A stress sensor of forward brillouin scattering

Abstract

The application relates to a stress sensor based on forward Brillouin scattering. The stress sensor comprises a light generation branch, a light interference branch, a feedback branch and a detection branch. The light generation branch is used for generating pump light and probe light respectively, and modulating the pump light to obtain modulated light; the light interference branch is used for exciting phonons under the action of the modulated light, and making the probe light modulated by the phonons interfere with the probe light not modulated by the phonons to obtain interference light; the feedback branch is used for feeding back the interference light to the light generation branch, so that the light signal generates self-excited oscillation in the stress sensor; and the detection branch is used for detecting the interference light and outputting a detection signal corresponding to stress. The radio frequency spectrum peak of the detection signal output by the stress sensor can be accurately captured, so that the precision of stress measurement is effectively improved.

Description

Technical Field

[0001] This application relates to the field of fiber optic sensing technology, and in particular to a stress sensor with forward Brillouin scattering. Background Technology

[0002] With the development of fiber optic sensing technology, the Brillouin scattering effect of optical fibers has been widely used for stress and temperature sensing, achieving great success. Existing stress sensors are based on the fact that the Brillouin frequency shift and gain bandwidth of optical fibers change with temperature and stress at different spatial locations. Temperature and stress parameters can be deduced by measuring the Brillouin frequency shift. The advantage of this type of method is that it can be used for long-distance distributed sensing.

[0003] However, since this Brillouin reflection is usually quite weak, the reflected signal is easily affected by factors such as birefringence fluctuations, resulting in low accuracy of stress measurement. Summary of the Invention

[0004] Therefore, it is necessary to provide a forward Brillouin scattering stress sensor that can improve the accuracy of stress measurement, addressing the aforementioned technical problems.

[0005] This application provides a stress sensor. The stress sensor includes a light generation branch, a light interference branch, a feedback branch, and a detection branch;

[0006] The light generation branch is used to generate pump light and probe light respectively, and to modulate the pump light to obtain modulated light;

[0007] The optical interference branch is used to excite phonons under the action of modulated light, and to make the phonon-modulated probe light interfere with the unmodulated probe light to obtain interference light;

[0008] The feedback branch is used to feed the interference light back to the light generation branch, so that the optical signal generates self-excited oscillation in the stress sensor.

[0009] The detection branch is used to detect the interference light and output a detection signal corresponding to the stress.

[0010] In one embodiment, the optical interference branch includes a Sagnac fiber ring, which includes a microstructured fiber and a first optical coupler, and the microstructured fiber is located at an asymmetric position within the Sagnac fiber ring.

[0011] Microstructured optical fibers are used to excite phonons under the action of modulated light;

[0012] The first optical coupler is used to interfere the phonon-modulated probe light with the unmodulated probe light to obtain interference light.

[0013] In one embodiment, the aforementioned Sagnac fiber loop further includes a single-mode fiber and a first polarization controller;

[0014] Single-mode fiber is used to delay phonon-modulated probe light;

[0015] The first polarization controller is used to adjust the polarization direction of the probe light.

[0016] In one embodiment, the aforementioned Sagnac fiber optic ring further includes a filter.

[0017] A filter used to remove pump light from the loop.

[0018] In one embodiment, the optical interference branch further includes a first optical amplifier and a second optical coupler;

[0019] The first optical amplifier is used to amplify the interference light to obtain amplified interference light;

[0020] The second optical coupler is used to separate the amplified interference light into interference light for feedback and interference light for detection.

[0021] In one embodiment, the feedback branch includes a first photoelectric converter and an electrical amplifier;

[0022] The first photoelectric converter is used to perform photoelectric conversion processing on the interference light to obtain the first electrical signal;

[0023] An electrical amplifier is used to amplify the first electrical signal and feed the amplified first electrical signal back to the optical generation branch.

[0024] In one embodiment, the aforementioned optical generation branch includes a first optical generation branch and a second optical generation branch; the Sagnac fiber ring also includes a third optical coupler;

[0025] The first light generation branch is used to generate pump light and modulate the pump light to obtain modulated light;

[0026] The second light generation branch is used to generate the probe light;

[0027] The third optical coupler is used to transmit the modulated light into the Sagnac fiber optic loop.

[0028] In one embodiment, the first optical generation branch includes a laser and an optical amplitude modulator;

[0029] Lasers are used to generate pump light;

[0030] An optical amplitude modulator is used to modulate pump light to obtain modulated light.

[0031] In one embodiment, the first optical generation branch further includes a second optical amplifier, an optical isolator, a third optical amplifier, and a second polarization controller;

[0032] The second optical amplifier is used to amplify the modulated light;

[0033] An optical isolator is used to transmit the modulated light after the first amplification to the third optical amplifier;

[0034] The third optical amplifier is used to amplify the modulated light after the first amplification to obtain the modulated light after the second amplification.

[0035] The second polarization controller is used to adjust the polarization direction of the modulated light.

