A Single-Photodiode Coherent ONU Receiver for 25G Line-Rate PON Application

Passive optical network (PON) employing coherent receiver is a promising technology for future high-speed optical access network. However, the commonly used phase and polarization diverse coherent receiver for long-haul communication is not suitable for cost stringent access network. Therefore, low-complexity (and thereby low-cost) coherent receiver design for access network becomes an attracting research field in current years. In this paper, we propose a simple heterodyne single-polarization coherent receiver by using a 3-dB coupler and a single-ended photodiode to realize a 25-Gb/s optical network unit (ONU) receiver. To make the receiver polarization-insensitive, Alamouti-coded dual polarization 14-Gbaud QPSK transmitter is used at the optical line terminal (OLT) side. By means of computer simulation, it is confirmed that the proposed ONU receiver allows a high split ratio of 1:512 for 30-km transmission length whereas a lower splitting ratio of 1:16 enable the use of long-reach PON (LR-PON) of 100 km.