# 3D Imaging of Optical Modes in Dielectric Photonic Nanocavities with Sub-wavelength Field Confinement

## TL;DR

This paper shows how to visualize light confinement in tiny silicon nanocavities using electron beam techniques, enabling better understanding for photonic and quantum technologies.

## Contribution

The study introduces a method to directly visualize 3D optical modes in dielectric nanocavities with sub-wavelength confinement.

## Key findings

- Tomographic reconstruction revealed 3D optical mode profiles matching simulations.
- A telecom wavelength resonance was tightly localized at the bowtie bridge.
- The method confirms sub-wavelength mode volumes in dielectric structures.

## Abstract

Dielectric optical cavities are emerging as viable platforms
for
efficiently concentrating light within extremely small volumes of
sub-wavelength dimensions. This breaks with the notion that only plasmonic
nanostructures can achieve this scale of confinement and enables strong
light–matter interactions without the losses typically associated
with metals. Here, we directly visualize the optical modes of a topology-optimized
silicon bowtie nanocavity using multi-orientation electron energy-loss
spectroscopy. Tomographic reconstruction of the resulting data sets
reveals the three-dimensional profiles of several polarized optical
modes in close agreement with simulations. A resonance near the telecom
wavelength (∼1550 nm) is shown to be tightly localized
at the bowtie bridge, confirming its deep sub-wavelength mode volume.
These findings establish electron beam spectroscopy as a powerful
tool for mapping three-dimensional field confinement in dielectric
photonic cavities with potential applications in future photonic and
quantum technologies.