CN101819073A - Distributed optical fiber Raman temperature sensor coding and decoding by adopting sequential pulse - Google Patents

Abstract

The invention discloses a distributed optical fiber Raman temperature sensor coding and decoding by adopting sequential pulses, which is a distributed optical fiber temperature measuring system coding and decoding a signal on the basis of S-matrix transformation and carrying out optical fiber on-line positioning temperature measurement by utilizing the effect of optical fiber Raman light intensity modulated by temperature and an optical time domain reflection principle. The distributed optical fiber Raman temperature sensor can obtain better signal-to-noise radio under the condition of spending same measuring time by using a sequential multidigit laser pulse coding and decoding technology, increase the number of emitted photons, enhance the space resolution by narrowing the thicknesses of laser pulses and also effectively prevent the nonlinear effect of optical fibers by lowering the requirements on the peak value power of a single laser pulse; and in addition, the invention effectively solves the contradiction of space resolution enhancement-signal-to-noise radio reduction and signal-to-noise radio enhancement-space resolution reduction or measuring time increase of the traditional optical fiber distribution temperature sensor, enhances the temperature measuring precision, can be used for a distributed optical fiber temperature sensor which has ultra long range and high space resolution.

Description

Adopt the distributed optical fiber Raman temperature sensor of train pulse coding and decoding

Technical field

The present invention relates to fibre optic temperature sensor, particularly distributed optical fiber Raman temperature sensor.

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 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 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 forecast the on-the-spot temperature and the orientation of temperature variation, the variation of on-line monitoring scene temperature, in certain temperature range alarm temperature is set, 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.

Typical distribution formula optical fiber Raman temperature sensor generally adopts laser pulse as pump Pu 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.Owing to determined by laser pulse width by the space orientation resolution of temperature spot then on the optical fiber, in order to obtain higher spatial resolution, laser pulse width need be pressed narrow, but the consequence of pressing narrow laser pulse width to bring is the useful photon number of laser to have tailed off, thereby make Stokes and the anti-lentor scattered light intensity signal to noise ratio (S/N ratio) that makes temperature signal that diminishes of taking advantage of reduce, have influence on temperature measurement accuracy.Along with system's ranging increases, it is serious that this problem seems all the more.In order to address this problem, traditional way is the emissive power that increases the laser burst pulse, can occur nonlinear effect but increase emissive power to a certain degree back Raman diffused light, makes the temperature demodulation become very difficult.Another kind of way is to increase the signals collecting number of times, improves signal to noise ratio (S/N ratio) by multiple averaging, but has increased the working time of system like this, thereby has reduced the real time reaction ability of thermometric.

Summary of the invention

The purpose of this invention is to provide a kind of distributed optical fiber Raman temperature sensor that adopts the train pulse coding and decoding, with this contradiction of effective solution traditional fiber districution temperature sensor " raising spatial resolution-reduction signal to noise ratio (S/N ratio); improve signal to noise ratio (S/N ratio)-reduction spatial resolution or increase Measuring Time ", improve temperature measurement accuracy.

The distributed optical fiber Raman temperature sensor of employing train pulse coding and decoding of the present invention, comprise optical fiber coupling multiple-pulse semiconductor laser transmitter module with Raman frequency shift, Erbium-Doped Fiber Amplifier (EDFA), bandpass filter 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 optical fiber coupling multiple-pulse semiconductor laser transmitter module links to each other with the input end of Erbium-Doped Fiber Amplifier (EDFA), the output terminal of Erbium-Doped Fiber Amplifier (EDFA) links to each other with an end of bandpass filter, the other end of bandpass filter links to each other with the input port of integrated-type optical fibre wavelength division multiplexer, first output port of integrated-type optical fibre wavelength division multiplexer links to each other with an end of fiber optic temperature sampling ring, 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, the 3rd input end of the output terminal of digital temperature detector and coding and decoding demodulated digital signal processor links to each other, the output terminal of coding and decoding demodulated digital signal processor links to each other with the input end of optical fiber coupling multiple-pulse semiconductor laser transmitter module, and the communication interface of coding and decoding demodulated digital signal processor connects 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.

