Abstract

Ti:LiNbO₃ directional coupler switches have consistently shown an extinction ratio in the −15 to −30-dB range but only rarely <−30 dB. This is illustrated by a set of 16 nominally identical directional coupler switches recently fabricated on a single substrate.¹ An approximately random distribution of extinction ratios was measured ranging from −11.6 to <−35 dB. In addition, their response curves show nonideal behavior, such as unequal side lobes and nonzero voltage values for the maxima of the crossed state. We hypothesize and demonstrate that there is a common explanation for all these nonideal characteristics: random fluctuations in the effective index along the length of the diffused waveguide. Local random variations in the Ti concentration of the diffused waveguide could produce random fluctuations in their effective index.

© 1986 Optical Society of America