CN108120525A - Optical fiber grating temperature/strain sensing system and its demodulation method - Google Patents
Optical fiber grating temperature/strain sensing system and its demodulation method Download PDFInfo
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- 239000000835 fiber Substances 0.000 claims abstract description 23
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/3537—Optical fibre sensor using a particular arrangement of the optical fibre itself
- G01D5/3538—Optical fibre sensor using a particular arrangement of the optical fibre itself using a particular type of fiber, e.g. fibre with several cores, PANDA fiber, fiber with an elliptic core or the like
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Abstract
A kind of optical fiber grating temperature/strain sensing system and its demodulation method, after generating sideband by phase modulation module by the seed laser that narrow-linewidth laser light source module generates, it is subject to the light activated Active Optical Fiber grating of pumping through the wavelength division multiplexer injection in circulator and Active Optical Fiber grating module；The photodetector that return light is connected with circulator carries out opto-electronic conversion and obtains beat signal, the component of phase modulation frequency is extracted by lock-in amplifier, reflect the error signal of the centre frequency deviation of narrow linewidth laser and Active Optical Fiber grating, feedback control module nationality generates feedback voltage signal to control the centre frequency of narrow linewidth laser by error signal, realizes that the injection between narrow linewidth laser and Active Optical Fiber grating locks.The present invention can reach the quasi-static precision of p ε；And with the adjustable characteristic of strain sensitivity；It can effectively solve the problems, such as moding, Henan relaxation concussion and the Low frequency phase noise in fiber laser sensor.
Description
Technical field
The present invention relates to a kind of technology of sensory field of optic fibre, be specifically a kind of fiber optic high-resolution grating temperature/
Strain sensing system and its demodulation method.
Background technology
Strain sensing technology is widely used in engineering field, such as the monitoring of underwater sound field, monitoring structural health conditions, oil
Monitoring pipeline safety, seismic wave monitoring etc..Traditional strain transducer is usually mechanical or electromagnetic type, exists and much asks
Topic, such as：In strong electric field environment, traditional strain transducer by electromagnetic interference, can not easily work normally；In inflammable and explosive environment
In, electric spark can be generated, triggers accident；Under water or in underground environment, electrical part can corrode；Requiring array
Application scenario, traditional strain transducer are difficult to be linked to be large scale array.These defects seriously limit traditional strain transducer
Practical application.
Since the 1970s, optical fiber was by invention, optical fiber sensing technology also flourishes therewith.In recent years due to
The development of photoetching technique, scribes the maturation of grating technology on optical fiber, and fiber grating sensing technology is always sensory field of optic fibre
Hot spot.Fiber-optic grating sensor is with its small size, low cost, multiplexing capacity are strong, electromagnetism interference, it is corrosion-resistant the advantages that, be
Solve the problems, such as that ultra-fine linear array and extensive sensor array application project provide new solution method.Fiber grating is mixed according to whetheing there is
Miscellaneous gain media can be divided into passive optical fiber grating and Active Optical Fiber grating.
Passive optical fiber grating sensor is more early studied, and when by extraneous effects of strain, fiber grating length becomes
Change, reflectance spectrum is caused to drift about.The drift value of reflectance spectrum is directly proportional to strain size.The first demodulation scheme and most often
Interferometer demodulation method, using wide spectrum light source incident optical Bragg grating (FBG), the light that frequency meets Bragg conditions will
It is reflected by FBG, it is ungratified, it transmits.The MZ interferometers demodulation narrowband reflection optical wavelength variation of arm length difference very little is recycled, from
And obtain extraneous strain information.Although such scheme has the characteristics of at low cost, to be easy to multiplexing, due to FBG reflection bandwidths
It is very wide, thus be difficult to improve on sensitivity behaviour.Second, be the PDH demodulation techniques occurred in recent years, using single-frequency laser
Device is locked in the resonance peak at the reflection peak edge of FBG, PSFBG (π phase shift FBG) or FFPI (optical fiber FP chambers), strain resolution
Hundreds of f ε even can be reached, the part however, PDH demodulation schemes come with some shortcomings：A, the strain precision of this scheme is direct
It is influenced be subject to the frequency stability of single-frequency laser, this proposes very high requirement for the frequency stabilization performance of laser；B, in length
Distance, extensive multiplexed sensing application scenario, the power attenuation of flashlight cause system strain precision to reduce.
