This study presents a simulation-based analysis to optimize the performance of Reflective Semiconductor Optical Amplifier-based Colorless Optical Network Units in Dense Wavelength Division Multiplexing Passive Optical Networks. Using OptiSystem software, we determined an optimal extinction ratio of 1.75, ensuring balanced performance for both downstream and upstream transmissions. We recommend a reflective Semiconductor Optical Amplifier bias current below 200 mA to minimize bit error rate while extending device lifespan. The impact of four-wave mixing in ultra-dense Wavelength Division Multiplexing systems with 6.25 GHz channel spacing was involved, confirming the feasibility of supporting up to 80 channels over 20 km of single-mode fiber. This work introduces a novel approach by optimizing extinction ratio and bias current simultaneously while involving four-wave mixing effects in ultra-dense Wavelength Division Multiplexing Passive Optical Networks, offering a cost-effective, scalable solution for high-capacity optical access networks. The analysis addresses challenges of residual data, four-wave mixing, and signal-to-noise ratio degradation, ensuring robust performance for next-generation Passive Optical Networks.