Unbalanced impairments compensation for low cost direct detection OFDM-PON systems

A simple high spectral efficiency directly-detected frequency guard band (FGB) free optical orthogonal frequency division multiplexing (OOFDM) system is proposed for passive optical network (PON) in this paper. The two main impairments, subcarriers mixing interference (ISMI) caused by square-law detection and frequency selective fading (FSF) deduced from the double side band modulation are mathematically analyzed. To reduce the performance deterioration, static adaptive modulation (SAM) and turbo codes are proposed in this system. A high spectral efficiency FGB-free DD-OOFDM system with 64-QAM (qadrature amplitude modulation) for subcarrier modulation is experimentally demonstrated. Thank to the static adaptive modulation and turbo codes implemented in the digital signal process domain, the system shows its significant robustness to both ISMI and FSF.