A Passively Mode-Locked Fiber Laser Only Based on D-Shaped Fiber

A passively mode-locked fiber ring laser only based on one section of D-shaped fiber is proposed, where the nonlinear polarization rotation mechanism arises without polarizer or wave plate. By increasing the pump power, mode locking is self-started, a laser pulse with a repetition rate of 6.04 MHz is generated, and its evolutions of temporal, spectral, and polarization properties under different pump powers are discussed.