The investigation of a refractometer principle based on index-sensitive resonant wavelength shifts in a fibre-to-planar-waveguide coupler is reported. Device fabrication, involving spin deposition and curing of a polymer onto a side-polished single-mode optical fibre, is relatively straightforward. Three devices of differing polymer waveguide thickness were fabricated and tested, and in all cases there was excellent agreement between experiment and a simple model of operation. The results demonstrated that index resolution down to about 10-5 is realistic. In addition, an active transducer, based on electro-optic polymers for closed-loop operation, was proposed and investigated.
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Johnstone et al. (1994) studied this question.