Strain-induced birefringence in Si1−xGex optical waveguides

For the design of Si1−xGex optical waveguide devices, one of the most important material parameters is the refractive index difference, δn, between the alloy layer and the silicon substrate. We have measured δn for pseudomorphic waveguide layers with germanium fractions between 1% and 9% by fitting measured mode profiles to theoretical mode shapes for a wavelength of 1.3 μm. For transverse electric modes, the measured δn varied with composition …