Active Optical Fiber grating sensor is also referred to as fiber laser sensor, is broadly divided into distributed Blatt reflective formula optical fiber and swashs
Light (DBR-FL) sensor and distributed feedback optical-fiber laser (DFB-FL) sensor.The output wavelength of DBR-FL and DFB-FL
Be consistent with the resonant frequency of its resonator, thus optical fiber laser extraneous strain signal effect under, the output of laser
Laser center wavelength also drifts about therewith.Since laserresonator is very sensitive for outer signals, and DBR-FL with
The line width of the output light of DFB-FL is very narrow, can reach several kHz, far smaller than the bandwidth of FBG.Recycle interferometer demodulation skill
Art, can realize very high-precision strain sensing, and the strain precision of this scheme is always maintained at so far up to 7f ε@7kHz
The world record in high-precision optical fiber strain sensing field.
Although fiber laser sensor has many advantageous characteristic and attractive prospect, this technology is also far from
Maturation, there are many more in theoretical and engineering the problem of, need to solve.Some main problems present in fiber laser sensor are such as
Under：A, lasing mode control problem, in the detection of small-signal, it is desirable that resonator is grown to lower most I survey letter as far as possible
Number intensity, while resonator also requires certain length to ensure output power.However the elongated multimode that will generate of resonator swashs
Hair；B, fiber laser sensor is demodulated dependent on interferometer, and interferometer can be subject to extraneous low-frequency noise (such as temperature, vibration) shadow
It rings, thus reduces the strain precision of low-frequency range；C, the noise problem of optical fiber laser, the laser of any free-running can not
Avoid there are certain intensity and phase noise, so as to influence the precision of fiber laser sensor.
The content of the invention
The present invention proposes that a kind of optical fiber grating temperature/strain passes for deficiency existing for existing fiber grating sensing technique
Sensing system and its demodulation method demodulate the center of Active Optical Fiber grating output laser using injection locking with PDH frequency lockings technology
Even if frequency drift in the case where detection of optical power is down to nW, remains able to realize high-precision sensing.
The present invention is achieved by the following technical solutions：
The present invention relates to a kind of optical fiber grating temperature/strain sensing system, including：The narrow-linewidth laser light source being sequentially connected
Module, phase modulation module, circulator and Active Optical Fiber grating module, wherein：The output terminal of circulator turns successively equipped with photoelectricity
Change the mold block, lock-in amplifier and feedback control module, the output terminal of feedback control module and the control of narrow-linewidth laser light source module
End processed is connected, after the seed laser that narrow-linewidth laser light source module generates generates sideband by phase modulation module, through circulator
And the wavelength division multiplexer injection in Active Optical Fiber grating module is subject to the light activated Active Optical Fiber grating of pumping；Return light and ring
The photodetector that shape device is connected carries out opto-electronic conversion and obtains beat signal, and phase modulation frequency is extracted by lock-in amplifier
Component, that is, reflect the error signal of the centre frequency deviation of narrow linewidth laser and Active Optical Fiber grating, feedback control module
Nationality generates feedback voltage signal to control the centre frequency of narrow linewidth laser by error signal, realizes narrow linewidth laser with having
Injection locking between the fiber grating of source.
The feedback control module includes：Sequentially connected data collecting card, times for exporting feedback voltage signal
Meaning waveform generator, for parsing the data that collect and generate feedback command that data collecting card and random waveform is controlled to occur
The computing unit and piezo controller of device, wherein：Data collecting card samples the electric signal of input, and piezo controller is realized
To the Linear Amplifer of feedback voltage signal.
The feedback voltage signal, preferably further the central frequency deviation information including active fiber grating, that is, wrap
Temperature/the strain signal acted on Active Optical Fiber grating is contained.
The narrow-linewidth laser light source module preferably uses：Narrow cable and wide optical fiber laser with adjustable optical attenuator.
The phase modulation module preferably uses：Phase-modulator with signal generator.
