An efficient non-invasive method to fabricate in-fiber microcavities using a continuous-wave laser

In-fiber microcavities are usually fabricated by inva-sive methods that require costly setups and time-consuming processes. Inspired by the fiber fuse effect, we propose an efficient non-invasive method to fabricate in-fiber microcavities. The setup of the method was economic, using a watt-level continuous-wave laser. Spherical in-fiber microcavities of ~hundred-of-micron sizes could be fabricated and freely integrated in fibers. The fabrication rate was seconds-per-microcavity, being hundreds of times faster than previous methods. The microcavities could have ~1-micron-thin cavity walls and ~104 high quality factors as Fabry-Perot reso-nators. The method offers many unique features for microcavities and can be useful for large-scale fabrication. It can benefit many applications such as sensing and nonlinear frequency generation.