Low radiation loss branching/combining of optical circuits using high-silica channel waveguides

A new branching/combining optical circuit structure using high-silica channel waveguides was proposed to reduce radiation loss where branching occurs. In this structure, an additional low-refractive-index layer was formed at the junction surface between the main and branching channels. The loss in a conventional circuit could be successfully reduced by over 0.4 dB in the through channel and 0.1 dB in the reflecting channel. The allowable conditions for a low-refractive-index layer were obtained through experimental and theoretical studies.