CN117029995A - High sensitivity vibration sensing system and method employing broadband light sources - Google Patents
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Abstract
The application discloses a high-sensitivity vibration sensing system and a method adopting a broadband light source, wherein the broadband light passes through a fiber bragg grating to realize the broadband pressure narrowing of the light source spectrum, the coherence length is controlled to enable two beams of light with optical path difference within a specific range to interfere, the noise of a sensing system can be obviously reduced, a heterodyne modulation and demodulation method is adopted, an optical fiber delay module and an acoustic light frequency shifter are introduced into a reference path, and the length of a cavity length compensation optical fiber is controlled to enable high-order reflection detection light in an optical fiber Fabry-Perot resonant cavity to interfere with first-order reflection reference light so as to realize the effect of improving the sensitivity. The application realizes multiplexing, high sensitivity and low cost heterodyne interference dynamic signal modulation and demodulation of the broadband light source by utilizing the advantages of the broadband light source spectrum width and the wavelength characteristics of the fiber grating.
Description
Technical Field
The application relates to the technical field of optical fiber sensing, in particular to a high-sensitivity vibration sensing system and method adopting a broadband light source.
Background
The optical fiber sensing system has the unique advantages of strong electromagnetic interference resistance, no electricity at a detection end, severe environment resistance and the like, and is widely applied to a plurality of practical occasions such as environment monitoring, resource exploration, biomedical treatment, aerospace and the like and scientific research fields. The optical fiber adopted by the interference type optical fiber vibration sensor has the functions of transmitting signals and sensing external signals. When the sensing unit of the system loads the vibration signal, the phase of the light wave transmitted in the optical fiber can be correspondingly changed, so that the relevant information of the vibration signal can be obtained by detecting the returned phase change. Phase-modulated fiber optic vibration systems are mainly of several types: mach-Zehnder type, michelson type, sagnac type and Fabry-Perot type, and their structural compositions are flexible and various. Compared with the traditional optical fiber sensing system, the optical fiber sensing system matched with the optical fiber Fabry-Perot interferometer has the advantages of high resolution, simple structure and easiness in array combination, is favored by scientific researchers, and has become a research hotspot for large-scale and light-weight optical fiber sensor array design.
The current widely applied optical fiber sensing system and demodulation method with higher resolution mostly depend on narrow linewidth kilohertz or even hundred hertz level light source with high coherence, the light source is high in cost, meanwhile, a narrow linewidth laser is not compatible with a wavelength division multiplexing type sensing system, the number of the wavelength of the light source needs to be increased, the number of the lasers needs to be increased, and the cost and the complexity of the sensing system are greatly improved. Thus, although the laser-driven optical fiber sensor achieves very high measurement accuracy, its application is very limited. Some of the current broadband light source driven sensing systems adopt PDH technology, which can achieve the resolution of skin strain, but each sensing unit needs closed-loop real-time feedback control, so that the inherent wavelength division multiplexing performance of the broadband light source cannot be well exerted (White-light-driven resonant fiber-optic strain sensor [ J ], optics Letters,2020, 45 (18), 5217-5220). And the resolution of a part of sensing systems driven by broadband light sources reaches nano strain, the requirement of high-sensitivity vibration sensing is still not met (Li Enbang, low-cost high-resolution multichannel wavelength demodulator [ J ] for fiber grating sensing, instrument and meter school, 2007, 28 (1), 1-6).
The existing optical fiber sensing vibration system and method are difficult to simultaneously consider the characteristics of low cost, higher sensitivity and easiness in array formation. Therefore, it is necessary to develop a system and a demodulation method that combine the above characteristics to improve the dynamic signal demodulation capability of the optical fiber sensing system and the array.
Disclosure of Invention
Aiming at the technical problems and the defects existing in the field, the application provides a high-sensitivity vibration sensing system adopting a broadband light source, wherein the broadband light passes through a fiber bragg grating to realize the wide-spectrum pressure narrowing of the light source, the coherence length is controlled to enable two beams of light with optical path difference within a specific range to interfere, the noise of the sensing system can be remarkably reduced, a heterodyne modulation and demodulation method is adopted, an optical fiber delay module and an acoustic optical frequency shifter are introduced into a reference path, and the length of a cavity length compensation optical fiber is controlled to enable the high-order reflection detection light in an optical fiber Fabry-Perot resonant cavity to interfere with first-order reflection reference light so as to realize the effect of improving the sensitivity. The system of the application utilizes the advantages of the broadband light source spectrum width and the fiber bragg grating wavelength characteristic to realize the heterodyne interference dynamic signal modulation and demodulation of the broadband light source with multiplexing, high sensitivity and low cost.
