Abstract
We have investigated the focusing properties of surface plasmon polariton floating dielectric lenses. An analysis of the scattering characteristics of surface plasmon polaritons using a floating dielectric block shows that the air-gap thickness between a floating dielectric block and a metal substrate can be an effective dynamic variable for modulating the amplitude and phase of the transmission coefficient of the surface plasmon polaritons. This property can be used to realize a variable-focusing surface plasmon dielectric lens with the air-gap thickness as the dynamic variable. The focusing properties of a Fresnel lens and a parabolic lens with respect to the air-gap thickness are compared and analyzed.
Highlights
Optical information processing on the nano-scale is considered to be a main objective in the field of nanophotonics
In contrast to radiational diffraction of surface plasmon polaritons (SPPs), such as beaming [5, 6], low-dimensional diffraction of SPPs means that the diffracted field of the SPP is still a low-dimensional wave confined at the metal/dielectric interface, even though, from the surface diffractive structures, part of the optical energy can radiate into the surrounds
We have shown that an air-gap control of a floating dielectric block can generate the dynamic phase and amplitude modulation of the SPP transmission coefficient
Summary
Optical information processing on the nano-scale is considered to be a main objective in the field of nanophotonics. Using RCWA, we investigate the scattering characteristics of the SPP eigenmode passing through the region of a finite-size dielectric block floating over a metal substrate. When the air-gap thickness is large enough to be out of this range, the SPP eigenmode is not perturbed by the dielectric block, since the evanescence tail has a finite length along the x-direction. In the same way as the dielectric block with a thickness of 1ฮผm , it can be seen that as the length increases, the amplitude of the transmission coefficient decreases monotonically because of ohmic loss and radiation loss when the air-gap is smaller than 50nm. Periodic amplitude fluctuations along the length axis are observed in the air-gap region above 50nm In this case, because the thickness of the dielectric block is double that of the former case, the fluctuation period is doubled. The phase fitting function, ฮฆ (h,t ) , is a polynomial that approximates the unwrapped phase profile
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