Nanometer-scale photon confinement inside dielectrics

Abstract

Optical nanocavities confine and store light, which is essential to increase the interaction between photons and electrons in semiconductor devices, enabling, e.g., lasers and emerging quantum technologies. While temporal confinement has improved by orders of magnitude over the past decades, spatial confinement inside dielectrics was until recently believed to be bounded at the diffraction limit. The conception of dielectric bowtie cavities (DBCs) shows a path to photon confinement inside semiconductors with mode volumes bound only by the constraints of materials and nanofabrication, but theory was so far misguided by inconsistent definitions of the mode volume and experimental progress has been impeded by steep nanofabrication requirements. Here we demonstrate nanometer-scale photon confinement inside 8 nm silicon DBCs with an aspect ratio of 30, inversely designed by fabrication-constrained topology optimization. Our cavities are defined within a compact device footprint of 4 lambda^2 and exhibit mode volumes down to V = 3E-4 lambda^3 with wavelengths in the lambda = 1550 nm telecom band. This corresponds to field localization deep below the diffraction limit in a single hotspot inside the dielectric. A crucial insight underpinning our work is the identification of the critical role of lightning-rod effects at the surface. They invalidate the common definition of the mode volume, which is prone to gauge meretricious surface effects or numerical artefacts rather than robust confinement inside the dielectric. We use near-field optical measurements to corroborate the photon confinement to a single nanometer-scale hotspot. Our work enables new CMOS-compatible device concepts ranging from few- and single-photon nonlinearities over electronics-photonics integration to biosensing.

Observation of strong backscattering in valley-Hall topological interface modes

“…Therefore, we instead benchmark our VH waveguides against conventional line-defect W1 waveguides fabricated on the same chip such that the structural disorder is approximately statistically identical. We extract a minimum propagation loss of (1 ± 1) dB/cm in the non-dispersive region of the W1-waveguide, which constitutes a record-low value for suspended silicon photonics (see Supplementary Section 5) and shows that our nanofabrication [5] provides an ideal testing ground for measuring VH-waveguides with the lowest level of roughness realized to date.…”

“…The fabrication process is detailed in Ref. [5] with some minor modifications. Sample 1 is fabricated using a high-resolution electron beam lithography process, the details of which may be found in Ref.…”

“…In a single realization, this corresponds to the formation of random optical cavities with distinct spatial patterns (Fig. 5b) and quality factors reaching ≃ 2⋅10 5 (Fig. 5c).…”

“…Planar nanostructures built with high-index dielectric materials using top-down nanofabrication techniques have enabled precise control of the spatial and spectral properties of electromagnetic fields at optical frequencies, fostering the development of integrated photonic devices such as quantum light sources [1], programmable photonics [2], nanolasers [3], and optical communication technology [4]. While highly optimized performance can be achieved with aperiodic structures [5], periodicicity offers simple building blocks that may be readily scaled to larger architectures. In particular, periodic structures allow tailoring the dispersion relation of light far beyond simple translationally invariant systems.…”

Cavity-induced exciton localisation and polariton blockade in two-dimensional semiconductors coupled to an electromagnetic resonator

“…Our calculations show that lateral dimensions of the order of 40 nm or smaller are required to see significant antibunching, g (2) (0) < 1/2, at cryogenic temperatures, whereas smaller dimensions of around 10 nm are required at room temperature. Such dimensions are within the limits of contemporary nanofabrication [53] using either plasmonic resonators [54,55] or optical cavities with extreme dielectric confinement of light [56,57].…”