A high sensitivity vibration sensing system employing a broadband light source, comprising:
the wide-spectrum light source module is used for emitting wide-spectrum light;
the fiber grating filter for bandwidth filtering of the wide-spectrum light comprises a first circulator, wherein the first circulator is used for outputting the wide-spectrum light to one or more fiber gratings with different center wavelengths and the same bandwidth, which are positioned on the same fiber, and the reflected wide-spectrum light is output through the first circulator;
the first coupler is used for dividing the wide-spectrum light subjected to bandwidth filtering into two paths of optical signals, wherein one path of optical signal is used as detection light to pass through the detection path, and the other path of optical signal is used as reference light to pass through the reference path;
the optical fiber Fabry-Perot resonant cavity array comprises a plurality of groups of optical fiber grating groups and is used for reflecting the detection path optical signals for a plurality of times, and the reflected signals are transmitted to the second coupler through the first coupler; each group of fiber bragg grating groups in the fiber Fabry-Perot resonant cavity array consists of a pair of fiber bragg gratings with the same bandwidth and center wavelength; the number and the center wavelength of the fiber bragg grating groups on each fiber in the fiber Fabry-Perot resonant cavity array are correspondingly set according to the number and the center wavelength of the fiber bragg gratings in the fiber bragg grating filter; the fiber grating group on each fiber in the fiber Fabry-Perot resonant cavity array and the corresponding fiber grating in the fiber grating filter have the same central wavelength; the bandwidth of the fiber bragg grating in the fiber bragg grating Fabry-Perot resonant cavity array is larger than that of the fiber bragg grating in the fiber bragg grating filter, so that insertion loss attenuation caused by reflection in a light path can be reduced, the sensitization value is improved, and the effect of improving the equivalent resolution is achieved;
the second circulator is used for outputting the reference path optical signal to the fiber grating array, and the reflected signal reflected by the fiber grating array is output to the acousto-optic frequency shifter through the second circulator;
the optical fiber grating array comprises a plurality of optical fiber gratings and is used for reflecting the reference path optical signals; the optical fibers in the fiber bragg grating array are arranged in one-to-one correspondence with the optical fibers in the fiber bragg fabry-perot resonant cavity array; the number and the central wavelength of the fiber bragg gratings on each fiber in the fiber bragg grating array are correspondingly set according to the number and the central wavelength of the fiber bragg grating groups on the corresponding fiber in the fiber bragg fabry-perot resonant cavity array; the fiber grating in the fiber grating array and the fiber grating group corresponding to the fiber grating in the fiber Fabry-Perot resonant cavity array have the same bandwidth and center wavelength;
the acousto-optic frequency shifter is used for carrying out frequency shifting of light on signals returned by the fiber grating array to realize noise reduction;
the optical fiber delay module comprises an electric adjustable optical fiber delay line and a cavity length compensation optical fiber, is arranged between the acousto-optic frequency shifter and the second coupler and is used for performing small-amplitude accurate and large-amplitude rough adjustment on the length of the optical fiber of the reference path so as to match the optical path difference between the reference path and the detection path;
the second coupler is used for performing cavity length matching heterodyne interference on reflected light of the detection path and the reference path and outputting interference signals;
the interference optical power adjusting device is arranged between the second coupler and the photoelectric detector and is used for adjusting the optical power of the interference light so that the optical power works in a linear working area of the photoelectric detector;
the photoelectric detectors are used for detecting beat frequency signals of interference signals of the detection path and the reference path, converting photoelectric signals and outputting the photoelectric signals to the band-pass filter; the number of the photoelectric detectors is consistent with the number of the fiber bragg gratings in the fiber bragg grating filter, the fiber bragg grating group in the fiber bragg grating Fabry-Perot resonant cavity array and the central wavelength types of the fiber bragg gratings in the fiber bragg grating array;
the band-pass filter is used for filtering frequency shift signals in the electric signals and extracting radio frequency signals carrying sensing phase shift information;
the real-time data acquisition module is used for acquiring radio frequency signals in real time;
the data processing module is used for processing the acquired radio frequency signals, demodulating the interference signals and obtaining the detection result of the heterodyne interference signals with the high-sensitivity cavity length matching of the broadband light source.
In the present application, "several" means that the number may be 1 or more.
In an embodiment, in the high-sensitivity vibration sensing system using a broadband light source, a first erbium-doped fiber amplifier for amplifying power of broad spectrum light is disposed between the fiber grating filter and the first coupler.
In one embodiment, the high sensitivity vibration sensing system using a broadband light source, the interferometric optical power adjustment device comprises a second erbium-doped fiber amplifier and an optical attenuator.
In one embodiment, the high-sensitivity vibration sensing system using a broadband light source, the fiber bragg grating filter comprises a plurality of fiber bragg gratings with different center wavelengths and the same bandwidth, which are positioned on the same optical fiber;
each optical fiber of the optical fiber Fabry-Perot resonant cavity array is provided with a plurality of groups of optical fiber grating groups with different center wavelengths, wherein the groups of optical fiber grating groups are in one-to-one correspondence with the optical fiber gratings in the optical fiber grating filter;
each optical fiber of the fiber grating array is provided with a plurality of fiber gratings with different center wavelengths, which are in one-to-one correspondence with the fiber gratings in the fiber grating filter;
and a wavelength division multiplexing device is arranged between the interference optical power adjusting device and the photoelectric detector and is used for separating signal lights with different wavelengths and respectively transmitting the signal lights to the photoelectric detector for processing signals with corresponding wavelengths.
In an embodiment, the high-sensitivity vibration sensing system adopting the broadband light source comprises an optical fiber fabry-perot resonant cavity array, wherein the optical fiber fabry-perot resonant cavity array comprises a first optical fiber beam splitter and a plurality of optical fibers connected with the first optical fiber beam splitter, each optical fiber of the optical fiber fabry-perot resonant cavity array is independently provided with a plurality of groups of optical fiber grating groups, and time division multiplexing is realized among the optical fibers of the optical fiber fabry-perot resonant cavity array through delay optical fibers;
the fiber grating array comprises a second fiber beam splitter and a plurality of fibers which are connected with the second fiber beam splitter and are in one-to-one correspondence with the fibers in the fiber Fabry-Perot resonant cavity array, the number and the center wavelength of the fiber gratings on each fiber in the fiber grating array are correspondingly set according to the number and the center wavelength of the fiber grating groups on the corresponding fibers in the fiber Fabry-Perot resonant cavity array, and the time division multiplexing consistent with the fiber Fabry-Perot resonant cavity array is realized among the fibers of the fiber grating array through delay fibers.
