Effect of buffer layer index on short range surface plasmon polariton based TE pass polarizer

Abstract

We investigate theoretically the dependence of the extinction ratio, metal layer thickness and buffer thickness of a short length plasmonic polarizer on the buffer layer index. The polarizer section consists of a thin metal layer above the single mode dielectric waveguide separated by a low index dielectric buffer layer. Strong coupling between the surface plasmon polariton (SPP) mode and the guided mode takes place when their phase constants are matched. The SPP mode being of TM type, interacts with the guided TM mode and is completely absorbed by metal film due to resonant coupling between the two modes. The TE guided mode does not couple to the SPP mode and is passed un-attenuated through the polarizer. The buffer layer thickness can be optimized to maximize the TM mode attenuation and reduce the TE losses, which provides a large extinction ratio. Since the polarizer is based on the interference of the SPP mode and the waveguide mode, a periodic coupling of the field takes place between these two modes. It is shown that for properly optimized layer thicknesses, an extinction ratio exceeding 200 dB can be achieved for various buffer layer indices. Effect of buffer layer index on the polarizer length is also presented.