Silicon-on-Insulator Echelle Grating WDM Demultiplexers With Two Stigmatic Points

We present ultracompact integrated optical echelle grating wavelength-division-multiplexing (de)multiplexers for on-chip optical networks, fabricated using high-index-contrast silicon-on-insulator photonic waveguide technology. These devices are based on a design with two stigmatic points, which enables compact geometries with reduced aberrations. In the example presented here, this design allows us to achieve an eight-channel (de)multiplexer with 3.2-nm channel spacing, within an ultracompact footprint of 250 times 200 mum. The channel-to-channel isolation of the devices is 19 dB. The minimum insertion loss, relative to a straight waveguide, is 3 dB with a channel-to-channel variation of 0.5 dB.