The Active Optical Fiber grating module includes：Wavelength division multiplexer and the Active Optical Fiber grating being attached thereto respectively.
Pump laser selectively can be further set in the Active Optical Fiber grating module.
The Active Optical Fiber grating is as the senser element in system, it is however preferred to have phase-shifted fiber grating mixes bait light
It is fine.
The photoelectric conversion module preferably uses：Avalanche photodetector.
The present invention relates to a kind of frequency stabilization of phase-modulation optical heterodyne (PDH) method based on above system, by swashing to single-frequency
Light carries out phase-modulation, by obtained carrier wave and two single order sideband injection optics resonators；Nationality by optical resonator transmission
The characteristic modulation different from the generation of sideband light to carrier light；Then it is extracted in from the beat signal of the return light of optical resonator
Component at phase modulation frequency obtains frequency discrimination curve as ordinate by abscissa of frequency departure；It is anti-finally by closed loop
The centre frequency of feedback control single-frequency laser or optical resonator so that the two keeps alignment and locking.
The modulation includes：It is the function of frequency to change phase and intensity, knots modification.
The optical resonator is Active Optical Fiber grating.
The transmission characteristic refers to the reflected intensity spectrum and phase spectrum of Active Optical Fiber grating.
The frequency discrimination curve refers to：The relation curve of error signal and frequency departure, by the way that narrow-linewidth single frequency is controlled to swash
Light device carries out linear frequency sweep, and the component at phase modulation frequency is extracted in the beat signal collected and is mapped with the time, you can
Obtain frequency discrimination curve.
Lock application the present invention relates to a kind of injection based on the above method, the laser that main laser is sent be injected into from
In laser, when principal and subordinate's laser frequency difference injection lock-in range in, then will be with main laser from the centre wavelength of laser
After keeping locking and locking, the phase difference between principal and subordinate's laser depends on centre frequency deviation between the two.
The main laser power is less than from laser power, and preferably main laser uses narrow-linewidth single frequency laser,
It is preferred that it is used from laser with pump laser and activates the Active Optical Fiber grating of gain, further preferably using DFB types
Active Optical Fiber grating, i.e. DFB optical fiber lasers.
The injection locking application, in lock-in range, the pass of phase difference and centre frequency deviation with approximately linear
System.
The injection lock-in range refers to：Injection can occur for principal and subordinate's laser, and to lock permitted minimum frequency poor, i.e.,Wherein：τpThe service life for being photon in chamber, PinRefer to main laser be injected into the luminous power from laser,
P is in the case where there is external optical injection, from the luminous power of laser output.
Technique effect
It is of the invention compared with existing PDH demodulation techniques, have following several advantages：
A, low power requirements；It is very low to the power requirement of narrow-linewidth single frequency laser, even as low as pW grades；Compared with passive
The PDH demodulation techniques of fiber grating sensing system reduce 40dB to the power requirement for detecting light.Efficiently solve over long distances with
The problem of strain precision deteriorates caused by optical power attenuation in extensive multiplexed sensing application.
B, strain sensitivity is adjustable；Frequency discrimination curve central task sector width is equal to the locking bandwidth of injection locking：By controlling injection ratio can be with control centre's work sector width；For DFB types used in the system
Active Optical Fiber grating, controlled range is from 100kHz~25MHz；Narrow central linear area means higher strain sensitivity, wide
Central task area mean the dynamic range of bigger；Thus according to specific application scenario suitable frequency discrimination can be selected bent
Line.Fig. 2 (a) illustrates the PDH signals for applying and being obtained after pumping, even if under the detection of optical power of 0.1nW, PDH signals
Signal-to-noise ratio is still very good, and PDH work sector widths only have 0.33MHz；In contrast, Fig. 2 (b), which is illustrated, is not added with pump light
Under PDH signals, hence it is evident that PDH works sector width broadening, and signal-to-noise ratio degradation.Fig. 3 is illustrated under different injection ratios
Obtained PDH work sector widths.Before making the present invention, the adjustable PDH frequency discrimination curves of central task sector width can be realized by not having also.