[0036] In one embodiment, the detection branch includes a second photoelectric converter;

[0037] The second photoelectric converter is used to perform photoelectric conversion on the interference light and output a second electrical signal, which corresponds to the stress.

[0038] The aforementioned forward Brillouin scattering stress sensor includes a light generation branch, an optical interference branch, a feedback branch, and a detection branch. The light generation branch generates pump light and probe light, respectively, and modulates the pump light to obtain modulated light. The optical interference branch excites phonons under the influence of the modulated light, and causes the phonon-modulated probe light to interfere with the unmodulated probe light to obtain interference light. The feedback branch feeds the interference light back to the light generation branch, causing the optical signal to oscillate in the stress sensor. The detection branch detects the interference light and outputs a detection signal corresponding to the stress. In this application, the pump light generated by the light generation branch is modulated to obtain modulated light, thereby causing the optical interference branch to excite phonons under the influence of the modulated light. Subsequently, the probe light forms interference light in the optical interference branch and is converted into an intensity-modulated light signal. This signal is then driven by the feedback branch to drive the light generation branch, and the pump light generated by the light generation branch is intensity-modulated. This forms a closed loop of opto-mechanical-electrical self-excited oscillation, which enables the precise capture of the spectral peaks of the detection signal output by the stress sensor, effectively improving the accuracy of stress measurement. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the stress sensor structure in one embodiment;

[0040] Figure 2 This is one of the structural schematic diagrams of the Sagnac fiber optic ring in one embodiment;

[0041] Figure 3a This is a second schematic diagram of the Sagnac fiber optic ring in one embodiment;

[0042] Figure 3b This is the third schematic diagram of the Sagnac fiber optic ring in one embodiment;

[0043] Figure 4a This is the fourth schematic diagram of the Sagnac fiber optic ring in one embodiment;

[0044] Figure 4b This is the fifth schematic diagram of the Sagnac fiber optic ring in one embodiment;

[0045] Figure 5 This is a schematic diagram of the optical interference branch in one embodiment;

[0046] Figure 6 This is a schematic diagram of the feedback branch structure in one embodiment;

[0047] Figure 7 This is a schematic diagram of the structure of the light generation branch in one embodiment;

[0048] Figure 8 This is one of the structural schematic diagrams of the first light generation branch in one embodiment;

[0049] Figure 9 This is a second schematic diagram of the structure of the first light generation branch in one embodiment;

[0050] Figure 10 This is a schematic diagram of the detection branch in one embodiment;

[0051] Figure 11 This is a schematic diagram of the stress sensor in another embodiment. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0053] First, before introducing the technical solutions of the embodiments of this application in detail, the technical background on which the embodiments of this application are based will be introduced.

[0054] In recent years, infrastructure construction in China has experienced explosive growth. Numerous bridges, tunnels, and other infrastructure projects have been built in remote, harsh environments or on high-intensity earthquake zones. These infrastructures must withstand the severe tests of such external environments. Maintaining the normal operation of this infrastructure requires a significant investment of human and material resources for monitoring and maintenance. For structural components of this type of infrastructure, such as bridge cables and tunnel deformation, the stress and strain of load-bearing components are the most critical health indicators. Once the stress exceeds a certain threshold, cable breakage or tunnel deformation will occur, leading to serious accidents. Another scenario is where stress monitoring of the main wing load-bearing beams of large aircraft and large wind turbine blades is crucial for the safe operation of the equipment. These scenarios require precise monitoring of the stress of structural components over short distances.

[0055] The Brillouin scattering effect based on optical fibers has been widely and successfully used for stress and temperature sensing. The basic principle is that the Brillouin frequency shift and gain bandwidth of the optical fiber change with temperature and stress at different spatial locations. Measuring the Brillouin gain characteristics, especially the Brillouin frequency shift, allows for the deduction of temperature and stress parameters. This method has the advantage of being suitable for long-distance distributed sensing. However, Brillouin reflection is typically weak, and the reflected signal is easily affected by factors such as birefringence fluctuations. Curve fitting of the original measurement data is necessary to eliminate measurement noise caused by birefringence fluctuations. The Brillouin gain peak is not sharp, limiting the accuracy of stress measurements. Currently, several commonly used Brillouin fiber sensing methods, such as Brillouin optical time-domain analysis, Brillouin optical time-domain reflectometry, and Brillouin optical correlation domain analysis, all employ open-loop structures, with technological advancements primarily focused on improving spatial resolution. Accurate measurement of stress changes remains a challenge.

[0056] In one embodiment, such as Figure 1 As shown, a stress sensor is provided, comprising a light generation branch 10, an optical interference branch 20, a feedback branch 30, and a detection branch 40. The light generation branch 10 generates pump light and probe light respectively, and modulates the pump light to obtain modulated light; the optical interference branch 20 excites phonons under the action of the modulated light, and causes the phonon-modulated probe light to interfere with the unmodulated probe light to obtain interference light; the feedback branch 30 feeds the interference light back to the light generation branch 10, causing the optical signal to generate self-excited oscillation in the stress sensor; the detection branch 40 detects the interference light and outputs a detection signal corresponding to the stress.

