Space variant fiber nanogratings induced by femtosecond laser direct writing

Light-matter interaction within ultrashort duration time contributes to the nonlinear photoionization that allows diverse nanostructures, especially subwavelength nanogratings, which comprises strong negative birefringence and recently chiroptic properties. Fiber nanograting, namely nanograting integrated in optical fibers, encountering the new possibility of realizing both "lab-on-fiber" and "lab-in-fiber" engineering, is leading to a novel and intriguing topic in ultrafast optics and integrated optics. However, the state-of-the-art fiber nanograting based technologies normally focus on the unidirectional distributions of nanogratings, which restricts the freedom of functionality. Here, we report a full control of the fiber nanogratings orientation by manipulating the laser polarization and a tailoring of space variant fiber nanogratings to extend the diversity towards on-demand fiber nanogratings engineering. As such, we believe that this will be beneficial for optical manipulation in fiber lasers, fiber communications and fiber based integrated systems.