1,721,446 research outputs found
Dynamics and bifurcations of a semiconductor laser with short external cavity
No full textWe present a theoretical study into the dynamics and bifurcations of a semiconductor laser subject to delayed optical feedback, as modelled by the Lang-Kobayashi equations. For the case of a short external cavity, of the order of a few centimeters, there is a limited number of external cavity modes (ECMs), which makes it possible to apply advanced techniques from dynamical systems, such as the continuation of ECMs and their bifurcations, and the computation of unstable manifolds. From the physical point of view, a short cavity is characterized by the fact that the delay time in the external cavity is of the same order of magnitude as the period of the relaxation oscillation of the laser. In this regime the optical feedback phase is known to play an important role. We provide a detailed overview of how the dynamics depends on the feedback phase, which is in good agreement with recent experimental measurements
The twin-stripe laser: a non-linear term in the coupling coefficient
No full textLaterally coupled laser-diode pairs, also called twin stripe lasers , are coupled by means of the evanescent em-field in between two dielectric laser cavities. The coupling strength between the two lasers is determined by the decay length of this evanescent em-field. This length depends on the indices of refraction of the material which separates the two cavities compared to the cavity material. However the index of refraction of the cavity material also depends on the inversion density in the lasing material. Therefore the coupling coefficient in the rate equation for the twin stripe device can be written as ¿0[1 + 1/2(ac(1) ¿1 + ac(2) ¿2)], where ¿1 and ¿2 are the inversion densities in the two stripes. We give an expression for ac>(i) in terms of the properties of the device
Silicon-based Broadband Amplifier Design
No full textDIMESElectrical Engineering, Mathematics and Computer Scienc
Dynamics of laterally coupled semiconductor lasers: transition to chaos.
No full textA method for the investigation of the dynamics of two semiconductor lasers, grown side-by-side on the same wafer to enhance the lateral optical coupling, is presented. Using steady state analysis, parameter regimes of relevant dynamics are identified. This is completed by a spectral analysis, were two routes to chaos are implicated. Finally, we confirm the calculations by showing an avoided crossing type of behavior for the coupling strength
Dynamical properties of mutually delayed coupled semiconductor lasers
No full textWe theoretically investigate the dynamical properties of a system of two semiconductor lasers (SLs) that are mutually coupled via their optical fields. An intrinsic feature of the coupling is its time delay which generically arises from the finite propagation time of the light form one SL to the other. In our system the coupling time is in the sub-ns range, which is of the same order of magnitude as the period of SL's internal relaxation oscillations. We model this system with Lang-Kobayashi-type rate equations where we account for the mutual coupling of the two SLs by a delay term. The resulting set of nonlinear delay differential equations, is analyzed by using recently developed numerical continuation. We consider the case of two nearly identical SLs with symmetrical coupling conditions but different frequencies, and present an analysis of the coupled laser modes (CLMs) of the system
Dynamics of delay-coupled semiconductor laser systems
Full text linkNonlinear laser dynamics has received considerable attention because of possible applications, but also fundamental physical and mathematical aspects are of great interest. This thesis is concerned with the dynamical behavior of semiconductor lasers subject to external delayed perturbations. In particular the time delay in the coupling to external elements is of importance, because it substantially complicates the dynamical behavior. This time delay arises from finite signal propagation times and, hence, is large
compared to the laser internal time scales so that it cannot be neglected.
Specifically, the thesis investigates two different delay-coupled semiconductor laser systems: (I) a semiconductor laser subject to delayed filtered optical feedback, where a part of the laser emission
is filtered by a Fabry-Perot filter and then feed back into the laser, and (II) two semiconductor lasers that are mutually delay-coupled via their optical fields. With concepts and tools from dynamical systems
theory a comprehensive study of the underlying bifurcation structure of two systems is presented. Knowledge of this underlying structure is
the key to understanding complicated laser dynamics. The results from the bifurcation analysis are interpreted in terms of the dynamics of
the real laser system and compared with experiments.Krauskopf, B. [Promotor]Lenstra, D. [Promotor
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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