[0057] Among them, the light generation branch 10 is connected to the light interference branch 20, and the light interference branch 20 is also connected to the feedback branch 30 and the detection branch 40 respectively.

[0058] In this embodiment, the optical generation branch 10 generates pump light and probe light respectively. The generating devices include, but are not limited to, lasers, interferometers, optical fibers, or gratings. After generating pump light and probe light, the optical generation branch 10 modulates the pump light to obtain modulated light. The modulation method can be optical signal modulation, optical wave modulation, or amplitude modulation; this embodiment does not specifically limit the method. After being modulated by the optical generation branch 10, the pump light enters the optical interference branch 20, causing the optical interference branch 20 to excite phonons under the action of the modulated light. After the probe light enters the optical interference branch 20, a portion of the probe light is phase-modulated by the phonons excited by the pump light, while the other portion is not. Subsequently, the two portions of probe light recombine and interfere to form interference light, converting the phase-modulated portion of the probe light signal into an intensity-modulated signal. Furthermore, a portion of the intensity-modulated light signal passes through the feedback branch 30, converting the intensity-modulated light signal into an electrical pulse signal. The electrical pulse signal can drive the light generation branch 10 and modulate the intensity of the pump light generated by the light generation branch 10, thereby forming a self-excited oscillating closed loop.

[0059] The stress sensor in this embodiment is a self-oscillating closed loop, which can generate a narrowband radio frequency (RF) signal with a high side-mode rejection ratio. The frequency of this narrowband RF signal changes with the stress on the object under test. In this embodiment, the RF signal can be detected via the detection branch 40, as follows: a portion of the phase-modulated probe light signal is converted into an intensity-modulated signal, and a portion of this intensity-modulated signal enters the detection branch 40, thereby causing the detection branch 40 to output a detection signal corresponding to the stress.

[0060] The aforementioned stress sensor includes a light generation branch, an optical interference branch, a feedback branch, and a detection branch. The light generation branch generates pump light and probe light, and modulates the pump light to obtain modulated light. The optical interference branch excites phonons under the action of the modulated light, and the phonon-modulated probe light interferes with the unmodulated probe light to obtain interference light. The feedback branch feeds the interference light back to the light generation branch, causing the optical signal to generate self-excited oscillation in the stress sensor. The detection branch detects the interference light and outputs a detection signal corresponding to the stress. In this embodiment, the pump light generated by the light generation branch is modulated to obtain modulated light, thereby causing the optical interference branch to excite phonons under the action of the modulated light. Subsequently, the probe light forms interference light in the optical interference branch and is converted into an intensity modulated light signal, which is then driven by the feedback branch to drive the light generation branch and modulate the intensity of the pump light generated by the light generation branch, thus forming a self-excited oscillating closed loop. This allows the spectral peaks of the detection signal output by the stress sensor to be accurately captured, effectively improving the accuracy of stress measurement.

[0061] In one embodiment, such as Figure 2 As shown, the aforementioned optical interference branch 20 includes a Sagnac fiber ring, which includes a microstructure fiber 200 and a first optical coupler 201. The microstructure fiber 200 is located at an asymmetric position within the Sagnac fiber ring. The microstructure fiber 200 is used to excite phonons under the action of modulated light. The first optical coupler 201 is used to cause the phonon-modulated probe light to interfere with the unmodulated probe light to obtain interference light.

[0062] In this design, the microstructured fiber 200 in the Sagnac fiber ring is located at an asymmetrical position within the ring. The microstructured fiber 200 and the first optical coupler 201 are interconnected within the Sagnac fiber ring. One end of the microstructured fiber 200 is connected to the light generation branch 10. The first optical coupler 201 is also connected to both the feedback branch 30 and the light generation branch 10.

[0063] The Sagnac fiber loop can split a beam of light emitted from the same source into two beams, which then converge after traveling in opposite directions within the same loop, producing interference. The microstructured fiber 200 is located inside the object under test; when the object is stretched, the microstructured fiber 200 is stretched synchronously. The microstructured fiber 200 is used to excite forward Brillouin scattering to generate phonons under the influence of modulated light.

[0064] In this embodiment, the pump light, after being modulated by the light generation branch 10, enters the Sagnac fiber ring in the light interference branch 20, causing the microstructure fiber 200 in the Sagnac fiber ring to generate phonons through forward Brillouin scattering under the action of the modulated light. Subsequently, the probe light enters the Sagnac fiber ring and splits into a clockwise probe light component and a counterclockwise probe light component. The clockwise probe light component enters the Sagnac fiber ring from the first port of the first optical coupler 201, undergoes phase modulation by the phonons excited by the pump light in the microstructure fiber 200, and then returns to the second port of the first optical coupler 201. The counterclockwise probe light component enters the Sagnac fiber ring from the second port, undergoes phase modulation by the phonons not excited by the pump light in the microstructure fiber 200, and then returns to the first port of the first optical coupler 201. After each propagating once within the ring, the clockwise and counterclockwise probe light components reach the first optical coupler 201 and interfere at the third port of the first optical coupler 201 to generate interference light.

