CN102680136A - Distributed stimulated Brillouin temperature strain sensing system based on double-sideband modulation - Google Patents

Abstract

The invention provides a distributed stimulated Brillouin temperature strain sensing system based on double-sideband modulation, which includes a narrow linewidth light source, a power divider, a microwave source, a pulse signal emitter, an optical receiver, an optical amplifier, an electrooptical modulator and a sensing optical fiber, wherein a pulse optical signal and a continuous signal that is modulated by double-sideband are input into the two ends of the sensing optical fiber respectively; the pulse optical signal serves as a pumping optical signal; the double-sideband continuous optical signal serves as a detecting optical signal; the pumping optical and detecting optical signals encounter to produce the stimulated Brillouin; and the continuous light carries the temperature or strain information of the points distributed along the sensing optical fiber. The double-sideband technology can effectively controls the Brillouin consumption of the pumping pulse during transmission, and greatly reduces the system error in measurement. The distributed stimulated Brillouin temperature strain sensing system is applicable to the fields as transmission cable and oil-gas pipeline monitoring and fire control, and is particularly applicable to sensing of long distance more than 50km.

Description

Distributed excited Brillouin temperature strain sensor-based system based on double-sideband modulation

Technical field

The invention belongs to the optical fiber technology field, relate to a kind of fiber optic temperature strain sensing system, particularly a kind of distributed excited Brillouin temperature strain method for sensing and structure based on double-sideband modulation.

Background technology

Based on the distribution type fiber-optic temperature stress sensor-based system of stimulated Brillouin effect, have obtain simultaneously tested regional temperature or stress in time with the ability of spatial variations information, be applicable to long-distance distributed detection range.Such sensor relies on its intrinsic explosion-proof, passive and long apart from characteristics, and the application in fields such as oil and gas pipes, electric power and fire-fightings has solved the technical barrier that many industries exist for many years always.At some important control area and pipeline, locate to monitor and provide accurate location like weapons and ammunitions storehouse, electric power cable, oil pipeline, traffic main artery, space launching site etc., be the important technology of fire-fighting domain.

The centre frequency of basic structure of the prior art laser instrument one 101 emissions as shown in Figure 1 is that the light signal of ν 1 is modulated into pulse as pump light through intensity modulator 104, imports from sensor fibre one end.Laser instrument 2 102 sends continuous light input sensor fibre 111 other ends that centre frequency is ν 2; The two is transmission in opposite directions in sensor fibre; The frequency of 2 laser instruments is synchronous through frequency lock device 103 holding frequencies, and the difference on the frequency of ν 1 and ν 2 is near Brillouin's frequency (≈ 11GHz) of optical fiber.Because continuous light is in the brillouin gain district of pump light, when meeting with pulse, is amplified by pulse.The centre frequency and the peak gain of the brillouin gain spectrum that pump light produces everywhere can be with the temperature and the strain variation at this place at optical fiber.Through ν 2 is carried out frequency sweep, wave filter 109 filtering Rayleigh scattering lights detect the variation of continuous light intensity and frequency spectrum with photo-detector 108, can solve the distribution along optical fiber of strain and temperature.

In the prior art, the light source of sensor-based system needs extra adding frequency lock device 103 to guarantee that the difference on the frequency of the two is stable, system's relative complex by two laser constitutions shown in Fig. 1.And, during the transmission of pumping pulse in sensor fibre can with survey light Brillouin's effect take place, power constantly reduces; Accumulation along with certain-length; Power will have tangible gap with theoretical value, cause occurring systematic measurement error, thereby distance sensing has received greatly restriction.

Summary of the invention

In view of the problems referred to above that exist in the prior art; The present invention provides a kind of distributed excited Brillouin temperature strain sensor-based system based on double-sideband modulation, comprises narrow linewidth light source, power splitter, microwave source, pulse signal transmitter, photoreceiver, image intensifer, electrooptic modulator and sensor fibre.

It is that the continuous light of ν 0 is divided into two bundles through 50: 50 coupling mechanisms that said narrow linewidth laser sends centre frequency, wherein a branch ofly is modulated into the pump light pulse signal through pulse signal generator and intensity modulator, amplifies the back through image intensifer and imports sensor fibre; It is f that microwave source produces frequency _mMicrowave signal, another Shu Guang is modulated into through carrier-suppressed double sideband to contain frequency be ν 0+f _mWith ν 0+f _mTwo bundle continuous probe light signals, from the other end input of optical fiber, with pump light signals transmission in opposite directions in optical fiber, the three satisfies steady-state equation:

$(\frac{d}{\mathrm{dz}}+\mathrm{\α})I_{\mathrm{pu}}=g_B{I}_{{\mathrm{CW}}_{v0+\mathrm{fm}}}{I}_{\mathrm{pu}}-g_B{I}_{{\mathrm{CW}}_{v0-\mathrm{fm}}}{I}_{\mathrm{pu}}---\left(1\right)$

