Compact broadband photonic crystal filters with reduced back-reflections for monolithic InP-based photonic integrated circuits

A photonic crystal grating filter with an extremely wide rejection band and reduced modal back-reflections is proposed and demonstrated with a stopband extinction of 20 dB and insertion loss of less than 5 dB. The reflection-mitigation technique is shown to provide 10-15-dB reduction in reflected power. Guidelines for performance improvement are presented.     

FDTD simulation of 30 /spl mu/m diameter polymer micro-ring

Numerical results on polymer surrounded by an air micro-ring coupled to waveguides are presented. The FDTD method predicts a filter width of 1.4 nm and an extraction efficiency of almost 80% for a gap of 0.15 /spl mu/m.     

电阻-时间线性转换电路

基于电阻的传感器,如应力规和压阻器件,常用于测量多种物理参数.对于使用数字处理器或微控制器进行数据采集和信号处理的设备来说,传感器的响应必须表现为一种适合于转换成数字格式的形式.把这类传感器的电阻变化转换成一个与之成比例的频率或时间间隔是可取的,所以你就能用一个计数器或定时器来方便地得到数字形式的输出信号.图1所示电路把传感器的电阻RS线性地转换成与之成比例的时间间隔.这一电路实际上是一个张驰振荡器,由一个电流源、一个桥式放大器、一个比较器和一个触发器组成.电流IS分成两路,分别通过R1和R2,就如同这两个电阻并联在一起一样.假定运算放大器是理想放大器,则当RX(R4+RS)大于R1R3/R2时,该电路就起一个振荡器的作用.     

Ionizing-Radiation Response of the GaAs/(Al, Ga)As PHEMT: A Comparison of Gamma- and X-ray Results

An experiment is reported on the effect of ⁶⁰Co gamma rays or 45-keV x-ray photons on the GaAs/(Al, Ga)As PHEMT. It is shown that x-ray treatment can improve the dc performance of the device in some cases. This finding is attributed in part to the annealing or modification of DX centers.     

Statistical analysis of subthreshold leakage current for VLSI circuits

We develop a method to estimate the variation of leakage current due to both intra-die and inter-die gate length process variability. We derive an analytical expression to estimate the probability density function (PDF) of the leakage current for stacked devices found in CMOS gates. These distributions of individual gate leakage currents are then combined to obtain the mean and variance of the leakage current for an entire circuit. We also present an approach to account for both the inter- and intra-die gate length variations to ensure that the circuit leakage PDF correctly models both types of variation. The proposed methods were implemented and tested on a number of benchmark circuits. Comparison to Monte Carlo simulation validates the accuracy of the proposed method and demonstrates the efficiency of the proposed analysis method. Comparison with traditional deterministic leakage current analysis demonstrates the need for statistical methods for leakage current analysis.     

The impact of publicly funded basic research: an integrative extension of Martin and Salter

This paper provides an integrative literature review of the research on the impact of the public funding of basic research, extending previous work done at the Science Policy Research Unit (SPRU), University of Sussex, East Sussex, UK. "Impact" is measured in terms of publications, patents, new drugs, employment, and new start-up companies. The primary focus of this paper is on empirical studies of the impact of biomedical research. However, a few key theoretical papers and empirical papers with a broader industrial focus are also reviewed to provide a more complete perspective. Conclusions, including an alternative view that basic research need not be public supported, and future research opportunities in this area are also discussed.     

Stable high-order delta-sigma digital-to-analog converters

Stability analysis of high-order delta-sigma loops is a challenge. In this brief, a sufficient design criterion is presented for high-order multibit error-feedback digital-to-analog converters (DACs) which are especially suitable for high-speed operation. This analytical criterion might be too conservative, but it allows for the design of stable, robust, and high-resolution delta-sigma DACs. Both analytical and numerical analysis are performed for verification. Also, experimental results of a discrete-component multiplier-free prototype demonstrate 10-b operation at a very low oversampling ratio of 4.     

Vibration thresholds for fretting corrosion in electrical connectors

Single frequency vibration tests were used to induce fretting corrosion in tin alloy plated contacts. The samples used in this study were connectors consisting of 25 pairs of mated pin and socket contacts. Experimental results for a variety of vibration levels, frequencies, and wiring tie-off lengths are presented. The experiments consisted of running a series of vibration tests at each frequency where the excitation level was stepped through a range of g-levels. During each test run contact resistance was monitored as a performance characteristic. The results exhibit threshold behavior at each frequency for the onset of fretting degradation. Typically a plateau region was observed where similar g-levels produced similar fretting rates. It was also found that outside the plateau region the g-levels varied according to the dynamic behavior of the mechanical system. In addition, a transfer matrix model was used to analyze these results. An empirical fit of the data correlated well with the model when damping was used. This analysis revealed the importance of the bending moment induced at the contact interface as a result of excitation levels and tie-off configurations. Consequently, it is concluded that dynamic response of the mechanical system under various g-levels and tie off configurations can greatly impact the performance of a connector system subjected to vibration stresses.     

Examining a curvilinear relationship between communication frequency and team performance in cross-functional project teams

The performance of a cross-functional team depends on the skillful and innovative combination of information and expertise from all team members. Communication is the medium through which team members share the information required for successful amalgamation. In this work, we postulate that both high and low levels of team communication can impede team performance, thus leading to a curvilinear relationship between team performance and team communication. To test this hypothesis, the relationships between face-to-face, e-mail, and telephone communication and team performance were examined for 60 cross-functional project teams. E-mail and face-to-face communication were curvilinearly associated with performance, but telephone communication was not. Further analysis of the communication frequency between colocations showed that e-mail is the only medium for which usage increased with distance.