Response of thin film Al₂O₃ optical waveguide to moisture in paper

Abstract

The response to paper moisture of thin film Al₂O₃ optical waveguide has been studied. The changes in the transmission of thin film optical waveguide due to changes in relative humidity of paper used as in touch overlay have been reported in this paper. The output decreases due to the overlay of paper. The transmission of the waveguide depends on the moisture content, texture and colour of the paper. Higher moisture content in paper tends to saturate the waveguide output. The sensitivity to moisture changes and type of paper is more for lower moisture content. Hysteresis is observed due to all the papers studied. The larger sensitivity in the lower moisture range may provide a means for detecting and controlling moisture in paper for packing, printing and other applications, as this overlay method requires only a small piece of paper.