Sensitivity of imaging properties of metal-dielectric layered flat lens to fabrication inaccuracies

We examine some of the optical properties of a metamaterial consisting of thin layers of alternating metal and dielectric. We can model this material as a homogeneous effective medium with anisotropic dielectric permittivity. When the components of this permittivity have different signs, the behavior of the system becomes very interesting: the normally evanescent parts of a P-polarized incident field are now transmitted, and there is a preferred direction of propagation. We show that a slab of this material can form an image with subwavelength details, at a position which depends on the frequency of light used. The quality of the image is affected by absorption and by the finite width of the layers; we go beyond the effective-medium approximation to predict how thin the layers need to be in order to obtain subwavelength resolution.

Optics Letters, 2010

Imaging with a layered superlens is a spatial filtering operation characterized by the point spread function (PSF). We show that in the same optical system the image of a narrow sub-wavelength Gaussian incident field may be surprisingly dissimilar to the PSF, and the width of PSF is not a straightforward measure of resolution. FWHM or std. dev. of PSF give ambiguous information about the actual resolution, and imaging of objects smaller than the FWHM of PSF is possible. A multiscale analysis of imaging gives good insight into the peculiar scale-dependent properties of sub-wavelength imaging.

Journal of Applied Physics, 2011

We optimise the effective skin-depth and resolution of Ag-TiO 2 , Ag-SrTiO 3 , and Ag-GaP multilayers for imaging with sub-wavelength resolution. In terms of transmission and resolution the optimised multilayers outperform simple designs based on combined use of effective medium theory, impedance matching and Fabry-Perot resonances. For instance, an optimised Ag-GaP multilayer consisting of only 17 layers, operating at the wavelength of 490 nm and having a total thickness equal to one wavelength, combines 78% intensity transmission with a resolution of 60 nm. It is also shown that use of the effective medium theory leads to sub-optimal multilayer designs with respect to the trade-off between the skin depth and resolution already when the period of the structure is on the order of 40 nm or larger.

Journal of the Optical Society of America B, 2014

After reviewing the requirements, which has to be satisfied by a metamaterial based sub-wavelength imaging systems a thin films lens is reported herein. The material of the lens is a composite of spherical Ag nanoparticles embedded in SiO 2 host material. The image of the lens is calculated, by solving the Maxwell equations, with the Transfer Matrix method. The procedure applies Maxwell-Garnet mixing rule and high frequency effective medium theory to calculate the electromagnetic parameters of the composite material. The formula of the composite material, the optimum working frequency and the thicknesses of the layers are determined by minimizing the absolute difference of the field distribution in the source and image planes. The details of the design procedure are presented and optimized configurations obtained under different constrains are discussed. The main advantage of the composite lens is that it can eliminate the hotspots present in the images of metallic superlens.

Journal of The Optical Society of America, 2011

We describe the change of the spatial distribution of the state of polarisation occurring during two-dimensional imaging through a multilayer and in particular through a layered metallic flat lens. Linear or circular polarisation of incident light is not preserved due to the difference in the amplitude transfer functions for the TM and TE polarisations. In effect, the transfer function and the point spread function that characterize 2D imaging through a multilayer both have a matrix form and cross-polarisation coupling is observed for spatially modulated beams with a linear or circular incident polarisation. The point spread function in a matrix form is used to characterise the resolution of the superlens for different polarisation states. We demonstrate how the 2D PSF may be used to design a simple diffractive nanoelement consisting of two radial slits. The structure assures the separation of non-diffracting radial beams originating from two slits in the mask and exhibits an interesting property of a backward power flow in between the two rings.

Journal of the Optical Society of America A, 2008

An optical refraction prism consisting of metal and dielectric, subwavelength, periodic multilayered thin films has been proposed. The multilayered structure of metal and dielectric thin films has a cylindrical dispersion surface for TM polarized light. The light behaviors are very different from those of conventional glass prisms and photonic crystal superprisms. Refraction and diffraction of the light wave for the metal-dielectric multilayered prism has been investigated by numerical simulations and graphical representation based on the dispersion surface. A prism with 0.2 m period had an angular dispersion of 0.20°/nm for ϳ0.8 m wavelength light. The finite thick metal-dielectric multilayered structure acted as a slab waveguide.

2006

Negative refraction is known to occur in materials that simultaneously possess a negative electric permittivity and magnetic permeability; hence they are termed negative index materials. However, there are no known natural materials that exhibit a negative index of refraction. In large part, interest in these materials is due to speculation that they could be used as perfect lenses with superresolution.

