CN118032026A - White light interference detection and multiplexing system and method with flying strain resolution magnitude - Google Patents
White light interference detection and multiplexing system and method with flying strain resolution magnitude Download PDFInfo
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Abstract
The invention discloses a system and a method for detecting and multiplexing white light interference of a flying strain resolution level, which utilize the characteristic of small coherence length of white light, and realize the effect of improving the phase change and the sensitivity of a system by heterodyne interference of multiple reflected light and primary reflected light in a fiber bragg grating group by adjusting the delay parameter of an optical fiber; meanwhile, a new interferometer demodulates a low-order interference light result to be used as a reference of a high-order interference light, so that the overall noise floor of the system is reduced. Finally, the advantages of wide white light spectrum and wavelength selectivity of the fiber bragg grating are fully utilized, and the large-scale array sensing which can be multiplexed, has high resolution and low cost is realized on one or more optical fibers.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to a system and a method for detecting and multiplexing white light interference of a flying strain resolution level.
Background
Compared with the traditional electronic sensor, the optical fiber sensor has the advantages of low long-distance transmission loss, light weight, electromagnetic interference resistance, corrosion resistance and the like, and can measure various physical quantities such as temperature, pressure, refractive index, acceleration and the like, so that the optical fiber sensor has wide application in the fields of mineral exploration, electric power systems, aerospace, medical biology and the like.
The optical fiber sensor is mainly classified into a phase modulation type, an intensity modulation type, a wavelength modulation type, and the like, and the phase modulation type optical fiber sensor is widely focused due to the advantages of higher sensitivity, and the like. When the photosensitive component is affected by external vibration, the phase of the light wave can be changed, and the vibration signal can be obtained by detecting the returned phase change amount.
Common phase modulation type sensors include michelson interferometers, fabry-perot interferometers, sagnac interferometers, etc., which may be used in conjunction with each other in actual engineering. Along with the continuous development and perfection of vibration testing technology and the expansion of application requirements of high-precision and high-sensitivity testing, the development of vibration sensors with high resolution, small volume and easy networking is one of the current and future development trends.
In the prior art, a sensing detection system reaching the flying strain resolution level needs to be realized by means of expensive narrow-linewidth lasers and even ultra-narrow-linewidth lasers, and meanwhile, due to the single wavelength characteristic, a wavelength division multiplexing sensing system is not compatible with the narrow-linewidth lasers, and the number of lasers is often required to be increased to realize multiplexing of the sensors. Although white light has the advantages of wide spectrum range and low cost, the existing white light sensing detection system which mainly uses the white light to drive is mainly of the skin or nano strain resolution magnitude (Geoffrey A.Cranch,Efficient Fiber Bragg Grating and Fiber Fabry–Pérot Sensor Multiplexing Scheme Using a Broadband Pulsed Mode-Locked Laser[J],Journal of Lightwave Technology,2005,23(11),3798-3807). and has ultrahigh resolution cannot well realize large-scale sensing (Shuting Liu,Ultrahigh-resolution and ultra-simple fiber-optic sensor with resonant Sagnac interferometer[J],Optics Letters,2023,48(13),3543-3546). due to the limitations of a sensing unit and closed loop control, and in addition, in practical application, the background noise level of the system is improved due to phase noise introduced by factors such as environmental interference, path fiber jitter and the like, so that the detection resolution of the system is limited.
The applicant has previously developed a high sensitivity vibration sensing system and method employing a broadband light source (see patent specification publication CN 117029995A) that can achieve a skin strain resolution level that is yet to be improved.
The existing optical fiber sensing vibration system and method are difficult to simultaneously consider the characteristics of low cost, high resolution and wavelength division multiplexing. Therefore, there is a need to develop a system and detection method that combines the above characteristics to improve the signal detection capabilities of fiber optic sensing systems and arrays.
Disclosure of Invention
The invention provides a system and a method for detecting and multiplexing white light interference of a flying strain resolution level, which utilize the characteristic of small coherent length of white light, and realize the effect of improving the phase change and the sensitivity of a system by heterodyne interference of multiple reflected light and primary reflected light in a fiber bragg grating group by adjusting the delay parameter of an optical fiber; meanwhile, a new interferometer demodulates a low-order interference light result to be used as a reference of a high-order interference light, so that the overall noise floor of the system is reduced. Finally, the advantages of wide white light spectrum and wavelength selectivity of the fiber bragg grating are fully utilized, and the large-scale array sensing which can be multiplexed, has high resolution and low cost is realized on one or more optical fibers.
