CN117073730A

CN117073730A - Optical fiber sensing system and optical fiber sensing method based on microwave photons

Info

Publication number: CN117073730A
Application number: CN202311344088.4A
Authority: CN
Inventors: 朱琛; 介瑞敏; 刘波
Original assignee: Zhejiang Lab
Current assignee: Zhejiang Lab
Priority date: 2023-10-17
Filing date: 2023-10-17
Publication date: 2023-11-17
Anticipated expiration: 2043-10-17
Also published as: CN117073730B

Abstract

The application provides an optical fiber sensing system and an optical fiber sensing method based on microwave photons. The optical fiber sensing system includes: the system comprises an optical signal generating unit for generating an optical signal, a microwave radio frequency oscillator for generating a first radio frequency signal and a second radio frequency signal, a microwave-optical modulator for modulating the optical signal based on the first radio frequency signal, a photoelectric conversion unit for converting the optical signal into a first electric signal, a microwave phase detector and a signal acquisition processing assembly. The microwave phase detector is used for determining the working frequency of the optical fiber sensing system before sensing the external physical quantity change information. The microwave phase detector is further configured to generate a second electrical signal indicative of a phase difference of the first electrical signal and the second radio frequency signal. The frequencies of the first radio frequency signal and the second radio frequency signal are both working frequencies. The signal acquisition processing component is used for demodulating the intensity of the second electric signal to obtain external physical quantity change information. The optical fiber sensing system has the advantages of quick response, low cost and high measurement sensitivity.

Description

Optical fiber sensing system and optical fiber sensing method based on microwave photons

Technical Field

The application relates to the technical field of optical fiber sensing, in particular to an optical fiber sensing system and an optical fiber sensing method based on microwave photons.

Background

With the continuous development of sensing technology, the requirement on sensitivity and response speed of a sensing system is also increasing. Rapid and accurate measurement is of great importance in many fields. For example, in the health monitoring of the structural body, the rapid and accurate measurement result can reflect the running condition of the structural body in time, and has important significance for ensuring the health state of the system and realizing rapid and timely equipment maintenance. In the implementation process of engineering projects, quick and accurate measurement data is one of key information which helps to ensure that project planning is carried out smoothly in an early stage, and the risks of project delay, reworking or restarting can be reduced. In the field of medical surgery, continuous and accurate measurement of tumor positions and the like can reduce unnecessary damage to adjacent tissues, reduce complications and is important for ensuring the safety and health of human bodies.

The optical fiber sensor has the characteristics of small inherent volume, light weight, electromagnetic interference resistance, long sensing distance and the like, so that the optical fiber sensor becomes an irreplaceable sensing solution in some application scenes and has been widely studied and applied.

Currently, microwave photon filter based techniques are used in fiber optic sensing systems. And monitoring physical quantities such as strain, pressure, temperature and the like according to the drift of the center frequency of a passband in the system radio frequency response. However, the information demodulation sensitivity based on the above technique is very low, several orders of magnitude lower than the method based on spectral shift in the optical domain, and the measurement speed is still to be improved.

Disclosure of Invention

The application provides an optical fiber sensing system and an optical fiber sensing method based on microwave photons, which have the advantages of high response speed, low cost and high measurement sensitivity.

The application provides an optical fiber sensing system for sensing external physical quantity change information, comprising:

an optical signal generating unit for generating an optical signal;

the microwave radio frequency oscillator is used for generating a first radio frequency signal and a second radio frequency signal;

the microwave-optical modulator is connected with the optical signal generating unit and the microwave radio frequency oscillator and is used for modulating the optical signal based on the first radio frequency signal and outputting a modulated optical signal;

a photoelectric conversion unit for converting the optical signal into a first electrical signal;

the microwave phase detector is used for determining the working frequency of the optical fiber sensing system before sensing the external physical quantity change information; the microwave phase detector is connected with the photoelectric conversion unit and the microwave radio frequency oscillator and is used for generating a second electric signal representing the phase difference of the first electric signal and the second radio frequency signal; the frequencies of the first radio frequency signal and the second radio frequency signal are the working frequency; a kind of electronic device with high-pressure air-conditioning system

And the signal acquisition and processing assembly is connected with the microwave phase detector and is used for acquiring and demodulating the intensity of the second electric signal to obtain the external physical quantity change information.

Optionally, the microwave phase detector includes a vector network analyzer for determining a phase change rule of the external physical quantity change information before sensing the external physical quantity change information.

Optionally, the signal acquisition processing component is configured to demodulate the intensity of the second electrical signal according to the phase change rule, so as to obtain the external physical quantity change information.

Optionally, the optical signal generating unit includes a light source and an interferometer assembly; the light source is used for generating broadband continuous light; the interferometer component is used for carrying out optical sampling on the broadband continuous light to obtain a sampled optical signal.

