CN102706475B - Distribution-type optical-fiber Raman temperature sensor adopting circulating pulse coding and decoding and Rayleigh demodulation - Google Patents

Abstract

The invention discloses a distribution-type optical-fiber Raman temperature sensor adopting circulating pulse coding and decoding and Rayleigh demodulation, and the sensor comprises a pulse optical-fiber laser, an acoustic-optic demodulator, an integrated optical-fiber wavelength division multiplexer with four ports, two photoelectric receiving amplification modules, a coding-decoding demodulation digital signal processor, an optical-fiber temperature sampling ring, an intrinsic temperature measuring optical fiber, a digital temperature detector and a personal computer (PC). The sensor codes and decodes a signal on the basis of the circulating S matrix conversion, and the online location temperature measurement of the optical fiber is realized by utilizing an effect that the optical-fiber Raman optical strength is demodulated by the temperature and utilizing an optical time domain reflection principle. The circulating laser pulse coding and decoding is realized, and a Rayleigh channel is used as a temperature demodulation reference channel, so that the signal-to-noise ratio of the system is greatly improved, and the measuring precision and the measuring distance of the system are improved.

Description

Adopt the distributed optical fiber Raman temperature sensor of cycle pulse coding and decoding and Rayleigh demodulation

Technical field

The present invention relates to distributed optical fiber Raman temperature sensor, particularly adopt the distributed optical fiber Raman temperature sensor of cycle pulse coding and decoding and Rayleigh demodulation, belong to technical field of optical fiber sensing.

Background technology

Distributed optical fiber temperature sensor system is a kind of for the sensing system that in real time measurement space temperature field distributes, in system optical fiber be transmission medium be also sensing media.Distributed optical fiber Raman temperature sensor utilizes the Raman spectrum effect of optical fiber, and the light carrier transmitting in optical fiber has been modulated in each point temperature field, optical fiber space of living in, after demodulation, the information of space temperature field is shown in real time.It is a special optical fiber telecommunications system; Utilize reflection (Optical time domain reflection the is called for short OTDR) technology in the light time territory of optical fiber, by the velocity of propagation of light in optical fiber and time of optical echo dorsad, to measured temperature point location, it is again a typical fiber temperature lidar system.Distributed optical fiber Raman temperature sensor is the temperature at real-time prediction scene and the orientation of temperature variation online, optical signal transmission fiber no power, therefore there is very strong anti-electromagnetic interference performance, be a kind of line-type heat detector of essential safe type, successfully apply in fields such as power industry, petroleum chemical enterprise, large scale civil engineering and hazard monitoring onlines.

Typical distributed optical fiber Raman temperature sensor generally adopts single laser pulse as pump signal, and with anti-Stokes Raman diffused light, as measuring temperature signal passage, Stokes Raman diffused light is as measuring temperature reference passage.Because Raman scattering light intensity is very weak, signal after opto-electronic conversion is often submerged in various noises, signal to noise ratio (S/N ratio) is very poor, and the size of signal to noise ratio (S/N ratio) is the heaviest more factor of decision systems temperature measurement accuracy or measuring distance, in order to improve signal to noise ratio (S/N ratio), way is to improve a peak power for pumping pulse laser as far as possible, but the peak power of pumping pulse laser while exceeding the non-linear threshold values of optical fiber Raman diffused light can produce nonlinear effect and cannot carry out effective temperature demodulation.Another kind of way is that data are carried out to repeatedly sample averaging, but requires a great deal of time for long system of distance, thereby has reduced the real time reaction ability of thermometric.Although under identical pumping pulse laser peak power, (signal to noise ratio (S/N ratio) is improved as train pulse arteries and veins coding and decoding technology (as: Simplex codes, Golay codes etc.) to obtain better signal to noise ratio (S/N ratio) than monopulse technology

n is code length), but due to the continuity of sequential coding pulse unit, nonlinear fiber threshold values is reduced greatly compared with monopulse, for example, for single-mode fiber, the non-linear valve value rate of sequential coding pulse is less than 1W, and 10ns monopulse system nonlinear fiber valve value rate is about 5W, therefore, if pumping pulse laser peak power all in nonlinear fiber threshold values, adopts the system of sequential coding decoding technique not obtain great improvement than the system reality in signal to noise ratio (S/N ratio) that adopts monopulse technology.

