°, and the phase difference between ports d, e, and f is also 120°. The length of the delay fiber 3 is L, and the time difference τ between the introduced CW and CCW light reaching the resonant cavity is:

[0075]

[0076] Where n is the refractive index of the optical fiber and c is the speed of light in a vacuum.

[0077] Considering the CW and CCW optical signals that pass through the L2 fiber segment only once as a set of interference signals, if there is a strain ε(t) on the L2 fiber segment inside the resonant cavity, where t refers to time, when the CW light arrives at the resonant cavity after a delay τ, while the CCW light arrives directly at the resonant cavity, there is a phase difference between the CW and CCW lights.

[0078]

[0079] Where, p e L is the photoelastic coefficient. s λ is the length of the sensing resonant cavity, and λ is the average light wavelength. This indicates the phase difference between CW and CCW light; represents the phase of the CW light; n represents the refractive index of the optical fiber; Let ε'(t) represent the phase of the CCW light. ε'(t) is the derivative of ε(t) with respect to time, i.e., the rate of change of ε(t).

[0080] Then, the electrical signals generated by the interference signals of the CW light and CCW light from ports a and c of the 3*3 coupler 2 detected at the BPD (Balanced Photodetector) are respectively:

[0081]

[0082]

[0083] Where α is the attenuation in the loop, R d For the responsivity of the photoelectric balance detector, P in This represents the input optical power of broadband light source 1, with the superscript 1 indicating the first group of CW and CCW; This refers to the electrical signal generated by the interference signals of the first set of CW and CCW lights with a phase shift of -120° detected at port a of the 3*3 coupler 2 at the BPD. This represents the electrical signal generated by the interference signals of the first set of CW and CCW beams with a +120° phase shift detected at port c of the 3*3 coupler 2, as detected at BPD.

[0084] Therefore, at this point, at the differential output terminal of the photoelectric balance detector, we can obtain...

[0085]

[0086] Where G is the photoelectric conversion coefficient of the photoelectric balance detector.

[0087] Within the resonant cavity, multiple sets of CW and CCW interference signals can be observed. For example, the second set of CW and CCW interference signals passes through fiber segments L1 and L2 one more time than the first set. Since this set of interference signals passes through strain segment L2 again, the phase difference between the second set of CW and CCW signals is... Then, at the differential output terminal of the photoelectric balanced detector, the same result can be obtained.

[0088]

[0089] Where R is the larger part of the coupling ratio between the first coupler 4 and the second coupler 5.

[0090] Therefore, by superimposing the differential output signals of multiple sets of CW and CCW light, we can finally obtain a superposition result:

[0091]

[0092] Among them, P out This represents the voltage signal ultimately output at the balanced photodetector; m represents the number of CW and CCW light groups.

[0093] exist When the value is small, the signal can be approximated as... The relationship is linear; that is, after obtaining the strain calibration coefficients by calibrating the system, the phase to be measured can be obtained by dividing the differential signal by the calibration coefficients. However, the signal obtained here corresponds to the phase of the strain change, so further data processing is required to integrate the signal and divide it by the slope to obtain the final strain.

[0094] The low-coherence broadband light source 1 is an erbium-doped superfluorescent fiber light source with a center wavelength of 1550nm, a spectral bandwidth of 35nm, and an output optical power of 80mW; the light source can be replaced with low-cost light sources such as LEDs.

[0095] The 3*3 coupler 2 is a single-mode coupler with a splitting ratio of 1:1:1 and a phase difference of 120 degrees. This coupler can be replaced with other couplers with a certain phase difference and other multi-channel configurations; it can also be replaced with a polarization-maintaining coupler.

[0096] Delay fiber 3 is a 1km long ordinary single-mode fiber, and the time delay τ between CW and CCW is 5µs. Delay fiber 3 can be replaced with ordinary single-mode fiber of other lengths.

[0097] The first fiber coupler is a 98:2 polarization-maintaining fiber coupler, and the second fiber coupler is a 98:2 polarization-maintaining fiber coupler. Theoretically, the resonant cavity precision is 155. The first and second fiber couplers can be replaced with single-mode or polarization-maintaining couplers with other coupling ratios.

[0098] Both L1 and L2 fiber segments are single-mode fibers, each 1.2m long. The resonant cavity length is 2.4m. L1 and L2 fiber segments can be replaced with other lengths of ordinary single-mode or polarization-maintaining fibers.

[0099] The resonant cavity adopts a ring resonant cavity structure, specifically consisting of two fiber couplers in a ring structure with optical fibers of different lengths welded together in the middle; the resonant cavity can be replaced with FP (Fabry-Perot cavity) cavity and other resonant structures.

[0100] The balanced photodetector 6 can be replaced with two photodetectors.

[0101] This invention also discloses a high-precision fiber optic strain sensing method, such as... Figure 1 and Figure 2 As shown, in step S1: the light source emits an optical signal; the coupler unit receives the optical signal and splits it into a first split beam and a second split beam; the first split beam passes through the delay fiber 3 and the resonant cavity in sequence to obtain a first direction beam; the second split beam passes through the resonant cavity and the delay fiber 3 in sequence to obtain a second direction beam; the first direction beam and the second direction beam return to the coupler unit, interfere at the coupler unit, and are split into beams to obtain an interference signal with a phase difference; a preset photodetector detects the interference signal and outputs a voltage signal.

[0102] Step S2: The signal processing unit 7 acquires and demodulates the voltage signal to obtain the phase information of the interference signal, calibrates the phase and strain signals, and outputs the vibration signal.

