A microwave photonic link strain measurement system based on a-t splitting

Abstract

The application discloses a microwave photon link strain measurement system based on A-T splitting, belongs to the weak strain monitoring technical field, and comprises a broadband light source, wherein the broadband light source is connected with port one of a circulator, port two of the circulator is connected with a fiber grating strain sensor, port three of the circulator is connected with an optical input port of an electro-optic modulator, a modulation port of the electro-optic modulator is connected with port one of a vector network analyzer, an optical output port of the electro-optic modulator is connected with an input end one of an optical coupler, a linear chirped fiber grating is arranged between an output end one and an output end two of the optical coupler and connected with each other, an input end two of the optical coupler is connected with a photoelectric detector, and the other end of the photoelectric detector is connected with the vector network analyzer. The microwave photon link strain measurement system based on A-T splitting is adopted, the problem of low resolution and small sensitivity in the micro strain measurement field is solved, and a strain measurement system with high sensitivity and high resolution is realized.

Description

Technical Field

[0001] This invention relates to the field of weak strain detection technology, and in particular to a microwave photonic link strain measurement system based on AT splitting. Background Technology

[0002] Public transportation facilities such as high-speed rail, ships, and airplanes, infrastructure such as railways and cross-sea bridges, and buildings have design lifespans of several decades or even centuries. As their service life increases, these facilities experience material aging and structural wear, leading to performance degradation and increased safety hazards, potentially resulting in collapses in extreme cases. Therefore, structural health monitoring is crucial for predicting and preventing major safety accidents. Common monitoring methods include mechanical and electrical methods, but the former has low sensitivity, and the latter is easily affected by the environment, making them unsuitable for long-term monitoring. In contrast, fiber optic sensing technology offers advantages such as small size, low loss, and strong resistance to electromagnetic interference and chemical corrosion, making it more suitable for long-term monitoring of large and complex facilities.

[0003] Fiber Bragg gratings (FBGs), as novel optical measurement elements, possess advantages such as small size, light weight, resistance to harsh environments, and ease of networking and installation, enabling real-time measurement of physical quantities such as temperature and stress. However, traditional grating demodulation methods suffer from numerous problems. Spectrometers are costly, bulky, and slow to demodulate, with resolutions rarely reaching the picometer level, failing to meet the requirements of fiber Bragg grating strain sensors. Matched grating methods have limited demodulation ranges, filter methods are expensive and require sophisticated light sources, interferometry is susceptible to environmental interference, and imaging spectroscopy involves complex processes and is prone to image distortion. Therefore, there is an urgent need for efficient, high-resolution, highly sensitive, and low-cost demodulation solutions.

[0004] The fiber grating demodulation scheme based on microwave photonics combines the advantages of optical system resolution and sensitivity with the characteristics of microwave signal quality, polarization insensitivity and high stability, effectively solving some problems existing in the existing fiber grating demodulation method. This invention combines the Autler-Townes splitting effect with microwave photonics to achieve fiber grating demodulation. Summary of the Invention

[0005] The purpose of this invention is to provide a microwave photonic link strain measurement system based on AT splitting, so as to solve the problems of system redundancy caused by dispersion accumulation and reliance on high-frequency demodulation instruments in traditional microwave photonic fiber grating demodulation schemes.

[0006] To achieve the above objectives, this invention provides a microwave photonic link strain measurement system based on AT splitting, comprising: a broadband light source (BBS), the broadband light source being connected to port one of a circulator (Cir); port two of the circulator being connected to a fiber Bragg grating (FBG) strain sensor; port three of the circulator being connected to the optical input port of an electro-optic modulator (EOM); the modulation port of the electro-optic modulator being connected to port one of a vector network analyzer (VNA); the optical output port of the electro-optic modulator being connected to input port one of an optical coupler (OC); a section of linear chirped fiber Bragg grating (LCFBG) is embedded between output port one and output port two of the optical coupler and connected thereto; input port two of the optical coupler is connected to a photodetector (PD); and the other end of the photodetector is connected to the vector network analyzer.

[0007] Preferably, the broadband light generated by the broadband light source enters the fiber optic strain sensor through port one of the circulator.

[0008] Preferably, the reflected light from the fiber optic strain sensor is used as an optical carrier to enter the electro-optic modulator through ports two and three of the circulator in sequence, and is modulated by the drive signal of port one of the vector network analyzer.

[0009] Preferably, the optical coupler is 2×2, with two input ports and two output ports, and its splitting ratio is 50:50.