[0065] The aforementioned stress sensor includes a Sagnac fiber ring in its optical interference branch. The Sagnac fiber ring comprises a microstructured fiber and a first optical coupler, with the microstructured fiber located at an asymmetric position within the ring. The microstructured fiber can generate phonons through forward Brillouin scattering under the influence of modulated light. The first optical coupler allows the phonon-modulated probe light to interfere with the unmodulated probe light to produce interference light. In this embodiment, the modulated light in the optical generation branch can excite phonons in the microstructured fiber of the Sagnac fiber ring, thereby modulating the phase of the probe light entering the Sagnac fiber ring clockwise. The asymmetric position of the microstructured fiber within the Sagnac fiber ring ensures that the clockwise probe light component is modulated by phonons, while the counterclockwise probe light component remains unmodulated. Subsequently, the phase-modulated probe light and the unmodulated probe light form interference light after passing through the first optical coupler, and the phase-modulated probe light is converted into an intensity-modulated light signal, which enables the precise capture of the spectral peaks of the detection signal output by the stress sensor, effectively improving the accuracy of stress measurement.

[0066] In one embodiment, the aforementioned Sagnac fiber ring further includes a single-mode fiber 202 and a first polarization controller 203; the single-mode fiber 202 is used to delay the phonon-modulated probe light; the first polarization controller 203 is used to adjust the polarization direction of the probe light.

[0067] One connection method includes: one end of a single-mode optical fiber 202 is connected to a first optical coupler 201 via a first polarization controller 203, and the other end is connected to a microstructure optical fiber 200, such as... Figure 3a As shown.

[0068] Another connection method includes: one end of the single-mode fiber 202 is connected to the first optical coupler 201, and the other end is connected to the microstructure fiber 200 through the first polarization controller 203, such as... Figure 3b As shown.

[0069] In this embodiment, the pump light, after being modulated by the light generation branch 10, enters the Sagnac fiber ring in the light interference branch 20, causing the microstructure fiber 200 in the Sagnac fiber ring to generate phonons through forward Brillouin scattering under the action of the modulated light. Subsequently, the probe light enters the Sagnac fiber ring and is divided into a clockwise probe light component and a counterclockwise probe light component. After the clockwise probe light component enters the microstructure fiber 200, it is phase-modulated by the phonons excited by the pump light and then delayed through the single-mode fiber 202. The polarization direction of the clockwise probe light component is adjusted by the first polarization controller 203. Subsequently, the clockwise probe light component returns to the first port of the first optical coupler 201 and enters the Sagnac fiber ring, where it is phase-modulated by the phonons excited by the pump light in the microstructure fiber 200. The counterclockwise probe light component enters the Sagnac fiber loop from the second port. After the polarization direction of the counterclockwise probe light component is adjusted by the first polarization controller 203, it is delayed through single-mode fiber 202, and then returns to the first port of the first optical coupler 201 through microstructure fiber 200. The clockwise and counterclockwise probe light components each propagate once within the loop and then reach the first optical coupler 201. The phase-modulated clockwise probe light component and the unmodulated counterclockwise probe light component interfere at the third port of the first optical coupler 201 to produce interference light.

[0070] The aforementioned stress sensor, including the Sagnac fiber ring, further comprises a single-mode fiber and a first polarization controller. The single-mode fiber delays the phonon-modulated probe light; the first polarization controller adjusts the polarization direction of the probe light. In this embodiment, the single-mode fiber delays the passing probe light. This delay allows the clockwise probe light component to undergo phase modulation due to the phonons in the microstructure fiber, while the counterclockwise probe light component does not. The first polarization controller adjusts the polarization directions of the clockwise and counterclockwise probe light components, strengthening their interference at the third port of the first optical coupler. This allows for more precise capture of the spectral peaks of the output detection signal.

[0071] In one embodiment, such as Figure 4a and Figure 4b As shown, the aforementioned Sagnac fiber optic ring also includes a filter 204; the filter 204 is used to filter out the pump light in the ring.

[0072] One connection method includes: one end of the filter 204 is connected to the microstructure optical fiber 200, and the other end is connected to the single-mode optical fiber 202, such as... Figure 4a As shown.

[0073] Another connection method includes: one end of the filter 204 is connected to the microstructure optical fiber 200, and the other end is connected to the first polarization controller 203, such as... Figure 4b As shown.