Furthermore, the high-sensitivity vibration sensing system adopting the broadband light source can be combined with wavelength division multiplexing on the basis of the time division multiplexing, namely, on the basis of the time division multiplexing scheme, the fiber bragg grating filter comprises a plurality of fiber bragg gratings with different center wavelengths and the same bandwidth, wherein the fiber bragg gratings are positioned on the same optical fiber;
each optical fiber of the optical fiber Fabry-Perot resonant cavity array is provided with a plurality of groups of optical fiber grating groups with different center wavelengths, wherein the groups of optical fiber grating groups are in one-to-one correspondence with the optical fiber gratings in the optical fiber grating filter;
each optical fiber of the fiber grating array is provided with a plurality of fiber gratings with different center wavelengths, which are in one-to-one correspondence with the fiber gratings in the fiber grating filter;
and a wavelength division multiplexing device is arranged between the interference optical power adjusting device and the photoelectric detector and is used for separating signal lights with different wavelengths and respectively transmitting the signal lights to the photoelectric detector for processing signals with corresponding wavelengths.
In one embodiment, the high sensitivity vibration sensing system using a broadband light source is a pulsed light when time division multiplexing is involved. In the rest of the cases, the broad spectrum light may be continuous light or pulsed light. The pulsed light may be generated using any of pulse modulation devices such as an acousto-optic modulator, an electro-optic modulator, and a Semiconductor Optical Amplifier (SOA).
When the high-sensitivity vibration sensing system adopting the broadband light source relates to wavelength division multiplexing, the absolute value of the optical path difference required by each wavelength interference is less than or equal to lambda FBG 2 /Δλ FBG ，λ FBG 、Δλ FBG The optical fiber grating array represents the central wavelength and the bandwidth of the optical fiber grating array respectively, and the interference of each wavelength requires consistent optical path difference.
In one embodiment, the high sensitivity vibration sensing system employs a broadband light source, the bandwidth of the broadband light Δλ ASE The method meets the following conditions:
Δλ ASE ≥Δλ FBG1 +…+Δλ FBGn
wherein n is a positive integer, Δλ FBG1 ，…，Δλ FBGn Representing the bandwidth of each fiber grating in the fiber grating array.
In one embodiment, any one of the fiber grating filter, the fiber Fabry-Perot resonator array, and the fiber grating array has a bandwidth Δλ FBG The method meets the following conditions:
Δλ FBG ≤λ FBG 2 /δL
wherein lambda is FBG And delta L is the optical path difference between the heterodyne interference detection light and the reference light matched with the cavity length for the central wavelength of the corresponding fiber bragg grating.
The high-sensitivity vibration sensing system adopting the broadband light source can be any one of broadband light sources such as ASE, SLD, LED light sources.
The high-sensitivity vibration sensing system adopting the broadband light source can be any one or a combination of a plurality of uniform fiber Bragg gratings and apodized fiber gratings.
The high-sensitivity vibration sensing system adopting the broadband light source comprises a first coupler, an optical fiber Fabry-Perot resonant cavity array, a second circulator, an optical fiber grating array, an acousto-optic frequency shifter, an optical fiber delay module and a second coupler, wherein the cavity length matching interferometer can adopt a Michelson type structure or a Mach-Zehnder type structure, and a heterodyne interferometry is adopted, and the optical path length of the cavity length compensation optical fiber in a reference path is adjusted to enable the optical path of reflected light of the optical fiber grating of the reference path to be approximately consistent with the optical path of high-order reflected light of interference participated by the Fabry-Perot cavity in a detection path, so that the sensitivity is improved.
The high-sensitivity vibration sensing system adopting the broadband light source adopts the light path structure which introduces the reference light path, and can effectively reduce the path noise by reasonably controlling the light path difference and the coherence length of the sensing light path and the reference light path, and simultaneously avoid the noise elevation problem caused by interference of the rest multi-order reflected light of the sensing light path.
When the cavity length matching interferometer adopts a Michelson type structure, in order to improve the high-order reflection light intensity, in one group of fiber bragg grating groups, when i is more than or equal to 2, the reflectivity of the fiber bragg grating of the first contact detection light is (i-1)/(i+1), when i=1, the reflectivity of the fiber bragg grating of the first contact detection light is 1, i is the reflective order of the fiber bragg grating Fabry-Perot resonant cavity participating in interference, and the reflectivity of the fiber bragg grating of the second contact detection light is 1; the fiber gratings of the reference path only play a role in reflection, and the sensitive elements are fibers among the fiber gratings. Meanwhile, the reflectivity of the fiber grating array of the reference path and the coupling ratio of the second coupler are changed according to the change of the reflection orders of the interference light, and the optical power of the reference light and the optical power of the detection light are required to be basically consistent, so that the optimal sensitization effect is achieved.
The application also provides a high-sensitivity vibration sensing method adopting the broadband light source, and a high-sensitivity vibration sensing system adopting the broadband light source is adopted;
the high-sensitivity vibration sensing method adopting the broadband light source comprises the following steps:
the wide-spectrum light source module emits wide-spectrum light, the wide-spectrum light is subjected to bandwidth filtering through the fiber bragg grating filter, and then is divided into two paths of optical signals after passing through the first coupler, one path of optical signal is used as detection light and passes through the detection path, and the other path of optical signal is used as reference light and passes through the reference path;
the detection light is changed into a light beam with cavity length matching interference sensing information through an optical fiber Fabry-Perot resonant cavity array, and then reflected to be transmitted to a second coupler through a first coupler;
the reference light enters a first port of a second circulator, and after exiting from a second port of the second circulator and being reflected by the fiber bragg grating array to become a light beam with cavity length matching interference intrinsic information, the light beam exits from a third port of the second circulator and is transmitted to a second coupler through an acousto-optic frequency shifter and a fiber delay module;
the detection light and the reference light generate heterodyne interference with matched cavity length, and an interference signal is output;
the output interference signals are subjected to power adjustment through an interference light power adjusting device, photoelectric signals of a photoelectric detector are converted, a band-pass filter filters frequency shift signals in the electric signals, and radio frequency signals carrying sensing phase shift information are extracted;
the real-time data acquisition module and the data processing module acquire and process the radio frequency signals, demodulate the interference signals and obtain the detection result of the high-sensitivity cavity length matching heterodyne interference signals of the broadband light source.
