CN102116684B - Self-correcting fully-distributed optical fiber Raman scattering sensor - Google Patents

Abstract

The invention discloses a self-correcting fully-distributed optical fiber Raman scattering sensor. In the invention, a duplex fiber cable is utilized as a sensing optical fiber, pump light is divided into a forward beam and a backward beam during the transmission process by welding the tail ends of the duplex fiber cable together so as to obtain two anti-Stokes Raman scattering light beams, and the intensity of the anti-Stokes Raman scattering light beams is measured so as to realize temperature measurement; and the intensity values of the two anti-Stokes Raman scattering light beams can be multiplied so as to achieve the purpose of self-correction of curvature, loss, strain and the like. The sensor disclosed by the invention comprises an optical fiber pulse laser, an optical fiber wavelength division multiplexer (WDM), the duplex fiber cable, a photoelectric receiving module, a digital signal processor (DSP) and a computer. The invention has the advantages that self-correction and temperature measurement can be carried out at the same time only by measuring the intensity of the anti-Stokes Raman scattering spectrums; and the system has a simple structure, and avoids the defects that the traditional measuring system has transmission loss and errors caused by different center wavelength and needs a plurality of photoelectric receivers.

Description

Can self-tuning fully distributed fiber Raman scattering sensor

Technical field

The invention belongs to Fibre Optical Sensor thermometric field, relate to a kind of can self-tuning fully distributed fiber Raman scattering sensor.This sensor is suitable for needs occasion simple in structure, that cost is low, use is wide, like the real-time continuous monitoring of production run, civil engineering work, disaster monitoring etc.

Technical background

In recent years Fibre Optical Sensor, particularly distributed fiber Raman scattering sensor because simple to operate, safely, can be applicable to advantage such as rugged surroundings and obtained to pay close attention to widely and study.Such sensor utilizes the intrinsic property of optical fiber, and fiber Rayleigh, Raman and Brillouin scattering effect adopt light time territory (OTDR) technology to realize the monitoring of temperature.Optical fiber in the full distribution optical fiber sensor net be transmission medium be again sensor information, do not exist and detect the blind area.Such sensor can be realized power engineering, petrochemical industry, traffic bridge, tunnel, subway station, the safety and Health monitoring of dam, embankment etc. and the forecast and the monitoring of disaster.Traditional distributed fiber Raman scattering sensor mainly is the temperature information of acquisition recently that utilizes temperature sensitive anti-Stokes Raman scattering light intensity and Rayleigh scattering light intensity or stokes scattering light intensity; This method can overcome the measuring error that causes owing to light source fluctuation; But increase along with measuring distance; In order to obtain higher measuring accuracy, by anti Stokes scattering, stokes scattering is different with Rayleigh scattering centre wavelength and loss that bring needs to revise.Therefore researched and proposed the method that adopts two light sources; This method adopts two main laser and secondary laser instruments that centre wavelength is different; Utilize the identical different errors of being brought of wavelength of eliminating of centre wavelength of the anti-Stokes Raman scattering wavelength and the secondary laser instrument of main laser; But this structure need increase a laser instrument, a photoswitch, two photodetection modules, also makes use cost rise when increasing system architecture.2010; Korea S Dusun Hwang etc. has proposed to add at the sensor fibre end method of a catoptron, carries out self-correcting when can realize temperature monitoring, (OPTICS EXPRESS; 2010; Vol.18, the No.10:9747-9754) energy of pump light and anti-Stokes light signal, the property that the has reduced system ratio of making an uproar but the increase of catoptron has decayed.

