CN102997859A - High-resolution large-range optical fiber strain sensor and probe thereof - Google Patents
High-resolution large-range optical fiber strain sensor and probe thereof Download PDFInfo
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- CN102997859A CN102997859A CN2012103942119A CN201210394211A CN102997859A CN 102997859 A CN102997859 A CN 102997859A CN 2012103942119 A CN2012103942119 A CN 2012103942119A CN 201210394211 A CN201210394211 A CN 201210394211A CN 102997859 A CN102997859 A CN 102997859A
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Abstract
The invention discloses a probe of a high-resolution large-range optical fiber strain sensor. The probe comprises an optical fiber annular cavity as a reference and an optical fiber grating for measuring strain. The optical fiber annular cavity is mutually close to that of the optical fiber grating. In terms of the high-resolution large-range optical fiber strain sensor, after laser produced by a laser device passes through a beam splitter, a beam of light is used for detecting the optical fiber annular cavity of the sensor after passing through a phase modulator, and an optical sideband signal generated by another beam of light passing through an intensity modulator is used for detecting the optical fiber grating of the sensor. Reflecting light of a detection signal is converted into an intensity signal through a light intensity signal and is demodulated by a demodulator to be used for controlling central frequency of the laser device and that of a sideband signal generator. A strain measuring range exceeding 100micro-strain can be achieved in low sideband modulation frequency of the sensor, and ultrahigh strain measuring precision is kept. Laser wavelength scanning process is avoided, and high-speed measurement can be achieved.
Description
Technical field
The present invention relates to a kind of high resolving power wide range fibre optic strain sensor, utilize optical fibre device as probe, crustal deformation etc. is accurately measured.
Background technology
The research of the disaster such as volcano and earthquake and prediction are the important social topics of densely inhabited district.In this field, for motion and the stress state of grasping the earth's crust, need to the deformation to the earth's crust carry out long-term monitoring in place as much as possible.The periodic cover of crustal deformation from a few tens of milliseconds in unlimited for a long time quasistatic scope, and the amplitude of its fluctuation a micro-strain does not wait from several nano-strain to hundreds of.In order to obtain exactly the deformation data of the earth's crust, used sensor need to have the measurement capability of static strain, the strain measurement precision of superelevation and large measurement range.
The used crustal strain sensor of current geophysics field has flexible strainometer and laser interferometer strainometer etc.Not only self is expensive for these instruments, and bulky, and length reaches several meters to rice up to a hundred.Because this class sensor need to be installed in underground to avoid the interference from ground usually, so large size is not only so that the quantities of sensor installation is very huge, the position of installing also is subject to the very big restriction of environment, be difficult to promote on a large scale installation, be not suitable for making up the sensor network of monitoring crustal deformation.
Fibre Optical Sensor is because its volume is little, lightweight, easy for installation, be not subject to chemical substance corrosion, be not subjected to electromagnetic interference, can remote sensing and the advantage of multiple spot sensing, be very suitable for the detection of strain, be widely used among buildings health monitoring and the intellectual material.But the technical indicator of existing Fibre Optical Sensor still can not satisfy the demand of earth's crust strain sensing fully.Work at present the measuring accuracy majority of fibre optic strain sensor in quasistatic field in the 1micro-strain magnitude, can not reach other accuracy requirement of nano-strain level of crustal strain far away.
There is a kind of high-precision optical fiber quasistatic strain transducer to adopt as a reference (T T.Y.Lam of atomic spectrum, et al., " High-resolution absolute frequency referenced fiber optic sensor for quasi-static strainsensing; " Applied Optics, vol.49, pp.4029-4033,2010), the range of the type sensor is subject to the bandwidth of atomic spectrum, and the strain measurement range only has several micro-strain.Another kind of wide range static strain sensor adopts tunable laser to scan a pair of fiber grating, obtained to surpass the static strain (Q.Liu of 100micro-strain, et al., " Ultra-high-resolution large-dynamic-range optical fiber static strain sensor usingPound-Drever-Hall technique; " Opt.Lett., vol.36, pp.4044-4046,2011)., but its measuring accuracy is subject to the nonlinear impact of laser wavelength in tuning, is difficult to obtain high precision.Another kind of high precision strain transducer adopts a kind of sideband Detection Techniques and surveys a pair of identical fibre-optical probe with Wavelength tunable laser and obtained high strain precision (Q.Liu, et al., " Sub-nano resolution fiber optic static strain sensor using a sideband interrogation technique; " Opt.Lett., 37 (3): 434-436 (2012)), but its measurement range is subject to the frequency range of sideband modulated signal, and measuring speed is also slow.Can realize simultaneously the fiber strain sensing technology of Under High Strain precision and super large strain measurement range, also not have good method before.