The application provides a high-sensitivity vibration sensing system and a high-sensitivity vibration sensing method which can reach the resolution of skin strain and adopt a broadband light source, which can solve the problems in the prior art that: 1) The narrow linewidth laser is used as a light source of the sensing system, is high in price and is incompatible with the wavelength division multiplexing sensing system; 2) The interference type sensing system has the problems of low sensitivity, poor optical path matching universality and the like in application.
Compared with the prior art, the application has the beneficial effects that:
1. compared with the prior Fabry-Perot interference type vibration sensing system which needs to use a narrow linewidth laser light source, the application has high cost and is incompatible with a wavelength division multiplexing type system, the application can use a wide-spectrum light source with low cost, reduce multi-order optical noise introduced by multiple reflections in the Fabry-Perot interferometer, realize dynamic sensing array measurement, and simultaneously reduce the cost and complexity of the system.
2. The cavity length matching interferometer is manufactured by adopting the electric adjustable optical fiber delay line, the cavity length compensating optical fiber, the acousto-optic frequency shifter and the fiber grating, heterodyne modulation and demodulation are realized, and the detection sensitivity of the sensing system is improved on the premise that the matching interferometer has better cavity length matching capability.
3. The system and the method are suitable for demodulating a single sensing unit, and can also realize time division multiplexing, wavelength division multiplexing and time division and wavelength division mixed multiplexing demodulation of a plurality of sensing units.
Drawings
Fig. 1 is a schematic structural diagram of a high sensitivity fabry-perot Luo Zhendong sensing system employing a broadband light source according to embodiment 1 of the present application;
FIG. 2 is a graph showing the comparison of the spectrum of the optical interference output signals of different orders of the sensing system according to embodiment 1 of the present application.
Fig. 3 is a schematic structural diagram of a wavelength division, time division and wavelength division hybrid multiplexing system according to embodiment 2 of the present application;
fig. 4 is a schematic diagram of a broad spectrum light source module of the time division and wavelength division multiplexing system according to embodiment 2 of the present application.
Detailed Description
The application will be further elucidated with reference to the drawings and to specific embodiments. It is to be understood that these examples are illustrative of the present application and are not intended to limit the scope of the present application.
Example 1
Referring to fig. 1, a high sensitivity vibration sensing system using a broadband light source includes a broad spectrum light source module 1, a fiber bragg grating filter 2, a first erbium-doped fiber amplifier 3, a first coupler 4, a fiber fabry-perot resonator array 5, a second circulator 6, a fiber bragg grating array 7, an acousto-optic frequency shifter 8, an electrically tunable fiber delay line 9, a cavity length compensation fiber 10, a second coupler 11, a second erbium-doped fiber amplifier 12, an optical attenuator 13, a wavelength division multiplexing device 14, two photodetectors 15, 16, a band-pass filter 17, a real-time data acquisition module 18, and a data processing module 19.
The broad spectrum light source module 1 is for emitting broad spectrum light.
The fiber grating filter 2 is used for bandwidth filtering of broad spectrum light, and comprises a first circulator 203 and 2 fiber gratings 201 and 202 with the same bandwidth and different center wavelengths, which are positioned on the same fiber. The first circulator 203 is used for outputting broad spectrum light to 2 optical fibers with center wavelengths lambda respectively 1 、λ 2 The fiber gratings 201 and 202 have the same bandwidth, and the reflected broad spectrum light is output through the first circulator 203.
The first erbium-doped fiber amplifier 3 is disposed between the fiber grating filter 2 and the first coupler 4 for power amplifying the broad spectrum light.
The first coupler 4 is configured to divide bandwidth-filtered broad spectrum light into two optical signals, where one optical signal is used as probe light and passes through the probe path, and the other optical signal is used as reference light and passes through the reference path.
The optical fiber fabry-perot resonator array 5 is used for reflecting the detection path optical signal for a plurality of times, and the reflected signal is transmitted to the second coupler 11 through the first coupler 4. The fiber Fabry-Perot resonant cavity array 4 comprises 2 groups of fiber bragg grating groups with different center wavelengths positioned on the same fiber, each group of fiber bragg grating group in the fiber Fabry-Perot resonant cavity array 5 consists of a pair of fiber bragg gratings with the same bandwidth and center wavelength, wherein the first group of fiber bragg grating groups consists of fiber bragg gratings with the same center wavelength lambda 1 The second group of fiber gratings is composed of fiber gratings 501 and 502 with center wavelength lambda 2 Is composed of fiber gratings 503, 504. The bandwidth of the fiber bragg grating in the fiber fabry-perot resonator array 5 is greater than the bandwidth of the fiber bragg grating in the fiber bragg grating filter 2.
The second circulator 6 is used for outputting a reference path optical signal to the fiber bragg grating array 7, and a reflected signal reflected by the fiber bragg grating array 7 is output to the acousto-optic frequency shifter 8 through the second circulator 6.
