Fast and Efficient Light Intensity Modulation in SOI with Gate-All-Around Transistor Phase Modulator

We report fast modulation (>30 GHz) in a SOI resonant cavity using integrated Bragg mirrors and a gate-all-around transistor as active element. Modulation depth >90% can be obtained in 12.5 μm long devices

Intensity modulation in two Mach-Zehnder interferometers using plasma dispersion in silicon-on-insulator

Two Mach-Zehnder interferometers (MZI), one with Y-junction-couplers and the other with multimode interference (MMI), were presented. Both MZI were developed in silicon-on-insulator (SOI) technology and used plasma dispersion effect for light phase modulation. Fiber-to-fiber insertion losses, absorption coefficients, optical coefficients modulated intensities as function of time and modulation extinction ratios versus signal frequencies were measured for these devices at various wavelengths. Both devices were found to be modulated up to a frequency of 3.5 MHz. Insertion losses at wavelengths equal to 1.3 μm were less than 9.5 dB and excess losses relative to a straight waveguide were less than 2.3 dB

Randomised trials relevant to mental health conducted in low and middle-income countries: a survey

<p>Abstract</p> <p>Background</p> <p>A substantial proportion of the psychiatric burden of disease falls on the world's poorest nations, yet relatively little is known about randomised trials conducted in these countries. Our aim was to identify and describe a representative sample of mental health trials from low and middle-income countries.</p> <p>Methods</p> <p>6107 electronic records, most with full text copies, were available following extensive searches for randomised or potentially randomised trials from low and middle-income countries published in 1991, 1995 and 2000. These records were searched to identify studies relevant to mental health. Data on study characteristics were extracted from the full text copies.</p> <p>Results</p> <p>Trials relevant to mental health were reported in only 3% of the records. 176 records reporting 177 trials were identified: 25 were published in 1991, 45 in 1995, and 106 in 2000. Participants from China were represented in 46% of trials described. 68% of trials had <100 participants. The method of sequence generation was described in less than 20% of reports and adequate concealment of allocation was described in only 12% of reports. Participants were most frequently adults with unipolar depression (36/177) or schizophrenia (36/177). 80% of studies evaluated pharmacological interventions, a third of which were not listed by WHO as essential drugs. 41% of reports were indexed on PubMed; this proportion decreased from 68% in 1991 to 32% in 2000.</p> <p>Conclusion</p> <p>In terms of overall health burden, trial research activity from low and middle-income countries in mental health appears to be low, and in no area adequately reflects need.</p

Silicon optical modulators

Optical technology is poised to revolutionize short-reach interconnects. The leading candidate technology is silicon photonics, and the workhorse of such an interconnect is the optical modulator. Modulators have been improved dramatically in recent years, with a notable increase in bandwidth from the megahertz to the multigigahertz regime in just over half a decade. However, the demands of optical interconnects are significant, and many questions remain unanswered as to whether silicon can meet the required performance metrics. Minimizing metrics such as the device footprint and energy requirement per bit, while also maximizing bandwidth and modulation depth, is non-trivial. All of this must be achieved within an acceptable thermal tolerance and optical spectral width using CMOS-compatible fabrication processes. This Review discusses the techniques that have been (and will continue to be) used to implement silicon optical modulators, as well as providing an outlook for these devices and the candidate solutions of the future

Thermally stable distributed MEMS phase shifter for airborne and space applications

This paper presents an in-depth study of the design, modelling, circuit parameter extraction and characterization of a distributed MEMS digital microwave phase shifter. Bridge-type digital capacitors periodically loaded on a 5mm CPW (with an actuation voltage of 22V) has been fabricated and successfully measured in a wide range of frequencies (1-14GHZ), achieving a true-time delay of 25ps. Experimental data are in very good agreement with the equivalent circuit model and high frequency 3D EM simulations for both single switches and phase shifters. These phase shifters are designed for beam steering applications in airborne and space which require operation within large range of temperatures. Therefore, temperature measurements fulfilling the applications requirements have been done in vacuum and in room air from -130°C to 50°C. It is demonstrated that the delay deviation of our phase shifter is 10% (2ps) at 14GHz for the full temperature range (T°=180°)

Reliability of rf mems capacitive switches and distributed mems phase shifters using aln dielectric

The reliability and charging/discharging dynamics of wideband (1.5-14GHz) phase shifters made of MEMS capacitive switches using Aluminum Nitride (AlN) as dielectric are originally reported. Phase shifter lifetimes exceeding 109 cycles are achieved in hot-cycling (+5dBm RF power). Dynamic tests were done for the first time under ambient conditions (5000 humidity) over 2x109 cycles with no major degradation of individual switches performances. It is demonstrated that the phase shifter is very robust (no permanent failure or stiction) and can withstand environmental effects as well as high temperature variations, without the need of expensive hermetical packaging. The excellent reliability is attributed to the slow dielectric charging (a square-root time law) and fast discharging mechanism of AlN (an exponential time law proposed and validated in our work). We extend the validity of charging and discharging models from single device to arrays of parallel MEMS capacitors. ©2009 IEEE