Abstract

A sensor architecture based on resonant evanescent coupling between a side polished single-mode (cut-off 1200 nm) fibre and a high index overlay waveguide is reported. A polarisation dependent channel dropping filter with an inverse response of a Fabry-Perot is exhibited by the structure. It is found that the resonance position (with respect to wavelength) is dependent on the refractive index of the superstate. This effect is utilised to demonstrate highly sensitive refractometry in an pseudo-continuous all fibre form. The device is constructed by spin coating a thin film (approximately 2 μm) of polymer (refractive index 1.6) onto a polished fibre half coupler, and curing this to form an asymmetric directional coupler. A thin protective coating of dielectric is then deposited on top of the polymeric waveguide. Various index matching oils are then placed on top of the structure (Fig. 1) and the effect on resonant wavelength position noted.

© 1994 IEEE