Optical near-field dynamics of active 2D semiconductors

When structures with a strong confinement of the electromagnetic fields are considered, the near-field dynamics becomes integral to the description of a semiconductor. Not only it provides feedback from the environment, as is the case in a laser system, but it further mediates the interaction between different, otherwise independent, positions. In such a context, a full-field spatio-temporal description is essential to faithfully describe the dynamics of either an extended semiconductor system or a set of spatially separated emitters. This thesis highlights the importance of combining a complex (many-body and band-resolved) model of semiconductor carrier dynamics with a full-field description of the electromagnetic fields by presenting some applications. With the recent rise in popularity of atomically thin materials, semiconductors can be embedded in increasingly smaller optical environments, whose properties can only be studied by self-consistently combining carrier and field dynamics. The ability to calculate the linear and non-linear response of a system under arbitrary excitation conditions is shown. This is performed without any prior knowledge of the electromagnetic environment and can thus be extended to complex geometries. By embedding active materials in a tailored environment, the complex interaction of the two can be exploited to engineer the optical response of the system by using a self-consistent modelling technique. The complex dynamical interaction between field and gain in a semiconductor laser is another example of a system in which a self-consistent model is required. Here, a set of one-dimensional simulations is reported showing how the output of a semiconductor laser is highly sensitive to perturbation arising from sub-wavelength dynamics of the gain medium. By introducing a random patterning of the laser cavity, a novel approach to the suppression of dynamical instabilities in a laser output is demonstrated. This scheme, based on complex wave interference, is introduced by spatially perturbing the optical environment.Open Acces

Suppressing spatio-temporal lasing instabilities with wave-chaotic microcavities

Spatio-temporal instabilities are widespread phenomena resulting from complexity and nonlinearity. In broad-area edge-emitting semiconductor lasers, the nonlinear interactions of multiple spatial modes with the active medium can result in filamentation and spatio-temporal chaos. These instabilities degrade the laser performance and are extremely challenging to control. We demonstrate a powerful approach to suppress spatio-temporal instabilities using wave-chaotic or disordered cavities. The interference of many propagating waves with random phases in such cavities disrupts the formation of self-organized structures like filaments, resulting in stable lasing dynamics. Our method provides a general and robust scheme to prevent the formation and growth of nonlinear instabilities for a large variety of high-power lasers

L’ICT asset management per beni e servizi: webgepetec, il sistema proposto dal CASPUR

L’efficienza dell’organizzazione e dei processi per le ICT è sempre più un fattore critico di successo nello sviluppo delle aziende. Un adeguato sistema per l’ICT Asset Management consente di ottenere le informazioni in tempo reale migliorando le capacità decisionali ed operative. WebGepetec è il sistema proposto per la gestione centralizzata, integrata e multidimensionale dei dati ICT

Highly parallel ultra-fast random number generation from a stable-cavity broad-area semiconductor laser

International audienc

Spatio-temporal dynamics of microlasers with chaotic ray dynamics

International audienc

Massively parallel ultrafast random bit generation with a chip-scale laser

International audienceRandom numbers are widely used for information security, cryptography, stochastic modeling, and quantum simulations. Key technical challenges for physical random number generation are speed and scalability. We demonstrate a method for ultrafast generation of hundreds of random bit streams in parallel with a single laser diode. Spatiotemporal interference of many lasing modes in a specially designed cavity is introduced as a scheme for greatly accelerated random bit generation. Spontaneous emission, caused by quantum fluctuations, produces stochastic noise that makes the bit streams unpredictable. We achieve a total bit rate of 250 terabits per second with off-line postprocessing, which is more than two orders of magnitude higher than the current postprocessing record. Our approach is robust, compact, and energy-efficient, with potential applications in secure communication and high-performance computation

Sensitive control of broad-area semiconductor lasers by cavity shape

The ray dynamics of optical cavities exhibits bifurcation points: special geometries at which ray trajectories switch abruptly between stable and unstable. A prominent example is the Fabry-Perot cavity with two planar mirrors, which is widely employed for broad-area semiconductor lasers. Such cavities support lasing in a relatively small number of transverse modes, and the laser is highly susceptible to filamentation and irregular pulsations. Here we demonstrate experimentally that a slight deviation from this bifurcation point (planar cavity) dramatically changes the laser performance. In a near-planar cavity with two concave mirrors, the number of transverse lasing modes increases drastically. While the spatial coherence of the laser emission is reduced, the divergence angle of the output beam remains relatively narrow. Moreover, the spatio-temporal lasing dynamics becomes significantly more stable compared to that in a Fabry-Perot cavity. Our near-planar broad-area semiconductor laser has higher brightness, better directionality and hence allows shorter integration times than an incandescent lamp while featuring sufficiently low speckle contrast at the same time, making it a vastly superior light source for speckle-free imaging. Furthermore, our method of controlling spatio-temporal dynamics with extreme sensitivity near a bifurcation point may be applied to other types of high-power lasers and nonlinear dynamic systems.Comment: 17 pages, 11 figure