Spoof-plasmon relevant one-way collimation and multiplexing at beaming from a slit in metallic grating

Diode and collimator/multiplexer functions are suggested to be combined in one device that is based on a thin metallic grating with a single subwavelength slit. A proper choice of the structural (a) symmetry of the grating can result in obtaining one-way collimation and multiplexing with a single on-axis or off-axis, or two off-axis narrow outgoing beams. It is possible due to freedom in utilizing different combinations of the excitation conditions of the spoof surface plasmons at the four grating parts - right and left front-side and right and left back-side ones. Such a combining provides one with an efficient tool to engineer one-way collimators and multiplexers with the desired characteristics. Strong asymmetry in transmission with respect to the incidence direction (forward vs backward case) can be obtained within a wide range of variation of the incident beam parameters, i.e., angle of incidence and frequency, while the outgoing radiation is concentrated within a narrow range of the observation angle variation. Most of the observed asymmetric transmission features can be qualitatively explained using the concept of the equivalent source placed inside the slit. (C) 2012 Optical Society of America