Adjustable High-Energy Soliton Fiber Laser Based on a Spatial Alignment Structure

We demonstrate a self-starting high-energy erbium-doped soliton fiber laser by utilizing a spatial alignment structure (SAS). The saturable absorption (SA) effect of the SAS is based on the nonlinear coupling efficiency variation. Stable solitons can exist in the 400 mW-1.5 W pump power range. The center wavelength, pulse duration, and repetition rate of the output pulse are 1560.9 nm, 2.75 ps, and 3.9 MHz, respectively. The maximum single pulse energy of 8.67 nJ is obtained by changing the output coupler position, and the pulse energy is almost entirely concentrated in the soliton. Adjusting the alignment condition of SAS can change its SA characteristics, and act as an adjustable attenuator to control the net loss in the cavity. A tunable center wavelength of the soliton pulse, ranging from 1557.4 nm to 1561.2 nm, can be achieved by simply adjusting the mount of collimator. Various types of soliton dynamics processes, including single and double soliton pulse generation, pulsating soliton state with broadened sidebands, and high-order soliton spectrum evolution, have been observed in the experiment. This mode-locking technology based on a SAS opens a promising way for high-energy ultrafast laser.