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Abstract: Coherent perfect absorption, as time‐reversed lasing, is achieved via appropriate interference of waves in absorbers and provides attractive opportunities for flexible control of light scattering and absorption. Here, the authors theoretically and experimentally demonstrate the realization of coherent perfect absorption by using photonic doping of zero‐index media with absorptive defects. Interestingly, the coherent perfect absorption is independent of the size and shape of this “doped” zero‐index medium absorber, as well as the position of the doping defects. This exceptional absorption property can be well explained via the photonic doping theory for zero‐index media. Moreover, the authors demonstrate that the doping scheme also enables novel ways to control absorption, such as multiple channels and multiple doping defects, etc. This work proposes a unique doping approach for advanced coherent perfect absorption with versatile control functionalities. [ABSTRACT FROM AUTHOR]

A zero-refractive-index metamaterial is one in which waves do not experience any spatial phase change, and such a peculiar material has many interesting wave-manipulating properties. These materials can in principle be realized using man-made composites comprising metallic resonators or chiral inclusions, but metallic components have losses that compromise functionality at high frequencies. It would be highly desirable if we could achieve a zero refractive index using dielectrics alone. Here, we show that by employing accidental degeneracy, dielectric photonic crystals can be designed and fabricated that exhibit Dirac cone dispersion at the centre of the Brillouin zone at a finite frequency. In addition to many interesting properties intrinsic to a Dirac cone dispersion, we can use effective medium theory to relate the photonic crystal to a material with effectively zero permittivity and permeability. We then numerically and experimentally demonstrate in the microwave regime that such dielectric photonic crystals with reasonable dielectric constants manipulate waves as if they had near-zero refractive indices at and near the Dirac point frequency. [ABSTRACT FROM AUTHOR]

In article number 1800081, Lei Zhou, Lin Chen, and co‐workers propose an alternative approach to realize high‐efficiency transmission‐mode metasurfaces to control electromagnetic wave‐fronts, based on hyperbolic metamaterial waveguides. An anomalous refracted beam is realized with a conversion efficiency of 42.9% in the microwave region and 77.9% in the near infrared region. This work may advance a new class of research to develop electromagnetic waves functional devices based on hyperbolic metamaterials, particularly at high frequencies, with the existing fabrication technology. [ABSTRACT FROM AUTHOR]

Metasurfaces have shown great potential to reshape the wavefront of electromagnetic (EM) waves, but transmissive meta‐devices face challenges of low‐efficiency and/or fabrication complexities. Here, an alternative approach to realize high‐efficiency transmission‐mode meta‐devices to control EM wavefronts, based on hyperbolic metamaterial (HMM) waveguides supporting tailored spoof surface plasmons (SSPs) on their side walls, is proposed. By manipulating the dispersions of SSPs through adjusting the HMM geometrical parameters, the phases of EM waves passing through such waveguides, which enables the design of meta‐devices with desired transmission‐phase profiles for particular wave‐manipulation applications, can be controlled. Microwave experiments are implemented to demonstrate two wave‐control effects based on the mechanism, that is, beam‐deflection and focusing, and a maximum conversion efficiency of 42.9% is achieved for the anomalous refracted beam. By scaling down the HMM meta‐devices, the proposal herein is applicable to optical frequencies and in principle promises significantly raised conversion efficiencies. The scheme herein can offer a higher effective refractive index and more tunable dispersion without using high‐index dielectric materials, and thus can serve as an effective and robust approach to make high‐efficiency transmissive meta‐devices with diversified functionalities. Hyperbolic metamaterial (HMM) meta‐devices are proposed to construct high‐efficiency transmissive metasurfaces for wavefront manipulation over the entire spectral regimes without the requirement of high‐index materials. HMM meta‐devices enable an anomalous refracted beam for linearly polarized and circularly polarized electromagnetic waves with conversion efficiencies of 42.9% in the microwave region and 77.9% in the near infrared region. [ABSTRACT FROM AUTHOR]