Demultiplexer with 120 channels and 0.29-nm channel spacing

A 120-channel WDM demultiplexer was fabricated by etching a concave grating into a SiO/sub 2/-SiON-SiO/sub 2/-Si slab waveguide. The grooves of the grating reflected light by two instances of total internal reflection. The device was suitable for demultiplexing wavelength channels in the 1530-1565-nm range with a 0.29-nm (36 GHz) channel spacing. Each channel had a spectral width (full width at half maximum) of about 0.18 nm. The fiber-to-fiber insertion loss was between -20 dB and -30 dB for most channels. The loss was predominantly due to waveguide absorption and increased dramatically for wavelengths below 1539 nm.