Optionally, the interferometer assembly comprises a bi-directional coupler and a first fiber optic interferometer; the bi-directional coupler includes a first port, a second port, and a third port; the first port is connected with the light source, the second port is connected with the first optical fiber interferometer, and the third port is connected with the microwave-optical modulator; the first optical fiber interferometer is used for optically sampling the broadband continuous light to obtain the sampled optical signal, and transmitting the sampled optical signal to the third port.

Optionally, the interferometer assembly comprises a coupler and a plurality of the first fiber optic interferometers; the coupler is connected between a second port of the bi-directional coupler and the plurality of first fiber interferometers; at least two of the first fiber interferometers have different free spectral ranges; the plurality of first optical fiber interferometers respectively carry out optical sampling on the broadband continuous light to obtain a plurality of sampled optical signals; the coupler is used for coupling a plurality of the sampled optical signals. Thereby enabling multi-sensor multiplexing.

Optionally, the light source comprises an amplified spontaneous emission light source or a superluminescent light emitting diode.

Optionally, the photoelectric conversion unit includes a dispersion component and a photodetector; the dispersion component is used for dispersing the modulated optical signal to obtain a dispersed optical signal; the photodetector is configured to convert the dispersed optical signal into the first electrical signal.

Optionally, the optical fiber sensing system includes an amplifier connected between the optical signal generating unit and the photodetector for amplifying the optical signal.

Optionally, the dispersion component includes at least one of a single mode fiber, a multimode fiber, and a dispersion compensating fiber.

Optionally, the microwave radio frequency oscillator comprises a vector network analyzer.

Optionally, the microwave-optical modulator comprises one of an electro-optic modulator, a mach-zehnder modulator, a phase modulator.

The application also provides an optical fiber sensing method based on microwave photons, which is applied to an optical fiber sensing system for sensing external physical quantity change information and comprises the following steps:

determining the working frequency of the optical fiber sensing system;

generating an optical signal;

modulating the optical signal based on a first radio frequency signal to obtain a modulated optical signal;

converting the optical signal into a first electrical signal;

generating a second electrical signal representative of a phase difference of the first electrical signal and a second radio frequency signal; the frequencies of the second radio frequency signal and the first radio frequency signal are the working frequency;

demodulating the intensity of the second electric signal to obtain the external physical quantity change information.

Optionally, the determining the operating frequency of the optical fiber sensing system includes:

generating broadband continuous light;

optical sampling is carried out on the broadband continuous light to obtain a sampled optical signal;

modulating the sampled optical signal based on a broadband radio frequency sweep signal to obtain a modulated optical signal;

dispersing the modulated optical signal to obtain a dispersed optical signal;

converting the dispersed optical signal into a third electrical signal;

determining any frequency in a radio frequency passband as the operating frequency according to the intensity of the third electrical signal;

and determining the phase change rule of the external physical quantity change information according to the phase of the third electric signal.

Optionally, before said demodulating the intensity of the second electrical signal, the optical fiber sensing method further comprises:

removing direct current information of the intensity of the second electric signal;

noise information of the intensity of the second electrical signal is removed.

In some embodiments, the first radio frequency signal and the second radio frequency signal have the same frequency, the microwave-optical modulator modulates the optical signal based on the first radio frequency signal, the microwave phase detector generates a second electric signal representing the phase difference between the first electric signal and the second radio frequency signal, so that the optical fiber sensing system does not need a frequency sweeping process, the response speed is high, and the cost of a single-frequency working device is low; the phase difference information of the first electric signal and the second radio frequency signal is obtained by demodulating the intensity of the second electric signal, and further the external physical quantity change information is obtained, so that the measuring sensitivity of the optical fiber sensing system is high.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the application as claimed.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the application and together with the description, serve to explain the principles of the application.

FIG. 1 is a block diagram illustrating one embodiment of a fiber optic sensing system of the present application.

FIG. 2 is a block diagram of another embodiment of the fiber optic sensing system of the present application.

Fig. 3 is a schematic spectrum of an optical signal of one embodiment of the optical source shown in fig. 2.

FIG. 4 is a schematic spectrum of the interferometer assembly of FIG. 2 after the schematic spectrum of FIG. 3 has been sampled.

FIG. 5 is a schematic diagram illustrating one embodiment of an interferometer assembly of FIG. 2.

FIG. 6 is a schematic diagram of another embodiment of the interferometer assembly of FIG. 2.

FIG. 7 is a schematic diagram of another embodiment of the interferometer assembly of FIG. 2.

FIG. 8 is a schematic diagram of another embodiment of the interferometer assembly of FIG. 2.

FIG. 9 is a schematic diagram illustrating one embodiment of the first fiber optic interferometer of FIG. 5.

FIG. 10 is a schematic diagram illustrating one embodiment of the second fiber optic interferometer of FIG. 7.