[0074] In this embodiment, the pump light, after being modulated by the light generation branch 10, enters the Sagnac fiber ring in the light interference branch 20, causing the microstructure fiber 200 in the Sagnac fiber ring to generate phonons through forward Brillouin scattering under the action of the modulated light. Subsequently, the residual pump light is filtered out by the filter 204. Then, the probe light enters the Sagnac fiber ring and is divided into a clockwise probe light component and a counterclockwise probe light component. The clockwise probe light component, after entering the microstructure fiber 200, is phase-modulated by the phonons excited by the pump light and is delayed through the single-mode fiber 202. Then, after the polarization direction of the clockwise probe light component is adjusted by the first polarization controller 203, it returns to a first port of the first optical coupler 201 and enters the Sagnac fiber ring, where it is phase-modulated by the phonons excited by the pump light in the microstructure fiber 200. The counterclockwise probe light component enters the Sagnac fiber ring from the second port, and after the polarization direction of the counterclockwise probe light component is adjusted by the first polarization controller 203, it is delayed through the single-mode fiber 202. Subsequently, the light returns to the first port of the first optical coupler 201 via the microstructured optical fiber 200. The clockwise and counterclockwise probe light components, after each propagating once within the loop, arrive at the first optical coupler 201. The clockwise probe light component, which is phase-modulated, and the counterclockwise probe light component, which is not phase-modulated, interfere at the third port of the first optical coupler 201, generating interference light.

[0075] The aforementioned stress sensor, including the Sagnac fiber optic ring, also includes a filter that can remove pump light from the ring. In this embodiment, a filter is used to remove residual pump light from the Sagnac fiber optic ring, preventing residual pump light from interfering with the interference light and further improving the accuracy of stress measurement.

[0076] In one embodiment, such as Figure 5 As shown, the optical interference branch 20 also includes a first optical amplifier 205 and a second optical coupler 206; the first optical amplifier 205 is used to amplify the interference light to obtain amplified interference light; the second optical coupler 206 is used to separate the amplified interference light to obtain interference light for feedback and interference light for detection.

[0077] One end of the first optical amplifier 205 is connected to the second optical coupler 206, and the other end is connected to the first optical coupler 201 of the Sagnac fiber optic ring.

[0078] In this embodiment, in the Sagnac fiber optic loop, the clockwise probe light component, which is phase-modulated, and the counterclockwise probe light component, which is not phase-modulated, interfere at the third port of the first optical coupler 201 to generate interference light. Based on the interference mechanism of light, the phase-modulated light is converted into intensity-modulated light (optical pulse signal). The optical pulse signal is amplified by the first optical amplifier 205 and then split into two paths by the second optical coupler 206. One path is used for feedback interference light, and the other path is used for detection interference light.

[0079] The aforementioned stress sensor, in its optical interference branch, further includes a first optical amplifier and a second optical coupler. The first optical amplifier amplifies the intensity-modulated light to obtain amplified intensity-modulated light. The second optical coupler separates the amplified intensity-modulated light into intensity-modulated light for feedback and intensity-modulated light for detection. In this embodiment, the first optical amplifier amplifies the intensity-modulated light, thereby enhancing the intensity-modulated light signal used for feedback, which is beneficial for subsequent signal detection and feedback.

[0080] In one embodiment, such as Figure 6 As shown, the feedback branch 30 includes a first photoelectric converter 301 and an electrical amplifier 302; the first photoelectric converter 301 is used to perform photoelectric conversion processing on the interference light to obtain a first electrical signal; the electrical amplifier 302 is used to amplify the first electrical signal and feed the amplified first electrical signal back to the light generation branch 10.

[0081] The first photoelectric converter 301 is connected at one end to the second optical coupler 206 in the optical interference branch 20, and at the other end to the electrical amplifier 302.

[0082] In this embodiment, interference occurs at the third port of the first optical coupler 201 in the optical interference branch 20, generating interference light. The phase-modulated light is then converted into intensity-modulated light (optical pulse signal). The optical pulse signal is amplified by the first optical amplifier 205. Subsequently, the optical pulse signal is transmitted to the first photoelectric converter 301 in the feedback branch 30 for photoelectric conversion and outputs a first electrical signal. The first electrical signal is input to the electrical amplifier 302, which amplifies the first electrical signal and feeds it back to the light generation branch 10 to drive the light generation branch 10, thereby forming a self-excited oscillation closed loop.

[0083] The aforementioned stress sensor includes a feedback branch comprising a first photoelectric converter and an electrical amplifier. The first photoelectric converter performs photoelectric conversion on the interference light to obtain a first electrical signal. The electrical amplifier amplifies the first electrical signal and feeds it back to the light generation branch. In this embodiment, the first photoelectric converter converts the optical pulse signal into a first electrical signal, which is beneficial for driving the light generation branch. The electrical amplifier amplifies the converted first electrical signal, improves the stability of the feedback branch, reduces noise, and increases the accuracy of the output first electrical signal. The amplified first electrical signal is fed back to the light generation branch to drive it, thus forming a closed loop. This application focuses on the coupling process between phonons and probe light in the forward Brillouin scattering process in optical fiber. Modulation light is introduced into the microstructured optical fiber, causing the microstructured optical fiber to excite phonon eigenmodes. The phonons then act on the probe light wave, and the phase-modulated probe light wave is converted into a first electrical signal through photoelectric conversion, which then acts back on the light generation branch, forming a closed loop. The above process increases the gain of the entire loop, making the stress sensor's measurement results more accurate.

