Unconventional localization of light with Mie-tronics

Abstract

Localization of light requires high-Q cavities or spatial disorder, yet the wave nature of light may open novel opportunities. Here we suggest to employ Mie-tronics as a powerful approach to achieve the hybridization of different resonances for the enhanced confinement of light via interference effects. Contrary to a conventional approach, we employ the symmetry breaking in finite arrays of resonators to boost the Q factors by in-plane multiple scattering. Being applied to photonic moire structures, our approach yields a giant enhancement of the Purcell factor via twist-induced coupling between degenerate collective modes. Our findings reveal how finely tuned cooperative scattering can surpass conventional limits, advancing the control of wave localization in many subwavelength systems.

Figures (10)

• Figure 1: Unconventional localization via merging collective and hybrid modes. (a) Supercavity with hole array (C) as cavity, surrounded by four mirror arrays (M$_{1,2,3,4}$) that backscatter in-plane leakage. (b) Purcell factor spectrum for a magnetic dipole ($m_x$) at the cavity center. Tuning the cavity-mirror gap to $G_{\text{MC}} = 541$ nm enhances the factor over tenfold at CM$_1$. (c,d) Near-field profiles of CM$_0$ and CM$_1$ showing strong enhancement from mirror-induced backscattering; insets show far-field patterns. (e) $Q$-factor versus gap $G_{\text{MC}}$ for mismatched ($a_M = 552$ nm, $a_C = 529$ nm), and matched ($a_M = a_C = 529$ nm) lattice periods; both yield similar $Q$ enhancement. (f) Purcell spectra at three gaps show $Q$ enhancement from HM$_0$–CM$_2$ coalescence. (g,h) Near-field profiles of HM$_0$ and CM$_2$.
• Figure 2: (a) Schematic of a magnetic dipole ($m_x$) coupled to a hole array with four reflective edges. (b) $Q$-factor enhancement from edge-induced feedback, further improved by introducing a quartz substrate.
• Figure 3: Twisted Mie-tronics. (a) Hexagonal hole array, with red circles indicating air holes. (b) Purcell spectra at point $O$ showing two degenerate collective modes, HX$_1$ and HX$_2$. (c,d) Magnetic field profiles of HX$_1$ and HX$_2$, with insets showing their $E_x$ field symmetries. (e) Twisted hexagonal structure formed by overlaying a rotated copy (green). (f) Coupling of HX$_1$ and HX$_2$ at twist angle $\theta = 1.45^\circ$ results in twisted modes tHX$_1$ and tHX$_2$. (g,h) Near-field profiles of tHX$_1$ and tHX$_2$.
• Figure 4: Magic angles in Mie-tronics. (a) $Q$ factor of the twisted mode tHX$_1$ versus twist angle $\theta$, showing multiple peaks—photonic analogs of electronic magic angles. (b) Purcell spectrum at $\theta = 1.675^\circ$, with two peaks (tHX$_3$, tHX$_5$) and a trough (tHX$_4$). (c) Spectrum at the magic angle $\theta_M = 1.6^\circ$, where $\mu_x$ excites only tHX$_1$. (d–f) Magnetic field profiles of tHX$_3$, tHX$_4$, and tHX$_5$ from (b).
• Figure 5: Merging of hybrid and collective modes, and impact of a quartz substrate. (a) Purcell factor spectra showing the merging of the hybrid mode (HM$_1$) with the collective mode (CM) as we tune the gap size $G_{\text{MC}}$ from 0 to 120 nm. Adding a quartz substrate slightly enhances the CM while suppressing HM$_1$. (b,c) Near-field profiles of HM$_1$ and CM, respectively. The inset in (c) shows the imaginary part of $H_x$, highlighting opposite magnetic field directions in hole-centered and silicon-centered unit cells.