Low-loss 1×2 multimode interference wavelength demultiplexer in silicon-germanium alloy

A low-loss multimode interference wavelength demultiplexer for 1.3- and 1.55-μm operations based on the silicon-germanium alloy material has been proposed and demonstrated. The device was fabricated by molecular beam epitaxy followed by lithography and plasma etching. The input/output facets were polished mechanically. The measured insertion losses are 4.29 and 4.28 dB and the extinction ratios are 25 and 22 dB at 1.3 and 1.55 μm, respectively.