Abstract
The optimisation of span length when designing optical communication systems is important from both performance and cost perspectives. In this paper, the optimisation of inter-amplifier spacing and the potential increase of span length at fixed information rates in optical communication systems with practically feasible nonlinearity compensation schemes have been investigated. It is found that in DP-16QAM, DP-64QAM and DP-256QAM systems with practical transceiver noise limitations, single-channel digital backpropagation can allow a 50% reduction in the number of amplifiers without sacrificing information rates compared to systems with optimal span lengths and linear compensation.
Highlights
The increasing information rate demands on optical fibre links require Nyquist-spaced wavelength division multiplexing (WDM) and high order dual-polarisation quadrature amplitude modulation formats (DP-QAM) [1]
We examine the mutual information (MI) as an indication of information rates [15] when the span length is varied in practical WDM systems with erbium doped fibre amplifiers (EDFAs) and transmitter and receiver limited in SNR performance
The span length design choice issue raised by single-channel DBP, which is a feasible digital nonlinearity compensation technique, was studied in terms of information rates for different modulation formats considering practical transceiver limitations
Summary
The increasing information rate demands on optical fibre links require Nyquist-spaced wavelength division multiplexing (WDM) and high order dual-polarisation quadrature amplitude modulation formats (DP-QAM) [1]. Due to the trade-off between the amplified spontaneous emission (ASE) noise from optical amplifiers and the nonlinear distortions in fibres there is a non-trivial optimal span length It has been studied in terms of energy optimisation [11,12], nonlinear phase shift in hybrid Raman-EDFA-amplified on-off keying systems [13], and Q-factor in quadrature phase-shift keying (QPSK) ultra-long haul submarine systems [14]. For the first time to our knowledge, the maximum achievable MI at optimal span lengths has been studied both with and without the use of nonlinearity compensation They show that for DP-16QAM, DP-64QAM and DP-256QAM, single-channel DBP can achieve the same MI with spans a factor of 2 longer than span-length-optimised EDC-based systems. This may lead to 50% reduction of number of amplifiers required without a decrease in information rates
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