Wavelength Reuse in a Symmetrical Radio Over WDM-PON Based on Polarization Multiplexing and Coherent Detection

A symmetrical radio over a colorless wavelength-division multiplexing passive optical network with wavelength reuse based on polarization multiplexing and coherent detection incorporating digital phase noise cancellation is proposed and experimentally demonstrated. For the downlink, two optical signals are intensity modulated by two different 16-QAM downstream microwave vector signals that are polarization multiplexed at the optical line terminal (OLT). Then, the two orthogonally polarized optical signals are transmitted to the optical network unit (ONU). At the ONU, one of the two orthogonally polarized optical signals is selected to be reused for the uplink transmission. Then, the reused optical signal is split into two channels by a 3-dB coupler. 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 a digital signal processing (DSP) unit is used to detect the upstream optical signals. Two DSP algorithms are developed to recover the two 16-QAM upstream microwave vector signals. The transmission of two 2.5-Gb/s 16-QAM downstream microwave vector signals and two 2.5-Gb/s 16-QAM upstream microwave vector signals over a 10.5-km single-mode fiber is experimentally demonstrated. The error vector magnitudes for both the down and upstream transmissions are measured to be 7.3% and 8.65%, which are good enough to achieve error-free transmission with forward error correction.