$(\frac{d}{\mathrm{dz}}-\mathrm{\α})I_{{\mathrm{CW}}_{v0+\mathrm{fm}}}=g_B{I}_{{\mathrm{CW}}_{v0+\mathrm{fm}}}{I}_{\mathrm{pu}}---\left(2\right)$

$(\frac{d}{\mathrm{dz}}-\mathrm{\α})I_{{\mathrm{CW}}_{v0-\mathrm{fm}}}=-g_B{I}_{{\mathrm{CW}}_{v0-\mathrm{fm}}}{I}_{\mathrm{pu}}---\left(3\right)$

Wherein α, I _Pu,

g _BRepresent light attenuation coefficient, pumping light power, high frequency detection of optical power, low-frequency acquisition luminous power, Brillouin's coefficient respectively; Utilize the method for perturbation; Because surveying light only has an effect at tiny area and pump light in transmission course; Can think that detection light only experiences optical fiber and decays naturally, therefore can solve the distribute power of pump light earlier along distance:

$I_{\mathrm{pu}}(z,v)={\mathrm{<figure-callout\; id="0"\; label="I\; pu"\; filenames="HSA00000726926700021.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{pu}}^{}\exp (-\mathrm{\&alpha;z})\exp ({\&Integral;}_0^z-g_B(z^{\&prime;},v)\mathrm{\&Delta;}{I}_{\mathrm{CW}}^L\exp (-\mathrm{\&alpha;}(L-z^{\&prime;})){\mathrm{dz}}^{\&prime;})---\left(4\right)$

Wherein:

$\mathrm{\&Delta;}{I}_{\mathrm{CW}}^L=I_{{\mathrm{CW}}_{v0-\mathrm{fm}}}^L-I_{{\mathrm{CW}}_{v0+\mathrm{fm}}}^L---\left(5\right)$

The expression initial high frequency is surveyed the difference power of light signal and low-frequency acquisition light signal.Can find out that pump light depends on this value significantly along the distribute power of optical fiber.

Formula (4) is brought in formula (2) and (3), can further solve the performance number of the detection light that different detectors constantly receive at the z=0 place:

Initially wherein represent c _gThe light velocity in the optical fiber, E _PuIndicating impulse is at t energy constantly.Can find out that for a definite frequency power of the detection light that we receive is decided by the energy of pulse.If the value of pulse energy is uncertain, can cause the measuring error of detection of optical power.

Convolution (4) and (5) can find out that the power of pulse is decided by that the initial power of two sidebands of continuous light is poor.At first consider prior art; Can think that the high frequency sideband power is 0; Lower sideband is only arranged; The variation that pulse power distributes along with Brillouin's frequency on the fiber lengths and changing, therefore the Brillouin's frequency that depends on whole piece optical fiber in the very big degree of pulse power of optical fiber far-end distributes, and the measurement of surveying light is caused error.Optical fiber is long more, and error is obvious more.In the present invention; Two sidebands have identical performance number, therefore then formula (4) can be expressed as:

$I_{\mathrm{pu}}(z,v)=I_{\mathrm{<figure-callout\; id="0"\; label="pu"\; filenames="HSA00000726926700021.png"\; state="\{\{state\}\}">pu</figure-callout>}}^0\exp (-\mathrm{\&alpha;z})---\left(7\right)$

Be optical fiber is only experienced in pulse in optical fiber decay naturally, can not change, compensated error to a great extent, increased distance sensing along with the difference of Brillouin's frequency distribution.

Beneficial effect of the present invention is, only uses a laser instrument as light source, has practiced thrift cost to a great extent.The more important thing is that survey the mode of gloss with double-side band, the Brillouin who has compensated pump light acts on, thereby offset and be present in the prior art system error, broken through the restriction that the prior art distance sensing has only 20km-40km, can reach kms up to a hundred.

Description of drawings

Fig. 1 is a Brillouin light fiber sensor system structure in the prior art;

Fig. 2 is Brillouin's temperature stress sensor-based system structural representation of the embodiment of the invention;

Fig. 3 is the power diagram that the different different frequencies constantly of the embodiment of the invention are surveyed light;

Fig. 4 is the brillouin gain spectrogram at 10km and 80km place in the embodiment of the invention;

Fig. 5 is the Brillouin shift of every of the optical fiber of forward in the instance of the present invention and reverse twice measurement;

Embodiment

The present invention provides a kind of distributed Brillouin's temperature strain sensor-based system based on double-sideband modulation.Below in conjunction with accompanying drawing the present invention is elaborated.

