Trapped boundary modes without a well-defined bulk gap

Subjects: Optics >> Quantum optics submitted time 2023-02-19

Tao Liu Kai Bai Yicheng Zhang Duanduan Wan Yun Lai C. T. Chan Meng Xiao

Abstract： 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.

Peer Review Status:Awaiting Review

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