Intrinsical thermometric optical fibre installation is at the thermometric scene, and thermometric optical fiber is not charged, anti-electromagnetic interference (EMI), radiation hardness, corrosion-resistant, optical fiber be transmission medium be again sensor information.During work, optical fiber coupling multiple-pulse semiconductor laser transmitter module drives and sends corresponding 255 coded pulse light by what coding and decoding demodulated digital signal processor was sent by regularly arranged 255 coded pulses of sequence of 255 * 255S matrix conversion, this coded pulse light amplifies through Erbium-Doped Fiber Amplifier (EDFA), obtain enough big luminous power, after bandpass filter filters, be defeated by the integrated-type optical fibre wavelength division multiplexer, and inject Intrinsical thermometric optical fiber by the integrated-type optical fibre wavelength division multiplexer.The laser anti-Stokes Raman that on Intrinsical thermometric optical fiber, produces, Stokes Raman light wavelet is through the beam splitting of integrated-type optical fibre wavelength division multiplexer, respectively by first, second photoelectricity reception amplification module converts analog electrical signal to and amplifies and be defeated by coding and decoding demodulated digital signal processor, coding and decoding demodulated digital signal processor is with the pointwise collection and convert digital signal to and decode respectively of the two-way analog electrical signal that receives, recover and react the value of anti-Stokes Raman light and Stokes Raman light intensity dorsad, the ratio of this two value reflects the temperature information of each section of optical fiber, carry out Temperature Scaling by the high-speed data processor demodulation and in conjunction with the sampling ring temperature value that the digital temperature detector is measured, provide the temperature of each point (segment) on the Intrinsical temperature optical fiber, and utilize optical time domain reflection to Raman photon temperature sensing detection point location on the temperature-sensitive optical fiber (optical fibre radar location), in 40 seconds, obtain the temperature and the temperature variation of each section on the Intrinsical thermometric optical fiber, on-line temperature monitoring is carried out in temperature measurement accuracy ± 1 ℃ in 0 ℃ of-300 ℃ of scope.Coding and decoding demodulated digital signal processor is transferred to PC with data result by communication interface, communications protocol, carries out graphic presentation, temperature alarming control.

Beneficial effect of the present invention is:

The distributed optical fiber Raman temperature sensor of employing train pulse coding and decoding of the present invention, with laser sequential coding pulse as emissive source, improve the photon number that transmits greatly, made that Raman scattering light intensity dorsad improves greatly, thereby improved the signal to noise ratio (S/N ratio) of system greatly.The space orientation resolution of this sensor is by the narrow pulse width decision of unit, owing to adopt sequential coding pulse emission, when improving the ballistic phonon number, can improve spatial resolution by pressing narrow laser pulse width again, and needn't improve single peak-power of laser pulse from and effectively prevented fiber nonlinear effect; Simultaneously,, improved extraction, the resolving ability of system greatly, under the spending same Measuring Time, can obtain better signal to noise ratio (S/N ratio) signal owing to adopted coding, decoding technique.This invention efficiently solves traditional fiber districution temperature sensor " raising spatial resolution-reduction signal to noise ratio (S/N ratio); improve signal to noise ratio (S/N ratio)-reduction spatial resolution or increase Measuring Time ", and this gives the shield problem, can realize the profile fiber temperature-sensing system of very-long-range, high spatial resolution.

Description of drawings

Fig. 1 is the synoptic diagram that adopts the distributed optical fiber Raman temperature sensor of train pulse coding and decoding.

Fig. 2 is train pulse coding and corresponding anti-Stokes dorsad (or Stokes) signal waveforms, a) being three bit sequence monopulses and corresponding anti-Stokes dorsad (or Stokes) signal waveform wherein, b) be anti-Stokes dorsad (or Stokes) signal waveform of tri-bit encoding train pulse and correspondence.