Single-mode fiber, because loss is low, is more suitable for the profile fiber temperature-sensing system of long distance, but single-mode fiber is because bending loss is larger, in practical engineering application, can impact temperature detection.For the impact of bending loss, general method is to adopt Stokes reference channel to carry out temperature solution to anti-Stokes signalling channel to transfer to offset, but because stoke phase passage optical wavelength is longer, than anti-Stokes signal much better than (being about 5 times for 1550nm system), therefore adopt Stokes reference channel cannot effectively offset the impact of bending loss of optical fiber at Bend Loss in Single-mode Fiber.In addition, because the nonlinear fiber valve value rate of stoke phase passage is more much lower than anti-Stokes passage, therefore adopt the input laser pump (ing) peak power of the system of Stokes reference channel to be mainly limited to the non-linear valve value rate of Stokes reference channel, and the laser pump (ing) peak power of input is lower, just mean that the signal to noise ratio (S/N ratio) of system is lower.

Summary of the invention

The object of this invention is to provide a kind of distributed optical fiber Raman temperature sensor that adopts cycle pulse coding and decoding and Rayleigh demodulation, to improve the signal to noise ratio (S/N ratio) of system, obtain higher measuring accuracy and farther measuring distance.

The distributed optical fiber Raman temperature sensor of employing cycle pulse coding and decoding of the present invention and Rayleigh demodulation, comprise pulse optical fiber, acousto-optic modulator, there is the integrated-type optical fibre wavelength division multiplexer of four ports, two photoelectricity receive amplification module, coding and decoding demodulated digital signal processor, fiber optic temperature sampling ring, Intrinsical temperature-measuring optical fiber, digital temperature detector and PC, the output terminal of pulse optical fiber is connected with an input end of acousto-optic modulator, the output terminal of acousto-optic modulator is connected with the input port of integrated-type optical fibre wavelength division multiplexer, the first output port of integrated-type optical fibre wavelength division multiplexer is connected with one end of fiber optic temperature sampling ring, the other end of fiber optic temperature sampling ring is connected with Intrinsical temperature-measuring optical fiber, second of integrated-type optical fibre wavelength division multiplexer is connected with the input end of the first and second photoelectricity reception amplification modules respectively with the 3rd output port, the output terminal that the first and second photoelectricity receive amplification module is connected with two input ends of coding and decoding demodulated digital signal processor respectively, the 3rd input end of coding and decoding demodulated digital signal processor is connected with the output terminal of digital temperature detector, an output terminal of coding and decoding demodulated digital signal processor is connected with the input end of pulse optical fiber, another output terminal is connected with another input end of acousto-optic modulator, the data transmission terminal of coding and decoding demodulated digital signal processor is connected with PC.

In order to guarantee the accuracy of fiber optic temperature sampling ring Temperature Scaling, can by fiber optic temperature sampling ring and digital temperature detector is adjacent be placed in same heat insulation container.

In the present invention, the centre wavelength of described pulse optical fiber is 1550nm, spectral width <5nm, and the unit pulse width <15ns of laser, pulse peak power is greater than 10W.The continuous square-wave signal of the fixed frequency that pulse optical fiber is sent by coding and decoding demodulated digital signal processor drives, the pulsed optical signals of output fixed intervals, fixed pulse width (for example 10ns).

In the present invention, the centre wavelength of described acousto-optic modulator is 1550nm, spectral light spectral width <5nm, and 1550nm loss is less than 3dB, and the response time is less than 50ns.The coded signal control that this acousto-optic modulator is sent by coding and decoding demodulated digital signal processor, light pulse to input is encoded, when the coded signal of sending when coding and decoding demodulated digital signal processor is high level, acousto-optic modulator allows the light pulse signal of input pass through, otherwise, when the coded signal of sending when coding and decoding demodulated digital signal processor is low level, does not let slip light pulse, thereby play the effect of coding.

