1,720,996 research outputs found
Geometry optimization of unidirectional integrated ring laser
Full text linkRing lasers, evanescently coupled to an adjacent optical waveguide, are essential components for the upcoming generation of integrated sources. In an ideally symmetric resonator, emission occurs from the both clockwise and counter-clockwise directions, resulting in a potential waste of emitted optical power, while unidirectional emission has been reported in different configurations, for example when asymmetric external reflectivities are used for the coupling waveguide. In the integrated form, a common approach consists in the inserting an S-bend waveguide in the ring, in such a way that the field propagating in the direction that we want to suppress is reinjected in the other direction. The S-bend waveguide must be carefully designed to reduce optical losses and to ensure a sufficient suppression of the undesired field. Using 2D finite- difference time-domain simulations performed with Synopsys RSof
Delayed differential equation based study of sub-terahertz emission in multi-section quantum dot ring lasers
Full text linkWe present a study of the generation of subterahertz pulses in multi-section quantum dot (QD) ring lasers based on an improved version of the well-established delayed differential equation model, and taking into account an arbitrary number of gain and absorber sections. Results of the analysis of an 8-section ring laser emitting at 1.3 μm are presented. The proposed approach provides a significant insight for the understanding of the onset of the harmonic mode-locking in this family of devices and shows to be an effective tool for the optimization of the real devices in terms of pulses quality and generated RF intensity
S-shaped waveguide-induced asymmetry between counter-propagating modes in a racetrack resonator
Full text linkOngoing progress in photonic integrated circuits necessitates the integration of semiconductor ring lasers (SRLs) with high performance and predictable behavior, which can be achieved when the symmetry of the SRL, which supports both clockwise and counterclockwise beam propagation, is unbalanced through loss mechanisms inside the resonator. In this work, numerical simulations were carried out on the symmetric layout of the racetrack resonator equipped with an asymmetric S-shaped internal waveguide. The simulations results were compared with the ones of analogue structures without internal waveguide showing the benefit induced by this additional element in term of the unidirectionality of the SRL
Design and simulation of quantum-dot-based push-pull DFB lasers
No full textWe present an analysis of Quantum Dot (QD) based Push-Pull modulated DFB (PP-DFB) laser, showing enhanced small and large signal modulation bandwidth thanks to the interaction between two longitudinal cavity modes. Using an analysis of the cavity modes at threshold, we propose a simple yet effective design technique which allow to select the cavity length and the coupling coefficient to obtain the desired extension of the modulation bandwidth. The design is validated using a Time Domain Travelling Wave (TDTW) model including a proper description of the Quantum Dot material and of the standing wave pattern generated by the cavity field. Our results show that QD PP-DFB can effectively take advantage of the Push-Pull modulation scheme to increase their modulation bandwidth
A simple coupled-bloch-mode approach to study active photonic crystal waveguides and lasers
Full text linkSimulation of Quantum Dot Fabry-Perot Comb Lasers: Role of the Carrier Grating
No full textWe report a systematic analysis of multi-mode dynamics and in Quantum Dot single section lasers using a Time Domain Travelling Wave model. We observed that the inclusion of the carrier grating effect in our model reduces the multi-mode instability threshold and eventually leads to the generation of optical frequency combs
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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