78 research outputs found
Presence of temporal dynamical instabilities in topological insulator lasers
No full textTopological insulator lasers are a newly introduced kind of lasers in which light snakes around a cavity without scattering. Like for an electron current in a topological insulator material, a topologically protected lasing mode travels along the cavity edge, steering neatly around corners and imperfections without scattering or leaking out. In a recent experiment, topological insulator lasers have been demonstrated using a square lattice of coupled semiconductor microring resonators with a synthetic magnetic field. However, laser arrays with slow population dynamics are likely to show dynamical instabilities in a wide range of parameter space corresponding to realistic experimental conditions, thus preventing stable laser operation. While topological insulator lasers provide an interesting mean for combating disorder and help collective oscillation of lasers at the edge of the lattice, it is not clear whether chiral edge states are immune to dynamical instabilities. In this work we consider a realistic model of semiconductor class-B topological insulator laser and show that chiral edge states are not immune to dynamical instabilities. Copyright (C) EPLA, 201
Tunable photonic oscillators
No full textLimit Cycle oscillators are used to model a broad range of periodic nonlinear phenomena. Using
the optically injected semiconductor oscillator as a paradigm, we have demonstrated that at specific
islands in the optical frequency detuning and injection level map, Period One Limit Cycle oscillation
frequency is simultaneously insensitive to multiple perturbation sources. In our system these include
the temperature fluctuations experienced by the master and slave lasers as well as fluctuations in the
bias current applied to the slave laser. Tuning of the oscillation frequency then depends only on the
injected optical field amplitude. Experimental measurements are in good quantitative agreement with
numerical modeling and analysis based on a reduced Adler}} phase dynamics type equations. These
special operating regions should prove valuable for developing ultra-stable nonlinear oscillators, such as
sharp linewidth, frequency tunable photonic microwave oscillators. Finally the concept of an Isochron
originally developed in mathematical biology will be reviewed and placed on context for efficient design
of stable frequency sources in systems of optically coupled limit cycles oscillators [1,2]
Design and Testing of a SiC-based Solid-State Bypass Switch for 1 kV Power Electronics Building Blocks
No full textOver the past two decades, power consumption has increased exponentially worldwide, posing new challenges to power grids to meet the load requirements. With this growing power demand, the need for efficient high-density medium-voltage (MV) power converters has increased to support flexible power distribution grids. The modular multilevel converters (MMC) became the most typical MV power converters in applications from 2010. This topology has many advantages, such as voltage scalability, excellent output performance, and low voltage ratings for switching devices. However, without the excellent reliability of the MMC, applications cannot reap these benefits.
The MMC topology comprises several series-connected submodules (typically a half-bridge or a full-bridge inverter). As a result of increased switching devices, the converter becomes vulnerable since a single device fault can disrupt the whole converter operation. Therefore, fault-tolerant strategies to replace faulty SM with a redundant SM are developed using additional bypass switches. Conventionally TRIACs and vacuum switches are employed as bypass switches that operate in the range of 2-10 microseconds.
Despite having performance advantages, MMCs are still not fully employed in aerospace and naval industries due to their enormous size. Many Power Electronics Building Blocks (PEBB) are proposed, with size optimization, as submodules for modular converters. The PEBB1000, a 1000 V- PEBB proposed by Dr. Jun Wang, achieved a significant size reduction of 80% with a novel switching cycle control (SCC) scheme. This novel control scheme requires high switching frequency and high di/dt-currents for MMC operation. Due to di/dt-rate limitations, TRIAC-based switch cannot perform bypass operation. Therefore, research work has been conducted on bypass switches for PEBB1000 using wide-bandgap SiC devices.
This thesis presents the design of a SiC MOSFET-based bypass switch for PEBB1000 in MMC application. A detailed fault case analysis is presented to show the feasibility of the bypass operation for 90% PEBB-level faults. Significant variations in PEBB1000 bypass requirements are observed through SCC-based MMC simulations. Accordingly, a 1700 V, 100 A bypass switch has been designed using the anti-series topology of MOSFETs. Various specifications, such as 142 nanoseconds operation time, 500 nanoseconds bypass commutation time, and 277A transient current conduction capability, are validated through practical tests. Results prove that SiC-MOSFETs work better than TRIACs in high di/dt-current conduction and operation times. For future work, false-triggering endurance has to be analyzed for 1000 V switching voltage.Master of ScienceWhen a building is on fire, the safety of people inside depends on the timely arrival of the fire rescue departments. Similarly, for an electrical fault, the safety of electrical systems depends on fast and secure fault protection devices.
This thesis presents work on one such fault-protection device used in the power distribution grid: solid-state bypass switch. Distribution grids supply power majorly to households and industries at the city or state level. They employ medium-voltage (MV) converters to step down the voltages to meet the distribution requirements. In MV converters, several low-voltage modules are connected in series to achieve the high-voltage power conversion.
When a fault occurs at one of the low-voltage modules in MV converters, power flow gets disrupted due to a series connection like a chain. Therefore, bypass switches are connected in parallel to low-voltage modules for an alternate power flow path. Conventionally used bypass switches have 2-10 microseconds operation time.
Recent advancements in semiconductor devices, SiC MOSFETs, allow operation times less than one microsecond. Therefore, research work has been conducted on bypass switches using SiC MOSFETs. Finally, the SiC-MOSFET based bypass switch is built and tested according to converter requirements. Results proved that the designed switch operates in 142 nanoseconds, ten times faster than a conventional switch
Quasiparticle Motion on a Chain with Alternating Site Energies and Intersite Interactions
No full text
Labyrinth bifurcations in optically injected diode lasers
No full textAlthough pulsating and chaotic regimes in injection-locked semiconductor lasers have been described often in the literature, so far their relative abundance has remained poorly explored.
Here, for two popular laser models, we report detailed Lyapunov phase (stability) diagrams characterizing the extension in parameter space of pulsating phases. Our phase (stability) diagrams discriminate regular from chaotic laser emissions and indicate where multistability is to be expected in injection-locked semiconductor lasers
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