Hardware-Efficient, Ultra-Fast and Joint Polarization and Carrier Phase Tracking Scheme Based on Frequency Domain Pilot Tones for DSCM Systems

The coherent digital subcarrier multiplexing (DSCM) has recently been proposed as a cost saving solution to realize flexible and scalable point-to-multipoint (PTMP) networks. In this work, a hardware-efficient, ultra-fast and joint polarization and carrier phase tracking scheme for the DSCM systems based on frequency domain pilot tones (named as PTJ) is proposed and demonstrated via both simulations and experiments. By extracting the amplitude and phase of the pilot tones with a low-pass filter (LPF), the transmission matrix of random birefringence and carrier phase can be obtained prior to subcarrier demultiplexing and channel equalization. For the hardware-efficient implementation, a simplified LPF based on sliding window averaging (SWA) is proposed to filter out the pilot tones. Compared to previous scheme using pilot tones to track polarization and carrier phase in a cascaded manner (named as PTC), our proposed scheme shows better BER performance over wide polarization rotation rates and reduces more than 90% of computation resources by the SWA and joint tracking of polarization and carrier phase. The experimental results show that the proposed scheme can track polarization rotation rate up to 20 Mrad/s with the OSNR penalty of 0.2 dB at 7% FEC threshold. This indicates that an OSNR sensitivity gain of 2.8 dB is achieved compared with the PTC scheme. The proposed scheme provides a hardware-efficient and fast-tracking solution to recovery the polarization and carrier phase for digital subcarrier multiplexing (DSCM) and polarization division multiplexing (PDM) based optical fiber communication system.