In the present invention, described integrated-type optical fibre wavelength division multiplexer is by optical fiber bidirectional coupler, optical fiber parallel light path, anti-Stokes Raman diffused light broad band pass filter and Rayleigh scattering light broad band pass filter are integrated, there are 4 ports, 1550nm acousto-optic modulator passes through optical fiber bidirectional coupler, be connected with Intrinsical temperature-measuring optical fiber through fiber optic temperature sampling ring by the first output port, the Raman scattering of anti-Stokes dorsad of temperature-measuring optical fiber and dorsad Rayleigh scattering echo through optical fiber parallel light path respectively by 1450nm and 1550nm broad band pass filter by second and the 3rd output port export.The Raman diffused light of anti-Stokes dorsad of temperature-measuring optical fiber is that 1450nm broad band pass filter is exported by the second output port by centre wavelength, and the Rayleigh scattering light dorsad of temperature-measuring optical fiber is that 1550nm broad band pass filter is exported by the 3rd output port by centre wavelength.

Coding and decoding demodulated digital signal processor in the present invention is made up of high speed analog-to-digital conversion collector and high-speed data processor.

Intrinsical temperature-measuring optical fiber in the present invention is G.652 single-mode fiber, G.651 multimode optical fiber or 62.5/125 multimode optical fiber of standard light communication, and thermometric Guang Xian Long degree is 100m～50km.

Intrinsical temperature-measuring optical fiber is laid on thermometric scene, and temperature-measuring optical fiber is not charged, anti-electromagnetic interference (EMI), and radiation hardness, corrosion-resistant, optical fiber is transmission medium and sensor information.The laser pulse that 1550nm pulse optical fiber sends is injected Intrinsical temperature-measuring optical fiber through acousto-optic modulator coding by integrated-type optical fibre wavelength division multiplexer, the anti-Stokes of the laser dorsad Raman producing on Intrinsical temperature-measuring optical fiber, Reyleith scanttering light wavelet is through integrated-type optical fibre wavelength division multiplexer Fen Bouquet, respectively with first, the second photoelectricity receives amplification module and connects, convert analog electrical signal to and amplify, high speed analog-to-digital conversion collector in coding and decoding demodulated digital signal processor is by the two-way analog electrical signal receiving pointwise collection convert digital signal to and give high-speed data processor respectively, high-speed data processor is decoded the digital signal receiving, recover and react the value of anti-Stokes Raman light and Reyleith scanttering light intensity dorsad, the ratio of this two value reflects the temperature information of each section of optical fiber, the sampling ring temperature value of measuring by high-speed data processor demodulation and in conjunction with digital temperature detector carries out Temperature Scaling, provide the temperature of each point on Intrinsical temperature-measuring optical fiber (segment), and utilize optical time domain reflection to Raman photon temperature sensing detection point location on temperature sensing optical fiber (optical fibre radar location), obtain within a certain period of time on Intrinsical temperature-measuring optical fiber temperature and the temperature variation of each section, within the scope of 0 ° of C-300 ° of C, carry out on-line temperature monitoring.Coding and decoding demodulated digital signal processor is transferred to PC by data result by communication interface, communications protocol, carries out figure demonstration, temperature alarming control.

Beneficial effect of the present invention is:

The distributed optical fiber Raman temperature sensor of employing cycle pulse coding and decoding of the present invention and Rayleigh demodulation adopts the pulse optical fiber of certain frequency as emissive source, utilizes acousto-optic modulator paired pulses to encode.Due to discontinuous between adjacent laser pulse unit, there is time enough interval, make the nonlinear fiber valve value rate of this system and monopulse system very approaching, thereby can greatly improve the peak power of coding laser pulse.The employing of loop coding decoding technique, makes again this system obtain with respect to monopulse system not reducing under spatial discrimination

