Pre-Distortion of Soliton Collision in Dual-Polarization Interaction-Tolerant Soliton Transmission

Nonlinear frequency division multiplexing (NFDM) is an innovative strategy for communication over the nonlinear optical fiber channel. Utilizing the Nonlinear Fourier Transform (NFT) coupled with coherent detection techniques, NFDM encodes and decodes the information on the nonlinear spectrum of signal. For discrete-spectrum modulation, interaction-tolerant (IT) soliton signal has been proposed to enhance the transmission capacity by inducing a group velocity difference between adjacent solitons. Previous study has demonstrated the performance gain of the IT signal in scenario of single-polarization transmission. However, when the discrete spectrum is modulated in dual polarization, the transmission distance is limited by the soliton collisions inherent in the configuration of IT signal. To address this, we derive the explicit formula for the collision distortion on the soliton quantities, utilizing the asymptotic solutions of two-soliton model in the Manakov equation. The formula reveals that the distortion is determined by the polarization angle and polarization differential phase of two solitons. To mitigate the symbol-dependent distortion on the quantities, a pre-distortion scheme is proposed to cancel the collision distortion, incorporating with a detection scheme by using the asymptotic solution. Numerical results indicate the notable performance enhancement of the IT signals incorporating the proposed pre-distortion scheme, in comparison with the normal soliton signals.