2,004 research outputs found
New five-dimensional Bianchi type magnetically charged hairy topological black hole solutions in string theory
We construct black hole solutions to the leading order of string effective
action in five dimensions with the source given by dilaton and magnetically
charged antisymmetric gauge -field. Presence of the considered -field
leads to the unusual asymptotic behavior of solutions which are neither
asymptotically flat nor asymptotically (A)dS. We consider the three-dimensional
space part to correspond to the Bianchi classes and so the horizons of these
topological black hole solutions are modeled by seven homogeneous Thurston
geometries of , , , , ,
nilgeometry, and solvegeometry. Calculating the quasi-local mass, temperature,
entropy, dilaton charge, and magnetic potential, we show that the first law of
black hole thermodynamics is satisfied by these quantities and the dilaton hair
is of the secondary type. Furthermore, for Bianchi type , the -dual black
hole solution is obtained which carries no charge associated with -field and
possesses a dilaton hair of secondary kind. Also, the entropy turns to be
invariant under the -duality
External control of semiconductor nanostructure lasers
Novel semiconductor nanostructure laser diodes such as quantum-dot and quantum-dash are key optoelectronic candidates for many applications such as data transmitters in ultra fast optical communications. This is mainly due to their unique carrier dynamics compared to conventional quantum-well lasers that enables their potential for high differential gain and modified linewidth enhancement factor. However, there are known intrinsic limitations associated with semiconductor laser dynamics that can hinder the performance including the mode stability, spectral linewidth, and direct modulation capabilities. One possible method to overcome these limitations is through the use of external control techniques. The electrical and/or optical external perturbations can be implemented to improve the parameters associated with the intrinsic lasers dynamics, such as threshold gain, damping rate, spectral linewidth, and mode selectivity. In this dissertation, studies on the impact of external control techniques through optical injection-locking, optical feedback and asymmetric current bias control on the overall performance of the nanostructure lasers were conducted in order to understand the associated intrinsic device limitations and to develop strategies for controlling the underlying dynamics to improve laser performance. In turn, the findings of this work can act as a guideline for making high performance nanostructure lasers for future ultra fast data transmitters in long-haul optical communication systems, and some can provide an insight into making a compact and low-cost terahertz optical source for future implementation in monolithic millimeter-wave integrated circuits.\u2
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