The present invention has following several advantages compared with the interferometer demodulation techniques of existing fiber laser sensor：
A, the moding problem of optical fiber laser sensor is overcome；In the detection of small-signal, it is desirable that resonator
It grows to lower minimum detectable signal intensity as far as possible, while resonator also requires certain length to ensure output power.However
Resonator is elongated will to generate moding.However in the present invention, using injection locking technique, seed injection light is to from laser
In device chamber, moding is eliminated.
B, strain precision of the optical fiber laser sensor-based system in low-frequency range is promoted；The laser of free-running exists very big
Low-frequency noise, however in locking system is injected, the phase of principal and subordinate's laser keep locking, thus from the low frequency phase of laser
Noise depends on main laser；Existing fiber laser sensor system is most to be demodulated using interferometer, however non-equilibrium dry
Interferometer is inevitably subject to the temperature of extraneous low frequency, strain noise；So as to influence sensing accuracy of the sensor-based system in low-frequency range.
Optical fiber laser sensor-based system can be improved in low-frequency range based on injection locking and the demodulation scheme of PDH frequency locking technologies in the present invention
Sensing accuracy.
C, the space complexity and volume of demodulating system are reduced；In the interferometer demodulation scheme of fiber laser sensor system
In, to improve sensing accuracy, the length that the arm length difference of non-equilibrium interferometer must be enough；Especially in the applied field being multiplexed on a large scale
It closes, demodulating system can become extremely complex, and volume is also very big.Demodulation based on injection locking with PDH frequency locking technologies in the present invention
Scheme is advantageously implemented the integrated of demodulating system.
Description of the drawings
Fig. 1 is Active Optical Fiber grating sensing system schematic diagram；
In figure：1 is narrow linewidth laser, and 2 be adjustable optical attenuator, and 3 be phase-modulator, and 4 be signal generator, and 5 are
Circulator, 6 be 980nm pump lasers, and 7 be 980nm/1550nm wavelength division multiplexers, and 8 be Active Optical Fiber grating, and 9 visit for photoelectricity
Device is surveyed, 10 be lock-in amplifier, and 11 be data collecting card, and 12 be computing unit, and 13 be arbitrary waveform generator, and 14 be voltage control
Device processed；
Fig. 2 (a) is to open the PDH signals obtained after pump light, and Fig. 2 (b) is to close the PDH signals obtained after pump light；
Fig. 3 illustrates the PDH central task sector widths under different injection ratios.；
It is to be in Fig. 4 in principal and subordinate's laser power ratioUnder, the power spectral density of obtained strain signal is shown
It is intended to；
Fig. 5 is in different detection of optical power PinUnder, obtained strain sensing precision (@150Hz)；
In Fig. 5：Circular mark line is represented not plus in the case of pumping, strain precision and main laser injecting power PinPass
System；Square indicia line represent apply pumping keep from laser output power as 100nW in the case of, strain precision and
Main laser injecting power PinRelation；
Fig. 6 is that the injection of DFB type Active Optical Fiber gratings locks peak and phase spectrum schematic diagram；In phase spectrum, due to noting
Enter outside lock-in range, constant phase difference is not present between principal and subordinate's laser, it is difficult to represent its phase relation, therefore use dotted line
It represents；
Specific embodiment
As shown in Figure 1, the present embodiment includes：It is narrow-linewidth laser light source module, phase-modulator module, circulator 5, active
Fiber grating module, photoelectric conversion module, lock-in amplifier and feedback control module, wherein：Narrow-linewidth laser light source module produces
The single-frequency seed laser of raw certain luminous power, phase-modulator module carry out phase-modulation to seed light, generate Carrier And Side Band,
And enter Active Optical Fiber grating module from 1 and 2 port of circulator；Seed laser into Active Optical Fiber grating will control active light
The frequency and phase of the laser of fine grating output, the laser of Active Optical Fiber grating output enter photoelectricity through 2 and 3 port of circulator and turn
Mold changing block, realization optical signal and electric signal are converted to beat signal；Lock-in amplifier extracts specific frequency from beat signal
The component of rate (phase modulation frequency) obtains error signal, and is exported after amplifying；In feedback control module, data collecting card pair
The error signal of lock-in amplifier output is acquired, and computing unit carries out signal processing and obtains feedback voltage signal, and passes through
Arbitrary waveform generator exports, and feedback voltage is after piezo controller amplifies to control the centre frequency of narrow linewidth laser.