Summary of the invention
The object of the invention is the application for the crustal strain fields of measurement, and a kind of Fibre Optical Sensor and probe thereof that Under High Strain resolution and super large are measured range that have is provided, and can be effectively the deformation of the earth's crust be detected.
The present invention adopts following technical scheme for achieving the above object:
A kind of high resolving power wide range fibre optic strain sensor probe is characterized in that: it comprises the optic fiber ring-shaped cavity and the fiber grating that is used for monitor strain that have as a reference; Described optic fiber ring-shaped cavity and fiber grating position are close to each other.
It is further characterized in that: described fiber grating is common grating or position phase shift grating.
Further:: laser beam is coupled into optic fiber ring-shaped cavity through beam splitter again through the light gyroscope, and the transmission laser bundle is got back to incident optical through the light gyroscope, realizes the multiplexing of up light and descending light with an optical fiber.
A kind of high resolving power wide range fibre optic strain sensor is characterized in that: it comprises laser instrument, signal generator, sideband signals generator, phase modulator, intensity modulator, divided beams device, light gyroscope, light intensity signal conversion equipment, detuner and sensor probe; The laser that laser instrument produces is behind the divided beams device, and one road light is used for the optic fiber ring-shaped cavity of acquisition sensor behind phase modulator, and another road light is through behind the intensity modulator, and the optics sideband signals of generation is used for the fiber grating of acquisition sensor; The reflected light of above-mentioned detectable signal converts strength signal to through the light intensity signal conversion equipment, again by the detuner demodulation, is used for the centre frequency of control laser instrument and the centre frequency of sideband signals generator.
It is further characterized in that: described sideband signals generator inside comprises an I/Q radiofrequency signal modulator, the modulation signal that the output intensity modulator is used.
Sensor of the present invention can be lower the sideband modulation frequency realize to surpass the strain measurement scope of 1000micro-strain, keep simultaneously the strain measurement precision of superelevation.Owing to utilized the method that laser and sideband frequency is locked respectively optic fiber ring-shaped cavity fiber ring and fiber grating FBG, avoided the scanning process of optical maser wavelength, can realize measuring at a high speed.
Description of drawings
Fig. 1 is sensor probe synoptic diagram of the present invention.Among the figure, with reference to (Reference), measure (Measuring), ring (ring), position phase shift grating (π-phase shifted FBG), CIR is the light gyroscope, CP is beam splitter.
Fig. 2 is sensor synoptic diagram of the present invention.Among the figure, computer (computer), laser instrument (laser), FG is signal generator, PM is phase modulator, IM is light intensity modulator, CP is beam splitter, and CIR is the light gyroscope, detuner (Demodulator), light intensity signal conversion equipment (PD), sensing probe (sensor head), sideband signals generator (sideband generator), laser phase-locked (lock loop for laser), sideband phase-locked (lock loop for sideband) FG(Mod) is the modulation radio-frequency signal generator.
Fig. 3 is the synoptic diagram of sideband modulated signal generator.I/Q Quadrature modulator is the I/Q modulator among the figure, and Quadrature phase splitter is the pi/2 phase-splitter, FG(Lo) is the high-frequency radio frequency signal generator, FG(Mod) is that to use radio-frequency signal generator, Output be output signal in modulation.
Fig. 4 is the experimental principle synoptic diagram.Spectrum of fiber ring is the spectrum of optic fiber ring-shaped cavity among the figure, and spectrum of π-phase shifted FBG is the spectrum of position phase shift grating, and sideband is sideband, and laser is laser.
Fig. 5 is the restituted signal curve.Transverse axis is the tuned frequency (frequency deviation) of laser instrument among the figure, and the longitudinal axis is the intensity of restituted signal.
