Wang K.Liu A.-Y.Hsiao H.-H.Genet C.Ebbesen T.HUI-HSIN HSIAO2022-09-192022-09-192022https://www.scopus.com/inward/record.uri?eid=2-s2.0-85123376616&doi=10.1021%2facs.nanolett.1c03876&partnerID=40&md5=d766137ae8e59d98cb09da6601794b1dhttps://scholars.lib.ntu.edu.tw/handle/123456789/621089Strong coupling provides a powerful way to modify the nonlinear optical properties of materials. The coupling strength of the state-of-the-art strongly coupled systems is restricted by a weak-field confinement of the cavity, which limits the enhancement of the optical nonlinearity. Here, we investigate a strong coupling between Mie resonant modes of high-index dielectric nanocavities and an epsilon-near-zero mode of an ultrathin indium tin oxide film and obtain an anticrossing splitting of 220 meV. Static nonlinear optical measurements reveal a large enhancement in the intensity-independent effective optical nonlinear coefficients, reaching more than 3 orders of magnitude at the coupled resonance. In addition, we observe a transient response of ∼300 fs for the coupled system. The ultrafast and large optical nonlinear coefficients presented here offer a new route towards strong coupling-assisted high-speed photonics. © 2022 American Chemical Societydielectric nanocavity; epsilon-near-zero mode; Mie resonances; strong coupling; third-order optical nonlinearityIndium compounds; Optical data processing; Optical properties; Oxide films; Resonance; Tin oxides; Transient analysis; Coupled systems; Dielectric nanocavity; Epsilon-near zeros; Epsilon-near-zero mode; Large optical nonlinearities; Mie resonance; Nano-cavities; Nonlinear optical properties; Strong-coupling; Third-order optical nonlinearities; Nonlinear opticsjournal article10.1021/acs.nanolett.1c038762-s2.0-85123376616