Phase optimization approach to control high peak-to-average power ratio in a second-order soliton-based NFDM system

Fiber-optic communication is an emerging technology that enables high-capacity data transmission using light waves. However, the inherent nonlinearity of the optical fiber limits the attainable capacity. As a result, nonlinearity compensation has become a significant focus in optical fiber communication, for which nonlinear frequency-division multiplexing (NFDM) is an effective solution. The signals generated in an NFDM system are fundamentally optical soliton signals and hence undergo the effect of multi-soliton periodicity. But this results in a higher signal peak-to-average ratio (PAPR) at the receiver front end of NFDM systems, negatively impacting system performance. This paper proposes a phase pre-equalization using optimal phase factors to reduce the high PAPR at the receiver. This technique jointly optimizes the transmitter and receiver, thereby reducing the large PAPR margin. Pre-equalization also results in better error performance. Analysis shows that using this technique, the NFDM system is less sensitive to perturbation. A maximum data rate of 24 Gbps is obtained for 1000 km with a 2-eigenvalue, pre-equalized unilateral spiral 8-quadrature amplitude modulation (QAM) NFDM system model, and 24.67 Gbps is obtained for 1000 km with a 2-eigenvalue, pre-equalized spiral 16-QAM NFDM system model. The maximum transmission distance extends to 2150 km for a data rate of 10 Gbps.