Excitation of Waveguides for Integrated Optics with Laser Beams

Abstract

We discuss in this paper the excitation of dielectric waveguides used for integrated optical circuitry. Thin optical films are usually excited by means of coupling prisms using frustrated total internal reflection. We propose instead excitation of thin-film waveguides directly by gaussian laser beams. Harmful effects of imperfect substrate edges can be avoided by letting the dielectric waveguide end inside of the substrate. The exciting laser beam is directed towards the end of the guide from the inside of the substrate material. The analysis is based on neglecting reflection at the end of the thin-film waveguide and on assuming that the thin film is infinitely extended in one dimension. The maximum excitation efficiency predicted with this model is 97 percent. It is expected that the excitation efficiency of more realistic guides for integrated optics can be as high as 90 percent.