An ultra-high sensitivity strain and temperature sensor with enhanced Vernier effect
By using a series broadband light source, fiber optic Solc-Saganc interferometer, and fiber optic Saganc interferometer, and utilizing a novel enhanced vernier effect, the shortcomings of traditional fiber optic sensors in high-sensitivity measurement are overcome, achieving ultra-high sensitivity detection of strain and temperature, suitable for structural health monitoring in aerospace, bridge and tunnel engineering, and precision industrial machinery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHEJIANG UNIV
- Filing Date
- 2026-03-03
- Publication Date
- 2026-06-12
AI Technical Summary
Existing fiber optic strain and temperature sensors cannot simultaneously meet the measurement requirements of high sensitivity and high accuracy. Especially in structural health monitoring in fields such as aerospace, bridges and tunnels, and precision industrial machinery, traditional fiber optic sensors have limited dynamic measurement range, high temperature cross-sensitivity, and complex manufacturing processes, resulting in high costs and limiting large-scale applications.
By employing a broadband light source, a fiber optic Solc-Saganc interferometer, and a fiber optic Saganc interferometer connected in series along the optical path, a secondary amplification of strain and temperature sensitivity is achieved through a novel enhanced vernier effect. The basic vernier effect is excited by the π/2 angle fusion splicing structure of the fiber optic Solc-Saganc interferometer, and an enhanced vernier effect is generated in the fiber optic Saganc interferometer, which simplifies the system structure and improves the sensing sensitivity.
A second-order step improvement in strain and temperature sensitivity was achieved, with the sensor's strain sensitivity increasing by 14.88 times and temperature sensitivity increasing by 16.62 times, significantly enhancing the sensor's detection capabilities and making it suitable for precision industrial measurement and structural health monitoring.
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Figure CN122192412A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of fiber optic sensing technology and relates to an ultra-high sensitivity strain and temperature sensor that enhances the vernier effect. Background Technology
[0002] In high-precision fields such as aerospace equipment, large bridges and tunnels, and precision industrial machinery, the service status of structures is a complex and dynamic process. Among these, the strain distribution and temperature field changes within the structure are two core physical indicators for jointly assessing its structural integrity, stability, and operational safety. Strain reflects the mechanical load and stress state borne by the structure, while temperature directly affects material properties and can induce thermal stress; both together determine the structure's operating condition. Strain and temperature measurements have a significant impact on structural health monitoring and engineering safety. Fiber optic sensors, with their inherent advantages such as resistance to electromagnetic interference, corrosion resistance, and high stability, have become ideal candidates for solutions in complex and extreme environments. Traditional fiber optic strain and temperature sensors can be mainly divided into interferometric fiber optic sensors and fiber Bragg grating sensors. Although fiber Bragg grating sensors are small and easy to integrate, their limited dynamic measurement range makes them difficult to meet extreme measurement requirements; their high temperature cross-sensitivity, complex manufacturing process, and high technical requirements lead to high production costs, limiting large-scale applications. Interferometric fiber optic strain and temperature sensors are high-precision sensors designed based on the principle of phase modulation. Changes in physical quantities such as the length and birefringence of the optical fiber cause changes in the phase of the light incident on the fiber. Interferometric strain-temperature sensors mainly include Fabry-Perot, Mach-Zehnder, and Sagnac interferometric types. These sensors can sensitively detect changes in strain and temperature, enabling strain and temperature measurements. However, traditional fiber optic strain and temperature sensors of this type struggle to meet increasingly stringent requirements for precision and high sensitivity monitoring, constituting a core bottleneck in the development of fiber optic sensing technology. Summary of the Invention
[0003] The purpose of this invention is to address the difficulty of achieving high sensitivity simultaneously in current mainstream fiber optic strain and temperature sensor research schemes. This invention proposes an ultra-high sensitivity strain and temperature sensor with enhanced vernier effect. This sensor achieves amplification of strain and temperature sensitivity through a novel enhanced vernier effect.
