WO2013020276A1

WO2013020276A1 - Brillouin optical time domain analyzer of chaotic laser-related integrated optical fiber raman amplifier

Info

Publication number: WO2013020276A1
Application number: PCT/CN2011/078179
Authority: WO
Inventors: 张在宣; 王剑锋; 金永兴; 余向东; 龚华平; 李裔; 金尚忠
Original assignee: 中国计量学院
Priority date: 2011-08-10
Filing date: 2011-08-10
Publication date: 2013-02-14

Abstract

A Brillouin optical time domain analyzer of a chaotic laser-related integrated optical fiber Raman amplifier, manufactured by using a chaotic laser-related principle, an optical fiber-stimulated Raman scattered light amplification effect, a strain of coherently amplified Brillouin scattered light, a temperature effect, and an optical time domain reflection principle. In the Brillouin optical time domain analyzer of the chaotic laser-related integrated optical fiber Raman amplifier, spatial resolution of a sensing system is improved by correlation processing a backward probing light of a sensing optical fiber and a local reference light. The difficulty of the optical fiber Brillouin optical time domain analyzer requiring a rigorous locking on a probe laser and a pump laser frequency is solved by employing a continuous-operation high power optical fiber Raman laser as a pump light source for the Brillouin optical time domain analyzer. By using a broadband optical fiber Raman amplifier to replace a narrowband optical fiber Brillouin amplifier, the gain of stimulated Brillouin scattered light backward correlation amplified is increased, the signal-to-noise ratio of the sensing system is improved, and correspondingly the measurement length and the measurement precision of the sensing system are improved.

Description

Brillouin optical time domain analyzer for chaotic laser-related integrated fiber Raman amplifier

The invention belongs to the technical field of distributed optical fiber sensors, and in particular relates to a Brillouin optical time domain analyzer for a chaotic laser related integrated fiber Raman amplifier.

Background technique

In the fiber Brillouin optical time domain analyzer, in order to improve the spatial resolution of the sensor, a narrow pulse light source is used, but due to the nonlinear effect of the fiber, the incident power of the fiber is limited, so that long distance and high are realized. The spatial resolution of the fiber Brillouin optical time domain analyzer is very difficult. The traditional method of compressing the pulse width of the laser, the method of double pulse pair, is difficult to achieve long-distance spatial resolution of less than 1 meter, and the book

And the spatial resolution is related to the measured length, and the system's signal-to-noise ratio is also low. In recent years, the principle of chaotic laser correlation has been applied to laser radar at home and abroad. The laser light time domain reflectometer has achieved remarkable results, achieving a centimeter-level spatial resolution that is not limited by distance, in order to apply the chaotic laser correlation principle to the distribution. Fiber optic sensors create the conditions. On the other hand, in order to improve the signal-to-noise ratio of the system, in 1989, T. Horiguchi et al. invented the Brillouin optical time domain analyzer, adding a coherent pump laser at the other end of the fiber to realize Brillouin amplification, using coherence. Amplified stimulated Brillouin scattering enhances the signal and improves the signal-to-noise ratio of the system. However, it is technically difficult to strictly lock the frequencies of narrow-band detection lasers and narrow-band pump lasers in fiber-optic Brillouin optical time domain analyzers. Zhang Zai-Xuan et al. proposed the "Fiber Brillouin Optical Time Domain Analyzer" ( Chinese invention patent, patent number: ZL200810063711.8, authorized on June 9, 2010) The use of broadband distributed fiber-optic Raman amplifiers to replace narrow-band fiber Brillouin amplifiers solves the difficulties of locking narrow-band detection lasers and narrow-band pump lasers; The fusion chaotic laser related technology and fiber Raman amplification technology can effectively improve the spatial resolution, measurement distance and measurement accuracy of the sensor system, and meet the safety and health monitoring of petroleum pipelines and transmission power cables in recent years. And the needs of temperature sensing networks.

Summary of the invention

The object of the present invention is to provide a Brillouin optical time domain analyzer for a chaotic laser-related integrated fiber Raman amplifier according to the deficiencies of the prior art. The invention has the characteristics of ultra-long-range, high spatial resolution and high measurement accuracy.

