Benefited from the well‐known Mie resonance, a plethora of physical phenomena and applications are attracting attention in current research on dielectric‐based nanophotonics. High‐index dielectric metastructures are favorable to enhance light‐matter interaction in nanoscale with advantages such as low loss, optical magnetism, and multipolar responses, which are superior to their plasmonic counterpart. In this review, we highlight the important role played by Mie resonance‐based multipolar and multimodal interaction in nanophotonics, introducing the concept of “multipole and multimode engineering” in artificially engineered dielectric‐based metastructures and providing an overview of the recent progress of this fast‐developing area. The scope of multipole and multimode engineering is restricted not only in multipolar interferences of meta‐atom and meta‐molecule but also in the nontrivial intermodal coupling (Fano resonance and bound states in the continuum), in the collective mode and the surface lattice mode appearing via periodic meta‐lattices and aperiodic meta‐assembly, in chiral enhancement via chiral and achiral dielectric metastructures, and in Mie resonance‐mediated hybrid structures (Mie‐plasmon and Mie‐exciton). Detailed examples and the underlying physics of this area are discussed in‐depth, in order to lead the multifunctional metastructures for novel applications in the future.

Silicon photonics have attracted significant interest because of their potential in integrated photonics components and all-dielectric meta-optics elements. One major challenge is to achieve active control via strong photon–photon interactions, i.e. optical nonlinearity, which is intrinsically weak in silicon. To boost the nonlinear response, practical applications rely on resonant structures such as microring resonators or photonic crystals. Nevertheless, their typical footprints are larger than 10 μm. Here, we show that 100 nm silicon nano-resonators exhibit a giant photothermal nonlinearity, yielding 90% reversible and repeatable modulation from linear scattering response at low excitation intensities. The equivalent nonlinear index is five-orders larger compared with bulk, based on Mie resonance enhanced absorption and high-efficiency heating in thermally isolated nanostructures. Furthermore, the nanoscale thermal relaxation time reaches nanosecond. This large and fast nonlinearity leads to potential applications for GHz all-optical control at the nanoscale and super-resolution imaging of silicon.

The realization of ultrabroadband absorption is a fundamental part of a thermal emitter, especially in the application of radiative cooling. This study involved proposing and systematically analyzing a novel structure termed as an embedded metal-dielectric-metal (EMDM) structure. The results in the case of an individual resonator indicated that the EMDM resonator displayed a broader full width at half maximum (FWHM) that was 1.9 times that of the metal-dielectric-metal (MDM) resonator due to mode matching at the terminated end and enhanced scattering intensity. With respect to the case of periodic resonators, single-sized periodic EMDM resonators are employed to achieve a broader FWHM that is 3.8 times that of the MDM resonators. In addition, a strong coupling effect is confirmed between localized MDM and hybrid modes. An application of lossy-dielectric based periodic three-dimensional EMDM resonators indicated that an average absorptivity of 0.85 in the entire atmospheric window (8–13 μm). The results revealed the potential of EMDM structures for radiative cooling devices and other ultrabroadband absorbers.