SPUTTER-DEPOSITED YTTRIA-ALUMINA THIN-FILMS FOR OPTICAL WAVE-GUIDING

Yttria-alumina: planar waveguides were fabricated by reactive codeposi tion from yttrium and aluminum targets. These waveguides were verified to be amorphous with yttria contents as high as 23.4% by x-ray diffra ction, both conventional and glancing angle, and by transmission elect ron microscopy. Above 41.8% yttria, the waveguides had mixed crystalli nity and contained microcrystallites (0.5-0.9 nm) dispersed throughout an amorphous matrix. These microstructures appeared to be unaffected by the oxygen content in the sputtering gas, The index of refraction w as found to increase strongly as a function of yttria content, but rem ain constant with oxygen content. Although the waveguides had wide tra nsmission windows, the infrared edges were observed to shift with comp osition toward the values of the end member edges of 11 (alumina) to g reater than or equal to 15 mu m (yttria). In general, the waveguides h ad optical losses of 10-20 dB/cm. However, films with compositions rou ghly equivalent to that of yttrium iron garnet had lower losses (1-5 d B/cm). These losses are the lowest reported to date for yttria-alumina waveguides, and combined with the extended infrared transparencies, m ake these films very promising hosts for waveguide amplifiers. (C) 199 8 American Institute of Physics.