Abstract
Two-dimensional photonic crystals, in analogy to AB/BA stacking bilayer graphene in electronic system, are studied. Inequivalent valleys in the momentum space for photons can be manipulated by simply engineering diameters of cylinders in a honeycomb lattice. The inequivalent valleys in photonic crystal are selectively excited by a designed optical chiral source and bulk valley polarizations are visualized. Unidirectional valley interface states are proved to exist on a domain wall connecting two photonic crystals with different valley Chern numbers. With the similar optical vortex index, interface states can couple with bulk valley polarizations and thus valley filter and valley coupler can be designed. Our simple dielectric PC scheme can help to exploit the valley degree of freedom for future optical devices.
Highlights
In the electronic crystal system, a pair of inequivalent energy extrema exhibits in the momentum space, called valleys[1,2]
Degenerated valleys appear around the corners of the first Brillouin zone (K and K′ points). This case is denoted as photonic crystal (PC) III, which is similar to monolayer graphene by replacing each carbon atom with an infinitely long dielectric cylinder
Topological unidirectional interface states are demonstrated to exist at the domain wall of two inverted PCs with none zero valley Chern numbers
Summary
In the electronic crystal system, a pair of inequivalent energy extrema exhibits in the momentum space, called valleys[1,2]. Using a designed chiral stimulus with different optical vortex index[32], the excitation of inequivalent bulk valley states are demonstrated.
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