Simultaneous upstream and inter optical network unit communication for long reach PON using single transmitter and self-phase modulation

Abstract

The conventional passive optical network (PON) architecture requires optical line terminal (OLT) arbitration for communication between the optical network units (ONUs). This approach increases OLT processing load, it may also increase security hazards and causes higher communication latency. Moreover this also leads to wastage of bandwidth that can be saved if ONUs are able to communicate directly. The direct communication of ONUs without involving OLT is known as inter ONU communication (IOC). Earlier reported IOC proposals either do not support simultaneous upstream communication or require dedicated or tunable transmitters and receivers for simultaneous communication. This increases the overall cost of the system and also degrades the system performance because of additional tuning delays of the tunable transmitter and receiver. Therefore, this study proposes an IOC enabled physical layer design for PON that supports simultaneous upstream and IOC communication using single transmitter and self-phase modulation mechanism at each ONU. A 1310 nm wavelength, return to zero signal is generated by the transmitter which passes through the self-phase modulator resulting in an additional side lobe signal generation that carries the IOC data without impacting the upstream transmission. These two signals are coupled at the remote node where IOC signal gets reflected back, while the upstream signal gets transmitted through it towards the OLT at the same time. A long reach PON scenario is assumed by keeping the OLT at a distance of 80 km or more. The simulation results show that the proposed design supports a maximum reach of 118 km for upstream link between remote node and OLT with bit error rate of 1.52 × 10−12 for 25 Gbps and 90 km with bit error rate of 7.1 × 10−12 for 30 Gbps data rate. The IOC communication also works well up to a split ratio of 32 with a maximum distance of approximately 5 km between the ONUs and remote node with an end to end bit error rate of 8.60 × 10−12. for 25 Gbps and 7.1 × 10−12 for 30 Gbps. Overall, the proposed design shows acceptable performance, in compliance to ITU G 987.1 recommendations for a maximum end to end reach of 122 km.