Abstract: A helium cadmium laser generates an output beam of radiation which is coupled through a spatial filter and beam expander to a beam splitter which in turn provides two enlarged beams of coherent radiation of approximately equal power. Two highly reflective mirrors are used to direct the two beams such that the two beams interfere and create the usual interference pattern in a positive photoresist layer covering an optical substrate. A thin sheet of high index glass is held by two blocks of quartz in a position adjacent to the photoresist layer and oriented such that a part of each beam of coherent radiation is caused to pass through the high index glass before interfering with the other beam on the photoresist layer. As a result, a grating having a quarter wavelength step or discontinuity in the middle of the grating is fabricated in the photoresist. The photoresist pattern is then transferred to the optical waveguide by ion-beam milling.