Enhancement and Speed‐Up of Carrier Dynamics in A Dielectric Nanocavity with Deep Sub‐Wavelength Confinement

ABSTRACT Dielectric bowtie cavities represent a breakthrough in simultaneously achieving ultrahigh quality factors and ultra‐small mode volumes, providing new opportunities for enhancing light‐matter interactions. Experimental work has so far emphasized the realization of these nanocavities. Here, we experimentally investigate the ultrafast dynamics of a topology‐optimized dielectric (silicon) bowtie nanocavity, with device dimensions down to 12 nm, that localizes light to a mode volume deep below the so‐called diffraction limit given by the half‐wavelength cubed. This strong spatial light concentration is shown to significantly enhance the carrier generation rate through two‐photon absorption, as well as reducing the time it takes for the carriers to recover. A diffusion time below 1 ps is achieved for the bowtie cavity, which is more than an order of magnitude smaller than for a conventional nanocavity. Additionally, parametric effects due to coherent interactions between pump and probe signals are also enhanced in the bowtie cavity, leading to an improved extinction ratio. These results demonstrate important fundamental advantages of dielectric bowtie cavities compared to conventional point‐defect cavities, laying a foundation for novel low‐power and ultrafast optical devices, including switches and modulators.