Upstream Power Budgets of IMDD Optical OFDMA PONs Incorporating RSOA Intensity Modulator-Based Colorless ONUs

In aggregated 11.25 Gb/s over 25 km SSMF intensity-modulation and direct-detection (IMDD) optical OFDM multiple access passive optical networks (OOFDMA PONs) incorporating colorless ONUs based on reflective semiconductor optical amplifier (RSOA) intensity modulators, excellent agreements are obtained between real-time upstream experimental measurements and numerical simulations for various system operating conditions. Making use of experimentally verified theoretical models and component/system parameters, extensive numerical explorations are undertaken, for the first time, of the impact of the number of ONUs on both upstream optical power budget and minimum ONU wavelength spacing required for eliminating the optical beat interference effect. It is shown that the minimum ONU wavelength spacing is independent of the number of ONUs, and that doubling the number of ONUs simultaneously accommodated in the aforementioned PON architectures gives a 1.9 dB reduction in upstream power budget. Results also show that the utilization of an optimum frequency-offset super-Gaussian optical filter at an order of 5 immediately after the RSOA intensity modulator in each ONU can significantly improve the upstream power budget by >5.3 dB, and simultaneously enhance the upstream power budget robustness to variations in the number of ONUs.