In order to achieve the above object, the present invention adopts the following technical solutions: The chaotic laser-related fiber Brillouin optical time domain analyzer of the present invention utilizes the chaotic laser correlation principle, the fiber stimulated Raman amplification effect, and the coherently amplified Brillouin scattered light. Fiber Brillouin light time made by strain, temperature effect and optical time domain reflection principle Domain analyzer, including semiconductor LD laser, first polarization controller, first fiber circulator, first fiber splitter, dimmable attenuator, second polarization controller, one-way device, erb-doped fiber amplifier EDFA, Second fiber splitter, optical modulator, second fiber circulator, optical heterodyne receiver module, digital signal processor, third fiber circulator, narrowband reflection filter, pump-signal coupler, fiber pull Man pump laser, sensing fiber, fourth fiber circulator, fiber grating reflection filter and computer. The semiconductor LD laser is connected to an input port of the first fiber circulator via a first polarization controller, and the other output end of the first fiber circulator is connected to the input end of the first fiber splitter, the first fiber splitter An output end is connected to the input end of the tunable optical attenuator, and the output end of the tunable optical attenuator is connected to an input end of the optical circulator through a second polarization controller, and then fed back to the semiconductor LD laser via the first polarization controller; The other output end of the first fiber optic splitter is connected to the EDFA with a doped fiber amplifier via a one-way device, the output of the EDFA of the doped fiber amplifier is connected to the input of the second fiber splitter, and one of the second fiber splitters The output end is connected to the optical modulator, one output end of the optical modulator is connected to the input end of the second optical fiber circulator, and the other output end of the second optical fiber splitter is connected to the input end of the third optical fiber circulator, the third An output end of the fiber circulator is connected to the narrow-band reflection filter of the optical fiber, and the other end of the narrow-band reflection filter of the optical fiber is connected to the sensing fiber through a pump signal coupler, the pump The other end of the PD coupler is connected to the fiber Raman pump laser, the other output of the third fiber circulator is connected to one end of the fourth fiber circulator, and the fourth fiber circulator is connected to the fiber grating reflection filter, The output end of the four fiber circulator is connected to the other end of the second fiber circulator, the output end of the second fiber circulator is connected to the optical heterodyne receiver module, and the optical heterodyne receiver module is connected to the digital signal processor and the computer. The optical heterodyne receiving module, the digital signal processor and the computer will heterodise the chaotic laser signal of the sensing fiber and the local reference light, and perform autocorrelation processing and fast Fourier transform demodulation to obtain a high field of the 100 km sensing fiber. The strain and temperature information with a spatial resolution of the order of centimeters is transmitted to the remote monitoring network via a wireless network or the Internet; the other output of the optical modulator 19 is connected to the computer 30.

Further, the chaotic laser-related integrated fiber Raman amplifier Brillouin optical time domain analyzer, the chaotic laser is a semiconductor LD laser, a first polarization controller, a first fiber circulator, a first fiber splitter, The tunable optical attenuator consists of a second polarization controller. The semiconductor LD laser is a DFB laser with an operating wavelength of 1550. Onrn, the output power is 10dBm. The branch ratio of the first fiber splitter is 20:80.

Further, the chaotic laser-related integrated fiber Raman amplifier Brillouin optical time domain analyzer, the light modulator is a Mach-Zehnder modulator (MZM). A computer controlled light modulator reduces the frequency of the laser by l lGHz.

Further, the chaotic laser-related integrated fiber Raman amplifier Brillouin optical time domain analyzer, the optical heterodyne receiver module is a photodetector with a frequency response of 2 Ghz or more, low noise broadband front The amplifier is integrated with a chip and a main amplifier.

Further, the chaotic laser-related integrated fiber Raman amplifier has a Brillouin optical time domain analyzer, and the sensing fiber is a 100 km single mode communication G652 fiber or a 100 km LEAF fiber.

Further, the chaotic laser-related integrated fiber Raman amplifier Brillouin optical time domain analyzer, the fiber Raman laser is a fiber Raman laser with a power ranging from 100 mW to 1200 mw and a wavelength of 1450 nm continuous operation. Back-to-pumped fiber Raman amplifier with sensing fiber (Fig. 1) Since the fiber Raman amplifier has bidirectional amplification characteristics and different unidirectional amplification characteristics of the fiber Brillouin amplifier, back pump or forward pump can be used. Way of working.

Further, the chaotic laser-related integrated fiber Raman amplifier Brillouin optical time domain analyzer has a center wavelength of 1450 nm, a spectral bandwidth of 0.3 nm, and an isolation greater than 35 dB. Suppressed fiber Raman laser 1450nm backscattered light.

Further, the chaotic laser-related integrated fiber Raman amplifier Brillouin optical time domain analyzer has a center wavelength of 1550.08 nm and a spectral bandwidth of 0.1 nm. Other light is filtered out, allowing the Stokes Brillouin scattering signal light of the sensing fiber to be received by the fourth fiber circulator and the local optical heterodyne.

