With the advent and rapid development of the transformation optics and metamaterials, invisibility cloaks have captivated much attention in recent years. While most cloaking schemes suffer from limited bandwidth, the carpet cloak, which can hide an object on a reflecting plane, can operate over a broadband frequency range. However, the carpet cloaks experimentally realized thus far still have several limitations. For example, the quasi-conformal mapping carpet cloak leads to a lateral shift of the reflected light ray, while the birefringent carpet cloak only works for a specific polarization. In this work, we propose a conformal transformation scheme to tackle these two problems simultaneously. As an example, we design a mid-infrared carpet cloak in a silicon platform and demonstrate its polarization-insensitive property as well as the minimized lateral shift over a broad frequency band from 24 to 28.3 THz.

Scattering from anisotropic geometries of arbitrary shape is relatively difficult to interpret physically, involving the intricate interplay between material and geometric effects. Insights into complex scattering mechanisms are often enabled by modal methods that decompose the response into the well-understood multipolar resonances. Here, we extend the generalized normal mode expansion to lossy and anisotropic scatterers. Unique to the method is that it decomposes the total response of any anisotropic resonator into the modes of the corresponding isotropic resonator. This disentangles the material and geometric contributions to the scattering of any anisotropic resonator. Furthermore, the method can identify absorption and scattering resonances with separate sets of modes. We illustrate our method by considering an infinitely long cylinder with concentric metallic/dielectric layers, targeting the complex case of an effective hyperbolic response. We show that by scanning the material composition of the hyperbolic medium, we can achieve any desired scattering effect, including backscattering cancellation.

Optical metasurfaces composed of two-dimensional arrays of densely packed nanostructures can project arbitrary holographic images at mid-infrared frequency. Our approach employs silicon nanopillars to control light properties, including polarization-independent phase response working with high-transmission efficiency over the 2π-phase modulation range at wavelength 4.7 μm. We experimentally dispose nanopillars accordingly to phase-only profiles calculated using the conventional Gerchberg–Saxton algorithm and revealed the optical performances of our devices using a mid-infrared on-axis optical setup. The total efficiency of our reflection hologram reaches 81%. Our experimental results agree well with the image of the desired object, opening up new perspectives for mid-infrared imaging and displaying for military, life science and sensing application.