A phase-sensitive optical time-domain reflectometer with dual-pulse phase modulated probe signal

Abstract

A novel configuration of a phase-sensitive optical time-domain reflectometer (OTDR) utilizing dual-pulse phase modulations of the probe signal is presented and experimentally demonstrated. The proposed modulation method enables one to perform the demodulation and reconstruction of an external perturbation signal which impacts the fiber using the phase diversity technique. The proposed phase-sensitive OTDR has some advantages in comparison with conventional solutions, which are discussed. The feasibility of a double pulse OTDR with phase modulation is demonstrated and theoretically proved.

Contributed Review: Distributed optical fibre dynamic strain sensing

“…This concept was later adopted and modified by Lewis and Russell 16,17 DVS capable of measuring the vibrations along the sensing fibre. In 2014, Alekseev et al 18 experimentally demonstrated this concept by controlling the relative phase of a dualpulse probe signal. The experimental results showed that this sensing technique is capable of measuring 230 Hz periodic perturbations along a 2 km long sensing fibre with a spatial resolution of 5 m and a phase sensitivity of 0.01 rad.…”

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

“…However, a more precise quantitative measurement of an external disturbance requires additional information on the change in signal behavior induced by strain or temperature changes. To this end, techniques which are based on frequency shift measurements [36][37][38][39] and others using direct demodulation of the phase change [35,[40][41][42][43][44] have been proposed. The frequency shift method for external impact extraction using ϕ-OTDR is based on the observation that the frequency of the probing pulses can be matched with a corresponding change in temperature or strain with some proportionality constant.…”

“…A ϕ-OTDR sensor, which emulates the 3 × 3 coupler used in [40,41] and resolves the receiver multiplicity and synchronization issues by making alternate use of a single photodiode and addressing drawbacks of interferometric stability with the use of a double-pulse scheme, has also been proposed [42]. The modulation of the pulses and the operating principle of the configuration is depicted in Figure 13.…”

“…Phase unwrapping, especially in the presence of fast and abrupt changes of phase, is a computationally costly process, and in the case of distributed sensing, it involves multidimensional computations the same as the ones necessary in image processing [46][47][48]. Note also that the dynamic range Figure 13: Operating principle of a dual-pulse ϕ-OTDR scheme: (a) phase modulation in the probing pulses and (b) phase change at a location with external impact traversed by a pulse pair [42].…”

High Frequency Distributed Optical Fibre Dynamic Strain Sensing: A Review

“…In 2014, Alekseev et al (Alekseev 2014) experimentally demonstrated a modified version of this concept by using a semiconductor optical amplifier to generate 100ns pulses while controlling the relative phase of pulse pair using an electro-optic modulator (EOM).…”