Optical fiber distributed acoustic sensing based on the self-interference of Rayleigh backscattering

Accepted Manuscript Optical fiber distributed acoustic sensing based on the self-interference of Rayleigh backscattering Ying Shang, Yuanhong Yang, Chen Wang, Xiaohui Liu, Chang Wang, Gangding Peng PII: DOI: Reference:

S0263-2241(15)00509-6 http://dx.doi.org/10.1016/j.measurement.2015.09.042 MEASUR 3598

To appear in:

Measurement

Please cite this article as: Y. Shang, Y. Yang, C. Wang, X. Liu, C. Wang, G. Peng, Optical fiber distributed acoustic sensing based on the self-interference of Rayleigh backscattering, Measurement (2015), doi: http://dx.doi.org/ 10.1016/j.measurement.2015.09.042

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Optical fiber distributed acoustic sensing based on the self-interference of Rayleigh backscattering Ying Shang,1,2,* YuanhongYang, 1 Chen Wang, 2 Xiaohui Liu,2 Chang Wang, 2 and Gangding Peng, 2,3 1

Department of Opto-Electronics Engineering, School of Instrumentation Science and Opto-Electronics Engineering, Beihang University,Beijing100191,China 2 Shandong Key Laboratory of Optical Fiber Sensing Technologies, Laser Institute of Shandong Academy of Sciences, Jinan, Shandong, 250014, China 3 School of Electrical Engineering & Telecommunications, the University of New South Wales, NSW, 2052, Australia *Corresponding author: [email protected]

Abstract: In order to detect the weak underwater acoustic signal, a Distributed Acoustic Sensing (DAS) scheme based on the selfinterference of Rayleigh backscattering is presented. Rayleigh backscattered light which contains a phase change induced by acoustic signal along the sensing fiber which is a standard telecom single-mode fiber is split and fed into an imbalance Michelson interferometer. With the self-interference of two Rayleigh backscattered beams, the phase change is amplified theoretically compared with phase-sensitive OTDR. We designed an experiment to prove the scheme, and successfully restored the acoustic information, meanwhile, the DAS system has preliminary realized around the acoustic phase sensitivity of -151 dB (re rad/μPa) at 600Hz, and the minimum detectable acoustic pressure of 6 Pa in the experiment. Keywords: Distributed Acoustic Sensing, Rayleigh backscattering, self-interference , acoustic phase sensitivity,

1.Introduction

scattering[10,11] based sensors are effective technologies for vibration

With the comprehensive utilization of marine science and technology

detection but not acoustic sensing. On the other hand, Dual interferometers

research and the development of national defense, demand for submarine

have been developed to get the acoustic position and acoustic information

environment monitoring is increasing, especially in the field of the ocean

(phase, amplitude and frequency) along the sensing fiber, such as Sagnac–

background noise, underwater target feature extraction and recognition,

Sagnac[12,13] Sagnac–MZ[14,15], Sagnac–Michelson[16] and MZ–

acoustic warning and submarine pipeline leak detection[1,2], etc. The

MZ[17,18]. However the optical path design and demodulation algorithm of

submarine detection technology is restricted by the adverse factors such as

dual interferometers are complex, making it difficult to be implemented in

the bad environment and difficulty of the sensor arrangement to cover the

practical application.

large areas of monitoring, and so on. However, the unique advantage of

To solve above problems, utilizing the elastic reflection and Gaussian

optical fiber distributed sensing technology is that the fiber itself can act as

phase distribution characteristic of Rayleigh backscattering[19],we proposed

the sensing element, then the technology segregates the fiber into an array of

the optical fiber Distributed Acoustic Sensing (DAS) technology based on

individual “microphones”, so the distributed information of the whole

self-interference of Rayleigh backscattering in the paper. This scheme differs

sensing area can be measured in real time, so the optical fiber distributed

from the previous schemes in that phase information of self-interference

sensing technology is becoming a research hot spot because of the sensor

light of the Rayleigh backscattering from the sensing fiber which record

arrangement simplicity and wide detection range.

location, frequency, amplitude and phase of the acoustic wave are amplified.

