4 May 2018 Photonic graphene with broken symmetry: complete photonic bandgap and defect modes
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Abstract
We explore photonic crystals based on a triangular lattice of rods. Non-circular rods break the inversion symmetry of the lattice and removes degenerate modes at the K-point (Dirac point) that are protected by symmetry from the band structure. A sizable complete photonic band gap of 7.5% relative gap width ▵w/w can be created by maximal symmetry breaking. We achieve this maximal symmetry breaking by rotating equilateral triangles over 30° relative to the lattice directions. The gap width depends on the rotation angle and a near perfect sinusoidal dependence is found, hinting at a simple mechanism for gap formalism. The gap can be further maximized by tuning the size of the triangles and we report a photonic bandgap map for a structure with inversion symmetry and with maximally broken inversion symmetry. Once a gap is formed interesting edge modes can be created by joining two crystals rotated by 180°. This restores inversion symmetry at the edge and creates line defect modes that are different for the different edges. These defect modes offer interesting possibilities for future nanophotonic devices where the on-chip functionality and localization of light is protected by the symmetry of the edges.
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Giel J. G. Keijsers, Giel J. G. Keijsers, Michiel J. A. de Dood, Michiel J. A. de Dood, } "Photonic graphene with broken symmetry: complete photonic bandgap and defect modes ", Proc. SPIE 10672, Nanophotonics VII, 106724H (4 May 2018); doi: 10.1117/12.2307659; https://doi.org/10.1117/12.2307659
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