Broadband Enhancement of Optical Nonlinearity in a Plasmonic Nanocavity Coupled with an Epsilon-Near-Zero Film

Abstract

Nonlinear optics plays a crucial role in various fields, including microscope, all-optical data processing, and quantum information. However, nonlinear optical responses in natural materials are generally very weak, and therefore it is extremely difficult to design all-optical active devices at the subwavelength scale. Here, a dielectric-metal hybrid system is proposed to acquire optical nonlinearity enhancement through the strong coupling between the epsilon-near-zero mode in an indium tin oxide (ITO) nanofilm and the localized surface plasmon in a nanocavity. Such a coupled system exhibits a nonlinear refractive index n2 up to 10.31 cm2/GW and an absorption coefficient β up to 1.0 × 106 cm/GW, over three orders and two orders of magnitude larger than those of bare ITO, respectively. In addition, enhanced nonlinear responses can be observed in a wide wavelength range (∼1400 nm bandwidth) in the near infrared region. Our results provide an efficient way for the development of low-power all-optical modulation devices.