Polarization dependence in waveguide-coupled micro-resonators.

One dominant issue for micro-resonator filters has been polarization sensitivity due to the form asymmetry in nanophotonic waveguides. Differences in the filter's transmission intensity for TE and TM polarizations is attributed to the polarization dependent coupling. Complete power transfer in ultra-small directional couplers is demonstrated in agreement with simulations. Polarization dependence is simulated for waveguides of various widths, showing the presence of a critical width at which the propagation constants are equal for TE and TM modes. A design for polarization-independent and single-mode waveguides is discussed, along with implications for the applications of micro-resonators in general.