doubly the signal to noise ratio (S/N ratio) of (N is code length) is improved.Loop coding decoding technique, owing to adopting circulation s-matrix to decode, makes the coding and decoding process of system more simple, and system only needs the identical coded pulse signal of continuous circulation transmitting a line, and the complexity that decoding is calculated also reduces greatly.Single-mode fiber, because loss is low, is more suitable for the profile fiber temperature-sensing system of long distance, but single-mode fiber is because bending loss is larger, in practical engineering application, can impact temperature detection.For the impact of bending loss, general method is to adopt Stokes reference channel to carry out temperature solution to anti-Stokes signalling channel to transfer to offset, but because stoke phase passage optical wavelength is longer, than anti-Stokes signal much better than (being about 5 times for 1550nm system), therefore adopt Stokes reference channel cannot effectively offset the impact of bending loss of optical fiber at Bend Loss in Single-mode Fiber.And the wavelength of the wavelength of Rayleigh scattering signal and anti-stoke phase signal is more approaching, bending loss of optical fiber value is also more approaching, and the present invention adopts Rayleigh passage can offset better the impact of bending loss of optical fiber as temperature demodulation reference channel.Adopt another benefit of Rayleigh passage to be, the nonlinear fiber valve value rate of system is determined by anti-Stokes passage, and the non-linear valve value rate of anti-phase lentor passage is high more a lot of than Stokes passage, contribute to like this raising system to allow the maximum pumping peak power of input, be conducive to further improve signal to noise ratio (S/N ratio), thereby make system can obtain higher measuring accuracy and farther measuring distance.

Accompanying drawing explanation

Fig. 1 is the schematic diagram that adopts the distributed optical fiber Raman temperature sensor of cycle pulse coding and decoding and Rayleigh demodulation.

Fig. 2 is the principle schematic of cycle pulse coding.

Embodiment

Further illustrate the present invention below in conjunction with accompanying drawing.

With reference to Fig. 1, adopt the distributed optical fiber Raman temperature sensor pulse optical fiber 19 of cycle pulse coding and decoding and Rayleigh demodulation, acousto-optic modulator 20, there is the integrated-type optical fibre wavelength division multiplexer 11 of four ports, two photoelectricity receive amplification module 12, 13, coding and decoding demodulated digital signal processor 14, fiber optic temperature sampling ring 17, Intrinsical temperature-measuring optical fiber 18, digital temperature detector 16 and PC 15, the output terminal of pulse optical fiber 19 is connected with an input end of acousto-optic modulator 20, the output terminal of acousto-optic modulator 20 is connected with the input port of integrated-type optical fibre wavelength division multiplexer 11, the first output port of integrated-type optical fibre wavelength division multiplexer 11 is connected with one end of fiber optic temperature sampling ring 17, the other end of fiber optic temperature sampling ring 17 is connected with Intrinsical temperature-measuring optical fiber 18, integrated-type optical fibre wavelength division multiplexer 11 second and the 3rd output port respectively with first and second photoelectricity receive amplification modules 12, 13 input end is connected, the first and second photoelectricity receive amplification module 12, 13 output terminal is connected with two input ends of coding and decoding demodulated digital signal processor 14 respectively, the 3rd input end of coding and decoding demodulated digital signal processor 14 is connected with the output terminal of digital temperature detector 16, an output terminal of coding and decoding demodulated digital signal processor 14 is connected with the input end of pulse optical fiber 19, another output terminal is connected with another input end of acousto-optic modulator 20, the data transmission terminal of coding and decoding demodulated digital signal processor 14 is connected with PC 15.

The centre wavelength of above-mentioned pulse optical fiber is 1550nm, spectral width <5nm, and the unit pulse width <15ns of laser, pulse peak power is greater than 10W.The continuous square-wave signal of the fixed frequency that pulse optical fiber is sent by coding and decoding demodulated digital signal processor drives, the pulsed optical signals of output fixed frequency, fixed intervals, fixed pulse width (for example 10ns).The size of driving frequency depends on length and the code length of system temperature-measuring optical fiber, and for example, for the system of the temperature-measuring optical fibers of 30 kilometers and 83 codings, driving frequency is 250kHz.The width of light pulse depends on required spatial resolution, the spatial resolution of corresponding 1m, and required light pulse half width is approximately 10ns.