[0084] In one embodiment, such as Figure 7 As shown, the aforementioned optical generation branch 10 includes a first optical generation branch 101 and a second optical generation branch 102; the Sagnac fiber ring also includes a third optical coupler 207; the first optical generation branch 101 is used to generate pump light and modulate the pump light to obtain modulated light; the second optical generation branch 102 is used to generate probe light; the third optical coupler 207 is used to transmit the modulated light into the Sagnac fiber ring.

[0085] The first optical generation branch 101 is connected to the third optical coupler 207 of the Sagnac fiber optic ring. The second optical generation branch 102 is connected to the first optical coupler 201 of the Sagnac fiber optic ring.

[0086] In this embodiment, the first optical generation branch 101 generates pump light. The generating device includes, but is not limited to, a laser, interferometer, optical fiber, photodetector, or grating. After generating the pump light, the optical generation branch 101 modulates the pump light to obtain modulated light. The modulation method can be optical signal modulation, optical wave modulation, or amplitude modulation; this embodiment does not specifically limit the method. The pump light, after being modulated by the optical generation branch 10, generates modulated light. The modulated light passes through the third coupler 207 and enters the optical interference branch 20, causing the microstructure optical fiber 200 of the optical interference branch 20 to undergo forward Brillouin scattering under the action of the modulated light, generating phonons. Then, the remaining pump light is filtered out by the filter 204.

[0087] The second optical generation branch 102 generates probe light, which enters the Sagnac fiber loop and splits into clockwise and counterclockwise probe light components. The clockwise probe light component, after entering the microstructure fiber 200, is phase-modulated by phonons excited by the pump light. After being delayed by the single-mode fiber 202, its polarization direction is adjusted by the first polarization controller 203. It then returns to the first port of the first optical coupler 201 and enters the Sagnac fiber loop again. After being phase-modulated by phonons excited by the pump light in the microstructure fiber 200, it returns to the second port of the first optical coupler 201. The counterclockwise probe light component enters the Sagnac fiber loop from the second port. After its polarization direction is adjusted by the first polarization controller 203, it is delayed by the single-mode fiber 202 and then returns to the first port of the first optical coupler 201 through the microstructure fiber 200. After the clockwise and counterclockwise probe light components are transmitted once in the loop, they reach the first optical coupler 201. The clockwise probe light component, which is phase-modulated, and the counterclockwise probe light component, which is not phase-modulated, interfere with each other at the third port of the first optical coupler 201, generating interference light.

[0088] For example, the first light generation branch 101 generates pump light through laser 1011. The second light generation branch 102 generates probe light through probe laser 1021.

[0089] The aforementioned stress sensor includes a first optical generation branch and a second optical generation branch. The Sagnac fiber ring also includes a third optical coupler. The first optical generation branch generates pump light and modulates it to obtain modulated light. The second optical generation branch generates probe light. In this embodiment, the modulated light generated by the first optical generation branch excites forward Brillouin scattering in the microstructured fiber to generate phonons, so that the probe light generated by the second optical generation branch can be converted into intensity-modulated light for subsequent stress detection.

[0090] In one embodiment, such as Figure 8 As shown, the first light generation branch 101 includes a laser 1011 and an optical amplitude modulator 1012; the laser 1011 is used to generate pump light; the optical amplitude modulator 1012 is used to modulate the pump light to obtain modulated light.

[0091] The output of laser 1011 is connected to the input of optical amplitude modulator 1012. The output of optical amplitude modulator 1012 is connected to optical interference branch 20.

[0092] In this embodiment, the laser 1011 in the first optical generation branch generates pump light. After the laser 1011 generates the pump light, it is input to the optical amplitude modulator 1012. The optical amplitude modulator 1012 performs suppressed carrier modulation on the pump light, generating modulated light with upper and lower sidebands. The frequency difference between the two sidebands is equal to the Brillouin frequency shift of the fiber under test, which excites phonons that vibrate laterally. The modulated light enters the optical interference branch 20 through the third coupler 207.

[0093] The aforementioned stress sensor includes a first optical generation branch comprising a laser and an optical amplitude modulator. The laser can be used to generate pump light. The optical amplitude modulator can modulate the pump light to obtain modulated light. In this embodiment, the pump light generated by the laser is modulated by the optical amplitude modulator to obtain modulated light, thereby enabling the microstructure fiber of the optical interference branch to excite phonons under the action of the modulated light, so as to perform phase modulation on the probe light.

[0094] In one embodiment, such as Figure 9 As shown, the first light generation branch 101 further includes a second optical amplifier 1013, an optical isolator 1014, a third optical amplifier 1015, and a second polarization controller 1016; the second optical amplifier 1013 is used to amplify the modulated light; the optical isolator 1014 is used to transmit the modulated light after the first amplification to the third optical amplifier 1015; the third optical amplifier 1015 is used to amplify the modulated light after the first amplification to obtain the modulated light after the second amplification; the second polarization controller 1016 is used to adjust the polarization direction of the modulated light.

