CN101261164A - Juxtaposed distributed optical fibre temperature sensor - Google Patents

Abstract

The invention relates to a parallel distribution type fiber temperature sensor, comprising a light source, a coupler, a wavelength division multiplexer and a light detection device, wherein, sensing optical fiber with multi-core are included; ports P2 and P3 of a coupler 8 are respectively butted to ports P1 of a coupler 9 and a coupler 11; ports P2 and P3 of a coupler 10 are respectively butted to ports P4 of the coupler 9 and the coupler 11; the ports P2 and P3 of the couplers 9 and 11 are respectively connected with the sensing optical fiber, wherein, the light source is input through the port P1 of the coupler 8; the port P4 of the coupler 10 is connected with a wavelength division multiplexer 4 which is connected with the light detection device; the parallel distribution type fiber temperature sensor applies the light interference principle to a Raman-scattering type optical fiber temperature sensor, thus achieving the purpose that the measurement precision is improved or the measurement distance is farther.

Description

Juxtaposed distributed optical fiber temperature sensor

Affiliated technical field

The present invention relates to a kind of fibre optic temperature sensor, especially a kind of juxtaposed distributed optical fiber temperature sensor.

Background technology

Compare with traditional sensor, distributed optical fiber temperature sensor has plurality of advantages, collects sensing and is transmitted in one, can realize telemeasurement and monitoring; Once measure the one dimension distribution plan that just can obtain whole fiber area, optical fibre frame is set as raster-like, just can measure the two and three dimensions distribution situation in tested zone, can one reach obtain tens on thousands of meters the sensor fiber loop, hundreds of even several thousand information, therefore the unit information cost significantly reduces, measurement range is wide, has high spatial resolution and high precision; Have under the rugged surroundings that strong electromagnetic or inflammable and explosive and other sensors can't be approaching, distributed optical fiber temperature sensor has unrivaled advantage.Therefore since the eighties in 20th century, people have launched broad research to the various technology that realize distributed fiber temperature sensing.At distributed optical fiber temperature sensor, what at first will solve is to the identification of the light signal that carries temperature information and determining of measuring position, and optical time domain reflection (OTDR) technology and optical frequency territory reflection (OFDR) technology provide good solution to this; And use for the distribution thermometric of longer distance, based on the distributed sensor system of scattering mechanism incomparable superiority being arranged then, this is because the power that is lost in the optical fiber this moment is directly used in the signal energy of being responded to.

The strongest scattering process is exactly a Rayleigh scattering in the optical fiber, be about incident light-35dBm, Rayleigh scattering is by due to the inhomogeneous and composition of the local density of non-propagation in the optical fiber inhomogeneous, experiment and theory find that all the temperature control of rayleigh scattering coefficient of the glass principal ingredient of optical fiber (composition) is extremely faint, therefore realize based on the Temperature Distribution system that consolidates optical fiber entirely of Rayleigh scattering very difficult, yet in some liquid, this temperature control is but very strong, as in benzene, its temperature control is up to 0.033dB/K.Because life-span of liquid-core optical fibre is short, and liquid has the existence of freezing point, boiling point, limited the scope of thermometric, and this scheme can not obtain actual application.Main application is Raman scattering type and Brillouin scattering type at present.

When light passed through optical fiber, the phonon that produces because of the spontaneous heating campaign in photon and the optical fiber can produce inelastic collision, thereby spontaneous Brillouin scattering takes place, and the frequency range of the relative incident light of scattering light frequency is at 10GHz ∽ 11GHz.Typical structure based on the sensor of this technology is Brillouin amplifier structure (as shown in Figure 4), the tunable laser that is in the optical fiber two ends is injected sensor fibre with a pulsed light and a continuous light respectively, when the difference on the frequency of two-beam is in the brillouin gain bandwidth in the fiber area of meeting, two-beam will produce the Brillouin amplifier effect at application point, energy takes place each other to be shifted, the frequency of two laser instruments is being carried out continuously adjustable simultaneously, by detecting the power of the continuous light that goes out from optical fiber one end-fire, the Brillouin shift in each section zone equates on the pairing difference on the frequency when brillouin gain that just can determine each segment zone of optical fiber reaches maximum, determined difference on the frequency and optical fiber.Therefore temperature and the strain that is directly proportional with Brillouin shift at optical fiber just determined thereupon.The measuring accuracy that this sensing technology can reach mainly depends on the tuning precision of two laser instruments.So this system is complicated, the cost height, pumping laser and exploring laser light must be placed on the two ends of tested optical cable, and can not survey breakpoint, and be very high to the requirement of the frequency stabilization of laser instrument and light source and control system.Therefore its application is subjected to certain limitation.

