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Register a new userCrosstalk Impacts on Homogeneous Weakly-Coupled Multicore Fiber Based IM/DD System
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We numerically discussed crosstalk impacts on homogeneous weakly-coupled multicore fiber based intensity modulation/direct-detection (IM/DD) systems taking into account mean crosstalk power fluctuation, walk-off between cores, laser frequency offset, and laser linewidth.
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To analyze a homogeneous weakly coupled multicore fiber (WC-MCF) based transmission system via simulation, we propose an efficient (fast and accurate) WC-MCFs channel model, which can describe the propagation effects including attenuation, walk-off, chromatic dispersion, self-phase modulation (SPM), and especially the frequency-dependent inter-core crosstalk (XT). We speed up the simulation with two orders of magnitude by simplifying the XTs calculation. On one hand, the calculation step size can be greatly increased by utilizing a new XTs coupling matrix. On the other hand, the calculation of XT can be further accelerated by down-sampling XTs coupling matrix in frequency domain. The XT power and average occurrence distance should be set manually based on the existing XT model to describe the frequency-dependent XT the same as a real WC-MCF. We numerically and experimentally observed that XTs de-correlation bandwidth decreases with relative time delay (RTD) by fractional linear function. The range of validity of the proposed channel model is also discussed with different walk-off and coupling strength. We believe the proposed efficient channel model can provide great help for analysis and optimization of homogeneous WC-MCF based optical communication systems.
We investigate the evolution of decorrelation bandwidth of inter core crosstalk (IC-XT) in homogeneous weakly coupled multicore fibers (WC-MCFs). The modified mode-coupled equations (MCEs) are numerically solved by combining the fourth order Runge-Kutta method and compound Simpson integral method. It can be theoretically and numerically observed that the decorrelation bandwidth of IC-XT decreases with transmission distance by fractional linear function. The evolution rule of IC-XTs decorrelation bandwidth is further confirmed by experiments, which can be used as an evaluation criterion for channel model. Finally, we propose a new channel model with the coupling matrix of IC-XT generated automatically by phase transfer function (PTF), which is in good agreement with the above evaluation criterion. We believe the proposed channel model can provide a good simulation platform for homogeneous WC-MCF based communication systems.
Probabilistic constellation shaping (PCS) has been widely applied to amplified coherent optical transmissions owing to its shaping gain over the uniform signaling and fine-grained rate adaptation to the underlying fiber channel condition. These merits stimulate the study of applying PCS to short-reach applications dominated by intensity modulation (IM) direct detection (DD) systems. As commercial IM-DD systems typically do not employ optical amplification to save the cost and power consumption, they are no longer subject to an average power constraint (APC) but a peak power constraint (PPC), which poses unique challenges to take full advantages of PCS. This paper provides a comprehensive investigation of PCS in IM-DD systems without optical amplifiers. In particular, we reveal that if the transmitter enhances the peak-to-average power ratio of the signal, a PPC system can be partially or even fully converted to an APC system in which the classical PCS offers its merits. The findings are verified through an IM-DD experiment using 4- and 8-ary pulse amplitude modulations.
We experimentally demonstrate the impact of inter-core crosstalk in multicore fibers on 56Gbaud PAM-4 signal quality after 2.5-km transmission over a weakly-coupled and uncoupled sevencore fibers, revealing the crosstalk dependence on carrier central wavelength in range of 1540-1560 nm.
We investigate approaches to reduce the computational complexity of Volterra nonlinear equalizers (VNLEs) for short-reach optical transmission systems using intensity modulation and direct detection (IM/DD). In this contribution we focus on a structural reduction of the number of kernels, i.e. we define rules to decide which terms need to be implemented and which can be neglected before the kernels are calculated. This static complexity reduction is to be distinguished from other approaches like pruning or L1 regularization, that are applied after the adaptation of the full Volterra equalizer e.g. by thresholding. We investigate the impact of the complexity reduction on 90 GBd PAM6 IM/DD experimental data acquired in a back-to-back setup as well as in case of transmission over 1 km SSMF. First, we show, that the third-order VNLE terms have a significant impact on the overall performance of the system and that a high number of coefficients is necessary for optimal performance. Afterwards, we show that restrictions, for example on the tap spacing among samples participating in the same kernel, can lead to an improved tradeoff between performance and complexity compared to a full third-order VNLE. We show an example, in which the number of third-order kernels is halved without any appreciable performance degradation.
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