The present invention adopts the terminal method that connects of twin fiber cable to replace catoptron; Provide a kind of structure more simple; Cost is low, signal to noise ratio (S/N ratio) good; What reliability was high can self-tuning distributed fiber Raman scattering sensor, and this sensor carries out self-correcting when only needing a laser instrument and a photodetection module just can realize temperature monitoring.Crucial terminal linking to each other of twin fiber cable can make pump light source become forward and reverse two bundles with the traditional single-mode fiber realization sensing measurement of twin fiber cable replacement, thereby obtains two bundle anti-Stokes light beams, is used for offsetting the loss of optical fiber itself.Can realize self-correcting to crooked, loss simultaneously, remedy the shortcoming of traditional distributed fiber raman scattering sensor, reduce cost.

Summary of the invention

The purpose of this invention is to provide that a kind of cost is low, simple in structure, signal to noise ratio (S/N ratio) is good, can self-tuning fully distributed fiber Raman scattering sensor.

Technical solution of the present invention is following:

Can self-tuning fully distributed fiber Raman scattering sensor, comprise fiber pulse laser, optical fibre wavelength division multiplexer, twin fiber cable, photoelectricity receiver module, digital signal processor and computing machine.Optical fibre wavelength division multiplexer has three ports; Wherein the 1550nm input end links to each other with fiber pulse laser; The COM output port links to each other with any end of twin fiber cable; The 1450nm output port links to each other with photoelectricity receiver module input end, and photoelectricity receiver module output terminal links to each other with digital signal processor, and the digital signal processor signal output part connects computing machine.The centre wavelength of wherein mentioned pulsed laser is 1550nm, and spectral width is 0.1nm, and laser pulse width is 10ns, and peak power 1-100w is adjustable, and repetition frequency is that 500Hz-20KHz is adjustable.Mentioned sensing optic cable is a twin fiber cable, and terminal linking to each other, optical fiber can adopt G652 communication unit mode fiber, also can adopt carbon to apply single-mode fiber.

Fiber pulse laser sends the 1550nm input port of laser pulse through optical fibre wavelength division multiplexer as pump light source and is injected in any end of twin fiber cable; In sensing optic cable, produce Rayleigh scattering dorsad; Stokes Raman scattering and anti-Stokes Raman diffused light wavelet; Because optical cable is twin fiber cable and terminal linking to each other; Therefore pump light source in any optical fiber of twin fiber cable fl transmission when terminal because terminal continuously transmit dorsad, thereby obtain the pump light of positive and negative both direction, obtain two and restraint the anti-Stokes Raman diffused lights; The Raman diffused light of the anti-Stokes dorsad wavelet that has temperature information is received by the photoelectricity receiver module behind optical fiber filter, converts light signal to electric signal and amplification.Obtain the temperature information of each section of optical fiber by the product of two bundle anti-Stokes Raman scattering light intensity; Simultaneously self-correcting has been carried out in bending, loss, strain etc., eliminated the cross influence of temperature, temperature changing speed and bending, strain and the temperature of each heat detection point.Link to each other with the computing machine communication interface through digital signal processor and to carry out the transmission of measurement result.

Beneficial effect of the present invention is:

Of the present invention can self-tuning fully distributed fiber Raman scattering sensor; Only use a pump light source and a photodetection module; Through monitoring measurement and the location that anti-Stokes Raman scattering light intensity just can realize temperature; Avoided the anti-Stokes Raman scattering different with Rayleigh scattering or stokes scattering centre wavelength and outside the transmission attenuation that causes, bending, strain, node loss equal error have been carried out self-correcting.Compare with traditional distributed fiber Raman temp measuring system, this temp measuring system is except that having self-correcting capability, and is simple in structure, cost is low.The present invention is applicable to the continuous temperature measurement that needs self-correcting, the low occasion of cost, prevents pipeline, various possible disasters such as tunnel.

Description of drawings

Fig. 1 be can self-tuning distributed fiber Raman scattering sensor structural representation.

Fig. 2 is that sensing is with the terminal johning knot composition of twin fiber cable.

Embodiment

Below in conjunction with accompanying drawing the present invention is further described.

