Offset prism for optical waveguide coupling.

High refractive index prisms have been used to couple optical beams into the thin film waveguides. To scan through various propagating modes normally requires rotating and repositioning of the prism-waveguide assembly. We have found that the required adjustment of the prism-position can be eliminated during the scanning of the various modes if the prism is properly offset with respect to the rotational axis. An analysis and a computer program are given for the calculation of this prism offset position on the basis of minimum deviation within the specified limits of the prism rotational angle.