Abstract
Superchannel transmission spaced at the symbol rate, known as Nyquist spacing, has been demonstrated for effectively maximizing the optical communication channel capacity and spectral efficiency. However, the achievable capacity and reach of transmission systems using advanced modulation formats are affected by fibre nonlinearities and equalization enhanced phase noise (EEPN). Fibre nonlinearities can be effectively compensated using digital back-propagation (DBP). However EEPN which arises from the interaction between laser phase noise and dispersion cannot be efficiently mitigated, and can significantly degrade the performance of transmission systems. Here we report the first investigation of the origin and the impact of EEPN in Nyquist-spaced superchannel system, employing electronic dispersion compensation (EDC) and multi-channel DBP (MC-DBP). Analysis was carried out in a Nyquist-spaced 9-channel 32-Gbaud DP-64QAM transmission system. Results confirm that EEPN significantly degrades the performance of all sub-channels of the superchannel system and that the distortions are more severe for the outer sub-channels, both using EDC and MC-DBP. It is also found that the origin of EEPN depends on the relative position between the carrier phase recovery module and the EDC (or MC-DBP) module. Considering EEPN, diverse coding techniques and modulation formats have to be applied for optimizing different sub-channels in superchannel systems.
Highlights
Nonlinear Kerr effects in optical fibre transmission systems[12,13,14,15,16,17,18,19,20,21,22]
Our results indicate that with both electronic dispersion compensation (EDC) and MC-digital back-propagation (DBP), enhanced phase noise (EEPN) causes a significant deterioration in the performance of all sub-channels, with penalties more severe for the outer sub-channels
Digital-to-analog convertor (DAC) with a resolution of 16-bit and root-raisedcosine (RRC) filter with a roll-off of 0.1% were used for the Nyquist pulse shaping (NPS)
Summary
Nonlinear Kerr effects in optical fibre transmission systems[12,13,14,15,16,17,18,19,20,21,22]. The impact of EEPN may differ for different sub-channels within the same superchannel, which must be taken into consideration for the optimization of optical fibre networks It is of both great practical importance and interest to study the impact of EEPN on the performance of superchannel transmission systems, for both EDC and MC-DBP. The LO phase noise will interplay with the EDC module to cause the effect of phase noise to amplitude noise conversion, and the induced EEPN will significantly affect the performance of long-haul high speed optical transmission systems[25,26,27,28,29,30,31,32,33,34]. Where ATx and ALO are the amplitudes of the transmitter laser carrier and the LO laser optical wave respectively, φTx(t) and φLO(t) are the phase fluctuation in the transmitter laser and the LO laser respectively, gEDC(L, t) is the time-domain transfer function of the electronic dispersion compensation filter, gFibre(L, t) is the time-domain transfer function of the fibre, L is the fibre length, t represents the temporal variable, and ⊗ indicates the convolution operation
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