Practical issues and some lessons learned from realization of phase sensitive parametric regenerators

Practical issues in pump phase synchronization necessary for coherent all-optical processing are discussed, including feed-forward carrier recovery of phase encoded signals

Field-trial of an all-optical PSK regenerator/multicaster in a 40 Gbit/s, 38 channel DWDM transmission experiment

The performance of future ultra-long haul communication systems exploiting phase-encoded signals is likely to be compromised by noise generated during signal transmission. One potential way to mitigate such noise is to use Phase Sensitive Amplifiers (PSAs) which have been demonstrated to help remove phase as well as amplitude noise from phase-encoded signals. Recently, we showed that a PSA-based signal regenerator based on degenerate four-wave mixing can be implemented in a network-compatible manner in which only the (noisy) signal is present at the device input (black-box operation). The developed regenerator was also able to perform simultaneous wavelength conversion and multicasting, details/analysis of which are presented herein. However, this scheme was tested only with artificial noise generated in the laboratory and with the regenerator placed in front of the receiver, rather than in-line where even greater performance benefits are to be expected. Here, we address both theoretically and experimentally the important issue of how such a regenerator, operating for convenience in a multicasting mode, performs as an in-line device in an installed transmission fiber link. We also investigate the dispersion tolerance of the approach

Robust design of all-optical PSK regenerator based on phase sensitive amplification

More compact, stable, and efficient configuration of a recently-developed regenerator is presented. The regenerator is assessed at data rates up to 56 Gbit/s using white phase noise for the first time

Organic matter governs N and P balance in Danube Delta lakes

The transformation of dissolved inorganic nitrogen (DIN) and soluble reactive phosphorous (SRP), and the release of dissolved organic and particulate N and P, were analyzed in two lake complexes (Uzlina-Isac and Puiu-Rosu-Rosulet) of the Danube Delta wetland during flood conditions in May and at low water level in September 2006. The Uzlina-Isac complex was hydrologically tightly-connected with the Danube River and was flushed with river-borne nutrients and organic matter. These lakes acted as effective transformers for nutrients and produced large amounts of fresh biomass, that promoted the excretion of dissolved organic N and P during active growth. Biomass breakdown created particulate matter (<0.45μm), which was widely liberated during low flow in the fall. The Puiu-Rosu-Rosulet complex was characterized by a more distant position to the Danube and proximity to the Black Sea, and received dominantly transformed organic compounds from the flow-through water and vast vegetation cover. Due to reduced nutrient input, the internal production of organic biomass also was reduced in these more remote lakes. Total N and P export from the lake nearest to the shelf was governed by dominantly dissolved organic and particulate compounds (mean 58 and 82%, respectively). Overall, this survey found that these highly productive wetlands efficiently transform nutrients into a large pool of dissolved organic and particulate N and P. Hence, wetland lakes may behave widely as net sources of organic N and P to downstream waters and coastal marine system

Phase regeneration of optical signals

We present recent advances in phase-sensitive amplification technology and its application to the regeneration of phase-encoded signals. Using a combination of parametric effects in fibers and optical injection locking of lasers, it is possible to observe phase regeneration in signals with multiple levels of phase encoding

QPSK phase and amplitude regeneration at 56 Gbaud in a novel idler-free non-degenerate phase sensitive amplifier

We introduce a novel input-idler-free non-degenerate phase sensitive amplifier (PSA) configuration and use it for simultaneous phase and amplitude regeneration of quadrature phase shift keyed (QPSK) signals demonstrated at symbol rates up to 56 Gbaud

Homodyne OFDM with Optical Injection Locking for Carrier Recovery

Homodyne detection provides the simplest digital signal processing (DSP) solution to optical coherent detection and minimizes the receiver bandwidth requirements. These features make it promising for high spectrally-efficient formats such as Optical Orthogonal Frequency Domain Multiplexing (OFDM), which has a flat optical spectrum and which is thus inherently sensitive to high frequency distortions, e.g., due to limited detector bandwidth. The key to homodyne detection is recovery of the carrier from the received signal all optically (as opposed to frequency offset compensation via digital signal processing. Herein we use optical injection locking (OIL) in conjunction with carrier tone-assisted OFDM to achieve this. In contrast to previous reports, we show that OIL carrier recovery with subsequent homodyne detection can operate without the need for any optical pre-filtering. First, we evaluate the performance as a function of the carrier tone guardband bandwidth. Further, we improve the robustness of this technique using a slow phase lock loop that compensates for drift in the laser’s temperature/current control electronics. Using this improved setup, we compare our all-optical-carrier-recovered homodyne and the ‘traditional’ DSP-assisted intradyne detection for the case of OFDM-16QAM signals. Finally, we compare the computing complexity necessary for both approaches and estimate the intradyne performance limitations due to the carrier-local oscillator frequency offse

Validation of spatial variability in downscaling results from the VALUE perfect predictor experiment

The spatial dependence of meteorological variables is crucial for many impacts, for example, droughts, floods, river flows, energy demand, and crop yield. There is thus a need to understand how well it is represented in downscaling (DS) products. Within the COST Action VALUE, we have conducted a comprehensive analysis of spatial variability in the output of over 40 different DS methods in a perfect predictor setup. The DS output is evaluated against daily precipitation and temperature observations for the period 1979?2008 at 86 sites across Europe and 53 sites across Germany. We have analysed the dependency of correlations of daily temperature and precipitation series at station pairs on the distance between the stations. For the European data set, we have also investigated the complexity of the downscaled data by calculating the number of independent spatial degrees of freedom. For daily precipitation at the German network, we have additionally evaluated the dependency of the joint exceedance of the wet day threshold and of the local 90th percentile on the distance between the stations. Finally, we have investigated regional patterns of European monthly precipitation obtained from rotated principal component analysis. We analysed Perfect Prog (PP) methods, which are based on statistical relationships derived from observations, as well as Model Output Statistics (MOS) approaches, which attempt to correct simulated variables. In summary, we found that most PP DS methods, with the exception of multisite analog methods and a method that explicitly models spatial dependence yield unrealistic spatial characteristics. Regional climate model?based MOS methods showed good performance with respect to correlation lengths and the joint occurrence of wet days, but a substantial overestimation of the joint occurrence of heavy precipitation events. These findings apply to the spatial scales that are resolved by our observation network, and similar studies with higher resolutions, which are relevant for small hydrological catchment, are desirable.Funding Information: EU. Grant Number: EU COST Action ES110