Microtoroids

Microtoroids are microscopic, torus-shaped optical resonators that have garnered significant interest in the fields of photonics and optoelectronics due to their high quality factors and compact size. These structures are typically fabricated from silica or other dielectric materials using advanced lithography and reflow techniques, enabling precise control over their geometry and optical properties.

The primary feature of microtoroids is their ability to confine light via whispering gallery modes (WGMs), where photons circulate around the inner circumference of the toroid with minimal loss. This high Q-factor, often exceeding 10^8, allows for prolonged light-matter interactions, making microtoroids highly suitable for applications such as sensing, nonlinear optics, and cavity quantum electrodynamics.

Microtoroids are often integrated with waveguides or fiber tapers to facilitate efficient coupling of light into and out of the resonator. Their small volume combined with high optical quality enables sensitive detection of minute environmental changes, such as variations in temperature, refractive index, or the presence of specific chemical or biological agents.

The fabrication process generally involves patterning a silica disk on a substrate, followed by a reflow process that transforms it into a toroidal shape. Innovations in fabrication have improved the reproducibility and performance of microtoroids, broadening their application scope.

Due to their unique optical properties and ease of integration with existing photonic systems, microtoroids continue to be a focus of research for developing compact, high-performance optical sensors and fundamental studies in light-matter interactions.