Fiber-optic multi-band transmission (MBT) aims at exploiting the low-loss spectral windows of single-mode fibers (SMFs) for data transport, expanding by ~11 times the available bandwidth of C-band line systems and by ~5 times C+L-band line systems'. MBT offers a high potential for cost-efficient throughput upgrades of optical networks, even in absence of available dark-fibers, as it utilizes more efficiently the existing infrastructures. This represents the main advantage compared to approaches such as multi-mode/-core fibers or spatial division multiplexing. Furthermore, the industrial trend is clear: the first commercial C+L-band systems are entering the market and research has moved toward the neighboring S-band. This article discusses the potential and challenges of MBT covering the ITU-T optical bands O -> L. MBT performance is assessed by addressing the generalized SNR (GSNR) including both the linear and nonlinear fiber propagation effects. Nonlinear fiber propagation is taken into account by computing the generated nonlinear interference by using the generalized Gaussian-noise (GGN) model, which includes the interaction of nonlinear fiber propagation with stimulated Raman scattering (SRS), and in general considers wavelength-dependent fiber parameters. For linear effects, we hypothesize typical components' figures and discussion on components' limitations, such as transceivers', amplifiers' and filters' are not part of this work. We focus on assessing the transmission throughput that is realistic to achieve by using feasible multi-band components without specific optimizations and implementation discussion. So, results are meant to address the potential throughput scaling by turning-on excess fiber transmission bands. As transmission fiber, we focus exclusively on the ITU-T G.652.D, since it is the most widely deployed fiber type worldwide and the mostly suitable to multi-band transmission, thanks to its ultra-wide low-loss single-mode high-dispersion spectral region. Similar analyses could be carried out for other single-mode fiber types. We estimate a total single-fiber throughput of 450 Tb/s over a distance of 50 km and 220 Tb/s over regional distances of 600 km: ~10 times and 8 times more than C-band transmission respectively and ~2.5 times more than full C+L.

We investigated the reach increase obtained through nonlinearity mitigation by means of transmission symbol rate optimization (SRO). First, we did this theoretically and simulatively. We showed that the nonlinearity model that properly accounts for the phenomenon is the EGN model, in its version that specifically includes four-wave mixing. We then found that for PM-QPSK systems at full C-band, the reach increase may be substantial, on the order of 10-25%, with optimum symbol rates on the order of 2-6 GBd. We show that for C-band PM-QPSK systems over SMF, the potential mitigation due to SRO is greater than that ideally granted by digital backpropagation (the latter applied over a bandwidth of a 32-GBd channel). We then set up an experiment to obtain confirmation of the theoretical and simulative predictions. It consisted of 19 PM-QPSK channels, operating at 128 Gb/s per channel, over PSCF, with span length 108 km and EDFA-only amplification. We demonstrated a reach increase of about 13.5%, when going from single-carrier per channel transmission, at 32 GBd, to eight subcarrier per channel, at 4 GBd, in line with the EGN model predictions. We also extended the theoretical investigation of SRO to PM-16QAM, where we found a qualitatively similar effect to PM-QPSK, although the potential reach increase appears to be typically only about 50% to 60% that of PM-QPSK. Further investigation is, however, in order, specifically to explore the effect on PM-16QAM SRO of the removal of long-correlated phase and polarization noise.

In this paper the first glass based resorbable optical fiber is manufactured and characterized, showing values of attenuation loss from one to two orders of magnitude lower than the polymeric based bioresorbable devices reported in literature. The fiber behaves as a single-mode waveguide at the lower limit of the first biological window (1300 nm) and as a multi-mode waveguide in the visible region (630 nm). Highly transparent calcium-phosphate glasses (PGs) are proposed as a new class of materials for biomedical optics, managing to combine for the first time in a vitreous material solubility in aqueous media, transparency in the near UV region, low intrinsic attenuation loss and thermal stability during fiber drawing. In-vitro tests in physiological conditions show dissolution kinetics of glass fibers in about a month.

A tellurite optical fiber doped with Er³⁺ and Ce³⁺ ions was designed and fabricated with the aim of assessing its suitability as laser and optical amplifier operating at 1550 nm, compatible with silica fiber standard dimensions. High-quality optical fibers, with an attenuation loss of 1.0 dB/m at 1320 nm, were obtained featuring a 6-μm diameter core. A fiber laser emitting at 1550 nm upon pumping at 976 nm and a fiber amplifier characterized by signal amplification of 8 dB for a length of 10 cm were demonstrated.