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Tutorial 2a

Geoffrey Cranch, Naval Research Laboratory, USA

Tutorial Description:

Undersea acoustic sensors for surveillance were one of the first successful applications of fiber optic sensor technology, whilst also being one of the most technologically advanced. They promised a technology with highly efficient multiplexing potential capable of realizing very large sensor arrays. In contrast to existing systems based on piezoceramic technology, these systems are lightweight, immune to electro-magnetic interference and generally electrically passive, which for marine systems leads to dramatically improved reliability and reduced through life cost. Since these early demonstrations the technology has moved beyond military applications to civil applications in the oil and gas industry and for both marine and terrestrial security. For example, in the oil and gas industry permanently installed acoustic and seismic sensor arrays have been developed for continuous well monitoring. These systems now form some of the largest fiber optic sensor installations in current use.

This tutorial will begin by outlining the fundamentals of fiber optic interferometry, which forms the basis of many of these systems, explain the operating principle of undersea hydrophones and inertial sensors, describe the underlying components and explain the basic design of typical systems as well as describing the inherent trade-offs necessary in a given system design. Data taken from real systems will be presented and explained in the context of sensor system performance.

Another area of major growth has been in distributed fiber optic sensing, which find applications in many of the same areas. This technology exploits the inherent capability of fiber optic sensors to provide continuous monitoring of temperature, pressure or strain over very long lengths of fiber. Typical applications may be border security, pipeline monitoring and down hole well monitoring. The fundamentals of various distributed sensing approaches based on linear and nonlinear scattering will be described in this tutorial along with an explanation of their relative merits.

Finally, a look towards future developments in these technologies will be given. In particular, the presenter will describe his own area of research in fiber laser sensors and their potential for transducer miniaturization and new sensing concepts. As well as providing a technological overview this tutorial will also provide a case study of the technology development process.


Geoffrey Cranch
Research Physicist
Optical Sciences Division
Naval Research Laboratory

Geoffrey Cranch received the BSc with Honors degree from the University of Bath in Physics in 1995 and PhD in Applied Physics from Heriot-Watt University in 2001 in the field of fiber optic sensors and fiber lasers. He has over 13 years experience in optics and fiber optic systems through positions held at GEC-Marconi Naval Systems (now Thales), the Defence Evaluation and Research Agency, UK and since 2000 at the Naval Research Laboratory, Washington DC. He has published over 40 papers in international conferences and journals, he holds four patents and has written two book chapters on the subjects of fiber optic hydrophones and fiber Bragg gratings devices.

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