To address the application bottlenecks of bright laser pulses in optical communications and fiber optic sensing, a mode-locked fiber ring laser based on semiconductor optical amplifiers（SOA） is designed. This laser consists of an SOA, a polarization controller, a filter, and a polarizer. The mechanism of the gain ratio and phase difference changes in transverse electric/transverse magnetic（TE/TM） mode optical fields when passing through SOA is analyzed. The relationship between total dispersion management within the ring cavity and dynamic gain of SOA is investigated, resulting in stable output of bright pulses and dark pulses, as well as the dynamic evolution process of both types of pulses. The experimental results show that when the operating current of SOA is 242 mA, bright pulses with a pulse width of 1.1 ns and dark pulses with a pulse width of 0.95 ns are successfully obtained at repetition rates of 14.83 MHz, respectively. It is also verified that under the same operating current conditions, the intensity of the dark pulses significantly exceeds that of the bright pulses.