[0103] That is, the specific steps of this embodiment are as follows:

[0104] Step 1: Output the continuous low-coherence broadband light source 1 to the input of the 3*3 coupler 2. Use a piezoelectric ceramic transducer to apply sinusoidal strain signals of 100Hz, 1kHz, and 5kHz to a portion of the L2 fiber in the resonant cavity. Use the signal processing unit 7 to start acquiring signals.

[0105] Step 2: Acquire the electrical signal U(t) generated by the photodetector and integrate the signal.

[0106] Step 3: Perform signal calibration on the integrated signal to obtain the magnitude of the strain to be measured.

[0107] Step four: Perform power spectral density measurement on the obtained strain signal to obtain the measurement accuracy of Example 1, such as... Figure 3 As shown, the strain measurement accuracy at 5kHz can be read.

[0108] The dynamic range of this embodiment is determined by the precision of the resonant cavity. The vibration frequency response bandwidth of this embodiment is determined by the delay of the delay fiber 3, which is 1 / τ. In this embodiment, the delay fiber 3 is 1 km, so τ is 5 μs, and therefore the vibration frequency response bandwidth is 200 kHz.

[0109] Compared to existing technologies, this example, based on a low-coherence broadband light source, can linearly recover the strain signal. The entire system requires no modulator-demodulator, and the strain accuracy is [insert accuracy here]. Furthermore, its system complexity and cost are significantly reduced, making it highly practical. @5kHz indicates the value at 5kHz. The high precision range of this invention is pε and above, with strain accuracy superior to the nano-strain level.

[0110] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0111] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. An optical fiber strain sensing system, characterized by, The light source, the coupler unit, the delay fiber (3), the resonant cavity, the preset photodetector and the signal processing unit (7); The light source emits a light signal; The coupler unit receives the light signal and splits it into a first split light and a second split light; The first split light passes through the delay fiber (3) and the resonant cavity in sequence to obtain a first direction light; The second split light passes through the resonant cavity and the delay fiber (3) in sequence to obtain a second direction light; The first direction light and the second direction light return to the coupler unit, and after interference at the coupler unit, the split light with a phase difference is obtained; The preset photodetector detects the interference signal and outputs a voltage signal; The signal processing unit (7) collects and demodulates the voltage signal to obtain the phase information of the interference signal, calibrates the phase and strain signals, and outputs a vibration signal; The light source includes a wide-spectrum light source (1); The coupler unit includes a 3*3 coupler unit; The resonant cavity includes a fiber ring resonant cavity; The preset photodetector includes a photoelectric balance detector; The first direction light includes clockwise light CW; The second direction light includes counterclockwise light CCW; The wide-spectrum light source (1) outputs continuous light to the 3*3 coupler unit to obtain split light; The split light enters the delay fiber (3) and the resonant cavity to form clockwise light CW and counterclockwise light CCW; The clockwise light CW and the counterclockwise light CCW interfere after returning to the 3*3 coupler unit to output a signal with a preset phase difference; The photoelectric balance detector detects the signal with the preset phase difference and outputs a differential electrical signal U(t); The signal processing unit (7) receives the differential electrical signal U(t) and outputs the strain information applied to the sensor array after signal processing ; The fiber ring resonant cavity includes a first coupler (4), a second coupler (5), a fiber segment 1 and a fiber segment 2; The first port of the first coupler (4) is connected to the fourth port of the coupler unit through the delay fiber (3); The third port of the first coupler (4) is connected to the first port of the second coupler (5) through the fiber segment 1; The fourth port of the first coupler (4) is connected to the second port of the second coupler (5) through the fiber segment 2; The third port of the second coupler (5) is connected to the sixth port of the coupler unit; The continuous light signal emitted by the wide-spectrum light source (1) is output to the second port of the coupler unit and then emitted from the fourth port and the sixth port of the coupler unit, respectively; The fifth port of the coupler unit is provided with a refractive index matching liquid; The first port and the third port of the coupler unit are respectively connected to the photoelectric balance detector.

2. The optical fiber strain sensing system of claim 1, wherein, The wide-spectrum light source (1) includes an erbium-doped superfluorescent fiber light source and an LED.

3. The optical fiber strain sensing system of claim 1, wherein, The 3*3 coupler unit includes a coupler unit with a 120-degree phase difference for each port.

4. The optical fiber strain sensing system of claim 1, wherein, The coupler unit includes a single-mode coupler and a polarization-maintaining coupler.

5. An optical fiber strain sensing method, characterized by, The fiber strain sensing system according to any one of claims 1-4 comprises the following steps: Step S1: The light source emits a light signal; The coupler unit receives the light signal and splits it into a first split light and a second split light; The first split light passes through the delay fiber (3) and the resonant cavity in sequence to obtain a first direction light; The second split light passes through the resonant cavity and the delay optical fiber (3) in sequence to obtain second direction light; The first direction light and the second direction light return to the coupler unit, and after interference occurs at the coupler unit, split light with a phase difference is obtained; The preset photodetector detects the interference signal and outputs a voltage signal; Step S2: The signal processing unit (7) collects and demodulates the voltage signal to obtain phase information of the interference signal, calibrates the phase and strain signals, and outputs a vibration signal.

6. The optical fiber strain sensing method of claim 5, wherein, In the step S1, a continuous low-coherence broadband light source (1) is output to an input end of the coupler unit, a plurality of sinusoidal strain signals are applied to an optical fiber in the resonant cavity, and a signal processing unit (7) starts to collect signals.

7. The optical fiber strain sensing method of claim 5, wherein, In the step S2, the electrical signal generated by the photometrically balanced detector is collected the electrical signal is integrated; The integrated electric signal is calibrated to obtain a to-be-measured strain; The to-be-measured strain is measured in power spectral density to obtain strain measurement accuracy.

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