分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： A boundary mode localized on one side of a finite-size lattice can tunnel to the opposite side which results in unwanted couplings. Conventional wisdom tells that the tunneling probability decays exponentially with the size of the system which thus requires many lattices before eventually becoming negligibly small. Here we show that the tunneling probability for some boundary modes can apparently vanish at specific wave vectors. Meanwhile, the number of wave vectors where tunneling probability vanishes equals the number of lattices perpendicular to the boundary. Thus, similar to bound states in the continuum, a boundary mode can be completely trapped within very few lattices whereat the bulk band gap is not even well-defined. Our idea is proven analytically, and experimentally validated in a dielectric photonic crystal. This feature allows for the extreme flexibility in tunning the hopping between localized states or channels, which facilitates unprecedented manipulation of light such as integrating multiple waveguides without crosstalk and photonic non-abelian braiding.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Impedance mismatch between free space and absorptive materials is a fundamental issue plaguing the pursue of high-efficiency light absorption. In this work, we design and numerically demonstrate a type of non-resonant impedance-matched optical metasurfaces exhibiting ultra-broadband reflectionless absorption based on anomalous Brewster effect, which are donated as optical Brewster metasurfaces here. Interestingly, such Brewster metasurfaces exhibit a unique type of extreme angular-asymmetry: a transition between perfect transparency and perfect absorption appears when the sign of the incident angle is changed. Such a remarkable phenomenon originates in the coexistence of traditional and anomalous Brewster effects. Guidelines of material selection based on an effective-medium description and strategies such as the integration of a metal back-reflector or folded metasurfaces are proposed to improve the absorption performance. Finally, a gradient optical Brewster metasurface exhibiting ultra-broadband and near-omnidirectional reflectionless absorption is demonstrated. Such high-efficiency asymmetric optical metasurfaces may find applications in optoelectrical and thermal devices like photodetectors, thermal emitters and photovoltaics.
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