FIG. 11 is a schematic diagram illustrating one embodiment of the second fiber optic interferometer of FIG. 7.

FIG. 12 is a schematic diagram illustrating one embodiment of the second fiber optic interferometer of FIG. 7.

FIG. 13 is a flow chart of one embodiment of a fiber sensing method of the present application.

FIG. 14 is a block diagram of another embodiment of a fiber optic sensing system of the present application.

FIG. 15 is a flow chart of one embodiment of the step "determine operating frequency of fiber optic sensing system" of FIG. 13.

Fig. 16 is a waveform diagram of one embodiment of a third electrical signal.

Fig. 17 is a waveform diagram of the phase of one embodiment of the third electrical signal.

FIG. 18 is a device diagram of another embodiment of a fiber optic sensing system.

FIG. 19 is a spectral diagram of a sampled optical signal of the fiber optic sensing system shown in FIG. 18.

FIG. 20 is a schematic diagram of the RF passband signal strength measured by the fiber optic sensing system of FIG. 18.

Fig. 21 is time domain information of signals measured by the fiber optic sensing system shown in fig. 18.

Fig. 22 is frequency domain information of signals measured by the fiber optic sensing system shown in fig. 18.

Detailed Description

Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, the same numbers in different drawings refer to the same or similar elements, unless otherwise indicated. The implementations described in the following exemplary examples do not represent all implementations consistent with the application. Rather, they are merely examples of apparatus and methods consistent with aspects of the application as detailed in the accompanying claims.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Unless defined otherwise, technical or scientific terms used herein should be given the ordinary meaning as understood by one of ordinary skill in the art to which this application belongs. The terms "first," "second," and the like in the description and in the claims, are not used for any order, quantity, or importance, but are used for distinguishing between different elements. Likewise, the terms "a" or "an" and the like do not denote a limitation of quantity, but rather denote the presence of at least one. "plurality" or "plurality" means two or more. Unless otherwise indicated, the terms "front," "rear," "lower," and/or "upper" and the like are merely for convenience of description and are not limited to one location or one spatial orientation. The word "comprising" or "comprises", and the like, means that elements or items appearing before "comprising" or "comprising" are encompassed by the element or item recited after "comprising" or "comprising" and equivalents thereof, and that other elements or items are not excluded. The terms "connected" or "connected," and the like, are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this specification and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any or all possible combinations of one or more of the associated listed items.

The optical fiber sensing system based on microwave photons comprises: the system comprises an optical signal generating unit for generating an optical signal, a microwave radio frequency oscillator for generating a first radio frequency signal and a second radio frequency signal, a microwave-optical modulator for modulating the optical signal based on the first radio frequency signal, a photoelectric conversion unit for converting the optical signal into a first electric signal, a microwave phase detector and a signal acquisition processing assembly. The microwave phase detector is used for determining the working frequency of the optical fiber sensing system before sensing the external physical quantity change information. The microwave phase detector is further configured to generate a second electrical signal indicative of a phase difference of the first electrical signal and the second radio frequency signal. The frequencies of the first radio frequency signal and the second radio frequency signal are working frequencies. The signal acquisition processing component is used for acquiring and demodulating the phase of the second electric signal to obtain external physical quantity change information. The optical fiber sensing system has the advantages of high response speed, low cost and high measurement sensitivity.

The application provides an optical fiber sensing system and an optical fiber sensing method based on microwave photons. The microwave photon based optical fiber sensing system and the optical fiber sensing method of the present application will be described in detail with reference to the accompanying drawings. The features of the examples and embodiments described below may be combined with each other without conflict.

FIG. 1 is a block diagram illustrating one embodiment of a fiber optic sensing system 10 of the present application. The optical fiber sensing system 10 of the present application is used to sense external physical quantity change information. The external physical quantity change information may be temperature, pressure, vibration, sound wave, strain, or the like. As shown in fig. 1, the optical fiber sensing system 10 includes: an optical signal generating unit 11, a microwave radio frequency oscillator 12, a microwave-optical modulator 13, a photoelectric conversion unit 14, a microwave phase detector 15 and a signal acquisition processing component 16.

The optical signal generating unit 11 is used for generating an optical signal. The optical signal changes with a change in the external physical quantity change information.

The microwave radio frequency oscillator 12 is used for generating a first radio frequency signal and a second radio frequency signal. The fiber optic sensing system 10 has an operating frequency. The frequencies of the first radio frequency signal and the second radio frequency signal are both working frequencies.

The microwave-optical modulator 13 is connected to the optical signal generating unit 11 and the microwave radio frequency oscillator 12, and is configured to modulate an optical signal based on the first radio frequency signal, to obtain a modulated optical signal. The microwave-optical modulator 13 receives the optical signal generated by the optical signal generating unit 11 and the first radio frequency signal generated by the microwave radio frequency oscillator 12, and modulates the optical signal based on the first radio frequency signal, generating a modulated optical signal. In some embodiments, the microwave-optical modulator 13 comprises one of an electro-optic modulator, a Mach-Zehnder modulator, a phase modulator.

