Optical microcavities with tubular geometry: properties and applications

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.