In this work, we propose and experimentally demonstrate a novel low-complexity technique for fiber nonlinearity compensation. We achieved a transmission distance of 2818 km for a 32-GBaud dual-polarization 16QAM signal. For efficient implantation, and to facilitate integration with conventional digital signal processing (DSP) approaches, we independently compensate fiber nonlinearities after linear impairment equalization. Therefore this algorithm can be easily implemented in currently deployed transmission systems after using linear DSP. The proposed equalizer operates at one sample per symbol and requires only one computation step. The structure of the algorithm is based on a first-order perturbation model with quantized perturbation coefficients. Also, it does not require any prior calculation or detailed knowledge of the transmission system. We identified common symmetries between perturbation coefficients to avoid duplicate and unnecessary operations. In addition, we use only a few adaptive filter coefficients by grouping multiple nonlinear terms and dedicating only one adaptive nonlinear filter coefficient to each group. Finally, the complexity of the proposed algorithm is lower than previously studied nonlinear equalizers by more than one order of magnitude.
We propose and experimentally demonstrate a novel sub-band multiplexed data architecture for chromatic dispersion (CD) mitigation. We have demonstrated 32 GBaud multi-sub-band (MSB) dual-polarization (DP) 16QAM transmission over 2400 km. Using this approach, the transmitted signal bandwidth is divided into multiple narrow-bandwidth sub-bands, each operating at a lower baud rate. Within each sub-band bandwidth, the CD frequency response can be approximated as a linear-phase band-pass filter, which can be considered as an analog delay that does not require compensation. Therefore, the resulting receiver digital signal processing (DSP) is simplified due to the removal of the CD compensation equalizer. In addition, this leads to efficient parallelization of DSP tasks by deploying multiple independent sub-band processors running at a lower clock rate. The proposed system reduces receiver computational complexity and offers 1 dB higher Kerr-nonlinearity tolerance and 2% extended transmission reach in comparison to the conventional single carrier systems.
Self-coherent detection with interferometric field reconstruction aims at retrieving the complex-valued optical field (amplitude and phase) by digitally processing delay interferometer (DI) measurements, in order to realize a differential direct detection receiver with capabilities akin to that of a fully coherent receiver with polarization multiplexing, albeit without requiring a local oscillator laser in the receiver. Here we introduce a novel digital recursive algorithm capable of accurately reconstructing the optical complex field (both amplitude and phase) solely from the quadrature DI outputs, eliminating the AM photo-detector branch. We analyze a key impairment namely the accumulation of errors and fluctuations in the reconstructed amplitude and phase due to ADC quantization noise, recirculating in the recursion. We introduce signal processing measures to effectively mitigate this noise impairment leading to a potentially practical self-coherent receiver, demonstrated in this paper for a single polarization. We also investigate the range of applicability of self-coherent detection concluding that it is most suitable to relatively low baud-rate systems such as passive optical networks, for which application the self-coherent receiver outperforms the coherent homodyne receiver due to its improved laser noise tolerance, obtained due to the removal of the optical local oscillator.
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