15:45 〜 16:00
▲ [17p-Z31-10] Investigation of enlarged topological band gaps in magneto-optical epsilon-near-zero photonic crystals
キーワード：photonic crystals, topological band gap, epsilon-near-zero
Topological photonic crystals (PhCs) based on magneto-optical (MO) materials enable a photonic analog of quantum hall (QH) effect and backscattering-immune chiral edge states[1]. Unfortunately, extremely weak MO responses in the optical band restrict achievable topological bandgap width[2], hence hindering the realization of robust QH-like edge states in the optical regime. A way to improve MO responses is the use of epsilon-near-zero (ENZ) materials with vanishing exx (diagonal element of permittivity)[3]. However, the potential of such materials has not yet been reported in enhancing a topological band gap.
Here, we for the first time report the enhancement of topological bandgap by using MO ENZ materials. Figure 1(a) shows a unit cell of the investigated PhCs of a honeycomb lattice: triangular areas of a Si substrate are filled by MO ENZ materials. Without magnetization (off-diagonal element of permittivity exy=0), the ENZ PhC (exx=0.01, filling ratio=81%)) exhibits two bands touching at a Dirac point as shown in Fig. 1(b). With magnetization (exy=0.1i), the complete MO topological gap is opened as shown in Fig. 1(c) with a 4.5% gap-mid gap ratio (Dw/wc), corresponding to a 69-nm gap at 1.55 mm wavelength, which is 3 orders of magnitude larger than the previous report (42 pm) [2]. Figure 1(d) shows that Dw/wc remarkably increases as reducing exx, highlighting the role of ENZ materials. Our results suggest that introducing ENZ property could boost the performance of topological MO PhCs even in the optical regime.
Here, we for the first time report the enhancement of topological bandgap by using MO ENZ materials. Figure 1(a) shows a unit cell of the investigated PhCs of a honeycomb lattice: triangular areas of a Si substrate are filled by MO ENZ materials. Without magnetization (off-diagonal element of permittivity exy=0), the ENZ PhC (exx=0.01, filling ratio=81%)) exhibits two bands touching at a Dirac point as shown in Fig. 1(b). With magnetization (exy=0.1i), the complete MO topological gap is opened as shown in Fig. 1(c) with a 4.5% gap-mid gap ratio (Dw/wc), corresponding to a 69-nm gap at 1.55 mm wavelength, which is 3 orders of magnitude larger than the previous report (42 pm) [2]. Figure 1(d) shows that Dw/wc remarkably increases as reducing exx, highlighting the role of ENZ materials. Our results suggest that introducing ENZ property could boost the performance of topological MO PhCs even in the optical regime.