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(a) Top view layout of the right spiral nanoslits. The nanobump position is shown to be at the location of the smaller optical vortex. (b) and (c) Ey field distribution of the optical vortex when illuminated by LCP and RCP light. (d) The side view showing the nanobump and the emerging PSP from the air nanoslits. The nanobump consists of a layer of dielectric material sandwiched between two gold layers. (e) and (f) The geometrical parameters that affect the nanobump.
Geometrical parameter effects on the normalized extinction coefficient at the metal layer. (a) Effect of length on the tapered nanobump. Inset: A tapered nanobump with tapering ratio of 1/30. (b) Effect of the width on the tapered nanobump. The length = 110 nm is from Fig. 2(a) . (c) Effect of h 1, thickness of metal layer. The length and width is l = 110 nm and w = 62 nm, respectively. (d) Effect of h 2, thickness of dielectric layer. From Figs. 2(a)–2(d) , the geometrical parameters of l = 110 nm, w = 62 nm, h 1 = 42 nm, and h 2 = 31 nm gave the highest normalized extinction coefficient for the tapered nanobump with tapering ratio of 1/30.
(a) Plot showing the effect of tapered nanobump length on the resonance peak wavelength. (b) Spectrum of the metal and dielectric layer at unoptimized and optimized geometrical parameters. It is observed that the peak resonance wavelengths coincide at the optimized geometrical parameters. (c) Field amplitude at the tapered end at various tapering fraction. The field amplitude increases with decreasing tapering fraction (shaper taper end).
Comparison of the various nanobump designs under different circular polarization. All the electric field amplitude, Ey are normalized with respect to the incident field amplitude, E 0. A sharper tapered nanobump gives higher amplitude due to higher surface charge density. It is also observed that the field amplitude is higher when left handed circular polarization is incident onto the spiral nanoslits. The dotted line shows the boundaries of the vortex ring. For LCP incident, the nanobump is placed on the vortex ring. For RCP incident, the nanobump is outside the vortex ring. This explains the lower electric field amplitude.
Ey field distribution of four tapered nanobump placed on the circumference of the optical vortex. It is observed that the Ey field is enhanced for all nanobumps.
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