Switching element having an expanding waveguide core

Abstract

A switching element that selectively couples a first optical path to a second optical path through an index-matching fluid includes a tapering region along each of the optical paths to achieve high coupling efficiency at both ends of substrate waveguides that form portions of the two optical paths. The two substrate waveguides are separated by a gap that is filled with the index-matching fluid in order to optically couple the two waveguides. The ends of the waveguides located at the gap have relatively large cross sectional areas to promote high coupling efficiency across the gap. For example, the cross sectional dimensions may be approximately 16 .mu.m.times.8 .mu.m at the interior ends of the two substrate waveguides. On the other hand, the exterior ends have significantly smaller cross sectional areas in order to promote high coupling efficiency to optical fibers. For example, the cross sectional dimensions of an external end may be 8 .mu.m.times.8 .mu.m. The substrate waveguides are adiabatically tapered in order to inhibit reflection. In another embodiment, the tapering regions of the two optical paths are formed along the optical fibers, rather than along the substrate waveguides.