[0004] To achieve the above objectives, the present invention adopts the following technical solution: An ultra-high sensitivity strain and temperature sensor with enhanced vernier effect includes a broadband light source, a fiber optic Solc-Saganc interferometer, a fiber optic Sagnac interferometer, and a spectrometer arranged in series along an optical path. The fiber optic Solc-Saganc interferometer receives incident light from the broadband light source and generates an envelope spectrum with a first free spectral range (FSR_SSI). The fiber optic Sagnac interferometer receives the envelope spectrum output by the fiber optic Solc-Saganc interferometer and is cascaded with the fiber optic Solc-Saganc interferometer to generate an enhanced vernier effect, achieving a secondary amplification of the sensing sensitivity. The free spectral range of the fiber optic Sagnac interferometer is 0.90–0.99 times that of the fiber optic Solc-Saganc interferometer.
[0005] Preferably, the fiber optic Solc-Saganc interferometer includes a first fiber coupler, a first polarization controller, a first polarization-maintaining fiber, and a second polarization-maintaining fiber; the first polarization-maintaining fiber and the second polarization-maintaining fiber are fused together at an angle of π / 2 through their fast axis or slow axis; the first port of the first fiber coupler is connected to a broadband light source, and the third and fourth ports of the first fiber coupler are respectively connected through an optical path composed of the first polarization controller, the first polarization-maintaining fiber, and the second polarization-maintaining fiber to form a Sagnac ring structure; the second port of the first fiber coupler is connected to the fiber optic Saganc interferometer.
[0006] Preferably, in the Sagnac ring structure of the fiber optic Solc-Saganc interferometer, the third port of the first fiber coupler is connected to the first port of the first polarization controller, the second port of the first polarization controller is connected to one end of the first polarization-maintaining fiber, the other end of the first polarization-maintaining fiber is fused to one end of the second polarization-maintaining fiber at an angle of π / 2 through their fast axes, and the other end of the second polarization-maintaining fiber is connected to the fourth port of the first fiber coupler.
[0007] Preferably, all four ports of the first fiber coupler have a 50% splitting ratio and an operating range of 1260–1625 nm.
[0008] Preferably, the first polarization-maintaining fiber and the second polarization-maintaining fiber are small-diameter panda-type polarization-maintaining fibers with a cladding diameter of 60 μm, an outer fiber diameter of 135 μm, and a beat length of 1.78 mm; the first polarization-maintaining fiber serves as a sensing unit.
[0009] Preferably, the fiber optic Saganc interferometer includes a second fiber optic coupler, a second polarization controller, and a third polarization-maintaining fiber; the first port of the second fiber optic coupler is connected to the fiber optic Solc-Saganc interferometer, the third and fourth ports of the second fiber optic coupler are respectively connected through an optical path composed of the second polarization controller and the third polarization-maintaining fiber to form a Sagnac ring structure, and the second port of the second fiber optic coupler is connected to a spectrometer.
[0010] Preferably, in the Sagnac ring structure of the fiber optic Saganc interferometer, the third port of the second fiber coupler is connected to one end of the third polarization-maintaining fiber, the other end of the third polarization-maintaining fiber is connected to the first port of the second polarization controller, and the second port of the second polarization controller is connected to the fourth port of the second fiber coupler.
[0011] Preferably, all four ports of the second fiber coupler have a 50% splitting ratio and an operating range of 1260–1625 nm.
[0012] Preferably, the third polarization-maintaining fiber is a small-diameter panda-type polarization-maintaining fiber with a cladding diameter of 60 μm, an outer diameter of 135 μm, and a beat length of 1.78 mm.
[0013] The beneficial effects of this invention are: 1. The fiber optic Solc-Saganc interferometer excites the basic vernier effect to achieve preliminary sensitivity amplification while physically outputting a pure envelope spectrum, fundamentally avoiding the complex envelope fitting algorithm and its errors of the traditional vernier effect.
[0014] 2. The novel enhanced vernier effect stimulated by this invention achieves a second-step increase in strain and temperature sensitivity.
[0015] 3. This invention provides a new and effective approach for developing ultra-high sensitivity sensing technology that is simple in structure, easy to demodulate, and has excellent performance, and has great application potential in fields such as precision industrial measurement and structural health monitoring. Attached Figure Description
[0016] Figure 1 This is a schematic diagram of the structure of an ultra-high sensitivity strain and temperature sensor with enhanced vernier effect according to an embodiment of the present invention.
