Spatial division multiplexing has been proposed as an option for further capacity increase of transmission fibers. Application of this concept is attractive only, if cost and energy efficient ...implementations can be found. In this work, optical amplification and optical filter based signal processing concepts are investigated. Deployment of multi mode fibers as the waveguide type for erbium doped fiber amplifiers potentially offers cost and energy efficiency advantages compared to using multi core fibers in preamplifier as well as booster stages. Additional advantages can be gained from optimization of the amplifier module design. Together with transponder design optimizations, they can increase the attractiveness of inverse spatial multiplexing, which is proposed as an intermediate step. Signal processing based on adaptive passive optical filters offers an alternative approach for the separation of channels at the receiver which have experienced mode coupling along the link. With this optical filter based approach, fiber capacity can potentially be increased faster and more energy efficiently than with solutions relying solely on electronic signal processing.
Roadmap of optical communications Agrell, Erik; Karlsson, Magnus; Chraplyvy, A R ...
Journal of optics,
06/2016, Letnik:
18, Številka:
6
Journal Article
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Lightwave communications is a necessity for the information age. Optical links provide enormous bandwidth, and the optical fiber is the only medium that can meet the modern society's needs for ...transporting massive amounts of data over long distances. Applications range from global high-capacity networks, which constitute the backbone of the internet, to the massively parallel interconnects that provide data connectivity inside datacenters and supercomputers. Optical communications is a diverse and rapidly changing field, where experts in photonics, communications, electronics, and signal processing work side by side to meet the ever-increasing demands for higher capacity, lower cost, and lower energy consumption, while adapting the system design to novel services and technologies. Due to the interdisciplinary nature of this rich research field, Journal of Optics has invited 16 researchers, each a world-leading expert in their respective subfields, to contribute a section to this invited review article, summarizing their views on state-of-the-art and future developments in optical communications.
Lightning events can cause fast polarization rotations and phase changes in optical transmission fibers due to strong electrical currents and magnetic fields. Whereas these are unlikely to affect ...legacy transmission systems with direct detection, different mechanisms have to be considered in systems with local oscillator based coherent receivers and digital signal processing. A theoretical analysis reveals that lightning events can result in polarization rotations with speeds as fast as a few hundred kRad/s. We discuss possible mechanisms how such lightning events can affect coherent receivers with digital signal processing. In experimental investigations with a high current pulse generator and transponder prototypes, we observed post FEC errors after polarization rotation events which can be expected from lightning strikes.
The scaling of nonlinear effects in multi-mode fibers with the mode count has been investigated by analytical studies and by numerical simulations. Increasing the core radius results in larger ...effective mode field areas, which reduces the impact of nonlinear effects. On the other hand, the presence of more interaction partners for intermodal nonlinear interactions due to a higher number of propagating modes strengthens the impact of nonlinear signal degradations on data transmission. Our results indicate that these two trends are mostly balanced even for large mode counts. Transmission reaches and system performance comparable to standard single-mode fibers are achievable for at least 100 modes.
The evolution of noise in transmission systems with multiple spans featuring forward pumped distributed Raman fiber amplifiers has been investigated experimentally and by numerical simulations. We ...found evidence that the transfer of relative intensity noise from the pump to the signal reveals characteristics of a nonlinear process, which cannot fully be captured by a Gaussian random variable added to the signal power. Power fluctuations of the pump radiation result in an intensity modulation of the amplified signal by stimulated Raman scattering. We have observed that a concatenation of multiple forward pumped amplifiers can lead to an increase of the bandwidth of the noise added to the signal compared to a single amplifier. A process acting like modulation instability of the pump radiation during propagation through the fiber was identified as a potential source of the bandwidth increase from span to span.
The selection of an appropriate pump concept has a major impact on amplifier cost and power consumption. The energy efficiency of different pump concepts is compared for multi core and multi mode ...active fibers. In preamplifier stages, pump power density requirements derived from full C-band low noise WDM operation result in superior energy efficiency of direct pumping of individual cores in a multi core fiber with single mode pump lasers compared to cladding pumping with uncooled multi mode lasers. Even better energy efficiency is achieved by direct pumping of the core in multi mode active fibers. Complexity of pump signal combiners for direct pumping of multi core fibers can be reduced by deploying integrated components.
The nonlinear signal propagation in fibers can be described by the nonlinear Schrödinger equation and the Manakov equation. Most commonly, split-step Fourier methods (SSFM) are applied to solve ...these nonlinear equations. The numerical simulation of the nonlinear signal propagation is especially challenging for multimode fibers, particularly if the calculation of very small step sizes or a large number of steps is required. Instead of utilizing SSFM, the fourth-order Runge-Kutta in the Interaction Picture (RK4IP) method can be applied. This method has the potential to reduce the numerical error while simultaneously allowing an increased step size. These advantages come at the price of a higher numerical effort compared to the SSFM method for the same step size. Since the simulation of the signal propagation in multimode fibers is already quite challenging, parallelization becomes an even more interesting option. We demonstrate the adaptation of the RK4IP method to simulate the nonlinear signal propagation in multimode fibers, including its parallelization. Besides comparing the performance of a parallelized implementation for multicore CPUs and a GPU-accelerated version, we discuss efficient strategies to implement the RK4IP method on a GPU accelerator with CUDA. In addition, the RK4IP implementation is numerically compared with a conventional SSFM implementation.
•Multi-GPU implementation for the nonlinear signal propagation in multimode fibers.•Different approaches to realize the GPU-GPU communication are explored and compared.•A mode-division multiplexed ...data transmission using 120 modes is evaluated.
Mode-division multiplexing (MDM) is seen as a possible solution to satisfy the rising capacity demands of optical communication networks. To make MDM a success, fibers supporting the propagation of a huge number of modes, i.e. several tens, are of interest. Many of the system aspects occurring during the propagation can be evaluated by using appropriate models. However, fibers are a nonlinear medium and, therefore, numerical simulations are required. For a large number of modes, the simulation of the nonlinear signal propagation in particular for telecommunication leads to new challenges, for example regarding the required memory, which we address with an implementation incorporating multiple GPU-accelerators. In this paper, we evaluate two different approaches to realize the communication between the GPUs and analyze the performance for simulations involving up to 8 Tesla GPUs. To the best of our knowledge, we are the first who explore a multi-GPU approach to simulate the nonlinear signal propagation in multimode fibers. This allows us to show results for an MDM transmission system utilizing the extremely large number of 120 spatial modes in a fiber with a core diameter of 62.5 µm as an application example and to analyze the impact of the nonlinear effects on the transmitted signals.
Mode division multiplexed transmission system performance is affected by linear mode coupling. Mitigating elements such as multiple-input multiple-output (MIMO) equalizers have to be able to follow ...temporal variations of the coupling. We investigate potential response time requirements for adaptive mitigating elements.
The dynamic switching of channels to adapt the capacity to the actually occurring traffic load is a promising method to improve the energy efficiency in optical networks. However, this approach is ...limited by the possible generation of optical power transients, which are able to disturb the transmission of the remaining channels. In transparent networks, spreading of transients can occur across several nodes. In this paper, we demonstrate the restrictions of the dynamic channel switching by the consideration of optical power transients and shows how to minimize these limitations.
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