Application of synthesized coherence function to distributed optical sensing

We have proposed and developed a technique to synthesize an optical coherence function into arbitrary shapes. By using this technique, which we call the `synthesis of an optical coherence function', various distributed optical sensing schemes have been developed, which have no mechanical moving parts nor data calculation. In these schemes, we do not use a pulsed lightwave but instead use a continuous wave, whose correlation is controlled by frequency modulation or phase modulation. We have proposed a reflectometry system to diagnose fibre optic subscriber networks. Fibre optic distributed force sensing systems have also been developed, which are applicable to smart structures and security systems. In a similar way, we have proposed a system to measure strain distribution along an optical fibre through the Brillouin scattering caused in the fibre. Spatial resolution of just 1 cm has been demonstrated by this system, which is 100 times higher than the practical limitation of conventional pulsed-lightwave techniques. Such a high spatial resolution is suitable for smart material applications. Two- or three-dimensional distributed sensing has also been developed by this technique. An optical tomography system has been proposed, which has fewer mechanical moving parts. A system for surface shape measurement for a multi-layered object has also been developed.

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