[0010] Preferably, optical fields E1 and E2 are input to the optical coupler at input terminals one and two, respectively. After entering the optocoupler, optical fields E1 and E2 are split into clockwise propagating light E3 and counterclockwise propagating light E4. E3 and E4 are transmitted and reflected light at the linearly chirped fiber grating, respectively. These four beams of light produce an Autel-Townes splitting effect at the coupler, and E3 and E4 reach the linearly chirped fiber grating with different time delays. After being processed by the linearly chirped fiber grating, they become optical field E3 with a specific phase and time delay. ' and E4 ' E3 ' It is the sum of the light intensities of the two beams, including the reflected light from E3 at the linearly chirped fiber grating and the transmitted light from E4 at the linearly chirped fiber grating. ' Similarly, E3' and E4 ' Recombined, forming the final output light field E1 ' and E2 ' .

[0011] Preferably, the light field E2 ' The formula for representing is as follows:

[0012]

[0013] Where r is the reflection coefficient, which is controlled by the reflection wavelength of the FBG and the slope of the falling edge of the linearly chirped fiber grating; t is the transmission coefficient; and α is the loss factor. and is the phase factor, corresponding to two different paths, and i is the imaginary unit.

[0014] Preferably, the photodetector converts the coupled optical signal into an electrical signal.

[0015] Preferably, the vector network analyzer observes and records the microwave frequency response under different strains.

[0016] Therefore, the present invention employs the above-mentioned microwave photonic link strain measurement system based on AT splitting, which has the following beneficial effects:

[0017] (1) This invention effectively improves the resolution and sensitivity of the system by introducing the Autler-Townes splitting effect into the microwave photonic demodulation system;

[0018] (2) The present invention eliminates the dispersion module, and the sensitivity can be improved without the need for dispersion accumulation, effectively reducing the bandwidth limitation of the demodulation instrument.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a microwave photonic link strain measurement system based on AT splitting according to the present invention;

[0021] Figure 2 This is a schematic diagram of the Autler-Townes splitting principle of a microwave photonic link strain measurement system based on AT splitting according to the present invention.

[0022] Figure 3 The graph shows the variation of the microwave interference spectrum under different reflection coefficients, with optical path differences of 0.12m and 1.2m, respectively. Detailed Implementation

[0023] The following detailed description of embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0024] Example

[0025] like Figure 1 As shown, this invention provides a microwave photonic link strain measurement system based on AT splitting, including a broadband light source (BBS). The broadband light source is connected to port one of a circulator (Cir). Port two of the circulator is connected to a fiber Bragg grating (FBG) strain sensor. Broadband light generated by the broadband light source enters the FBG strain sensor through port one of the circulator. Port three of the circulator is connected to the optical input port of an electro-optic modulator (EOM). The modulation port of the electro-optic modulator is connected to port one of a vector network analyzer (VNA). The reflected light from the FBG strain sensor, as an optical carrier, sequentially passes through ports two and three of the circulator into the electro-optic modulator and is modulated by the drive signal at port one of the vector network analyzer. The optical output port of the electro-optic modulator is connected to an optical coupler. The optical coupler (OC) is connected to its input port 1. A 2×2 optical coupler is used, with two input ports and two output ports, and a splitting ratio of 50:50. The modulated light is input into the optical coupler. A linear chirped fiber grating (LCFBG) is built into and connected between the output ports 1 and 2 of the optical coupler. The light entering the optical coupler propagates in opposite directions and returns to the optical coupler for coupling. The input port 2 of the optical coupler is connected to a photodetector (PD). The photodetector converts the coupled optical signal into an electrical signal. The other end of the photodetector is connected to a vector network analyzer. The second port of the vector network analyzer observes and records the microwave frequency response under different strains.

[0026] like Figure 2As shown, optical fields E1 and E2 are input to the optical coupler at input terminals one and two, respectively. After entering the optocoupler, optical fields E1 and E2 are divided into clockwise propagating light E3 and counterclockwise propagating light E4. E3 and E4 reach the linear chirped fiber grating after experiencing different time delays. When the carrier is within the total reflection bandwidth of the linearly chirped fiber grating, the system behaves like a traditional Michelson interferometer. After E3 and E4 reach the linearly chirped fiber grating, they return to the optical coupler via their original paths. When the carrier is within the total transmission bandwidth of the linearly chirped fiber grating, after E3 and E4 reach the linearly chirped fiber grating, they are transmitted back to the optical coupler through the linearly chirped fiber grating, and the path difference between the two paths is 0, so no interference occurs. When the carrier is located at the upper or lower edge of the reflection bandwidth of the linearly chirped fiber grating, after E3 and E4 reach the linearly chirped fiber grating, they each have transmitted and reflected light passing through the linearly chirped fiber grating. At this time, the four beams of light reach the optical coupler and couple, working together to produce the Auttler-Townes splitting effect.