A system for white light interferometry detection and multiplexing of the order of magnitude of femtostrain resolution, comprising:
The white light source module is used for emitting wide-spectrum light;
The fiber grating filter is used for carrying out bandwidth filtering on wide-spectrum light and comprises a first circulator and a fiber grating array; the fiber grating array comprises one or more fiber gratings with different center wavelengths and the same bandwidth, which are positioned on the same fiber; the first circulator is used for transmitting the broad spectrum light to the fiber bragg grating array, and the reflected broad spectrum light is output through the first circulator;
A sensor element array for reflecting and transmitting light waves carrying reference and sensor signals, comprising a second circulator; the second circulator is connected with an optical fiber or is connected with a plurality of optical fibers which realize time division multiplexing through a delay optical fiber through an optical fiber beam splitter, the optical fibers are all provided with optical fiber grating groups, each optical fiber grating group consists of a pair of optical fiber gratings with the same bandwidth and center wavelength, the number and the center wavelength of the optical fiber grating groups on the same optical fiber are correspondingly arranged according to the number and the center wavelength of the optical fiber gratings in the optical fiber grating array, and the bandwidth of the optical fiber gratings in the optical fiber grating groups is larger than that of the optical fiber gratings in the optical fiber grating array; the bandwidth filtered light wave enters from the second circulator, is reflected by the fiber bragg grating group, and is output by the second circulator;
The first coupler is used for dividing the reflected light waves into two paths of optical signals, wherein one path of optical signals is used as detection light to pass through the detection path, and the other path of optical signals is used as reference light to pass through the reference path; the detection light consists of light waves reflected for many times inside each fiber bragg grating group; the reference light consists of light waves reflected once by a first fiber grating in each fiber grating group;
The acousto-optic frequency shifter is arranged between the first coupler and the reference path beam splitting coupler and is used for shifting the frequency of the reference path light wave to remove zero frequency noise;
The reference path beam splitting coupler and the detection path beam splitting coupler are respectively used for dividing reference path light waves and detection path light waves into two groups of high-order light signals and low-order light signals, wherein the low-order light signals of the reference path and the detection path enter the low-order light interferometer to detect low-order sensing light signals, and the high-order light signals of the reference path and the detection path enter the high-order light interferometer to detect high-order sensing light signals;
the optical fiber delay module is arranged between the reference path beam-splitting coupler and the third coupler and comprises a first optical path compensation optical fiber, a first electric adjustable optical fiber delay line and a second optical path compensation optical fiber and a second electric adjustable optical fiber delay line of the high-order optical interferometer, wherein the first optical path compensation optical fiber and the second optical path compensation optical fiber are respectively used for performing large-amplitude rough adjustment on the optical paths of the high-order optical interferometer and the low-order optical interferometer, and the first electric adjustable optical fiber delay line and the second electric adjustable optical fiber delay line are respectively used for performing small-amplitude accurate adjustment on the optical paths of the high-order optical interferometer and the low-order optical interferometer so as to match the optical path difference between the reference path and the detection path;
A third coupler comprising a high order optical interference coupler and a low order optical interference coupler; the high-order optical interference coupler and the low-order optical interference coupler are respectively used for performing optical path matching heterodyne interference on the high-order optical signal and the low-order optical signal, and outputting the high-order interference optical signal and the low-order interference optical signal;
the photoelectric detectors are respectively used for detecting high-order and low-order interference light beat frequency signals of corresponding wavelengths and converting photoelectric signals; the number of the photoelectric detectors is twice the number of the types of the central wavelengths of the fiber bragg gratings in the fiber bragg grating array;
The real-time data acquisition and processing module is connected with the photoelectric detector and used for acquiring and processing radio frequency signals in real time, demodulating interference signals to obtain detection results of corresponding wavelength high-order and low-order heterodyne interference signals, and taking low-order interference as a reference item of high-order interference to perform noise reduction processing.
In the white light interference detection and multiplexing system with the flying strain resolution, the reference light signal and the sensing light signal can be reflected and transmitted on the same optical fiber of the sensing element array.
The wide-spectrum light can be wide-spectrum continuous light or wide-spectrum pulse light.
The first erbium-doped fiber amplifier for amplifying and adjusting the optical power of the bandwidth-filtered light wave can be arranged between the fiber grating filter and the sensor array.
The wavelength division multiplexing device can be arranged among the high-order optical interference coupler, the low-order optical interference coupler and the photoelectric detector and is used for separating interference optical signals with different wavelengths and respectively transmitting the interference optical signals to the photoelectric detector for processing signals with corresponding wavelengths.
The high-order optical interference coupler, the low-order optical interference coupler and the wavelength division multiplexing device can be provided with a second erbium-doped optical fiber amplifier which is used for amplifying and adjusting the optical power of the high-order and low-order interference optical signals so as to match the saturated input optical power of the photoelectric detector.
The white light source module can be driven by a broadband light source, and the broadband light source can be an SLD, ASE or LED light source.
In one embodiment, the bandwidth Δλ ASE of the broad spectrum light of the white light interference detection and multiplexing system with the flying strain resolution level satisfies the following conditions:
△λASE≥ΔλFBG1+…+ΔλFBGn
Wherein n is a positive integer, and Deltalambda FBG1,…,ΔλFBGn represents the bandwidths of all the fiber gratings on the same fiber in the sensor array.
