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 I 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.