Referring to shown in Figure 1, can self-tuning distributed fiber Raman scattering sensor, comprise fiber pulse laser 11, optical fibre wavelength division multiplexer 12, twin fiber cable 13, photoelectricity receiver module 14, digital signal processor 15 and computing machine 16.Optical fibre wavelength division multiplexer 12 has three ports; Wherein the 1550nm input port links to each other with the output terminal of fiber pulse laser 11; The COM output port links to each other with any end of sensing optic cable 13; The 1450nm output port links to each other with the input end of photoelectricity receiver module 14, and the output terminal of photoelectricity receiver module 14 links to each other with the input port of digital signal processor 15, and digital signal processor 15 signal output parts connect computing machine 16.

Referring to shown in Figure 2, described twin fiber cable comprises outer package 5 and the twin-core fiber 6 that is formed side by side by common single mode optical fibres, and wherein the end of twin-core fiber links to each other.

The centre wavelength of above-mentioned pulsed laser is 1550nm, and spectral width is 0.1nm, and laser pulse width is 10ns, and peak power is that 1-100w is adjustable, and repetition frequency is that 500Hz-20KHz is adjustable.

Above-mentioned sensing optic cable is a twin fiber cable; Terminal linking to each other, when pump light transmits like this, can be divided into opposite both direction light beam in optical fiber through the terminal mode that links to each other of twin fiber cable; Obtain two bundle anti-Stokes Raman diffused lights; Through calculating to two bundle anti-Stokes Raman diffused lights, can realize the self calibration of bending, loss etc., improved the measuring accuracy of fully distributed fiber temperature sensor.

Above-mentioned digital signal processor adopts general signal processing card, is inserted in the computing machine.

The present invention is based on following principle:

Energy is P ₀The pump light fl transmission time produce dorsad that anti-Stokes Raman scattering light intensity is I _N1, the energy when pump light is transferred to the temperature measuring optical cable end and carries out reverse transfer is P ₁, the Raman scattering of the anti-Stokes dorsad light intensity of generation is P _N2According to distributed fiber Raman scattered photon sensor temperature-measurement principle, anti-Stokes Raman scattering light intensity dorsad is in optical fiber:

$I_{n1}\left(z\right)=P_{0}g(z,T)\exp (-\underset{0}{\overset{z}{\∫}}{\mathrm{\α}}_p\left(z\right)\mathrm{dz}-\underset{0}{\overset{z}{\∫}}{\mathrm{\α}}_{\mathrm{AS}}\left(z\right)\mathrm{dz})+C---\left(1\right)$

$I_{n2}\left(z\right)=P_{0}g(z,T)\exp (-\underset{0}{\overset{{\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="HSA00000424918000011.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0}{\&Integral;}}{\mathrm{\&alpha;}}_p\left(z\right)\mathrm{dz}-\underset{z}{\overset{{\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="HSA00000424918000011.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0}{\&Integral;}}{\mathrm{\&alpha;}}_p\left(z\right)\mathrm{dz}-\underset{0}{\overset{{\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="HSA00000424918000011.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0}{\&Integral;}}{\mathrm{\&alpha;}}_{\mathrm{AS}}\left(z\right)\mathrm{dz}-\underset{z}{\overset{{\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="HSA00000424918000011.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0}{\&Integral;}}{\mathrm{\&alpha;}}_{\mathrm{AS}}\left(z\right)\mathrm{dz})+C---\left(2\right)$

Wherein, P ₀Be the pumping light intensity, (z T) is the Raman scattering function relevant with temperature T at thermometric optical fiber z place, α to g _p(z) and α _AS(z) be respectively the total loss when in optical fiber, transmitting of pump light and anti-Stokes Raman diffused light, such as absorption loss, weld loss, junction loss, bending loss or the like.Z ₀Be the length in monitor temperature zone, C is a constant, refers to the background dark current when the photodetection module is surveyed anti-Stokes Raman scattering light intensity dorsad.