In an embodiment, the white light interference detection and multiplexing system with the flying strain resolution level adjusts the optical path length so that the optical path length difference satisfies δl:
δL≤λFBG 2/ΔλFBG
Wherein lambda FBG is the center wavelength of the corresponding fiber grating, and delta lambda FBG is the bandwidth of any fiber grating in the fiber grating filter and the sensor array.
The optical fiber grating can be any one or a combination of a plurality of phase shift optical fiber gratings, uniform optical fiber Bragg gratings and apodized optical fiber gratings.
The invention relates to a white light interference detection and multiplexing system with the flying strain resolution level, and the sensing system can be used for time division multiplexing, wave division multiplexing or time division and wave division mixed multiplexing demodulation. The sensing system adopts pulse light as the white light source module in time division multiplexing and continuous light or pulse light in other cases. The pulsed light can be generated by modulating white light by any pulse modulation device such as a Semiconductor Optical Amplifier (SOA), an acousto-optic modulator, an electro-optic modulator and the like.
The invention relates to a white light interference detection and multiplexing system with the flying strain resolution level, which comprises a sensing element array, a first coupler, an acousto-optic frequency shifter, a second coupler (comprising a reference path beam splitting coupler and a detection path beam splitting coupler), an optical fiber delay module and a third coupler, wherein the optical path matching interferometer can adopt a Michelson structure or a Mach-Zehnder structure, and adopts a heterodyne interferometry method, so that the optical path length of primary reflected light of a reference path fiber grating is approximately consistent with the optical path length of multiple reflected light of a fiber grating in the detection path by adjusting the optical path compensation fiber length in the reference path, thereby realizing the improvement of sensitivity.
The invention relates to a white light interference detection and multiplexing system with the magnitude of the flying strain resolution, which is characterized in that a low-order interferometer is arranged for detecting a low-order sensing light signal, a high-order interferometer is arranged for detecting a high-order sensing light signal, the low-order interference light is used as a reference group of the high-order interference light, and broadband noise with weak correlation between the low-order interference light and the high-order interference light sensing is eliminated based on the periodic difference of random noise and vibration signals, and meanwhile, the vibration signal with strong correlation is reserved.
A method for detecting and multiplexing the white light interference of the magnitude of the flying strain resolution adopts the white light interference detection and multiplexing system of the magnitude of the flying strain resolution;
The method for detecting and multiplexing the white light interference of the flying strain resolution level comprises the following steps:
The white light source module emits wide-spectrum light, bandwidth filtering is carried out through the fiber bragg grating filter, then the light wave enters from the first port of the second circulator through the sensor array, the light wave exits from the second port of the second circulator and is reflected by the fiber bragg grating group, the light exits from the third port of the second circulator and passes through the first coupler to be divided into two paths of optical signals, one path of optical signal serves as detection light to pass through the detection path, and the other path of optical signal serves as reference light to pass through the reference path;
The detection light consists of light waves reflected for many times inside each fiber grating group, the light waves pass through the first coupler and are divided into two light beams by the detection path beam splitting coupler after passing through the first coupler, one light beam participates in low-order light interference transmission to the low-order light interference coupler, and one light beam participates in high-order light interference transmission to the high-order light interference coupler;
The reference light consists of light waves reflected once by a first fiber grating in each fiber grating group, no sensing signal is carried, the reference light is subjected to frequency shift by an acousto-optic frequency shifter in a reference path after passing through a first coupler, and then is divided into two beams of light through a reference path beam splitting coupler, one beam of light participates in low-order light interference, the light path of the low-order light interferometer is matched and regulated by a second optical path compensation fiber and a second electrically adjustable fiber delay line and then is transmitted to the low-order light interference coupler, and the light beam participates in high-order light interference and is transmitted to the high-order light interference coupler after being matched and regulated by a first optical path compensation fiber and a first electrically adjustable fiber delay line;
optical path matching heterodyne interference is generated between detection light and reference light of the high-order interferometer and the low-order interferometer, and interference signals are output;
the output interference signal is converted into a photoelectric signal by a photoelectric detector;
The real-time data acquisition and processing module acquires and processes the radio frequency signals in real time, demodulates the interference signals to obtain detection results of corresponding wavelength high-order and low-order heterodyne interference signals, and performs noise reduction processing by taking the low-order interference as a reference item of the high-order interference.
In an embodiment, in the method for detecting and multiplexing the white light interference of the flying strain resolution level, the output interference signals sequentially pass through the second erbium-doped fiber amplifier to be amplified and adjusted, the wavelength division multiplexing device separates signal lights with different wavelengths, and photoelectric signals of the photoelectric detector are converted.
The invention provides a system and a method for detecting and multiplexing white light interference of a flying strain resolution level, which can solve the problems in the background art that: 1) High resolution sensing systems rely on expensive narrow linewidth and even ultra-narrow linewidth lasers, which are incompatible in wavelength division multiplexed sensing systems due to single wavelength characteristics; 2) The white light driving type sensing system has higher noise level and can not fully develop the problem of the wavelength division multiplexing potential of the white light; 3) Noise caused by path optical fiber disturbance and the like in the practical application process is reduced.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention selects a low-cost broadband light source to replace an expensive narrow linewidth laser for sensing detection, realizes the detection of high-order interference light signals in the fiber bragg grating group by precisely controlling the optical path difference of the interferometer, improves the sensitivity of the system and reduces the cost of the system.
