121,793 research outputs found
Role of microstructure and layer thickness in porous silicon conductometric gas sensors
No full textThe electrical injection in porous silicon fabricated with heavily doped p-type silicon is very sensitive to NO 2. The known effect is an injection increase associated to NO 2. We show experimentally a strong correlation between two structural properties and the sensitivity of electrical injection to NO 2. The first property is the microstructure, i.e. the pore morphology at nm scale. A structure with straight, elongated pores shows large sensitivity, as opposed to a branching structure. The second property is the layer thickness, which determines the sign of the effect of NO 2. If the thickness is sufficiently low - of the order of few Urn - the injection in presence of NO 2 decreases, instead of increasing. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Mechanical oscillations in lasing microspheres
No full textThis is the preprint version of the paper available at: https://dx.doi.org/10.1063/1.4997182
A. Toncelli, N. E. Capuj, B. Garrido, M. Sledzinska, C. M. Sotomayor-Torres, A. Tredicucci, D. Navarro-Urrios. Mechanical oscillations in lasing microspheres. Journal of Applied Physics, 2017, 122:
Vertical coupling of laser glass microspheres to buried silicon nitride ellipses and waveguides
No full textWe demonstrate the integration of Nd3+ doped barium-titanium-silicate microsphere lasers with a silicon nitride photonic platform. Devices with two different geometrical configurations for extracting the laser light to buried waveguides have been fabricated and characterized. The first configuration relies on a standard coupling scheme, where the microspheres are placed over strip waveguides. The second is based on a buried elliptical geometry whose working principle is that of an elliptical mirror. In the latter case, the input of a strip waveguide is placed on one focus of the ellipse, while a lasing microsphere is placed on top of the other focus. The fabricated elliptical geometry (ellipticity = 0.9) presents a light collecting capacity that is 50% greater than that of the standard waveguide coupling configuration and could be further improved by increasing the ellipticity. Moreover, since the dimensions of the spheres are much smaller than those of the ellipses, surface planarization is not required. On the contrary, we show that the absence of a planarization step strongly damages the microsphere lasing performance in the standard configuration
Polymeric waveguides using oxidized porous silicon cladding for optical amplification
No full textWe report on a new hybrid approach to realize optical slab waveguides for optical amplification purposes. The structure consists of a dye-doped polymer core (PMMA) deposited over an oxidized porous silicon (PS) cladding layer formed on a silicon wafer. The very low refractive index (n = 1.16) achievable in the cladding allows obtaining monomodal behavior with high confinement factors (GTE = 96%) even for very thin cores (400 nm). Optically excited guided luminescence shows stimulated emission, strong line narrowing and a clear threshold and superlinear behavior with pump energy. By means of the variable stripe length (VSL) technique, values of net optical gain up to 113 dB/cm (constant over 3 mm) and absolute amplification values up to 34 dB have been measured at 694 nm when pumping with 80 mJ/cm2 energy pulses. These results validate the use of oxidized PS as a cladding layer in silicon photonics
Tunneling escape process from a spin-polarized two-dimensional electron system
No full textIn this work, we have numerically integrated in space and time the effective-mass nonlinear Schrödinger equation for an electron wave packet in a double barrier heterostructure. Considering both polarized and unpolarized magnetic phases, we have studied the tunneling escape process from the two-dimensional electron gas. Due to the nonlinear effective-mass equation, it is found that the charge trapped dynamically in the quantum well produces a reaction field, which modifies the tunneling escape process in the quantum well. At different electronic sheet densities, we have shown the possibility of having magnetic phase-dependent tunneling rates. © 2001 Elsevier Science Ltd
Optical gain in conjugated polymer hybrid structures based on porous silicon waveguides
No full textThe fabrication and optical characterization of a hybrid waveguide formed by a MDMO-PPV semiconductor layer deposited on a porous silicon cladding is reported. Evidence of amplified spontaneous emission is observed when the intensity of the excitation pump pulses is higher than a certain threshold. A net gain coefficient of about 50 ± 8 cm-1 is estimated, which is similar to those reported for other PPV derivate conjugated polymers. The demonstration of positive optical gain in these hetero-structures is very promising because new photonic structures could be envisaged due to the versatility of the porous silicon cladding
Fabrication and optimization of rugate filters based on porous silicon
No full textWe report an experimental study of porous silicon-based rugate filters. Possible optimisations that can improve different features of the filters are investigated. We demonstrate sidelobe attenuation by means of half-apodization of the structures with a sinusoidal window. Reduction of interference ripples are experimentally observed through the insertion of index-matching layers on the boundaries of the structure. The superposition of two different designs to obtain a multi-stop-band filter is also demonstrated. We show the possibility of controlling the bandwidth of the stop-bands by varying the index contrast. All the results are discussed and compared with numerical calculations. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
A Multi-Language Comparison of Influences on Author Verification using Character N-Grams
No full textWe create a new multi-language corpus for author verification based on Wikipedia talkpages, and evaluate the influence that differences in topic and time have on character n-gram author profiles. Topic alignment between two texts is found to increase author verification precision, and an authors writing style is found to change over time, but not more significantly after 3 years than after 1 year.Information ArchitectureWISElectrical Engineering, Mathematics and Computer Scienc
Waveguiding, absorption and emission properties of dye-impregnated oxidized porous silicon
No full textThe waveguiding, absorption and emission properties of oxidised porous silicon waveguides when impregnated with Nile Blue have been studied. We present m-line measurements before and after the impregnation showing that the effective indices of the modes remain the same. When performing guided luminescence experiments, a structured emission band is measured. Using the refractive index profile extracted from m-line measurements it has been possible to simulate the emission lineshape assuming the observation of an interference pattern formed across the waveguide. We demonstrate that these oscillations appear because in the first hundreds of nanometers the dye concentration is several orders of magnitude higher than in the rest of the sample. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
