Nanodot coupler with a surface plasmon polariton condenser for optical far/near-field conversion

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Abstract
To transmit an optical signal to a nanophotonic device, a nanodot coupler was fabricated from a linear array of closely spaced metallic nanoparticles. To increase the optical far- to near-field conversion efficiency for transmission, a surface plasmon polariton (SPP) condenser was also fabricated from hemispherical metallic nanoparticles so that it worked as a “phased array”. The SPP was focused with a spot size as small as 400 nm at λ = 785 nm . When the focused SPP was incident into the nanodot coupler, its transmission length through the nanodot coupler was confirmed to be 4.0 μm, which is three times longer than that of a metallic core waveguide owing to the efficient near-field coupling between the localized surface plasmon of neighboring nanoparticles. Furthermore, the transmission length through a zigzag-shaped nanodot coupler was as long as that through a linear one.