Up to now, optical fiber distributed sensing technology mainly consists of

Furthermore, in our experiment, self-interference light phase of the Rayleigh

optical time/frequency domain reflection technology and optical fiber dual

backscattering recorded acoustic wave generated by an underwater speaker,

interferometer

domain

then we simultaneously restored the acoustic wave information such as

reflection(OTDR/OFDR) technology makes use of Rayleigh, Raman and

location, frequency, amplitude and phase with the DAS technology and the

Brillouin effects induced by external disturbance on the optical

Phase Generated Carrier (PGC) technology. This scheme really has realized

fiber[5].Currently the Coherent optical time domain reflectometers

the distributed acoustic sensing with the optical fiber sensing technology.

(COTDR)[6,7],

technology

[3,4].

phase-sensitive

Optical

time/frequency

OTDR(Φ-OTDR)[8,9]and

Brillouin

2.Principle , 2.1.The principle of self-interference of Rayleigh backscattering According to the measurement principle of one-dimensional impulse response model of the backscattering from a fiber, when we launch a coherent light pulse with pulse-width W and optical frequencyf into a fiber ,

at t=0, we obtain a backscattered wave at the input end of the fiber which is

,

given by[20-21]：

L1 L2

ero(t)

(1) Where

and

constant, c is the velocity of light in vacuum, fiber, and

L1 L2

erd(t)

are the amplitude and delay of the ith scattered wave

respectively, N is the total number of scattering,

……

τi+τs .

i

is the fiber attenuation

is the refractive index of the

,when

……

.τ +τ +τ s

d

……

einter(t) τd

, and is zero

otherwise. The delay corresponds to the distance zi from the input end to the ith scatterer through the relation

. The term

accounts for the change in the scattering volume seen as

as

optical fiber

circulator

. L2=L1=

is

or

.The scheme can realize backward Rayleigh scattering light

……

er(t)

interference not only within the scope of a single pulse but also within scope FRM

einter(t)

coupler s

d

ero(t) FRM erd(t)

of different pulses such as

Fig. 1.Optical path of self-interference principle of Rayleigh backscattering As shown in Fig.1, when

is injected into the Michelson

Interferometer, we obtain two reflected waves at the coupler as shown in

of L2 length of fiber. So the phase information is amplified by the path imbalance length of the interferometer. As shown in Eq.4, it is known that the interference signal contains phase information induced by the acoustic signal, so as long as phase information

Fig.2 which is given respectively by ]

,

, for example, backward Rayleigh scattering

light of L1 length of fiber interferes with backward Rayleigh scattering light

Michelson Interferometer

Where

is defined as

interference within the scope of a single pulse (L1 or L2 length of fiber )such

W,v AOM

The spatial resolution

made in the Fig. 2. Φ-OTDR can achieve backward Rayleigh scattering light

the pulse propagates.

DFB-LD

Fig 2. Self-interference schematic diagram of Rayleigh backscattering

(2)

can be demodulated, the DAS system can quantitatively restored the acoustic

(3)

field such as the acoustic signal amplitude, phase and frequency.

.s is the one path length of the

Michelson interferometer, d is the path imbalance length of Michelson interferometer.

2.2.Modulation and demodulation techniques of phase generated carrier Interferometer output signal can be expressed as

Two reflected waves at the coupler interfere，The interferometer signal intensity I(t) is given by

(5) Where A is the average optical power of interferometer output signal, ,

and

is interference fringe visibility,

generated carrier, (4)

induced by the tested signal,

Where

,

is phase change

is slow variation of the initial phase

caused by environment. ,

is phase

Eq.5 can be expressed with Bessel function expansion:

scattering, this signal is demodulated by the PGC module and then acquired (6)

with PC with 100 MHz sampling rate. DFB-LD

AOM

optical fiber

circulator

Filter

EDFA

ωs PM

Fig 3. PGC demodulation scheme.⊗- -multiplier; LPF- -low pass filter;

PD

Filter

PGC

PC

EDFA

…… FRM

coupler FRM

d

Fig.4. DAS detection system block diagram

df∕dt- -derivative;∫- -integrator; HPF- - high pass filter. As shown in Fig.3, the signal I goes through this process, so the final output S(t) of the PGC which contains the tested signal

