Probabilistic Shaping for the Optical Phase Conjugation Channel

Abstract

Probabilistic constellation shaping is studied and developed for optical phase conjugation (OPC)-based nonlinearity compensation of Kerr nonlinearities in optical fiber links. The mid-link OPC scenario is considered for dispersion compensated systems. It is demonstrated in simulations and experimentally that transmission strategies optimal for classical additive white Gaussian noise (AWGN) channels can be sub-optimal for these systems without nonlinearity compensation. On the contrary, when nonlinearity compensation is applied with mid-link OPC, the channel noise is demonstrated to be Gaussian and AWGNlike transmission strategies thus remain effective. A channelagnostic probability mass function (PMF) optimization algorithm is proposed for the input constellation in order to further improve the shaping gains in both scenarios. Operating arbitrary PMFs on arbitrary channels is enabled by a channel-agnostic digital signal processing (DSP) chain. After ≈2000 km of transmission, mid-link OPC is demonstrated to provide ≈1 dB of gain in effective SNR, which translates to ≈0.4 bits/QAM symbol of gain in achievable information rate. The gain is then increased by an extra ≈0.2 bits/QAM symbol by applying probabilistic shaping.

Enhancing the Signal Power Symmetry for Optical Phase Conjugation Using Erbium-Doped-Fibre-Assisted Raman Amplification

“…chromatic dispersion) and deterministic nonlinear (e.g. intra channel effects due to the Kerr nonlinearity) optical fibre impairments [1][2][3][4][5][6][7][8][9][10][11][12][13]. This technique could help exceed the "nonlinear Shannon limit" and significantly improve the maximum transmission distance or the system data capacity in a long-haul transmission system [10][11][12][13][14][15][16].…”

SNR Optimization of Multi-Span Fiber Optic Communication Systems Employing EDFAs With Non-Flat Gain And Noise Figure

“…Offline processing is then applied to measure the performance in terms of SNR, NGMI and bit error rate (BER). The processing is identical to that of [18].…”

Optical Phase Conjugation Using Nonlinear SOA for Nonlinearity and Dispersion Compensation of Coherent Multi-Carrier Lightwave Systems

“…Polarization coding scheme and its equivalent phase conjugated twin wave based fiber nonlinearity compensation are alternate methods to digital domain-only nonlinearity compensation, but requires additional processing at the transmitter and halves the spectral efficiency [11], [12]. A promising method to augment digital equalization is the use of optical phase conjugation (OPC) to optically compensate for the accumulated CD and distortion due to fiber Kerr nonlinearities in both single carrier and multi-carrier systems [13]- [18]. Long haul and ultra long haul links with OPC have been demonstrated in [15], [19], thus proving its practical viability.…”