Converting surface plasmon polaritons into spatial bending beams through graded dielectric rectangles over metal film

Spatial bending beams, which preserve their spatial shape while propagating along curved trajectories in free space, offer important application in the fields of fiber sensor, optical trapping, and micro manipulation. In this work, two slits are designed on a metal film to excite surface plasmon polaritons (SPPs), and a group of dielectric rectangles over metal film is theoretically proposed to directly convert SPPs into spatial beams showing arbitrary bending. The appropriate locations of the dielectric rectangles are calculated by phase-modulation method. Transverse acceleration and nondiffraction characteristics of spatial bending beams are observed. We further demonstrate that the intensity distribution, shape, and propagation length of spatial beams showing arbitrary bending rely on structural parameters of dielectric rectangles and on the distance between dielectric rectangles and metal film. These findings provide guidance in the design and optimization of bending beam generators. (C) 2016 Elsevier B.V. All rights reserved.