Active control of anapole states by structuring the phase-change alloy Ge2Sb2Te5

Abstract

High-index dielectric nanoparticles supporting a distinct series of Mie resonances have enabled a new class of optical antennas with unprecedented functionalities. The great wealth of multipolar responses has not only brought in new physical insight but also spurred practical applications. However, how to make such a colorful resonance palette actively tunable is still elusive. Here, we demonstrate that the structured phase-change alloy Ge2Sb2Te5 (GST) can support a diverse set of multipolar Mie resonances with active tunability. By harnessing the dramatic optical contrast of GST, we realize broadband (Δλ/λ ~ 15%) mode shifting between an electric dipole resonance and an anapole state. Active control of higher-order anapoles and multimodal tuning are also investigated, which make the structured GST serve as a multispectral optical switch with high extinction contrasts (>6 dB). With all these findings, our study provides a new direction for realizing active nanophotonic devices.

Advanced Optical Programming of Individual Meta‐Atoms Beyond the Effective Medium Approach

“…Commonly, active infrared MSs based on PCMs exhibit different operation states by switching the entire MS via heating and short electrical or optical pulses . Intermediate states of the PCM crystallization have also been exploited to obtain partial resonance shifts by adjusting the annealing conditions. Microscopically, these states are determined by the random distribution of nanoscale crystallites in the PCM layer, while macroscopically they are typically treated within effective medium theory.…”

Infrared dielectric metamaterials from high refractive index chalcogenides

“…For more details of the multipole analysis, refer to Supplementary Information section I. Such highorder modes supported by the metamaterial [28][29][30] enable strong light localization and confinement, which may be suitable for applications in nonlinear and laser optics, 31,32 Overall, the TI chalcogenide crystal family is an exceptionally versatile material platform for infrared applications based on high-index, low-loss dielectric metamaterial architectures, including ultrathin flat optical elements 33 , sub-diffraction light confinement and waveguiding 34 , and nonlinear optics 35 . Low-loss mid-IR metamaterials are also highly sought for enhanced sensing of molecular fingerprints based on strong light confinement.…”

All-optical switch and logic gates based on hybrid silicon-Ge2Sb2Te5 metasurfaces

“…Similarly, all-dielectric active hybrid MMs with low loss also need to be explored [26]. Up to now, liquid crystal [27,28] and PCM Ge2Sb2Te5 (GST) [29][30][31] have been integrated as efficient active dielectrics. However, most related works utilize active media as claddings, substrates or meta-elements, few works have attempted to adopt hybrid dielectric meta-resonators.…”

“…The substrate is chosen as silicon nitride with n= 1.98 [33]. The effective dielectric constants of GST with different degrees of crystallinity are calculated following the Lorentz-Lorenz relation [30]:…”