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

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 degrees 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-mum-wide and 7-mum-long line defect of GammaM orientation is well confined within the width of similar to3 mum, while the SPP propagation inside the periodic structure is completely damped. Relating the SPP intensity profiles measured before and after the 900 bend composed of three 2-mum-separated 30 degrees bends, we directly evaluate the bend loss for the SPP line-defect mode, which constitutes similar to 16 dB for the wavelength of 727 nm.