Image Credit: GUGAI/Shutterstock.comBackgroundThe foundation of ultrafast pulse generation in fiber lasers relies on harnessing nonlinear effects within the laser cavity. On the other hand, polarization-based nonlinear effects, such as nonlinear polarization rotation (NPR) and nonlinear polarization evolution (NPE), take advantage of Kerr-induced changes in the pulse’s polarization state as it travels through the fiber. Studies Highlighted in this ReviewThe review explores a range of techniques for generating ultrafast pulses by combining nonlinear optical effects with advanced control strategies. Nonlinear polarization rotation (NPR) and nonlinear polarization evolution (NPE) exploit the intensity-dependent Kerr effect to induce phase shifts in the polarization state of the light inside the cavity. Meanwhile, nonlinear polarization techniques such as nonlinear polarization rotation (NPR) and nonlinear polarization evolution (NPE) have enabled access to a wide range of pulse durations, including sub-100-femtosecond regimes, while supporting high repetition rates.