CN108120525B - Fiber grating temperature/strain sensing system and demodulation method thereof - Google Patents
Fiber grating temperature/strain sensing system and demodulation method thereof Download PDFInfo
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- 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
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- 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
Abstract
A fiber grating temperature/strain sensing system and its demodulation method, after generating the sideband through the phase modulation module through the seed laser that the narrow line width laser light source module produces, inject into the active fiber grating excited by pump light through the circulator and wavelength division multiplexer in the active fiber grating module; the feedback control module generates a feedback voltage signal by the error signal to control the central frequency of the narrow linewidth laser, so as to realize injection locking between the narrow linewidth laser and the active fiber bragg grating. The invention can reach the quasi-static precision of p; the strain sensitivity is adjustable; the problems of mode jump, relaxation oscillation and low-frequency phase noise in the optical fiber laser sensor can be effectively solved.
Description
Technical Field
The invention relates to a technology in the field of optical fiber sensing, in particular to a high-resolution optical fiber grating temperature/strain sensing system and a demodulation method thereof.
Background
The strain sensing technology is widely applied to the engineering field, such as underwater sound field monitoring, structural health monitoring, petroleum pipeline safety monitoring, seismic wave monitoring and the like. Conventional strain sensors are generally mechanical or electromagnetic and suffer from a number of problems, such as: in a strong electric field environment, the traditional strain sensor is easily subjected to electromagnetic interference and cannot work normally; in a flammable and explosive environment, electric sparks can be generated to cause accidents; in underwater or underground environments, electrical devices can corrode; in applications requiring arrays, conventional strain sensors are difficult to connect into large-scale arrays. These defects severely limit the practical application of conventional strain sensors.
Since the invention of optical fiber in the 70's of the 20 th century, the development of optical fiber sensing technology has been vigorous. In recent years, due to the development of the photolithography technology, the technology of etching gratings on optical fibers is mature, and the optical fiber grating sensing technology is always a hot spot in the field of optical fiber sensing. The fiber grating sensor has the advantages of small size, low cost, strong multiplexing capability, electromagnetic interference resistance, corrosion resistance and the like, and provides a new solution for solving the problems of superfine linear arrays and large-scale sensing array application engineering. The fiber grating can be divided into a passive fiber grating and an active fiber grating according to the presence or absence of a doped gain medium.
The passive fiber grating sensor is researched earlier, and when the passive fiber grating sensor is subjected to external strain, the length of the fiber grating changes, so that the reflection spectrum drifts. The amount of shift in the reflectance spectrum is proportional to the magnitude of the strain. The first demodulation scheme, also the most commonly used interferometer demodulation method, uses a wide-spectrum light source to input a Fiber Bragg Grating (FBG), and the light whose frequency satisfies the Bragg condition will be reflected by the FBG, and transmitted if it is not satisfied. And then, demodulating the wavelength change of the narrow-band reflected light by using the MZ interferometer with small arm length difference so as to obtain external strain information. Although the scheme has the characteristics of low cost and easy multiplexing, the FBG has wide reflection bandwidth, so that the sensitivity performance is difficult to improve. Second, a PDH demodulation technique that has appeared in recent years, and the strain resolution can even reach several hundred f by using a single-frequency laser to lock at the reflection peak edge of the FBG, the resonance peak of the PSFBG (pi phase shift FBG) or the FFPI (fiber FP cavity), however, the PDH demodulation scheme has some disadvantages: a. the strain precision of the scheme is directly influenced by the frequency stability of the single-frequency laser, which puts high requirements on the frequency stabilization performance of the laser; b. in long-distance and large-scale multiplexing sensing application occasions, the strain precision of the system is reduced due to the power attenuation of signal light.
The active fiber grating sensor is also called a fiber laser sensor, and is mainly classified into a distributed bragg reflection type fiber laser (DBR-FL) sensor and a distributed feedback type fiber laser (DFB-FL) sensor. The output wavelengths of the DBR-FL and the DFB-FL are consistent with the resonant frequency of the resonant cavity, so that the central wavelength of the output laser of the laser drifts under the action of an external strain signal. Because the laser resonant cavity is very sensitive to external signals, and the linewidths of the output light of the DBR-FL and the DFB-FL are very narrow, the linewidths can reach several kHz and are far smaller than the bandwidth of the FBG. And the interferometer demodulation technology is utilized to realize high-precision strain sensing, the strain precision of the scheme can reach 7f @7kHz, and the world record of the high-precision optical fiber strain sensing field is kept up to now.
