CN202582784U - Distributed optical fiber Raman temperature sensor by utilizing rotary pulse coding and decoding and Rayleigh demodulation - Google Patents

Abstract

The utility model discloses a distributed optical fiber Raman temperature sensor by utilizing rotary pulse coding and decoding and Rayleigh demodulation. The distributed optical fiber Raman temperature sensor by utilizing the rotary pulse coding and decoding and the Rayleigh demodulation comprises a pulse optical fiber laser, an acousto-optic modulation device, an integrated optical fiber wavelength division multiplexer with four ports, two photoelectricity receiving and amplifying modules, a coding and decoding demodulation digital signal processor, an optical fiber temperature sampling ring, an intrinsic type temperature measurement optical fiber, a digital temperature probe and a personal computer (PC). The sensor codes and decodes signals based on a rotation S matrix conversion, and carries out on-line location temperature measurement of optical fibers by utilizing effect of optical fiber Raman light intensity modulated by temperature and a light time domain reflection principle. By utilizing rotary laser pulse coding and decoding and a Rayleigh channel as a temperature demodulation reference channel, a signal to noise ratio of a system is improved greatly, and measurement accuracy and measurement distance of the system are improved.

Description

A kind of distributed optical fiber Raman temperature sensor that adopts cycle pulse coding and decoding and Rayleigh demodulation

Technical field

The utility model relates to distributed optical fiber Raman temperature sensor, particularly adopts the distributed optical fiber Raman temperature sensor of cycle pulse coding and decoding and Rayleigh demodulation, belongs to technical field of optical fiber sensing.

Background technology

The profile fiber temperature sensor system is a kind of sensing system that real-time measurement space temperature field distributes that is used for, in system optical fiber be transmission medium also be the sensing medium.Distributed optical fiber Raman temperature sensor utilizes the Raman spectrum effect of optical fiber, and the light carrier that transmits in the optical fiber has been modulated in each point temperature field, optical fiber space of living in, after demodulation, the information real-time of space temperature field is shown.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 the optical fiber and time of optical echo dorsad; To the measured temperature point location, it is again a typical optical-fiber laser temperature radar system.Distributed optical fiber Raman temperature sensor can online in real time the orientation of forecast field temperature and temperature variation; Optical signal transmission fiber and no power; Therefore has very strong anti-electromagnetic interference performance; Be a kind of line-type heat detector of essential safe type, successfully use in fields such as power industry, petroleum chemical enterprise, large scale civil engineering and online disaster monitorings.

The typical distributed optical fiber Raman temperature sensor generally adopts single laser pulse as pump signal, and as measuring the temperature signal passage, the Stokes Raman diffused light is as measuring the temperature reference passage with the anti-Stokes Raman diffused light.Since the Raman scattering light intensity very a little less than; Signal after opto-electronic conversion often is submerged in the 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); A kind of way is to improve the peak power of pumping pulse laser as far as possible, but the peak power of pumping pulse laser when surpassing the non-linear threshold values of optical fiber Raman diffused light can produce nonlinear effect and can't carry out the effective temperature demodulation.Another kind of way is that data are carried out 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.Train pulse arteries and veins coding and decoding technology (as: Simplex codes; Golay codes etc.) though under identical pumping pulse laser peak power; Can obtain better signal to noise ratio (S/N ratio) (it is code length that signal to noise ratio (S/N ratio) is improved as

N) than monopulse technology; But because the continuity of sequential coding pulse unit makes the nonlinear fiber threshold values reduce greatly than 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 the pumping pulse laser peak power all is in the nonlinear fiber threshold values, adopt the system of sequential coding decoding technique not obtain great improvement than the system's reality on signal to noise ratio (S/N ratio) that adopts monopulse technology.

Single-mode fiber is low because of loss, more be applicable to the profile fiber temperature-sensing system of long distance, but single-mode fiber is bigger because of bending loss, in practical engineering application, can impact temperature detection.Influence for bending loss; General method is to adopt the Stokes reference channel that the anti-Stokes signalling channel is carried out temperature to separate the counteracting of transferring; But because stoke phase passage optical wavelength is longer; Therefore bending loss adopts the Stokes reference channel can't effectively offset the influence of bending loss of optical fiber than anti-Stokes signal much better than (being about 5 times for the 1550nm system) 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; So the input laser pump (ing) peak power that adopts the system of Stokes reference channel mainly is subject to the non-linear valve value rate of Stokes reference channel; And the laser pump (ing) peak power of input is low more, just means that the signal to noise ratio (S/N ratio) of system is low more.