Embodiment

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

With reference to Fig. 1, the distributed optical fiber Raman temperature sensor of employing train pulse coding and decoding of the present invention, comprise optical fiber coupling multiple-pulse semiconductor laser transmitter module 21 with Raman frequency shift, Erbium-Doped Fiber Amplifier (EDFA) 19, bandpass filter 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 optical fiber coupling multiple-pulse semiconductor laser transmitter module 21 links to each other with the input end of Erbium-Doped Fiber Amplifier (EDFA) 19, the output terminal of Erbium-Doped Fiber Amplifier (EDFA) 19 links to each other with an end of bandpass filter 20, the other end of bandpass filter 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, the second and the 3rd output port of integrated-type optical fibre wavelength division multiplexer 11 receives amplification module 12 with first and second photoelectricity respectively, 13 input end links to each other, first and second photoelectricity receive amplification module 12,13 output terminal links to each other with two input ends of coding and decoding demodulated digital signal processor 14 respectively, the 3rd input end of the output terminal of digital temperature detector 16 and coding and decoding demodulated digital signal processor 14 links to each other, the output terminal of coding and decoding demodulated digital signal processor 14 links to each other with the input end of optical fiber coupling multiple-pulse semiconductor laser transmitter module 21, and the communication interface of coding and decoding demodulated digital signal processor 14 connects PC 15.

The centre wavelength of the optical fiber coupling multiple-pulse semiconductor laser transmitter module 21 of the Raman frequency shift among the present invention can be 1550nm, spectral width＜5nm, the unit pulse width＜6ns of laser; Bandpass filter 20 spectral bandwidths are 8nm, and passband ripple＜0.3dB inserts loss＜0.3dB.

Integrated-type optical fibre wavelength division multiplexer 11 among the present invention is integrated by optical fiber bidirectional coupler, optical fiber parallel light path, anti-Stokes Raman diffused light broad band pass filter and Stokes Raman diffused light broad band pass filter, has 4 ports.The optical fiber coupling multiple-pulse semiconductor laser transmitter module of the Raman frequency shift of corresponding 1550nm centre wavelength, the wavelength of the input port of optical fibre wavelength division multiplexer is 1550nm, the wavelength of three output ports is respectively: 1550nm, 1450nm and 1650nm.Wherein, the centre wavelength of 1450nm anti-Stokes Raman diffused light broad band pass filter is 1450nm, and spectral bandwidth is 36nm, and passband ripple＜0.3dB inserts loss＜0.3dB, to the isolation＞35dB of 1550nm light.The centre wavelength of 1650nm Stokes Raman diffused light broad band pass filter is 1650nm, and spectral bandwidth is 38nm, and passband ripple＜0.3dB inserts loss＜0.3dB, to the isolation＞35dB of 1550nm light.

The optical fiber coupling multiple-pulse semiconductor laser transmitter module 21 of the Raman frequency shift among the present invention also is applicable to the wavelength of other wave band, for example: 1060nm, 1310nm etc.

First, second optical fiber photoelectricity among the present invention receives amplification module 13,14, constitute by the low noise InGaAs photoelectricity avalanche diode of optical fiber coupling, low noise AD8015 prime amplifier and by the adjustable gain main amplifier that AD8129 and AD8361 constitute respectively.

Coding and decoding demodulated digital signal processor among the present invention can adopt the ADS62P49 acquisition chip of producing with Texas Instruments (TI) to be the high speed acquisition device of core and to 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 among the present invention adopts 18B20 digital temperature detector.

Intrinsical thermometric optical fiber among the present invention is logical instrument 62.5/125 multimode optical fiber of light, and the thermometric fiber lengths is 100m～50km.

Fiber optic temperature sampling ring among the present invention adopts the logical instrument of 50 meters light to form with the little ring of 62.5/125 multimode optical fiber coiled multi-turn.

Adopt the coding and decoding principle of the distributed optical fiber Raman temperature sensor of train pulse coding and decoding:

The train pulse coding of this sensor realizes that by s-matrix conversion the s-matrix conversion is a kind of variant that the standard hadamard gets (Hadamard) conversion, and also can be described as hadamard must change.The element of s-matrix is formed by " 0 " and " 1 ", and these characteristics are applicable to laser train pulse coding very much, and on behalf of laser instrument, available in actual applications " O " close, and represents laser instrument to open with " 1 ".The coded system of this employing " 0 ", " 1 " can be described as simple code again.And the process of decoding is corresponding contrary s-matrix conversion.Coding and decoding process below in conjunction with one 3 is further set forth principle.