Although fiber laser sensors have many superior characteristics and attractive prospects, the technology is far from mature, and many theoretical and engineering problems need to be solved. Some of the major problems present in fiber laser sensors are as follows: a. the laser mode control problem is that in the detection of weak signals, the resonant cavity is required to be as long as possible to reduce the minimum detectable signal intensity, and meanwhile, the resonant cavity also needs to be of a certain length to ensure the output power. However, a longer cavity will produce multimode excitation; b. the fiber laser sensor relies on the demodulation of an interferometer, and the interferometer is influenced by external low-frequency noise (such as temperature and vibration), so that the strain precision of a low frequency band is reduced; c. the noise problem of the fiber laser, any free running laser inevitably has certain intensity and phase noise, thereby influencing the precision of the fiber laser sensor.
Disclosure of Invention
Aiming at the defects of the existing fiber grating sensing technology, the invention provides a fiber grating temperature/strain sensing system and a demodulation method thereof, which demodulate the central frequency drift of laser output by an active fiber grating by using injection locking and PDH frequency locking technologies, and can still realize high-precision sensing even under the condition that the detection light power is as low as nW.
The invention is realized by the following technical scheme:
the invention relates to a fiber grating temperature/strain sensing system, comprising: narrow linewidth laser light source module, phase modulation module, circulator and the active fiber grating module that links to each other in proper order, wherein: the output end of the circulator is sequentially provided with a photoelectric conversion module, a phase-locked amplifier and a feedback control module, the output end of the feedback control module is connected with the control end of the narrow-linewidth laser light source module, and seed laser generated by the narrow-linewidth laser light source module generates a sideband through a phase modulation module and then is injected into an active fiber bragg grating excited by pump light through the circulator and a wavelength division multiplexer in the active fiber bragg grating module; the feedback control module generates a feedback voltage signal by the error signal to control the central frequency of the narrow linewidth laser, so as to realize injection locking between the narrow linewidth laser and the active fiber bragg grating.
The feedback control module comprises: the data acquisition card that connects gradually, arbitrary waveform generator for exporting feedback voltage signal, be used for the data analysis of gathering and generate feedback instruction in order to control data acquisition card and arbitrary waveform generator's computational element and piezoelectric controller, wherein: the data acquisition card samples input electric signals, and the piezoelectric controller realizes linear amplification of feedback voltage signals.
The feedback voltage signal preferably further includes center frequency shift information of the active fiber grating, i.e. includes a temperature/strain signal acting on the active fiber grating.
The narrow linewidth laser light source module preferably adopts: a narrow linewidth fiber laser with a variable optical attenuator.
The phase modulation module preferably adopts: a phase modulator with a signal generator.
The active fiber grating module includes: wavelength division multiplexer and active fiber grating connected to the multiplexer.
The active fiber grating module can be optionally provided with a pump laser.
The active fiber grating is used as a sensing device in the system, and is preferably an erbium-doped fiber with a phase-shifting fiber grating.
The photoelectric conversion module preferably adopts: an avalanche photodetector.
The invention relates to a phase modulation optical heterodyne frequency stabilization (PDH) method based on the system, which comprises the steps of carrying out phase modulation on single-frequency laser and injecting an obtained carrier and two first-order sidebands into an optical resonant cavity; the carrier light and the sideband light are modulated differently by the transmission characteristic of the optical resonant cavity; then, extracting a component at the phase modulation frequency from a beat frequency signal of the return light of the optical resonant cavity as a vertical coordinate, and obtaining a frequency discrimination curve by taking the frequency deviation as a horizontal coordinate; and finally, controlling the center frequency of the single-frequency laser or the optical resonant cavity through closed-loop feedback to keep the alignment and the locking of the single-frequency laser and the optical resonant cavity.
The modulation comprises the following steps: the phase and intensity are varied as a function of frequency.
The optical resonant cavity is an active fiber grating.
The transmission characteristics refer to a reflection intensity spectrum and a phase spectrum of the active fiber grating.
