Statistical quantification of nonlinear interference noise components in coherent systems.

We present and validate a statistical method able to separate nonlinear interference noise (NLIN) into a residual Gaussian (ResN) and a phase noise (NLPN) component. We take into account the interaction of the NLIN with the receiver's DSP, mainly through carrier phase recovery (CPR), by considering the amount of correlation of the NLPN component. This allows obtaining in a straightforward way an accurate prediction of the achievable post-DSP transmission performance. We apply our method on simulated data in different scenarios. For this purpose: (i) several different quadrature amplitude modulation (QAM) and probabilistically shaped (PS) formats are investigated and (ii) simulations with standard single mode fiber (SSMF) and dispersion shifted fiber (DSF) are performed. In all these cases we validate the results provided by our method through comparison with ideal data-aided CPR and a more practical blind phase search (BPS) algorithm. The results obtained are finally compared with the predictions of existing theoretical models and the differences with our approach are pointed out.

Quaternary TDM-PAM as upgrade path of access PON beyond 10Gb/s.

A 20 Gb/s quaternary TDM-PAM passive optical network with chirped and non-linear optical transmitters is experimentally demonstrated. The migration from legacy TDM-PONs and the implications of using available 10 Gb/s components are analyzed. We show that a loss budget of 27.3 dB is compatible together with a packet power ratio of 10 dB between loud and soft optical network units.

Flexible quadrature amplitude modulation with semiconductor optical amplifier and electroabsorption modulator.

Optical quadrature amplitude modulation (QAM) is experimentally demonstrated with a low-complexity modulator based on a semiconductor optical amplifier and electroabsorption modulator. Flexible amplitude/phase format transmission is achieved. The applicability of octary QAM for coherent optical access networks with sustainable 3 Gb/s per-user bandwidth is investigated for a long reach of 100 km, and its compatibility with a potentially high split is verified.

Bandpass sampling in heterodyne receivers for coherent optical access networks.

A novel digital receiver architecture for coherent heterodyne-detected optical signals is presented. It demonstrates the application of bandpass sampling in an optical communications context, to overcome the high sampling rate requirement of conventional receivers (more than twice the signal bandwidth). The concept is targeted for WDM coherent optical access networks, where applying heterodyne detection constitutes a promising approach to reducing optical hardware complexity. The validity of the concept is experimentally assessed in a 76 km WDM-PON scenario, where the developed DSP achieves a 50% ADC rate reduction with penalty-free operation.