The present invention provides a kind of distributed Brillouin's temperature strain sensor-based system based on double-sideband modulation; As shown in Figure 2, this system comprises narrow linewidth light source 201, microwave source 205, pulse signal generator 204, image intensifer 208, electric light intensity modulator 203, photo-detector 209 and sensor fibre 212; Wherein, it is that ν 0 continuous light is divided into two bundles through 50: 50 coupling mechanisms that narrow linewidth laser sends centre frequency, wherein a branch ofly is modulated into the pump light pulse through pulse signal generator and intensity modulator, after image intensifer amplifies, squeezes into sensor fibre; It is f that microwave source produces frequency _mMicrowave signal, another Shu Guang is modulated into through carrier-suppressed double sideband to contain frequency be ν 0+f _mWith ν 0+f _mTwo the bundle continuous probe light, squeeze into from the other end of optical fiber, with pump light in optical fiber in opposite directions the transmission.Through surveying the different detection light signals constantly in z=0 place, can obtain the temperature stress information of optical fiber diverse location.

In the present embodiment, having adopted wavelength in the said light source 201 is the narrow linewidth laser of 1550nm, the microwave signal that said microwave source 205 produces about 11GHz, and said pulse signal generator 204 produces the electric pulse of 100ns.

Said electrooptic modulator 203 adopts lithium niobate modulator.

Said image intensifer 208 adopts Erbium-Doped Fiber Amplifier (EDFA).

Said photo-detector 209 adopts avalanche photo diode (APD).

It is four sections general single mode fibers of 82km that said sensor fibre 212 adopts total length, and length is respectively 25km, 25km, 25km, 7km.Brillouin's frequency is respectively 10.692GHz, 10.625GHz, 10.650GHz, 10.622GHz.

In the present embodiment, the pulsewidth of pump light pulse is 100ns, and corresponding spatial resolution is 10m, and pulse peak power is 60mW.The power of surveying each sideband of light is 0.1mW.The time locus that is in the pairing detection light of different frequency difference at z=0 is as shown in Figure 3; Wherein, (a) and (b), (c) are illustrated respectively in pump light and survey the light frequency difference track of pairing detection of optical power when being 10.622GHz, 10.608GHz, 10.544GHz.The remote signaling that can find out optical fiber clearly, the detection light of different frequency is different in the zones of different enlargement factor of whole section optical fiber.

10km that records and the brillouin gain of 80km position spectrum and Lorentz match are as shown in Figure 4; Full width at half maximum is respectively 34.9MHz and 35.7MHz; No significant change, side light pumping pulse almost do not receive the influence of brillouin gain or loss effect.

In order to further specify the counteracting of the present invention to systematic error, on above-mentioned based measurement, pump light is squeezed into from optical fiber connector, squeeze into from the optical fiber front end surveying light, promptly change pump light and the input position of surveying light, as the measurement result second time.Obviously, the near-end of measuring has for the first time become the far-end of measuring for the second time, and the far-end of measuring has for the first time become the near-end of measuring for the second time.Owing to the increase of measuring error along with distance increases, so the systematic error of near-end is very little, and far-end is very big.As shown in Figure 5, (a) Brillouin shift of whole piece optical fiber diverse location is measured in expression for the first time, and (b) Brillouin shift of whole piece optical fiber diverse location is measured in expression for the second time.The result of twice measurement is very identical, is enough to explain that the present invention has offset systematic error significantly.

The foregoing description only is used to explain the present invention, but not is used to limit the present invention.

Claims (5)

1. distributed excited Brillouin temperature strain sensor-based system based on double-sideband modulation; Comprise narrow linewidth light source, power splitter, microwave source, pulse signal transmitter, photoreceiver, image intensifer, electrooptic modulator and sensor fibre; It is characterized in that the continuous light signal after pulsed optical signals and the double-sideband modulation squeezes into from the two ends of sensor fibre respectively; Pulsed optical signals is as pump light signals; Double-side band continuous light signal is as surveying light signal, and pump light produces stimulated Brillouin effect with surveying when light signal meets in optical fiber, and the continuous light signal has carried along the temperature or the strain information of the each point of sensor fibre distribution.

2. temperature strain sensor-based system according to claim 1 is characterized in that the narrow linewidth light source is divided into two-way by power splitter, and one the tunnel is modulated into pulsed optical signals as pump light signals, and another road is modulated into double-side band continuous light signal as surveying light signal.

3. temperature strain sensor-based system as claimed in claim 1; It is characterized in that pump light signals and survey the same narrow linewidth light source generation of optical signals; Pump light signals and the frequency-splitting of surveying between the light signal are stable, do not receive the influence of narrow linewidth light source frequency drift.

4. temperature strain sensor-based system as claimed in claim 1 is characterized in that surveying light signal and comprises two sidebands, and the frequency of two sidebands is positioned at the both sides of pump light signals frequency, and two sidebands equate with the difference on the frequency of pump light signals.

5. temperature strain sensor-based system according to claim 1; It is characterized in that surveying in two sidebands of light signal; The sideband that frequency is high shifts energy to pump light signals through brillouin effect, and the sideband that frequency is low absorbs energy through brillouin effect from pump light, makes pump light signals in transmission course, only experience the decay naturally of optical fiber; Can not experience the energy loss that brillouin effect causes, reduce systematic error greatly.

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