2. According to the invention, by arranging the low-order interferometer, the low-order interference light signal is utilized to perform noise elimination on the detection of the high-order interference light signal, so that the noise level of the sensing system is reduced, and the vibration resolution of the system is increased to the flying strain level.
3. The invention etches a plurality of fiber grating groups on one or a plurality of optical fibers, realizes the time division wavelength division mixed multiplexing array detection of a plurality of sensing units, and simultaneously eliminates most path interference by utilizing a mode that reference light and sensing light share the optical path as much as possible.
Drawings
FIG. 1 is a schematic diagram of a system for detecting and multiplexing white light interferometry of the magnitude of the femto-strain resolution of embodiment 1;
FIG. 2 is a graph showing the comparison of strain resolution of optical interference output signals of different orders in the sensor system of example 1;
FIG. 3 is a graph showing the effects of example 1 before and after noise reduction using a low-order interferometer;
FIG. 4 is a strain resolution spectrum of the WDM system of example 1;
Fig. 5 is a diagram showing an optical path configuration of time-division multiplexing and wavelength-division multiplexing in example 2.
Detailed Description
The invention 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 invention and are not intended to limit the scope of the present invention.
Example 1
Referring to fig. 1, a white light interference detection and multiplexing system with a flying strain resolution level includes a white light source module 1, a fiber grating filter 2, a first erbium-doped fiber amplifier 3, a sensor array 4, a first coupler 5, an acousto-optic frequency shifter 6, a second coupler 7, a fiber delay module 8, a third coupler 9, a second erbium-doped fiber amplifier 10, a wavelength division multiplexing device 11, a photodetector 12, and a real-time data acquisition and processing module 13. The second coupler 7 includes a reference path beam-splitting coupler 701 and a probe path beam-splitting coupler 702.
The white light source module 1 is for emitting a wide spectrum of light. The broad spectrum light may be broad spectrum continuous light or broad spectrum pulsed light.
The fiber grating filter 2 is used for bandwidth filtering of broad spectrum light, and comprises a first circulator 201 and a fiber grating array. The fiber grating array includes 2 fiber gratings 202, 203 of the same bandwidth at different center wavelengths on the same fiber. The first circulator 201 is used for transmitting the broad spectrum light to the fiber grating array, and the reflected broad spectrum light is output through the first circulator 201.
The first erbium-doped fiber amplifier 3 is arranged between the fiber grating filter 2 and the sensor array 4, and is used for amplifying and adjusting the optical power of the optical wave after bandwidth filtering.
The sensor element array 4 is used for reflecting and transmitting light waves carrying reference and sensor signals, and comprises a second circulator 401. The second circulator 401 is connected with an optical fiber, and 2 fiber grating groups are arranged on the optical fiber, each fiber grating group consists of a pair of fiber gratings 402, 403 or 404 and 405 with the same bandwidth and central wavelength, the central wavelengths of the fiber grating groups are correspondingly arranged according to the central wavelengths of the fiber gratings in the fiber grating array, and the bandwidth of the fiber gratings in the fiber grating groups is larger than that of the fiber gratings in the fiber grating array. The bandwidth-filtered light waves enter from the second circulator 401, are reflected by the fiber grating group, and the reflected light waves are output by the second circulator 401.
The first coupler 5 is configured to split the reflected light wave into two optical signals, one of which is used as a probe light and passes through the probe path, and the other of which is used as a reference light and passes through the reference path. The detection light consists of light waves reflected by the inside of each fiber bragg grating group for multiple times. The reference light is composed of light waves reflected once by the first fiber grating in each fiber grating group.
An acousto-optic frequency shifter 6 is disposed between the first coupler 5 and the reference path beam-splitting coupler 701, and is used for frequency shifting the reference path optical wave to remove zero frequency noise.
The reference path beam splitting coupler 701 and the detection path beam splitting coupler 702 are respectively used for splitting reference path light and detection path light into two groups of high-order and low-order optical signals, wherein the low-order optical signals of the reference path and the detection path enter the low-order optical interferometer to detect the low-order sensing optical signals, and the high-order optical signals of the reference path and the detection path enter the high-order optical interferometer to detect the high-order sensing optical signals.
The optical fiber delay module 8 is disposed between the reference path beam-splitting coupler 701 and the third coupler 9, and includes a first optical path compensating fiber 801 of the high-order optical interferometer, a first electrically tunable optical fiber delay line 802, a second optical path compensating fiber 803 of the low-order optical interferometer, and a second electrically tunable optical fiber delay line 804. The first optical path compensating fiber 801 and the second optical path compensating fiber 803 are respectively used for performing rough adjustment on the optical paths of the high-order optical interferometer and the low-order optical interferometer to a large extent, and the first electrically adjustable optical fiber delay line 802 and the second electrically adjustable optical fiber delay line 804 are respectively used for performing precise adjustment on the optical paths of the high-order optical interferometer and the low-order optical interferometer to a small extent so as to match the optical path difference between the reference path and the detection path.