Applied Optics, Vol. 53, Issue 26, pp. 6096-6102, 2014

A nanolens based on a metallic nanorod has been considered as a prospective candidate for transporting subwavelength information. Such a lens is tuned to a particular frequency by tailoring the length of the nanorod. In this paper, we have investigated the impact of filling ratio on the subwavelength imaging capabilities of such a lens. Through full-wave electromagnetic simulation, we have demonstrated that the imaging performance of a silver (Ag) nanorod array depends not only on the length and periodicity but also on the filling ratio or the radius of the nanorod. We have studied this impact for nanorods having different cross-sectional shapes such as cylindrical and triangular and examined their performances for various filling ratios.

Journal of Applied Optics, 2014

Nanolens based on metallic nanorod has been considered as a prospective candidate for transporting subwavelength information. Such a lens is tuned to a particular frequency by tailoring the length of the nanorod. In this paper, we have investigated the impact of filling ratio on the subwavelength imaging capabilities of such a lens. Through full-wave electromagnetic simulation, we have demonstrated that the imaging performance of silver (Ag) nanorod array does not only depend on the length and periodicity but also on the filling ratio or the radius of the nanorod. We have studied this impact for nanorod having different cross-sectional shapes such as cylindrical and triangular and examined their performances for various filling ratios.

Physical Review A, 2009

We study the influence of gain on negative refraction and super-resolution in transparent resonant metaldielectric photonic band gap structures in the visible and near infrared ranges. We find that while the introduction of gain can compensate for losses caused by the excitation of surface waves, it also improves the resolving characteristics of the lens and leads to gain-tunable super-resolution.

MRS Proceedings, 2006

Conventional optical imaging systems cannot resolve the features smaller than approximately half the size of the working wavelength, called the diffraction limit. The superlens theory predicts that a flat lens made of an ideal material with negative permittivity and/or permeability is able to resolve features much smaller than working wavelength through the restoration of evanescent waves. We experimentally demonstrated the superlens concept for the first time using a thin silver slab in a quasi-static regime; a 60nm half-pitch object was imaged with 365nm illumination wavelength, λ/6 resolution, and the imaging of 50nm half-pitch object under the same light source, λ/7, was also reported. Here, we present mainly experimental studies of near-field optical superlens imaging.

2006

We considered theoretically and experimentally one-dimensional multilayered metallodielectric nanofilms with nanometric thickness for imaging below the diffraction limit. We investigated their behavior in the ultraviolet and visible spectrum from the point of view of near field optics, but also considered some of their properties in the far field. We designed our structures using the transfer matrix method and utilized RF sputtering to fabricate them. We consider some possible approaches to extract optical information from such multilayers

Optics express, 2014

Metamaterials offer exciting opportunities that enable precise control of amplitude, polarization and phase of the light beam at a subwavelength scale. A gradient metasurface consists of a class of anisotropic subwavelength metamaterial resonators that offer abrupt amplitude and phase changes, thus enabling new applications in optical device design such as ultrathin flat lenses. We propose a highly efficient gradient metasurface lens based on a metal-dielectric-metal structure that operates in the terahertz regime. The proposed structure consists of slotted metallic resonator arrays on two sides of a thin dielectric spacer. By varying the geometrical parameters, the metasurface lens efficiently manipulates the spatial distribution of the terahertz field and focuses the beam to a spot size on the order of a wavelength. The proposed flat metasurface lens design is polarization insensitive and works efficiently even at wide angles of incidence.

Optics Express, 2005

The optical transmission through a subwavelength aperture in a metal film is strongly enhanced when the incident light is resonant with surface plasmons at the corrugated metal surface surrounding the aperture. Conversely, the aperture acts as a novel probe of the surface plasmons, yielding useful insights for optimizing the transmission enhancement. For the optimal corrugation geometry, a set of concentric circular grooves, three times more light is transmitted through the central subwavelength aperture than directly impinges upon it. This effect is useful in the fabrication of near-field optical devices with extremely high optical throughput.

Physical Review B, 2013

We show that any metallo-dielectric multilayer with a hyperbolic dispersion relation can actually be characterized by a complex effective index. This refractive index, extracted from the complex Bloch band diagram, can be directly linked to the super-resolution of a flat lens made of this socalled indefinite medium. This allows for a systematic optimization of the lens design, leading to structures that are outperforming state-of-art flat lenses. We show that, even when fully taking absorption into account, our design provides super-resolved images for visible light up to a distance of one wavelength from the lens edge.