The photoelectric conversion unit 14 is configured to convert an optical signal into a first electrical signal. After converting the optical signal into the first electrical signal, the first electrical signal is more easily detected and resolved.

The microwave phase detector 15 is used to determine the operating frequency of the optical fiber sensing system 10 before sensing the external physical quantity change information. The fiber optic sensing system 10 requires pre-calibration to determine the operating frequency prior to sensing the external physical quantity change information. The operating frequency determines the frequencies of the first radio frequency signal and the second radio frequency signal. In some embodiments, the microwave phase detector 15 comprises a vector network analyzer.

The microwave phase detector 15 is connected to the photo-conversion unit 14 and to the microwave radio frequency oscillator 12 for generating a second electrical signal indicative of a phase difference of the first electrical signal and the second radio frequency signal. The microwave phase detector 15 receives the first electric signal and the second radio frequency signal, and detects a phase difference of the first electric signal and the second radio frequency signal, and generates the second electric signal based on the phase difference. In some embodiments, the second electrical signal is a voltage value reflecting the phase difference.

The signal acquisition and processing component 16 is connected with the microwave phase detector 15 and is used for acquiring and demodulating the intensity of the second electric signal to obtain external physical quantity change information. The signal acquisition and processing component 16 can acquire the second electric signal, and obtain external physical quantity change information through intensity demodulation of the second electric signal.

In some embodiments, the first rf signal and the second rf signal have the same frequency, the microwave-optical modulator 13 modulates the optical signal based on the first rf signal, and the microwave phase detector 15 generates a second electrical signal that characterizes a phase difference between the first electrical signal and the second rf signal, so that the optical fiber sensing system 10 does not need a frequency sweeping process, and has a fast response speed and low cost of a single-frequency working device; by demodulating the intensity of the second electrical signal, the phase difference information of the first electrical signal and the second radio frequency signal is obtained, and further, the external physical quantity change information is obtained, so that the measurement sensitivity of the optical fiber sensing system 10 is high.

Before sensing the external physical quantity change information, the optical fiber sensing system 10 needs to be pre-calibrated to determine the phase change rule of the external physical quantity change information. The phase change rule characterizes the change rule of the intensity of the second electric signal along with the change information of the external physical quantity. The phase change law is used for demodulation of the physical quantity change information.

The microwave phase detector 15 is used for determining a phase change rule of the external physical quantity change information before sensing the external physical quantity change information.

The signal acquisition and processing component 16 is configured to demodulate the intensity of the second electrical signal according to the phase change rule, so as to obtain the change information of the external physical quantity. The signal acquisition and processing component 16 corresponds the intensity of the second electric signal to the external physical quantity change information according to the phase change rule determined in the pre-calibration process, and demodulates the second electric signal to obtain the external physical quantity change information.

Fig. 2 is a block diagram illustrating another embodiment of the fiber optic sensing system 10 of the present application.

The optical signal generating unit 11 comprises a light source 17 and an interferometer assembly 18.

The light source 17 is used to generate broadband continuous light. In some embodiments, the light source 17 comprises an amplified spontaneous emission light source or a superluminescent light emitting diode.

The interferometer assembly 18 is configured to optically sample the broadband continuous light to obtain a sampled optical signal. Interferometer assembly 18 is a sensing element of fiber optic sensing system 10, and may be an interferometer or a combination of interferometers, which optically samples the spectrum of broadband continuous light generated by light source 17, and changes in external physical quantity cause changes in the sampled spectrum, thereby enabling multi-sensor multiplexing. ω is the angular frequency of the broadband continuous light, the transfer function of interferometer assembly 18 is T (ω), and the sampled optical signal can be expressed as S (ω) x T (ω).

Fig. 3 shows a schematic spectrum of the optical signal of one embodiment of the light source 17 shown in fig. 2.

Fig. 4 is a schematic spectrum of the optical spectrum of fig. 3 sampled by the interferometer assembly 18 of fig. 2.

Referring to fig. 3 to 4, the spectrum of the optical signal generated by the light source 17 is gaussian. The spectrum sampled by the interferometer assembly 18 exhibits a continuous sinusoidal shape.

Referring to fig. 2, the photoelectric conversion unit 14 includes a dispersion member 141 and a photodetector 142. The dispersion component 141 is configured to disperse the modulated optical signal to obtain a dispersed optical signal. The dispersion component 141 may introduce dispersion into the signal, introducing frequency domain characteristics of the signal into the time domain, thereby obtaining a passband signal of the radio frequency domain, forming a passband radio frequency filter. The dispersion component 141 can minimize high-order dispersion through an optimized design, and can reduce nonlinearity of the phase detected by the microwave phase detector 15, which changes along with the change information of the external physical quantity. In some embodiments, the dispersion component 14 comprises at least one of a single mode fiber, a multimode fiber, a dispersion compensating fiber.