Raman scattering is that thermal vibration and the photon interaction generation energy exchange owing to the optical fiber molecule produces when laser pulse is propagated in optical fiber.Specifically, if a part of transform light energy becomes thermal vibration, to send a light longer so and be called Raman's stokes light,, will send a light shorter so and be called Raman's anti-Stokes light than optical source wavelength if a part of thermal vibration is converted to luminous energy than optical source wavelength.Based on the distributed temperature sensing system of spontaneous raman scattering as shown in Figure 5, two kinds of Raman's rear orientation lights, stokes light and anti-Stokes light are separated behind wavelength division multiplexer, received amplifier module reception changing into electric signal and amplification by photoelectricity then, handle through signal processing system again and change temperature signal into, can effectively eliminate the influence of the random noise of the instability of light source and Optical Fiber Transmission and coupling as a kind of binary channels measuring method.The pass of back scattering Raman light and incident light is:

$P_o=\frac{1}{2}{P}_i\mathrm{Sexp}(-2\mathrm{\αL})---\left(1\right)$

P wherein _oBe back scattering Raman light power, L is a sensor fibre length, and α is the average loss coefficient of optical fiber, and S is Raman

Back dispersion factor (containing temperature information), P _iBe incident optical power.

Unique weak point of Raman's distributed fiberoptic sensor be return signal quite a little less than, because anti Stokes scattering intensity has only incident light-75dBm, signal averaging overlong time in the signal processing, the peak power of pulsed laser source is quite high, but can not surpass the threshold power that Raman scattering is excited, and measuring distance is long more, and threshold power is more little, P _iMaximal value be the threshold power P that Raman scattering is excited _i ^Cr:

$P_i^{\mathrm{cr}}(1-\exp (-\mathrm{\αL}))/\mathrm{\α}=C---\left(2\right).$

Wherein C is a constant.

Summary of the invention

The present invention is long more in order to overcome Raman scattering type fibre optic temperature sensor measuring distance, the shortcoming that the back light signal is weak more, and provide a kind of juxtaposed distributed optical fiber temperature sensor, this sensor adopts the multicore sensor fibre and puts, light source along separate routes, utilize the sudden change of three-dB coupler pi/2 phase and fiber cross phase modulation same facies principle in three-dB coupler, the back light signal interference is long mutually, can be with of the light incident of every road near threshold power, realize that the signal averaging time shortens the purpose that purpose that measuring accuracy improves on the contrary or measuring distance are farther in the signal processing.

Purpose of the present invention can realize by following measure:

A kind of juxtaposed distributed optical fiber temperature sensor (Fig. 1), this sensor comprises light source, coupling mechanism, wavelength division multiplexer and optical detection device; Comprising the sensor fibre of multicore stranding, coupling mechanism 8 port P ₂, P ₃Respectively with coupling mechanism 9,11 port P ₁Butt joint, coupling mechanism 10 port P ₂, P ₃Respectively with coupling mechanism 9,11 port R ₄Butt joint, coupling mechanism 9,11 port P ₂, P ₃Connect sensor fibre respectively; Wherein light source is through coupling mechanism 8 port P ₁Input, coupling mechanism 10 port P ₄Connect wavelength division multiplexer 4, wavelength division multiplexer 4 connects optical detection device.

According to said apparatus, light source to coupling mechanism 8 is provided with isolator.

Described light source is a laser instrument, comprises that semiconductor laser adds image intensifer and fiber laser.

Described optical fiber is low loss fiber.

Described optical detection device is a detector.

The Signal and Signal Treatment device of described optical detection device links to each other.

The present invention's advantage compared to existing technology mainly is:

1. the present invention has adopted new principle of work.The present invention is applied to Raman scattering type fibre optic temperature sensor with interference of light principle; It can obtain stronger back light signal according to this principle, improves the signal to noise ratio (S/N ratio) of sensor, the total system reliable operation, and its cost performance is higher.

2. the present invention has broken through the restriction that total incident optical power is subjected to threshold power, because the long mutually cause of back light signal interference has realized that sensor can obtain higher measuring accuracy.

3. the present invention can obtain the measuring distance longer than single-path system under identical signal handling capacity.

