Highly directional output from long-lived resonances in optical microcavity.

We report a simple and robust mechanism that can result in highly directional emission from long-lived resonances in microcavities. By placing a nanoparticle (NP) into the evanescent wave region of microcavities, highly directional outputs with divergence angle ~1.9°-10° can be obtained in single or double directions. The perturbation of NP on evanescent waves preserves the high-quality (Q) factors, and the collimation of microcavities generates the highly directional outputs. Our numerical simulations show that this mechanism is very robust to the size of NP and the refractive index/separation distance/size of microcavities.