The fiber grating array 7 is used for reflecting the reference path optical signal. Optical fiber grating arrayThe number and the center wavelength of the fiber gratings in the column 7 are correspondingly set according to the number and the center wavelength of the fiber grating groups in the fiber Fabry-Perot resonant cavity array 5, and the fiber gratings on the fiber grating array 7 and the fiber grating groups corresponding to the fiber gratings on the fiber Fabry-Perot resonant cavity array 5 have the same bandwidth and the same center wavelength. Specifically, the fiber grating array 7 includes 2 fiber grating groups which are located on the same fiber and are in one-to-one correspondence with 2 fiber grating groups on the fiber corresponding to the fiber fabry-perot resonator array 5, where the 2 center wavelengths are λ, respectively 1 And lambda (lambda) 2 Is provided, fiber gratings 701, 702 of (a).
The acousto-optic frequency shifter 8 is used for performing frequency shifting of light on the signal returned by the fiber grating array 7 to realize noise reduction.
An electrically adjustable optical fiber delay line 9 and a cavity length compensating optical fiber 10 form an optical fiber delay module which is arranged between the acousto-optic frequency shifter 8 and the second coupler 11. The electrically tunable optical fiber delay line 9 and the cavity length compensating optical fiber 10 are used to make small-amplitude precise and large-amplitude rough adjustments to the reference path optical fiber length to match the optical path difference between the reference path and the probe path, respectively.
The second coupler 11 is used for performing cavity length matching heterodyne interference on reflected light of the detection path and the reference path, and outputting interference signals.
The second erbium-doped fiber amplifier 12 and the optical attenuator 13 form an interference optical power adjusting device, and the interference optical power adjusting device is arranged between the second coupler 11 and the wavelength division multiplexing device 14 and is used for adjusting the optical power of interference light, so that the optical power works in the linear working areas of the photodetectors 15 and 16.
The wavelength division multiplexing device 14 is disposed between the interference optical power adjusting device and the photodetectors 15, 16, and is used for separating signal lights of different wavelengths and transmitting the signal lights to the photodetectors 15, 16, respectively, which process signals of corresponding wavelengths.
The photodetectors 15 and 16 are configured to detect beat signals of the interference signals of the detection path and the reference path, convert the photoelectric signals, and output the converted signals to the band-pass filter 17. The photodetector 15 is used for detecting a wavelength lambda 1 Is a signal light of (a) a signal light of (b). The photodetector 16 is used for detecting a wavelength lambda 2 Is a signal light of (a) a signal light of (b).
The band-pass filter 17 is used for filtering the frequency shift signal in the electric signal and extracting the radio frequency signal carrying the sensing phase shift information.
The real-time data acquisition module 18 is used for acquiring radio frequency signals in real time.
The data processing module 19 is used for processing the collected radio frequency signals, demodulating the interference signals, and obtaining the detection result of the heterodyne interference signals with high sensitivity cavity length matching of the broadband light source.
The high-sensitivity vibration sensing method using the broadband light source by using the high-sensitivity vibration sensing system using the broadband light source comprises the following steps:
the wide-spectrum light source module 1 emits wide-spectrum light, bandwidth filtering is carried out by the fiber bragg grating filter 2, power amplification is carried out by the first erbium-doped fiber amplifier 3, and the wide-spectrum light source module is divided into two paths of optical signals by the first coupler 4, wherein one path of optical signal is used as detection light to pass through a detection path, and the other path of optical signal is used as reference light to pass through a reference path;
the detection light is changed into a light beam with cavity length matching interference sensing information through the optical fiber Fabry-Perot resonant cavity array 5, and then reflected to be transmitted to the second coupler 11 through the first coupler 4;
the reference light enters the first port of the second circulator 6, and after the second port of the second circulator 6 exits and is reflected by the fiber grating array 7 to become a light beam with cavity length matching interference intrinsic information, the light beam exits from the third port of the second circulator 6 and is transmitted to the second coupler 11 through the acousto-optic frequency shifter 8 and the fiber delay module;
the detection light and the reference light generate cavity length matching heterodyne interference, output interference signals and realize the wavelength division multiplexing of the signals;
the output interference signals are subjected to power adjustment through an interference optical power adjusting device in sequence, photoelectric signal conversion is carried out by photoelectric detectors 15 and 16 after a wavelength division multiplexing device 14 is used, and a band-pass filter 17 is used for filtering frequency shift signals in the electric signals and extracting radio frequency signals carrying sensing phase shift information;
the real-time data acquisition module 18 and the data processing module 19 acquire and process the radio frequency signals, demodulate the interference signals, and obtain the detection result of the high-sensitivity cavity length matching heterodyne interference signals of the broadband light source.
Bandwidth delta lambda of broad spectrum light ASE The method meets the following conditions:
Δλ ASE ≥Δλ FBG1 +Δλ FBG2
wherein Deltalambda FBG1 ，Δλ FBG2 Representing the bandwidth of each fiber grating in the fiber grating array 7.
The bandwidth delta lambda of any fiber grating in the fiber grating array 7 FBG The method meets the following conditions:
Δλ FBG ≤λ FBG 2 /δL
wherein lambda is FBG Is the center wavelength of the corresponding fiber grating, taken from lambda 1 Or lambda 2 δL is the optical path difference between the heterodyne interference detection light and the reference light with matched cavity length.