[0017] Figure 2 This is a spectrum of an ultra-high sensitivity strain and temperature sensor with enhanced vernier effect according to an embodiment of the present invention, outputting under different strains.
[0018] Figure 3 The strain response curves of an ultra-high sensitivity strain and temperature sensor with enhanced vernier effect and the strain response curve of the basic vernier effect are shown in the embodiments of the present invention.
[0019] Figure 4 This is a spectrum of an ultra-high sensitivity strain and temperature sensor with enhanced vernier effect, as shown in an embodiment of the present invention, output at different temperatures.
[0020] Figure 5 The temperature response curves of an ultra-high sensitivity strain and temperature sensor with enhanced vernier effect and the temperature response curve of the basic vernier effect are shown in the embodiments of the present invention. Detailed Implementation
[0021] To illustrate the invention more clearly, preferred embodiments of the invention will be described below with reference to the accompanying drawings.
[0022] like Figure 1 As shown, an embodiment of the present invention provides an ultra-high sensitivity strain and temperature sensor with enhanced vernier effect, comprising a broadband light source 1, a first fiber coupler 2, a first polarization controller 3, a first polarization-maintaining fiber 4, a second polarization-maintaining fiber 5, a second fiber coupler 6, a second polarization controller 7, a third polarization-maintaining fiber 8, and a spectrometer 9. The broadband light source has a wavelength range of 1250–1650 nm. The first fiber coupler 2 and the second fiber coupler 6 are 3dB couplers with an operating range of 1260–1625 nm.
[0023] The specific connection structure is as follows: the broadband light source 1 is connected to the first port 201 of the first fiber coupler 2; the third port 203 of the first fiber coupler 2 is connected to the first end 301 of the first polarization controller 3; the second port 302 of the first polarization controller 3 is connected to one end of the first polarization-maintaining fiber 4; the other end of the first polarization-maintaining fiber 4 is fused to one end of the second polarization-maintaining fiber 5 at a fast axis π / 2 angle; the other end of the second polarization-maintaining fiber 5 is connected to the fourth port 204 of the first fiber coupler 2; the second port 202 of the first fiber coupler 2 is connected to the first port 601 of the second fiber coupler 6; the third end 603 of the second fiber coupler 6 is connected to one end of the third polarization-maintaining fiber 8; the other end of the third polarization-maintaining fiber 8 is connected to the first port 701 of the second polarization controller 7; the second port 702 of the second polarization controller 7 is connected to the fourth port 604 of the second fiber coupler 6; and the second port 602 of the second fiber coupler 6 is connected to the spectrometer 9.
[0024] The specific specifications of the polarization-maintaining fiber used in this embodiment of the invention are as follows: a small-diameter panda-type polarization-maintaining fiber with a cladding diameter of 60 μm, an outer fiber diameter of 135 μm, and a beat length of 1.78 mm. Specifically, the first polarization-maintaining fiber 4 has a length of 30 cm, the second polarization-maintaining fiber 5 has a length of 20 cm, and the third polarization-maintaining fiber 8 has a length of 9.3 cm.
[0025] The basic principle of an ultra-high sensitivity strain and temperature sensor with enhanced vernier effect according to an embodiment of the present invention is as follows: When the optical signal output from the broadband light source enters the fiber optic Solc-Saganc interferometer through the first fiber optic coupler, it is equally split into two beams propagating in clockwise and counterclockwise directions. These beams then pass through the first polarization-maintaining fiber, the second polarization-maintaining fiber, and a polarization controller, gaining a phase difference before re-converging and interfering at the first fiber optic coupler, thus exciting the basic vernier effect. The interfering light then enters the fiber optic Saganc interferometer through the second fiber optic coupler, where it is again equally split into two beams propagating in clockwise and counterclockwise directions. These two beams each pass through the third polarization-maintaining fiber, gaining a phase difference before re-interfering at the second fiber optic coupler, thus exciting a novel enhanced vernier effect. The final output optical signal is acquired in real time by a spectrometer.