3.2. DAS experiment system design The experiment system is shown in Fig.5. An underwater speaker is fixed in

is (7)

where G and H is the amplitude of fundamental and double frequency signal, respectively. U is the coefficient of demodulation system. In our experiment, the value of U is 1. 3.Experiment

the tank. To enhance the acoustic phase sensitivity of the DAS system, we wrapped the sensing fiber into a 10 m length of fiber ring at the 180 m location of the sensing fiber from the DAS instrument. The fiber ring and a piezoelectric hydrophone are placed 5cm away from the underwater speaker.

3.1. DAS detection system design

During the experiment, the underwater speaker is driven by the signal

DAS detection system diagram is shown in Fig.4. Distributed-feedback laser

generator, and we use the piezoelectric hydrophone to measure the acoustic

diode (DFB-LD) with narrow line width of 5 kHz is used as a light source,

pressure at the location of the fiber ring. Meanwhile, we use the DAS

which generates the CW light with power of 10 mW. The CW light is

instrument to get the location of acoustic source and the phase change of

modulated into sequence of pulses by acoustic-optic modulator

Rayleigh backscattered light, and simultaneously the acoustic field

(AOM).Those pulses have repetition rate(f) of 20 kHz and pulse-width(W)of

information such as the acoustic signal frequency, amplitude and phase is

100 ns. Repetition rate(f) of 20 kHz determines 5 kilometer monitoring

demodulated. The acoustic phase sensitivity and the minimum detective

ranges of the DAS system, Taking 500 m length of fiber for example, the

acoustic pressure of the DAS system are calculated.

experiment prove the above scheme .Pulse-width(W)of 100 ns determines that spatial resolution of the DAS system is 10 m .The modulated pulses are

signal generator

the demodulation instrument of DAS the demodulation instrument of piezoelectric hydrophone

modulated pulses are gated into 500 m length of sensing fiber which is a

wire 300m

filtered by a narrow-band filter to remove spontaneous emission. The

wire

amplified by Erbium-doped fiber amplifier(EDFA), the output of EDFA is sensing fiber

Fiber ring

standard telecom single-mode fiber with by a circulator, and when the sensing fiber detects the acoustic wave, the phase information of Rayleigh

5cm

tank

underwater speaker piezoelectric hydrophone

backscattered light changes, the Rayleigh backscattered light is then split into two paths by a 3dB fiber coupler (50:50), One path is utilized as delay light,

Fig.5.DAS experiment system diagram

while the other path is modulated by Phase Modulator (PM) with 40 KHz frequency, and the optical path imbalance is half spatial resolution of 10 m

C.Experiment result

according to pulse-width(W)of 100 ns. Modulated light interfere with delay

The underwater speaker driven by the 600Hz signal with the amplitude of

light at the 3dB coupler, then interference light is amplified by an EDFA,

500 mV generated an acoustic pressure signal，the signal demodulated by

filtered and then received by a Photoelectric Detector(PD) to produce the

the DAS system is in the Fig.6. There is an obvious 600Hz signal at the 180

electrical signal that contains the coherent light information of the Rayleigh

m location of the sensing fiber in the three-dimensional acoustic intensity

figure. The spatial resolution of the acoustic signal is almost 10 m in two-

hydrophone. So the minimum detectable acoustic pressure of the

dimensional acoustic intensity figure at the bottom of the Fig.6. In order to

DAS system is 6 Pa in the experiment

calculate the phase change induced by the acoustic pressure signal, the

When we do the experiment of the minimum detective acoustic pressure

demodulation signal of 175 m~185 m location of the sensing fiber are

of the DAS system, and the acoustic phase sensitivity experiment is

superimposed and averaged ,then the time domain of the signal is shown in

done at the same time, so we calculated the acoustic sensitivity of the DAS

the red line of the Fig.7, we obviously obtain a propagating 600Hz signal in

system at the 600 Hz , The experiment result is shown in the Tab.1, from

100 ns. The fast Fourier transform (FFT) result of the demodulated signal is

Tab.1, it is known that acoustic phase sensitivity is almost -150 dB (re

shown in the the red line of the Fig.8, and the signal-to-noise ratio of the

rad/μPa) at 600Hz.