The third coupler 9 includes a high-order optical interference coupler 901 and a low-order optical interference coupler 902. The high-order optical interference coupler 901 and the low-order optical interference coupler 902 are respectively used for performing optical path matching heterodyne interference on the high-order optical signal and the low-order optical signal, and outputting the high-order interference optical signal and the low-order interference optical signal.
The second erbium-doped fiber amplifier 10 is disposed between the high-order optical interference coupler 901, the low-order optical interference coupler 902 and the wavelength division multiplexing device 11, and is used for amplifying and adjusting the optical power of the high-order and low-order interference optical signals to match the saturated input optical power of the photodetector 12.
The wavelength division multiplexing device 11 is disposed between the second erbium doped fiber amplifier 10 and the photodetector 12, and is used for separating interference optical signals of different wavelengths and transmitting the interference optical signals to the photodetector 12 for processing signals of corresponding wavelengths, respectively.
The number of the photodetectors 12 is twice the number of the types of the central wavelengths of the fiber gratings in the fiber grating array, and the photodetectors are respectively used for detecting the beat frequency signals of the high-order interference light and the low-order interference light of the corresponding wavelengths and converting the photoelectric signals.
The real-time data acquisition and processing module 13 is connected with the photoelectric detector 12 and is used for acquiring and processing radio frequency signals in real time, demodulating interference signals to obtain detection results of corresponding wavelength high-order and low-order heterodyne interference signals, and taking low-order interference as a reference item of high-order interference to perform noise reduction processing.
In the white light interference detection and multiplexing system with the flying strain resolution, the reference light signal and the sensing light signal can be reflected and transmitted on the same optical fiber of the sensing element array.
The method for performing the white light interference detection and multiplexing of the flying strain resolution level by adopting the white light interference detection and multiplexing system of the flying strain resolution level comprises the following steps:
The white light source module 1 emits wide-spectrum light, bandwidth filtering is carried out by the fiber bragg grating filter 2, then the sensing element array 4 is carried out, light waves are incident from a first port of the second circulator 401, the light waves are reflected by the fiber bragg grating group at the second port of the second circulator 401, the light waves are emitted from a third port of the second circulator 401 and are divided into two paths of optical signals after passing through the first coupler 5, one path of optical signals is used as detection light, the other path of optical signals is used as reference light, and the other path of optical signals passes through the reference path;
The detection light consists of light waves reflected for many times inside each fiber grating group, the light waves pass through the first coupler 5 and are divided into two light beams by the detection path beam splitting coupler 702 after passing through the first coupler 5, one light wave participates in low-order light interference transmission to the low-order light interference coupler 902, and one light wave participates in high-order light interference transmission to the high-order light interference coupler 901;
The reference light consists of light waves reflected once by the first fiber grating in each fiber grating group, does not carry sensing signals, is shifted in frequency by the acousto-optic frequency shifter 6 in the reference path after passing through the first coupler 5, is split into two beams of light after passing through the reference path beam splitting coupler 701, one beam of light participates in low-order light interference, the optical path of the interferometer of the low-order light is matched and adjusted through the second optical path compensation optical fiber 803 and the second electrically adjustable optical fiber delay line 804 and then transmitted to the low-order optical interference coupler 902, one beam of light participates in the high-order light interference, and the optical path of the interferometer of the high-order light is matched and adjusted through the first optical path compensation optical fiber 801 and the first electrically adjustable optical fiber delay line 802 and then transmitted to the high-order optical interference coupler 901;
optical path matching heterodyne interference is generated between detection light and reference light of the high-order interferometer and the low-order interferometer, and interference signals are output;
The output interference signals are sequentially subjected to power amplification and adjustment through a second erbium-doped fiber amplifier 10, signal lights with different wavelengths are separated by a wavelength division multiplexing device 11, and photoelectric signals of a photoelectric detector 12 are converted;
the real-time data acquisition and processing module 13 acquires and processes the radio frequency signals in real time, demodulates the interference signals to obtain detection results of the corresponding wavelength high-order heterodyne interference signals and low-order heterodyne interference signals, and performs noise reduction processing by taking the low-order interference as a reference item of the high-order interference.
The white light source module 1 may be a broadband light source driving, which may be an SLD, ASE or LED light source.
The bandwidth Δλ ASE of the broad spectrum light satisfies:
ΔλASE≥ΔλFBG1+…+ΔλFBGn
wherein n is a positive integer, and Δλ FBG1,…,ΔλFBGn represents the bandwidths of all fiber gratings on the same fiber in the sensor array 4.
The optical path length is adjusted so that the optical path difference satisfies δl:
δL≤λFBG 2/ΔλFBG
Wherein lambda FBG is the center wavelength of the corresponding fiber grating, delta lambda FBG is the bandwidth of any fiber grating of the fiber grating filter 2 and the sensor array 4.
