Long-range surface plasmon polariton waveguides with TE and TM guiding

Abstract

Long-range surface plasmon polariton (LRSPP) waveguides supporting both TE and TM polarized light are demonstrated experimentally. The waveguides consist of metallic nanowires with approximately 150-nm square cross sections embedded in a polymer matrix. The wavelength dependence of propagation loss and coupling loss to single mode fibers is presented. At wavelengths around 1550 nm, the nanowires exhibit a propagation loss around 4.0 dB/cm for the TM mode and 4.5 dB/cm for the TE mode. The mode field is close to symmetric and suitable for coupling to and from optical fibers. A small increase in the waveguide width, resulting in a deviation from a square cross section, is sufficient to extinguish the TE mode, making asymmetric nanowire waveguides similar to the more conventional LRSPP thin stripe waveguides. Finally, we demonstrate a compact thermo-optical variable optical attenuator based on a LRSPP nanowire waveguide.