Plasmonic waveguides with low polarization dependence.

Plasmonic waveguides essentially support only transverse magnetic modes. A novel plasmonic waveguide consisting of hybrid plasmonic waveguides in both vertical and horizontal directions is proposed to reduce the polarization dependence. In a combined waveguide, surface plasmon polariton (SPP) modes polarized in both vertical and horizontal directions exist in the correspondingly oriented hybrid plasmonic waveguide. In an optimized structure, anticrossing mode coupling is observed between these two SPP modes with a low birefringence by finite-difference time-domain simulation. The energy flux clearly shows the polarization-selective coupling between the polarized guided modes in the feeding silicon waveguide and those in the combined waveguide. Coupling efficiency above 65% is obtained for both polarizations. The proposed plasmonic combined waveguide has a potential application in guiding and processing of light from a fiber with a random polarization state.