The photodetector 142 is used to convert the dispersed optical signal into a first electrical signal.

The complex frequency response of the fiber optic sensing system 10 can be expressed by the following equation:

wherein omega is the angular frequency of the first radio frequency signal and the second radio frequency signal; h is the complex transfer function of the dispersive component 141; m is the modulation factor of the optical field output by the microwave-optical modulator 13.

In some embodiments, the fiber optic sensing system 10 includes an amplifier coupled between the optical signal generating unit 11 and the photodetector 142 for amplifying the optical signal. In some embodiments, an amplifier is connected between the interferometer assembly 18 and the microwave-optical modulator 13 for amplifying the sampled optical signal. In some embodiments, an amplifier is coupled between the microwave-optical modulator 13 and the dispersive component 141 for amplifying the modulated optical signal. In some embodiments, an amplifier is coupled between the dispersive component 141 and the photodetector 142 for amplifying the dispersed optical signal. The amplifier can improve the signal intensity, and is convenient for subsequent detection.

FIG. 5 is a schematic diagram illustrating one embodiment of the interferometer assembly 18 of FIG. 2.

Interferometer assembly 18 includes a bi-directional coupler 181 and a first fiber optic interferometer 182. The bi-directional coupler 181 includes a first port T1, a second port T2, and a third port T3. The first port T1 is connected to the light source 17 and receives broadband continuous light. The second port T2 is connected to the first fiber optic interferometer 182. The third port T3 is connected to the microwave-optical modulator 13. The first optical fiber interferometer 182 is configured to optically sample the broadband continuous light to obtain a sampled optical signal, and transmit the sampled optical signal to the third port T3, where the sampled optical signal is transmitted to the microwave-optical modulator 13 through the third port T3.

FIG. 6 is a schematic diagram of another embodiment of the interferometer assembly 18 of FIG. 2.

Interferometer assembly 18 includes coupler 183 and a plurality of first fiber optic interferometers 182. The coupler 183 is connected between the second port T2 of the bi-directional coupler and the plurality of first fiber interferometers 182. At least two first fiber interferometers 182 have different free spectral ranges and can detect physical quantity change information for a plurality of measurement points. The plurality of first optical fiber interferometers 182 optically sample the broadband continuous light, respectively, to obtain a plurality of sampled optical signals. The coupler 183 is used for coupling a plurality of sampled optical signals, and transmits the signals to the microwave-optical modulator 13 through the third port T3. The signal acquisition processing component 16 can demodulate radio frequency signals corresponding to different sampled optical signals, and further obtain physical quantity change information of a plurality of measurement points, so that multi-sensor multiplexing can be realized.

FIG. 7 is a schematic diagram of another embodiment of the interferometer assembly 18 of FIG. 2. Interferometer assembly 18 includes a second fiber optic interferometer 184. The input end of the second optical fiber interferometer 184 is connected to the light source 17, and after the broadband continuous light is optically sampled, the sampled light signal is transmitted to the microwave-optical modulator 13 through the output end.

FIG. 8 is a schematic diagram of another embodiment of the interferometer assembly 18 of FIG. 2.

Interferometer assembly 18 includes coupler 185, coupler 186, and a plurality of second fiber optic interferometers 184. Broadband continuous light is input to the plurality of second fiber optic interferometers 184 through couplers 185. At least two second fiber interferometers 184 have different free spectral ranges and can detect physical quantity change information for a plurality of measurement points. The plurality of second optical fiber interferometers 184 sample the broadband continuous light to obtain a plurality of sampled optical signals, the coupler 186 couples and outputs the plurality of sampled optical signals, and the signal acquisition processing assembly 16 can demodulate radio frequency signals corresponding to different sampled optical signals, so as to obtain physical quantity change information of a plurality of measuring points, thereby realizing multi-sensor multiplexing.

FIG. 9 is a schematic diagram illustrating one embodiment of the first fiber optic interferometer 182 of FIG. 5. The first fiber optic interferometer 182 comprises a fabry-perot interferometer. The first optical fiber interferometer 182 comprises two reflection points 191 and 192, and the optical fiber between the reflection point 191 and the reflection point 192 is a sensing section.

FIG. 10 is a schematic diagram illustrating one embodiment of the second fiber optic interferometer 184 of FIG. 7.

The second fiber optic interferometer 184 comprises a sagnac interferometer. The second fiber interferometer 184 includes two couplers 193 and 194, a reference section fiber 195, a time delay section fiber 196, and a reflection point 197. The fiber intermediate coupler 194 and reflection point 197 is the sensing segment.

