Theoretical investigation of surface plasmonic polariton-based electro-optical modulator with low polarization dependence

Plasmonic modulators essentially support only transverse magnetic mode. A plasmonic modulator 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 the vertical and horizontal directions exist in the correspondingly oriented hybrid plasmonic waveguide. The light modulation is investigated by tuning the carrier density of the accumulated layer where occurs at the dielectric-ITO interfaces. In an optimized structure, a ΔI_ER (a difference between the extinction ratios of two polarization modes) under 0.01 dB/μm is demonstrated at ITO "ENZ"-state by 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 74% is obtained for both polarizations. The proposed plasmonic combined modulator has a potential application in guiding and processing of light from a fiber with a random polarization state.