Nonlinear mitigation on subcarrier-multiplexed PM-16QAM optical systems.

We report a comprehensive set of experimental, simulation and analytical results on the benefit of nonlinear mitigation strategies for multi-subcarrier (MSC) PM-16QAM transmission systems. First, we demonstrate ~9% maximum reach gain enabled by symbol-rate optimization (SRO) of MSC-PM-16QAM in a 31 channels WDM transmission experiment. Then, we demonstrate that, in the considered experimental scenario, the gain provided by digital backpropagation (DBP) over single-carrier (SC) transmission is similar to that achieved by SRO over MSC transmission. Furthermore, we show that the SRO phenomenon can be weakened after self-channel interference (SCI) removal through DBP. As a result, and due to DBP performance limitations in the experiment, the combined effect of SRO and DBP was found to enable only an additional 4% gain in maximum reach. Finally, we address the impact and symbol-rate dependence of nonlinear phase noise (NLPN) in MSC-PM-16QAM transmission, discussing on the NLPN mitigation capability of standard carrier phase estimation (CPE) and on respective gains that could be achieved through its enhanced mitigation.

1306-km 20x124.8-Gb/s PM-64QAM transmission over PSCF with net SEDP 11,300 (b ∙ km)/s/Hz using 1.15 samp/symb DAC.

We demonstrated the transmission of a Nyquist-WDM signal based on PM-64QAM modulation in an EDFA-only submarine configuration composed of 54.4 km-long fiber spans: 20 channels at 124.8-Gb/s were propagated over 1306 km of low-loss pure-silica-core fiber (PSCF). Thanks to an aggressive digital spectral shaping, we achieved a raw spectral efficiency (SE) of 10.4 b/s/Hz, corresponding to 8.67 b/s/Hz net SE when considering a 20% FEC overhead. Transmitter DACs are operated at a record-low 1.15 samples/symbol, enabled by the insertion of advanced anti-alias filters. The achieved SE-times-distance product was 11,327 (b ∙ km)/(s ∙ Hz), the highest reported so far for PM-64QAM. Combining the experimental results with the performance predictions obtained using an analytical model of nonlinear propagation in uncompensated coherent optical systems (the so-called "GN-model"), we show that PM-64QAM is a realistic option for ultra-high capacity systems in the 1,000 km range, carrying up 40 Tb/s in the C-band.

Experimental validation of an analytical model for nonlinear propagation in uncompensated optical links.

Link design for optical communication systems requires accurate modeling of nonlinear propagation in fibers. This topic has been widely analyzed in last decades with partial successes in special conditions, but without a comprehensive solution. Since the introduction of coherent detection with electronic signal processing the scenario completely changed because this category of systems shows better performances in links without in-line dispersion management. This change to uncompensated transmission allowed to modify the approach in the study of nonlinear fiber propagation and in recent years a series of promising analytical models have been proposed. In this paper, we present an experimental validation over different fiber types of an analytical model for nonlinear propagation over uncompensated optical transmission links. Considering an ultra-dense WDM system, we transmitted ten 120-Gb/s PM-QPSK signals over a multi-span system probing different fiber types: SSMF, PSCF and NZDSF. A good matching was found in all cases showing the potential of the analytical model for accurate performance estimation that could lead to powerful tools for link design.

Early complications with flexible intramedullary nailing in childhood fracture: 100 cases managed with precurved tip and shaft nails.

BACKGROUND AND PURPOSE: Diaphyseal and metaphyseal fractures in children are frequently treated with the flexible intramedullary nailing (FIN) method. The aim of this study was to record postoperative complications and outcome in consecutive fracture patients treated with the new precurved tip and shaft nails and dedicated ergonomic instrumentation. METHODS: We report the analysis of 100 consecutive fractures followed up for a minimum of 6 months. Ninety-seven children were included, comprising 77 shaft and 23 metaphyseal fractures. Demographic data, duration of surgery, nail and medullary canal diameter, date of nail removal, clinical assessment, follow-up radiographs and all complications were recorded. RESULTS: Mean age was 9.7 years, and mean body weight 35.1 kg. Twenty-one fractures had associated lesions. Mean duration of surgery was 42.4 minutes. Nail removal was at a mean 6.1 months. Twelve percent of patients had complications, with six insufficient reductions, one delayed union, one non-union, one iterative fracture, and three skin impingements. Unexpected surgical revision was required in seven cases. At follow-up, only one patient showed functional impairment, with 20° pronation loss, and three showed more than 10° axial deviation on X-ray. CONCLUSION: The low rate of skin impingement compared with the literature may be due to the new dedicated instruments. We believe that other complications can be avoided if one follows the FIN principles, avoiding weak assembly due to an insufficient nail/medullary canal diameter ratio, which is a limiting factor for indications in adolescents. The surgeons reported that precurved shaft nails facilitated the FIN procedure, although this subjective judgment may be due simply to the novelty of the nails. LEVEL OF EVIDENCE: Level IV. Retrospective study.