1,721,066 research outputs found
Assessment of the orthogonal and non-orthogonal coupled-mode theory for parallel optical waveguide couplers
No full textThe coupled-mode theory (CMT) is a powerful approach routinely used to calculate the effects of spatial mode interactions in perturbed structures, such as optical waveguides. One of its basic hypotheses requires that perturbations are weak. This is usually not the case for devices fabricated with modern semiconductor-based technologies. In this paper, the CMT is studied in these critical cases to assess its validity. Attention will be focused on the quite common case of parallel coupled waveguides. For these structures, results can in fact be compared to the exact ones, obtained using super-modes. The study will show that not all the possible expressions of the coupling coefficients are equivalent, and which one can be pragmatically used to obtain results with minimum errors with respect to exact solutions
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
Differential Optical Sensing through Coupled Micro Ring Resonators
No full textWe theoretically investigate the performance of a double micro ring resonator for integrated optical sensing applications. The transmission characteristics of the proposed device can be driven in two distinct operations by controlling the difference of the round-trip phase shifts of the coupled resonators. The enhancement of the limit of detection by a factor of 5.6 compared to a single micro ring based sensor is demonstrated. Beside the fact that the single and double ring based schemes have the same spectral wavelength sensitivity of 918 nm per refractive index unit, the latter scheme also supports the intensity interrogation which can be used for on-chip thermal noise compensation via integrated micro heaters
Transfer matrix and full Maxwell time domain analysis of nonlinear gratings
No full textIn this paper we show that the transfer matrix method and the finite difference time domain technique applied to the full time-dependent Maxwell equations (in their one-dimensional form) permit to improve the description of nonlinear distributed feedback structures such as Bragg gratings. In fact, no simplifying hypothesis are introduced in the electromagnetic problem by these two numerical approaches.
The two techniques validate qualitatively the results based on the standard coupled-mode theory for weakly nonlinear and shallow gratings, while significant quantitative deviations can appear in other cases
Nonlinear Characterization and Modeling of Periodically Poled Lithium Niobate Waveguides for 1.5-mm-Band Cascaded Wavelength Conversion
No full textVariations 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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