Design and simulation of DBR lasers with extended modulation bandwidth exploiting photon-photon resonance effect

In high-speed laser devices the occurrence of a pho-ton-photon resonance increases the modulation bandwidth sub-stantially. In this paper our attention is focused on the design of DBR lasers in which this effect is exploite

The equations of motion of a secularly precessing elliptical orbit

The equations of motion of a secularly precessing ellipse are developed using time as the independent variable. The equations are useful when integrating numerically the perturbations about a reference trajectory which is subject to secular perturbations in the node, the argument of pericenter and the mean motion. Usually this is done in connection with Encke's method to ensure minimal rectification frequency. Similar equations are already available in the literature, but they are either given based on the true anomaly as the independent variable, or in mixed mode with respect to the time through the use of a supporting equation to track the anomaly. The equations developed here form a complete and independent set of six equations in the time. Reformulations both of Escobal's and Kyner and Bennett's equations are also provided which lead to a more concise form.Comment: Accepted in Monthly Notices of the Royal Astronomical Society. Paper presented at the "New Trends in Astrodynamics and Applications VI" conference, Courant Institute of Mathematical Sciences, New York University New York, NY, 6-8 June 201

Analysis of self-pulsating three-section DBR lasers

The characteristics of a three-section distributed Bragg reflector laser showing self-pulsation have been analyzed using a large signal time-domain traveling-wave simulator. The device dynamic properties have been investigated in all their complexity and analyzed as functions of the linewidth enhancement factor and of the injected current in the active and in the phase control sections. The simulation results have clearly shown the fundamental role of four wave mixing on the laser characteristics (output power, spectrum, etc.) and have been quantitatively correlated with the few available theoretical and experimental results. The considered self-pulsation operation frequencies around 40 GHz are of interest for practical applications

Modeling passive mode-locking in InAs quantum dot lasers with tapered gain sections

We propose a computationally efficient approach for the simulation and design of index-guided quantum-dot (QD) passively mode-locked lasers with tapered gain section; the method is based on the combination of simulations based on a finite differ-ence beam-propagation-method and dynamic simulations of mode-locking via a multi-section delayed differential equation model. The impact of varying the taper full angle on the pulse duration and peak power is investigated; simulations show that a correct choice of this parameter enables the generation of sub-picosecond optical pulses with peak power exceeding 5

Topology of local information dynamics during motor decision in the premotor cortex of primates

Complex systems are very large systems comprising millions of agents interacting with each other and whose collective behaviour cannot be understood from the elementary features. In this sense the brain is the complex system par excellence: hundreds of billions of densely packed electrically excitable cells called neurons with hundred of millions of connections each. All exchanging electrochemical signals over short and long distances every few milliseconds and functionally interacting over multiple scales of time. Within this apparent chaotic bundle some deep questions arise. A single neuron is not in itself "intelligent" but a vast network of neurons can think, perceive, remember and generate the many extraordinary phenomena that they are collectively known as mind. How the mind can emerge from the interconnection between different neurons? How can single interactions between neurons organize themselves into manifestations collectively coherent like perception and movement

Explicit analytical solutions for the full plane-stress field in sandwich beams under flexure governed by zigzag warping

We provide analytical solutions for the full stress field of straight sandwich beams with identical skins subject to linear elastic flexure governed by zigzag warping, where all layers obey Timoshenko’s kinematics. As a main novelty, we make use of an equilibrium equation for the Cauchy continuum to recover of the through-the-thickness normal stress component, sy. The new estimates are accurate for a wide range of relative stiffness between skins and core and suitable boundary conditions, as it can be demonstrated through the comparison with detailed finite element simulations where the sandwich is modelled as a two-dimensional continuum. As a main practical result concerned with the study of delamination, we find that at a core-skin interface of a cantilever sandwich subjected to a uniformly distributed load, in a region close to the fully-clamped crosssection, sy is a tensile stress of magnitude larger than that of the shear stress. On this basis, we infer that the availability of good estimates for sy, along with those for the longitudinal and shear stresses, may be important for the accurate design of sandwich panels

Hierarchical organization of functional connectivity in the mouse brain: a complex network approach

This paper represents a contribution to the study of the brain functional connectivity from the perspective of complex networks theory. More specifically, we apply graph theoretical analyses to provide evidence of the modular structure of the mouse brain and to shed light on its hierarchical organization. We propose a novel percolation analysis and we apply our approach to the analysis of a resting-state functional MRI data set from 41 mice. This approach reveals a robust hierarchical structure of modules persistent across different subjects. Importantly, we test this approach against a statistical benchmark (or null model) which constrains only the distributions of empirical correlations. Our results unambiguously show that the hierarchical character of the mouse brain modular structure is not trivially encoded into this lower-order constraint. Finally, we investigate the modular structure of the mouse brain by computing the Minimal Spanning Forest, a technique that identifies subnetworks characterized by the strongest internal correlations. This approach represents a faster alternative to other community detection methods and provides a means to rank modules on the basis of the strength of their internal edges.Comment: 11 pages, 9 figure

Semiconductor racetrack resonator coupled to an S‐bent waveguide: Influence of the coupling coefficients on the unidirectional operation

Semiconductor ring lasers have attracted remarkable interest as laser sources in photonic integrated circuits. They result in bidirectional laser owing to the rotation symmetry between the two counter-propagating modes of the ring cavity. This symmetry can be broken incorporating in a racetrack resonator an S-bend waveguide, which generates an unbalanced loss mechanism and a nonreciprocal gain between clockwise and counter-clockwise direction beams. The propagating field along the resonator in the undesirable direction is evanescently coupled to the S element in correspondence of two coupling regions and converted into the preferred one. In this work, we examined how the field coupling coefficients of the couplers impact the resonator unidirectionality. In numerical simulations, we changed the coupler gap distance and the coupler length of the directional couplers to scan the full range of variability of the coefficients. The simulated performances of the resonator are discussed in term of the extinction ratio between the clockwise and the counter-clockwise modes as well as the power truly circulated in the two directions of the resonator net of all losses. The finite-difference time-domain method within Synopsys RSoft© suite was used to simulate the evolution of the counterpropagating field along the racetrack

A Python Tool to Control and Virtualize Laser Diodes Characterization Benches

We present a Python tool for the control of the laboratory instruments (thermal electric control, power meter, optical spectrum analyzer) used for the characterization of semiconductor laser sources in the framework of master degree courses available at Politecnico di Torino. This software can be used to control real benches, acquiring and elaborating the measurement data, but it can also work offline emulating the behavior of instruments and laser sources, thus allowing the students to work in a completely virtualized environmen