signal is almost 40dB. At the same time, we use the piezoelectric hydrophone to restore the acoustic pressure signal , the time domain of the signal is shown in black line of the Fig.7, the FFT result of the demodulated data is shown in black line of the Fig. 8. From the Fig .8, it is known that -30.44935 dB amplitude of the 600 Hz signal is converted to 30 mV amplitude of the signal. According to 500 Pa/V of acoustic pressure sensitivity of the piezoelectric hydrophone, the acoustic pressure is 15 Pa. From the Fig .8, amplitude of the 600 Hz signal of DAS is 0.654 V by the FFT calculation. According to the principle of PGC demodulation of the experiment system, and the phase change induce by the 15 Pa acoustic

Fig.6. The DAS demodulation result of the 500mV drive signal

pressure is 0.654 rad, so the phase sensitivity is 0.0436 rad/Pa, and equal to 147dB re rad/μPa. From the Fig.7and Fig.8, the DAS system has realized to restore the underwater acoustic field information such as the acoustic signal frequency, amplitude and phase. In order to test the minimum acoustic pressure value distinguished by the DAS system, the drive signal value of the underwater speaker is gradually reduced from 500 mV .to 200 mV . When the driven signal value of the underwater speaker is 200 mV, The

Fig.7. the acquired data time domain of a 500mV drive signal

experiment data of the DAS system is shown in the Fig.9. From the Fig .9, There is an signal at the 180 m location of the sensing fiber in the threedimensional acoustic intensity figure,but the amplitude of the signal is close to the amplitude of the noise, the time domain of the acquired data is shown in red line of the Fig.10 and the FFT result is shown in the red line of the Fig.11. From the Figtures, the signal-to-noise ratio of the signal is almost reduced to 20dB, and amplitude of the signal is 0.154 V by the FFT calculation. From the black line of the Fig.11, the acoustic pressure induced by the underwater speaker is 6 Pa by the measurement of the piezoelectric

Fig.8. the acquired data frequency domain of the of the 500mV drive signal

proves that the scheme can restore the acoustic information with the standard telecom single-mode fiber, we realized acoustic phase sensitivity of DAS system achieved around -151 dB (re rad/μPa) at 600Hz ,and the minimum detectable acoustic pressure acoustic pressure of 6 Pa is found through the experiment. This work provides basis on further study and performance improvement.

Reference 1.Wang zhen, LIU Zhen-jiang, “Design and Experiment of Data Acquisition System of Submerged Buoy”. OCEAN TECHNOLOGY,32(4):6-10（2013） Fig.9.The DAS demodulation result of the 200mV drive signal

Fig.10. the acquired data time domain of the 200mV drive signal

Fig.11. the acquired data frequency domain of the of the 200mV drive signal Table 1. the experiment data Piezoelectric hydrophone Amplitude (mV) 30 24 18 12

Acoustic pressure (Pa) 15 12 9 6

DAS Phase chage (rad) 0.654 0.312 0.243 0.154

Acoustic phase sensitivity (dB (re rad/μPa)) -147 -152 -151 -151

4.Conclusion An optical fiber distributed acoustic sensing technology based on the selfinterference of Rayleigh backscattering is demonstrated. Our experiment

