Wavelength Reuse in a Symmetrical Radio Over WDM-PON Based on Polarization Multiplexing and Coherent Detection With Digital Phase Noise Cancellation

A symmetrical radio over a colorless WDM-PON with wavelength reuse based on polarization multiplexing and coherent detection incorporating digital phase noise cancellation is proposed and demonstrated. For the downlink, two optical signals are intensity-modulated by two 16-QAM downstream microwave vector signals that are polarization multiplexed at the optical line terminal (OLT). The two signals are transmitted to the optical network unit (ONU). At the ONU, one orthogonally polarized optical signal is reused for uplink transmission. One portion of the reused optical signal is phase-modulated by a 16-QAM upstream microwave vector signal, while the other portion is intensity-modulated by another 16-QAM upstream microwave vector signal. Again, the two portions of the optical signals are polarization multiplexed and transmitted back to the OLT. At the OLT, a coherent receiver with digital signal processing (DSP) is used to detect the upstream optical signals. Two DSP algorithms are developed to recover the 16-QAM upstream microwave vector signals. The transmission of two 2.5-Gbps 16-QAM downstream microwave signals and two 2.5-Gbps 16-QAM upstream microwave signals over a 10.5-km single-mode fiber is experimentally demonstrated. The error vector magnitudes (EVMs) for the downstream and the upstream signals are measured to be 7.3%, and 8.65%.