Passive integrated-optical waveguide structures by Ge-diffusion in silicon

The realization of low loss optical channel waveguides and passive waveguide structures by a germanium indiffusion process into silicon will be discussed. Employing relatively simple technological processing like standard lithography, e-beam evaporation and diffusion, single-mode waveguides could be produced exhibiting polarization independent losses of as low as 0.3 dB/cm at wavelengths of λ=1.3 μm and λ=1.55 μm. S-bends fabricated with the same technology offered an excess loss of 1 dB at a radius of around 5 mm without any optimization. For a Y-junction designed with S-bends the maximum opening angle was determined to be 1.8° if an excess loss of 1 dB is allowed. The examination of directional couplers with various coupling lengths and distances revealed an excellent agreement between measurement and theory