FIG. 11 is a schematic diagram illustrating one embodiment of the second fiber optic interferometer 184 of FIG. 7.

The second fiber interferometer 184 comprises a mach-zehnder interferometer. Including two couplers 193 and 194, a reference section fiber 195, and a time delay section fiber 196. The time delay section fiber 196 is the sensing section of the system.

FIG. 12 is a schematic diagram illustrating one embodiment of a second fiber optic interferometer 184 of FIG. 7.

The second fiber optic interferometer 184 comprises a michelson interferometer. The second fiber interferometer 184 includes a coupler 193, a reference section fiber 195, a time delay section fiber 196, and two reflection points 197 and 198. The delay section fiber 196 is the sensing section.

Fig. 13 is a flow chart of one embodiment of the fiber sensing method 20 of the present application.

The optical fiber sensing method 20 is applied to the optical fiber sensing system 10 for sensing external physical quantity change information. The optical fiber sensing method 20 includes: step 21 to step 26.

Step 21, determining the operating frequency of the fiber optic sensing system 10. Step 21 is to determine the operating frequency of the microwave radio frequency oscillator 12 in the fiber optic sensing system 10.

Step 22, generating an optical signal. The optical signal is generated by the optical signal generating unit 11. The optical signal changes with a change in the external physical quantity change information.

Step 23, modulating the optical signal based on the first radio frequency signal, to obtain a modulated optical signal. The microwave-optical modulator 13 receives the optical signal generated by the optical signal generating unit 11 and the first radio frequency signal generated by the microwave radio frequency oscillator 12, and modulates the optical signal based on the first radio frequency signal, generating a modulated optical signal.

The optical signal is converted into a first electrical signal, step 24. The photoelectric conversion unit 14 converts the optical signal into a first electrical signal.

Step 25, generating a second electrical signal indicative of a phase difference of the first electrical signal and the second radio frequency signal. The frequencies of the second radio frequency signal and the first radio frequency signal are working frequencies. The microwave phase detector 15 receives the first electric signal and the second radio frequency signal, and detects a phase difference of the first electric signal and the second radio frequency signal, and generates the second electric signal based on the phase difference.

And step 26, demodulating the intensity of the second electric signal to obtain external physical quantity change information. The signal acquisition processing component 16 acquires and demodulates the phase of the second electrical signal to obtain external physical quantity change information.

In some embodiments, the fiber sensing method 20 further comprises: removing the direct current information of the intensity of the second electric signal; noise information of the intensity of the second electrical signal is removed. Thus, the external physical quantity change information can be obtained more accurately.

FIG. 14 is a block diagram of another embodiment of the fiber optic sensing system 10 of the present application. The embodiment is used for determining the operating frequency and the phase change law, i.e. the pre-calibration process, before measuring the physical quantity. The calibration system 210 includes: an optical signal generating unit 11, a microwave-optical modulator 13, a photoelectric conversion unit 14, a signal acquisition processing component 16 and a vector network analyzer 19. Wherein the optical signal generating unit 11, the microwave-optical modulator 13, the photoelectric conversion unit 14, and the signal acquisition processing assembly 16 are identical to those in the optical fiber sensing system 10 shown in fig. 2.

The vector network analyzer 19 is connected to the microwave-optical modulator 13, and provides a broadband rf sweep signal for modulating the optical signal generated by the optical signal generating unit 11, thereby generating an rf passband electrical signal after passing through the photoelectric conversion unit 14.

The vector network analyzer 19 is connected to the photoelectric conversion unit 14, and is configured to collect the radio frequency passband electrical signal generated by the photoelectric conversion unit 14, i.e. the third electrical signal.

The signal acquisition and processing component 16 is connected with the vector network analyzer 19 and acquires and processes the radio frequency passband electrical signals. The operating frequency of the fiber optic sensing system 10 is determined based on the intensity information of the third electrical signal. According to the phase information of the third electric signal, the phase change rule of the optical fiber sensing system 10 along with the change information of the external physical quantity is determined.

Fig. 15 is a flow chart of one embodiment of step 21 in fig. 13.

Step 21 comprises: step 211 to step 216. In performing step 21, the calibration system 210 shown in fig. 14 is used, i.e. the microwave radio frequency oscillator 12 and the microwave phase detector 15 are replaced by the vector network analyzer 19.

Step 211, generating broadband continuous light. The light source 17 generates broadband continuous light.

Step 212, optical sampling is performed on the broadband continuous light, so as to obtain a sampled optical signal. The interferometer assembly 18 optically samples the broadband continuous light to obtain a sampled optical signal.

In step 213, the sampled optical signal is modulated based on the broadband RF sweep signal, and a modulated optical signal is obtained. The vector network analyzer may provide a broadband rf sweep signal, and the microwave-optical modulator 13 modulates the sampled optical signal based on the broadband rf sweep signal to obtain a modulated optical signal.

