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 experimentally demonstrate a dual-stage 150nm discrete Raman amplifier with 15dB gain and maximum ∼8dB noise figure enabling SCL-band (1475-1625nm) WDM transmission through a 70km SMF using 30GBaud PM-QPSK signals with low transmission penalties.

150nm SCL-Band Transmission through 70km SMF using Ultra-Wideband Dual-Stage Discrete Raman Amplifier

We experimentally investigate three Raman fibre laser based amplification techniques with second-order bidirectional pumping. Relatively intensity noise (RIN) being transferred to the signal can be significantly suppressed by reducing first-order reflection near the input end.

RIN Mitigation in Second-Order Pumped Raman Fibre Laser Based Amplification

We characterise the linear and nonlinear noise of dual stage broadband discrete Raman amplifiers (DRAs) based on conventional Raman gain fibres. Also, we propose an optimised dual stage DRA setup that lowers the impact of nonlinear noise (generated in the amplifier) on the performance of a transmission link (with 100-km amplifier spacing). We numerically analyse the design of a backward pumped cascaded dual stage 100-nm DRA with high gain (∼20 dB) and high saturated output power (>23 dBm). We show that the noise figure (NF) of the dual stage DRA is mainly dominated by the first stage irrespective of the type of gain fibre chosen in the second stage, and we also demonstrate that optimising the length and the type of Raman gain fibre can have significant impact on the size of inter/intrasignal nonlinearities generated. Here, we report a theoretical model to calculate the nonlinear noise power generated in transmission spans with dual stage DRAs considering piecewise signal power evolution through the Raman gain fibres. The predicted signal-to-noise ratio (SNR) performances are calculated from the combined contributions from NF and nonlinear product power obtained using the proposed analytical model for transmission systems deployed with 100-km transmission span compensated by different dual stage DRAs. Finally, an optimised IDF 6 km–SMF 10 km dual stage configuration has been identified using the theoretical model, which allows maximum SNR of 14.6 dB at 1000 km for 1 THz Nyquist wavelength division multiplexed signal and maximum transmission reach of 3400 km at optimum launch power assuming 8.5 dB HD-FEC limit of the Nyquist PM-QPSK signal.

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Linear and Nonlinear Noise Characterisation of Dual Stage Broadband Discrete Raman Amplifiers

We demonstrate a novel design of dual stage backward pumped broadband discrete Raman amplifier with distributed pumping architecture which improves the short wavelength noise performance compared with conventional backward pumped single stage design. Overall noise figure (NF) performance has been improved by 2.8 dB over 70 nm bandwidth without introducing forward pumping. Nonlinear phase shift has been numerically calculated and compared with single stage design to evaluate the overall performance improvement. Finally, we report that our proposed dual stage design with ∼14 dB net gain improves low wavelength NF by 3.3 dB providing 1.2 dB Q2 factor improvement and 1134 km reach extension versus a conventional single stage design for 18 × 120 Gb/s PM-QPSK transmission.

Noise Performance Improvement of Broadband Discrete Raman Amplifiers Using Dual Stage Distributed Pumping Architecture

In this paper, gain, noise and nonlinear performance characterization of cascaded broadband discrete Raman amplifiers with different gain fibre combinations is presented. We numerically demonstrate the design of a backward-pumped cascaded dual stage broadband (∼70 nm) discrete Raman amplifier with high gain (∼19 dB), low noise (∼ 6 dB noise figure) and lower nonlinear penalty by optimizing two different types of gain fibres.

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Asif Iqbal

Papers

150nm SCL-Band Transmission through 70km SMF using Ultra-Wideband Dual-Stage Discrete Raman Amplifier

RIN Mitigation in Second-Order Pumped Raman Fibre Laser Based Amplification

Linear and Nonlinear Noise Characterisation of Dual Stage Broadband Discrete Raman Amplifiers

Noise Performance Improvement of Broadband Discrete Raman Amplifiers Using Dual Stage Distributed Pumping Architecture

Performance characterization of high gain, high output power and low noise cascaded broadband discrete Raman amplifiers