講演情報
[15a-K505-6]Effect of the Dirac frequency in valley photonic crystal heterostructure waveguides
〇(M1)Xiaomeng Chi1,2, Chengkun Zhang1,2, Nao Harada1,2, Satoshi Iwamoto1,2 (1.RCAST, The Univ. of Tokyo, 2.IIS, The Univ. of Tokyo)
キーワード：
Valley photonic crystal heterostructure waveguides、Dirac frequency、graphene-like photonic crystal
Valley photonic crystal (VPhC) waveguides leveraging valley kink states can exhibit robustness against sharp bends and certain types of disorders, rendering them as an attractive platform for topological integrated photonics. The topological edge states are confined at the boundaries between two topologically distinct VPhCs, resulting in limited mode width. In contrast, recently proposed VPhC heterostructure waveguides, consisting of two topologically distinct VPhCs and a graphene-like photonic crystal (PhC) featuring a photonic Dirac point, can host wide-mode-area single modes. However, the influence of the Dirac frequency in graphene-like PhC on the guided mode properties in VPhC heterostructure waveguides remains largely unexplored. In this study, we examined the evolution of band structures and the variations in the frequency bandwidth of single modes within VPhC heterostructures by systematically altering the Dirac frequency.
We illustrates an ABC heterostructure waveguide, consisting of 8 layers of graphene-like PhC B sandwiched by two topologically distinct VPhC A and C. The Dirac frequency in PhC B can be tuned by modifying the side length of equilateral triangular holes Lmid. As the Lmid increases, the fDirac increseas. We found even when the Dirac frequency lies outside the bulk bandgap of the VPhCs, a single-mode guided mode emerges. And the maximum normalized bandwidth is achieved when Lmid=1.05a/sqrt*(3), corresponding to the Dirac frequency being located at the mid gap. Additionally, the single-mode in-gap states disappear when VPhC C is replaced by VPhC A. This indicates that the presence of these states is associated with the distinctness of VPhC A and C.
We illustrates an ABC heterostructure waveguide, consisting of 8 layers of graphene-like PhC B sandwiched by two topologically distinct VPhC A and C. The Dirac frequency in PhC B can be tuned by modifying the side length of equilateral triangular holes Lmid. As the Lmid increases, the fDirac increseas. We found even when the Dirac frequency lies outside the bulk bandgap of the VPhCs, a single-mode guided mode emerges. And the maximum normalized bandwidth is achieved when Lmid=1.05a/sqrt*(3), corresponding to the Dirac frequency being located at the mid gap. Additionally, the single-mode in-gap states disappear when VPhC C is replaced by VPhC A. This indicates that the presence of these states is associated with the distinctness of VPhC A and C.