The fiber grating may be any one or a combination of a plurality of phase shift fiber gratings, uniform fiber Bragg gratings and apodized fiber gratings.
The system in this embodiment realizes the process and principle of adopting the high-resolution white light interference detection and multiplexing method as follows:
the optical path matching high-order optical sensing interferometer is composed of a sensing element array 4, a first coupler 5, an acousto-optic frequency shifter 6, a second coupler 7, a first optical path compensation optical fiber 801, a first electrically adjustable optical fiber delay line 802 and a high-order optical interference coupler 901.
The sensor array 4, the first coupler 5, the acousto-optic frequency shifter 6, the second coupler 7, the second optical path compensation fiber 803, the second electrically tunable optical fiber delay line 804 and the low-order optical interference coupler 902 form an optical path matching low-order optical reference interferometer.
In this embodiment, the optical path 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 wide spectrum light is narrowed after passing through the fiber grating filter 2, and the light wave is divided into two types of light waves after passing through the sensor array 4.
The reference light wave is reflected once only by a first fiber grating of the same group, does not carry a sensing signal, is a reference light wave, is subjected to frequency shift by an acousto-optic frequency shifter 6 after passing through a reference path, is divided into two beams of light after passing through a reference path beam splitting coupler 701, one beam of light participates in low-order light interference, is transmitted to a low-order light interference coupler 902 after being subjected to optical path matching adjustment of a low-order light interferometer through a second optical path compensation optical fiber 803 and a second electrically adjustable optical fiber delay line 804, and is transmitted to the high-order light interference coupler 901 after being subjected to optical path matching adjustment of a high-order light interferometer through a first optical path compensation optical fiber 801 and a first electrically adjustable optical fiber delay line 802. The reference optical signal is represented by e=a ′ej[ pi [ (f+Δf) ]+Φ (t) ], wherein a ′ is the amplitude corresponding to the reference optical signal, Δf is the frequency shift amount of the acousto-optic frequency shifter 6, j is an imaginary unit, f is the center frequency of the fiber grating 202, 203, and Φ (t) is the initial phase.
The other light wave is a detection light wave, multiple reflections are carried out between the same group of fiber gratings, the detection light wave passes through the first coupler 5 and is divided into two beams of light by the detection path beam splitting coupler 702, one beam of light wave participates in low-order light interference and transmits to the low-order light interference coupler 902, and the other beam of light wave participates in high-order light interference and transmits to the high-order light interference coupler 901, and the two beams of light waves are separated into two beams of light according to a phase change formulaEpsilon is the strain applied on the sensing optical fiber, N is the refractive index of the optical fiber, N is the interference light order, i.e. sensitization multiple, l is the length between the fiber grating groups, and lambda is the center wavelength of the fiber gratings 202 and 203. The sensed light signal is denoted/>Wherein A' is the amplitude corresponding to the detected light signal, j is the imaginary unit, f is the center frequency of the fiber bragg gratings 202 and 203, phi (t) is the initial phase,/>, andTo sense phase changes.
In this embodiment, the optical fiber delay module 8 in the reference path is adjusted to accurately adjust the length of the reference path optical fiber, so that interference phenomenon cannot occur when interference light is required by the optical path matching interference technology, and interference can occur only when the optical path difference of the reference path and the detection path is approximately the same, namely, the requirements are satisfied: Δl < < L FBG, Δl is the optical path difference between the reference path and the detection path, referring to fig. 1, the improvement of the system sensitivity can be achieved by adjusting the optical fiber delay module.
The final interference optical signal can be expressed as: wherein Deltaf is the frequency shift amount of the acousto-optic frequency shifter 6, t is the time domain independent variable, phi (t) is the initial phase,/> For sensing the phase change, most of the transmission path noise can be eliminated because the same sensor element is arranged on one grating, and the reference light and the probe light are identical in the paths of other optical fibers except for the demodulation interferometer part. In addition, the low-order interference light is used as a reference group of the high-order interference light, and based on the periodic difference of random noise and vibration signals, broadband noise with weak correlation between the low-order interference light and high-order interference light sensing is eliminated, and meanwhile, the vibration signals with strong correlation are reserved. The electrical signal may represent/>, after passing through the photodetector 12 and the real-time data acquisition and processing moduleB is the amplitude of the alternating current item, and vibration signal information is obtained according to the electric signal.
The spectrum contrast diagram of the optical interference output signals with different orders of the system in the embodiment is shown in fig. 2, and when the magnitude of the applied signal is unchanged and the amplitude height of the sensing signal is unified, the equivalent strain resolution of the interference of the five-order reflected light is better. The experimental result shows that the invention can well improve the equivalent resolution and sensitivity of the system, and further illustrates the feasibility of the system and the method.
The effect diagram of the system before and after noise reduction by using low-order interference light is shown in fig. 3, and the experimental result shows that the system random noise can be effectively eliminated, the size of a detection signal is hardly influenced, and the feasibility of the system and the method is further illustrated.
