A thin-film prism as a beam separator for multimode guided waves in integrated optics

We discuss a new application of a thin-film prism as a beam separator for multimode guided waves in integrated optics. For each mode of propagation, the angle of deflection by the thin-film prism is different and each deflected beam can be processed subsequently. Deflection angles for different modes can be predicted by using the concept of effective index of refraction. The thickness and index of refraction of the guiding film are determined simultaneously by measuring the coupling angles of the laser beam and a simple graphical method. Calculated and observed angles of deflection are in good agreement. The thin-film prism is made by using preferential etching technique in order to obtain linear, well defined, tapered edges. Furthermore, silicon is used as the base material for possible future integration of optical and electronic components.