Sub-metre spatial resolution temperature compensated distributed strain sensor

We propose and demonstrate a scheme which utilizes the temperature dependence of spontaneous Raman scattering to provide temperature compensation for a sub-metre spatial resolution Brillouin frequency based strain sensor. Temperature compensated strain sensor measurements have been demonstrated with a strain resolution of 94µ.ε and a spatial resolution of 10cms. This paper describes the combination of Brillouin frequency based BOCDA technique [1] with an independent measurement of temperature, based on the determination of the intensity of the anti-Stokes Raman scattering (R-OTDR) with very much higher spatial resolution than previously reported [2], in order to produce a fully temperature compensated strain sensor with high spatial resolution

1.65µm long range distributed testing of optical fibres using a compact Q-switched fibre laser

A simple Q-switched Erbium-doped fibre laser operating at 1.5µm forms the basis of a high peak power pulsed source at 1.65µm. Applications include monitoring of active telecommunication links, loss measurement at 1.65µm and distributed temperature sensing

Distributed optical fibre sensing at 1.65µm using a Q-switched fibre laser

It is becoming increasingly vital to monitor telecommunication links during operation and installation process. By using a high peak power source and the optical time domain reflectometry (OTDR) technique operating at the wavelength region of 1.6µm, it is possible to monitor conventional C-band Erbium-doped fibre amplifier (EDFA) systems whilst transmitting data, and to characterise losses at the higher wavelengths of extended bandwidth systems designed around the L-band EDFA systems. We describe a compact design based on Raman shifting the output of an Erbium-doped Q-switched fibre laser operating at 1.5µm for obtaining a pulsed source at 1.6µm. This source was used for an OTDR measurement and also as a source for a 1.65µm Raman-based distributed temperature sensor, in contrast to distributed temperature sensors normally operating at 1.5µm. OTDR measurements at 1.65µm provide more accurate determination of macro and micro-bend losses than at 1.5µm as such losses increase with wavelength. The temperature measurement extracted from the anti-Stokes Raman signal at 1.5µm was made over a sensing range of 10.1km, with a spatial resolution of 10m and temperature resolution of 4°C

A novel method of increasing the range of 1.65µm OTDR using a Q-switched erbium fibre laser

This paper demonstrates a novel method of increasing the range of a 1.65µm optical time domain reflectometer system (OTDR). OTDR measurements at 1.65µm are more sensitive to fibre macro and micro bending losses than those produced at wavelengths 1.3 and 1.55µm. This enables problems to be identified in their early stages reducing the risk of total system failure. However, the dynamic range of current 1.65µm OTDR systems

Self-starting passive mode-locked fibre ring laser exploiting non-linear polarisation switching

Nonlinear birefringence effects in an all-fibre ring laser cavity have been exploited to produce self-starting passive mode-locking with pulse durations lying in the nanosecond region

Double-pass configured fibre Mach-Zehnder interferometric optical filter for distributed fibre sensing

A double-pass configured all-fibre Mach-Zehnder interferometric optical filter has been developed and used in a distributed fibre-optic sensor for separation of Rayleigh and Brillouin signals. Its superior performance over a single-pass all-fibre Mach-Zehnder interferometer is highlighted by its 15dB improved rejection of the Rayleigh signal and comparable throughput

Characterisation of strain dependence of the Landau-Placzek ratio for distributed sensing

The authors report on the strain dependence of the Landau-Placzek ratio (LPR). This, together with the known temperature dependence of the LPR and the Brillouin frequency dependence on strain and temperature, may be used to form the basis of a combined distributed strain and temperature sensor

100km distributed temperature sensor based on coherent detection of spontaneous Brillouin back-scatter

We report the longest distributed temperature sensor based on microwave heterodyne detection of the frequency of the anti-Stokes Brillouin signal. At a sensing range of 100km, the temperature accuracy was 8degC, with a spatial resolution of 50m

High spatial resolution microwave detection system for long range Brillouin-based distributed sensors

We present a microwave detection system for long range Brillouin-based sensing with a potential spatial resolution of 60cm. It was demonstrated over 30km, with temperature accuracy of 1.6C, and spatial resolution of 2m