To effectively operate multi-vendor disaggregated networks, performance of physical layer needs to be assessed by a quality-of transmission estimator (QoT-E) delivering quick results with a given reliability range. Beside ASE noise accumulation, nonlinear propagation impairments on WDM optical channels based on multilevel modulation formats relying on DSP-operated coherent receivers and propagating on uncompensated and amplified optical links are well summarized by the accumulation of a Gaussian-distributed disturbance: the nonlinear interference (NLI). When exploiting a transmission bandwidth exceeding the C-band, the interaction of NLI generation with the stimulated Raman scattering (SRS) must be properly considered. We present the derivation of the generalized Gaussian noise (GGN) model for NLI generation, including the SRS and, in general, a spectral and spatial variation of gain/loss. We validate its accuracy by comparing performances predicted by a QoT-E based on the GGN-model with measurements on a testbed exploiting commercial equipment, including 100 Gbps transponders. Considering that operational parameters of commercial equipment are known with a large range of uncertainty, an excellent agreement with errors within 0.5 dB on the generalized $\snr$ is shown, demonstrating that the GGN-model can be used for QoT-E in multi-vendor network scenarios. Moreover, the GGN-model has shown the capability to predict the spectral tilting due to SRS in $\snr$ performances, enabling its application to evaluate the impact of linear pre-tilting for SRS pre-compensation and NLI generation.

We present a novel scheme to cancel signal-signal beat interference in direct-detection systems with single-sideband modulation. We use this scheme to successfully transmit 80-Gb/s SSB-DMT at 1550 nm over 80-km SSMF with margin.

We demonstrate an up to 115-Gb/s line-rate short-reach system using a single 1550-nm VCSEL with discrete multi-tone modulation and direct detection, which can cover 500-m to 4-km standard-single-mode fiber at 95-Gb/s to 105-Gb/s bit rates.

We generate a 72-GBd single-carrier 64-QAM signal using high-speed digital-to-analog converters. We obtain a record line rate of 864 Gb/s on a single wavelength and demonstrate 5-channel WDM transmission over 400 km of fiber.

In this paper, we compare the performance of probabilistically-shaped 64QAM with uniform 16QAM and 32QAM modulation formats at the same net data rate in long-haul coherent optical communications systems. Experimental results at 16 GBaud are shown, with off-line post-processing of the data performed using either an ideal or a realistic carrier phase estimation (CPE) scheme. We show that the choice of CPE algorithm at the receiver is crucial, since, as predicted by current models, most of the additional nonlinear noise introduced by the shaping is non-linear phase noise (NLPN). Thanks to the use of probabilistic shaping (PS), maximum reach gains ranging from 15.5% and 34% are obtained over pure silica-core fiber (PSCF), where the NLPN can be efficiently compensated for by standard CPE algorithms, whilst over non-zero dispersion-shifted fiber (NZDSF) the gain of PS is drastically reduced, due to residual short-correlated NLPN.

Given the ubiquity of optical fiber networks in both terrestrial and submarine environments, leveraging these facilities for sensing anomalous conditions alongside telecommunications can provide significant added value. In this context, distributed acoustic sensing (DAS) systems have been widely employed and discussed due to their sensitivity and ability to locate events. However, integrating them within existing networks is complex and expensive. On the other hand, the received state of polarization (SOP) is also sensitive to external factors, and it can be used for sensing: in this case, no extra hardware would be required since the SOP is already estimated in coherent receivers for data demodulation. The sensing information is provided “for free” by the already installed hardware, potentially requiring only a software upgrade. In this work, we analyze the feasibility of using polarization-based sensing to detect anomalous conditions in metropolitan environments. A polarimeter was used to evaluate SOP noise induced by urban factors, while a commercial coherent transceiver was employed to assess SOP estimation noise. We propose two algorithms for processing polarization data: a time-based method called SOP angular speed (SOPAS) and an adaptive, frequency-based approach named SOP-power spectral density gap (SOP-PSDG). These algorithms were compared by processing Stokes vector samples from the polarimeter when different sinusoidal vibrations are applied to the fiber through a mechanical shaker. Results demonstrate that a sampling rate of just a few tens of Hz is sufficient to effectively identify various hazardous conditions, with SOP-PSDG consistently outperforming SOPAS. Additionally, preliminary findings on the performances of these algorithms using SOP samples from a commercial coherent receiver are discussed.