Sputtered Glass Waveguide for Integrated Optical Circuits

Abstract

A series of papers which appeared in the September 1969 issue of the Bell System Technical Journal treated the theory of dielectric wave guides and stressed the potential use of such media for optical communi cation circuits.'"* Here we report on the realization of low-loss, thin glass films which can be used for circuit fabrication. Methods of pre paring planar films and waveguides having rectangular cross section are described along with the techniques used in evaluating their optical characteristics.The films we used for waveguide fabrication have been prepared by RF Sputtering of suitable glasses. The sputtering system used was oildiffusion pumped and had five-inch diameter electrodes. Oxygen was used as the sputtering gas. The best films obtained to date were made by sputtering Coming 7059 glass. For convenience, in the early stages of this work, laboratory sUdes have been used as substrates. Necessary steps were taken to ensure that the substrates were clean.The index of refraction of the films Λvas measured to be 1.62 by determining Brewster's Angle for the films as described by Abeles.* From the color of the film and by interferometer methods the film thickness was found to be about 0.3 μm.The transmission loss of the films was measured by two methods. Both use prisms to launch a Ught beam into the film.*'^ In method 1 it is assumed that the scattering centers in the films are uniformly distrib uted. A fiber optic probe is then used to measure the intensity of the Ught scattered at right angles to the film. In method 2, the intensity of the output beam is measured as a function of launcher position along the film. Method 2 appears least accurate due to variations in launching efiiciency as a function of prism movement. Method 1 works well to losses of the order of 1 db per cm. Below this level, the variabiUty in the strength of the scattering centers makes reUable measurements difficult. An increase in film length would partiaUy overcome the difficulty of measuring low level scattering from random centers. 3445

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