Acousto-optic modulators are widely used for rapid switching and shuttering of laser beams. In many applications, the concomitant frequency shift is undesirable and must be compensated for elsewhere in the system. Here we present a simple method of achieving rapid laser power switching without an accompanying laser frequency shift. The demonstrated acousto-optic shutter achieves a switching tim...

Code switching (the process of switching from one language to another during a conversation) is a common phenomenon in multilingual environments. Where a minority and dominant language coincide, code switching from the minority language to the dominant language can become particularly frequent. We analyse one such scenario: Sepedi spoken in South Africa, where English is the dominant language; ...

We have studied experimentally effects of two-frequency optical injection on a multimode vertical-cavity surface-emitting laser (VCSEL). The injected signal comes from another VCSEL. Polarization switching (PS) with and without frequency locking occurs for relatively small frequency detuning. Outside the regime of polarization switching, the VCSEL demonstrates two types of instabilities. The in...

This paper presents a detailed theoretical analysis and performance assessment of the capacitor voltage balancing strategies for staircase modulated modular multilevel converters (MMC) in terms of the algorithm structures, voltage balancing effect, and switching frequency. A constant-frequency redundancy selection (CFRS) method with minimal switching loss is proposed and the function realizatio...

This paper demonstrates an optimum methodology to capture the worst case switching activity when performing the power integrity analysis for the core power of ASIC. The key approach is to capture the resonant frequency of the complete power delivery network (PDN), including the chip, package and board. From the FFT of the switching activity, the worst case pattern can be obtained by identifying...

The Direct Torque Control (DTC) of induction machine has received wide acceptance in many Variable Speed Drive (VSD) applications due to its simple control structure and excellent torque dynamic control performances. However, the conventional DTC which employs a two-level inverter and hysteresis controllers produces two major drawbacks, namely, larger torque ripple and variable switching freque...

In this letter, we propose a simple adaptive switching scheme to enhance the performance of space-time/frequency block coded OFDM systems (STBC/SFBC-OFDM). Since STBC-OFDM and SFBCOFDM undergo severe performance degradation in timeand frequencyselective fading channels, respectively, performance enhancement can be achieved by switching between STBC-OFDM and SFBC-OFDM over a continuously varying...

We demonstrate a fast optical modulator capable of switching large amount of optical retardation (a few microns) in less than 1ms. The result is achieved by employing a dual frequency nematic in cells with high pre-tilt alignment and by providing a special addressing scheme that features amplitude and frequency modulated voltage. We explore the effect of surface alignment and dielectric heating...

A zero-voltage, zero-current switching (ZVZCS) PWM DC-DC power converter with secondary active rectifier tested as a dc current source for arc welding is described in this paper. The soft switching DC-DC converter consists of high frequency inverter, high frequency power transformer and controlled output rectifier with new secondary energy recovery turn-off snubber. Circulating current in the c...

This paper presents a unique PWM switching pattern and a novel power factor control scheme for high power GTO ac/dc converters. This switching pattern has a switching frequency of 360Hz, which is the lowest possible frequency to achieve 5th and 7th harmonic elimination and an adjustable dc output current simultaneously. Using both feedback and feedforward control techniques, the proposed power ...