<p>This study examines polarization evolution in a single-mode fiber using a two-section model and uniform twists. By considering nonlinear phenomena including optically induced birefringence, cross-phase modulation, and self-phase modulation, we used the coupled nonlinear Schrödinger equations governing the propagation of continuous waves through the two fiber sections. These equations are numerically solved using the Runge–Kutta method for two different cases: without and with nonlinear effects. The results indicate that the amplitude of the ellipticity oscillations depends on the twisting rate, but not on the birefringence of the fiber sections. Specifically, the amplitude of the ellipticity fluctuations decreases as the twisting rate increases. Furthermore, twist has a greater impact on polarization behavior in twisted fibers than birefringence. While nonlinear phenomena in fibers with high twist rates are negligible, they significantly affect polarization in the fibers with lower twist rates. The results of this study provide useful insights into predicting the output polarization state in transmission fibers composed of multiple sections.</p>