Advanced Digital Signal Processing Techniques for High-Speed Optical Links

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Longitudinal Power Monitoring Performance with Subcarrier Multiplexing Transmission

We investigate the performance of Longitudinal Power Monitoring (LPM) algorithms at the small symbol rates achieved with subcarrier multiplexing. We show that at those symbol rates LPM is still effective, albeit with a noisier estimation profile

Observing the effect of polarization mode dispersion on nonlinear interference generation in wide-band optical links

With the extension of the spectral exploitation of optical fibers beyond the C-band, accurate modeling and simulation of nonlinear interference (NLI) generation is of the utmost performance. Models and numerical simulation tools rely on the widely used Manakov equation (ME): however, this approach when also considering the effect of polarization mode dispersion (PMD) is formally valid only over a narrow optical bandwidth. In order to analyze the range of validity of the ME and its applicability to future wide-band systems, we present numerical simulations, showing the interplay between NLI generation and PMD over long dispersion-uncompensated optical links, using coherent polarization division multiplexing (PDM) quadrature amplitude modulation (QAM) formats. Using a Monte-Carlo analysis of different PMD realizations based on the coupled nonlinear Schrödinger equations, we show that PMD has a negligible effect on NLI generation, independently from the total system bandwidth. Based on this, we give strong numerical evidence that the ME can be safely used to estimate NLI generation well beyond its bandwidth of validity that is limited to the PMD coherence bandwidth

Estimation Accuracy of Polarization State from Coherent Receivers for Sensing Applications

We experimentally investigate on the intrinsic accuracy in fiber State of Polarization estimation from the DSP of commercial coherent tranceivers, in terms of angular uncertainty on the Poincaré’s sphere vs. received OSNRs, for sensing applications. We then demonstrate how using a moving average enhances accuracy

Bidirectional 4-PAM to Double Per-Fiber Capacity in 2-km Intra-Datacenter Links

This paper presents an experimental demonstration of bidirectional 4-PAM transmission for intra-datacenter links using a pair of SMF fibers. In the proposed architecture, each transceiver laser feeds both fibers, which are thus used bidirectionally to double the capacity per used fiber, wavelength, and laser. Besides the experimental demonstration, we also report a theoretical and simulative investigation on the penalty induced in this architecture by spurious connector back-reflections. We show that the resulting penalty can be kept under control for typical realistic connector reflection values, provided that each pair of lasers in both directions are separated by at least twice the system symbol rate

Impact of finite-resolution DAC and ADC on probabilistically-shaped QAM constellations

We analyze the impact of finite resolution of DAC and ADC on the performance of coherent-detection optical communication systems using probabilistically-shaped 64-QAM constellations. We show that no substantial additional penalty is incurred with respect to uniformly distributed constellations with the same net data rate