594 research outputs found
Time-Domain Traveling Wave Model of Quantum Dot DFB Lasers
No full textWe present a time-domain traveling wave model for the simulation of InAs/GaAs quantum dot DFB lasers. The optical susceptibility of the quantum dot (QD) active material is represented through a series of numerical filters that account for the interplay between homogeneous and inhomogeneous broadening of the gain spectrum of the self-assembled QDs. We also consider separate rate equations for electrons and holes for representing the different dynamics of carriers in the conduction and the valence band. We present examples of simulation results focusing in particular on the dynamic properties of the laser (modulation bandwidth, nonreturn-to-zero direct modulation, chirp, α-parameter, etc.) with the purpose of comparing these simulation results with the experimental ones found in the literatur
Un approccio meccatronico per la progettazione e lo sviluppo di sistemi di controllo in asservimento visivo
No full textModern robots and mechatronic systems are equipped with a large number of sensors which give them the possibility to accomplish complex tasks. In recent years the integration of robots and vision system has become critical to improve machinery productivity and versatility. Nevertheless, the most widely used approach is still the "look then move" fashion, in which the vision system simply supports a manipulator without taking part in the robot control task. An alternative technique that allows to merge the vision task and the control one is named "visual servoing" or "vision in the loop". Following this approach, a visual-feedback loop can be added to the standard manipulator control loop in order to drive the robot directly with the information coming from the vision system.
This further controller brings a lot of benefits including: (i) a general increase of the accuracy of the subsystem and its robustness towards environment noise and changes; (ii) the capability to follow fast moving objects; (iii) the possibility to adapt the system to different situations and tasks. On the contrary hand, designing and developing an efficient and robust visual control is tipically a difficult task as it involves various issues like computer vision lgorithms, control theory, robot kinematics and so on. The analysis carried out in this thesis aims to highlight the aspects common to all visual servoing tasks in order to provide a general solution schema for this kind of problems. Firstly, the image acquisition process and image elaboration techniques are presented, with particular attention to their application to "tracking" fast moving objects or scenes; secondly, visual servoing controller design is ntroduced and its kinematic and dynamic issues are studied; eventually, a software architecture for the mplementation of visually guided task is shown along with simple experimental applications used to evaluate the results of the work
FDTW Approach for Simulation of QD lasers and SOAs
No full textWe present a Finite Difference Travelling Wave (FDTW) approach for the simulation of InAs/GaAs quantum dot devices. Several examples of applications will be discussed starting from simple QD-SLDs structures up to passive single section and two section mode-locked lasers
Numerical Investigation of Power Tunability in Two-Section QD Superluminescent Diodes
No full textWe present the results of a one-dimensional (1D) numerical model for the simulation of quantum dot (QD) multi-section superluminescent diodes (SLD) using a rate equation approach. A comparison between experimental and simulated P-I characteristics of a single section SLD is provided in order to validate the model parameters. Using these parameters we analyzed more complicated structures with non-uniform injection and waveguide cross section. The purpose has been to investigate how to increase power at the broad-band emission condition (equal power emission from ground state and excited state) and to tune this condition in a wide range of power. We found that applying a non uniform injection in the two sections no improvement in the maximum output power is achieved at the broad bandwidth condition in devices with uniform waveguide. On the contrary, when a tapered section is introduced, the use of two electrodes and non-uniform current injection allows to obtain larger output power and tunability range respect to the case with uniform injection
Time-domain Travelling-wave Model for Quantum Dot Passive Mode-locked Lasers
No full textWe present a time-domain travelling-wave model for the simulation of passive mode-locking in quantum dot (QD) lasers; accurate expressions for the time varying QD optical susceptibility and the QD spontaneous emission noise source are introduced in the 1-D wave equations and numerically described using a set of infinite-impulse response filters. The inhomogeneous broadening of the density of states of the whole QD ensemble as well as the homogeneous linewidth of each QD interband transition are properly taken into account in the model. Population dynamics in the QD, quantum well, and barrier states under both forward and reverse bias conditions are modeled via proper sets of multi-population rate equations coupled with the field propagation equations. The model is first applied to the study of gain and absorption recovery in a QD semiconductor optical amplifier under both forward and reverse bias conditions. Simulations of passive mode-locking in a two-section QD laser are then performed as a function of the bias parameters. Gain and absorption dynamics leading to the generation of mode-locking pulses is described. The onset of a trailing-edge instability at low currents is observed and fully explained in the framework of the described model
In the shadow of the church: the building of mosques in early medieval Syria
No full textIn his book In the Shadow of the Church: The Building of Mosques in Early Medieval Syria Mattia Guidetti examines the establishment of Muslim religious architecture within the Christian context in which it first appeared in the Syrian region, contributing to the debate on the transformation of late antique society to a Muslim one. He scrutinizes the slow process of conversion to Islam of the most important town centers by looking at religious places of both communities between the seventh and the eleventh century. The author assesses the relevancy of churches by analyzing the location of mosques and by researching phenomena of transfer of marble material from churches to mosques
A Formal High-level Modeling Approach to Develop Reliable Components in Vision-based Robotics
No full textA time-domain travelling-wave model including multi-population rate-equations for passively mode-locked quantum-dot lasers
No full textSimulation and design of high power gain guided quantum dot tapered lasers operating in passive mode-locking regime
No full textModelling passive mode-locking in quantum-dot lasers using a finite difference travelling-wave model with multi-population rate equations
No full text- …
