Plasmon Waveguides on Silver Nanoplates

Current interest in photonic nanodevices motivates search for efficient transport of energy in plasmon waveguides. Chains of nanoelements made of noble metals guide light in channels of below-the-diffraction-limit size due to surface plasmon coupling. We calculate attenuation factors in a chain of parallel pairs of nanoplates for visible and near infrared range of wavelengths. Nanoplates are embedded in a medium with refractive index reaching n = 1.5. Advantages of the proposed waveguide are its small size and tunability by adjustment of geometrical parameters. However, the waveguide highly attenuates signals due to radiation into the far field and internal damping. For 595 nm wavelength, the energy transmission of 2 micrometers long chain of parallel nanoplates reaches 39%.We use the finite difference time domain (FDTD) method to investigate properties of a waveguide illuminated with polarized light. The permittivity of silver is described by Drude model. The simulation area is 780times1400times2225 nm discretized with Deltar = 5 nm step surrounded by 10 layers of UPML absorbing conditions at all boundaries. Simulation time step is Deltat = 8.34middot10^-18 s. The source has a Gaussian field distribution with half width 372 nm. The source is introduced with total/scattered field split of simulation volume. Theoretically, for the wavelength of 514.5 nm the intensity of surface plasmons propagating on an infinite smooth surface decreases to 37% of its initial value after 22 mum. Our result confirms the prediction that transmission in a waveguide made of discrete plates is considerably smaller. A sample result where z-axis component of the Poynting vector calculated at a cross-section plane of the waveguide at half height is depicted. The output beam has a distinct central maximum with small side lobes in the x-axis direction