[0026] Utilizing the unique π / 2 angle fusion structure of the fiber optic Solc-Saganc interferometer, it not only acts as a filter, physically extracting the envelope that requires algorithmic fitting in the traditional vernier effect, but also introduces basic vernier amplification itself. The free spectral range of the fiber optic Solc-Saganc interferometer is thus: Wherein, B1 and L1 represent the birefringence and length of the first polarization-maintaining fiber, and B2 and L2 represent the birefringence and length of the second polarization-maintaining fiber.
[0027] Therefore, compared to the free spectral range of the fiber Saganc interferometer, the magnification factor can be expressed as: in, , representing the free spectral range characterized by the Saganc interferometer for a polarization-maintaining fiber access fiber of length L1; , representing the free spectral range characterized by the Saganc interferometer for a polarization-maintaining fiber access fiber of length L2.
[0028] When the light beam output from the fiber optic Solc-Saganc interferometer passes through the fiber optic Saganc interferometer and is output from the spectrometer, the free spectral range of the sensor can be expressed as: Due to the excitation of the novel enhanced vernier effect, the amplification factor M2 of the sensor's free spectral range at this stage relative to the FSR of the fundamental vernier effect excited by the fiber Solc-Saganc interferometer can be expressed as: Therefore, the strain and temperature sensitivity of the entire sensor can be expressed as: In the formula, For strain sensitivity, For temperature sensitivity, it can be seen that the excitation of the novel enhanced vernier effect enables the strain and temperature sensitivity caused by the basic vernier effect in the fiber Solc-Saganc interferometer to be simultaneously amplified by a factor of M², achieving a sensitivity enhancement effect. Compared with the strain and temperature sensitivity of a single fiber Saganc interferometer, the excitation of the novel enhanced vernier effect amplifies it by a factor of M²M¹. This mechanism establishes an effective method for achieving ultra-high sensitivity strain and temperature detection.
[0029] In one example, strain response testing was performed by gradually increasing the horizontal strain from 0 µε to 400 µε, with data recorded every 100 µε. The experimental results of the response are as follows: Figure 2 As shown, the overall transmission spectrum of the sensor exhibits a redshift of 384.34 nm with increasing strain. The strain response fitting results are as follows. Figure 3 As shown, the strain sensitivity of the basic vernier effect is 65.5 pm / µε, while the strain sensitivity of the novel enhanced vernier effect is 974.9 pm / µε, further amplifying the strain sensitivity of the basic vernier effect by 14.88 times. Then, the temperature response characteristics of the sensor were systematically studied. The chamber temperature was increased from 27 ℃ to 31 ℃, and data were recorded every 1 ℃. The experimental results are shown below. Figure 4 As shown, the sensor exhibits a blue shift as temperature increases. The temperature response fitting results are as follows. Figure 5 As shown, the strain sensitivity of the basic vernier effect is -4.47 nm / ℃, while the strain sensitivity of the novel enhanced vernier effect is -74.28 nm / ℃, further amplifying the strain sensitivity of the basic vernier effect by 16.62 times. The theoretical value and the experimental measurement value are basically in agreement, and the existing error may be caused by inaccurate measurement of the fiber length. Based on the strain and temperature sensitivities obtained from the experiment, dual-parameter measurement of strain and temperature can be achieved.
[0030] The present invention achieves a novel enhanced vernier effect by arranging a fiber optic Solc-Saganc interferometer in parallel with a fiber optic Saganc interferometer, thereby enhancing and amplifying the sensitivity of strain and temperature. Compared with existing fiber optic strain and temperature sensors, its high sensitivity makes it applicable to a wide range of applications, and the system structure is simple and easy to integrate. This structure can monitor temperature and stress with higher sensitivity and accuracy.
[0031] For the purposes of illustration and description, the foregoing illustrative examples relating to the invention are provided. This is not intended to be an exhaustive description of the invention or to limit it to the precise forms described; modifications and variations can be made based on the foregoing description. The embodiments were chosen and described to explain the principles of the invention and as practical applications thereof, enabling those skilled in the art to use the invention in various embodiments and to make various modifications for specific purposes. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of this invention should be considered within the scope of protection of this invention.
