Distributed vibration sensing based on forward transmission and coherent detection

📝 Abstract

A novel ultra-long distributed vibration sensing (DVS) system using forward transmission and coherent detection is proposed and experimentally demonstrated. In the proposed scheme, a pair of multi-span optical fibers are deployed for sensing, and a loop-back configuration is used by connecting the two fibers at the far end. The homodyne coherent detection is used to retrieve the phase and state-of-polarization (SOP) fluctuations caused by a vibration while the localization of the vibration is realized by tracking the phase changes along the two fibers. The proposed scheme has the advantage of high signal-to-noise ratio (SNR) and ultra-long sensing range due to the nature of forward transmission and coherent detection. In addition, using forward rather than backward scattering allows detection of high frequency vibration signal over a long sensing range. More than 50dB sensing SNR can be obtained after long-haul transmission. Meanwhile, localization of 400 Hz, 1 kHz and 10 kHz vibrations has been experimentally demonstrated with a spatial resolution of less than 50 m over a total of 1008 km sensing fiber. The sensing length can be further extended to even trans-oceanic distances using more fiber spans and erbium-doped fiber amplifiers (EDFAs), making it a promising candidate for proactive fault detection and localization in long-haul and ultra-long-haul fiber links.

💡 Analysis

A novel ultra-long distributed vibration sensing (DVS) system using forward transmission and coherent detection is proposed and experimentally demonstrated. In the proposed scheme, a pair of multi-span optical fibers are deployed for sensing, and a loop-back configuration is used by connecting the two fibers at the far end. The homodyne coherent detection is used to retrieve the phase and state-of-polarization (SOP) fluctuations caused by a vibration while the localization of the vibration is realized by tracking the phase changes along the two fibers. The proposed scheme has the advantage of high signal-to-noise ratio (SNR) and ultra-long sensing range due to the nature of forward transmission and coherent detection. In addition, using forward rather than backward scattering allows detection of high frequency vibration signal over a long sensing range. More than 50dB sensing SNR can be obtained after long-haul transmission. Meanwhile, localization of 400 Hz, 1 kHz and 10 kHz vibrations has been experimentally demonstrated with a spatial resolution of less than 50 m over a total of 1008 km sensing fiber. The sensing length can be further extended to even trans-oceanic distances using more fiber spans and erbium-doped fiber amplifiers (EDFAs), making it a promising candidate for proactive fault detection and localization in long-haul and ultra-long-haul fiber links.

📄 Content

Distributed vibration sensing based on forward transmission and coherent detection YAXI YAN,3,1 CHANGJIAN GUO,1,3,* XIONG WU,3 ZIQI LIN,1 XIAN ZHOU,2 FAISAL NADEEM KHAN,4 ALAN PAK TAO LAU,4 AND CHAO LU3 1South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou, China 2Research Center for Convergence Networks and Ubiquitous Services, University of Science & Technology Beijing (USTB), No.30 Xue Yuan Road, Haidian, Beijing, 100083, China
3Department of Electronic and Information Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong (SAR), China 4Department of Electrical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong (SAR), China *changjian.guo@coer-scnu.org Abstract: A novel ultra-long distributed vibration sensing (DVS) system using forward transmission and coherent detection is proposed and experimentally demonstrated. In the proposed scheme, a pair of multi-span optical fibers are deployed for sensing, and a loop-back configuration is used by connecting the two fibers at the far end. The homodyne coherent detection is used to retrieve the phase and state-of-polarization (SOP) fluctuations caused by a vibration while the localization of the vibration is realized by tracking the phase changes along the two fibers. The proposed scheme has the advantage of high signal-to-noise ratio (SNR) and ultra-long sensing range due to the nature of forward transmission and coherent detection. In addition, using forward rather than backward scattering allows detection of high frequency vibration signal over a long sensing range. More than 50dB sensing SNR can be obtained after long-haul transmission. Meanwhile, localization of 400 Hz, 1 kHz and 10 kHz vibrations has been experimentally demonstrated with a spatial resolution of less than 50 m over a total of 1008 km sensing fiber. The sensing length can be further extended to even trans-oceanic distances using more fiber spans and erbium-doped fiber amplifiers (EDFAs), making it a promising candidate for proactive fault detection and localization in long-haul and ultra-long- haul fiber links.

1. Introduction Driven by the bandwidth-consuming applications such as video streaming, cloud computing, and proliferation of smart devices, the data traffic in long-haul, metro and optical access networks has increased dramatically. The survivability has increasingly become a challenge for these optical networks due to the huge internet traffic. It is therefore imperative for network operators to have an early warning and proactive protection mechanism incorporated into their networks. Traditional network monitoring uses optical time-domain reflectometry (OTDR) schemes which can only localize the fault event without knowledge of the root cause of the failure [1-2]. Recently, fault detection and classification schemes by monitoring the state of polarization (SOP) rotation using either a commercial polarimeter [3] or a standard coherent receiver [4] were proposed. However, such schemes still lack the capability to localize the fault events. Fiber-optic vibration sensors can be used for leakage detection of oil and gas pipelines, structure health monitoring, perimeter security protection, and fault detection in optical communication links. In the past few decades, distributed vibration sensors (DVS) have attracted much research attention because of their advantages like resistance against electromagnetic interference, high precision, good chemical stability, and long sensing distance [5]. The DVS can be mainly divided into two categories. First is based on the OTDR technique, including phase-sensitive OTDR [6,7], polarization OTDR [8] and Brillion scattering based OTDR [9]. Another is based on the interferometer technique, including Michelson interferometer (MI) [10], Mach-Zehnder interferometer (MZI) [11,12] and Sagnac interferometer [13]. In OTDR based DVS systems, since the back-scatterred light is very small, the sensing distance and spatial resolution are limited. In [14], a hybrid amplification scheme was proposed to extend the sensing distance of OTDR-based DVS and consequently a 175km sensing range was obtained with 25m spatial resolution. Meanwhile, since the frequency response of vibration is related to the pulse repetition rate, the dynamic response will be a problem in long distance OTDR-based DVS. In interferometric DVS systems, the detectable frequency is no more a problem. However, most of these systems are not appropriate for long sensing distance because of the influence of the Rayleigh backscattering noise. For Sagnac interferometric DVS, a 41km sensing range with 100m spatial resolution was reported [15]. For MI-based DVS, a 51m spatial resolution was achieved over 4012m of sensing fiber [10]. In [16], a record of 320km sensing distance using MZI was reported. It should be noted that MZI- based DVS requires a stable r

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