Summary of the invention

The purpose of the utility model provides 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, obtains higher measuring accuracy and farther measuring distance.

The employing cycle pulse coding and decoding of the utility model and the distributed optical fiber Raman temperature sensor of Rayleigh demodulation; Comprise pulse optical fiber; Acousto-optic modulator has the integrated-type optical fibre wavelength division multiplexer of four ports, and two photoelectricity receive amplification modules; Coding and decoding demodulated digital signal processor; Fiber optic temperature sampling ring, Intrinsical thermometric optical fiber, digital temperature detector and PC; The output terminal of pulse optical fiber links to each other with an input end of acousto-optic modulator; The output terminal of acousto-optic modulator links to each other with the input port of integrated-type optical fibre wavelength division multiplexer, and first output port of integrated-type optical fibre wavelength division multiplexer links to each other with an end of fiber optic temperature sampling ring, and the other end of fiber optic temperature sampling ring links to each other with Intrinsical thermometric optical fiber; Second of integrated-type optical fibre wavelength division multiplexer links to each other with the input end that first and second photoelectricity receive amplification module respectively with the 3rd output port; The output terminal that first and second photoelectricity receive amplification module links to each other with two input ends of coding and decoding demodulated digital signal processor respectively, and the 3rd input end of coding and decoding demodulated digital signal processor links to each other with the output terminal of digital temperature detector, and an output terminal of coding and decoding demodulated digital signal processor is connected with the input end of pulse optical fiber; Another output terminal links to each other with another input end of acousto-optic modulator, and the data transmission terminal of coding and decoding demodulated digital signal processor links to each other with PC.

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

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

In the utility model, the centre wavelength of described acousto-optic modulator is 1550nm, the spectral light spectral width 5nm, and the 1550nm loss is less than 3dB, and the response time is less than 50ns.The coded signal control that this acousto-optic modulator is seen off by coding and decoding demodulated digital signal processor; Light pulse to input is encoded, and when the coded signal of seeing off when coding and decoding demodulated digital signal processor was high level, acousto-optic modulator let the light pulse signal of input pass through; Otherwise; When the coded signal of seeing off 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 utility model; Described integrated-type optical fibre wavelength division multiplexer is integrated 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; Have 4 ports; The 1550nm acousto-optic modulator passes through optical fiber bidirectional coupler; Link to each other with Intrinsical thermometric optical fiber through fiber optic temperature sampling ring by first output port, the Raman scattering of anti-Stokes dorsad of thermometric optical fiber and dorsad the Rayleigh scattering echo pass through the optical fiber parallel light path and pass through 1450nm and 1550nm broad band pass filter respectively and export by the second and the 3rd output port.The Raman diffused light of anti-Stokes dorsad of thermometric optical fiber is that the 1450nm broad band pass filter is exported by second output port through centre wavelength, and the Rayleigh scattering light dorsad of thermometric optical fiber is that the 1550nm broad band pass filter is exported by the 3rd output port through centre wavelength.

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

Intrinsical thermometric optical fiber in the utility model for standard light communication with single-mode fiber G.652, G.651 multimode fibre or 62.5/125 multimode fibre, the thermometric fiber lengths is 100m～50km.

Intrinsical thermometric optical fibre installation is on-the-spot at thermometric, and thermometric optical fiber is not charged, anti-electromagnetic interference (EMI), radiation hardness, corrosion-resistant, optical fiber be transmission medium be again sensor information.1550nm pulsed fiber laser emits laser pulses through the acousto-optic modulator encoded by integrating optical fiber WDM injection temperature of the intrinsic optical fiber, optical fiber in the intrinsic temperature generated on the back of laser anti-Stokes Raman, Rayleigh waves by photonic integrated optical WDM of Bouquet, respectively, and first and second photoelectric receiver amplifier module, converted into analog signals and amplified coding and decoding the demodulated digital signal processor High-speed analog-digital converter converts the received acquisition analog signals respectively by two points collected and converted into a digital signal to the high-speed data processor, high-speed data processor the received digital signal is decoded to recover the response back counter Stokes Raman light and Rayleigh light intensity value, which reflects the ratio of two values of the temperature information of each section fibers, and high-speed data processor demodulates digital temperature sensor with the measured temperature value for temperature sample loop calibration, given the intrinsic fiber optic temperature measurement points on the (short) temperature, and the use of optical time domain reflectometer for temperature sensing fiber Raman photon temperature fire detection point positioning (optical radar positioning), within a certain time obtained on the intrinsic temperature of the section of optical fiber temperature and the temperature change amount, in the range of 0 ℃ -300 ℃-line temperature monitoring.Coding and decoding demodulated digital signal processor is transferred to PC with data result through communication interface, communications protocol, carries out graphic presentation, temperature alarming control.