The system in this embodiment realizes the process and principle of the high sensitivity fabry-perot Luo Zhendong sensing method using a broadband light source as follows:
the first coupler 4, the optical fiber Fabry-Perot resonant cavity array 5, the second circulator 6, the optical fiber grating array 7, the acousto-optic frequency shifter 8, the optical fiber delay module and the second coupler 11 form a cavity length matching interferometer. In this embodiment, the cavity length matching interferometer is designed in advance, and the interferometer adopts a Michelson type structure or a Mach-Zehnder type structure, and adopts a heterodyne interferometry.
The bandwidth of the broad spectrum light is narrowed after the broad spectrum light passes through the fiber grating filter 2, and the optical signal can be expressed as e=ae j[2πf+φ(t)] Wherein A is the amplitude corresponding to the transmitted optical signal, f is the center frequency of the fiber gratings 201 and 202, phi (t) is the initial phase, j is the imaginary unit, and the coherence length of the optical signal can be expressed asWherein Deltalambda FBG Is the bandwidth lambda of the fiber gratings 201, 202 FBG Is the center wavelength of the fiber gratings 201, 202, L FBG Is the coherence length of the optical signal after the broad spectrum light passes through the fiber gratings 201 and 202.
The optical signal is divided into two paths after passing through the first coupler 4, and one path of optical signal is used as reference light to pass throughThe reference optical signal is reflected by the fiber gratings 701 and 702, enters the third port of the second circulator 6, exits and is transmitted to the second coupler 11 through the acousto-optic frequency shifter 8 and the fiber delay module, and the frequency-shifted reference optical signal is represented as e=a' E at this time j[2π[(f+Δf)]+φ(t)] Wherein A' is the amplitude corresponding to the reference optical signal, Δf is the frequency shift of the acousto-optic frequency shifter 8, j is the imaginary unit, f is the center frequency of the fiber gratings 701 and 702, and φ (t) is the initial phase.
The other path of optical signal is used as detection light to pass through the detection path, when the optical signal passes through the detection path, the signal is reflected for multiple times in the optical fiber Fabry-Perot resonant cavity, and at the moment, the phase change of the n-order reflected light affected by vibration is changed intoIn (1) the->For sensing phase change, n is the number of reflections of the reflected light, j is the imaginary unit, β is the transmission constant, l FBG-FP For the optical fiber Fabry-Perot resonant cavity length, the expression of the optical signal reflected by the detection path and transmitted to the second coupler 11 is +.> Wherein A' is the amplitude corresponding to the detected light signal, j is the imaginary unit, f is the center frequency of the fiber gratings 501, 502, 503, 504, phi (t) is the initial phase,/">To sense phase changes.
In this embodiment, the length of the cavity length compensating fiber 10 in the reference path is changed to perform a large-amplitude rough adjustment, and the length of the reference path fiber is precisely changed by adjusting the electric adjustable fiber delay line 9 to a small amplitude, so that the cavity length matching heterodyne interferometry technique requires that the wide spectrum light will not interfere when passing through the sensing interferometerFor example, only when the optical path difference of the reference path and the detection path is close to the same, interference occurs, namely, the requirements are satisfied: ΔL<<L FBG Δl is the optical path difference between the reference path and the detection path, and with reference to fig. 1, it is required to satisfy L 2 ≈l 1 +2i×L FBG-FP And an optical path difference Δl= |l 2 -l 1 -2n×l FBG-FP |<<L FBG N is the reflection times of the optical fiber Fabry-Perot resonant cavity participating in interference, i=n+1, l 1 The Fabry-Perot array wavelength is lambda from the first coupler 4 for light 1 The distance l of the reflection of the fiber grating 501 to the second coupler 12 2 The wavelength lambda of the light emitted from the first coupler 4 and passing through the second circulator 6 is obtained by the fiber grating array 1 The distance from the fiber grating 701 to the second coupler 12 can be adjusted to improve the sensitivity of the system by adjusting the fiber delay module, and the light with different wavelengths is separated by the wavelength division multiplexing device 14.
The final interference optical signal can be expressed as: wherein Δf is the shift frequency of the acousto-optic frequency shifter 8, t is the time domain argument, phi (t) is the initial phase, < ->To sense the phase change, the electrical signal can be represented by the electrical signal after passing through the photodetectors 14, 15 and the band-pass filter 16>B is the amplitude of the alternating current item, and vibration signal information can be obtained according to the electric signal through signal demodulation processing.
The spectrum comparison chart of the optical interference output signals with different orders of the system in the embodiment is shown in fig. 2, and the experimental result shows that the application can well improve the signal-to-noise ratio and the sensitivity of the system, and further illustrates the feasibility of the system and the method.
Example 2
Referring to fig. 3 and 4, the high-sensitivity vibration sensing system using a broadband light source in the present embodiment is a hybrid multiplexing link of wavelength division multiplexing and time division multiplexing. The components and connection relationships of the system of this embodiment similar to those of embodiment 1 and fig. 1 are not described here again.
The optical fiber fabry-perot resonator array 5 of this embodiment includes a first optical fiber splitter 505 and 2 optical fibers connected to the first optical fiber splitter 505, 2 sets of optical fiber grating sets identical to those of embodiment 1 are independently provided on each optical fiber of the optical fiber fabry-perot resonator array 5, and time division multiplexing is achieved between the 2 optical fibers of the optical fiber fabry-perot resonator array 5 through a delay optical fiber 506.
The fiber bragg grating array 7 of the present embodiment includes a second fiber bragg splitter 703 and 2 fibers connected to the second fiber bragg splitter 703 and corresponding to each fiber in the fiber bragg grating array 5, where the number and the center wavelength of the fiber bragg gratings disposed on each fiber in the fiber bragg grating array 7 are set corresponding to the number and the center wavelength of the fiber bragg grating groups on the corresponding fiber in the fiber bragg grating array 5, and time division multiplexing consistent with the fiber bragg grating array 5 is implemented between 2 fibers of the fiber bragg grating array 7 through the delay fiber 506.