Claims
1. A high-sensitivity strain and temperature sensor with enhanced vernier effect, characterized in that, The system includes a broadband light source (1), a fiber optic Solc-Saganc interferometer, a fiber optic Sagnac interferometer, and a spectrometer (9) arranged in series along the optical path. The fiber optic Solc-Sagnac interferometer is used to receive incident light from the broadband light source (1) and generate an envelope spectrum with a first free spectral range FSR_SSI. The fiber optic Sagnac interferometer is used to receive the envelope spectrum output by the fiber optic Solc-Saganac interferometer and is cascaded with the fiber optic Solc-Saganac interferometer to generate an enhanced vernier effect, thereby achieving a secondary amplification of the sensing sensitivity. The free spectral range of the fiber optic Sagnac interferometer is 0.90-0.99 times that of the fiber optic Solc-Saganc interferometer.
2. The ultra-high sensitivity strain and temperature sensor with enhanced vernier effect according to claim 1, characterized in that, The fiber optic Solc-Saganc interferometer includes a first fiber coupler, a first polarization controller, a first polarization-maintaining fiber, and a second polarization-maintaining fiber. The first polarization-maintaining fiber and the second polarization-maintaining fiber are fused together at an angle of π / 2 through their fast or slow axes. The first port of the first fiber coupler is connected to a broadband light source. The third and fourth ports of the first fiber coupler are connected through optical paths formed by the first polarization controller, the first polarization-maintaining fiber, and the second polarization-maintaining fiber, respectively, forming a Sagnac ring structure. The second port of the first fiber coupler is connected to the fiber optic Saganc interferometer.
3. The ultra-high sensitivity strain and temperature sensor with enhanced vernier effect according to claim 2, characterized in that, In the Sagnac ring structure of the fiber optic Solc-Saganc interferometer, the third port of the first fiber coupler is connected to the first port of the first polarization controller, the second port of the first polarization controller is connected to one end of the first polarization-maintaining fiber, the other end of the first polarization-maintaining fiber is fused to one end of the second polarization-maintaining fiber at an angle of π / 2 through their fast axis, and the other end of the second polarization-maintaining fiber is connected to the fourth port of the first fiber coupler.
4. The ultra-high sensitivity strain and temperature sensor with enhanced vernier effect according to claim 2, characterized in that, The first fiber coupler has a 50% splitting ratio at all four ports and operates in the range of 1260-1625 nm.
5. The ultra-high sensitivity strain and temperature sensor with enhanced vernier effect according to claim 2, characterized in that, The first and second polarization-maintaining fibers are narrow-diameter panda-type polarization-maintaining fibers with a cladding diameter of 60 μm, an outer diameter of 135 μm, and a beat length of 1.78 mm; the first polarization-maintaining fiber serves as a sensing unit.
6. The ultra-high sensitivity strain and temperature sensor with enhanced vernier effect according to claim 1, characterized in that, The fiber optic Saganc interferometer includes a second fiber optic coupler, a second polarization controller, and a third polarization-maintaining fiber. The first port of the second fiber optic coupler is connected to the fiber optic Solc-Saganc interferometer. The third and fourth ports of the second fiber optic coupler are connected through optical paths formed by the second polarization controller and the third polarization-maintaining fiber, respectively, forming a Sagnac ring structure. The second port of the second fiber optic coupler is connected to a spectrometer.
7. The ultra-high sensitivity strain and temperature sensor with enhanced vernier effect according to claim 6, characterized in that, In the Sagnac ring structure of the fiber optic Saganc interferometer, the third port of the second fiber coupler is connected to one end of the third polarization-maintaining fiber, the other end of the third polarization-maintaining fiber is connected to the first port of the second polarization controller, and the second port of the second polarization controller is connected to the fourth port of the second fiber coupler.
8. The ultra-high sensitivity strain and temperature sensor with enhanced vernier effect according to claim 6, characterized in that, The second fiber coupler has a 50% splitting ratio at all four ports and operates in the range of 1260 – 1625 nm.
9. A high-sensitivity strain and temperature sensor with enhanced vernier effect according to claim 6, characterized in that, The third polarization-maintaining fiber is a small-diameter panda-type polarization-maintaining fiber with a cladding diameter of 60 μm, an outer diameter of 135 μm, and a beat length of 1.78 mm.