Description of drawings

Fig. 1 is the structural representation of embodiments of the invention one 4 tunnel juxtaposed distributed optical fiber temperature sensor

Fig. 2 is the structural representation of embodiments of the invention 22 tunnel juxtaposed distributed optical fiber temperature sensors

Fig. 3 is the structural representation of embodiments of the invention 38 tunnel juxtaposed distributed optical fiber temperature sensors

Fig. 4 is a kind of structural representation of Brillouin scattering type distributed optical fiber temperature sensor

Fig. 5 is the structural representation of a kind of Raman scattering type distributed optical fiber temperature sensor of generally acknowledging

Number in the figure is described as follows:

1-light source 2-isolator 3-sensing optic cable 4-wavelength division multiplexer 5-detector assembly 6-microprocessor 7-driver 8--15-3dB coupling mechanism

Concrete embodiment

With reference to Fig. 1, be the structural representation of embodiments of the invention one 4 tunnel juxtaposed distributed optical fiber temperature sensor.The present invention adopts 4 core sensor fibres and puts, and incident light divides 4 the tunnel, utilizes the sudden change of three-dB coupler pi/2 phase and fiber cross phase modulation same facies principle in three-dB coupler, and the back light signal interference is long mutually, and back light power and single channel incident optical power close and be:

P _o＝4P _iSexp(-2αL) (3)

Described Transmission Fibers adopts low loss fiber, and the laser that requires to be fit to lambda1-wavelength carries out low-loss transmission.

Described photo-detector adopt can under the above-mentioned laser wavelength of incidence of selecting for use to spontaneous Raman after scattered light signal carry out the semiconductor photo detector of high sensitivity opto-electronic conversion, the light signal that is used for carrying temperature information converts electric signal to.

Other: light source isolator, driver, electric signal amplify and microprocessor control and data processing etc.

Principle of the present invention is as follows:

If the light intensity coupling coefficient of coupling mechanism 2,3,5,6 is k, incident light propagation constant in optical fiber is β ₁, Raman scattered light propagation constant in optical fiber is β ₂, $j=-\sqrt{1},$ Transmission matrix by fiber coupler gets:

${\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="A20071004858100071.png"\; state="\{\{state\}\}">E</figure-callout>}}_1=(1-k)E_i,{\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="A20071004858100071.png,A20071004858100072.png"\; state="\{\{state\}\}">E</figure-callout>}}_2=j\sqrt{(1-k)k}{E}_i,{\mathrm{<figure-callout\; id="3"\; label="E"\; filenames="A20071004858100072.png,A20071004858100081.png"\; state="\{\{state\}\}">E</figure-callout>}}_3=j\sqrt{(1-k)k}{E}_i,{\mathrm{<figure-callout\; id="4"\; label="E"\; filenames="A20071004858100071.png,A20071004858100072.png"\; state="\{\{state\}\}">E</figure-callout>}}_4=-k{E}_i---\left(4\right)$

Return light field and not only obtained linear phase shift, but also obtained to modulate the nonlinear phase shift of introducing from phase modulation (PM) and cross-phase:

$E_m^{\&prime;}=E_m\sqrt{S}\exp \{-\mathrm{\&alpha;L}+j({\mathrm{\&beta;}}_1-{\mathrm{\&beta;}}_2)L+\mathrm{j\&gamma;L}[{\left|E_m^{\&prime;}\right|}^2+(2-f_R){\left|E_m\right|}^2\left)\right]\},(m=\mathrm{1,2,3,4})---\left(5\right)$

Wherein γ is the nonlinear fiber parameter, f _RBe Raman's parameter (value is about 0.18), because back light is very faint, and γ is very little, so γ L|E ' in the following formula _m| ²Can ignore.

$E_o=-\mathrm{<figure-callout\; id="1"\; label="k\; E"\; filenames="A20071004858100071.png"\; state="\{\{state\}\}">k</figure-callout>}{E}_{}^{}{}_1^{\&prime;}+j\sqrt{(1-k)k}{\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="A20071004858100071.png,A20071004858100072.png"\; state="\{\{state\}\}">E</figure-callout>}}_2^{\&prime;}+j\sqrt{(1-k)k}{\mathrm{<figure-callout\; id="3"\; label="E"\; filenames="A20071004858100072.png,A20071004858100081.png"\; state="\{\{state\}\}">E</figure-callout>}}_3^{\&prime;}+(1-k){\mathrm{<figure-callout\; id="4"\; label="E"\; filenames="A20071004858100071.png,A20071004858100072.png"\; state="\{\{state\}\}">E</figure-callout>}}_4^{\&prime;}---\left(6\right)$