The working principle of the optical path structure of this embodiment is the same as that of embodiment 1, and detailed description thereof is omitted. It should be specifically noted that, unlike embodiment 1, the broad spectrum light source module 1 of this embodiment adopts a pulse form: referring to fig. 4, a broad spectrum continuous light is emitted from a broad spectrum light source 101, and an arbitrary signal generator 102 generates a periodic pulse signal to a pulse modulation device 103, and becomes a broad spectrum pulse signal when the broad spectrum continuous light passes through the pulse modulation device 103.
Further, it is to be understood that various changes and modifications of the present application may be made by those skilled in the art after reading the above description of the application, and that such equivalents are intended to fall within the scope of the application as defined in the appended claims.
Claims (10)
1. A high sensitivity vibration sensing system employing a broadband light source, comprising:
a broad spectrum light source module (1) for emitting broad spectrum light;
the fiber grating filter (2) is used for bandwidth filtering of broad spectrum light and comprises a first circulator (203), wherein the first circulator (203) is used for outputting the broad spectrum light to one or more fiber gratings with different center wavelengths and the same bandwidth, which are positioned on the same fiber, and the reflected broad spectrum light is output through the first circulator (203);
the first coupler (4) is used for dividing the wide-spectrum light subjected to bandwidth filtering into two paths of optical signals, wherein one path of optical signal is used as detection light to pass through the detection path, and the other path of optical signal is used as reference light to pass through the reference path;
the optical fiber Fabry-Perot resonant cavity array (5) comprises a plurality of groups of optical fiber grating groups and is used for reflecting the detection path optical signals for a plurality of times, and the reflected signals are transmitted to the second coupler (11) through the first coupler (4); each group of fiber bragg grating groups in the fiber Fabry-Perot resonant cavity array (5) consists of a pair of fiber bragg gratings with the same bandwidth and center wavelength; the number and the center wavelength of the fiber bragg grating groups on each fiber in the fiber Fabry-Perot resonant cavity array (5) are correspondingly set according to the number and the center wavelength of the fiber bragg gratings in the fiber bragg grating filter (2); the fiber grating group on each fiber in the fiber Fabry-Perot resonant cavity array (5) and the corresponding fiber grating in the fiber grating filter (2) have the same central wavelength; the bandwidth of the fiber bragg grating in the fiber Fabry-Perot resonant cavity array (5) is larger than that of the fiber bragg grating in the fiber bragg grating filter (2);
the second circulator (6) is used for outputting a reference path optical signal to the fiber bragg grating array (7), and a reflected signal reflected by the fiber bragg grating array (7) is output to the acousto-optic frequency shifter (8) through the second circulator (6);
the optical fiber grating array (7) comprises a plurality of optical fiber gratings and is used for reflecting the reference path optical signals; the optical fibers in the fiber bragg grating array (7) are arranged in one-to-one correspondence with the optical fibers in the fiber fabry-perot resonant cavity array (5); the number and the central wavelength of the fiber bragg gratings on each fiber in the fiber bragg grating array (7) are correspondingly set according to the number and the central wavelength of the fiber bragg grating groups on the corresponding fiber in the fiber bragg fabry-perot resonant cavity array (5); the fiber grating in the fiber grating array (7) and the fiber grating group corresponding to the fiber grating in the fiber Fabry-Perot resonant cavity array (5) have the same bandwidth and center wavelength;
the acousto-optic frequency shifter (8) is used for carrying out frequency shifting of light on signals returned by the fiber grating array (7) to realize noise reduction;
the optical fiber delay module comprises an electric adjustable optical fiber delay line (9) and a cavity length compensation optical fiber (10), is arranged between the acousto-optic frequency shifter (8) and the second coupler (11) and is used for performing small-amplitude accurate and large-amplitude rough adjustment on the length of the optical fiber of the reference path so as to match the optical path difference between the reference path and the detection path;
the second coupler (11) is used for performing cavity length matching heterodyne interference on reflected light of the detection path and the reference path and outputting interference signals;
the interference light power adjusting device is arranged between the second coupler (11) and the photoelectric detector and is used for adjusting the light power of the interference light so that the light power works in a linear working area of the photoelectric detector;
the photoelectric detectors are used for detecting beat frequency signals of interference signals of the detection path and the reference path, converting photoelectric signals and outputting the photoelectric signals to the band-pass filter (17); the number of the photoelectric detectors is consistent with the number of the types of the central wavelengths of the fiber gratings in the fiber grating filter (2), the fiber grating group in the fiber Fabry-Perot resonant cavity array (5) and the fiber gratings in the fiber grating array (7);
the band-pass filter (17) is used for filtering frequency-shift signals in the electric signals and extracting radio-frequency signals carrying sensing phase-shift information;
the real-time data acquisition module (18) is used for acquiring radio frequency signals in real time;
and the data processing module (19) is used for processing the acquired radio frequency signals, demodulating the interference signals and obtaining the detection result of the heterodyne interference signals with the high-sensitivity cavity length matching of the broadband light source.
2. The high sensitivity vibration sensing system using a broadband light source according to claim 1, wherein a first erbium-doped fiber amplifier (3) for amplifying power of a broad spectrum light is provided between the fiber grating filter (2) and the first coupler (4).
3. The high sensitivity vibration sensing system employing a broadband light source according to claim 1, wherein the interferometric optical power adjustment means comprises a second erbium doped fiber amplifier (12) and an optical attenuator (13).
