An optical-fibre data-telemetry system for use in remote or hazardous locations

This paper describes the evolution of a form of optical-fibre telemetry highway that is believed to be unique. The system is based upon the modulation of the phase of coherent light within an optical fibre by passing ultrasound across the fibre. This phase modulation is cofiverted to amplitude modulation by the partial detection of the light received at the output. The fibre used is commercially available multimode fibre, and by using a number of ultrasonic transducers, each modulated at different frequencies, a multichannel data collection system can be implemented. The system is ideally suited to applications involving telemetry from remote or hazardous environments, since the power consumption of these simple clip-on modulator structures, including all the associated electronics, may be below 1 m W. Transmission distances of up to several kilometres may be realised using the same basic system format.