Building-in quality rather than assessing quality afterwards: a technological solution to ensuring computational accuracy in learning materials

[Abstract]: Quality encompasses a very broad range of ideas in learning materials, yet the accuracy of the content is often overlooked as a measure of quality. Various aspects of accuracy are briefly considered, and the issue of computational accuracy is then considered further. When learning materials are produced containing the results of mathematical computations, accuracy is essential: but how can the results of these computations be known to be correct? A solution is to embed the instructions for performing the calculations in the materials, and let the computer calculate the result and place it in the text. In this way, quality is built into the learning materials by design, not evaluated after the event. This is all accomplished using the ideas of literate programming, applied to the learning materials context. A small example demonstrates how remarkably easy the ideas are to apply in practice using the appropriate technology. Given that the technology is available and is easy to use, it would appear imperative that the approach discussed is adopted to improve quality in learning materials containing computational results

Silicon nanophotonic waveguide circuits and devices

Silicon on Insulator is an ideal platform for largescale nanophotonic integration. We show that tight process control is needed for well-functioning filters, and discuss a number of devices based on these filters

Master of Science

thesisAdvances in silicon photonics are enabling hybrid integration of optoelectronic circuits alongside current complementary metal-oxide-semiconductor (CMOS) technologies. To fully exploit the capability of this integration, it is important to explore the effects of thermal gradients on optoelectronic devices. The sensitivity of optical components to temperature variation gives rise to design issues in silicon on insulator (SOI) optoelectronic technology. The thermo-electric effect becomes problematic with the integration of hybrid optoelectronic systems, where heat is generated from electrical components. Through the thermo-optic effect, the optical signals are in turn affected and compensation is necessary. To improve the capability of optical SOI designs, optical-wave-simulation models and the characteristic thermal operating environment need to be integrated to ensure proper operation. In order to exploit the potential for compensation by virtue of resynthesis, temperature characterization on a system level is required. Thermal characterization within the flow of physical design automation tools for hybrid optoelectronic technology enables device resynthesis and validation at a system level. Additionally, thermally-aware routing and placement would be possible. A simplified abstraction will help in the active design process, within the contemporary computer-aided design (CAD) flow when designing optoelectronic features. This thesis investigates an abstraction model to characterize the effect of a temperature gradient on optoelectronic circuit operation. To make the approach scalable, reduced order computations are desired that effectively model the effect of temperature on an optoelectronic layout; this is achieved using an electrical analogy to heat flow. Given an optoelectronic circuit, using a thermal resistance network to abstract thermal flow, we compute the temperature distribution throughout the layout. Subsequently, we show how this thermal distribution across the optoelectronic system layout can be integrated within optoelectronic device- and system-level analysis tools

Design of FerroElectric MEMS energy harvesting devices

Waste heat is a widely available but little used source of power. Converting a thermal gradient into electricity is conventionally done using the Seebeck effect, but devices that use this effect are naturally inefficient. An alternate approach uses microelectromechanical systems (MEMS) to generate movement and time-varying temperature from a constant temperature gradient. Ferroelectric materials can harvest electricity from moving structures and temperature variations. This concept was realized using traditional silicon microprocessing techniques. A silicon on insulator (SOI) wafer was backside Deep Reactive Ion Etched (DRIE) to form a one mm2 by 7 micron thick silicon/silicon dioxide membrane. Lead zirconate titanate (PZT) was deposited on the membrane and acts as a ferroelectric material. Heating the bulk of the SOI substrate causes an increase in stress and upward deflection of the membrane. The membrane then enters into contact with a cold sink fixed above the substrate. Cooling of the membrane from contact with the cold sink causes actuation downwards of the membrane. The alternating heating and cooling of the PZT layer generates electricity from the pyroelectric effect. The actuation of the membrane generates stress on the PZT layer resulting in electricity from the piezoelectric effect

Extremely uniform lasing wavelengths of InP microdisk lasers heterogeneously integrated on SOI

A standard deviation in lasing wavelength lower than 500pm is characterized on nominally identical and optically-pumped microdisk lasers, heterogeneously integrated on the same SOI circuit. This lasing wavelength uniformity is obtained using electron-beam lithography

Silicon photonics for on-chip spectrophotometry

Silicon and Silicon Nitride photonics arc on their way to open the route towards integrated on-chip spectropholometers, Cost, miniaturization, miniaturization, hut also performance advantages ace at the origin of their potential We will discuss several integrated on-chip spectropholometers that are on the eve of commercial take up