Fiber Nonlinearity and Tight Filtering Impairments Mitigation of DP-16QAM Nyquist-WDM Systems Using Multiplier-Free MAP Detection

Tight filtering and fiber Kerr effect both cause severe pattern-dependent distortions that need to be combated to achieve higher spectral efficiency (SE), larger capacity and greater achievable transmission distance in the next generation wavelength division multiplex (WDM) optical transmission system. In this paper, a novel multiplier-free maximum-a-posteriori-probability (MAP) detection scheme is proposed and verified in dual-polarization (DP) 16-ary quadrature amplitude modulation (16-QAM) Nyquist-WDM systems. Based on the innovative technique of approximate calculation of Euclidean distance, the competitive performance is obtained in terms of pattern-dependent impairments mitigation. Besides, the computational complexity (CC) is drastically reduced to about 34%, as the multiplier of the proposed MAP detection is completely removed. Comprehensive simulation results of triple-carrier Nyquist DP 16-QAM demonstrate that the MAP scheme could effectively mitigate the tight filtering and fiber nonlinearity impairments with much lower CC, i.e., achieve desirable SE and nonlinearity tolerance in long-haul transmissions. In addition, a 1.1 dB reduction of the required OSNR and 2.6 dB launch power range extension are observed in the triple-carrier 480 Gb/s Nyquist DP 16-QAM back-to-back and 700 km transmission experiments, respectively. The advantages of the proposed low-complexity MAP scheme make it a preferable impairment mitigation technique for practical Nyquist-WDM systems.