Integrated polarization insensitive 1.3/1.55 micrometer duplexer on silica-based technology

This paper deals with the realization of a 1.3/1.55 micrometers duplexer integrated on a silica on silicon substrate. The design consists of two cascaded directional couplers in order to enhance the rejection bandwidth. Fabrication is based on plasma enhanced chemical vapor deposition and reactive ionic etching of silica films. The channel guide structure has been optimized to comply with the small distance between guides along the coupler, that would still ensure low loss fiber coupling. The results show an excellent spectral response: insertion loss lower than 3 dB on a 150 nm bandwidth at both wavelengths, crosstalk as low as 20 dB on a 100 nm bandwidth. Moreover, quite a total independence on polarization and temperature has been checked, for the required 1.3/1.55 micrometers separation.