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| 1 | A hybrid invisibility cloak based on integration of transparent metasurfaces and zero-index materials显示文摘The invisibility cloak,a long-standing fantastic dream for humans,has become more tangible with the development of metamaterials.Recently,metasurface-based invisibility cloaks have been proposed and realized with significantly reduced thickness and complexity of the cloaking shell.However,the previous scheme is based on reflection-type metasurfaces and is thus limited to reflection geometry.In this work,by integrating the wavefront tailoring functionality of transparent metasurfaces and the wave tunneling functionality of zero-index materials,we have realized a unique type of hybrid invisibility cloak that functions in transmission geometry.The principle is general and applicable to arbitrary shapes.For experimental demonstration,we constructed a rhombic double-layer cloaking shell composed of a highly transparent metasurface and a double-zero medium consisting of dielectric photonic crystals with Dirac cone dispersions.The cloaking effect is verified by both full-wave simulations and microwave experimental results.The principle also reveals exciting possibilities for realizing skin-thick ultrathin cloaking shells in transmission geometry,which can eliminate the need for spatially varying extreme parameters.Our work paves a path for novel optical and electromagnetic devices based on the integration of metasurfaces and metamaterials. | Hongchen Chu Qi Li Bingbing Liu Jie Luo Shulin Sun Zhi Hong Hang Lei Zhou Yun Lai | 2018 | Light(Science & Applications)2018，7，1： | 13 |
| 2 | Highly efficient achromatic subdiffraction focusing lens in the near field with large numerical aperture显示文摘The achromatic subdiffraction lens with large numerical aperture(NA)is of significant importance in optical imaging,photolithography,spectroscopy,and nanophotonics.However,most of the previous research on sub-diffraction lenses has been restricted by limited bandwidth and efficiency as well as severe chromatic aberrations.In this paper,a semicircular gradient index lens(sGRIN)with a modified refractive index profile originated from a Maxwell fish-eye lens is put forward to achieve highly efficient(above 81%)achromatic(4–20 GHz)subdiffraction focusing at the focusing line(around 0.28λ)with large NA of 1.3 and broadband diffraction-limited far-field radiation(4–16 GHz)theoretically,which overcomes the drawbacks of previous works.The presented lens is designed by gradient dielectric metamaterials.Evanescent waves ignited at the lens/air interface and transformation of electromagnetic(EM)waves with high spatial frequency in sGRIN to EM waves with low spatial frequency in air are responsible for subdiffraction focusing and diffraction-limited far-field radiation,respectively.Experimental results demonstrate the excellent performance of achromatic subdiffraction focusing and diffraction-limited far-field radiation.The presented lens has great potential to be applied in subdiffraction imaging systems. | JIN CHEN HONGCHEN CHU YUN LAI HUANYANG CHEN WEILI SONG MINGJI CHEN DAINING FANG | 2021 | Photonics Research2021，9，10： | 3 |
| 3 | Breakdown of Maxwell Garnett theory due to evanescent fields at deep-subwavelength scale显示文摘Deep-subwavelength all-dielectric composite materials are believed to tightly obey the Maxwell Garnett effective medium theory. Here, we demonstrate that the Maxwell Garnett theory could break down due to evanescent fields in deep-subwavelength dielectric structures. By using two-and three-dimensional dielectric composite materials with inhomogeneities at a scale of λ∕100, we show that local evanescent fields generally occur near the dielectric inhomogeneities. When tiny absorptive constituents are placed there, the absorption and transmission of the whole composite will show strong dependence on the positions of the absorptive constituents. The Maxwell Garnett theory fails to predict such position-dependent characteristics because it averages out the evanescent fields. By taking the distribution of the evanescent fields into consideration, we have made a correction to the Maxwell Garnett theory so that the position-dependent characteristics become predictable. We reveal not only the breakdown of the Maxwell Garnett theory, but also a unique phenomenon of 'invisible' loss induced by the prohibition of electric fields at deep-subwavelength scales. We believe our work promises a route to control the macroscopic properties of composite materials without changing their composition, which is beyond the traditional Maxwell Garnett theory. | TING DONG JIE LUO HONGCHEN CHU XIANG XIONG RUWEN PENG MU WANG YUN LAI | 2021 | Photonics Research2021，9，5： | 1 |
| 4 | Ultra-broadband reflectionless Brewster absorber protected by reciprocity显示文摘The Brewster’s law predicts zero reflection of p-polarization on a dielectric surface at a particular angle.However,when loss is introduced into the permittivity of the dielectric,the Brewster condition breaks down and reflection unavoidably appears.In this work,we found an exception to this long-standing dilemma by creating a class of nonmagnetic anisotropic metamaterials,where anomalous Brewster effects with independently tunable absorption and refraction emerge.This loss-independent Brewster effect is bestowed by the extra degrees of freedoms introduced by anisotropy and strictly protected by the reciprocity principle.The bandwidth can cover an extremely wide spectrum from dc to optical frequencies.Two examples of reflectionless Brewster absorbers with different Brewster angles are both demonstrated to achieve large absorbance in a wide spectrum via microwave experiments.Our work extends the scope of Brewster effect to the horizon of nonmagnetic absorptive materials,which promises an unprecedented wide bandwidth for reflectionless absorption with high efficiency. | Jie Luo Hongchen Chu Ruwen Peng Mu Wang Jensen Li Yun Lai | 2021 | Light(Science & Applications)2021，10，5： | 0 |
| 5 | Experimental observation of multiple edge and corner states in photonic slabs heterostructures显示文摘The photonic topological insulator has become an important research topic with a wide range of applications.Especially the higher-order topological insulator,which possesses gapped edge states and corner or hinge states in the gap,provides a new scheme for the control of light in a hierarchy of dimensions.In this paper,we propose a heterostructure composed of ordinary-topological-ordinary(OTO)photonic crystal slabs.Two coupled edge states(CESs)are generated due to the coupling between the topological edge states of the ordinary-topological interfaces,which opens up an effective way for high-capacity photonic transport.In addition,we obtain a new band gap between the CESs,and the two kinds of coupled corner states(CCSs)appear in the OTO bend structure.In addition,the topological corner state is also found,which arises from the filling anomaly of a lattice.Compared with the previous topological photonic crystal based on C-4 lattice,CESs,CCSs,and the topological corner state are all directly observed in experiment by using the near-field scanning technique,which makes the manipulation of the electromagnetic wave more flexible.We also verify that the three corner states are all robust to defects.Our work opens up a new way for guiding and trapping the light flow and provides a useful case for the coupling of topological photonic states. | MINGXING LI YUEKE WANG TIAN SANG HONGCHEN CHU YUN LAI GUOFENG YANG | 2022 | Photonics Research2022，10，1： | 0 |
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