Si/Si1-xGex waveguide components for WDM demultiplexing

We report on the development of building blocks of Si/Si1-xGex/Si planar waveguide WDM circuits - an optical splitter/combiner and the first demonstration of a Si/ Si1-xGex/Si arrayed waveguide grating (AWG) demultiplexer. The prototype AWG is a four channel device with a 400 GHz (Delta h = 2.3 nm) channel spacing, and operates in the 1300 nm wavelength range. Strain and refractive index in the Si1-xGex epilayers play a critical role in device performance. The AWG waveguide heterostructure has total Si1-xGex layer thickness well beyond the measured critical thickness for lattice relaxation, but is stabilized against dislocation formation by the insertion of Si capping layers during growth. Single mode curved ridge waveguides formed from this material show no obvious bend losses for radii of curvature as small as 4 mm.