The theoretical fundamentals of fiber-based optical parametric amplifiers(OPA) are reviewed,and their applications are discussed in this paper.In the end the future research aspects are expected.

Fiber-based Optical Parametric Amplifiers and Their Applications

Fiber-optic multi-band transmission (MBT) aims at exploiting the low-loss spectral windows of single-mode fibers (SMFs) for data transport, expanding by $\sim\!11\times$ the available bandwidth of C-band line systems and by $\sim\!5\times$ 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  $\rightarrow$  L. MBT performance is assessed by addressing the generalized SNR (GSNR) including both the linear and non-linear fiber propagation effects. Non-linear fiber propagation is taken into account by computing the generated non-linear interference by using the generalized Gaussian-noise (GGN) model, which takes into account the interaction of non-linear 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: $\sim\!10\times$ and 8× more than C-band transmission respectively and $\sim\!2.5\times$ more than full C+L.

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Assessment on the Achievable Throughput of Multi-Band ITU-T G.652.D Fiber Transmission Systems

Current optical fibre transmission systems rely on modulation, coding and multiplexing techniques that were originally developed for linear communication channels. However, linear transmission techniques are not fully compatible with a transmission medium with a nonlinear response, which is the case for an optical fibre. As a consequence, the Kerr nonlinearity in fibre imposes a limit on the performance and the achievable transmission rate of the conventional optical fibre communication systems. Here we show that a transmission performance beyond the conventional Kerr nonlinearity limit can be achieved by encoding all the available degrees of freedom and nonlinearly multiplexing signals in the so-called nonlinear Fourier spectrum, which evolves linearly along the fibre link. This result strongly motivates a fundamental paradigm shift in modulation, coding and signal-processing techniques for optical fibre transmission technology. The Kerr nonlinearity limit for optical fibre communications is surpassed by using nonlinear multiplexing.

Nonlinear signal multiplexing for communication beyond the Kerr nonlinearity limit

In this paper, we review the historical evolution of predictions of the performance of optical communication systems. We will describe how such predictions were made from the outset of research in laser based optical communications and how they have evolved to their present form, accurately predicting the performance of coherently detected communication systems.

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Performance limits in optical communications due to fiber nonlinearity

The ability to process optical signals without passing into the electrical domain has always attracted the attention of the research community. Processing photons by photons unfolds new scenarios, in principle allowing for unseen signal processing and computing capabilities. Optical computation can be seen as a large scientific field in which researchers operate, trying to find solutions to their specific needs by different approaches; although the challenges can be substantially different, they are typically addressed using knowledge and technological platforms that are shared across the whole field. This significant know-how can also benefit other scientific communities, providing lateral solutions to their problems, as well as leading to novel applications. The aim of this Roadmap is to provide a broad view of the state-of-the-art in this lively scientific research field and to discuss the advances required to tackle emerging challenges, thanks to contributions authored by experts affiliated to both academic institutions and high-tech industries. The Roadmap is organized so as to put side by side contributions on different aspects of optical processing, aiming to enhance the cross-contamination of ideas between scientists working in three different fields of photonics: optical gates and logical units, high bit-rate signal processing and optical quantum computing. The ultimate intent of this paper is to provide guidance for young scientists as well as providing research-funding institutions and stake holders with a comprehensive overview of perspectives and opportunities offered by this research field.

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Roadmap on all-optical processing

We analyse, both numerically and experimentally, the relative intensity noise transfer in ultra-long Raman laser amplifiers isolating the combined effect of front-FBG reflectivity and pump power split and quantitatively showing their impact on a 100 km, 2 nd -order, bidirectionally pumped configuration.

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FBG reflectivity impact on RIN in ultralong laser amplifiers

The performance of a multi-span transmission link compensated with a >75nm broadband discrete Raman amplifier is experimentally evaluated using multiple DP-x-QAM modulation formats over a multi-channel C + L band WDM grid with up to 182 × 50 GHz spaced channels.

High-capacity multi-span transmission performance characterization of broadband discrete Raman amplifier

We propose a novel first order incoherent broadband amplified spontaneous emission (ASE) pump which can be used as a seed pump in dual order backward-pumped distributed Raman amplification. Using this broadband ASE pump mitigates the relative intensity noise (RIN) transfer from the backward-propagated second order pump to the signal, and extends the reach of $10\times120$ Gb/s DP-QPSK WDM transmission to 7915 km, giving a minimum of 12% (833 km) increase, compared with using low RIN semiconductor laser diode and random distributed feedback fiber laser.

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Enhanced Transmission Performance Using Backward-Propagated Broadband ASE Pump

We report a simple analytical approximation and experimental validation describing four wave mixing efficiency in distributed Raman transmission system with different pumping schemes. The experimental results match the theoretical predictions with error margin <0.7dB.

Four wave mixing in distributed Raman amplified optical transmission systems

The paper reviews distributed Raman amplification technologies which can provide near symmetric signal power profiles, in order to maximize the efficiency of optical nonlinearity compensation in long-haul optical transmission systems using mid-link optical phase conjugation.

Asif Iqbal

Papers

FBG reflectivity impact on RIN in ultralong laser amplifiers

High-capacity multi-span transmission performance characterization of broadband discrete Raman amplifier

Enhanced Transmission Performance Using Backward-Propagated Broadband ASE Pump

Four wave mixing in distributed Raman amplified optical transmission systems

Distributed Raman Amplification for Combating Optical Nonlinearities in Fibre Transmission