Low loss slow light propagation in silicon slot waveguide

Silicon slot waveguide Bragg gratings have been designed, fabricated and the experimental data has been analyzed for its slow light properties. Slow light with a group index of 12.38 at a wavelength near 1555 nm and having a low propagation loss of 5.1 dB/mm has been determined for internally corrugated slot waveguide Bragg gratings on a silicon-on-insulator platform. The combination of slow light and low propagation loss make the internally corrugated slot waveguide Bragg gratings especially attractive as a phase shifter section for low drive voltage, high speed and compact electro-optic modulators.Web of Science2718262172620

Legacy of pre-disturbance spatial pattern determines early structural diversity following severe disturbance in mountain spruce forests in Czech Republic

Background Severe canopy-removing disturbances are native to many temperate forests and radically alter stand structure, but biotic legacies (surviving elements or patterns) can lend continuity to ecosystem function after such events. Poorly understood is the degree to which the structural complexity of an old-growth forest carries over to the next stand. We asked how predisturbance spatial pattern acts as a legacy to influence post-disturbance stand structure, and how this legacy influences the structural diversity within the early-seral stand. Methods Two stem-mapped one-hectare forest plots in the Czech Republic experienced a severe bark beetle outbreak, thus providing before-and-after data on spatial patterns in live and dead trees, crown projections, down logs, and herb cover. Results Post-disturbance stands were dominated by an advanced regeneration layer present before the disturbance. Both major species, Norway spruce (Picea abies) and rowan (Sorbus aucuparia), were strongly self-aggregated and also clustered to former canopy trees, predisturbance snags, stumps and logs, suggesting positive overstory to understory neighbourhood effects. Thus, although the disturbance dramatically reduced the stand’s height profile with ~100% mortality of the canopy layer, the spatial structure of post-disturbance stands still closely reflected the pre-disturbance structure. The former upper tree layer influenced advanced regeneration through microsite and light limitation. Under formerly dense canopies, regeneration density was high but relatively homogeneous in height; while in former small gaps with greater herb cover, regeneration density was lower but with greater heterogeneity in heights

Horizontal control for stable cadastre and second military survey (Franziszeische Landesaufnahme) in Bohemia, Moravia and Silesia

The paper deals about significant projects of large scale mapping at the beginning of 19th century in the Habsburg Empire. They have been already based on uniform geodetic horizontal control. Basic parameters and features of Second Military Survey in the territory of the Czech Lands as well as links with project of Stable cadastre are delineated. Technology of establishing the horizontal control (1st order trigonometric networks) is described in detail. Qualitative parameters of geodetically measured data and the survey documentation are analysed. Accuracy analysis of angular measurements and methodology of co-ordinate computations in the Gusterberg coordinate system are also discussed.By means of identical points the horizontal control enables unambiguous transformation from the Gusterberg and St. Stephen co-ordinate systems into the national co-ordinate system (JTSK) or WGS 84 with the accuracy higher than graphical accuracy of original maps. This transformation, published here as the global transformation key (GTK), is of great importance. The results of tests of GTKs compiled separately for Bohemia and Moravia+Silesia together with the analysis of contact zone of both above mentioned historical co-ordinate systems are introduced.As an example of GTK application georeferenced map sheets from Second Military Survey are presented. GTKs are of fundamental importance in unification of heterogeneous geodetic information files of cadastre of real estates in the Czech Republic

THE FUNDAMENTAL SPATIAL DATA IN THE PUBLIC ADMINISTRATION REGISTERS

The system of basic registers was launched in the Czech Republic in 2012. The system provides a unique solution to centralize and keep actual most common and widely used information as a part of the eGovernment. The basic registers are the central information source for information systems of public authorities. In October 2014, the Czech government approved the conception of The Strategy for the Development of the Infrastructure for Spatial Information in the Czech Republic to 2020 (GeoInfoStrategy) that serves as a basis for the NSDI. The paper describes the challenges in building the National Spatial Data Infrastructure (NSDI) in the Czech Republic with focus on the fundamental spatial data and related basic registers. The GeoInfoStrategy should also contribute to increasing of the competitiveness of the economy. Therefore the paper also reflects the Directive 2014/61/EU of the European Parliament and of the Council on measures to reduce the cost of deploying high-speed electronic communication networks. The Directive states that citizens as well as the private and public sectors must have the opportunity to be part of the digital economy. A high quality digital infrastructure underpins virtually all sectors of a modern and innovative economy. To ensure a development of such infrastructure in the Czech Republic, the Register of passive infrastructure providing information on the features of passive infrastructure has to be established

Silicon slot waveguide electro-optic Kerr effect modulator

The theoretical background to calculate the effective index tuning using the ultrafast electro-optic Kerr effect and a design of slot waveguide geometry are presented. Analysis of the slot waveguide ring resonator with silicon nanocrystals as the active medium to implement the CMOS compatible electrooptic Kerr effect modulator indicates a modulation bandwidth of 51 GHz, therefore, allowing for 90 Gb/s data rate transmission, and a low energy consumption of 22.99 fJ/bit.Web of Science30987687

Efficient coupling to slow light in a silicon slot waveguide with internal corrugations

We modeled, simulated and experimentally observed efficient slow light coupling to internally corrugated slot Bragg grating (ICSBG) waveguide on a silicon-on-insulator platform. A short step taper is utilized to evanescently couple to the slow light mode near the stopband edge, resulting in minimization of Fabry-Perot reflections due to group index mismatch and a minimum slow light coupling enhancement of similar to 1 dB. This is important as it results in a lower insertion loss ICSBG waveguide, which is capable of low loss slow light propagation and therefore is an attractive option as a phase shifter structure for an on-chip slow light enhanced electro-optic modulator or integrated optic sensor applications.Web of Science598art. no. 08200

Both Cyclone‐induced and Convective Storms Drive Disturbance Patterns in European Primary Beech Forests

Abstract Wind is the leading disturbance agent in European forests, and the magnitude of wind impacts on forest mortality has increased over recent decades. However, the atmospheric triggers behind severe winds in Western Europe (large‐scale cyclones) differ from those in Southeastern Europe (small‐scale convective instability). This geographic difference in wind drivers alters the spatial scale of resulting disturbances and potentially the sensitivity to climate change. Over the 20th century, the severity and prevalence of cyclone‐induced windstorms have increased while the prevalence of atmospheric instability has decreased and thus, the trajectory of Europe‐wide windthrow remains uncertain. To better predict forest sensitivity and trends of windthrow disturbance we used dendrochronological methods to reconstruct 140 years of disturbance history in beech‐dominated primary forests of Central and Eastern Europe. We compared generalized linear mixed models of these disturbance time series to determine whether large‐scale cyclones or small‐scale convective storms were more responsible for disturbance severity while also accounting for topography and stand character variables likely to influence windthrow susceptibility. More exposed forests, forests with a longer absence of disturbance, and forests lacking recent high severity disturbance showed increased sensitivity to both wind drivers. Large‐scale cyclone‐induced windstorms were the main driver of disturbance severity at both the plot and stand scale (0.1–∼100 ha) whereas convective instability effects were more localized (0.1 ha). Though the prevalence and severity of cyclone‐induced windstorms have increased over the 20 century, primary beech forests did not display an increase in the severity of windthrow observed over the same period