Embodiment
A kind of high resolving power wide range fibre optic strain sensor is popped one's head in as shown in Figure 1, have as a reference an optic fiber ring-shaped cavity (fiber ring) and a fiber grating (FBG who is used for monitor strain, comprise common grating and position phase shift grating π-phase shifted FBG, position phase shift grating has better performance).Fiber grating FBG is the strain measurement parts, and deformation to be measured namely is applied on the FBG; Fiber ring is reference part, is not subjected to the impact of extraneous strain.The position of Fiber ring and FBG is close to each other, has the purpose of uniform temp to reach both.FBG has a resonance frequency, and (this resonance frequency refers to have the light frequency at high reflectance place for common FBG; For π-phase shifted FBG, refer to the very narrow high-transmission rate light frequency in the high reflectance frequency range), this frequency is the linear function of strain to be measured and temperature, and fiber ring has the discrete resonance frequency of some series, and its resonance frequency only is subjected to the impact of temperature.By the resonance frequency of comparison FBG and the resonance frequency of fiber ring, just can obtain the information of strain.Because fiber ring has the uniform resonance frequency in a series of interval, therefore for the resonance frequency of FBG arbitrarily, always there is a resonance frequency of closing on object as a comparison in fiberring.
A kind of high resolving power wide range fibre optic strain sensor as shown in Figure 2, the light that laser instrument Laser sends is divided into two-way by optical splitter CP, one road light is modulated mutually by phase modulator PM position, be used for surveying the fiber ring of sensing probe, the light that returns is converted to strength signal by light intensity signal conversion equipment PD, again by phase demodulation device Demodulator demodulation, utilize the signal of detuner Demodulator output as feedback signal, the centre frequency of tuned laser Laser makes it to lock onto on the resonance frequency of fiber ring.After another road light process intensity modulator IM intensity modulated of optical splitter CP output, the one group of sideband signals that utilizes modulation to produce is surveyed the FBG in the sensing probe, the light that returns is converted to strength signal by light intensity signal conversion equipment PD, again by phase demodulation device Demodulator demodulation, utilize the signal of detuner Demodulator output as feedback signal, adjust the centre frequency of intensity-modulated signal, thereby the centre frequency of one group of sideband light signal is locked onto on the resonance frequency of FBG.At this moment, strain signal to be measured can be calculated by the centre frequency of intensity-modulated signal.
Fig. 3 is the sideband modulated signal generator, for generation of driving the used radiofrequency signal of intensity modulator.The driving signal demand of intensity modulator IM comprises three frequency contents with fixed bit phase and strength relationship:
IM:k·sin(Ω
St)+sin(Ω
St+Ω
Mt)-sin(Ω
St-Ω
Mt)
＝k·sin(Ω
St)+2·sin(Ω
St)·cos(Ω
Mt)
K is a constant in the formula, and system has optimized performance during k=2.Related sideband signals generator comprises the I/Q radio-frequency modulator of a quadrature, utilizes two groups of radiofrequency signal Ω
MAnd Ω
SProduce needed IM and drive signal.Utilize this signal that laser is carried out intensity modulated, will produce two groups of sidebands about laser center frequency symmetry, the centre frequency that the centre frequency of every group of sideband all departs from laser reaches Ω
S, its instantaneous frequency is with frequency omega simultaneously
MBeing sinusoidal rule changes.By adjusting centre frequency and the Ω of laser instrument
SSize, it is consistent and keep locking that one group of sideband signals is adjusted to resonance frequency with the FBG sensor.
As shown in Figure 2, after laser was divided into two-way, one road laser was modulated mutually by the position, and its centre frequency is sinusoidal rule and changes; Another road is by intensity modulated, and the centre frequency of the sideband of generation is sinusoidal rule and changes.This two-way is surveyed light signal and is used for respectively fiber ring and the FBG of acquisition sensor probe, as shown in Figure 4.After exploring laser light returned from sensing probe, the variation of surveying the light center frequency was converted the Strength Changes of light signal.By the position of comparison intensity of reflected light signal and the position phase of modulation signal, obtain demodulated output signal.In the certain frequency scope, this output signal is light frequency and fiber ring(or FBG) the poor linear function of resonance frequency, and when difference on the frequency was 0, the output signal amplitude also was 0, as shown in Figure 5.Utilize this output signal, the centre frequency that two-way can be surveyed light locks onto respectively on the resonance frequency of fiber ring and FBG.
