A simple spiral plasmonic lens is studied both analytically and numerically. Owing to the geometric phase effect, a spiral plasmonic lens focuses the left-hand and right-hand circular polarizations into spatially separated plasmonic fields. Such a spatial multiplexing of the field distribution is utilized in miniature circular polarization analyzer design. A circular polarization extinction ratio better than 100 is obtainable with a device size as small as 4lambda(spp). The spiral plasmonic lens provides efficient plasmonic focusing while it eliminates the requirement of centering the incident beam to the plasmonic lens, making it suitable for full Stokes parameter polarimetric imaging applications.
Evanescent coupling between two parallel nanowires is investigated using the finite-difference time-domain method. Silica, tellurite, and silicon nanowires are used as typical materials in the simulation. Compared with weakly coupled waveguides, strongly coupled nanowires show much smaller transfer lengths without sacrificing high coupling efficiencies, suggesting possibilities for developing highly compact evanescent-coupling-based nanowire photonic devices, as well as for achieving high-efficiency interconnection between nanowires and external optical systems. Meanwhile, the polarization-dependent coupling properties, the considerably high minimum coupling efficiency, and the supermode-cutoff-like behavior are also observed. Evanescent coupling properties of strongly coupled nanowires demonstrated may provide valuable references for practical applications of optical nanowires.
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