Above-mentioned acousto-optic modulator centre wavelength is 1550nm, spectral light spectral width <5nm, and the loss of 1550nm place is less than 3dB, and response speed is less than 50ns.The coded signal control that this acousto-optic modulator is sent by coding and decoding demodulated digital signal processor, encodes to the light pulse of input.When the coded signal of sending when coding and decoding demodulated digital signal processor is high level, acousto-optic modulator allows the light pulse signal of input pass through, otherwise, when the coded signal of sending when coding and decoding demodulated digital signal processor is low level, do not let slip light pulse, thereby play the effect of coding.The signal to noise ratio (S/N ratio) of system is improved degree by formula

determine, N is coding figure place, and coding figure place is higher, and it is better that signal to noise ratio (S/N ratio) is improved degree.

Integrated-type optical fibre wavelength division multiplexer is integrated by optical fiber bidirectional coupler, optical fiber parallel light path, 1450nm anti-Stokes Raman diffused light broad band pass filter and 1550nm Rayleigh scattering light optical filter, there are four ports, one of them 1550nm input port, three output port: 1550nm(the first output ports), 1450nm(the second output port) and 1550nm(the 3rd output port).The coded light pulses of acousto-optic modulator output is passed through optical fiber bidirectional coupler, be connected with long-range temperature-measuring optical fiber through fiber optic temperature sampling ring by the first output port, the anti-Stokes Raman scattering echo of temperature-measuring optical fiber and Rayleigh scattering echo pass through optical fiber parallel light path respectively by 1450nm and 1550nm broad band pass filter by second and the 3rd output port export.The centre wavelength of 1450nm anti-Stokes Raman diffused light broad band pass filter is 1450nm, spectral bandwidth is 36nm, passband ripple <0.3dB, insertion loss <0.3dB, to the isolation >35dB of 1550nm light.The centre wavelength of 1550nm Rayleigh scattering light broad band pass filter is 1550nm, and spectral bandwidth is 5nm, passband ripple <0.3dB, insertion loss <0.3dB.

First, second optical fiber photoelectricity in the present invention receives amplification module 12,13, low noise InGaAs photoelectricity avalanche diode, the low noise AD8015 prime amplifier being connected by optical fiber respectively and the adjustable gain main amplifier being made up of AD8129 and AD8361 form.

Coding and decoding demodulated digital signal processor adopting embedded design in the present invention, the coding and decoding demodulated digital signal processor that the ADSP-BF561 chip that can adopt the ADS62P49 acquisition chip of producing take Texas Instruments (TI) to produce as the high speed acquisition device of core with take ADI (AD) forms as the high speed numerical processor of core.

Digital temperature detector in the present invention can be used 18B20 digital temperature detector.

Intrinsical temperature-measuring optical fiber available standards optical communication in the present invention G.652 single-mode fiber, G.651 multimode optical fiber or 62.5/125 multimode optical fiber, thermometric Guang Xian Long degree is 100m～50km.

Fiber optic temperature sampling ring in the present invention adopts 50 meters of standard light communications with G.652 single-mode fiber, G.651 multimode optical fiber or 62.5/125 multimode optical fiber are coiled into the little ring formation of multi-turn.

Adopt the coding and decoding principle of the distributed optical fiber Raman temperature sensor of cycle pulse coding and decoding and Rayleigh demodulation:

The ultimate principle of loop coding is circulation sends binary coding light pulse signal from row of N position to temperature-measuring optical fiber, the cycle period of N position coded light pulses signal should be equal to or greater than (can increase Measuring Time) light signal in temperature-measuring optical fiber required time back and forth, whole like this temperature-measuring optical fiber has been full of light pulse signal, the scattered signal time-domain curve that system measures is alternately overlapping phenomenon, because N position coded light pulses signal is evenly distributed in cycle period, the light pulse of adjacent code bit has enough large interval time, effectively improve the non-linear valve value rate of temperature-measuring optical fiber, make system can adopt large peak power pulses laser instrument, obtain better signal to noise ratio (S/N ratio).Fig. 2 is the loop coding fundamental diagram of 7, and the binary code of its transmission is P={0 11101 0}.

