High-pulse-energy mode-locked and Q-switched large-mode-area thulium fiber laser

Abstract

A 2μm large-mode-area (LMA) Tm-doped fiber laser passively mode-locked and Q-switched with a semiconductor saturable absorber mirror (SESAM) is reported. Based on the combination of spatial-mode-filtering from the SESAM’s feedback and spectral-mode-selection of a few-mode fiber Bragg grating (FBG), near-fundamental-mode is selected out. Continuous-wave mode-locking (CWML) is achieved through elaborately adjusting the state of the SESAM. The CWML pulses operate at a repetition rate of 16.6 MHz with an average power of 0.87 W, pulse duration of 17 ps and pulse energy of 52.4 nJ. By tuning the SESAM closer to the fiber end, Q-switched mode-locking (QSML) operation is realized. In the Q-switching state, maximum average power of 1.67 W is achieved with shortest pulse duration of 1.55μs and maximum pulse energy of 29.2 μJ at the maximum repetition rate of 57.1 kHz. Such passively modulated LMA thulium fiber laser thus provides a promising platform to generate near-fundamental-mode high-energy 2-μm pulses in both the picosecond and microsecond regimes.