Planar waveguide echelle gratings: an embeddable diffractive element for photonic integrated circuits

We have demonstrated a 40-channel echelle grating demultiplexer with a 100 GHz channel spacing, using silica-on-silicon planar waveguides. We show the output spectrum of several channels, measured using a tunable laser source. The measured cross-talk is better than -35 dB, the insertion loss is approximately 5 dB including fibre-to-waveguide coupling, and the polarization birefringence has been eliminated using a modified compensator design which eliminates losses due to mode mismatch. Planar waveguide EG devices are also easily scalable to higher channel counts and the device described here is currently being adapted to a 256-channel demultiplexer chip.