The system of the embodiment separates the sensing signals with different wavelengths through the wavelength division multiplexing device 11 and transmits the sensing signals to different photoelectric detectors 12 for photoelectric detection. The vibration signal is applied to the sensitive optical fibers between the fiber bragg grating groups 402 and 403 of the wavelength 1 sensing element, the vibration signal is not applied to the sensitive optical fibers between the fiber bragg grating groups 404 and 405 of the wavelength 2 sensing element, and meanwhile, the vibration sensing signals of two wavelengths and the crosstalk between the two are detected, as shown in fig. 4, and as can be seen from experimental results, the invention can detect the sensing signals of a plurality of wavelengths at the same time, and meanwhile, the detection result of the wavelength 2 is not influenced by the wavelength 1, thereby further illustrating the feasibility of the system and the method of the invention.
Example 2
Referring to fig. 5, the white light interference detection and multiplexing system with the magnitude of the femto-strain resolution in the present embodiment is a hybrid multiplexing link of wavelength division 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. In addition, the working principle of the optical path structure of the present 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 white light source module 1 in this embodiment adopts a pulse form. The sensor array 4 of the present embodiment includes a second circulator 401, a fiber splitter 406, and a plurality of optical fibers connected to the fiber splitter 406, where each optical fiber of the sensor array 4 is independently provided with a plurality of groups of fiber gratings similar to those of embodiment 1, and time division multiplexing is achieved between the plurality of optical fibers of the sensor array 4 through a delay optical fiber 406.
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 (9)
1. A system for white light interferometry and multiplexing of the order of magnitude of femtostrain resolution, comprising:
A white light source module (1) for emitting a broad spectrum of light;
A fiber grating filter (2) for bandwidth filtering of broad spectrum light, comprising a first circulator (201) and a fiber grating array; the fiber grating array comprises one or more fiber gratings with different center wavelengths and the same bandwidth, which are positioned on the same fiber; the first circulator (201) is used for transmitting the broad spectrum light to the fiber grating array, and the reflected broad spectrum light is output through the first circulator (201);
An array of sensor elements (4) for reflecting and transmitting light waves carrying reference and sensor signals, comprising a second circulator (401); the second circulator (401) is connected with an optical fiber or is connected with a plurality of optical fibers which are realized by time division multiplexing through a delay optical fiber (407) through an optical fiber beam splitter (406), the optical fibers are provided with optical fiber grating groups, each optical fiber grating group consists of a pair of optical fiber gratings with the same bandwidth and center wavelength, the number and the center wavelength of the optical fiber grating groups on the same optical fiber are correspondingly arranged according to the number and the center wavelength of the optical fiber gratings in the optical fiber grating array, and the bandwidth of the optical fiber gratings in the optical fiber grating groups is larger than that of the optical fiber gratings in the optical fiber grating array; the bandwidth filtered light wave enters from the second circulator (401), is reflected by the fiber grating group, and the reflected light wave is output by the second circulator (401);
The first coupler (5) is used for dividing the reflected light waves 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 detection light consists of light waves reflected for many times inside each fiber bragg grating group; the reference light consists of light waves reflected once by a first fiber grating in each fiber grating group;
The acousto-optic frequency shifter (6) is arranged between the first coupler (5) and the reference path beam splitting coupler (701) and is used for shifting the frequency of the reference path light wave to remove zero frequency noise;
The reference path beam splitting coupler (701) and the detection path beam splitting coupler (702) are respectively used for dividing reference path light waves and detection path light waves into two groups of high-order light signals and low-order light signals, wherein the low-order light signals of the reference path and the detection path enter a low-order light interferometer to detect low-order sensing light signals, and the high-order light signals of the reference path and the detection path enter a high-order light interferometer to detect high-order sensing light signals;
The optical fiber delay module (8) is arranged between the reference path beam-splitting coupler (701) and the third coupler (9), and comprises a first optical path compensation optical fiber (801) of the high-order optical interferometer, a first electrically adjustable optical fiber delay line (802) and a second optical path compensation optical fiber (803) of the low-order optical interferometer, and a second electrically adjustable optical fiber delay line (804), wherein the first optical path compensation optical fiber (801) and the second optical path compensation optical fiber (803) are respectively used for performing large-amplitude rough adjustment on the optical paths of the high-order optical interferometer and the low-order optical interferometer, and the first electrically adjustable optical fiber delay line (802) and the second electrically adjustable optical fiber delay line (804) are respectively used for performing small-amplitude accurate adjustment on the optical paths of the high-order optical interferometer and the low-order optical interferometer so as to match the optical path difference between the reference path and the detection path;
a third coupler (9) comprising a high-order optical interference coupler (901) and a low-order optical interference coupler (902); the high-order optical interference coupler (901) and the low-order optical interference coupler (902) are respectively used for performing optical path matching heterodyne interference on the high-order optical signals and the low-order optical signals, and outputting the high-order interference optical signals and the low-order interference optical signals;
The photoelectric detectors (12) are respectively used for detecting high-order and low-order interference light beat frequency signals of corresponding wavelengths and converting photoelectric signals; the number of the photoelectric detectors (12) is twice the number of the types of the central wavelengths of the fiber bragg gratings in the fiber bragg grating array;
And the real-time data acquisition and processing module (13) is connected with the photoelectric detector (12) and is used for acquiring and processing radio frequency signals in real time, demodulating interference signals to obtain detection results of corresponding wavelength high-order and low-order heterodyne interference signals, and taking low-order interference as a reference item of high-order interference to perform noise reduction processing.
