Highly compact optical waveguides with a novel pedestal geometry

A structure with a large refractive index ratio between waveguide and cladding materials can be fabricated with low scattering losses by using Ge on GaAs waveguides at 10-μm wavelengths. We demonstrate two types of ultra-high confinement (UHC) dielectric waveguides using separate geometries: A ridge and a novel pedestal. Computer simulations using a time-domain finite element method and microwave-scale experiments are performed on both waveguide types. We show a waveguide thickness of 0.18 of the free-space wavelength or greater guide well-confined single-mode light for both geometries. Numerical and experimental values of the effective index agree to better than 0.5%.