Design of compact and efficient polarization-insensitive taper coupler for SiGe photonic integration

We have proposed a polarization-insensitive laterally tapered coupler for the integration of the active Ge/SiGe multi-quantum-well device with a passive SiGe waveguide. A 45-μm-long taper is designed to achieve more than 90% coupling efficiency for both TE- and TM-polarized modes. The mode interference is utilized to obtain a compact taper coupler with high coupling efficiency. Fabrication tolerances are analyzed in terms of taper width, thickness, material refractive and operation wavelength. The results indicate that a width variation of ± 200 nm and a thickness variation of ± 100 nm are allowed. The designed taper coupler can provide efficient coupling under normal operating conditions in the wavelength range of 1460-1625nm.