The narrow-linewidth laser light source module includes：The narrow cable and wide optical fiber laser 1 and variable optical attenuation being sequentially connected
Device 2, by adjusting the attenuation coefficient of adjustable optical attenuator, so as to change the injecting power of main laser in injection locking system
Pin。
The phase modulation module includes：Phase-modulator 3 and signal generator 4, signal generator 4 are used to generate
Phase modulated signal, phase-modulation waveform be sinusoidal waveform, phase modulation frequency 1MHz, phase-modulation voltage 2V.
The Active Optical Fiber grating module includes：Pump laser 6, the 980nm/1550nm wavelength division multiplexers of 980nm
7th, Active Optical Fiber grating 8, wherein：Active Optical Fiber grating uses erbium ion, and as gain media, optical grating construction is π phase shift optical fiber light
Grid, grid region length 40mm, resonance peak line width 25MHz；The output power from laser can be changed by adjusting pumping light power
P。
The photodetector 9 is avalanche photodetector FPD, maximal input 10mW, 0~200MHz of bandwidth.
The lock-in amplifier 10, time constant is arranged to 10us.
The feedback control module includes：Data collecting card 11, computing unit 12, arbitrary waveform generator 13, piezoelectricity
Controller 14.
11 precision of data collecting card is 18bit；13 precision of arbitrary waveform generator is 18bit.
Described piezo controller 0~10V of input voltage range, 0~75V of output voltage range, voltage amplification coefficient
7.5。
The computing unit 12 in this embodiment, for laboratory apparatus control and signal processing.
The present embodiment is related to the course of work of above system, specifically includes following steps：
Step 1 carries out frequency sweep operation first, to determine in the output laser of narrow linewidth laser 1 and Active Optical Fiber grating 8
The relative position of cardiac wave length.The wavelength for making laser by controlling laser temperature first carries out a wide range of frequency sweep；Computing unit 12
Arbitrary waveform generator 13 is controlled to generate triangular signal, to control the small range frequency sweep repeatedly of narrow linewidth laser 1；It sweeps on a large scale
Frequency is carried out at the same time with small range frequency sweep.Computing unit 12 controls data collecting card 11 to be acquired error signal；Frequency sweep triangle
Ripple signal amplitude 2V, voltage bias 2V, frequency 20Hz, swept frequency are 73MHz/V with sweep voltage ratio；Data collecting card is adopted
Sample rate 200kHz, sampled point 10000.
The error voltage signal that step 2, observation collect, if it is possible to observe PDH frequency discrimination curves, illustrate that narrow linewidth swashs
Light device 1 and the output laser center wavelength of Active Optical Fiber grating 8 are close enough；Suspend a wide range of frequency sweep at this time.
Step 3 calculates the swept-frequency signal and PDH frequency discrimination curves collected, and it is right to obtain institute at PDH curve zero crossings
The sweep voltage value answered is denoted as V (1)；Suspend small range frequency sweep at this time.
Step 4 proceeds by frequency locking operation, control arbitrary waveform generator output voltage values V (1), to carry out head below
Secondary frequency locking operation.
Step 5 resets data collecting card sample rate 50kHz, and sampling number 10 is denoted as e (1), e (2) ... e
(10).It is averaged, and calculates to this 10 pointsWherein ρ be feedback factor, feedback factor it is big
Depending on the small center of curve linear zone slope according to PDH.
Step 6 controls arbitrary waveform generator output voltage values V (2) again, carries out second of frequency locking, while according to step 5
E (11), e (12) ... e (20) and V (3) are obtained, one time frequency locking operates used time 0.2ms, feedback frequency 5kHz.
Step 7 repeats step 6 always；
Step 8, the gathered data after frequency locking stabilization gather the value of 500k feedback voltage V (n), corresponding sampling time
100s。
Step 9 changes main laser injecting power Pin, repeat the above process, obtain the sensing under different detection of optical power
Data.
