Absorption from Thin-Film Waveguides*

The mechanism of optical absorption from thin-film waveguides is investigated analytically for three cases: ideal waveguides, scattering in waveguides, and surface phenomena associated with molecular adsorption. Preliminary experimental results with methylene-blue dye placed on a waveguide surface show absorption magnitudes approximately ten times greater than is predicted for an ideal waveguide. Enhanced absorption based on modal variation is shown to be attributed to both scattering and molecular-adsorption effects.