In this paper through the basic components of fiber optic communication, a novel transmission system for seamless integration of ROF (Radio Over Fiber) with centralized lightwave OFDM-PON based on an integrated external modulator is demonstrated. Here we have investigated the transmission performance of a modulation based on a proposed technique of Orthogonal Frequency Division Multiplexing (OFDM) for Next-Generation Passive Optical Network (NG-PON). The signal is generated by direct modulation of cost-effective and low bandwidth commercially available CW Lasers of 193.1 THz. The Downstream OFDM-PON transmission (5 Gbits/sec total, 2.5 Gbits/sec for each user) are experimentally demonstrated over a 50 km standard single mode fiber and additionally simulated through 1: 2 splitter. And finally experimental results are analyzed based on optical signal spectrum in time-domain and compared with numerical results for different QAM (Quadrature Amplitude Modulation) and PSK (Phase Shift Keying) modulation schemes to demarcate concluding statements.