1,721,040 research outputs found
Slow and Stopped Light in Dynamic Moire Gratings
No full textDataset for paper 'Slow and Stopped Light in Dynamic Moire Gratings' published in Physical Review A (PRA) </span
Slow light propagation through a Moire grating at the zero dispersion wavelength
No full textThe reduction in the group velocity of a light pulse, or ‘slow light’, has many practical applications including optical switching and buffers. We investigate slow light propagating near the band edge of a Bragg grating. At the Bragg wavelength a resonance occurs in the reflection spectrum creating a photonic band gap. At wavelengths close to the band edge light is transmitted through the grating and a reduction in group velocity is observed, but also an increase in group velocity dispersion (GVD) leading to large pulse broadening preventing any practical use. We present a possible resolution to this problem.We analyse single period Bragg gratings using coupled mode theory. For a pulse with a given carrier frequency and desired group velocity, there exist two grating periods for a chosen AC grating modulation which produce a band gap above and below the carrier frequency respectively. In both cases, as the group velocity tends to zero the GVD diverges causing substantial pulse broadening. One grating period produces normal and the other anomalous GVD, suggesting that a Moiré grating that superimposes both grating periods could be used to create a zero dispersion wavelength at the carrier frequency. To simulate pulse propagation through such a grating, we employ matrix transfer methods and numerical optimisation to find the grating parameters which produce the smallest group velocity and GVD for a given pulse bandwidth.Our initial results demonstrate a group velocity reduction by a factor of 4 with negligible pulse broadening. We are currently examining the use of apodisation which will provide an improvement in the grating transmission spectrum and increase the allowable pulse bandwidth. With this we expect to achieve group velocity reduction by a further two orders of magnitude whilst minimising pulse broadening
Slow and stopped light in dynamic Moiré gratings
No full textWe investigate a theoretical model for a dynamic Moiré grating which is capable of producing slow and stopped light with improved performance when compared with a static Moiré grating. A Moiré grating superimposes two grating periods, which creates a narrow slow light resonance between two band gaps. A Moiré grating can be made dynamic by varying its coupling strength in time. By increasing the coupling strength the reduction in group velocity in the slow light resonance can be improved by many orders of magnitude while still maintaining the wide bandwidth of the initial, weak grating. We show that for a pulse propagating through the grating this is a consequence of altering the pulse spectrum, and therefore the grating can also perform bandwidth modulation. Finally we present a possible realization of the system via an electro-optic grating by applying a quasistatic electric field to a poled χ(2) nonlinear medium.</p
Slow-light enhanced second-harmonic generation using a π-phase shifted Moiré grating in a quasi-phased-matched medium
No full textSlow light is the phenomenon of a large reduction in group velocity, normally due to a material resonance. Slow light causes spatial compression and consequently large field enhancement which has been suggested as a method for increasing nonlinear optical effects. Here we investigate the use of a Moiré grating for enhancing second-harmonic generation (SHG) in a χ(2) medium.&more...<br/
Grating-induced slow-light enhancement of second harmonic generation in periodically poled crystals
No full textThe effect of slow light on second-harmonic generation in a periodically poled χ(2) nonlinear medium is investigated theoretically. A linear π phase-shifted grating is used to slow the group velocity of the fundamental frequency, and the resulting field enhancement greatly increases the second-harmonic conversion efficiency. A second linear grating at the input end ensures that all output is in the forward direction. We show that almost 100% conversion efficiency can be achieved for continuous wave pumping at low intensities that generate negligible conversion in the absence of the slow-light grating.</p
Grating-induced slow-light enhancement of second-harmonic generation in periodically poled crystals
No full textDataset for paper 'Grating-induced slow-light enhancement of second-harmonic generation in periodically poled crystals' published in Physical Review A (PRA) </span
Integrated quantum photonics
No full textThis chapter will only be concerned with quantum photonics; systems where the photons themselves act as carriers of quantum informatio
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
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