The frequency discrimination curve refers to: and (3) controlling the narrow-linewidth single-frequency laser to perform linear frequency sweep by using a relation curve of the error signal and the frequency deviation, and drawing a component at the phase modulation frequency and time from the collected beat frequency signal to obtain a frequency discrimination curve.
The invention relates to an injection locking application based on the method, laser emitted by a master laser is injected into a slave laser, when the frequency difference of the master laser and the slave laser is within the injection locking range, the central wavelength of the slave laser is locked and locked with the master laser, and the phase difference between the master laser and the slave laser depends on the central frequency deviation between the master laser and the slave laser.
The power of the master laser is smaller than that of the slave laser, preferably, the master laser adopts a narrow linewidth single-frequency laser, preferably, the slave laser adopts an active fiber grating which is provided with a pump laser and activates gain, and further preferably, a DFB type active fiber grating, namely a DFB fiber laser is adopted.
In the injection locking application, the phase difference and the central frequency deviation have approximately linear relation in the locking range.
The injection locking range refers to that: the minimum frequency difference allowed by injection locking can occur for the master and slave lasers, i.e.
Wherein: tau ispIs the lifetime, P, of photons in the cavityinThe term "optical power" means the optical power injected from the master laser to the slave laser, and "P" means the optical power output from the slave laser when external light is injected.
Technical effects
Compared with the existing PDH demodulation technology, the method has the following advantages:
a. low power requirements; the power requirement on the narrow-linewidth single-frequency laser is very low, even as low as pW level; compared with the PDH demodulation technology of a passive fiber grating sensing system, the power requirement on the probe light is reduced by 40 dB. The problem of strain precision deterioration caused by optical power attenuation in long-distance and large-scale multiplexing sensing application is effectively solved.
b. The strain sensitivity is adjustable; the frequency discrimination curve center working region width is equal to the injection locked locking bandwidth:
the width of the central working area can be controlled by controlling the injection ratio; for the DFB type active fiber grating used in the system, the controllable range is from 100kHz to 25 MHz; a narrow centerline region means higher strain sensitivity, a wide central working region means greater dynamic range; and thus an appropriate frequency discrimination curve may be selected depending on the particular application. Fig. 2(a) shows the PDH signal obtained after applying the pump, the signal-to-noise ratio of the PDH signal is still good even at a probe optical power of 0.1nW, and the PDH working region width is only 0.33 MHz; in contrast, fig. 2(b) shows the PDH signal without pump light, with a significant PDH working region width broadening and a deteriorated signal-to-noise ratio. Figure 3 shows the resulting PDH working zone widths at different injection ratios. Before the present invention, no PDH frequency discrimination curve with adjustable central working zone width could be realized.
Compared with the interferometer demodulation technology of the existing fiber laser sensor, the fiber laser sensor provided by the invention has the following advantages:
a. the mode hopping problem of the fiber laser sensor is solved; in the detection of weak signals, the resonant cavity is required to be as long as possible to reduce the minimum detectable signal intensity, and meanwhile, the resonant cavity is required to have a certain length to ensure the output power. However, a longer cavity length will produce mode hops. In the present invention, however, mode hops are eliminated by injecting seed light into the slave laser cavity using an injection locking technique.
b. The strain precision of the fiber laser sensing system in a low frequency band is improved; free-running lasers have significant low frequency noise, however in injection-locked systems the phase of the master and slave lasers remains locked, and thus the low frequency phase noise of the slave laser depends on the master laser; most of the existing fiber laser sensing systems adopt interferometer demodulation, but the unbalanced interferometer can inevitably be subjected to external low-frequency temperature and strain noise; thereby affecting the sensing accuracy of the sensing system in the low frequency band. The demodulation scheme based on the injection locking and PDH frequency locking technology can improve the sensing precision of the fiber laser sensing system in a low frequency band.
c. The space complexity and the volume of the demodulation system are reduced; in an interferometer demodulation scheme of an optical fiber laser sensing system, in order to improve sensing precision, the arm length difference of a non-equilibrium interferometer needs to be long enough; especially in large-scale multiplexing applications, the demodulation system becomes very complex and bulky. The demodulation scheme based on the injection locking and PDH frequency locking technology is beneficial to realizing the integration of the demodulation system.
