Enhanced optical superfocusing effect at an all-dielectric nanocone tip.

We present a novel method for generating an extremely confined nanoscale light field using an all-dielectric conical nanotip coupled to a microfiber. By launching a radially polarized TM01 mode into the tip, we achieve constructive interference of longitudinal electric field components at the apex, resulting in a highly localized optical hotspot with sub-10 nm dimensions and a mode volume as small as 10-7 λ3. This approach overcomes the limitations of conventional dielectric tips and rivals plasmonic superfocusing without incurring ohmic losses. Numerical simulations reveal that the focal spot features a high intensity enhancement ratio (> 3500), strong peak-to-background contrast (> 30 dB), and circular symmetry. Furthermore, we demonstrate the ability to shape the light field into arbitrary nanoscale patterns by modifying the tip geometry. These findings open new avenues for low-loss, high-precision light confinement in applications such as optical nano tweezers, nanoscopy, nano lasers, and nanoparticle spectroscopy.