Digital all-optical Physical-layer Network Coding for 2Gbaud DQPSK signals in mm-wave radio-over-fiber networks

We propose the first digital All-Optical Physical-layer Network Coding (AOPNC) scheme for up to 2Gbaud Differential Quadrature Phase Shift Keyed - Sub-Carrier Modulated (DQPSK-SCM) signals in future Radio-over-Fiber (RoF) networks. The proposed encoding unit employs Delay Interferometers (DIs) for the DQPSK-to-OOK conversion, a first stage of Semiconductor Optical Amplifier-Mach Zehnder Interferometers (SOA-MZIs)as optical OOK-XOR and OOK-NXOR logic gates, and a second stage of SOA-MZIs as phase regenerators of the final four-level phase-formatted encoded signal. The proposed encoding operation is performed on-the-fly at the Central Office (CO) and the resulting packet is broadcasted at the end-users, where the electrical decoding takes place. The proof of concept scheme is demonstrated for 4 Gb/s Non-Return-to-Zero (NRZ) DQPSK-SCM signals modulated on a 60 GHz Sub-Carrier (SC). The encoding and decoding operation are investigated and evaluated, achieving error free operation for both synchronous and asynchronous data.