71,038 research outputs found
Dynamic modeling of Terahertz Quantum cascade lasers
In this paper, the influence of the simplifications made in the four-equation-based set of rate equations describing the dynamic behavior of a Quantum Cascade Laser (QCL) is studied. Numerical simulations based on the set of four rate equations has been developed, enabling the theoretical study of the influence of different parameters on the direct modulation response of the laser. These equations have been then linearized in order to deduce a set of state system equations, which was written in a matrix formalism. Finally, an approximate second order transfer function has been derived with the linearized dependence of its times constant
SymbolDesign: A User-centered Method to Design Pen-based Interfaces and Extend the Functionality of Pointer Input Devices
A method called "SymbolDesign" is proposed that can be used to design user-centered interfaces for pen-based input devices. It can also extend the functionality of pointer input devices such as the traditional computer mouse or the Camera Mouse, a camera-based computer interface. Users can create their own interfaces by choosing single-stroke movement patterns that are convenient to draw with the selected input device and by mapping them to a desired set of commands. A pattern could be the trace of a moving finger detected with the Camera Mouse or a symbol drawn with an optical pen. The core of the SymbolDesign system is a dynamically created classifier, in the current implementation an artificial neural network. The architecture of the neural network automatically adjusts according to the complexity of the classification task. In experiments, subjects used the SymbolDesign method to design and test the interfaces they created, for example, to browse the web. The experiments demonstrated good recognition accuracy and responsiveness of the user interfaces. The method provided an easily-designed and easily-used computer input mechanism for people without physical limitations, and, with some modifications, has the potential to become a computer access tool for people with severe paralysis.National Science Foundation (IIS-0093367, IIS-0308213, IIS-0329009, EIA-0202067
Thermal analysis of mid-infrared quantum-cascade lasers
We present a theoretical thermal analysis of mid-infrared quantum-cascade lasers (QCLs) using a two-dimensional anisotropic heat diffusion model. Several InP-based devices are simulated over a range of operating conditions in order to extract temperature-dependent thermal resistances. These thermal resistances are used to compare the effectiveness of various heat management techniques. Finally, heat flow analysis is performed in order to understand the internal thermal dynamics of these devices
On Time Synchronization Issues in Time-Sensitive Networks with Regulators and Nonideal Clocks
Flow reshaping is used in time-sensitive networks (as in the context of IEEE
TSN and IETF Detnet) in order to reduce burstiness inside the network and to
support the computation of guaranteed latency bounds. This is performed using
per-flow regulators (such as the Token Bucket Filter) or interleaved regulators
(as with IEEE TSN Asynchronous Traffic Shaping). Both types of regulators are
beneficial as they cancel the increase of burstiness due to multiplexing inside
the network. It was demonstrated, by using network calculus, that they do not
increase the worst-case latency. However, the properties of regulators were
established assuming that time is perfect in all network nodes. In reality,
nodes use local, imperfect clocks. Time-sensitive networks exist in two
flavours: (1) in non-synchronized networks, local clocks run independently at
every node and their deviations are not controlled and (2) in synchronized
networks, the deviations of local clocks are kept within very small bounds
using for example a synchronization protocol (such as PTP) or a satellite based
geo-positioning system (such as GPS). We revisit the properties of regulators
in both cases. In non-synchronized networks, we show that ignoring the timing
inaccuracies can lead to network instability due to unbounded delay in per-flow
or interleaved regulators. We propose and analyze two methods (rate and burst
cascade, and asynchronous dual arrival-curve method) for avoiding this problem.
In synchronized networks, we show that there is no instability with per-flow
regulators but, surprisingly, interleaved regulators can lead to instability.
To establish these results, we develop a new framework that captures industrial
requirements on clocks in both non-synchronized and synchronized networks, and
we develop a toolbox that extends network calculus to account for clock
imperfections.Comment: ACM SIGMETRICS 2020 Boston, Massachusetts, USA June 8-12, 202
Thermal effects in InGaAs/AlAsSb quantum-cascade lasers
A quantum-cascade laser (QCL) thermal model is presented. On the basis of a finite-difference approach, the model is used in conjunction with a self-consistent carrier transport model to calculate the temperature distribution in a near-infrared InGaAs/AlAsSb QCL. The presented model is used to investigate the effects of driving conditions and device geometries on the active-region temperature, which has a major influence on the device performance. A buried heterostructure combined with epilayer-down mounting is found to offer the best performance compared with alternative structures and has thermal time constants up to eight times smaller. The presented model provides a valuable tool for understanding the thermal dynamics inside a QCL and will help to improve operating temperatures
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