Abstract
We numerically demonstrate negative refraction of the Poynting vector and sub-wavelength focusing in the visible part of the spectrum using a transparent multilayer, metallo-dielectric photonic band gap structure. Our results reveal that in the wavelength regime of interest evanescent waves are not transmitted by the structure, and that the main underlying physical mechanisms for sub-wavelength focusing are resonance tunneling, field localization, and propagation effects. These structures offer several advantages: tunability and high transmittance (50% or better) across the visible and near IR ranges; large object-image distances, with image planes located beyond the range where the evanescent waves have decayed. From a practical point of view, our findings point to a simpler way to fabricate a material that exhibits negative refraction and maintains high transparency across a broad wavelength range. Transparent metallo-dielectric stacks also provide an opportunity to expand the exploration of wave propagation phenomena in metals, both in the linear and nonlinear regimes.
Highlights
Pendry predicted that a flat slab of an isotropic material having ε= μ=-1 would make a perfect lens capable of focusing both the far and near field components of a point object, achieving super-resolution [1], which refers to the ability to resolve details of an object below the Rayleigh limit, set at ~0.6λ
We numerically demonstrate negative refraction of the Poynting vector and sub-wavelength focusing in the visible part of the spectrum using a transparent multilayer, metallo-dielectric photonic band gap structure
Our results reveal that in the wavelength regime of interest evanescent waves are not transmitted by the structure, and that the main underlying physical mechanisms for sub-wavelength focusing are resonance tunneling, field localization, and propagation effects
Summary
Pendry predicted that a flat slab of an isotropic material having ε= μ=-1 would make a perfect lens capable of focusing both the far and near field components of a point object, achieving super-resolution [1], which refers to the ability to resolve details of an object below. In order to reduce the losses incurred in the single metal layer lens, a structures was proposed consisting of alternating layers of metal and dielectric materials having thicknesses much smaller than the incident wavelength [10] In this arrangement, and in this regime, the structure displays strong anisotropic properties that make it possible for it to behave as a waveguide, with little or no diffraction taking place, in a scheme that helps the formation of a super-resolved image of the object (two apertures) on the exit surface [10]. The small skin depth at optical frequencies has motivated the choice of very thin metal layers for applications in the visible range, and so it is not unusual to find designs of metallo-dielectric stacks containing layers that are less than 5nm thick, even in the ultraviolet region [10, 12], in order to access the natural transparency that characterizes noble metals for such thicknesses. Multilayer stacks composed of very thin layers are difficult to fabricate in practice
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