Suppose the binary coded patterns P={P of a N position ₀... P _n-1, P _j=0,1, j=0 ..., N-1, by the backscattering curve segmentation collecting become N interval, with the coding mode of corresponding N position, the initial time position in each interval and the light pulse x time of corresponding code bit are mutually one to, and N position coded light pulses circulation transmitting.If the sampling number of backscatter signals is L, H is each interval corresponding sampling number, L=H × N.If i=0 ..., H-1, Y _i, X _ibe the matrix that two N capable 1 are listed as, and:

$Y_i=\left[\begin{array}{c}y[i+0H]\\ ...\\ y[i+\mathrm{jH}]\\ ...\\ y[i+(N-1)H]\end{array}\right],$ $X_i=\left[\begin{array}{c}x[i+0H]\\ ...\\ x[i+\mathrm{jH}]\\ ...\\ x[i+(N-1)H]\end{array}\right]$

Wherein y[i+jH] represent backscatter signals jH interval i sampled value, wherein x[i+jH] represent to need i the sampled value in monopulse corresponding backscatter signals jH interval recovered, can draw following rule in conjunction with Fig. 2:

$Y_i=\left[\begin{array}{ccccc}{P}_0& P_{N-1}& ...& P_2& P_1\\ P_1& {\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="120525102636.png"\; state="\{\{state\}\}">P</figure-callout>}}_0& ...& P_3& P_2\\ ...& ...& ...& ...& ...\\ P_{N-1}& P_{N-1}& ...& P_1& P_0\end{array}\right]X_i---\left(1\right)$

If the capable N row of the N of above formula binary matrix is S, this matrix is with P ₀p _n-1... P ₂p ₁for the ring shift right matrix of first trip, from above formula, interval i the sampled value of loop coding backscatter signals jH is corresponding backscatter signals N interval i the sampled value of monopulse stack result in various degree.

If s-matrix is reversible and inverse matrix is S ^-1, to the decode procedure of loop coding backscatter signals be:

X _i=S ^-1Y _i （2）

It is simpler in realization that the relative train pulse arteries and veins coding of process of loop coding is separated (as: Simplex codes, Golay codes etc.), only needs cyclically to send P to temperature-measuring optical fiber ₀p ₁... P _n-2p _n-1code.

Under identical input pumping peak light power and identical duplicate measurements number of times, loop coding decoding technique is improved as with respect to the signal to noise ratio (S/N ratio) of monopulse technology:

${\mathrm{SNR}}_N=\frac{N+1}{2\sqrt{N}}---\left(3\right)$

Wherein N is coding code length, and it is higher that the longer signal to noise ratio (S/N ratio) of code length is improved degree, but the complexity realizing is higher.General 255 following codings are more suitable.In the time that N gets 255:

${\mathrm{SNR}}_{255}=\frac{255+1}{2\sqrt{255}}\&ap;8.02$

Adopt the temperature-measurement principle of the distributed optical fiber Raman temperature sensor of cycle pulse coding and decoding and Rayleigh demodulation:

1. optical fiber Time Domain Reflectometry (OTDR) principle:

In the time that laser pulse transmits in optical fiber, owing to there being the microinhomogeneity of refractive index in optical fiber, can produce Rayleigh scattering, in time domain, it is t that incident light turns back to the required time of optical fiber incident end through backscattering, the distance that laser pulse is passed by optical fiber is 2L, 2L=V × t, V is the speed that light is propagated in optical fiber, V=C/n, C is the light velocity in vacuum, the refractive index that n is optical fiber.What measure in the t moment is to be the Rayleigh scattering light dorsad of L place local from optical fiber incident end fiber lengths.With optical time domain reflection technology, can determine the loss at optical fiber place, the position of fiber failure point, breakpoint, positions measurement point, therefore also can be described as optical-fiber laser radar.