[0095] One connection method includes: a laser 1011, an optical amplitude modulator 1012, a second optical amplifier 1013, an optical isolator 1014, a third optical amplifier 1015, and a second polarization controller 1016 connected in sequence. The output terminal of the second polarization controller 1016 is connected to the optical interference branch 20, such as... Figure 9 As shown.

[0096] In this embodiment, the pump light generated by the laser 1011 is modulated by the optical amplitude modulator 1012 to obtain modulated light. The modulated light is then sequentially isolated and amplified by the second optical amplifier 1013, the optical isolator 1014, and the third optical amplifier 1015. The polarization direction of the isolated and amplified modulated light is then adjusted by the second polarization controller 1016, making the polarization direction of the modulated light parallel to that of the probe light. Subsequently, the modulated light enters the microstructure fiber 200 of the optical interference branch 20, causing the microstructure fiber 200 to undergo forward Brillouin scattering under the action of the modulated light, generating phonons. By adjusting the gain coefficients of the second optical amplifier 1013 and the third optical amplifier 1015, when the pump light reaches a certain threshold, the gain and loss of the Sagnac fiber ring are balanced, thus forming an opto-mechanical-electrical oscillation.

[0097] For example, the modulated light sequentially passes through the optical isolator 1014, the second optical amplifier 1013, the third optical amplifier 1015, and the second polarization controller 1016 before entering the optical interference branch.

[0098] The aforementioned stress sensor, in its first light generation branch, further includes a second optical amplifier, an optical isolator, a third optical amplifier, and a second polarization controller. The second optical amplifier amplifies the modulated light. The optical isolator transmits the first amplified modulated light to the third optical amplifier. The third optical amplifier amplifies the first amplified modulated light to obtain a second amplified modulated light. The second polarization controller adjusts the polarization direction of the modulated light. In this embodiment, the second polarization controller makes the polarization directions of the modulated light and the probe light parallel, thereby improving the gain of the Sagnac fiber ring. By adjusting the gain coefficients of the second and third optical amplifiers, when the pump light is amplified to a certain threshold, the gain and loss of the Sagnac fiber ring reach a balance, thus forming an opto-mechanical-electrical oscillation, making the detection signal output by the stress sensor more accurate. The optical isolator prevents interference to the modulated light during propagation, further improving the measurement accuracy of the stress sensor.

[0099] In one embodiment, such as Figure 10 As shown, the detection branch 40 includes a second photoelectric converter 401. The second photoelectric converter 401 is used to perform photoelectric conversion on the interference light and output a second electrical signal, which corresponds to the stress.

[0100] The input terminal of the second photoelectric converter 401 in the detection branch 40 is connected to the second optical coupler 206 in the optical interference branch 20.

[0101] In this embodiment, after the probe light travels through the Sagnac fiber loop once, interference light is formed at the third port of the first optical coupler 201. Based on the principle of light interference, the phase-modulated probe light is converted into intensity-modulated light and emits an optical pulse signal. Subsequently, the optical pulse signal is input into the second photoelectric converter 401. The second photoelectric converter 401 performs photoelectric conversion on the optical pulse signal to generate a narrowband radio frequency signal (second electrical signal). When the object under test is stretched, the microstructured optical fiber 200 is stretched simultaneously. The phonon frequency of the transverse vibration caused by stress in the microstructured optical fiber 200 changes. By measuring the frequency change of the narrowband radio frequency signal output by the second photoelectric converter 401, the stress on the microstructured optical fiber 200 can be sensed.

[0102] The stress sensor described above includes a second photoelectric converter in its detection branch. This second photoelectric converter can perform photoelectric conversion on the interference light and output a second electrical signal, which corresponds to the stress. In this embodiment, the detection signal output by the second photoelectric converter is the output signal of the stress sensor. When the object under test is stretched, the second photoelectric converter can output a narrowband radio frequency signal, and the spectral peaks of the narrowband radio frequency signal can be accurately captured, effectively improving the accuracy of stress measurement.

[0103] In one embodiment, such as Figure 11 As shown, the stress sensor also includes a laser 1011, an optical amplitude modulator 1012, a second optical amplifier 1013, an optical isolator 1014, a third optical amplifier 1015, a second polarization controller 1016, a third optical coupler 207, a microstructure fiber 200, a filter 204, a single-mode fiber 202, a first polarization controller 203, a first optical coupler 201, a first optical amplifier 205, a second optical coupler 206, a first photoelectric converter 301, an electrical amplifier 302, a second photoelectric converter 406, a detection laser 1021, and a third polarization controller 1022.

[0104] The laser 1011, optical amplitude modulator 1012, second optical amplifier 1013, optical isolator 1014, third optical amplifier 1015, and second polarization controller 1016 are connected in sequence. The output of the second polarization controller 1016 is connected to the third optical coupler 207. The third optical coupler 207, microstructure fiber 200, filter 204, single-mode fiber 202, first polarization controller 203, and first optical coupler 201 are connected in a clockwise direction. The first optical coupler 201 is also connected to the third optical coupler 207, the first optical amplifier 205, and the first polarization controller 203, and is also connected to the probe laser 1021 through the third polarization controller 1022. The first optical amplifier 205, second optical coupler 206, first photoelectric converter 301, electrical amplifier 302, and optical amplitude modulator 1012 are connected in sequence. The second optical coupler 206 is also connected to the second photoelectric converter 406.

