Stuart Russell

Real-time location of multiple time-varying strain disturbances, acting over a 40-km fiber section, using a novel dual-Sagnac interferometer

Updated results using a novel sensing architecture based on a Sagnac interferometer are presented and, for the first time, real-time separation and positioning of multiple disturbances has been realized. A 40-km long dual-Sagnac sensor was formed by spectral slicing of light from a single, broad-band erbium-doped-fiber super-luminescent source and wavelength division multiplexed (WDM) routing around the loop to form an inherently low loss system. Independent active phase biasing of each Sagnac was employed, allowing the use of a single optical detector. The effects of residual optical cross talk between the two Sagnacs has been accurately modeled, allowing resulting errors to be corrected. The new system has capability for narrow-band fast Fourier transform (FFT) analysis of detected disturbance signals, and hence their separation in the frequency domain. For audio-frequency excitation, an average positional resolution of 100 m over a 40-km length was achieved with a postdetection signal processing bandwidth of 8 Hz.

Location of time-varying strain disturbances over a 40km fibre section using a dual-Sagnac interferometer with a single source and detector

This paper reports on results with a novel Sagnac-loop sensor, using spectral slicing of a broadband Er-doped fibre source and has a 40km long sensor loop. Our new WDM arrangement allows use of a single source and optical receiver, yet has low intrinsic losses. The residual optical crosstalk due to non-ideal WDM components is modelled and the initial position dependent results presented.

Sensor network for structural strain and high hydraulic pressure using optical fiber grating pairs interrogated in the coherence domain

This paper reports on progress with the coherence-domain method for interrogation of Bragg grating pairs, presenting for the first time a simple theoretical analysis of the interrogation procedure and describing the first measurements of useful engineering parameters (strain, pressure) with the system.

Direct monitoring of fiber extension by correlation-based coherent optical time-domain reflectometry

We propose a novel method of strain sensing where the displacement is measured by correlation of the coherent Rayleigh backscatter trace from a reference section of fiber. The potential performance is considered analytically and the theoretical results compared with the results of numerical simulations.

Distributed optical fibre sensing methods for localisation of disturbances and the position of optical fibre cables in the ground

This paper firstly presents a novel optical sensor technology developed to locate, from above ground, the lateral position of a buried dielectrically sheathed optical cable. Then, optical sensor methods for the distributed sensing and longitudinal positioning of time-varying acoustic disturbances are presented. It is hoped to present results of a novel field-trial capable OTDR based system in the verbal presentation.

A novel method for location of buried optical cables, where an incident EM wave modulates the polarization of guided light, using the Faraday effect

This paper presents results and detailed theoretical analysis of a novel method to locate the position of buried optical cables. A travelling EM wave (RF), generated from above ground, modulates the state of polarization of the light propagating in the single-mode fibre to be located. The magnitude and phase of this modulation are detected at the end of the fibre route and the results are relayed to the operator of the locator. By observing the amplitude of this modulation, the lateral position of the buried service can be determined. We have demonstrated an 18 dB signal-to-noise ratio, at a buried depth of 1.5 m, in wet clay soil, using a radiated RF power of 38 W at 144 MHz.