Figure 1.

Illustration of the idea and geometry. (a) Pictorial sketch (not in scale) of an optical-fiber MT. A plasmonic metasurface (with details magnified in the inset) is laid on the tip of an optical fiber, covering the entire core region. The metasurface impresses a linear-phase profile (constant gradient, along the x-direction) in the wavefront of a given component of an impinging beam. This yields splitting in the transmitted beam, with an ordinary (co-polarized) component propagating along the incidence direction, and an anomalous component (with generally different polarization) undergoing a phase-gradient-induced steering of an angle. A similar phenomenon (not shown for better visibility) occurs in reflection as well. (b) Illustration of the generalized Snell's refraction/reflection laws in Equation (1). (c) Geometry (not in scale) of the unit cell: a rectangular nanohole (rotated of 45° in the x – y plane) milled in a gold layer.