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showing 10 items of 2078 documents
Enhanced Q-switched distributed feedback fiber laser based on acoustic pulses
2009
An acoustically Q-switched distributed feedback fiber laser with enhanced performance is presented. It is based on an FBG written in an erbium doped fiber, in which a dynamic defect is introduced by means of a short acoustic pulse. The performance of the laser depends on the reflectivity of the grating. In this work, we present two different Q-switched distributed feedback fiber lasers realized with active gratings of different reflectivities. Both lasers are characterized at different pump powers and repetition rates. It is shown that the performance of the laser based on the weaker grating was significantly improved with respect to the laser based on the stronger grating. In terms of peak…
Active Q-switched distributed feedback erbium-doped fiber lasers
2005
This letter presents a distributed feedback fiber laser that operates in an actively controlled Q-switched regime. The laser is based on a Bragg grating made in an erbium-doped fiber. The grating has a defect induced by a magnetostrictive transducer that configures the distributed feedback laser structure. The phase shift generated by the defect can be dynamically modified by an electric current, permitting active Q-switching of the laser. The laser generates pulses of 75 ns duration and the repetition rate can be continuously adjusted from 0 to 10 kHz.
4W continuous-wave narrow-linewidth tunable solid-state laser source at 546nm by externally frequency doubling a ytterbium-doped single-mode fiber la…
2009
A high-power continuous-wave coherent light source at 545.5nm is described. We use 8.3W from a solid-state ytterbium-doped single-mode fiber oscillator/amplifier system as input into an external frequency doubling stage. This system produces up to 4.1 W of stable green single-frequency laser radiation. We characterize the light source by performing absorption spectroscopy on iodine across the full tuning range of the fiber laser and saturation spectroscopy on one strong iodine line of the doppler-broadened spectrum.
Dissipative Solitons, a Novel Paradigm for Mode-locked Lasers
2013
The concept of a "dissipative soliton" provides an excellent framework for understanding complex mode-locked laser pulse dynamics from a unified picture. It has stimulated innovative laser cavity designs in the past few years. This tutorial lecture provides conceptual pictures illustrated with universal dynamics, highlights recent achievements and prospects for mode-locked laser development.
Direct solution of compensated radial distribution networks with constant impedance/current loads
2009
In this paper, a methodology to solve radial distribution networks, with constant current and/or impedance loads as well as shunt capacitor banks, is proposed. The techniques currently available to solve such systems are based either on iterative methods or on the bus impedance matrix. In both cases, the elaboration times are quite high since these are related, for iterative methods, to the overall number of iterations, and, for those methods based on the impedance matrix, to the inversion of the admittance matrix. The method developed here is the extension of a technique that is valid to solve networks made of impedances with one supply point. The methodology can also be applied in the sol…
Decoupled solution of radial and weakly meshed distribution networks through a backward method
2008
A methodology for the analysis of radial or weakly meshed distribution systems supplying voltage dependent loads is developed. The solution process is iterative and, at each step, the loads are simulated by means of impedances. The network is divided into two sub-networks which must be solved separately and sequentially; in the first, named RP-net, only the lines resistances and the loads shunt equivalent resistances are considered; in the second, named XQ-net, only the lines reactances and the shunt equivalent reactances are taken into account. After a brief presentation of the b/f method, which is currently the most commonly used technique to solve distribution networks, the proposed meth…
Exploring the major depletions of conodont diversity during the Triassic
2014
International audience; In this paper, we show that the Triassic fossil record reflects just two great depletions of conodont diversity before the Rhaetian, which occurred in the Smithian (Olenekian, Early Triassic) and in the Julian (Carnian, Late Triassic). By exploring this context, our results highlighted that they respond to different origination?extinction dynamics. Thus, while the Smithian diversity depletion can be interpreted as a consequence of elevated extinction, the Julian diversity depletion was triggered by fluctuations in origination regime. This evidence suggests that, despite the role of extinction on diversity losses, conodonts suffered crucial changes on the origination …
Topology Management in wireless sensor networks
2020
Wireless sensor networking is ingratiating itself into almost every area of human endeavors. Its drivers include its usages, improvements in microelectronics and manufacturing techniques. The network is made up of multiple tiny sensor nodes deployed in the area to be sensed, with nodes having processing, communicating, and sensing capabilities that enable them to perform their function collaboratively. Nodes sense events and transmit their data to the sink directly or through intermediate nodes acting as relay.Despite all the tremendous advances that have been made on this technology over the past few years, energy has not kept pace. This is based mostly on the fact that battery is its main…
Finite-Timel1-Gain Control for Positive Switched Systems with Time-Varying Delay via Delta Operator Approach
2014
This paper is concerned with the problem of finite-timel1-gain control for positive switched systems with time-varying delay via delta operator approach. Firstly, sufficient conditions which can guarantee thel1-gain finite-time boundedness of the underlying system are given by using the average dwell time approach and constructing an appropriate copositive type Lyapunov-Krasovskii functional in delta domain. Moreover, the obtained conditions can unify some previously suggested relevant results seen in literature of both continuous and discrete systems into the delta operator framework. Then, based on the results obtained, a state feedback controller is designed to ensure that the resulting …
Robust H∞ reliable control for delta operator switched systems with time-varying delays under asynchronous switching
2014
The problem of robust H∞ reliable control for a class of delta operator switched systems with time-varying delays and actuator faults under asynchronous switching is considered in this paper. Asynchronous switching means that the switches between the candidate controllers and system modes are asynchronous. Based on the average dwell time approach and delta operator theory, a state feedback controller is designed such that the closed-loop system is exponentially stable with H∞ performance in the presence of actuator faults. The obtained results are formulated in the form of linear matrix inequalities (LMIs). Finally, a numerical example is provided to demonstrate explicitly the feasibility …