High performance optical sensing of alcohol by guided wave mode geometry composed of two polymer layers

A new method to improve both sensitivity and response time in optical sensing of alcohol based on chemical reactions is proposed by using guided wave mode (GWM) geometry composed of low refractive index polymer and dye-doped polymer layers. A lactone dye, Rhodamine B base, was selected as a key material which shows remarkable and reversible changes in absorption and fluorescence spectra in nonpolar and polar microenvironments. The effect of water on alcohol sensing was successfully excluded by using an appropriate polymer matrix having very small equilibrium water content. Both sensitivity and response were improved by using very thin sensor film and confined light in it with the GWM geometry. Repeated and fast responsive alcohol sensing was achieved at a ppm level.