Further, the chaotic laser-related integrated fiber Raman amplifier Brillouin optical time domain analyzer, the digital signal processor uses a high-speed 5G sampling rate with autocorrelation processing and fast Fourier transform software 500MHz bandwidth digital signal processor.

Chaotic laser correlation principle:

The semiconductor laser continuously generates a random undulating chaotic laser when it receives optical feedback. The correlation curve has a δ function shape. The bandwidth of the nonlinear chaotic oscillation of the semiconductor laser can be greater than 15 GHz, achieving high resolution and high precision independent of the measurement length. Measurement.

Let the reference light be f ( t ) and the probe light be g ( t ) = Kf ( t- τ );

Cross-correlation function:

When τ = τ. When, the cross-correlation peak is related to the intensity of the probe light. The signal and the reference light are collected, accumulated and correlated by a digital signal processor and a computer to obtain information on strain and temperature on the sensing fiber. The signal-to-noise ratio of the system determines the measurement length.

How the Brillouin Time Domain Analyzer works:

In the optical fiber, the detecting laser of the incident fiber interacts with the nonlinear wave of the acoustic wave in the optical fiber, and the optical wave generates acoustic waves by electrostriction, causing periodic modulation of the refractive index of the optical fiber (refractive index grating), generating Brillouin scattering with frequency downshift Light, the frequency shift ν _背 of the back Brillouin scattering produced in the fiber is:

λ (2 ) Where n is the refractive index at the wavelength λ of the incident light, V is the speed of sound in the fiber, and for the quartz fiber, _β is approximately llGHz around λ = 1550 nm.

The Brillouin scattered light frequency shift in the fiber V 8 has strain and temperature effects:

Dv dv ( ) ν _Β =ν _Β +— ε(με) +—Τ(°€) ,

^{Β Β} . Ds dT

Frequency shift of Brillouin scattered light:

Sv _B = C _vs Ss + C _vT ST (4) where the strain coefficient c _{ν ε of the} frequency shift and the temperature coefficient C _ν τ are:

C _vs = 0.0482 ± 0.004MHz / = 1.10 ± 0.02 3⁄4 IK;

Optical fiber stimulated Raman amplification principle

When incident laser light V. A nonlinear interaction scattering with the fiber molecule, releasing a phonon called a Stokes Raman scattered photon, absorbing a phonon called the anti-Stokes Raman scattering photon ΔV, the phonon frequency of the fiber molecule is 13.2ΤΗζ.

ν = V. The switching gain of the Δ V (5) amplifier is:

G _A = exp( g _R P ₀ L _eff IA _eff ) (6) where A _ff is the pumping light input power of the amplifier, is the Raman gain coefficient Λ _# is the effective cross section of the fiber, and L _eff is the effective length of the fiber (Considering the absorption loss of the fiber to the pump), the expression is as follows:

L _eff =—[\-cxp( -a _p L)] (7) For fiber Raman amplifiers, when the pump power exceeds a certain threshold, it is possible to generate stimulated Raman amplification of the signal in the fiber. Stokes wave v = V. -ΔV increases rapidly in the fiber medium. Most of the pump light power can be converted into Stokes light and has Raman amplification. The gain can suppress the transmission loss of the fiber and produce coherent amplification in the sensing fiber. The Brillouin scattering, replacing the narrowband fiber Brillouin amplifier with a wideband distributed fiber Raman amplifier solves the frequency problem of locking narrowband probe lasers and narrowband pump lasers.

The beneficial effects of the invention are as follows: The Brillouin optical time domain analyzer of the chaotic laser-related integrated fiber Raman amplifier proposed by the invention adopts the chaotic laser correlation principle, and the chaotic laser has a wide bandwidth, and passes the signal light and the local light. Correlated processing achieves high spatial resolution, effectively improves sensor reliability and spatial resolution, increases the number of pump photons entering the sensing fiber, improves the signal-to-noise ratio of the sensor system, and increases the measurement length of the sensor; Continuously operating high power fiber Raman lasers The pump source of the new Brillouin optical time domain analyzer replaces the coherently pumped narrowband laser, overcoming the difficulty of requiring the rigorous locking of the probe laser and pump laser frequencies in the fiber Brillouin optical time domain analyzer. The high-power fiber Raman laser produces a strong laser that achieves stimulated Raman scattered light amplification in a single-mode fiber instead of narrow-band Brillouin amplification, increasing the gain of stimulated Brillouin scattered light that is back-coherently amplified. The signal-to-noise ratio of the system is increased, the measurement length is increased, and the accuracy of simultaneous measurement of strain and temperature is improved.

