In this paper, we demonstrate an ultra-thin, low-loss optical metamaterial filter with high transmission and near constant
group delay across a broad pass-band from 3.0 to 3.5μ m. Deep-subwavelength air hole inclusions positioned at the corners
of a conventional metallodiectric fishnet were used engineer the dispersive properties of the structure to have an impedance
match to free space over the pass-band. The optical properties of the metamaterial filter were verified by experimentally
fabricating and characterizing the optimized free-standing nano-notched fishnet. The measured experimental results agreed
well with the simulated response, showing a high transmission band over the targeted wavelength band.
Transformation Optics (TO) has enabled new methodologies for the design and specification of gradient-index (GRIN) lenses for radio-frequency and optical applications by linking refractive index gradients to a mathematically equivalent change in geometry in another dimension. With the new mathematical design tools, there have been many interesting devices introduced in the literature, such as optical collimators and absorbers (optical “black holes”), GRIN couplers and bends for optical waveguides, and compressed or flattened collimating lenses for imaging and non-imaging applications. Many of the most interesting TO designs are not feasible for implementation, however, due to the complex anisotropic, inhomogeneous material parameters required by the full TO formulation. Instead, restricting the geometric transformations to be mathematically conformal or quasi-conformal (qTO) eliminates the anisotropic material requirements and allows implementation with an isotropic 2D or 3D GRIN profile, for which multiple fabrication methods exist in the RF and IR wavelength ranges and are under development for the complete optical spectrum. We present an overview of the usefulness of combining TO, qTO, and GRIN optics for energy concentration along with the associated design and analysis techniques. Moving away from traditional lenses to GRIN and TO optics for which, in general, no analytical geometric optics or full-wave solution exists, involves the development of new design strategies for individual lenses and systems of lenses. We demonstrate results obtained using advanced, multivariate optimizations that are tightly coupled to a fast, advanced inhomogeneous ray tracing engine for electrically-large lenses, and to an efficient body-of-revolution solver for electrically-small cylindrically-symmetric lenses.
We demonstrate a flexible thin film zero refractive index optical metamaterial with matched impedance to free space and
low absorption loss at 1.55 μm. The metallo-dielectric multilayer structure with fishnet geometry was optimized by a
genetic algorithm. The fabrication process and characterization approach are described. The experiment results agree
well with the theoretical predictions, showing an effective index of neff = 0.072 + 0.51i and an impedance of Zeff/Z0 = 1.009 – 0.021i.
In this study, we report multilayer metallo-dielectric stacks that simultaneously possess a zero refractive index and an
impedance match to free space in the near-IR. A genetic algorithm (GA) was used to optimize the screen geometries and
dimensions of the zero index metamaterials (ZIMs) that consisted of alternating gold (Au) and polyimide films.
Examples of three- and nine-layer ZIMs are shown. The fabrication procedure and characterization methods of the
multilayer metallo-dielectric ZIMs are also described.
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