200 G bidirectional simplified coherent PON with a single DFB at the ONU side

As the demand for higher bandwidth in fiber optic access networks grows, passive optical network (PON) technology is evolving to support higher data transmission rates. Conventional intensity modulation and direct detection (IM-DD) methods encounter limitations in terms of bit rate and power budget. As a result, coherent technology is becoming a viable alternative to overcome these challenges. In this paper, we demonstrate a 200-Gb/s bidirectional time-and-frequency division multiplexing (TFDM) PON based on digital subcarrier multiplexing (DSCM) technology. A single distributed feedback laser (DFB) is used at the optical network unit (ONU) side, acting as a local oscillator (LO) to receive a downstream signal and also as a carrier to transmit an upstream signal. A 50-Gbaud Alamouti-coded 16 quadrature amplitude modulation (QAM) downstream signal and a 35-Gbaud single-sideband (SSB) single-polarization (SP) 64QAM upstream signal is employed to achieve bidirectional 200-Gb/s transmission. We also demonstrate a hybrid and flexible rate in upstream transmission, achieving data rates from ∼50 to ∼200-Gb/s based on SP-4/16/64QAM modulation. The experimental results show that the power budget can achieve 29-dB after a 20-km standard single-mode fiber (SSMF) link for both 200 G downstream and upstream transmission.