Mid-IR Electromagnetic Topological Edge Modes: Design, Fabrication, and Polarization States Confirmed by High-Angle-Resolution Reflection Spectroscopy

Yuanzhao Yao; Afshan Begum; Naoki Ikeda; Yoshihiko Takeda; Takashi Kuroda; Kazuaki Sakoda

doi:10.7566/jpsj.94.101004

Article Mid-IR Electromagnetic Topological Edge Modes: Design, Fabrication, and Polarization States Confirmed by High-Angle-Resolution Reflection Spectroscopy

Yuanzhao Yao ; Afshan Begum ; Naoki Ikeda ; Yoshihiko Takeda ; Takashi Kuroda ; Kazuaki Sakoda

Download file (9.77 MB)
Download as zip (8.51 MB)

Collection

Citation

Yuanzhao Yao, Afshan Begum, Naoki Ikeda, Yoshihiko Takeda, Takashi Kuroda, Kazuaki Sakoda. Mid-IR Electromagnetic Topological Edge Modes: Design, Fabrication, and Polarization States Confirmed by High-Angle-Resolution Reflection Spectroscopy. Journal of the Physical Society of Japan. 2025, 94 (10), 101004. https://doi.org/10.7566/jpsj.94.101004

(BibTeX)

Description:

(abstract)

We review our recent studies on the design, fabrication, and experimental verification by angle-resolved reflection spectroscopy of topological photonic crystals (PhCs) and topologically protected edge modes in the mid-infrared frequency range. We adopted a sample design based on the symmetry reduction from the honeycomb lattice to the C6v-symmetric lattice to tune the frequencies of E1- and E2-symmetric eigenmodes on the gamma point of the Brillouin zone. In addition to topologically trivial and non-trivial band gaps, we also succeeded in observing double Dirac cones with an isotropic linear dispersion relation by accidental degeneracy of the E1- and E2-symmetric modes. Our specimens had simple structures of PhC slabs fabricated in SOI (silicon-on-insulator) wafers without under-etching of a sacrificial layer beneath the PhC. Therefore, the photonic band gaps are generally narrow due to the small contrast of refractive indexes. Nevertheless, we achieved a sufficiently wide band gap of 6% relative to the midgap frequency, which facilitated our observation of the edge modes. We also verified experimentally that the edge modes were linearly polarized on the gamma point due to the 1:1 mixture of the original left- and right-circular polarizations. All these experimental observations were achieved by using our home-made reflection measurement apparatus with a 0.3 degree angle resolution.

Rights: