Polarization-insensitive subwavelength sharp bends in asymmetric metal/multi-insulator configuration

A new silicon-based sharp waveguide bend in asymmetric metal/multi- insulator configuration is described. TE and TM modes are calculated rigorously electromagnetically from which the general design rules are derived. Numerical simulations show that the respective insertion losses of < 0.085 dB and < 0.229 dB for TE and TM modes can be achieved by introducing a low-index layer between the metal and high-index core. The bending length is determined by the TE mode and has much smaller impacts on the TM that exhibits no resonance-like behavior as does the TE. The combined TE modal and radiation power in the air region is shown to couple back to the Si core through an asymmetric output taper, yielding a high transmission efficiency. Structure-enabled successive photonic-plamsonic mode conversions are shown to increase the TM mode confinement in the high-index core while the plasmonic mode carries up to 42.6% of the input power along the bending section.