Optical microcavities with tubular geometry: properties and applications

Abstract Optical microcavities with whispering‐gallery modes (WGMs) have large potential and, in particular, those with a tubular geometry have attracted increasing attention due to their special geometry and interesting properties such as trimmed resonant modes, simplicity as fluidic channels, three‐dimensionally (3D) mode confinement, unique evanescent wave, and so on. Optical microcavities with the tubular geometry meet the challenge of assembly of conductive, semiconductive and insulating materials into a tubular geometry, thus spurring multifunctional applications to optofluidic devices, optical microdevices like microlasers, and bio/chemical sensors. Fabrication methods such as the fiber‐drawing method, rolled‐up nanotechnology, electrospin technique, and template‐assistant method have been developed to address the various requirements. These tubular optical microcavities enable researchers to explore and construct novel optical microdevices for a wide range of potential applications. This review describes the tubular optical microcavities from the perspectives of theoretical consideration, optical characterization, and potential applications.