When k=1/2

$E_o=-E_i\sqrt{S}\exp (-\mathrm{\&alpha;L}+j({\mathrm{\&beta;}}_1-{\mathrm{\&beta;}}_2)L+j0.455\mathrm{\&gamma;L}{\left|E_i\right|}^2)---\left(7\right)$

Back light power $P_o=<E^{*}{E}_o^{*}>=4P_i\mathrm{Sexp}(-2\mathrm{\&alpha;L})---\left(8\right)$

The back light power P of Fig. 2 structural representation _o=2P _iSexp (2 α L) (9)

The back light power P of Fig. 3 structural representation _o=8P _iSexp (2 α L) (10)

By that analogy, by 2 ⁿ(n=1,2,3 ...) the back light power P of the juxtaposed sensor in road _o=2 ⁿP _iSexp (2 α L) (11)

This shows that the luminous power of formula (11) is 2 of a formula (1) ^N+1(n=1,2,3 ...) doubly, realized the raising of sensor signal to noise ratio (S/N ratio), thus the corresponding raising of temperature accuracy measured.If under follow-up identical signal handling capacity, can obtain with the measurement length relation of single-path system be:

$\frac{1}{2}\exp (-2\mathrm{\&alpha;L})\mathrm{C\&alpha;}/(1-\exp (-\mathrm{\&alpha;L}))=2^n\exp (-2\mathrm{\&alpha;l})\mathrm{C\&alpha;}/(1-\exp (-\mathrm{\&alpha;l}))---\left(12\right)$

Separating formula (12) gets:

$l=\frac{1}{\mathrm{\&alpha;}}\ln \{\frac{1}{2}+\sqrt{\frac{1}{4}+2^{n+1}[\exp \left(2\mathrm{\&alpha;L}\right)-\exp \left(\mathrm{\&alpha;L}\right)]}\}---\left(13\right)$

α=0.25dB/km for example, L=8km, calculating formula (13) l=17.7km.

We propose juxtaposed distributed optical fiber temperature sensor as can be known by last analysis, are not the stacks of simple single-path system, but introduce interference of light principle, the innovation of setting up the interfere type distributed optical fiber temperature sensor.

With reference to Fig. 2, be the structural representation of 2 tunnel juxtaposed distributed optical fiber temperature sensors of embodiments of the invention two, all the other structures of present embodiment and example together just constitute the two-way input forms with coupling mechanism 8.

With reference to Fig. 3, structural representation for 8 tunnel juxtaposed distributed optical fiber temperature sensors of embodiments of the invention three, all the other structures of present embodiment and example together just constitute 8 tunnel input forms with coupling mechanism 8,9,10,11,12,13,14,15,16,17.

Claims (6)

1. juxtaposed distributed optical fiber temperature sensor, this sensor comprises light source, coupling mechanism, wavelength division multiplexer and optical detection device; Comprising the sensor fibre of multicore stranding, coupling mechanism 8 port P ₂, P ₃Respectively with coupling mechanism 9,11 port P ₁Butt joint, coupling mechanism 10 port P ₂, P ₃Respectively with coupling mechanism 9,11 port P ₄Butt joint, coupling mechanism 9,11 port P ₂, P ₃Connect sensor fibre respectively; Wherein light source is through coupling mechanism 8 port P ₁Input, coupling mechanism 10 port P ₄Connect wavelength division multiplexer 4, wavelength division multiplexer 4 connects optical detection device.

2. as claimed in claim 1 based on juxtaposed distributed optical fiber temperature sensor, it is characterized in that light source to coupling mechanism 8 is provided with isolator.

3. as claimed in claim 1 based on juxtaposed distributed optical fiber temperature sensor, it is characterized in that optical detection device is a detector.

4. as claimed in claim 1 based on juxtaposed distributed optical fiber temperature sensor, it is characterized in that light source is a laser instrument, comprise that semiconductor laser adds image intensifer and fiber laser.

5. as claimed in claim 1 based on juxtaposed distributed optical fiber temperature sensor, it is characterized in that optical fiber is low loss fiber.

6. as claimed in claim 1 based on juxtaposed distributed optical fiber temperature sensor, it is characterized in that adopting symmetric mode to expand to 2 index power output line structure, or get the output line structure between 2 index power according to actual needs.

Images