Multiple reflections of light in the prism coupler

The problem of multiple reflections of light in the prism coupler at waveguide spectroscopy of thin films is investigated. With the use of a 2D ray model, algorithms for computing the trajectory of a light beam in the triangular prism coupler and the prism reflectivity are developed. Criteria for optimal choice of the prism angles and rotation axis are proposed and illustrated numerically. The criteria imply stabilization of the light insertion point into the layered medium under investigation and minimization of influence of high-order rays to full reflectivity of the prism coupler. Examples of the waveguide spectroscopy inverse problem solution for a bi-layer structure of silicon oxinitride on a silicon substrate are presented.