The beneficial effect of the utility model is:

The employing cycle pulse coding and decoding of the utility model and the distributed optical fiber Raman temperature sensor of Rayleigh demodulation adopt the pulse optical fiber of certain frequency as emissive source, utilize the acousto-optic modulator paired pulses to encode.Since discontinuous between adjacent laser pulse unit, time enough had at interval, make that the nonlinear fiber valve value rate of this system and monopulse system are very approaching, thereby can improve the coding peak-power of laser pulse greatly.The employing of loop coding decoding technique makes this system not reduce the signal to noise ratio (S/N ratio) improvement that has obtained under the spatial discrimination with respect to monopulse system

times (N is a code length) again.The loop coding decoding technique makes the coding and decoding process of system more simple owing to adopt the circulation s-matrix to decode, and system only needs the identical coded pulse signal of the emission delegation of circulation continuously, and the complexity that decoding is calculated also reduces greatly.Single-mode fiber is low because of loss, more be applicable to the profile fiber temperature-sensing system of long distance, but single-mode fiber is bigger because of bending loss, in practical engineering application, can impact temperature detection.Influence for bending loss; General method is to adopt the Stokes reference channel that the anti-Stokes signalling channel is carried out temperature to separate the counteracting of transferring; But because stoke phase passage optical wavelength is longer; Therefore bending loss adopts the Stokes reference channel can't effectively offset the influence of bending loss of optical fiber than anti-Stokes signal much better than (being about 5 times for the 1550nm system) in single-mode fiber.And the wavelength of the wavelength of Rayleigh scattering signal and anti-stoke phase signal is more approaching, and the bending loss of optical fiber value is also more approaching, and the utility model adopts the Rayleigh passage can offset the influence of bending loss of optical fiber better as temperature demodulation reference channel.Adopt another benefit of Rayleigh passage to be; The nonlinear fiber valve value rate of system is determined by the anti-Stokes passage; And the non-linear valve value rate of anti-phase lentor passage is high more a lot of than Stokes passage; Help the raising system to allow the maximum pumping peak power of input like this, help further improving signal to noise ratio (S/N ratio), thereby make system can obtain higher measuring accuracy and farther measuring distance.

Description of drawings

Fig. 1 is the synoptic 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 specify the utility model 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; Integrated-type optical fibre wavelength division multiplexer 11 with four ports; Two photoelectricity receive amplification module 12,13, coding and decoding demodulated digital signal processor 14, fiber optic temperature sampling ring 17; Intrinsical thermometric optical fiber 18; Digital temperature detector 16 and PC 15, the output terminal of pulse optical fiber 19 links to each other with an input end of acousto-optic modulator 20, and the output terminal of acousto-optic modulator 20 links to each other with the input port of integrated-type optical fibre wavelength division multiplexer 11; First output port of integrated-type optical fibre wavelength division multiplexer 11 links to each other with an end of fiber optic temperature sampling ring 17; The other end of fiber optic temperature sampling ring 17 links to each other with Intrinsical thermometric optical fiber 18, and second of integrated-type optical fibre wavelength division multiplexer 11 links to each other with the input end of first and second photoelectricity reception amplification module 12,13 respectively with the 3rd output port, and the output terminal of first and second photoelectricity reception amplification module 12,13 links to each other 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 links to each other 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, and another output terminal links to each other with another input end of acousto-optic modulator 20, and the data transmission terminal of coding and decoding demodulated digital signal processor 14 links to each other with PC 15.