Step 214, performing dispersion on the modulated optical signal to obtain a dispersed optical signal. The dispersion component 141 disperses the modulated optical signal, and introduces the frequency domain characteristics of the signal into the time domain, thereby obtaining a passband signal of the radio frequency domain, forming a passband radio frequency filter, and obtaining the dispersed optical signal.

Step 215, converting the dispersed optical signal into a third electrical signal. The photodetector 142 converts the dispersed optical signal into a third electrical signal.

In step 216, any frequency within the radio frequency passband is determined as the operating frequency based on the intensity of the third electrical signal. The vector network analyzer is connected to the photodetector 142 and measures the intensity of the third electrical signal. Fig. 15 is a waveform diagram of one embodiment of a third electrical signal. As shown in fig. 16, a radio frequency passband is formed between the frequency f1 and the frequency f2, and any frequency in the radio frequency passband can be used as an operating frequency, for example, a frequency f3, a frequency f4, and a frequency f. If the optical fiber sensing system 10 includes a plurality of sensors, the rf pass-bands of the signals detected by the photodetectors 142 may also be plural, and the frequency corresponding to the rf pass-band of the corresponding sensor is selected as the operating frequency of the optical fiber sensing system 10, so that the sensing information of the corresponding sensor can be obtained by measurement.

In step 217, according to the phase of the third electrical signal, the phase change rule of the optical fiber sensing system 10 along with the change information of the external physical quantity is determined. The phase of the third electric signal is measured by the vector network analyzer 19, the external physical quantity to be measured is changed, and the phase change rule of the external physical quantity change information is obtained.

In some embodiments, step 216 comprises: the microwave frequency within the radio frequency passband is determined to be the operating frequency. Phase wrapping may occur due to phase changes of the sensing element when it is subject to wide fluctuations. At this time, unwrapping of the phase signal is realized by using the amplitude variation characteristic, and a wide range of measurement can be realized.

Fig. 17 is a waveform diagram of the phase of one embodiment of the third electrical signal. In the embodiment shown in fig. 17, dispersion component 141 is free of third-order dispersion. The phase within the passband of the signal varies linearly with frequency. Therefore, when the fiber optic sensing system 10 is used for sensing detection, the phase change of the system detection caused by the passband frequency drift caused by the change of the external physical quantity also shows a linear trend. The phase change rule of the phase along with the external physical quantity is obtained through pre-calibration, and the phase change value and the physical quantity change value can be correspondingly demodulated.

Fig. 18 is a device diagram of another embodiment of the fiber optic sensing system 10. In this embodiment, this device serves as both the fiber optic sensing system 10 and the calibration system 210. When this device is used as a fiber optic sensing system 10, a Vector Network Analyzer (VNA) is used as a microwave phase detector 15, and also as a microwave radio frequency oscillator 12. The rf signal output at the first port of the VNA is then used as both the first rf signal and the second rf signal of the microwave rf oscillator 12.

In the embodiment shown in fig. 18, the light source 17 uses an Amplified Spontaneous Emission (ASE) light source, and the center wavelength of the light source 17 is 1545.5nm and the spectral width is 35nm. The interferometer assembly 18 is a fabry-perot (FP) cavity. The ASE emitted light is coupled through a circulator into a fabry-perot (FP) cavity consisting of Hollow Core Fibers (HCF) and Single Mode Fibers (SMF). Here, the two end faces at the junction of SMF and HCF serve as the two reflecting surfaces of the FP cavity. The cavity length of the FP cavity, i.e. the length of the hollow core fiber, is about 300 μm. After optical sampling by the FP cavity, the spectrum of the sampled optical signal reflected back is output through the third port of the circulator, and coupled to an erbium-doped fiber amplifier (EDFA).

FIG. 19 is a spectral diagram of the sampled optical signal of the fiber optic sensing system 10 shown in FIG. 18.

As can be seen from FIG. 19, the Free Spectral Range (FSR) of the FP cavity was 3.95nm, which was calculated to be 303 μm in cavity length. The microwave-optical modulator 13 uses an electro-optical modulator (EOM). The signals are amplified by EDFA and then enter an electro-optical modulator (EOM) to realize radio frequency modulation. The radio frequency signal is provided by a first port of a Vector Network Analyzer (VNA), the radio frequency signal input into the EOM is a linear sweep frequency signal, and the sweep frequency range is 10 kHz-500 MHz. The optical signal is input into a dispersion compensation optical fiber (DCF) module after radio frequency modulation in EOM, and the total dispersion introduced by the DCF module is-997 ps/nm. The signal after DCF is detected by a photoelectric detector with the bandwidth of 1.6GHz and then is input to a second port of the VNA for processing and displaying, and the strength and phase information of the signal are obtained. And the VNA is connected with a signal acquisition processing module for signal acquisition and processing.

