Silica based optical waveguide coupler with asymmetric structure in single-mode to multi-mode coupling regime

The coupling characteristics of a silica based waveguide type directional coupler with asymmetrical structure are studied by the beam propagation method. The coupling behavior of optical power from a single mode 3 mm guide into a multi-mode guide in silica are clearly demonstrated. The coupling into a second guide of <27 /spl mu/m causes only a small loss, but the coupling into a 54 /spl mu/m guide involves a significant loss.