Operation in step 4 to step 7 is the process of PDH frequency lockings, and feedback control module is by exporting feedback voltage
Value V (n) feeds back to the Piezo control terminals of laser, to realize the note between narrow-linewidth single frequency laser and Active Optical Fiber grating
Enter locking.Feedback signal V (n) represents the drift of Active Optical Fiber grating resonant frequency namely the external world is added in Active Optical Fiber light
Strain/temperature signal on grid.
Lock-out state feature and determination method：If system is in the lock state down, error signal e will be zero-mean,
And undulating value is smaller；Determination method：Change the centre wavelength of narrow-linewidth single frequency laser, if play is presented in feedback voltage signal V
Strong monotone increasing or reduction, then system be in the lock state；On the contrary then losing lock.
In the present embodiment, Active Optical Fiber grating is in relaxed state, as in isoperibol, and is applied using loudspeaker
The voice signal of 150Hz.And it according to the frequency sweep coefficient 73MHz/V measured and fibre strain coefficient 135kHz/n ε, can will feed back
Voltage signal is converted into strain signal.Fig. 4 illustrates the power of straining spectrum density measured；On the whole, strain make an uproar bottom from 1Hz to
1kHz existsHereinafter, at 150Hz, strain precision existsCaused by measuring applied sound
Strain size is 80p ε.
In the present embodiment, we are in different main laser injecting power PinUnder, obtain multigroup sensing data；Fig. 5 exhibitions
Show under different main laser injecting powers, the strain precision at 150Hz.Circular mark line represents the feelings for not adding pumping
Under condition, strain precision and main laser injecting power PinRelation；Not plus in the case of pumping, this is also classical PDH demodulation
Scheme, it can be seen that when luminous power is less than -25dBm (3uW), strain precision starts to deteriorate with the attenuation of power.It is square
Shape mark line represent apply pumping keep from laser output power as 100nW in the case of, strain precision and main laser
The relation of injecting power it will be seen that even if the injecting power of main laser decays to -65dBm (0.3nw), does not have yet
The deterioration of any strain precision.Result in Fig. 5 demonstrates the present invention still having very under ultra-low light power well
High strain sensing precision.For the circular mark line in Fig. 5, when increasing luminous power, strain low final stabilization of making an uproar and existLeft and right, which demonstrate strain the low frequency noise rather than intensity noise for being mainly derived from main laser of making an uproar.
The present embodiment is demodulated Active Optical Fiber grating sensing system with injection locking technique based on PDH, in detection light
Power is arrived down to the voice signal in the case of -65dBm, successfully having demodulated the 150Hz applied, strain precision in 1Hz
In the frequency range of 1kHz better thanThe present embodiment has measured multigroup sensing data under different luminous powers,
Confirm that the present invention still has very high strain precision in the case of ultra-low light power；And PDH central task sector widths
Adjustable characteristic so that system is adjustable with strain sensitivity.And due to using injection locking technique, Active Optical Fiber grating
Output laser is in slave mode, can effectively inhibit the Low frequency phase noise in Active Optical Fiber grating, Henan relaxation is shaken, pattern
The problems such as saltus step.Therefore the present invention has unrivaled advantage compared with other demodulation schemes.
Above-mentioned specific implementation can by those skilled in the art on the premise of without departing substantially from the principle of the invention and objective with difference
Mode carry out local directed complete set to it, protection scope of the present invention is subject to claims and not by above-mentioned specific implementation institute
Limit, each implementation within its scope is by the constraint of the present invention.
Claims (13)
1. a kind of optical fiber grating temperature/strain sensing system, which is characterized in that including：The narrow-linewidth laser light source being sequentially connected
Module, phase modulation module, circulator and Active Optical Fiber grating module, wherein：The output terminal of circulator turns successively equipped with photoelectricity
Change the mold block, lock-in amplifier and feedback control module, the output terminal of feedback control module and the control of narrow-linewidth laser light source module
End processed is connected, after the seed laser that narrow-linewidth laser light source module generates generates sideband by phase modulation module, through circulator
And the wavelength division multiplexer injection in Active Optical Fiber grating module is subject to the light activated Active Optical Fiber grating of pumping；Return light and ring
The photodetector that shape device is connected carries out opto-electronic conversion and obtains beat signal, and phase modulation frequency is extracted by lock-in amplifier
Component, that is, reflect the error signal of the centre frequency deviation of narrow linewidth laser and Active Optical Fiber grating, feedback control module
Nationality generates feedback voltage signal to control the centre frequency of narrow linewidth laser by error signal, realizes narrow linewidth laser with having
Injection locking between the fiber grating of source.