The signal intensity of the radio frequency passband measured by the system is shown in fig. 20, the center frequency f of the passband is 248.4MHz according to the signal intensity information, and the pre-calibration process is completed.

After the passband center frequency is obtained, an outside physical quantity measurement process is performed using the fiber optic sensing method 20. The frequency of the radio frequency signal output by the first port of the VNA is set as the center frequency f of the passband, and the continuous radio frequency signal with the frequency f is loaded on the EOM for modulation. The fiber FP cavity is tightly wound on the periphery of a tubular piezoelectric ceramic (PZT), and an electric signal with the amplitude of 10Vpp and the frequency of 10Hz is loaded on the PZT to drive the PZT to vibrate.

The signal after DCF is detected by the photoelectric detector and then is input to the second port of the VNA for processing and displaying, and phase information of the signal is obtained. The IF Bandwidth of the VNA is set to 100Hz. The system can use a lower-cost microwave phase detector in practical engineering application, so that higher economic benefit is realized.

After the measured phase information is subjected to DC removal and noise removal, the conversion relation of phase conversion into strain is obtained through the calibration process of strain and phase variation. Finally, the time domain information of the obtained vibration signal is shown in fig. 21, the Power Spectral Density (PSD) of the frequency domain is shown in fig. 21, and fig. 21 and 22 show that the vibration signal with the frequency of 10Hz is well recovered in the time domain, and the signal-to-noise ratio is more than 43.7 dB. The high detection sensitivity of the fiber optic sensing system 10 provided by the present application is demonstrated.

Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of the application following, in general, the principles of the application and including such departures from the present disclosure as come within known or customary practice within the art to which the application pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the application being indicated by the following claims.

It is to be understood that the application is not limited to the precise arrangements and instrumentalities shown in the drawings, which have been described above, and that various modifications and changes may be effected without departing from the scope thereof. The scope of the application is limited only by the appended claims.

Claims

1. An optical fiber sensing system based on microwave photons, for sensing external physical quantity change information, comprising:

an optical signal generating unit for generating an optical signal;

2. The fiber optic sensing system of claim 1, wherein the microwave phase detector comprises a vector network analyzer for determining a phase change law of the external physical quantity change information prior to sensing the external physical quantity change information.

3. The optical fiber sensing system according to claim 2, wherein the signal acquisition processing component is configured to demodulate the intensity of the second electrical signal according to the phase change rule, so as to obtain the external physical quantity change information.

4. The fiber optic sensing system of claim 1, wherein the optical signal generation unit comprises a light source and an interferometer assembly; the light source is used for generating broadband continuous light; the interferometer component is used for carrying out optical sampling on the broadband continuous light to obtain a sampled optical signal.

5. The fiber optic sensing system of claim 4, wherein the interferometer assembly comprises a bi-directional coupler and a first fiber optic interferometer; the bi-directional coupler includes a first port, a second port, and a third port; the first port is connected with the light source, the second port is connected with the first optical fiber interferometer, and the third port is connected with the microwave-optical modulator; the first optical fiber interferometer is used for optically sampling the broadband continuous light to obtain the sampled optical signal, and transmitting the sampled optical signal to the third port.

6. The fiber optic sensing system of claim 5, wherein the interferometer assembly comprises a coupler and a plurality of the first fiber optic interferometers; the coupler is connected between a second port of the bi-directional coupler and the plurality of first fiber interferometers; at least two of the first fiber interferometers have different free spectral ranges; the plurality of first optical fiber interferometers respectively carry out optical sampling on the broadband continuous light to obtain a plurality of sampled optical signals; the coupler is used for coupling a plurality of the sampled optical signals.

7. The fiber optic sensing system of claim 4, wherein the light source comprises an amplified spontaneous emission light source or a superluminescent light emitting diode.

8. The fiber optic sensing system of claim 1, wherein the photoelectric conversion unit comprises a dispersion component and a photodetector; the dispersion component is used for dispersing the modulated optical signal to obtain a dispersed optical signal; the photodetector is configured to convert the dispersed optical signal into the first electrical signal.

9. The optical fiber sensing system according to claim 8, wherein the optical fiber sensing system comprises an amplifier connected between the optical signal generating unit and the photodetector for amplifying the optical signal.

10. The fiber optic sensing system of claim 8, wherein the dispersion component comprises at least one of a single mode fiber, a multimode fiber, a dispersion compensating fiber.

11. The fiber optic sensing system of claim 1, wherein the microwave radio frequency oscillator comprises a vector network analyzer; and/or

The microwave-optical modulator comprises one of an electro-optic modulator, a Mach-Zehnder modulator, a phase modulator.

12. The optical fiber sensing method based on microwave photons is applied to an optical fiber sensing system for sensing external physical quantity change information, and is characterized by comprising the following steps of: