This research presents a study to evaluate the effect of polarization mode dispersion (PMD) on fiber optic transmission systems using performance metrics such as quality factor (Q-Factor) and bit error rate (BER). The results of the (Q-Factor) and (BER) were evaluated for the system duty cycle (D) variable. The system duty cycle (D) is a crucial metric in fiber optic systems، as it indicates the pulse width relative to the total bit duration used in modulation modes. Variations in the system duty cycle (D) significantly impact system efficiency. This study demonstrated that this variable affects the performance and quality of transmission systems. The results showed that as the system's duty cycle (D) increases، the quality factor (Q-Factor) decreases and the bit error rate (BER) increases. Therefore، it is crucial to consider the impact of the system's duty cycle (D) when designing and implementing an optical communication system.................. Keywords:.............. Polarization Mode Dispersion (PMD), Duty Cycle, Optical Wave Carrier, the Waveguide, Modulation, (Bit Error Rate (BER), Q-Factor