Refractive index sensor with a guided-mode resonant grating filter

This paper describes a novel refractive index sensor with a guided-mode resonant grating (GMRG) filter. The GMRG filter is a narrowband wavelength reflection filter. The incident light is reflected at a resonance condition of incident angle and wavelength. When the grating filter is covered by a liquid to be tested, the resonant condition depends upon its refractive index. The refractive index of the liquid can be determined from the resonance angle for a known wavelength. Since a full-half width of incident angle for the resonance is very narrow (less than 0.1 degree(s)), a high resolution is expected. We designed the GMRG filters for the refractive index sensor. And the resonance angle of incidence was investigated experimentally for the mixture of water and ethyl alcohol.