The centre wavelength of above-mentioned pulse optical fiber is 1550nm, and < 5nm, < 15ns, pulse peak power is greater than 10W for the unit pulse width of laser for spectral width.Pulse optical fiber is driven by the continuous square-wave signal of the fixed frequency that coding and decoding demodulated digital signal processor is seen off, the pulsed optical signals of output fixed frequency, fixed intervals, fixed pulse width (for example 10ns).The size of driving frequency depends on system's thermometric length of fiber and code length, and for example, for the system of 30 kilometers thermometric optical fiber 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, the 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 seen off by coding and decoding demodulated digital signal processor is encoded to the light pulse of input.When the coded signal of seeing off when coding and decoding demodulated digital signal processor is high level; Acousto-optic modulator lets the light pulse signal of input pass through, otherwise, when the coded signal of seeing off 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 and is determined by formula

; N is the coding figure place; The coding figure place is high more, and it is good more that signal to noise ratio (S/N ratio) is improved degree.

The 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; Have four ports; One of them 1550nm input port; Three output port: 1550nm (first output port), 1450nm (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; Linked to each other with long-range thermometric optical fiber through fiber optic temperature sampling ring by first output port, the anti-Stokes Raman scattering echo of thermometric optical fiber and Rayleigh scattering echo are exported by the second and the 3rd output port through 1450nm and 1550nm broad band pass filter respectively through the optical fiber parallel light path.The centre wavelength of 1450nm anti-Stokes Raman diffused light broad band pass filter is 1450nm, and spectral bandwidth is 36nm, and < 0.3dB inserts loss < 0.3dB is to the isolation of 1550nm light>35dB to passband ripple.The centre wavelength of 1550nm Rayleigh scattering light broad band pass filter is 1550nm, and spectral bandwidth is 5nm, and < 0.3dB inserts loss < 0.3dB to passband ripple.

First, second optical fiber photoelectricity in the utility model receives amplification module 12; 13, the low noise InGaAs photoelectricity avalanche diode that connects by optical fiber respectively, low noise AD8015 prime amplifier and constitute by the adjustable gain main amplifier that AD8129 and AD8361 constitute.

Coding and decoding demodulated digital signal processor adopting embedded design in the utility model, can to adopt the ADS62P49 acquisition chip of producing with Texas Instruments (TI) be the high speed acquisition device of core and be the coding and decoding demodulated digital signal processor that the high speed numerical processor of core is formed with the ADSP-BF561 chip that ADI (AD) produces.

Digital temperature detector in the utility model can be used 18B20 digital temperature detector.

Intrinsical thermometric optical fiber available standards optic communication in the utility model is with single-mode fiber G.652, G.651 multimode fibre or 62.5/125 multimode fibre, and the thermometric fiber lengths is 100m～50km.

Fiber optic temperature sampling in the utility model encircles adopts 50 meters standard light communications with G.652 single-mode fiber, G.651 multimode optical fiber or the little ring formation of the many circles of 62.5/125 multimode optical fiber coiled.

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 the row of N position is sent in a binary coding light pulse signal from circulation to thermometric 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 the required back and forth time of thermometric optical fiber; Whole like this thermometric optical fiber has been full of light pulse signal, and the scattered signal time-domain curve that system measures is alternately overlapping phenomenon, because N position coded light pulses signal is evenly distributed in the cycle period; The light pulse of adjacent code position has enough big interval time; Effectively improve the non-linear valve value rate of thermometric optical fiber, made system can adopt big peak power pulses laser instrument, obtained better signal to noise ratio (S/N ratio).Fig. 2 is 7 a loop coding fundamental diagram, 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, with the backscattering curve segmentation that collects become N interval, with the coding mode of corresponding N position, the light pulse x time of each interval initial moment position and correspondence code position mutually one to, and N position coded light pulses circulates and launches.If the sampling number of backscatter signals is L, H is each interval corresponding sampling points number, then L=H * N.If i=0 ..., H-1, Y _i, X _iBe the matrix of two capable 1 row of N, 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] representes interval i the sampled value of backscatter signals jH, and wherein x [i+jH] expression needs interval i sampled value of monopulse correspondence backscatter signals jH of recovery, can draw following rule in conjunction with Fig. 2:

$Y_i=\left[\begin{array}{ccccc}{P}_0& P_{N-1}& ...& P_2& P_1\\ P_1& {\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="120525105443.png"\; state="\{\{state\}\}">P</figure-callout>}}_0& ...& P_3& P_2\\ ...& ...& ...& ...& ...\\ P_{N-1}& P_{N-1}& ...& P_1& P_0\end{array}\right]X_i---\left(1\right)$

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

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

X _i=S ^-1Y _i （2）

It is simpler in realization that the relative train pulse arteries and veins coding of the process of loop coding is separated (as: Simplex codes, Golay codes etc.), only needs to send P to thermometric optical fiber circularly ₀P ₁... P _N-2P _N-1Sign indicating number gets final product.