In spatial domain, the rayleigh backscattering photon flux of optical fiber:

${\mathrm{\&phi;}}_R=K_R\&CenterDot;S\&CenterDot;v_0^4\&CenterDot;{\mathrm{\&phi;}}_e\&CenterDot;\exp (-2{\mathrm{\&alpha;}}_{0}L)---\left(4\right)$

φ _e: at the photon flux of the laser pulse of optical fiber incident end; K _r: the coefficient relevant to fiber Rayleigh scattering cross section; v ₀: the frequency of incident laser; S is the backscattering factor of optical fiber; α ₀for the loss of incident photon frequency place optical fiber; L is the fiber lengths of local place from incident end:

$L=\frac{C*t}{2n}---\left(5\right)$

2. optical fiber Raman back scattering and temperature effect thereof:

In frequency domain, Raman scattering photon is divided into Stokes and anti-Stokes Raman scattering photon:

Stokes-Raman scattering photon: v _s=v ₀-Δ v (6)

Anti-Stokes Raman scattering photon: v _a=v ₀+ Δ v (7)

Δ v: vibration frequency Δ v=1.32 × 10 of optical fiber phonon ¹³hz.

Stokes-Raman scattering photon flux at optical fiber L place local:

${\mathrm{\&phi;}}_s=K_s\&CenterDot;S\&CenterDot;v_s^4\&CenterDot;{\mathrm{\&phi;}}_e\&CenterDot;\exp [-({\mathrm{\&alpha;}}_0+{\mathrm{\&alpha;}}_s)\&CenterDot;L]\&CenterDot;R_s\left(T\right)---\left(8\right)$

Anti-Stokes Raman scattering photon flux at optical fiber L place local:

${\mathrm{\&phi;}}_a=K_a\&CenterDot;S\&CenterDot;v_a^4\&CenterDot;{\mathrm{\&phi;}}_e\&CenterDot;\exp [-({\mathrm{\&alpha;}}_0+{\mathrm{\&alpha;}}_a)\&CenterDot;L]\&CenterDot;R_a\left(T\right)---\left(9\right)$

K _s, K _arespectively the coefficient relevant with anti-Stokes Raman Scattering Cross-sections with optical fiber Stokes; S is the backscattering factor of optical fiber; v _s, v _abe respectively optical fiber Stokes and anti-Stokes Raman scattering photon frequency; α ₀, α _s, α _abe respectively the fiber transmission attenuation of incident light, stokes-Raman scattering light, anti-Stokes Raman scattered light; T is temperature; L is the length at optical fiber local to be measured place; R _s(T), R _a(T) be respectively the coefficient relevant with population number on optical fiber molecule low-lying level and high level, relevant with the temperature at optical fiber local place.

R _s(T)=[1-exp(-hΔv/kT)] ^-1 (10)

R _a(T)＝[exp(hΔv/kT)-1] ^-1 (11)

In formula, h is Planck's constant; K is Boltzmann constant, general demodulation method is to carry out demodulation anti-Stokes Raman scattering OTDR curve with stokes-Raman scattering OTDR curve, the present invention adopts Rayleigh scattering OTDR curve to carry out demodulation anti-Stokes Raman scattering OTDR curve, to reduce better the impact of bending loss of optical fiber, and effectively improve the pumping laser peak power of system maximum:

$\frac{{\mathrm{\&phi;}}_{\mathrm{aL}}}{{\mathrm{\&phi;}}_{\mathrm{RL}}}=\frac{K_a}{K_R}\&CenterDot;{\left[\frac{v_a}{v_R}\right]}^4\&CenterDot;{[\exp (\mathrm{h\&Delta;v}/\mathrm{kT})-1]}^{-1}\&CenterDot;\exp [-({\mathrm{\&alpha;}}_a-{\mathrm{\&alpha;}}_0)L]---\left(12\right)$

As known sampling ring L ₀temperature T=the T of place ₀time, obtained by (12) formula:

$\frac{{\mathrm{\&phi;}}_{a{L}_0}\left(T_0\right)}{{\mathrm{\&phi;}}_{R{L}_0}\left(T_0\right)}=\frac{K_a}{K_R}\&CenterDot;{\left[\frac{v_a}{v_R}\right]}^4\&CenterDot;{[\exp (\mathrm{h\&Delta;v}/k{T}_0)-1]}^{-1}\&CenterDot;\exp [-({\mathrm{\&alpha;}}_a-{\mathrm{\&alpha;}}_0)L_0]---\left(13\right)$

(12) formula obtains except (13):

$\frac{{\mathrm{\&phi;}}_{\mathrm{aL}}\left(T\right)\&CenterDot;{\mathrm{\&phi;}}_{R{L}_0}\left(T_0\right)}{{\mathrm{\&phi;}}_{a{L}_0}\left(T_0\right)\&CenterDot;{\mathrm{\&phi;}}_{\mathrm{RL}}\left(T\right)}=\frac{\exp (\mathrm{h\&Delta;v}/k{T}_0)-1}{\exp (\mathrm{h\&Delta;v}/\mathrm{kT})-1}\&CenterDot;\exp [-({\mathrm{\&alpha;}}_a-{\mathrm{\&alpha;}}_0)(L-L_0)]---\left(14\right)$

T0 in (14) formula,

be oneself and know, can obtain the temperature T at local L place.

Claims (4)

1. adopt the distributed optical fiber Raman temperature sensor of cycle pulse coding and decoding and Rayleigh demodulation, it is characterized in that comprising pulse optical fiber (19), acousto-optic modulator (20), there is the integrated-type optical fibre wavelength division multiplexer (11) of four ports, two photoelectricity receive amplification module (12, 13), coding and decoding demodulated digital signal processor (14), fiber optic temperature sampling ring (17), Intrinsical temperature-measuring optical fiber (18), digital temperature detector (16) and PC (15), the output terminal of pulse optical fiber (19) is connected with an input end of acousto-optic modulator (20), the output terminal of acousto-optic modulator (20) is connected with the input port of integrated-type optical fibre wavelength division multiplexer (11), the first output port of integrated-type optical fibre wavelength division multiplexer (11) is connected with one end of fiber optic temperature sampling ring (17), the other end of fiber optic temperature sampling ring (17) is connected with Intrinsical temperature-measuring optical fiber (18), integrated-type optical fibre wavelength division multiplexer (11) second and the 3rd output port respectively with first and second photoelectricity receive amplification modules (12, 13) input end is connected, the first and second photoelectricity receive amplification module (12, 13) output terminal is connected with two input ends of coding and decoding demodulated digital signal processor (14) respectively, the 3rd input end of coding and decoding demodulated digital signal processor (14) is connected with the output terminal of digital temperature detector (16), an output terminal of coding and decoding demodulated digital signal processor (14) is connected with the input end of pulse optical fiber (19), another output terminal is connected with another input end of acousto-optic modulator (20), the data transmission terminal of coding and decoding demodulated digital signal processor (14) is connected with PC (15).

2. the distributed optical fiber Raman temperature sensor of employing cycle pulse coding and decoding according to claim 1 and Rayleigh demodulation, the centre wavelength that it is characterized in that pulse optical fiber (19) is 1550nm, spectral width <5nm, the unit pulse width <15ns of laser, the continuous square-wave signal of the fixed frequency that pulse optical fiber (19) is sent by coding and decoding demodulated digital signal processor (14) drives, the pulsed optical signals of output fixed intervals, fixed pulse width.

3. the distributed optical fiber Raman temperature sensor of employing cycle pulse coding and decoding according to claim 1 and Rayleigh demodulation, is characterized in that fiber optic temperature sampling ring (17) and digital temperature detector (16) is adjacent is placed in same heat insulation container.

4. the distributed optical fiber Raman temperature sensor of employing cycle pulse coding and decoding according to claim 1 and Rayleigh demodulation, is characterized in that Intrinsical temperature-measuring optical fiber (18) is for G.652 single-mode fiber, G.651 multimode optical fiber or 62.5/125 multimode optical fiber.

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