2 research outputs found
Digital signal processing techniques for fiber nonlinearity compensation in coherent optical communication systems
The capacity of long-haul coherent optical communication systems is limited by the
detrimental effects of fiber Kerr nonlinearity. The power-dependent nature of the
Kerr nonlinearity restricts the maximum launch power into the fiber. That results in
the reduction of the optical signal-to-noise ratio at the receiver; thereby, the maximum
transmission reach is limited. Over the last few decades, several digital signal
processing (DSP) techniques have been proposed to mitigate the effects of fiber nonlinearity,
for example, digital back-propagation (DBP), perturbation based nonlinearity
compensation (PB-NLC), and phase-conjugated twin wave (PCTW). However, low-complexity
and spectrally efficient DSP-based fiber nonlinearity mitigation schemes
for long-haul transmission systems are yet to be developed.
In this thesis, we focus on the computationally efficient DSP-based techniques that
can help to combat various sources of fiber nonlinearity in long-haul coherent optical
communication systems. With this aim, we propose a linear time/polarization coded
digital phase conjugation (DPC) technique for the mitigation of fiber nonlinearity
that doubles the spectral efficiency obtained in the PCTW technique. In addition,
we propose to investigate the impact of random polarization effects, like polarization-dependent loss and polarization mode dispersion, on the performance of the linear-coded
DPC techniques. We also propose a joint technique that combines single-channel
DBP with the PCTW technique. We show that the proposed scheme is computationally efficient and achieves similar performance as multi-channel DBP in
wavelength division multiplexed superchannel systems.
The regular perturbation (RP) series used to analytically approximate the solution
of the nonlinear Schrödinger equation (NLSE) has a serious energy divergence problem
when truncated to the first-order. Recent results on the transmission of high data-rate
optical signals reveal that the nonlinearity compensation performance of the first-order
PB-NLC technique decreases as the product of the transmission distance and
launch power increases. The enhanced RP (ERP) method can improve the accuracy of
the first-order RP approximation by partially solving the energy divergence problem.
On this ground, we propose an ERP-based nonlinearity compensation technique to
compensate for the fiber nonlinearity in a polarization-division multiplexed dispersion
unmanaged optical communication system. Another possible solution to improve
the accuracy of the PB-NLC technique is to increase the order of the RP solution.
Based on this idea, we propose to extend the first-order solution of the NLSE to the
second-order to improve the nonlinearity compensation performance of the PB-NLC
technique. Following that, we investigate a few simplifying assumptions to reduce the
implementation complexity of the proposed second-order PB-NLC technique