In line with Our World in Data analysts’ Internet user growth statistics, the exponential growth of user data and customer demands for high-quality data transmission speeds drive demand for next-generation (NG) access networks — fiber optic access networks with improved parameters. This paper evaluates the performance of (DB) and non-return to zero (NRZ) modulation formats widely spread in wavelength division multiplexed passive optical networks (WDM-PONs). Within wavelength division multiplexing (WDM) transmission systems, forward error correction methods have emerged as most indispensable techniques for enhancing data transmission reliability and bolstering service quality (QoS). The paper’s authors also compare different FEC codes, due to its abilities to attain the lowest bit error ratio (BER) as possible. Alongside FEC code utilization and digital equalization, methods enhance the performance of WDM-PON systems by smoothening the system’s imperfection. This paper studies the efficiency of WDM-PON systems with 8 and 16 channels by implementing FEC techniques such as Reed-Solomon (RS) with 6.69% and 8.5% overheads (OH). These codes are employed for long haul data transmission systems as described in ITU-T G.975 standardization. This paper evaluates the performance of 8 and 16-channel DB, and NRZ modulated WDM-PON transmission systems with 100 GHz spacing, each operating at data rates of 10, 20 and 40 Gbit/s (for each channel), utilizing ITU-T G.652 standardization-corresponding optical link section.