2. optical fiber grating temperature according to claim 1/strain sensing system, it is characterized in that, the feedback control mould
Block includes：Sequentially connected data collecting card, for export feedback voltage signal arbitrary waveform generator, for parse gather
To data and generate feedback command to control the computing unit of data collecting card and arbitrary waveform generator and piezo controller,
Wherein：Data collecting card samples the electric signal of input, and piezo controller realizes the Linear Amplifer to feedback voltage signal.
3. optical fiber grating temperature according to claim 2/strain sensing system, it is characterized in that, feedback voltage letter
Number, further comprise the central frequency deviation information of Active Optical Fiber grating, that is, contain the temperature acted on Active Optical Fiber grating
Degree/strain signal.
4. optical fiber grating temperature according to claim 1/strain sensing system, it is characterized in that, the narrow-linewidth laser
Light source module uses：Narrow cable and wide optical fiber laser with adjustable optical attenuator.
5. optical fiber grating temperature according to claim 1/strain sensing system, it is characterized in that, the Active Optical Fiber light
Grid module includes：Wavelength division multiplexer and the Active Optical Fiber grating being attached thereto respectively.
6. optical fiber grating temperature according to claim 5/strain sensing system, it is characterized in that, the Active Optical Fiber light
Pump laser is further provided in grid module.
7. a kind of phase-modulation optical heterodyne frequency-stabilizing method based on system described in any of the above-described claim, which is characterized in that logical
It crosses and phase-modulation is carried out to single-frequency laser, by obtained carrier wave and two single order sideband injection optics resonators；Nationality is humorous by optics
It shakes the transmission characteristic modulation different from the generation of sideband light to carrier light of chamber；Then believe from the beat frequency of the return light of optical resonator
The component at phase modulation frequency is extracted in number as ordinate, frequency discrimination curve is obtained by abscissa of frequency departure；Finally
Pass through the centre frequency of closed loop feedback control single-frequency laser or optical resonator so that the two keeps alignment and locking.
8. according to the method described in claim 7, it is characterized in that, the modulation includes：Changing phase and intensity, knots modification is
The function of frequency.
9. according to the method described in claim 7, it is characterized in that, the transmission characteristic refers to that the reflection of Active Optical Fiber grating is strong
Degree spectrum and phase spectrum.
10. according to the method described in claim 7, it is characterized in that, the frequency discrimination curve refers to：Error signal and frequency departure
Relation curve, be extracted in phase by the way that narrow-linewidth single frequency laser is controlled to carry out linear frequency sweep, in the beat signal collected
Component at modulating frequency is mapped with the time, i.e. frequency discrimination curve.
11. a kind of injection based on any the method in claim 7~10 locks application, which is characterized in that by main laser
The laser that device is sent is injected into for locking the centre frequency from laser from laser, when principal and subordinate's laser frequency difference is being noted
Enter in lock-in range, then locking will be kept with main laser from the centre wavelength of laser, and after locking between principal and subordinate's laser
Phase difference depend on centre frequency deviation between the two.
12. application according to claim 11, it is characterized in that, the main laser uses narrow-linewidth single frequency laser,
It is used from laser with pump laser and activates the Active Optical Fiber grating of gain.
13. application according to claim 11, it is characterized in that, injection locking application, in lock-in range, phase
Difference and centre frequency deviation have the relation of approximately linear；Injection lock-in range between principal and subordinate's laser, i.e.,Wherein：τpThe service life for being photon in chamber, PinRefer to main laser be injected into the luminous power from laser,
P is in the case where there is external optical injection, from the luminous power of laser output.
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