Ultrafast fiber laser at 0.9 µm with a gigahertz fundamental repetition rate by a high gain Nd<sup>3+</sup>-doped phosphate glass fiber
Yafei Wang, Jing Zhang, Junpeng Wen, Baotian Qiu, Jianrong Qiu, Zhongmin Yang, Xiaoming Wei, Guoping Dong
Abstract
Fiber lasers, owing to the advantages of excellent beam quality and unique robustness, play a crucial role in lots of fields in modern society. Developing optical glass fibers with superior performance is of fundamental importance for wide applications of fiber lasers. Here, a new Nd 3+ -doped phosphate single-mode fiber that enables a high gain at 0.9 µm is designed and fabricated. Compared to previous Nd 3+ -doped silica fibers, the developed phosphate fiber exhibits a significant gain promotion, up to 2.7 dB cm −1 at 915 nm. Configuring in a continuous-wave fiber laser, this phosphate fiber can provide a slope efficiency of 11.2% in a length of only 4.5 cm, about 6 times higher than that of Nd 3+ -doped silica fiber. To showcase its uniqueness, an ultrafast fiber laser with ultrashort cavity is constructed, such that an ultrashort pulse train with a fundamental repetition rate of up to 1.2 GHz is successfully generated. To the best of our knowledge, this is the highest fundamental repetition rate for mode-locked fiber lasers at this wavelength range — two orders of magnitude higher than that of prior works. These results indicate that this Nd 3+ -doped phosphate fiber is an effective gain medium for fiber amplifiers and lasers at 0.9 µm, and it is promising for two-photon biophotonics that requires long-term operation with low phototoxicity.