Drawings
FIG. 1 is a schematic diagram of an active fiber grating sensing system;
in the figure: 1 is a narrow linewidth laser, 2 is a variable optical attenuator, 3 is a phase modulator, 4 is a signal generator, 5 is a circulator, 6 is a 980nm pump laser, 7 is a 980nm/1550nm wavelength division multiplexer, 8 is an active fiber grating, 9 is a photoelectric detector, 10 is a phase-locked amplifier, 11 is a data acquisition card, 12 is a calculation unit, 13 is an arbitrary waveform generator, and 14 is a piezoelectric controller;
fig. 2(a) is a PDH signal obtained after the pump light is turned on, and fig. 2(b) is a PDH signal obtained after the pump light is turned off;
fig. 3 shows PDH center working region widths at different injection ratios. (ii) a
In FIG. 4, the power ratio of the master laser to the slave laser is
Next, obtaining a power spectral density diagram of the strain signal;
FIG. 5 shows different detected optical powers PinNext, the obtained strain sensing accuracy (@150 Hz);
in fig. 5: the round mark line represents the strain accuracy and the injection power P of the main laser without pumpinginThe relationship of (1); the square mark lines represent the strain accuracy and the main laser injection power P with the pump applied, keeping the output power from the laser at 100nWinThe relationship of (1);
FIG. 6 is a diagram of injection locking peak and phase spectrum of DFB type active fiber grating; in the phase spectrum, since there is no constant phase difference between the master and slave lasers outside the injection locking range, it is difficult to express the phase relationship thereof, and it is indicated by a dotted line;
Detailed Description
As shown in fig. 1, the present embodiment includes: 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: the narrow-linewidth laser light source module generates single-frequency seed laser with certain optical power, the phase modulator module performs phase modulation on the seed laser to generate a carrier and a sideband, and the carrier and the sideband enter the active fiber grating module from ports 1 and 2 of the circulator; the seed laser entering the active fiber bragg grating controls the frequency and the phase of the laser output by the active fiber bragg grating, the laser output by the active fiber bragg grating enters the photoelectric conversion module through the ports 2 and 3 of the circulator, and the optical signal and the electric signal are converted to obtain a beat frequency signal; the phase-locked amplifier extracts a component with a specific frequency (phase modulation frequency) from the beat frequency signal to obtain an error signal, and the error signal is amplified and then output; in the feedback control module, a data acquisition card acquires an error signal output by a phase-locked amplifier, a computing unit performs signal processing to obtain a feedback voltage signal and outputs the feedback voltage signal through an arbitrary waveform generator, and the feedback voltage is amplified by a piezoelectric controller to control the central frequency of the narrow-linewidth laser.
The narrow linewidth laser light source module comprises: the narrow linewidth optical fiber laser 1 and the adjustable optical attenuator 2 which are connected in sequence change the injection power P of the main laser in the injection locking system by adjusting the attenuation coefficient of the adjustable optical attenuatorin。
The phase modulation module comprises: the phase modulator 3 and the signal generator 4, the signal generator 4 is used for generating a phase modulation signal, the phase modulation waveform is a sine waveform, the phase modulation frequency is 1MHz, and the phase modulation voltage is 2V.
The active fiber grating module includes: 980nm pump laser 6, 980nm/1550nm wavelength division multiplexer 7, active fiber grating 8, wherein: the active fiber grating uses erbium ions as a gain medium, the grating structure is a pi phase shift fiber grating, the length of a gate region is 40mm, and the line width of a resonance peak is 25 MHz; the output power P from the laser can be varied by adjusting the pump light power.
The photoelectric detector 9 is an avalanche photoelectric detector FPD, the maximum input power is 10mW, and the bandwidth is 0-200 MHz.
The time constant of the lock-in amplifier 10 is set to 10 us.
The feedback control module comprises: a data acquisition card 11, a computing unit 12, an arbitrary waveform generator 13 and a piezoelectric controller 14.
The precision of the data acquisition card 11 is 18 bit; the arbitrary waveform generator 13 has a precision of 18 bits.
The input voltage range of the piezoelectric controller is 0-10V, the output voltage range is 0-75V, and the voltage amplification factor is 7.5.
The computing unit 12 is used for laboratory instrument control and signal processing in this embodiment.
The embodiment relates to a working process of the system, which specifically comprises the following steps:
And 4, starting frequency locking operation below, and controlling the output voltage value V (1) of the arbitrary waveform generator to perform first frequency locking operation.
