1,720,978 research outputs found
Design considerations for quasi-phase-matching in doubly resonant Lithium Niobate hexagonal micro-resonators
No full textFabrication capabilities of high optical quality hexagonal superstructures by chemical etching of inverted ferroelectric domains in Lithium Niobate platform suggests a route for successful implementation of compact hexagonal microcavities. Such nonlinear optical hexagonal micro-resonators proposed as a platform for second harmonic generation (SHG) by the combined mechanisms of total internal reflection (TIR) and quasi-phase-matching (QPM). The proposed scheme for SHG via TIR-QPM in a hexagonal microcavity can improve the efficiency and also the compactness of SHG devices compared to traditional linear-type based devices. A simple theoretical model based on six-bounce trajectory and phase matching conditions was capable for obtaining the optimal cavity size. Furthermore numerical simulation results based on finite difference time domain (FDTD) Beam Propagation Method (BPM) analysis confirmed the solutions obtained by demonstrating resonant operation of the microcavity for the second harmonic wave produced by TIR-QPM. Design aspects, optimization issues and characteristics of the proposed nonlinear device are presented
Design optimization of gold-coated fiber tips with embedded plasmonic slot nano-resonators
No full textNanostructures of dimensions around the operating wavelength of light can support optical resonances enhancing the incident light by orders of magnitude and concentrating it in the nanoscale. Their integration to optical fiber tips with thin metallic claddings, forming plasmonic slot nanoresonators (PSNRs), provides ease of light coupling from the fiber’s core modes to the slot and a robust platform which can find many applications in nano-optics and sensing. Guiding and modal properties of metal-coated optical fiber tips with embedded PSNRs are investigated through finite element method (FEM) simulations towards the identification of their optimization parameters. It was found that the placement of a PSNR at the cut-off radius of a metal-coated fiber tip, where the group velocity tends to zero, leads to considerable intensity enhancement of the field confined beyond the diffraction limit. Maximum intensity enhancement of optimally placed PSNRs at different radii shows a linear dependence between excitation wavelength and radius, making it feasible to engineer the proper radius for a specific wavelength for maximum enhancement
Second harmonic generation via total internal reflection quasi-phase-matching in a hexagonal nonlinear optical microresonator
No full textWe propose the enhancement of the second harmonic generation process in an optical hexagonal microcavity, consisting of a nonlinear material, via total internal reflection quasi-phasematching technique. We present preliminary numerical simulation results showing resonance operation in a suitably designed hexagonally shaped optical microresonator, which demonstrates the operating feasibility of the proposed scheme. The SHG efficiency was calculated using lithium niobate as the nonlinear material. High optical quality hexagonal superstructures can be manufactured routinely by chemical etching of inverted ferroelectric domains in this material
UV written waveguides using crosslinkable PMMA-based copolymers
No full textCrosslinkable copolymers poly(methylmethacrylate/2-methacryloylethylmethacrylate) (P(MMA/MAOEMA)) were developed for waveguide applications. P(MMA/MAOEMA) can crosslink under either UV exposure or heating. The UV-induced refractive index change in unreacted P(MMA/MAOEMA) is found to depend on-the fluence. UV exposure of thermally crosslinked P(MMA/MAOEMA) can induce further structure change and thus index change, and therefore, was found to be useful for creating the core layers in optical waveguides. The photosensitivity of the thermally crosslinked polymers is sufficient for the fabrication of low, loss (<1 dB/cm) channel waveguides in the thermally crosslinked copolymer system
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
All-fiber plasmonic platform based on hybrid composite metal/glass microwires
No full textMetal tips are emerging plasmonic structures that can offer high field intensity at the tip apex and high confinement in the nanoscale. The fabrication though of smooth metal tips with well-defined geometrical characteristics, crucial for optimizing the performance of the plasmonic structure, is not trivial.Furthermore pure metal tips are exposed to the environment and fragile, thus, complicating their use in real applications. The proposed platform based on hybrid composite glass metal microwires can offer the required robustness for device development. An optimized fabrication process of high quality all-fiberplasmonic tips by tapering such hybrid metal core/dielectric cladding microfibers is proposed and demonstrated experimentally. The presence of the dielectric cladding offers continuous re-excitation of the plasmon modes due to repeated total internal reflection at the glass/air interface which can dramaticallyreduce the high losses induced by the metal core. This enables direct light coupling from the distal end of fiber instead of side excitation of the tip, allowing thus their integration in optical fiber and planar circuits.Plasmonic tips were successfully demonstrated in a highly controllable manner and their performance was related to simulation results predicting high field enhancement factors up to 105
Demonstration and accurate beam propagation method modeling of direct UV written shallow angle X-couplers
No full textBPM modeling of UV written X-couplers shows excellent agreement with measured data by careful choice of launch conditions, index values and allowance for hydrogen outdiffusion effects. Comparison with recent analytical model is also presented
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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