[0027] E3 and E4 arrive at the linearly chirped fiber grating with different time delays. After processing by the linearly chirped fiber grating, they become an optical field E3 with specific phase and time delay. ' and E4 ' E3 ' It is the sum of the light intensities of the two beams, including the reflected light from E3 at the linearly chirped fiber grating and the transmitted light from E4 at the linearly chirped fiber grating. ' Similarly, E3 ' and E4 ' Recombined, forming the final output light field E1 ' and E2 ' .

[0028] Light field E2 ' The formula for representing is as follows:

[0029]

[0030] Where r is the reflection coefficient, which is controlled by the reflection wavelength of the FBG and the slope of the falling edge of the linearly chirped fiber grating; t is the transmission coefficient; and α is the loss factor. and is the phase factor, corresponding to two different paths, and i is the imaginary unit.

[0031] As can be seen from the formula, the Autler-Townes splitting effect is composed of the combined action of four beams, E1, E2, E3, and E4, whose intensities are determined by the reflection coefficient r. Figure 3 As shown, the splitting peak gradually narrows with the change of the reflection coefficient r. The smaller the optical path difference, the more obvious the narrowing. Therefore, the micro-strain of the fiber grating can be demodulated by measuring the drift of the splitting peak.

[0032] Therefore, the present invention adopts the above-mentioned microwave photonic link strain measurement system based on AT splitting, which solves the problems of low resolution and low sensitivity in the field of micro-strain measurement, and realizes a strain measurement system with high sensitivity and high resolution.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A microwave photonic link strain measurement system based on AT splitting, characterized in that, include: A broadband light source is connected to port one of a circulator; port two of the circulator is connected to a fiber Bragg grating strain sensor; port three of the circulator is connected to the optical input port of an electro-optic modulator; the modulation port of the electro-optic modulator is connected to port one of a vector network analyzer; the optical output port of the electro-optic modulator is connected to input one of an optical coupler; a linear chirped fiber Bragg grating is built into and connected between output one and output two of the optical coupler; input two of the optical coupler is connected to a photodetector; and the other end of the photodetector is connected to the vector network analyzer. The optical coupler inputs a light field at input terminals one and two, respectively. Harmony and light field light field Harmony and light field After entering the optocoupler, the light is split into clockwise propagating beams. and counterclockwise propagating light , and The transmitted and reflected light at the linear chirped fiber grating propagates to the optocoupler, generating the Autler-Townes splitting effect. and The light particles arrive at the linearly chirped fiber grating after experiencing different time delays, and after being processed by the linearly chirped fiber grating, they become an optical field with specific phase and time delay. and , It is the sum of the light intensities of the two beams, including Reflected light at a linearly chirped fiber grating and Transmitted light at a linearly chirped fiber grating Similarly, and Recombined to form the final output light field and .

2. The microwave photonic link strain measurement system based on AT splitting according to claim 1, characterized in that: The broadband light generated by the broadband light source enters the fiber optic strain sensor through port one of the circulator.

3. The microwave photonic link strain measurement system based on AT splitting according to claim 1, characterized in that: The reflected light from the fiber optic strain sensor passes sequentially through ports two and three of the circulator into the electro-optic modulator, and is modulated by the drive signal from port one of the vector network analyzer.

4. The microwave photonic link strain measurement system based on AT splitting according to claim 1, characterized in that: The optical coupler is 2×2, with two input ports and two output ports, and its splitting ratio is 50:

50.

5. The microwave photonic link strain measurement system based on AT splitting according to claim 1, characterized in that, The light field The formula for representing is as follows: ； in, The reflection coefficient, The transmittance is the coefficient of light. As the loss factor, and These are phase factors, corresponding to two different paths. It is the imaginary unit.

6. The microwave photonic link strain measurement system based on AT splitting according to claim 1, characterized in that: The photodetector converts the coupled optical signal into an electrical signal.

7. The microwave photonic link strain measurement system based on AT splitting according to claim 1, characterized in that: The vector network analyzer observes and records the microwave frequency response under different strains.

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