Plessey Overseas Limited

David J Pratt

John P Dakin

Christopher A Wade

An optical time domain reflectometry system in which laser level reference signals are derived from the respective laser outputs from the laser sources and fed into a single receiver provided for receiving the back-scattered or returned light along an optical fibre. The receiver is thus continuously calibrated in accordance with the relative intensities of the optical signals at different frequencies being launched into the optical fibre so that the receiver provides an accurate measurement of temperature or other parameter being measured by the system.

Multi-wavelength time domain reflectometer

A two-wavelength referencing optical sensing arrangement comprises two laser sources for producing simultaneous optical pulse signals of two different wavelengths for transmission over a plurality of discrete optical fibre paths to the sensors terminating such paths. Time-displaced return signals of different wavelengths received over the optical paths from sensors are fed into a single receiver which uses the intensity of signals of one wavelength in order to compensate for unknown losses in the system when indicating measurement of conditions sensed at the locations of the optical sensors.

Optical sensing arrangements with wavelength and time-displacement

An optical sensing arrangement in which optical signals are transmitted along a plurality of discrete optical fibre paths of different lengths which are terminated in respective sensors adapted for sensing temperature, pressure or any other condition to be sensed at appropriate locations and in which optical signals reflected or otherwise caused to be transmitted back along the optical fibres of different lengths in response to the transmission of the optical signals along said fibres and in accordance with variations in conditions at the aforesaid locations are detected by optical time domain or frequency domain reflectometer means for determining the conditions at the sensor locations.

Optical sensing arrangements

An optical transmission system comprises a plurality of transducers located at intervals along a continuous optical fibre data transmission path. Data signals are derived from respective transmitters associated with the transducers and are applied to the transducers to produce mechanical stressing or deformation of the data transmission path optical fibre for imparting corresponding modulation of the polarization state of light being propagated along the optical fibre. A receiver connected to the far end of the transmission path includes means for determining the exact state of polarization of the received light and for extracting the modulation information and hence transmitted data therefrom.

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Suffolk, United Kingdom

David J Pratt