Gap plasmon resonator arrays for unidirectional launching and shaping of surface plasmon polaritons

We report the design and experimental realization of a kind of miniaturized devices for efficient unidirectional launching and shaping of surface plasmon polaritons (SPPs). Each device consists of an array of evenly spaced gap plasmon resonators with varying dimensions. Particle swarm optimization is used to achieve a theoretical two dimensional launching efficiency of about 51%, under the normal illumination of a 5-{\mu}m waist Gaussian beam at 780 nm. By modifying the wavefront of the SPPs, unidirectional SPPs with focused, Bessel and Airy profiles are launched and imaged with leakage radiation microscopy.