And 5, resetting the sampling rate of the data acquisition card to be 50kHz and the number of sampling points to be 10, and recording as e (1) and e (2). The 10 points are averaged and calculated
Where ρ is a feedback coefficient whose magnitude depends on the slope of the linear region in the PDH curve.
And 6, controlling the output voltage value V (2) of the arbitrary waveform generator, carrying out secondary frequency locking, and simultaneously obtaining e (11), e (12), e.e (20) and V (3) according to the step 5, wherein the time of primary frequency locking operation is 0.2ms, and the feedback frequency is 5 kHz.
and 8, acquiring data after the frequency locking is stable, and acquiring 500k values of the feedback voltage V (n), wherein the sampling time corresponds to 100 s.
In the operation from step 4 to step 7, which is a PDH frequency locking process, the feedback control module feeds back the feedback voltage value v (n) to the Piezo control end of the laser, so as to realize injection locking between the narrow-linewidth single-frequency laser and the active fiber grating. The feedback signal v (n) represents the shift of the resonant frequency of the active fiber grating, i.e. the strain/temperature signal applied to the active fiber grating from the outside.
Locking state characteristics and determination method: if the system is in a locking state, the error signal e is zero-mean and has a small fluctuation value; the judging method comprises the following steps: changing the central wavelength of the narrow-linewidth single-frequency laser, and if the feedback voltage signal V shows sharp monotonic increase or decrease, the system is in a locking state; otherwise, the lock is lost.
In this embodiment, the active fiber grating is in a relaxed state, placed in a constant temperature environment, and a 150Hz acoustic signal is applied using a horn. And the feedback voltage signal can be converted into a strain signal according to the measured sweep frequency coefficient of 73MHz/V and the optical fiber strain coefficient of 135 kHz/n. FIG. 4 shows the measured strain power spectral density; the whole strain noise floor is from 1Hz to 1kHz
Below, at 150Hz, the strain accuracy is
The magnitude of the applied sound induced strain was measured to be 80 p.
In this embodiment, we inject power P at different main lasersinNext, obtaining a plurality of groups of sensing data; fig. 5 shows the strain accuracy at 150Hz at different main laser injection powers. The round mark line represents the strain accuracy and the injection power P of the main laser without pumpinginThe relationship of (1); without pumping, which is also a classical PDH demodulation scheme, it can be seen that strain accuracy begins to deteriorate with power decay when the optical power is below-25 dBm (3 uW). The square mark lines represent the strain accuracy and the main laser light with the pump applied, keeping the output power of the slave laser at 100nWRelationship of the injection power of the master laser, we can see that there is no degradation of the strain accuracy even if the injection power of the master laser is attenuated to-65 dBm (0.3 nw). The results in fig. 5 are good evidence that the present invention has a high strain sensing accuracy at ultra low optical power. For the circular mark lines in fig. 5, the strain noise decreases and eventually stabilizes at increasing optical power
Left and right, this confirms that the strain noise reduction is mainly due to the frequency noise of the main laser, not the intensity noise.
In the embodiment, the active fiber grating sensing system is demodulated based on PDH and injection locking technology, an applied sound signal of 150Hz is successfully demodulated under the condition that the detection light power is as low as-65 dBm, and the strain precision is better than that of an applied sound signal in the frequency range of 1Hz to 1kHz
In the embodiment, multiple groups of sensing data are measured under different optical powers, and the fact that the optical fiber strain sensor still has high strain precision under the condition of ultralow optical power is proved; and the adjustable width of the PDH central working zone enables the strain sensitivity of the system to be adjustable. And because of adopting the injection locking technology, the output laser of the active fiber grating is in a controlled state, and the problems of low-frequency phase noise, relaxation oscillation, mode jump and the like in the active fiber grating can be effectively inhibited. The present invention therefore has incomparable advantages over other demodulation schemes.
The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims (13)
1. A fiber grating temperature/strain sensing system, comprising: narrow linewidth laser light source module, phase modulation module, circulator that link to each other in proper order and as the active fiber grating module of optical resonator, wherein: an output end of the circulator is sequentially provided with a photoelectric conversion module, a phase-locked amplifier and a feedback control module, the output end of the feedback control module is connected with a control end of the narrow-linewidth laser light source module, and seed laser generated by the narrow-linewidth laser light source module generates a sideband through a phase modulation module and then is injected into an active fiber grating excited by pump light through the circulator and a wavelength division multiplexer in the active fiber grating module; the feedback control module generates a feedback voltage signal by the error signal to control the central frequency of the narrow-linewidth laser, so as to realize injection locking between the narrow-linewidth laser and the active fiber bragg grating.