2. The system of claim 1, wherein the broad spectrum light is broad spectrum continuous light or broad spectrum pulsed light.
3. The system for detecting and multiplexing the white light interference of the flying strain resolution level according to claim 1, wherein a first erbium-doped fiber amplifier (3) for amplifying and adjusting the optical power of the optical wave after the bandwidth filtering is arranged between the fiber grating filter (2) and the sensor array (4).
4. The system for detecting and multiplexing white light interferometry of the magnitude of the femto-strain resolution according to claim 1, wherein a wavelength division multiplexing device (11) is arranged between the high-order optical interference coupler (901), the low-order optical interference coupler (902) and the photodetector (12) for separating interference optical signals of different wavelengths and transmitting the interference optical signals to the photodetector (12) for processing signals of corresponding wavelengths, respectively.
5. The system of claim 4, wherein a second erbium-doped fiber amplifier (10) is disposed between the high-order optical interference coupler (901), the low-order optical interference coupler (902) and the wavelength division multiplexing device (11) for amplifying and adjusting the optical power of the high-order and low-order interference optical signals to match the saturated input optical power of the photodetector (12).
6. The system for detecting and multiplexing the white light interferometry of the magnitude of the flying strain resolution according to claim 1, wherein the white light source module (1) is a broadband light source drive, and the broadband light source is an SLD, ASE or LED light source;
The bandwidth Δλ ASE of the broad spectrum light satisfies:
ΔλASE≥ΔλFBG1+…+ΔλFBGn
Wherein n is a positive integer, and Deltalambda FBG1,…,ΔλFBGn respectively represents the bandwidths of all the fiber gratings on the same fiber in the sensor element array (4).
7. The system of claim 1, wherein the optical path length is adjusted such that the optical path length difference satisfies δl:
δL≤λFBG 2/ΔλFBG
Wherein lambda FBG is the center wavelength of the corresponding fiber grating, delta lambda FBG is any fiber grating bandwidth of the fiber grating filter (2) and the sensor array (4).
8. The system of claim 1, wherein the fiber grating is any one or a combination of a plurality of phase shift fiber gratings, uniform fiber bragg gratings, apodized fiber gratings.
9. A method for detecting and multiplexing the white light interference of the magnitude of the flying strain resolution, which is characterized in that the system for detecting and multiplexing the white light interference of the magnitude of the flying strain resolution is adopted according to any one of claims 1 to 8;
The method for detecting and multiplexing the white light interference of the flying strain resolution level comprises the following steps:
The white light source module (1) emits wide-spectrum light, bandwidth filtering is carried out through the fiber bragg grating filter (2), then the light waves enter from a first port of the second circulator (401) through the sensing element array (4), the light waves are reflected by the fiber bragg grating group at a second port of the second circulator (401), the light waves are emitted from a third port of the second circulator (401) and are divided into two paths of optical signals after passing through the first coupler (5), one path of optical signals is used as detection light and passes through a detection path, and the other path of optical signals is used as reference light and passes through a reference path;
The detection light consists of light waves reflected for many times inside each fiber grating group, the light waves pass through the first coupler (5) and are divided into two light beams by the detection path beam splitting coupler (702), one light beam participates in low-order light interference transmission to the low-order light interference coupler (902), and one light beam participates in high-order light interference transmission to the high-order light interference coupler (901);
The reference light consists of light waves reflected once by a first fiber grating in each fiber grating group, no sensing signal is carried, after the reference light passes through a first coupler (5), the reference light is shifted in frequency by an acousto-optic frequency shifter (6), then is divided into two beams of light by a reference path beam splitting coupler (701), one beam of light participates in low-order light interference, the light is transmitted to a low-order light interference coupler (902) after being subjected to low-order light interferometer optical path matching adjustment by a second optical path compensation fiber (803) and a second electrically adjustable fiber delay line (804), the light is involved in high-order light interference, and the light is transmitted to the high-order light interference coupler (901) after being subjected to high-order light interferometer optical path matching adjustment by a first optical path compensation fiber (801) and a first electrically adjustable fiber delay line (802);
optical path matching heterodyne interference is generated between detection light and reference light of the high-order interferometer and the low-order interferometer, and interference signals are output;
the output interference signal is converted by photoelectric signals of a photoelectric detector (12);
the real-time data acquisition and processing module (13) acquires and processes the radio frequency signals in real time, demodulates the interference signals to obtain detection results of the corresponding wavelength high-order and low-order heterodyne interference signals, and performs noise reduction processing by taking the low-order interference as a reference item of the high-order interference.
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