DRAWINGS

Figure 1 is a schematic block diagram showing the structure of the present invention.

detailed description

Referring to FIG. 1, a Brillouin optical time domain analyzer of a chaotic laser-related integrated fiber Raman amplifier of the present invention includes a semiconductor LD laser 10, a first polarization controller 11, a first fiber circulator 12, and a first fiber splitter. 13. The tunable optical attenuator 14, the second polarization controller 15, the one-way device 16, the erbium-doped fiber amplifier EDFA 17, the second fiber splitter 18, the light modulator 19, the second fiber circulator 20, and the light Differential receiver module 21, digital signal processor 22, third fiber circulator 23, narrowband reflection filter 24, pump-signal coupler 25, fiber Raman pump laser 26, sensing fiber 27, fourth fiber The circulator 28, the fiber grating reflective filter 29, and the computer 30. The semiconductor LD laser 10 is connected to an input port of the first fiber circulator 12 via the first polarization controller 11, and the output end of the first fiber circulator 12 is connected to the input end of the first fiber splitter 13, the first fiber is divided into An output of the illuminator 13 is connected to the input of the tunable optical attenuator 14, and the output of the tunable optical attenuator 14 is connected to the other input of the first optical circulator 12 via a second polarization controller 15, and The first polarization controller 11 feeds back the semiconductor LD laser 10; the other output end of the first fiber splitter 13 is connected to the erbium-doped fiber amplifier EDFA17 via the one-way device 16, and the output of the EDFA17 is coupled with the second and second. An input end of the optical fiber splitter 18 is connected, an output end of the second optical fiber splitter 18 is connected to the optical modulator 19, and an output end of the optical modulator 19 is connected to an input end of the second optical fiber circulator 20; The other output of the splitter 18 is connected to the third fiber circulator 23, and one output of the third fiber circulator 23 is connected to the narrow band reflection filter 24, and the other end of the narrow band reflection filter 24 is pump-signal Coupler 25 The input is connected, the output of the pump-signal coupler 25 is connected to the sensing fiber 27; the other input of the pump-signal coupler 25 is connected to the fiber Raman pump laser 26, and the third fiber circulator 23 is The other output is connected to one end of the fourth fiber circulator 28, the fourth fiber circulator 28 is connected to the fiber grating reflection filter 29, and the output end of the fourth fiber circulator 28 is connected to the other end of the second fiber circulator 20. The output of the second fiber circulator 20 is connected to the optical heterodyne receiver module 21, the optical heterodyne receiver module 21 is connected to the computer 30 via a digital signal processor 22, and the other output of the optical modulator 19 is connected to the computer 30. In operation, the chaotic laser is amplified by the fiber amplifier EDFA 17 and split into two turns. One chaotic laser passes through the optical modulator 19, which reduces the frequency of the laser by 11 GHz as the local reference light, and the other chaotic laser passes through the pump-signal coupler. After 25, it enters the sensing fiber 27, and the Brillouin light with strain and temperature information facing away, is coherently amplified in the fiber amplifier pumped by the fiber Raman pump laser, and the amplified stimulated Brillouin scattered light v. ± v _B passes through the fiber grating reflection filter, filtering out v. , v ₀ + v _B , obtain V 0-V _B signal light, and the local reference light is passed through the optical heterodyne receiving module, the digital signal processor 22 and the computer 30 demodulate and perform autocorrelation processing and fast Fourier transform, The optical time domain reflection principle is located to obtain high spatial resolution strain and temperature information on each segment of the sensing fiber.

The invention is made by using chaotic laser correlation principle, fiber stimulated Raman scattering light amplification effect and coherent amplified Brillouin scattering light strain, temperature effect and optical time domain reflection principle; the invention adopts chaotic laser correlation principle in time domain The random fluctuation of the optical pulse sequence improves the spatial resolution of the sensor system by the correlation processing of the back-detected light of the sensing fiber and the local reference light; and the continuous operation of the high-power fiber Raman laser as the Brillouin light The domain analyzer's pumping source overcomes the difficulty of fiber-optic Brillouin optical time domain analyzers requiring tight locking of the probe laser and pump laser frequencies, replacing the narrowband fiber Brillouin amplifier with a wideband fiber Raman amplifier, adding back The gain of the stimulated Brillouin scattered light, which is amplified, increases the signal-to-noise ratio of the sensor system, and accordingly increases the measurement length and measurement accuracy of the sensor.

