Review of femtosecond laser direct writing fiber-optic structures based on refractive index modification and their applications

Abstract Femtosecond (fs) laser pulses direct writing technology has been extensively employed to achieve microfabrication in various optical fibers for a broad range of applications. In this paper, the latest development of fiber-optic structures based on refractive index (RI) modification under fs-laser irradiation and their applications are reviewed. Firstly, the processing mechanism of fs-laser direct writing for optical fiber RI modification is described. And then, the fiber-optic structures including various fiber gratings and interferometers based on RI modification are summarized. It shows that the fs-laser direct writing technology has great advantages in the fabrication of various fiber structures with excellent properties. Furthermore, the applications of these RI-modified fiber-optic structures in sensors, lasers, birefringence adjustable elements, and couplers are also discussed. To conclude, the performances of RI-modified structures and their applications are presented and compared.