625 research outputs found
Dynamics of a class A nonlinear mirror mode-locked laser
Using a delay differential equation model we study theoretically the dynamics
of a unidirectional class-A ring laser with a nonlinear amplifying loop mirror.
We perform linear stability analysis of the CW regimes in the large delay limit
and demonstrate that these regimes can be destabilized via modulational and
Turing-type instabilities, as well as by an instability leading to the
appearance of square-waves. We investigate the formation of square-waves and
mode-locked pulses in the system. We show that mode-locked pulses are
asymmetric with exponential decay of the trailing edge in positive time and
faster-than-exponential (super-exponential) decay of the leading edge in
negative time. We discuss asymmetric interaction of these pulses leading to a
formation of harmonic mode-locked regimes.Comment: 9 pages
Refractory times for excitable dual state quantum dot laser neurons
Excitable photonic systems show promise for ultrafast analog computation,
several orders of magnitude faster than biological neurons. Optically injected
quantum dot lasers display several excitable mechanisms with dual state quantum
lasers recently emerging as true all or none excitable artificial neurons. For
use in applications, deterministic triggering is necessary and this has
previously been demonstrated in the literature. In this work we analyse the
crucially important \emph{refractory time} for this dual state system, which
defines the minimum possible time between distinct pulses in any excitable
pulse train. Ultrashort times on the order of 1~ns are obtained suggesting
potential use where ultrafast analog computing is desired
Traveling wave modeling, simulation and analysis of quantum-dot mode-locked semiconductor lasers
We analyze the dynamics of a mode-locked quantum-dot edge-emitting semiconductor laser consisting of reversely biased saturable absorber and forward biased amplifying sections. To describe spatial non-uniformity of laser parameters, optical fields and carrier distributions we use the traveling wave model, which takes into account carrier exchange processes between wetting layer and quantum dots. A comprehensive parameter study and an optical mode analysis of operation regimes are presented
Traveling wave modeling, simulation and analysis of quantum-dot mode-locked semiconductor lasers
We analyze the dynamics of a mode-locked quantum-dot edge-emitting semiconductor laser consisting of reversely biased saturable absorber and forward biased amplifying sections. To describe spatial non-uniformity of laser parameters, optical fields and carrier distributions we use the traveling wave model, which takes into account carrier exchange processes between wetting layer and quantum dots. A comprehensive parameter study and an optical mode analysis of operation regimes are presented
An aerostatic pad with an internal pressure control
Because of their almost zero friction and wear, aerostatic pads are widely used in applications where very precise positioning is required. However, this kind of bearing suffers from poor damping and low specific stiffness. This paper presents a new compensation strategy to increase air pad stiffness. This method exploits a custom-built pneumatic valve which can be easily integrated with any commercial pad. The design and the working principle of the proposed system are described and studied with the aid of a lumped parameter model. The effectiveness of the proposed compensation is numerically and experimentally evaluated. The results demonstrate that the solution represents a good and cost-effective method to enhance the static stiffness of aerostatic pads
Unbalance Response Analysis of a Spindle Supported on Gas Bearings: A Comparison between Different Approaches
Gas journal bearings are widely employed in high-speed spindles for the micromachining industry. Compared to their oil and rolling counterparts, gas bearings have a longer life span, lower friction and a lower level of noise. In order to design accurate high-speed spindles supported by externally pressurized gas bearings, it is vital to analyze the characteristics of rotor bearing systems. In this paper, we present an analysis of the unbalance response of a high-speed spindle supported by gas journal bearings. A number of aspects to enhance the accuracy of the system are discussed. We performed the analysis by considering a nonlinear and a linearized numerical model validated through experimental measurements
On the Design of a Diaphragm Valve for Aerostatic Bearings
Because of their almost zero friction, cleanness and long life, aerostatic bearings are commonly used in many applications where high precision of positioning is required, e.g. machine tools, measuring machines, semiconductor manufacturing and power board testing. However, air bearings suffer from low relative stiffness and poor damping. Active and passive compensation are two effective methods to enhance the static and dynamic performance of these kinds of bearings. Despite their higher performance, active compensation solutions are too expensive to be used in industrial applications, as a consequence of the costs related to their controllers, actuators and sensors. This paper presents the design and performance of a passive compensation method that exploits a diaphragm valve. Thanks to its ease of integration, satisfactory performance and relatively low cost, this method could be a valuable solution to increasing the stiffness of aerostatic bearings. This work provides a procedure to design diaphragm valves depending on the type of the integrated pad and the desired nominal air gap height. Results demonstrate that, once correctly designed, the diaphragm valve makes it possible to obtain bearings with quasi-static infinite stiffness at the selected air gap height
Air Pad Controlled by Means of a Diaphragm-Valve: Static and Dynamic Behaviour
This paper presents the analysis of the static and dynamic performance of a passively compensated air pad. The proposed method consists in the integration of a custom-built diaphragm valve and a commercial aerostatic pad. A lumped model is used to simulate the static and dynamic performance of the pad. Results demonstrate that the proposed method is very effective when the system works with excitation frequencies below 10Â Hz
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