Subwavelength dielectric resonators for nonlinear nanophotonics

Enhancing optical nonlinearity Intense pulses of light interacting with a dielectric material can induce optical nonlinear behavior, whereby the frequency of the output light can be doubled or tripled or excited to even higher harmonics of the input light. Usually this interaction is weak and occurs over many thousands of wavelengths, typically requiring the combination of bulk volumes of material with a confining cavity. Using a mechanism of light confinement called bound states in the continuum, Koshelev et al. show that enhanced second-harmonic generation can be obtained in nanoscale subwavelength cylinders of a dielectric material. The results on these optical nanoantennas offer a platform for developing integrated nonlinear nanophotonic devices. Science, this issue p. 288 Nanoscale optical antennas can be designed to enhance optical nonlinearity. Subwavelength optical resonators made of high-index dielectric materials provide efficient ways to manipulate light at the nanoscale through mode interferences and enhancement of both electric and magnetic fields. Such Mie-resonant dielectric structures have low absorption, and their functionalities are limited predominantly by radiative losses. We implement a new physical mechanism for suppressing radiative losses of individual nanoscale resonators to engineer special modes with high quality factors: optical bound states in the continuum (BICs). We demonstrate that an individual subwavelength dielectric resonator hosting a BIC mode can boost nonlinear effects increasing second-harmonic generation efficiency. Our work suggests a route to use subwavelength high-index dielectric resonators for a strong enhancement of light–matter interactions with applications to nonlinear optics, nanoscale lasers, quantum photonics, and sensors.