CN202255424U - Pulse coding optical fiber Brillouin optical time domain analyzer - Google Patents

Abstract

The utility model discloses a pulse coding optical fiber Brillouin optical time domain analyzer, which comprises a pulse coding waveform generator, a narrow-band single-frequency optical fiber laser, an optical fiber shunt, an optical pulse code modulation device, two optical fiber circulators, a heterodyning receiver, a digital signal processor, an optical fiber grating filter, a sensing optical fiber, an optical fiber Raman pump laser and an industrial personal computer. A sensor adopts time series to encode laser pulse, thereby increasing the number of emitted photons and simultaneously improving space resolution by narrowing the width of the laser pulse in pressing mode. The continuously-operated optical fiber Raman pump laser serves as a pump light source, thereby resolving the problem that the optical fiber Brillouin optical time domain analyzer has the requirements for strictly locking frequency of a detection laser and a pump laser. High-power laser generated by the continuously-operated optical fiber Raman pump laser achieves stimulated Raman scattering light amplification in the sensing optical fiber to replace narrow-band Brillouin amplification. Gain of stimulated Raman scattering light of back coherent amplification can be increased, signal to noise ratio is increased, measurement accuracy is improved, and measurement length is prolonged.

Description

A kind of pulse code optical fiber Brillouin light time domain analyzer

Technical field

The utility model relates to the pulse code optical fiber Brillouin light time domain analyzer, belongs to the distributed fiberoptic sensor technical field.

Background technology

In the optical fiber Brillouin light time domain analyzer field; The optical fiber Brillouin optical time domain reflectometer adopts the spontaneous Brillouin scattering of optical fiber; Therefore dorsad brillouin scattering signal very a little less than; Utilize the frequency displacement of optical fiber Brillouin scattered light and precision that intensity is recently measured strain and temperature very low, ranging is short, and spatial resolution is lower.T.Horiguchi etc. have invented Brillouin light time domain analyzer, add a relevant pump laser at the other end of optical fiber, realize that Brillouin amplifies, and adopt relevant stimulated Brillouin scattering of amplifying, and have strengthened signal, have improved the signal to noise ratio (S/N ratio) of system.But optical fiber Brillouin light time domain analyzer locks the frequency of arrowband detecting laser and arrowband pump laser strictly, and is very difficult technically.And the safety and Health of petroleum pipe line, transferring electric power cable monitoring in recent years has active demand to the strain of very-long-range fully distributed fiber, TEMP net.

Summary of the invention

The purpose of the utility model is to propose a kind of easy operating, and gain is high, and system signal noise ratio is strong, the pulse code optical fiber Brillouin light time domain analyzer that measuring accuracy is high.

The pulse code optical fiber Brillouin light time domain analyzer of the utility model comprises the pulse code waveform generator, the arrowband single frequency optical fiber laser; Optical fiber splitter, light pulse coding demodulator, two fiber optical circulators; Heterodyne receiver, digital signal processor, fiber grating filter; Sensor fibre, fiber Raman pump laser and industrial computer, the input end of pulse code waveform generator links to each other with industrial computer; The output terminal of pulse code waveform generator links to each other with an input end of light pulse coding demodulator; The input end of optical fiber splitter links to each other with the arrowband single frequency optical fiber laser, and an output terminal of optical fiber splitter links to each other with another input end of light pulse coding demodulator, and another output terminal of optical fiber splitter links to each other with the input end of second fiber optical circulator; The output terminal of light pulse coding demodulator links to each other with the input end of first fiber optical circulator; The common port of first fiber optical circulator successively with fiber grating filter, sensor fibre links to each other with the fiber Raman pump laser, the output terminal of first fiber optical circulator links to each other with the common port of second fiber optical circulator; The output terminal of second fiber optical circulator successively with heterodyne receiver; Digital signal processor links to each other with industrial computer, coded pulse that digital signal processor and industrial computer will be gathered, add up decoding demodulation, obtain sensor fibre at the scene strain, temperature information and send the remote monitoring net to.

In the utility model, said arrowband single frequency optical fiber laser is that centre wavelength is 1550nm, and spectral bandwidth is that the 100mW of 200kHz moves fiber laser continuously.

In the utility model, described smooth coding demodulator is lithium niobate Mach-Ze Deer modulator (Mach-Zehnder modulator (MZM)).

In the utility model, described heterodyne receiver is that frequency response is the above photodetector of 12Ghz.

In the utility model, the centre wavelength of said fiber grating filter is 1455nm, and spectral bandwidth is 0.3nm, and isolation is greater than 35dB.

In the utility model, said sensor fibre is 100km single mode communication G652 optical fiber or 100km LEAF optical fiber.

In the utility model, the wavelength of said fiber Raman pump laser is 1455nm, and power is adjustable in the 100mw-1200mw scope.

