Revisiting Multi-Step Nonlinearity Compensation with Machine Learning

For the efficient compensation of fiber nonlinearity, one of the guiding principles appears to be: fewer steps are better and more efficient. We challenge this assumption and show that carefully designed multi-step approaches can lead to better performance-complexity trade-offs than their few-step counterparts.Comment: 4 pages, 3 figures, This is a preprint of a paper submitted to the 2019 European Conference on Optical Communicatio

Generating green to red light with semiconductor lasers

Diode lasers enable one to continuously cover the 730 to 1100 nm range as well as the 370 to 550 nm range by frequency doubling, but a large part of the electro-magnetic spectrum spanning from green to red remains accessible only through expensive and unpractical optically pumped dye lasers. Here we devise a method to multiply the frequency of optical waves by a factor 3/2 with a conversion that is phase-coherent and highly efficient. Together with harmonic generation, it will enable one to cover the visible spectrum with semiconductor lasers, opening new avenues in important fields such as laser spectroscopy and optical metrology.Comment: to be published on Optics Expres

Model-Based Machine Learning for Joint Digital Backpropagation and PMD Compensation

In this paper, we propose a model-based machine-learning approach for dual-polarization systems by parameterizing the split-step Fourier method for the Manakov-PMD equation. The resulting method combines hardware-friendly time-domain nonlinearity mitigation via the recently proposed learned digital backpropagation (LDBP) with distributed compensation of polarization-mode dispersion (PMD). We refer to the resulting approach as LDBP-PMD. We train LDBP-PMD on multiple PMD realizations and show that it converges within 1% of its peak dB performance after 428 training iterations on average, yielding a peak effective signal-to-noise ratio of only 0.30 dB below the PMD-free case. Similar to state-of-the-art lumped PMD compensation algorithms in practical systems, our approach does not assume any knowledge about the particular PMD realization along the link, nor any knowledge about the total accumulated PMD. This is a significant improvement compared to prior work on distributed PMD compensation, where knowledge about the accumulated PMD is typically assumed. We also compare different parameterization choices in terms of performance, complexity, and convergence behavior. Lastly, we demonstrate that the learned models can be successfully retrained after an abrupt change of the PMD realization along the fiber.Comment: 10 pages, 11 figures, to appear in the IEEE/OSA Journal of Lightwave Technolog

Model-Based Machine Learning for Joint Digital Backpropagation and PMD Compensation

We propose a model-based machine-learning approach for polarization-multiplexed systems by parameterizing the split-step method for the Manakov-PMD equation. This approach performs hardware-friendly DBP and distributed PMD compensation with performance close to the PMD-free case.Comment: 3 pages, 2 figure

Significant enhancements of nitrogen oxides, black carbon, and ozone in the North Atlantic lower free troposphere resulting from North American boreal wildfires

Copyright © 2006 American Geophysical Union. All Rights Reserved.Extensive wildfires burned in northern North America during summer 2004, releasing large amounts of trace gases and aerosols into the atmosphere. Emissions from these wildfires frequently impacted the PICO-NARE station, a mountaintop site situated 6–15 days downwind from the fires in the Azores Islands. To assess the impacts of the boreal wildfire emissions on the levels of aerosol black carbon (BC), nitrogen oxides and O3 downwind from North America, we analyzed measurements of CO, BC, total reactive nitrogen oxides (NO y ), NO x (NO + NO2) and O3 made from June to September 2004 in combination with MOZART chemical transport model simulations. Long-range transport of boreal wildfire emissions resulted in large enhancements of CO, BC, NO y and NO x , with levels up to 250 ppbv, 665 ng mˉ³, 1100 pptv and 135 pptv, respectively. Enhancement ratios relative to CO were variable in the plumes sampled, most likely because of variations in wildfire emissions and removal processes during transport. Analyses of ΔBC/ΔCO, ΔNO y /ΔCO and ΔNO x /ΔCO ratios indicate that NO y and BC were on average efficiently exported in these plumes and suggest that decomposition of PAN to NO x was a significant source of NO x . High levels of NO x suggest continuing formation of O3 in these well-aged plumes. O3 levels were also significantly enhanced in the plumes, reaching up to 75 ppbv. Analysis of ΔO3/ΔCO ratios showed distinct behaviors of O3 in the plumes, which varied from significant to lower O3 production. We identify several potential reasons for the complex effects of boreal wildfire emissions on O3 and conclude that this behavior needs to be explored further in the future. These observations demonstrate that boreal wildfire emissions significantly contributed to the NO x and O3 budgets in the central North Atlantic lower free troposphere during summer 2004 and imply large-scale impacts on direct radiative forcing of the atmosphere and on tropospheric NO x and O3

North American Boreal Wildfire and Anthropogenic Emissin Impacts in the Lower Free Troposphere over the North Atlantic Region: observations at the PICO-NARE station

AGU Fall Meeting. San Francisco, California, 11-15 December 2006.We present analyses of CO, O3, nitrogen oxides (NOx and NOy) and aerosol black carbon (BC) measurements made in the lower free troposphere (FT) over the North Atlantic region during summers 2004 (ICARTT period) and 2005

Eignung des Anbaues von Körnerleguminosen zur Humanernährung im Alpenvorland

Die Anbaueignung sechs verschiedener traditioneller Speisekörnerleguminosen (Alblinse, Berglinse, Rotholzer Trockenbohne, Black Turtle Buschbohne, Palerbse und blaue Lupine) im Alpenvorland wurde in diesem Versuch getestet. Die Versuchsfragen waren Anbaueignung, Unterschiede im Saatsystem (Breitsaat und Reihensaat) sowie Deckungsbeiträge. Unter allen Speisekörnerleguminosen erzielten die Bohnen die höchsten Erträge (1028 und 1628 kg/ha), gefolgt von der Palerbse (766 kg/ha) und den Linsen (457 und 537 kg/ha). Zwischen den beiden Saatsystemen zeigten sich keine signifikanten Unterschiede

The association of wildfire smoke with respiratory and cardiovascular emergency department visits in Colorado in 2012: a case crossover study

In 2012, Colorado experienced one of its worst wildfire seasons of the past decade. The goal of this study was to investigate the relationship of local PM2.5 levels, modeled using the Weather Research and Forecasting Model with Chemistry, with emergency department visits and acute hospitalizations for respiratory and cardiovascular outcomes during the 2012 Colorado wildfires. Methods: Conditional logistic regression was used to assess the relationship between both continuous and categorical PM2.5 and emergency department visits during the wildfire period, from June 5th to July 6th 2012. Results: For respiratory outcomes, we observed positive relationships between lag 0 PM2.5 and asthma/wheeze (1 h max OR 1.01, 95 % CI (1.00, 1.01) per 10 mu g/m(3)24 h mean OR 1.04 95 % CI (1.02, 1.06) per 5 mu g/m(3)), and COPD (1 h max OR 1.01 95 % CI (1.00, 1.02) per 10 mu g/m(3)24 h mean OR 1.05 95 % CI (1.02, 1.08) per 5 mu g/m(3)). These associations were also positive for 2-day and 3-day moving average lag periods. When PM2.5 was modeled as a categorical variable, bronchitis also showed elevated effect estimates over the referent groups for lag 0 24 h average concentration. Cardiovascular results were consistent with no association. Conclusions: We observed positive associations between PM2.5 from wildfire and respiratory diseases, supporting evidence from previous research that wildfire PM2.5 is an important source for adverse respiratory health outcomes