Chemical detector employing surface plasmon resonance excited using an

Abstract

A highly sensitive surface plasmon waveguide sensor monitors the refractive index and thickness of thin adsorbed films. The sensor includes an optical waveguide formed by ion-exchange in a glass substrate, by selective densification of substrate material or by the incorporation of high refractive index materials during deposition of a dielectric layer. Two dielectric thin films are deposited on top of the waveguide. The layer closest to the waveguide has a lower refractive index than the guiding layer to form a buffer layer. The second dielectric layer, or tuning layer, has a higher refractive index. The tuning and buffer layers allow optimization of the resonance wavelength, full-width half maximum of the resonance wavelength range and amplitude of the resonance. The tuning layer is coated with a thin metallic layer, to effect surface plasmon resonance, such as gold, silver, aluminum or one or more semiconducting materials. Alternatively the optical waveguide is coated with the buffer layer and the thin metal layer. The tuning layer and a second buffer layer are deposited on top of the metallic layer. Light is introduced to the waveguide and interaction between the light and the thin metal layer results in attenuation of the TM polarization. The ratio of the TM and TE polarization intensities is monitored by a polarization beam splitter. The relatively unchanged TE polarization intensity serves as an integral reference for the sensor. The sensor has numerous applications in the environmental and biomedical fields.