During work; Waveform generator is under industrial computer control; Output is by regularly arranged 255 coded pulse control of the sequence light coding demodulator of 255 * 255S matrix conversion, and the continuous laser of arrowband single frequency optical fiber laser output is divided into two bundles through optical fiber splitter, and wherein beam of laser is modulated into time series coded pulse light through the light pulse coding demodulator; Get into single-mode fiber through fiber grating filter; With single-mode fiber generation nonlinear interaction, produce Brillouin scattering dorsad, the frequency of Brillouin scattering and intensity are modulated by temperature of each section of single-mode fiber and strain.Light laser pumping by single-mode fiber distal optical fiber Raman pump laser produces produces non-linear amplification in single-mode fiber, have the dual amplification that Raman amplifies and Brillouin amplifies, and full gain reaches 55dB, the stimulated Brillouin scattering light ν that is exaggerated ₀± ν _BThrough fiber grating filter, filtering 1455nm fiber Raman pump laser remaining light after laser pump (ing) in the single-mode fiber gets into second fiber optical circulator and another this flash of light preceding an earthquake of bundle ν from optical fiber splitter through first fiber optical circulator ₀Mixing, the output after the mixing after digital signal processor and the industrial computer decoding demodulation, obtain the strain and the temperature amount of each point in optical fiber, strain and temperature changing speed and direction through heterodyne receiver.Utilize optical time domain reflection that the position of each section on the single-mode fiber is positioned (optical fibre radar location).Through overstrain and Temperature Scaling, obtain the stress and the temperature variation of single-mode fiber each point, surveying the strain precision is 10 μ ε, temperature measurement accuracy ± 1 ℃ is shown or is carried out the telecommunication network transmission through communication interface, communications protocol by the industrial computer display.

The coding and decoding principle of pulse code optical fiber Brillouin light time domain analyzer:

The train pulse coding of this sensor realizes that through 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 practical application " 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.

Learn by the coding principle derivation, adopt the obtainable signal to noise ratio (S/N ratio) of train pulse coding and decoding of N position to be improved as:

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

Can know that by (1) formula signal to noise ratio (S/N ratio) is improved along with the raising of coding figure place and improved.

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

The space orientation resolution of Fibre Optical Sensor is by the narrow pulse width decision of unit; Owing to adopt the multiple-pulse emission; When improving the ballistic phonon number, can improve spatial resolution through pressing narrow laser pulse width again, and needn't improve single peak-power of laser pulse from and prevented that effectively fiber nonlinear effect from causing the distortion of anti-Stokes Raman light Time Domain Reflectometry (OTDR) curve dorsad.

The principle of work of Brillouin's Time Domain Analyzer:

In optical fiber; The nonlinear interaction of sound wave in the exploring laser light of incident optical and the optical fiber; Light wave produces sound wave through electrostriction; Cause the periodic modulation (refractive-index grating) of optical fibre refractivity, produce the Brillouin scattering that frequency moves down, the frequency displacement ν of the Brillouin scattering dorsad that in optical fiber, produces _BFor:

ν _B=2nv/λ (2)

Wherein n is the refractive index at lambda1-wavelength λ place, and ν is the velocity of sound in the optical fiber, to silica fibre, and near λ=1550nm, ν _BBe about 11GHz.

Brillouin scattering optical frequency shift ν in optical fiber _BFrequency displacement with strain and temperature effect Brillouin scattering

(3)

δν _B＝C _νεδε+C _νtδT (4)

The coefficient of strain C of frequency displacement wherein _{ν ε}With temperature coefficient C _{ν T}For

C _νε＝0.0482±0.004MHz/με，C _νT＝1.10±0.02MHz/K

The intensity of Brillouin scattering also has strain and temperature effect in the optical fiber, and the strength ratio of Brillouin scattering in the optical fiber (Landau-Plazcek ratio) also depends on the strain and the temperature of optical fiber

$\frac{100{\mathrm{\δI}}_B}{I_B}=C_{\mathrm{P\ϵ}}\mathrm{\δ\ϵ}+C_{\mathrm{PT}}\mathrm{\δT}---\left(5\right)$

Which intensity ratio gauge factor? and the temperature coefficient?

is

$C_{\mathrm{P\ϵ}}=-(7.7\±1.4)\×{10}^{-4}\%/\mathrm{\μ\ϵ},C_{\mathrm{PT}}=0.36\±0.06\%/K$

By (3) formula and (4) formula, as long as measure strain δ ε and the temperature difference δ T that each section frequency displacement and strength ratio on the optical fiber can demodulate this section optical fiber.

The advantage of the utility model:

The pulse code optical fiber Brillouin light time domain analyzer that the utility model proposes adopts time series coding laser pulse, when improving the ballistic phonon number, can improve spatial resolution through pressing narrow laser pulse width again; The high power light fibre optic Raman laser of operation is as the pump light source of Novel Brillouin optical time domain analyzer continuously; Replaced relevant pumping narrow band laser; Overcome the difficulty that locks detecting laser and pump laser frequency in the optical fiber Brillouin light time domain analyzer strictly; The light laser of the high power light fibre optic Raman laser of operation generation has realized that in single-mode fiber the stimulated Raman scattering light amplification has replaced arrowband Brillouin and amplified continuously; Increased the gain of the relevant stimulated Brillouin scattering light that amplifies dorsad, Raman amplifies the full gain of amplifying with Brillouin and reaches 55dB, has improved the signal to noise ratio (S/N ratio) of system; Increase measurement length, improved the precision of strain and temperature simultaneously measuring.