4. The high-sensitivity vibration sensing system using a broadband light source according to claim 1, wherein the fiber grating filter (2) comprises a plurality of fiber gratings with different center wavelengths and same bandwidths on the same fiber;
each optical fiber of the optical fiber Fabry-Perot resonant cavity array (5) is provided with a plurality of groups of optical fiber grating groups with different center wavelengths, which are in one-to-one correspondence with the optical fiber gratings in the optical fiber grating filter (2);
each optical fiber of the optical fiber grating array (7) is provided with a plurality of optical fiber gratings with different center wavelengths, which are in one-to-one correspondence with the optical fiber gratings in the optical fiber grating filter (2);
a wavelength division multiplexing device (14) is arranged between the interference optical power adjusting device and the photoelectric detector and is used for separating signal lights with different wavelengths and transmitting the signal lights to the photoelectric detector for processing signals with corresponding wavelengths respectively.
5. The high-sensitivity vibration sensing system adopting the broadband light source according to claim 1, wherein the optical fiber fabry-perot resonant cavity array (5) comprises a first optical fiber beam splitter (505) and a plurality of optical fibers connected with the first optical fiber beam splitter (505), a plurality of groups of optical fiber grating groups are respectively and independently arranged on each optical fiber of the optical fiber fabry-perot resonant cavity array (5), and time division multiplexing is realized among the optical fibers of the optical fiber fabry-perot resonant cavity array (5) through delay optical fibers;
the fiber grating array (7) comprises a second fiber beam splitter (703) and a plurality of fibers which are connected with the second fiber beam splitter (703) and are in one-to-one correspondence with the fibers in the fiber Fabry-Perot resonant cavity array (5), the number and the center wavelength of the fiber gratings on each fiber in the fiber grating array (7) are correspondingly set according to the number and the center wavelength of the fiber grating groups on the corresponding fibers in the fiber Fabry-Perot resonant cavity array (5), and the time division multiplexing consistent with the fiber Fabry-Perot resonant cavity array (5) is realized among the fibers of the fiber grating array (7) through delay fibers.
6. The high-sensitivity vibration sensing system using a broadband light source according to claim 5, wherein the fiber grating filter (2) comprises a plurality of fiber gratings with different center wavelengths and same bandwidths on the same fiber;
each optical fiber of the optical fiber Fabry-Perot resonant cavity array (5) is provided with a plurality of groups of optical fiber grating groups with different center wavelengths, which are in one-to-one correspondence with the optical fiber gratings in the optical fiber grating filter (2);
each optical fiber of the optical fiber grating array (7) is provided with a plurality of optical fiber gratings with different center wavelengths, which are in one-to-one correspondence with the optical fiber gratings in the optical fiber grating filter (2);
a wavelength division multiplexing device (14) is arranged between the interference optical power adjusting device and the photoelectric detector and is used for separating signal lights with different wavelengths and transmitting the signal lights to the photoelectric detector for processing signals with corresponding wavelengths respectively.
7. The high sensitivity vibration sensing system using a broadband light source according to claim 5 or 6, wherein the broad spectrum light is pulsed light.
8. The high sensitivity vibration sensing system employing a broadband light source according to claim 1, wherein the bandwidth of the broad spectrum light Δλ ASE The method meets the following conditions:
Δλ ASE ≥Δλ FBG1 +…+Δλ FBGn
wherein n is a positive integer, Δλ FBG1 ，…，Δλ FBGn Representing the bandwidth of each fiber grating in the fiber grating array (7).
9. The high-sensitivity vibration sensing system using a broadband light source according to claim 1, wherein any one of the fiber bragg grating filter (2), the fiber fabry-perot resonator array (5), and the fiber bragg grating array (7) has a fiber bragg grating bandwidth Δλ FBG The method meets the following conditions:
Δλ FBG ≤λ FBG 2 /δL
wherein lambda is FBG And delta L is the optical path difference between the heterodyne interference detection light and the reference light matched with the cavity length for the central wavelength of the corresponding fiber bragg grating.
10. A high-sensitivity vibration sensing method using a broadband light source, characterized in that the high-sensitivity vibration sensing system using a broadband light source according to any one of claims 1 to 9 is employed;
the high-sensitivity vibration sensing method adopting the broadband light source comprises the following steps:
the wide-spectrum light source module (1) emits wide-spectrum light, bandwidth filtering is carried out through the fiber bragg grating filter (2), and then the wide-spectrum light source module is divided into two paths of optical signals after passing through the first coupler (4), one path of optical signal is used as detection light to pass through the detection path, and the other path of optical signal is used as reference light to pass through the reference path;
the detection light is changed into a light beam with cavity length matching interference sensing information through an optical fiber Fabry-Perot resonant cavity array (5), and then reflected to be transmitted to a second coupler (11) through a first coupler (4);
the reference light enters a first port of a second circulator (6), and after exiting from the second port of the second circulator (6) and being reflected by a fiber bragg grating array (7) to become a light beam with cavity length matching interference intrinsic information, the light beam exits from a third port of the second circulator (6) and is transmitted to a second coupler (11) through an acousto-optic frequency shifter (8) and a fiber delay module;
the detection light and the reference light generate heterodyne interference with matched cavity length, and an interference signal is output;
the output interference signals are subjected to power adjustment through an interference light power adjusting device, photoelectric signals of a photoelectric detector are converted, and a band-pass filter (17) filters frequency shift signals in the electric signals to extract radio frequency signals carrying sensing phase shift information;
the real-time data acquisition module (18) and the data processing module (19) acquire and process the radio frequency signals, demodulate the interference signals and obtain the detection result of the high-sensitivity cavity length matching heterodyne interference signals of the broadband light source.
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