In this paper we present a novel physical layer impairment (PLI) aware routing and wavelength assignment (RWA)
approach combined with PLI-aware regenerator placement. We consider the dominant linear and nonlinear signal quality
degrading effects in 10 Gb/s non-return to zero (NRZ) on-off keying (OOK) systems by analytical models for amplified
spontaneous emission noise (ASE), filter crosstalk, group-velocity dispersion (GVD) and polarization mode dispersion
(PMD) as well as cross-phase modulation (XPM) and four wave mixing (FWM). As a topology for our study we have
chosen the COST266 reference network, which is a pan-European meshed network with a total of 28 nodes and 41
(bidirectional) edges. For this network demands have been defined based on a population-based model. To facilitate
transmission over very long path lengths regenerator pools have been placed sparsely at certain nodes due to cost
considerations. The regenerator sites are selected based on a heuristic algorithm taking into account the physical effects
resulting in signal quality degradation. Due to the high cost of optical-electrical-optical (OEO) conversion as few
regenerators as possible are deployed. In our investigations we assumed a 1+1 path protection scheme in the optical
layer. The exact assessment of the signal quality based on the current traffic situation using our methods permits a
network performance (wavelength blocking probability) comparable to an opaque network with only a small number of
regenerators.
Due to the tenfold capacity increase of Ethernet from one generation to the next, 100 Gbps will be the straight forward next step after 10 Gbps. Demand can be predicted for the following years based on increasing internet data traffic and the lack of efficient packet based link aggregation mechanisms in the Ethernet protocol. Solutions have to be found for short haul intra-office and long haul inter-office interconnections of large routers. This contribution focuses on options for physical layer interfaces. Optical component aspects are discussed as well as transmission aspects. The selection of a suitable modulation format in combination with equalizer technologies opens a path towards robust transmission systems for this ultra-high datarate.
In this paper four-wave mixing (FWM) and its impact on multi-span NRZ-modulated wavelength division multiplexing (WDM) systems are examined. The impact of the inline dispersion compensation map on FWM impairments is crucial. From re-circulating loop experiments as well as our analytical model worst-case conditions for the dispersion map are found. Furthermore, the impact of increasing the number of WDM channels is investigated. An analytical model is presented to assess the signal degradation. The impairments due to FWM are related to a Q-factor or an EOP. The presented formulas are applied to different dispersion compensation schemes and also mixed-fiber systems. The analytical model is verified by system simulations employing the split-step Fourier method as well as re-circulating loop experiments.
In this paper cross-phase modulation (XPM) and its impact on multispan NRZ-modulated wavelength division multiplexing (WDM) systems is examined. An analytical model is presented to assess the signal degradation. The impairments due to XPM are related to a Q-factor. The presented formulas are examined for different dispersion compensation schemes and also mixed-fiber systems. The analytical models are verified by system simulations employing the split-step Fourier method. To determine the impairments due to XPM the pump-probe model is used, which assesses the distortion of an unmodulated probe channel. It is shown that this model is applicable to NRZ systems. Existing analytical models are extended for certain conditions, e.g. given dispersion compensation schemes such as the distributed under-compensation scheme (DUCS) or the full-inline and optimized post compensation scheme (FOCS). Furthermore, a formula will be suggested to estimate the degradation of performance, if further WDM channels are added to an existing system.
A general modeling and simulation strategy suitable for the fast and accurate analysis of a fiber-optical WDM system is presented, that may also include multi-span systems. Noise and fiber dispersion are considered as well as nonlinear effects like four wave mixing, self-phase modulation and cross-phase modulation. Furthermore, amplified spontaneous emission noise of the optical amplifiers and polarization-dependencies (e.g. PMD) are taken into account. Performance evaluation by means of eye patterns, spectral power densities, optical signal-to-noise ratio, the Q-Factor and the bit error rate are addressed. An analysis of the degradation effects against the position within the fiber is shown to get a better overview of the fibers behavior. An improved Split-Step algorithm is outlined as a fast alternative to supplement the FFT calculation within the fiber. A parameter variation, which can also be influenced during the simulation by the user, is presented in order to get an overview of the parameter space. Different modulation formats are taken into account, e.g. return-to-zero, non-return-to-zero and differential phase-shift keying. Both the separated channels and the total field approach are demonstrated. In the separated channels approach the different nonlinear effects can be switched on and off independently for detailed studies of inter-channel effects. Based on this work, a complete design environment (PHOTOSS, The Photonic System Simulator) has been developed. This simulation tool has been tested extensively by several industry partners. Simulation examples are presented here e.g. for PMD simulations.
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