Description of drawings

Fig. 1 is the synoptic diagram of the pulse code optical fiber Brillouin light time domain analyzer of the utility model.

Embodiment

With reference to Fig. 1, the pulse code optical fiber Brillouin light time domain analyzer of the utility model comprises pulse code waveform generator 10; Arrowband single frequency optical fiber laser 11, optical fiber splitter 12, light pulse coding demodulator 13; Two fiber optical circulators 14,15, heterodyne receiver 16, digital signal processor 17; Fiber grating filter 18; Sensor fibre 19, fiber Raman pump laser 20 and industrial computer 21, the input end of pulse code waveform generator 10 links to each other with industrial computer 21; The output terminal of pulse code waveform generator 10 links to each other with an input end of light pulse coding demodulator 13; The input end of optical fiber splitter 12 links to each other with arrowband single frequency optical fiber laser 11, and an output terminal of optical fiber splitter 12 links to each other with another input end of light pulse coding demodulator 13, and another output terminal of optical fiber splitter 12 links to each other with the input end of second fiber optical circulator 15; The output terminal of light pulse coding demodulator 13 links to each other with the input end of first fiber optical circulator 14; The common port of first fiber optical circulator 14 successively with fiber grating filter 18, sensor fibre 19 links to each other with fiber Raman pump laser 20, fibre optic Raman laser 20 constitutes pumping optical fiber raman amplifier dorsad with sensor fibre 19.The output terminal of first fiber optical circulator 14 links to each other with the common port of second fiber optical circulator 15; The output terminal of second fiber optical circulator 15 successively with heterodyne receiver 16; Digital signal processor 17 links to each other with industrial computer 21; The coded pulse decoding demodulation that digital signal processor 17 and industrial computer 21 will be gathered, add up, 19 of acquisition sensor fibres at the scene strain, temperature information and send the remote monitoring net to.

Digital signal processor adopts spectrum analyzer, the spectrum analyzer ESA (E4407B) of Agilent (Agilent) company for example, spectral range 9kHz-26.5GHz.

Claims (8)

1. a pulse code optical fiber Brillouin light time domain analyzer is characterized in that comprising pulse code waveform generator (10), arrowband single frequency optical fiber laser (11); Optical fiber splitter (12); Light pulse coding demodulator (13), two fiber optical circulators (14,15), heterodyne receiver (16); Digital signal processor (17); Fiber grating filter (18), sensor fibre (19), fiber Raman pump laser (20) and industrial computer (21); The input end of pulse code waveform generator (10) links to each other with industrial computer (21); The output terminal of pulse code waveform generator (10) links to each other with an input end of light pulse coding demodulator (13), and the input end of optical fiber splitter (12) links to each other with arrowband single frequency optical fiber laser (11), and an output terminal of optical fiber splitter (12) links to each other with another input end of light pulse coding demodulator (13); Another output terminal of optical fiber splitter (12) links to each other with the input end of second fiber optical circulator (15); The output terminal of light pulse coding demodulator (13) links to each other with the input end of first fiber optical circulator (14), and the common port of first fiber optical circulator (14) links to each other with fiber grating filter (18), sensor fibre (19) and fiber Raman pump laser (20) successively, and the output terminal of first fiber optical circulator (14) links to each other with the common port of second fiber optical circulator (15); The output terminal of second fiber optical circulator (15) successively with heterodyne receiver (16); Digital signal processor (17) links to each other with industrial computer (21), coded pulse that digital signal processor (17) and industrial computer (21) will be gathered, add up decoding demodulation, obtain sensor fibre (19) at the scene strain, temperature information and send the remote monitoring net to.

2. pulse code optical fiber Brillouin light time domain analyzer according to claim 1 is characterized in that arrowband single frequency optical fiber laser (11) is that centre wavelength is 1550nm, and spectral bandwidth is that the 100mW of 200kHz moves fiber laser continuously.

3. pulse code optical fiber Brillouin light time domain analyzer according to claim 1 is characterized in that light coding demodulator (13) is lithium niobate Mach-Ze Deer modulator.

4. pulse code optical fiber Brillouin light time domain analyzer according to claim 1 is characterized in that heterodyne receiver (16) is that frequency response is the above photodetector of 12Ghz.

5. pulse code optical fiber Brillouin light time domain analyzer according to claim 1, the centre wavelength that it is characterized in that fiber grating filter (18) is 1455nm, and spectral bandwidth is 0.3nm, and isolation is greater than 35dB.

6. pulse code optical fiber Brillouin light time domain analyzer according to claim 1 is characterized in that sensor fibre (19) is 100km single mode communication G652 optical fiber or 100km LEAF optical fiber.

7. pulse code optical fiber Brillouin light time domain analyzer according to claim 1, the wavelength that it is characterized in that said fiber Raman pump laser (20) is 1455nm, power is adjustable in the 100mw-1200mw scope.

8. pulse code optical fiber Brillouin light time domain analyzer according to claim 1 is characterized in that said digital signal processor is the spectrum analyzer of spectral range 9kHz-26.5GHz.

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