2.Chen Shili,Huang Xinjing. “Feasibility Research on Spherical Inner Detector for Tiny Leakage of Subsea Pipeline,” Petroleum Engineering Construction,40(2):19-26.(2014) 3.SergiVillalba,JoanR.Casas ， “Application of optical fiber distributed sensing to health monitoring of concrete structures,”Mechanical Systems and Signal Processing,39 ,441-451(2013). 4.YAN Bing,DONG Feng-zhong,“Application of pipeline safety real-time monitoring with distributed optical fiber sensing technique based on coherent Rayleigh Backscattering,” CHINESE JOURNAL OF QUANTUM ELECTRONICS,30,3,341-347(2013). 5.Xiaoyi Bao,Liang Chen,“Recent Progress in Distributed Fiber Optic Sensors ,”Sensors, 12, 8601-8639(2012). 6.YuelanLu,TaoZhu,“Distributed Vibration Sensor Based on CoherentDetection of Phase-OTDR,”JOURNAL OF LIGHTWAVE TECHNOLOGY, 28, 22, 3243-3248(2010). 7.Yahei Koyamada,“Fiber-Optic Distributed Strain and Temperature Sensing With Very High Measurand Resolution OverLong Range Using Coherent OTDR,” JOURNAL OF LIGHTWAVE TECHNOLOGY, 27, 9, 1142-1145(2009). 8.Xiaonan Hui, Shilie Zheng, Jinhai Zhou,“Electro-optic modulator feedback control in phase-sensitive optical time-domain reflectometer distributed sensor,” APPLIED OPTICS ,52, 35 ,8581-8584(2013). 9.Peng F,Wu H,Jia XH,“Ultra-long high-sensitivity Φ-OTDR for high spatial resolution intrusion detection of pipelines,”Opt Express,22,11,1380413810,(2014). 10.Kazuo Hotate,“Fiber distributed Brillouin sensing with optical correlation domain techniques,” Optical Fiber Technology ,19 ,700-719 (2013). 11.Feng Wang, Xuping Zhang, Xiangchuan Wang,“Distributed fiber strain and vibration sensor based on Brillouin optical time-domain reflectometry and polarization optical time-domain reflectometry,” OPTICS LETTERS 15, 38, 14 ,2437-2439( 2013 ). 12.G. Zhang, C. Xi, Y. Liang, “Dual-Sagnac opticalfiber sensor used in acoustic emission source location,”in Proceedings of IEEE Conference on Cross Strait Quad- Regional Radio Science and Wireless Technology (IEEE,2011), pp. 1598–1602. 13.Bian Pang, Wu Yuan, Jia Bo, “Dual-wavelength Sagnac interferometer as perimetersensor with Rayleigh backscatter rejection,”Optical Engineering ,53,4, 044111 (2014). 14.Qingming Chen, Chao Jin,“A distributed fiber vibration sensor utilizing dispersion induced walk-off effect in aunidirectional Mach-Zehnder interferometer,”OPTICS EXPRESS,22,3,2167-2173(2014). 15.Pu Wei, Xuekang Shan, Xiaohan Sun.“Frequency response of distributed fiber-optic vibration sensor basedon nonbalanced Mach-Zehnder interferometer,”Optical Fiber Technology ,19 ,47–51(2013).

16.M. KONDRAT, M. SZUSTAKOWSKI, N. PALKA, “A SagnacMichelson fibre optic interferometer: Signal processing for disturbance localization,”OPTO-ELECTRONICS REVIEW 15,3, 127-132(2007). 17.J. Li, T. Ning, L. Pei, “Photonic generation of triangular waveform signalsby using a dual-parallel Mach–Zehnder modulator,” OPTICSLETTERS , 36, 19 , 3828-3830,(2011). 18.Lihui Jiang，Ruoyu Yang，“Identification Technique for the Intrusion ofAirport Enclosure Based on Double Mach-Zehnder Interferometer,” JOURNAL OF COMPUTERS,7,6,1453-1458(2012). 19.ARTHUR H. HARTOG , MARTIN P. GOLD ,“On theTheory of Backscattering in Single-Mode Optical Fibers ,”JOURNAL OF LIGHTWAVE TECHNOLOGY,LT-2, 2, 76-82(1984). 20.MasatakaNakazawa, “ Rayleigh backscattering theory for single-mode optical fibers,” J. Opt. Soc. Am, 73, 9,1175-1180(1983). 21.R. Juskaitis, “Interferometry with Rayleigh backscattering in a singlemode optical fiber,”OPTICS LETTERS,19,3,225-227(1994).

Highlights

1. a distributed acoustic signal measurement 2. initial measurements of acoustic pressure sensitivity 3. minimum detectable acoustic pressure measurement