At this moment, the modulating frequency (Ω of Laser sideband
S) just be equal to resonance frequency poor of fiber ring and FBG.The resonance frequency of FBG and fiber ring all is the linear function of temperature and strain, the design of sensing probe is so that they have identical temperature, and only have FBG to be subject to the impact of strain stress to be measured, so their resonance frequency poor be the linear function of strain stress to be measured.Fiber ring has a series of resonance frequencies with fixed intervals (FSR), for the resonance frequency of FBG arbitrarily, adjacent resonance frequency benchmark is as a comparison arranged, therefore, take the resonance frequency of certain selected fiber ring as benchmark, strain to be measured can be expressed as:
ε＝a·(j·FSR+Ω
S)
A is strain-frequency constant of FBG in the formula, and j is the reference frequency selected and the integral multiple part of the poor middle FSR of FBG resonance frequency.This sensor can be lower the sideband modulation frequency realize to surpass the strain measurement scope of 1000micro-strain, keep simultaneously the strain measurement precision of superelevation.Owing to utilized the method that laser and sideband frequency is locked respectively fiber ring and FBG, avoided the scanning process of optical maser wavelength, can realize measuring at a high speed.
Claims (5)
1. a high resolving power wide range fibre optic strain sensor is popped one's head in, and it is characterized in that: it comprises the optic fiber ring-shaped cavity and the fiber grating that is used for monitor strain that have as a reference; Described optic fiber ring-shaped cavity and fiber grating position are close to each other.
2. high resolving power wide range fibre optic strain sensor according to claim 1 is popped one's head in, and it is characterized in that: described fiber grating is common grating or position phase shift grating.
3. high resolving power wide range fibre optic strain sensor according to claim 1 is popped one's head in, and it is characterized in that: laser beam is coupled into optic fiber ring-shaped cavity through beam splitter again through the light gyroscope, and the transmission laser bundle is got back to incident optical through the light gyroscope.
4. high resolving power wide range fibre optic strain sensor, it is characterized in that: it comprises laser instrument, signal generator, sideband signals generator, phase modulator, intensity modulator, divided beams device, light gyroscope, light intensity signal conversion equipment, detuner and sensor probe; The laser that laser instrument produces is behind the divided beams device, and one road light is used for the optic fiber ring-shaped cavity of acquisition sensor behind phase modulator, and another road light is through behind the intensity modulator, and the optics sideband signals of generation is used for the fiber grating of acquisition sensor; The reflected light of above-mentioned detectable signal converts strength signal to through the light intensity signal conversion equipment, again by the detuner demodulation, is used for the centre frequency of control laser instrument and the centre frequency of sideband signals generator.
5. high resolving power wide range fibre optic strain sensor according to claim 4, it is characterized in that: described sideband signals generator inside comprises an I/Q radiofrequency signal modulator, the modulation signal that the output intensity modulator is used.
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| CN103940362A (en) * | 2014-04-30 | 2014-07-23 | 中国科学院半导体研究所 | High-precision fiber bragg grating low-frequency strain sensing demodulation system |
| CN105136057A (en) * | 2015-09-30 | 2015-12-09 | 上海交通大学 | Fiber grating strain sensing system |
| CN105352446A (en) * | 2015-11-30 | 2016-02-24 | 上海交通大学 | Sub-nano strain level multi-point multiplexing fiber grating quasi static strain sensor system |
| CN106091973A (en) * | 2016-07-05 | 2016-11-09 | 哈尔滨理工大学 | Based on annular Research on Cavity Ring Down Spectroscopy strain transducer and strain detecting method |
| CN107957502A (en) * | 2017-10-19 | 2018-04-24 | 山东微感光电子有限公司 | Laser fiber tachogenerator, Boolean value output sensor and measuring method |
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103940362A (en) * | 2014-04-30 | 2014-07-23 | 中国科学院半导体研究所 | High-precision fiber bragg grating low-frequency strain sensing demodulation system |
| CN103940362B (en) * | 2014-04-30 | 2017-04-19 | 中国科学院半导体研究所 | High-precision fiber bragg grating low-frequency strain sensing demodulation system |
| CN105136057A (en) * | 2015-09-30 | 2015-12-09 | 上海交通大学 | Fiber grating strain sensing system |
| CN105352446A (en) * | 2015-11-30 | 2016-02-24 | 上海交通大学 | Sub-nano strain level multi-point multiplexing fiber grating quasi static strain sensor system |
| CN105352446B (en) * | 2015-11-30 | 2018-01-30 | 上海交通大学 | Levels of strain multipoint multiplexing fiber grating quasistatic strain sensing system is received in Asia |
| CN106091973A (en) * | 2016-07-05 | 2016-11-09 | 哈尔滨理工大学 | Based on annular Research on Cavity Ring Down Spectroscopy strain transducer and strain detecting method |
| CN107957502A (en) * | 2017-10-19 | 2018-04-24 | 山东微感光电子有限公司 | Laser fiber tachogenerator, Boolean value output sensor and measuring method |
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Application publication date: 20130327 |