GHz-level all-fiber harmonic mode-locked laser based on microfiber-assisted nonlinear multimode interference

Light-matter interaction can be strongly enhanced in tiny core fibers, and it holds significant potential for stable harmonic mode-locking at gigahertz and a higher repetition rate. In this paper, we propose and demonstrate a GHz harmonic mode-locked fiber laser based on a microfiber-assisted nonlinear multimode interference (NL-MMI), which is achieved by the enhanced mode-filtering of nonlinear self-imaging in multimode fiber with a waist diameter of 12μ m. A stable mode-locked is achieved with a repetition rate of 1.26 GHz at 1560.15 nm, corresponding to the 22nd harmonic of the fundamental frequency. Our results provide new insight into implementing high repetition frequency mode-locking fiber lasers.