Microfibers with diameter ranging from several hundred nanometers to several micrometers have many advantages to make it an open platform for miniaturization and integration of fiber-optic devices. These advantages include large evanescent field, high nonlinearity, strong light confinement, great configurability and low-loss connection to other fiberized components. The functions and applications of microfibers can be greatly expanded by using various functional materials and microstructures, and harnessing the fruitful intrinsic nonlinearities. In particular, by integration of multiple functions in a single microfiber, lab on a fiber can be achieved. In this article, we summarize the recent progress in the microfibers research, covering fundamental characteristics of microfibers, implementation of several crucial devices, integration of external materials and applications of microfiber-based devices.
