Long reach UDWDM PON with direct and coherent detection

The wavelength division multiplexed passive optical network (WDM PON) is a promising technology for next generation access networks as it provides greater bandwidth to the home, enhanced security and increased reach. One of the major obstacles to the adoption of the WDM PON architecture is the associated capital and operational expenditure required to implement such a distribution access network. However, substantial cost savings and network simplification can be achieved by adopting the long reach ultra-dense WDM PON (LR UDWDM PON), which improves the physical reach of the conventional PON. Additionally, WDM-PON technology can be combined with advanced modulation formats to increase the information spectral density, thereby improving the overall efficiency of the network. However, there are significant obstacles to the widespread deployment of WDM PONs, such as the high cost and energy consumption of current Optical Line Terminal (OLT) transmitters and Optical Network Unit (ONU) receivers. The authors present a few different types of multi-carrier transmitters and their performances when employed in a next generation access network. A WDM PON architecture is adopted and each of the multi-carrier tones is imposed with higher order modulation formats such as QPSK, 16QAM (experimental set-up as in Fig. 1) and OFDM (experimental set-up as in Fig. 2). The authors also present a performance comparison between the commonly used coherent detection scheme and a novel receiver architecture based on a pilot tone aided direct detection scheme.