After formula (1) multiplies each other with formula (2), can eliminate the relevant integral in position, obtain only following with the equation of temperature correlation:

$I_m\left(z\right)=\sqrt{(I_{n1}-C)(I_{n2}-C)}={\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="HSA00000424918000011.png"\; state="\{\{state\}\}">P</figure-callout>}}_0\mathrm{Ag}(z,T)---\left(3\right)$

Wherein, Be illustrated in whole temperature measuring optical cable Z ₀Various total losses in the scope can be approximated to be constant.Again temperature funtion g (z, T) with anti-Stokes Raman scattering intensity proportional, that is:

$g(z,T)=\frac{B}{{{\mathrm{\&lambda;}}_{\mathrm{AS}}}^4}\exp {(\frac{\mathrm{hc\&Delta;v}}{k_{B}T\left(z\right)}-1)}^{-1}---\left(4\right)$

Wherein, B is the scale-up factor relevant with the sensor fibre numerical aperture, and h is spectrum bright gram (Planck) constant, and Δ v is the phonon frequency of an optical fiber molecule, k _BBe Boltzmann constant, T (z) is Kai Erwen (Kelvin) absolute temperature at thermometric optical fiber z place in the position.

Formula (4) substitution formula (3), obtaining tested length is Z ₀The intensity after two bundle anti-Stokes Raman scatterings in the scope are handled and the relation of temperature are following:

$I_m\left(z\right)={\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="HSA00000424918000011.png"\; state="\{\{state\}\}">P</figure-callout>}}_0\&CenterDot;A\&CenterDot;\frac{B}{{{\mathrm{\&lambda;}}_{\mathrm{AS}}}^4}\exp {(\frac{\mathrm{hc\&Delta;v}}{k_{B}T\left(z\right)}-1)}^{-1}---\left(5\right)$

Adopting measuring optical fiber length in the present invention is z ₀Optical fiber anti-Stokes Raman scattering passage do reference signal, only come the demodulation temperature with anti-Stokes Raman scattering intensity, obtain the thermometric function according to formula (5):

$T\left(z\right)={\left(\frac{k_B}{\mathrm{hc\&Delta;v}}(\log \left(\frac{I_m\left(z_0\right)}{I_m\left(z\right)}\exp (\frac{\mathrm{hc\&Delta;v}}{k_{B}T\left(z_0\right)}-1)\right)+1)\right)}^{-1}---\left(6\right)$

By the anti-Stokes Raman scattering light intensity of fiber Raman optical time domain reflection (OTDR) curve at the optical fiber check point; Can obtain the temperature signal of each section of optical fiber, the influence to test result that can be brought by bending, strain, all kinds of losses etc. from NMO correction simultaneously.

Claims (3)

1. can self-tuning fully distributed fiber Raman scattering sensor, it is characterized in that comprising fiber pulse laser (11), optical fibre wavelength division multiplexer (12), twin fiber cable (13), photoelectricity receiver module (14), digital signal processor (15) and computing machine (16).Optical fibre wavelength division multiplexer (12) has three ports; Wherein the 1550nm input port links to each other with fiber pulse laser (11); The COM output port links to each other with any end of twin fiber cable (13); The 1450nm output port links to each other with the input end of photoelectricity receiver module (14), and the output terminal of photoelectricity receiver module (14) links to each other with digital signal processor (15) input port, and digital signal processor (15) signal output part connects computing machine (16).

2. according to claim 1 can self-tuning fully distributed fiber Raman scattering sensor; The centre wavelength that it is characterized in that fiber pulse laser (11) is 1550nm; Spectral width is 0.1nm; Laser pulse width is 10ns, and peak power is that 1-100w is adjustable, and repetition frequency is that 500Hz-20KHz is adjustable.

3. according to claim 1 can self-tuning fully distributed fiber Raman scattering sensor, it is characterized in that twin fiber cable (13) is a sensor fibre, terminal linking to each other, optical fiber wherein is that G652 communication unit mode fiber or carbon apply single-mode fiber.

Images