Shown in Fig. 2 (a), P ₁(t), P ₂(t), P ₃(t) represent pulsewidth and spacing to be the laser pulse of τ, R respectively ₁(t), R ₂(t), R ₃(t) represent anti-Stokes dorsad (or Stokes) signal of respective pulses respectively.Three s-matrix is:

$S=\left[\begin{array}{ccc}1& 0& 1\\ 0& 1& 1\\ 1& 1& 0\end{array}\right]---\left(1\right)$

Result with the s-matrix conversion is:

$S\left[\begin{array}{c}{P}_1\left(t\right)\\ P_2\left(t\right)\\ P_3\left(t\right)\end{array}\right]=\left[\begin{array}{c}{P}_1\left(t\right)+P_3\left(t\right)\\ P_2\left(t\right)+P_3\left(t\right)\\ P_1\left(t\right)+P_2\left(t\right)\end{array}\right]---\left(2\right)$

P shown in Fig. 2 (b) ₁(t)+P ₃(t), P ₂(t)+P ₃(t), P ₁(t)+P ₂(t) be with 3 coding laser pulse sequence after the s-matrix conversion.R in Fig. 2 (b) ₁(t)+R ₃(t), R ₂(t)+R ₃(t), R ₁(t)+R ₂(t) represent coding laser pulse sequence P respectively ₁(t)+P ₃(t), P ₂(t)+P ₃(t), P ₁(t)+P ₂(t) anti-Stokes dorsad (or Stokes) signal.If R ' ₁(t), R ' ₂(t), R ' ₃(t) represent R respectively ₁(t)+R ₃(t), R ₂(t)+R ₃(t), R ₁(t)+R ₂(t) actual anti-Stokes dorsad (or Stokes) signal that records.e ₁(t), e ₂(t), e ₃(t) represent R respectively ₁(t)+R ₃(t), R ₂(t)+R ₃(t), R ₁(t)+R ₂(t) noise of introducing in the actual detected.Then:

$\left[\begin{array}{c}{R}_1^{\′}\left(t\right)\\ R_2^{\′}\left(t\right)\\ R_3^{\′}\left(t\right)\end{array}\right]=S\left[\begin{array}{c}{R}_1\left(t\right)\\ R_2\left(t\right)\\ R_3\left(t\right)\end{array}\right]+\left[\begin{array}{c}{e}_1\left(t\right)\\ e_2\left(t\right)\\ e_3\left(t\right)\end{array}\right]---\left(3\right)$

If

For decoding back anti-Stokes dorsad (or Stokes) signal that recovers then:

$\left[\begin{array}{c}{\stackrel{\‾}{R}}_1\left(t\right)\\ {\stackrel{\‾}{R}}_2\left(t\right)\\ {\stackrel{\‾}{R}}_3\left(t\right)\end{array}\right]=S^{-1}\left[\begin{array}{c}{R}_1^{\′}\left(t\right)\\ R_2^{\′}\left(t\right)\\ R_3^{\′}\left(t\right)\end{array}\right]=\frac{1}{2}\left[\begin{array}{ccc}1& -1& 1\\ -1& 1& 1\\ 1& 1& -1\end{array}\right]\left[\begin{array}{c}{R}_1^{\′}\left(t\right)\\ R_2^{\′}\left(t\right)\\ R_3^{\′}\left(t\right)\end{array}\right]---\left(4\right)$

By (4) Shi Kede:

${\stackrel{\‾}{R}}_1\left(t\right)=\frac{1}{2}[R_1^{\′}\left(t\right)-R_2^{\′}\left(t\right)+R_3^{\′}\left(t\right)]=R_1\left(t\right)+\frac{e_1\left(t\right)-e_2\left(t\right)+e_3\left(t\right)}{2}---\left(5\right)$

${\stackrel{\‾}{R}}_2\left(t\right)=\frac{1}{2}[{-R}_1^{\′}\left(t\right)+R_2^{\′}\left(t\right)+R_3^{\′}\left(t\right)]=R_2\left(t\right)+\frac{-e_1\left(t\right)+e_2\left(t\right)+e_3\left(t\right)}{2}---\left(6\right)$

${\stackrel{\‾}{R}}_3\left(t\right)=\frac{1}{2}[R_1^{\′}\left(t\right)+R_2^{\′}\left(t\right)-R_3^{\′}\left(t\right)]=R_3\left(t\right)+\frac{e_1\left(t\right)+e_2\left(t\right)-e_3\left(t\right)}{2}---\left(7\right)$

By (5) (6) (7) Shi Kede:

$\frac{{\stackrel{\‾}{R}}_1\left(t\right)+{\stackrel{\‾}{R}}_2(t+\mathrm{\τ})+{\stackrel{\‾}{R}}_3(t+2\mathrm{\τ})}{3}=R_1\left(t\right)+\frac{e_1\left(t\right)-e_2\left(t\right)+e_3\left(t\right)}{6}+---\left(8\right)$

$\frac{-e_1(t+\mathrm{\τ})+e_2(t+\mathrm{\τ})+e_3(t+\mathrm{\τ})+e_1(t+2\mathrm{\τ})+e_2(t+2\mathrm{\τ})-e_3(t+3\mathrm{\τ})}{6}$

If noise e _i(t) be irrelevant, have zero-mean, its variance is σ ², then the average of noise and mean square deviation can be expressed as:

(9)

E[e _i(t)e _j(t+ζ)]＝0((i≠j)or(i＝j，ζ≠0))

Can get anti-Stokes dorsad (or Stokes) the signal mean square deviation of finally recovering by (8) (9) formula is:

$E\left\{{[\frac{{\stackrel{\‾}{R}}_1\left(t\right)+{\stackrel{\‾}{R}}_2(t+\mathrm{\τ})+{\stackrel{\‾}{R}}_3(t+2\mathrm{\τ})}{3}-R_1\left(t\right)]}^2\right\}=\frac{{9\mathrm{\σ}}^2}{36}=\frac{1}{4}{\mathrm{\σ}}^2---\left(10\right)$

Adopting 3 average mean square deviations of tradition is σ ²/ 3, the signal to noise ratio (S/N ratio) that 3 methods of average of corresponding tradition adopt 3 digit pulse sequential codings decoding to obtain is improved as:

${\mathrm{SNR}}_3=\sqrt{\frac{{\mathrm{\σ}}^2}{3}}/\sqrt{\frac{{\mathrm{\σ}}^2}{4}}=\frac{2}{\sqrt{3}}---\left(11\right)$

Analogize as stated above, adopt the obtainable signal to noise ratio (S/N ratio) of train pulse coding and decoding of N position to be improved as:

${\mathrm{SNR}}_N=\sqrt{\frac{{\mathrm{\σ}}^2}{N}}/\sqrt{\frac{{\mathrm{\σ}}^2}{{(N+1)}^2}}=\frac{N+1}{2\sqrt{N}}---\left(12\right)$

By (12) formula as can be known, the signal to noise ratio (S/N ratio) improvement improves along with the raising of coding figure place.

When N gets 255: ${\mathrm{SNR}}_{255}=\frac{255+1}{2\sqrt{255}}\≈8.02$

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

1. optical fiber optical time domain reflection (OTDR) principle:

When laser pulse transmits in optical fiber, owing to there is the microinhomogeneity of refractive index in the optical fiber, can produce Rayleigh scattering, in time domain, it is t that incident light turns back to the required time of optical fiber input end through backscattering, 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 determine 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:

${\mathrm{\φ}}_R=K_R\·S\·v_0^4\·{\mathrm{\φ}}_e\·\exp (-2{\mathrm{\α}}_{0}L)---\left(13\right)$

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:

$L=\frac{C*t}{2n}---\left(14\right)$

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 (15)

Anti-Stokes Raman scattering photon: v _a=v ₀+ Δ v (16)

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:

${\mathrm{\φ}}_s=K_s\·S\·v_s^4\·{\mathrm{\φ}}_e\·\exp [-({\mathrm{\α}}_0+{\mathrm{\α}}_s)\·L]\·R_s\left(T\right)---\left(17\right)$

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

${\mathrm{\φ}}_a=K_a\·S\·v_a^4\·{\mathrm{\φ}}_e\·\exp [-({\mathrm{\α}}_0+{\mathrm{\α}}_a)\·L]\·R_a\left(T\right)---\left(18\right)$

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; 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 (19)

R _a(T)＝[exp(hΔv/kT)-1] ^-1 (20)

H is a Planck's constant in the formula; K is a Boltzmann constant, and general demodulation method is to come demodulation anti-Stokes Raman scattering OTDR curve with stokes-Raman scattering OTDR curve:

$\frac{{\mathrm{\φ}}_{\mathrm{aL}}}{{\mathrm{\φ}}_{\mathrm{sL}}}=\frac{K_a}{K_s}\·{\left[\frac{v_a}{v_s}\right]}^4\·\exp (-\mathrm{h\Δv}/\mathrm{kT})\·\exp [-({\mathrm{\α}}_a-{\mathrm{\α}}_s)L]---\left(21\right)$

As known sampling ring L ₀Temperature T=the T of place ₀The time, get by (21) formula:

$\frac{{\mathrm{\φ}}_{a{L}_0}\left(T_0\right)}{{\mathrm{\φ}}_{s{L}_0}\left(T_0\right)}=\frac{K_a}{K_s}\·{\left[\frac{v_a}{v_s}\right]}^4\·\exp (-\mathrm{h\Δv}/k{T}_0)\·\exp [-({\mathrm{\α}}_a-{\mathrm{\α}}_s)L_0]---\left(22\right)$

(21) formula is removed (22)

$\frac{{\mathrm{\φ}}_{\mathrm{aL}}\left(T\right)\·{\mathrm{\φ}}_{{\mathrm{sL}}_0}\left(T_0\right)}{{\mathrm{\φ}}_{{\mathrm{aL}}_0}\left(T_0\right)\·{\mathrm{\φ}}_{\mathrm{sL}}\left(T\right)}=\frac{\exp (-\mathrm{h\Δv}/\mathrm{kT})}{\exp (-\mathrm{h\Δv}/k{T}_0)}\·\exp [-({\mathrm{\α}}_a-{\mathrm{\α}}_s)(L-L_0)]---\left(23\right)$

From (23) formula:

$\frac{1}{T}=\frac{1}{T_0}-\frac{k}{\mathrm{h\Δv}}[\ln \frac{{\mathrm{\φ}}_{\mathrm{aL}}\left(T\right)\·{\mathrm{\φ}}_{{\mathrm{sL}}_0}\left(T_0\right)}{{\mathrm{\φ}}_{{\mathrm{aL}}_0}\left(T_0\right)\·{\mathrm{\φ}}_s\left(T\right)}+({\mathrm{\α}}_a-{\mathrm{\α}}_s)(L-L_0)]---\left(24\right)$

In (24) formula

Be known, then can obtain the temperature T at local L place.

Distributed optical fiber Raman temperature sensor of the present invention is applicable to the decoding of 255 bit sequence pulse codes, also is applicable to the coding of other figure place, for example: 127 etc.

Claims (3)

1. adopt the distributed optical fiber Raman temperature sensor of train pulse coding and decoding, it is characterized in that comprising optical fiber coupling multiple-pulse semiconductor laser transmitter module (21) with Raman frequency shift, Erbium-Doped Fiber Amplifier (EDFA) (19), bandpass filter (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 optical fiber coupling multiple-pulse semiconductor laser transmitter module (21) links to each other with the input end of Erbium-Doped Fiber Amplifier (EDFA) (19), the output terminal of Erbium-Doped Fiber Amplifier (EDFA) (19) links to each other with an end of bandpass filter (20), the other end of bandpass filter (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), the second and the 3rd output port of integrated-type optical fibre wavelength division multiplexer (11) receives amplification module (12) with first and second photoelectricity respectively, (13) input end links to each other, first and second photoelectricity receive amplification module (12), (13) output terminal links to each other with two input ends of coding and decoding demodulated digital signal processor (14) respectively, the 3rd input end of the output terminal of digital temperature detector (16) and coding and decoding demodulated digital signal processor (14) links to each other, the output terminal of coding and decoding demodulated digital signal processor (14) links to each other with the input end of optical fiber coupling multiple-pulse semiconductor laser transmitter module (21), and the communication interface of coding and decoding demodulated digital signal processor (14) connects PC (15).

2. the distributed optical fiber Raman temperature sensor of employing train pulse coding and decoding 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.

3. the distributed optical fiber Raman temperature sensor of employing train pulse coding and decoding according to claim 1, the centre wavelength that it is characterized in that the optical fiber coupling multiple-pulse semiconductor laser transmitter module (21) of Raman frequency shift is 1550nm, spectral width＜5nm, the unit pulse width＜6ns of laser; Bandpass filter (20) spectral bandwidth is 8nm, and passband ripple＜0.3dB inserts loss＜0.3dB.

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