Surface plasmon polariton propagation along a 90° bent line defect in a periodically corrugated metal surface

Abstract

Propagation of surface plasmon polaritons (SPPs) excited in the wavelength range of 720–860 nm at a gold (45-nm-thick) film surface with lithographically fabricated (170-nm-wide and 50-nm-high) scatterers arranged in a 400-nm-period triangular lattice containing a 90° bent line defect is investigated by using near-field optical microscopy. We find that, in the range of 720–750 nm, the SPP mode propagating along a 2.5-μm-wide and 7-μm-long line defect of ΓM orientation is well confined within the width of ∼3 μm, while the SPP propagation inside the periodic structure is completely damped. Relating the SPP intensity profiles measured before and after the 90° bend composed of three 2-μm-separated 30° bends, we directly evaluate the bend loss for the SPP line-defect mode, which constitutes ∼16 dB for the wavelength of 727 nm.