Claims

Claim

A Brillouin optical time domain analyzer for a chaotic laser-related integrated fiber Raman amplifier, characterized in that it comprises a semiconductor LD laser (10), a first polarization controller (11), and a first fiber circulator ( 12), first fiber splitter (13), dimmable attenuator (14), second polarization controller (15), one-way device (16), erbium-doped fiber amplifier EDFA (17), second fiber a splitter (18), a light modulator (19), a second fiber circulator (20), an optical heterodyne receiver module (21), a digital signal processor (22), a third fiber circulator (23), Narrowband reflection filter (24), pump-signal coupler (25), fiber Raman pump laser (26), sensing fiber (27), fourth fiber circulator (28), fiber grating reflection filter And a computer (30); wherein the semiconductor LD laser (10) is connected to an input port of the first fiber circulator (12) via the first polarization controller (11), the first fiber circulator The output of (12) is connected to the input of the first fiber splitter (13), the first fiber branch One output of the (13) is connected to the input of the dimmable attenuator (14), and the output of the dimmable attenuator (14) is passed through the second polarization controller (15) and the first optical circulator (12) The other input is connected to the semiconductor LD laser (10) via the first polarization controller (11); the other output of the first fiber splitter (13) is coupled via the one-way device (16) The bait fiber amplifier EDFA (17) is connected, the output of the erbium-doped fiber amplifier EDFAC17) is connected to the input of the second fiber splitter (18), and the second fiber splitter (18) has an output and a light modulator (19). Connected, the output of the optical modulator (19) is connected to one input of the second fiber circulator (20); the second fiber splitter (18) is connected to the third fiber circulator (23) An output of the third fiber circulator (23) is connected to the narrowband reflection filter (24), and the other end of the narrowband reflection filter (24) is connected to the input of the pump-signal coupler (25). The output of the pump-signal coupler (25) is connected to the sensing fiber (27) The other input of the pump-signal coupler (25) is connected to the fiber Raman pump laser (26), the other output of the third fiber circulator (23) and the fourth fiber circulator (28) One end is connected, the fourth fiber circulator (28) is connected to the fiber grating reflection filter (29), the output end of the fourth fiber circulator (28) is connected to the other end of the second fiber circulator (20), and the second fiber ring is connected. (20) output and optical heterodyne receiver module

(21) Connected, the optical heterodyne receiver module (21) is connected to the digital signal processor (22) and the computer (30); the optical modulator (19) is connected to the computer (30).

2. A Brillouin optical time domain analyzer for a chaotic laser-related integrated fiber Raman amplifier according to claim 1, wherein said semiconductor LD laser (10), first polarization controller (11), A fiber circulator (12), a first fiber splitter (13), a tunable optical attenuator (14) and a second polarization controller (15) constitute a chaotic laser; the semiconductor LD laser (10) is a DFB laser , Its working wavelength is 1550. Onm, the output power is lOdBm; the branch ratio of the first fiber splitter (13) is 20:80.

3. A Brillouin optical time domain analyzer for a chaotic laser related integrated fiber Raman amplifier according to claim 1, wherein said light modulator (19) is a lithium niobate Mach-Zehnder modulator.

4. The Brillouin optical time domain analyzer of a chaotic laser-related integrated fiber Raman amplifier according to claim 1, wherein the optical heterodyne receiver module (21) has a frequency response of 2 Ghz or more. Photodetector, preamplifier and main amplifier.

5. The Brillouin optical time domain analyzer of a chaotic laser-related integrated fiber Raman amplifier according to claim 1, wherein the sensing fiber (27) is a 100 km single mode communication G652 fiber or a 100 km LEAF fiber. .

6. The Brillouin optical time domain analyzer of a chaotic laser-related integrated fiber Raman amplifier according to claim 1, wherein the fiber Raman laser (26) is adjustable in a power range of 100 mW to 1200 mw. A fiber-optic Raman laser operating continuously at a wavelength of 1450 nm.

7. The Brillouin optical time domain analyzer of a chaotic laser-related integrated fiber Raman amplifier according to claim 1, wherein the narrowband reflection filter (24) has a center wavelength of 1450 nm and a spectral bandwidth of 0.3nm, isolation greater than 35dB.

8. The Brillouin optical time domain analyzer of a chaotic laser-related integrated fiber Raman amplifier according to claim 1, wherein the fiber grating reflection filter (29) has a center wavelength of 1550.08 nm, and a spectrum The bandwidth is 0.1 nm.

9. The Brillouin optical time domain analyzer of a chaotic laser-related integrated fiber Raman amplifier according to claim 1, wherein said digital signal processor (22) uses autocorrelation processing and fast Fourier The leaf transform software has a high speed 5G sampling rate and a 500MHz bandwidth digital signal processor.