Our paper H. Taghvaee*, F. Liu*, A. Díaz-Rubio, and S. Tretyakov, "Subwavelength focusing by engineered power-flow conformal metamirrors" was published in Physical Review B, and it is selected as Editors' Suggestions.

Teaser:

    It is highly desirable to break the diffraction limit on the resolution of optical devices and achieve subwavelength focusing. Here, the authors show that curved and inhomogeneous reflectors offer a practical method for achieving this goal. The surface profile of the focusing reflector is designed to be tangential to the desired power flow so that the metamirror can be described locally by lossless impedance boundaries and can be easily implemented using simple lossless meta-atoms. We envisage some practical applications of subwavelength focusing that become possible using this method.

Abstract:

    Many advances in reflective metasurfaces have been made during the last few years, implementing efficient manipulations of wave fronts, especially for plane waves. Despite numerous solutions that have been developed throughout the years, a practical method to obtain subwavelength focusing without the generation of additional undesired scattering is a challenge to this day. In this paper, we introduce and discuss lossless reflectors for focusing incident waves into a point. The solution is based on the so-called power-flow conformal surfaces that allow theoretically arbitrary shaping of reflected waves. The metamirror shape is adapted to the power flow of the sum of the incident and reflected waves, allowing a local description of the reflector surface based on the surface impedance. In particular, we present a study of two scenarios. First, we study the scenario when the field is emitted by a point source and focused at an image point (in the considered example, with the $\lambda /20$ resolution). Second, we analyze a metasurface capable of focusing the power of an illuminating plane wave. This work provides a feasible strategy for various applications, including detecting biological signals near the skin, sensitive power focusing for cancer therapy, and point-to-point power transfer.

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​​​​​​​DOI: https://doi.org/10.1103/PhysRevB.104.235409