  All-dielectric optical resonators, exhibiting exotic near-field distributions
upon excitations, have emerged as low-loss, versatile and highly adaptable
components in nanophotonic structures for manipulating electromagnetic waves
and enhancing light-matter interactions. However, achieving experimental full
three-dimensional characterization of near-fields within dielectric materials
poses significant challenges. Here, we develop a novel technique using
high-order sideband generation to image near-field wave patterns inside
dielectric optical resonators. By exploiting the phase-sensitivity of various
harmonic orders that enables the detection of near-field distributions at
distinct depths, we realize three-dimensional tomographic and super-resolution
near-field imaging inside a micrometer-thick silicon anapole resonator.
Furthermore, our method offers high-contrast polarization sensitivity and
phase-resolving capability, providing comprehensive vectorial near-field
information. Our approach can potentially be applied to diverse dielectric
metamaterials, and becomes a valuable tool for comprehensive characterization
of near-field wave phenomena within dielectric materials.
