Self-Q-switched Yb<sup>3+</sup>-doped All-fiber Laser Based on the Saturable Absorption Effect of a Multimode Fiber

A self-Q-switched Yb<sup>3+</sup>-doped all-fiber laser based on the saturable absorption effect in multimode communication fiber was investigated. The laser used an 11m long Yb<sup>3+</sup>-doped double-clad fiber as the gain medium. The high-reflection end of the resonator employed a fiber Bragg grating with a center wavelength of 1083nm, while the output end was the cleaved end-face of the gain fiber. A segment of multimode communication fiber was spliced to the output end of the resonator to act as a saturable absorber, enabling self-Q-switched pulse operation. Under a pump power of 5.3W, the laser achieved stable self-Q-switched pulse operation with a repetition rate of 46kHz, a single pulse energy of 13µJ, and a pulse width of 2.8µs. The influence of the multimode fiber length on the output pulse characteristics was also studied. It was found that optimal Q-switching performance was obtained with a 3.3m long multimode fiber. Meanwhile, the experiment employed custom-built air-cooling and thermo-electric cooler systems to independently control the temperatures of the two diode lasers, with both systems achieving a temperature control precision of ±0.1°C. Furthermore, a qualitative analysis was conducted to investigate the mechanism of self-Q-switched pulse generation utilizing the saturable absorption effect in multimode fiber. This self-Q-switched all-fiber laser features a simple structure, low cost, and high stability, showing promising application prospects in scientific research, material processing, and lidar.