[0105] The aforementioned stress sensor also includes a laser, an optical amplitude modulator, a second optical amplifier, an optical isolator, a third optical amplifier, a second polarization controller, a third optical coupler, a microstructured optical fiber, a filter, a single-mode optical fiber, a first polarization controller, a first optical coupler, a first optical amplifier, a second optical coupler, a first photoelectric converter, an electrical amplifier, a second photoelectric converter, a third polarization controller, and a probe laser. In this embodiment, a self-excited oscillation closed loop is formed by the coupling of light waves, mechanical waves caused by forward Brillouin scattering in the optical fiber, and electrical signals, oscillating at the peak frequency of the Brillouin frequency shift. Because it is a self-excited oscillation, a narrowband radio frequency signal with a high side-mode rejection ratio is generated at the Brillouin frequency shift. The frequency of this narrow-band radio frequency signal changes with the stress on the microstructured optical fiber. Due to its high side-mode rejection ratio and narrow linewidth, the spectral peaks can be accurately captured. Furthermore, because it is a self-excited oscillation within a cavity, even small changes in the Brillouin frequency can be reflected in the oscillation frequency, effectively improving the accuracy and reliability of stress measurement.

[0106] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0107] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0108] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A stress sensor, characterized in that, The stress sensor includes a light generation branch, a light interference branch, a feedback branch, and a detection branch; The light generation branch is used to generate pump light and probe light respectively, and to modulate the pump light to obtain modulated light; The optical interference branch is used to excite phonons under the action of the modulated light, and to cause the probe light modulated by the phonons to interfere with the probe light not modulated by the phonons to obtain interference light; the optical interference branch includes a Sagnac fiber ring, the Sagnac fiber ring includes a microstructure fiber and a first optical coupler, and the microstructure fiber is located at an asymmetric position within the Sagnac fiber ring. A feedback branch is used to feed the interference light back to the light generation branch, so that the optical signal generates self-excited oscillation in the stress sensor. The detection branch is used to detect the interference light and output a detection signal corresponding to the stress.

2. The stress sensor according to claim 1, characterized in that, The microstructured optical fiber is used to excite phonons under the action of the modulated light; The first optical coupler is used to cause the probe light modulated by the phonons to interfere with the probe light not modulated by the phonons to obtain interference light.

3. The stress sensor according to claim 2, characterized in that, The Sagnac fiber optic ring also includes a single-mode fiber and a first polarization controller; The single-mode optical fiber is used to delay the probe light modulated by the phonons; The first polarization controller is used to adjust the polarization direction of the probe light.

4. The stress sensor according to claim 2, characterized in that, The Sagnac fiber optic ring also includes a filter; The filter is used to filter out the pump light in the loop.

5. The stress sensor according to any one of claims 2-4, characterized in that, The optical interference branch also includes a first optical amplifier and a second optical coupler; The first optical amplifier is used to amplify the interference light to obtain amplified interference light; The second optical coupler is used to separate the amplified interference light to obtain interference light for feedback and interference light for detection.

6. The stress sensor according to claim 1, characterized in that, The feedback branch includes a first photoelectric converter and an electrical amplifier; The first photoelectric converter is used to perform photoelectric conversion processing on the interference light to obtain a first electrical signal; The electrical amplifier is used to amplify the first electrical signal and feed the amplified first electrical signal back to the light generation branch.

7. The stress sensor according to claim 2, characterized in that, The optical generation branch includes a first optical generation branch and a second optical generation branch; the Sagnac fiber ring also includes a third optical coupler. The first light generation branch is used to generate the pump light and modulate the pump light to obtain the modulated light; The second light generation branch is used to generate the probe light; The third optical coupler is used to transmit the modulated light into the Sagnac fiber optic loop.

8. The stress sensor according to claim 7, characterized in that, The first optical generation branch includes a laser and an optical amplitude modulator; The laser is used to generate the pump light; The optical amplitude modulator is used to modulate the pump light to obtain the modulated light.

9. The stress sensor according to claim 8, characterized in that, The first optical generation branch also includes a second optical amplifier, an optical isolator, a third optical amplifier, and a second polarization controller; The second optical amplifier is used to amplify the modulated light; The optical isolator is used to transmit the modulated light after the first amplification to the third optical amplifier; The third optical amplifier is used to amplify the modulated light after the first amplification to obtain the modulated light after the second amplification. The second polarization controller is used to adjust the polarization direction of the modulated light.

10. The stress sensor according to claim 1, characterized in that, The detection branch includes a second photoelectric converter; The second photoelectric converter is used to perform photoelectric conversion on the interference light and output a second electrical signal, which corresponds to the stress.

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