1,720,959 research outputs found
The theoretical design and fabrication of a prism-coupled polarization conversion ferroelectric liquid-crystal light-modulator
No full textIt is possible to probe directly the optical dielectric tensor configuration within thin smectic layers (less than 6 µm thick) of ferroelectric liquid crystals (FLCs) by the propagation of optical prism-coupled leaky Fabry-Pérot modes. Incident polarized monochromatic light couples into the resonant modes of the system and may be coupled out of the cell in an orthogonal polarization. The observed reflectivity is a series of sharp peaks on a low background response at certain well-defined incident angles. These sharp resonant features make the prism-coupling technique a possible route for commercial fabrication of voltage-modulated devices. However, previous prism-coupled cells with sharp resonant guided mode features are not practical from a device point of view because they incorporate silver layers not used in conventional cell design. In this paper we demonstrate for the first time operating a leaky guided mode FLC cell with conventional surface layers, in a sp-mixed polarization mode of operation, allows sharp features to be observed which are modulated in intensity by an applied d.c. voltage. The prism-coupled cells used here are designed to be compatible with current FLC device technology
Optical probing of thin liquid-crystal layers using the prism-coupling technique
No full textPrism-coupling work in polymer aligned liquid crystal layers is presented with special emphasis being placed on the ferroelectric chiral smectic C phase, of interest to electro-optic device fabrication. Experimental results as a function of temperature, wavelength and DC applied voltage are presented, together with a study of sp mixing which may have potential device applications as well as being an elegant technique with which to establish the optical dielectric tensor configuration in thin, aligned liquid crystal layers
Characterisation of secondary silver ion-exchange into potassium ion-exchanged glass waveguides
No full textLocal enhancement of refractive index in potassium-ion-exchanged optical waveguides in glass is of interest for realization of low-loss bends and intersections and more complex structures such as gratings for reflection and phase-matching. Local enhancement may be realized through subsequent ion exchange with an ion having higher polarizability, such as silver. However, in order to design such structures, the diffusion of silver ions into potassium ion-exchanged waveguides must be characterized. In this paper, we present and compare diffusion profiles and coefficients of silver ions in soda-lime glass and in potassium-ion-exchanged waveguides in this glass
A preliminary investigation of the anomalous out-of plane tilt alignment in an orthogonal-twist ferroelectric liquid-crystal cell using the prism-coupling technique
No full textRecent prism-coupling results are presented which clearly demonstrate that in ferroelectric liquid crystal cells, prepared with the alignment directions of the two surfaces orthogonal, with sputtered indium tin oxide conductive layers and spun polyimide alignment layers, there is no out-of-plane tilt of the liquid crystal optic axis. Unlike most techniques which give an integrated optical response throughout a cell, the prism-coupling technique allows a separate analysis of in-plane and out-of-plane tilt. Conventional optical polarized microscopy yields good lateral resolution but poor section resolution. For a uniform sample we can obtain information on the section (across the cell) resolution. We report that an optical dielectric tensor configuration is formed in which the major optic axis lies in the plane of the surface across the cell, but that as expected, in an orthogonal-twist cell, there is no axis of preferred alignment within this surface plane
Electrochemically controlled optical waveguide sensors
No full textOptical techniques are at the forefront of modern analytical methods due to their inherent high specificity. From the point of view of sensor technology, the transfer of chemical information into a measurable signal is of utmost importance. In this respect, planar optical waveguides show great promise for realising novel chemical and biological sensors which use evanescent fields to probe specifically sensitised films on the waveguide surface. Such sensors may detect changes in the refractive index of films using, for example, surface plasmon resonance (SPR) [1], light emission from the binding of proteins labelled with fluorophores [2], or the change in absorption spectrum of a film caused by a chemical reaction [3]. The use of photolithography in integrated optics technology allows mass production of complex multisensors on small and robust substrates. Electrochemical methods allow electrical resetting of reactions, or improved sensitivity through phase-sensitive detection
Electrochemically-controlled waveguide-coupled surface plasmon sensing
No full textA surface plasmon resonance sensing device has been constructed, in which excitation of a surface plasmon on a metal film is achieved by coupling from light propagating in an optical waveguide. The metal film cladding has been used as an electrode surface and it is proposed that these structures may be applied as novel optoelectrochemical sensors. Specific cationic adsorption has been monitored in potential regions where the metal free-electron contribution is small, and the sensitivity of this sensing technique has been deduced by comparison with ellipsometric measurements. The interfacial model used to analyse the ellipsometric results has been tested by calculating coverage by water in the water + ethylene glycol mixture employed in the surface plasmon device. The high sensitivity of this technique to adsorbed films is found to be greater than that predicted by the theoretical model described, and reasons for this discrepancy are discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
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