Abstract

We proposed a dual-tapered waveguide type spot-size transformer (SST),¹ and demonstrated a low-loss and wide range transformation ration (5 and 1/5). However, this structure requires precise control of refractive index because the index difference between the core and the cladding must be small to satisfy the single-mode condition in the spot-enlarged waveguide. It is difficult to control the refractive index precisely by a sputtering technique and other thin-film deposition techniques.

© 1991 Optical Society of America