2. The fiber grating temperature/strain sensing system of claim 1, wherein the feedback control module comprises: the data acquisition card that connects gradually, arbitrary waveform generator for exporting feedback voltage signal, be used for the data analysis of gathering and generate feedback instruction in order to control data acquisition card and arbitrary waveform generator's computational element and piezoelectric controller, wherein: the data acquisition card samples input electric signals, and the piezoelectric controller realizes linear amplification of feedback voltage signals.
3. The fiber grating temperature/strain sensing system of claim 2, wherein the feedback voltage signal further comprises center frequency shift information of the active fiber grating, including the temperature/strain signal applied to the active fiber grating.
4. The fiber grating temperature/strain sensing system of claim 1, wherein the narrow linewidth Wei light source module comprises: a narrow linewidth fiber laser with a variable optical attenuator.
5. The fiber grating temperature/strain sensing system of claim 1, wherein said active fiber grating module comprises: wavelength division multiplexer and active fiber grating connected with it.
6. The fiber grating temperature/strain sensing system according to claim 5, wherein the active fiber grating module further comprises a pump laser, and the pump laser is connected to the active fiber grating module through a wavelength division multiplexer.
7. A phase modulation optical heterodyne frequency stabilization method based on the system of claim 6, characterized in that the obtained carrier and two first-order sidebands are injected into the optical resonator by phase modulating a single-frequency laser; the carrier light and the sideband light are modulated differently by the transmission characteristic of the optical resonant cavity; then, extracting a component at the phase modulation frequency from a beat frequency signal of the return light of the optical resonant cavity as a vertical coordinate, and obtaining a frequency discrimination curve by taking the frequency deviation as a horizontal coordinate; and finally, controlling the center frequency of the single-frequency laser or the optical resonant cavity through closed-loop feedback to keep the alignment and the locking of the single-frequency laser and the optical resonant cavity.
8. The method of claim 7, wherein said modulating comprises: the phase and intensity are varied as a function of frequency.
9. The method of claim 7, wherein the transmission characteristics are a reflection intensity spectrum and a phase spectrum of the active fiber grating.
10. The method of claim 7, wherein the frequency discrimination curve is: and (3) controlling the narrow-linewidth laser light source module to perform linear frequency sweep on a relation curve of the error signal and the frequency deviation, and extracting a component at the phase modulation frequency from the collected beat frequency signal to be plotted with time, namely a frequency discrimination curve.
11. An injection locking application based on the method of any one of claims 7 to 10, wherein the laser emitted from the narrow linewidth laser light source module is injected into the pump laser of the fiber grating temperature/strain sensing system to lock the central frequency of the pump laser, when the frequency difference between the narrow linewidth Wei light source module and the pump laser is within the injection locking range, the central wavelength of the pump laser will remain locked with the narrow linewidth laser light source module, and the phase difference between the locked narrow linewidth Wei light source module and the pump laser depends on the central frequency deviation between the two.
12. The use of claim 11, wherein the narrow linewidth laser light source module uses a narrow linewidth single frequency laser, and the pump laser uses an active fiber grating with a pump laser and activated gain.
13. The use of claim 11, wherein said injection locking application has an approximately linear relationship of phase difference to center frequency deviation over the locking range; narrow linewidth Wei injection locking range between light source module and pump laser, i.e.
Wherein: tau ispIs the lifetime, P, of photons in the cavityinThe optical power of the laser light source module with narrow linewidth injected into the pump laser is shown, and P is the optical power output by the pump laser under the condition of external light injection.
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| CN109752033B (en) * | 2019-02-22 | 2024-01-30 | 上海交通大学 | High-precision fiber bragg grating strain measurement system |
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| CN113343419B (en) * | 2021-04-30 | 2022-06-14 | 成都飞机工业（集团）有限责任公司 | Design and evaluation method for line width of mutual injection locking light source |
| CN113654582B (en) * | 2021-09-01 | 2023-06-02 | 哈尔滨工程大学 | Scheme for simultaneously measuring strain and temperature by using few-mode FBG-FP |
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