Under identical input pumping peak light power and identical duplicate measurements number of times, the 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 the coding code length, and it is high more that the long more signal to noise ratio (S/N ratio) of code length is improved degree, but the complexity that realizes is high more.General coding below 255 is more suitable.When 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. fiber optic, light Time Domain Reflectometry (OTDR) principle:

When laser pulse transmits,, can produce Rayleigh scattering owing to there is the microinhomogeneity of refractive index in the optical fiber in optical fiber; In time domain, it is t that incident light turns back to the required time of optical fiber input end through backscattering, and the distance that laser pulse is passed by in optical fiber is 2L; 2L=V * t, V are the speed that light is propagated in optical fiber, V=C/n; C is the light velocity in the vacuum, and n is the refractive index of optical fiber.What measure constantly at t is to be the Rayleigh scattering light dorsad of L place local from optical fiber input end fiber lengths.Use optical time domain reflection technology, can confirm the loss at optical fiber place, the position of fiber failure point, breakpoint positions measurement point, therefore also can be described as the 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 input end; K _R: the coefficient relevant with the fiber Rayleigh scattering cross section; v ₀: the frequency of incident laser; S is the backscattering factor of optical fiber; α ₀Loss for incident photon frequency place optical fiber; L is the fiber lengths of local place from the incident end:

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

2. optical fiber Raman backscattering and temperature effect thereof:

In frequency domain, the 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:

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

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

${\mathrm{\&phi;}}_a=K_a\&CenterDot;S\&CenterDot;v_a^4\&CenterDot;{\mathrm{\&phi;}}_e\&CenterDot;\exp [-({\mathrm{\&alpha;}}_0+{\mathrm{\&alpha;}}_a)\&CenterDot;L]\&CenterDot;R_a\left(T\right)---\left(8\right)$

K _s, K _aBe respectively the coefficient relevant with anti-Stokes Raman scattering cross section with the 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 a temperature; L is the length at optical fiber local to be measured place; R _s(T), R _a(T) be respectively with optical fiber molecule low-lying level and high level on the relevant coefficient of population number, 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)

H is a Planck's constant in the formula; K is a Boltzmann constant; General demodulation method is to come demodulation anti-Stokes Raman scattering OTDR curve with stokes-Raman scattering OTDR curve; The utility model adopts Rayleigh scattering OTDR curve to come demodulation anti-Stokes Raman scattering OTDR curve; Reducing the influence of bending loss of optical fiber better, and effectively improve the maximum pumping laser peak power of system:

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

As known sampling ring L ₀Temperature T=the T of place ₀The time, get by (12) formula:

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

(12) formula gets except that (13):

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

T in (14) formula ₀,

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

Claims (4)

1. distributed optical fiber Raman temperature sensor that adopts cycle pulse coding and decoding and Rayleigh demodulation; It is characterized in that comprising pulse optical fiber (19); Acousto-optic modulator (20); Integrated-type optical fibre wavelength division multiplexer (11) with four ports; Two photoelectricity receive amplification module (12,13), coding and decoding demodulated digital signal processor (14), fiber optic temperature sampling ring (17); Intrinsical thermometric optical fiber (18); Digital temperature detector (16) and PC (15), the output terminal of pulse optical fiber (19) links to each other with an input end of acousto-optic modulator (20), and the output terminal of acousto-optic modulator (20) links to each other with the input port of integrated-type optical fibre wavelength division multiplexer (11); First output port of integrated-type optical fibre wavelength division multiplexer (11) links to each other with an end of fiber optic temperature sampling ring (17); The other end of fiber optic temperature sampling ring (17) links to each other with Intrinsical thermometric optical fiber (18), and second of integrated-type optical fibre wavelength division multiplexer (11) links to each other with the input end of first and second photoelectricity reception amplification modules (12,13) respectively with the 3rd output port, and the output terminal of first and second photoelectricity reception amplification modules (12,13) links to each other 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) links to each other 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), and another output terminal links to each other with another input end of acousto-optic modulator (20), and the data transmission terminal of coding and decoding demodulated digital signal processor (14) links to each other with PC (15).

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

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

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

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