A high-frequency GaAs optical guided-wave electrooptic interferometric modulator

The characteristics and frequency response of a GaAs monolithic guided-wave interferometric modulator operating at 1.3 μm are presented. The interfetometer consists of three-guide coupler input and output sections and single-mode p+-n--n+ slab-coupled rib-waveguide active arms. The measured electrical bandwidth of an interferometer with 2 mm long active arms was 2.2 GHz and limited by parasitics. This corresponds to a small signal optical bandwidth of ≈ 3.0 GHz when the interferometer is biased in a linear portion of the optical output versus voltage characteristics. Reduction of parasitics should result in a substantial increase in the bandwidth of these devices.     

Three-guide optical couplers in GaAs

Three-guide optical couplers consisting of three 4.75-μm-wide slab-coupled rib guides separated by 4.25μm have been fabricated in GaAs. The performance of these couplers at 1.28 μm is in close agreement with that predicted using a modified effective-index method to obtain an approximate analytical solution for this type of coupler. The coupling length needed to symmetrically transfer power from the center guide to the two outside guides was 3.2 mm. At this length, less than 1 percent of the power remained in the center guide. The length needed to transfer power from one outside guide to the other outside guide was ≈ 6.4 mm, which isapprox sqrt{2}- times that of a similar two-guide coupler and twice that required to couple power from the center guide to the two outside guides. The power transfer efficiency in this case is not as good as when power was inputted into the center guide. Three-guide couplers of this type should prove useful as power dividers and combiners, especially in cases where waveguide bend losses preclude the use of"Y"- junctions. They may also prove useful as replacements for two-guide couplers where either sharper transfer characteristics are desired or where losses due to waveguide bends are again unacceptable.     

Perspectives on utility central station photovoltaic applications

This report develops nominal cost and performance goals for solar photovoltaic conversion devices intended for large-scale electric utility applications. The objective is to provide an improved basis for establishing research and development priorities for photovoltaic devices and conversion concepts. Comparisons are made among a number of generic power plant conceptual designs, with the aid of an array design parameter that is defined to include array-area-related costs, overall power plant efficiency, and average available insolation. The analysis indicates that flat plate approaches without concentration or tracking have good prospects for commercial viability if device conversion efficiencies near 10 per cent can be combined with installed device costs under $20/m² ($2/ft²) and device lifetimes in excess of 20 years. Thin-film approaches have potential for achieving these cost and performance goals because of low material content and potentially low fabrication costs. Very high efficiency devices coupled with concentrations in excess of about 100:1 represent a viable alternative if sufficiently high conversion efficiencies (25% or more) can be achieved. Such devices are likely to be expensive, but high concentration may make their costs acceptable. Several device types and converter approaches exist or have been proposed that have potential for reaching these efficiencies. In contrast to flat plate approaches, however, high-concentration approaches may have the disadvantage of requiring active cooling. Approaches employing low-to-medium concentration appear to have limited potential for large-scale applications. Required effieciencies are likely to be comparable to those needed for high-concentration approaches, but the concentration ratios are not likely to be high enough to make the photovoltaic device costs tolerable.     

Utility Wind Integration and Operating Impact State of the Art

In only six years, from 2000 to 2006, wind energy has become a significant resource on many electric utility systems, with nearly 74 000 MW of nameplate capacity installed worldwide at the end of 2006. Wind energy is now "utility scale" and can affect utility system planning and operations for both generation and transmission. The utility industry in general, and transmission system operators in particular, are beginning to take note. At the end of 2005, the Power Engineering Society (PES) published a special issue of its Power & Energy Magazine that focused on integrating wind into the power system. This paper provides a summary and update on many of the salient points from that special issue about the current state of knowledge regarding utility wind integration issues.     

Three cases of comprehensive dietary therapy and pharmacotherapy of patients with complex obesity-related diseases

The effect of weight loss with anorectic medications on sleep apnea, non-insulin-dependent diabetes, and steatohepatitis is illustrated in three cases from practice in a clinical nutrition setting. Prevention of obesity, a chronic disorder, is preferable, but when obesity becomes a major obstacle in the care of patients with respiratory, cardiovascular, and metabolic disorders and osteoarthritis, an intense course of weight reduction using anorectic medications under medical and dietetic guidance is essential for patients' survival and reduction of medical cost.     

GaSb Thermophotovoltaic Cells Grown on GaAs Substrate Using the Interfacial Misfit Array Method

We present gallium antimonide (GaSb) p–i–n photodiodes for use as thermophotovoltaic (TPV) cells grown on gallium arsenide (100) substrates using the interfacial misfit array method. Devices were grown using molecular beam epitaxy and fabricated using standard microfabrication processes. X-ray diffraction was used to measure the strain, and current–voltage (I–V) tests were performed to determine the photovoltaic properties of the TPV cells. Energy generation at low efficiencies was achieved, and device performance was critically analyzed.     

Wind plant integration [wind power plants]

This paper discusses the key issues that confront power system planners and operators when integrating wind power plants into the electric power system. A key question is how the variations in wind plant outputs affect the operation of the power system on a daily basis and what the associated costs are. These costs are lower than initially expected by some utility engineers. The main reason for this is that wind tends to behave more like negative load than traditional firm-block generation, and the power system has been designed to handle significant load variations on a routine basis. This paper summarizes the key results of wind integration studies conducted to date and provides insights from individual studies. The studies present simulations of system operations that employ well-established production-costing and unit-commitment computational tools.     

Single-mode optical waveguides and phase modulators in the InP material system

The characteristics of several different single-mode optical waveguides in the InP material system are discussed. Slab-coupled rib waveguides in GaInAsP (lambda_{gap} approx 1 mum) epitaxial layers grown on InP have shown propagation losses as low as 1.7 cm^-1at 1.3 μm and 2.7 cm^-1at 1.15 μm. Oxide-confined InP rib guides fabricated using a lateral overgrowth technique have losses of about 1.5 cm^-1at 1.15 μm. Three-guide couplers have been made by fabricating three parallel oxide-confined guides in close proximity. InP p+-n-n+ guides capable of modulating TE-polarized radiation have been fabricated using epitaxial techniques and Be-ion implantation. By measuring the phase difference between the TE-like and TM-like modes as a function of applied voltage, an estimate of the r41electrooptic coefficient in InP at 1.3 μm that is in good agreement with a previously reported value was obtained. Guides of this type should find use as the active components in InP switches and interferometers.     

Wind power myths debunked

The rapid growth of wind power in the United States and worldwide has resulted in increasing media attention to--and public awareness of--windgeneration technology. Several misunderstandings and myths have arisen due to the characteristics of wind generation, particularly because wind-energy generation only occurs when the wind is blowing. Wind power is therefore not dispatchable like conventional energy sources and delivers a variable level of power depending on the wind speed. Wind is primarily an energy resource and not a capacity resource. Its primary value is to offset fuel consumption and the resulting emissions, including carbon. Only a relatively small fraction of wind energy is typically delivered during peak and high-risk time periods; therefore, wind generators have limited capacity value. This leads to concerns about the impacts of wind power on maintaining reliability and the balance between load and generation. This article presents answers to commonly asked questions concerning wind power. It begins by addressing the variability of wind and then discusses whether wind has capacity credit. The article addresses whether wind can stop blowing everywhere at once, the uncertainty of predicting wind generation, whether it is expensive to integrate wind power, the need for new transmission, and whether wind generation requires backup generation or dedicated energy storage. Finally, we discuss whether there is sufficient system flexibility to incorporate wind generation, whether coal is better than wind because coal has greater capacity factors, and whether there is a limit to how much wind power can be incorporated into the grid.