In this work, a record of 16 channels, with future channel spacing in the telecommunication standardization sector of the International Telecommunications Union G.694.1 (ITU-T G.694.1) for Dense Wavelength Division Multiplexing (DWDM) (i.e., 12.5 GHz), is simulated and tested. This work is done to realize a proposed high capacity DWDM-Passive Optical Network (DWDM-PON) system. These specifications are associated with enhancing the upstream (US) capacity to 2.5 Gb/s over a 25 km Single-Mode Fiber (SMF) transmission and producing a noteworthy average Bit Error Rate (BER) of 10 −12 during the system's evaluation process. These performance indicators are achieved through design optimization of the cross-seeding Rayleigh Backscattering (RB) elimination technique. This optimization has successfully reduced (compared to the cross-seeding related literature) the simulated DWDM-PON components and maintained an effective Rayleigh Backscattering elimination with the aforementioned system's performance enhancement and capacity enlargement.(1) injection-locked Fabry-Perot Lasers (FP-Ls) [5,6], (2) Reflective Semiconductor Optical Amplifiers (RSOAs) [7], and (3) Semiconductor Optical Amplifier (SOAs) with Reflective Electro-Absorption Modulators (R-EAMs) [8]. However, reflective transmitters that utilize FP-L require polarization and temperature control, which add complexity [5]. Those that use RSOAs suffer from a limited bit ratẽ 1.25 Gb/s due to internal noises and nonlinearities [9]. Finally, any colorless ONU that uses SOA with R-EAM (SOA-REAM) suffers from chromatic dispersion and high interference in the signal due to the wide bandwidth of R-EAM [10]. As a result, the reflective transmitter technique generates a high level of Rayleigh Backscattering (RB), which affects the signal received at the CO [11]. Before reviewing the DWDM-PON system's key requirements, it is useful to conduct a review of the origins and effects of RB. Rayleigh Scattering is a dominant intrinsic loss mechanism in the low-absorption window between the ultraviolet and infrared absorption tails. It results from random inhomogeneities occurring on a small scale compared to the operating wavelength. These inhomogeneities act as refractive index fluctuations (or induced dipole moment) within the fiber and arise from density and compositional variations, which are frozen into the glass lattice upon cooling [12,13].Optical losses, due to RB in optical fibers, have caused considerable problems. Some examples of these problems include lowering the allowable bit rate, increasing the system's noise levels, and minimizing the transmission distances [14][15][16][17]. Detailed examples and deeper analyses can be found for bi-directional wavelength-reuse fiber systems and WDM-PON Systems in [14][15][16][17]. To the author's best knowledge, this work is one of the rare studies that considers RB for DWDM-PON systems with remarkable operating conditions. Now, methods for satisfying the most critical requirements for DWDM-PON systems (i.e., a low-cost ONU colorless o...