High spatial resolution phase-sensitive optical time domain reflectometer with a frequency-swept pulse

Abstract

A high spatial resolution phase-sensitive optical time domain reflectometer (ϕ-OTDR) with an optical frequency-swept pulse (FSP) is proposed, and the experimental results are presented in the Letter. The FSP ϕ-OTDR uses optical pulses with linear frequency modulation with higher pulse energy for longer sensing fiber and uses matched filter in the receiver to compress the processed pulse width. Thus, the contradiction between spatial resolution and the working distance in ordinary ϕ-OTDR is relaxed. A spatial resolution of 30 cm, a sensing distance of 19.8 km, and a signal-to-noise ratio of 10 dB for vibration sensing were obtained experimentally. To our best of our knowledge, this is the first time that a sub-meter spatial resolution over such a long sensing range has been reported in ϕ-OTDR sensors.

Recent Advances in Distributed Acoustic Sensing Based on Phase-Sensitive Optical Time Domain Reflectometry

“…Most notably, an interesting technique to implement ϕ-OTDR with enhanced spatial resolution which is decoupled from the probing pulse width has also been proposed and demonstrated, using swept-frequency pulse [34]. The technique is based on the principle used in optical pulse compression reflectometry (OPCR) which uses frequencymodulated pulse compression.…”

“…Nonetheless, theoretical analysis shows that measurement using a matched filter is as though the original LFM pulse is compressed as a narrow sinc-like pulse. In this technique, the spatial resolution R (defined as FWHM of the processed signal in this particular demonstration) is given as follows [34]:…”

“…The spatial resolution performance limit of the proposed sensor is coupled with the frequency sweeping range which also determines receiver bandwidth where as expected, more spatially resolved measurements require higher receiver bandwidth. Figure 9: Schematic of a high spatial resolution ϕ-OTDR using a frequency-swept pulse [34]. 8 Journal of Sensors…”

“…Since these techniques do not require the use of pulses, a typical OFDR offers spatially resolved measurements with high probing energy suitable for measurements in the presence of noise [51,52]. Note also that there have recently been time-domain techniques which seek to address this long-standing issue of spatially resolved measurements, by decoupling the spatial resolution from the pulse width and demonstrating reduced measurement resolution down to few centimeters, albeit at a lower performance than frequency domain ones, as discussed in Section 5 [34].…”

Recent Progress in the Performance Enhancement of Phase-Sensitive OTDR Vibration Sensing System

“…A common approach to this limitation is the pulse coding method (described in section3) that improves the SNR through the energy sent into the FUT while keeping the SR unchanged. Recently, some techniques involving mainly the linear frequency modulation (LFM) pulse-compression and the chirp pulse amplification (CPA) emerged to break totally this dilemma in the Φ-OTDR system and enabled to improve significantly the SR [36][37][38][39][40]. The LFM pulse-compression inspired from the radar communication, is utilized here in a coherent detection based -OTDR system.…”