EXTRAORDINARY VERSUS ORDINARY REFRACTIVE-INDEX CHANGE IN PLANAR LINBO3-TI WAVE-GUIDES

Various planar waveguides are fabricated by indiffusion of one or two titanium layers into y-cut LiNbO//3 substrates. The effective indices of guided TE- and TM-modes are measured for red, green, and blue light. The refractive index profiles are reconstructed by a new reliable inverse WKB procedure. Despite widely differing profiles there is, for each wavelength, a one to one relationship between the changes DELTA n//o of the ordinary and DELTA n//e of the extraordinary refractive index. For low and for high refractive index changes DELTA n//e and the DELTA n//o grow proportionally, but their ratios differ appreciably. The results support recent findings that the LiNbO//3:Ti system exists in two distinct phases.