期刊
NANOPHOTONICS
卷 11, 期 7, 页码 1345-1354出版社
WALTER DE GRUYTER GMBH
DOI: 10.1515/nanoph-2021-0762
关键词
inverse design; odd-order band gap; photonic crystal; second-order topological insulators
资金
- National Natural Science Foundation of China [1210020421]
- Hong Kong Scholars Program [XJ2020004]
- Research Grants Council of Hong Kong SAR [C6013-18G, AoE/P-502/20]
This study proposes a new principle of second-order photonic topological insulators (SPTIs) and realizes second-order topological states in lattices with an odd number of sites. By topology optimization, second-order topological phases and highly localized corner states are successfully created within sizable band gaps. This offers a new route for exploring high-order topological states in photonics and other classical systems.
Second-order photonic topological insulators (SPTIs) with topologically protected corner states provide a unique platform for realizing the robust manipulation of light in lower dimensions. Previous SPTIs proposed in C (4v )-symmetric lattices are mainly based on the two-dimensional (2D) Su-Schrieffer-Heeger (SSH) model consisting of an even number of sites in the unit cell. Moreover, second-order topological phases within high-order band gaps are rarely explored. Here, we propose a new principle of SPTIs beyond the 2D SSH model, which is realized in C (4v)-symmetric lattices consisting of an odd number of sites in the unit cell. The midgap-gap-ratios of these odd-order band gaps, from the first-order to the nineteenth-order with step of two-order, are maximized by the method of topology optimization. Second-order topological phases are successfully created within these sizeable band gaps and highly localized corner states are observed. Our work offers a new route for exploring high-order topological states in photonics and other classical systems.
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