Simulation and experimental verification of W-band finite frequency selective surfaces on infinite background with 3D full wave solver NSPWMLFMA

We present the design, processing and testing of a W-band finite by infinite and a finite by finite Grounded Frequency Selective Surfaces (FSSs) on infinite background. The 3D full wave solver Nondirective Stable Plane Wave Multilevel Fast Multipole Algorithm (NSPWMLFMA) is used to simulate the FSSs. As NSPWMLFMA solver improves the complexity matrix-vector product in an iterative solver from O(N(2)) to O(N log N) which enables the solver to simulate finite arrays with faster execution time and manageable memory requirements. The simulation results were verified by comparing them with the experimental results. The comparisons demonstrate the accuracy of the NSPWMLFMA solver. We fabricated the corresponding FSS arrays on quartz substrate with photolithographic etching techniques and characterized the vector S-parameters with a free space Millimeter Wave Vector Network Analyzer (MVNA)

Survey of Backward Error Recovery Techniques for Multicomputers Based on Checkpointing and Rollback

For implementing fault-tolerance in multicomputer systems, backward error recovery, based on checkpointing and rollback, is often used. During failurefree operation, the process states are regularly saved, and after a fault is detected, the system is rolled back to a previously saved state. We can distinguish four classes of techniques: semi-automatic techniques, message logging, coordinated checkpointing and hybrid techniques. In this paper a survey is given, and the possibly involved overhead is discussed. This will allow the user to choose an optimal checkpointing and rollback technique for given facilities and applications. Keywords---fault-tolerance, backward error recovery, checkpointing, rollback 1. Introduction Fault-tolerance is essential to work reliably, because the probability that a failure occurs is not negligible in large systems. Implementing fault-tolerance in multicomputers (multiprocessors as well as distributed systems) by backward error recovery can be seen as a..

X-valley influence on hot free electron absorption and optical nonlinearities at 10.6

A theoretical overview is given about the influence of the presence of the X-valley in highly doped n-GaAs on hot free-electron absorption and optical nonlinearities at 10.6 μm wavelength. The implications of the extension of the quantum-mechanical model from two to three valleys are discussed. For electron temperatures above 600 K the X-valley presence starts to be observed. We reveal that it is difficult to trace the individual contributions of different X-electron related inter- and intravalley absorption and relaxation phenomena and therefore we suggest to introduce an effective X-valley related deformation potential which is a weighted combination of all the X-valley contributions. We discuss how nonlinear optical experiments can be conducted to determine the LL-intervalley and this effective X-valley deformation potential

A multi-valley model for hot free-electron nonlinearities at 10.6

When the frequency of infrared light and the plasma frequency of highly doped n-GaAs are in resonance (e.g. for a doping concentration N = 7 × 1018cm−3 and a wavelength $\lambda=10.6 \mu$m), the free-electron induced optical nonlinearity is soundly pronounced. At such high doping concentrations it is necessary to extend the rigid quantum mechanical description of the free-electron induced nonlinearity to a multi-valley model. The central valley of GaAs was treated as a fully nonparabolic degenerated electron gas, whereas the satellite valley was modeled as an anisotropic electron gas of arbitrary degeneracy. The following intra- and intervalley absorption mechanisms were taken into account: impurity assisted, thermal and hot polar optical phonon assisted intravalley absorption on one hand and intervalley phonon assisted absorption in equivalent and nonequivalent intervalley absorption on the other hand. The dependence of the different absorption and energy relaxation mechanisms on the doping concentration, free electron heating, optical power density and the equivalent LL-intervalley deformation potential are discussed. We demonstrated for the first time that the behavior of the optical intervalley nonlinearity, i.e. the nonlinear absorption and nonlinear intervalley transfer, strongly depend on the equivalent LL-intervalley deformation potential. In the linear regime the model calculations are in good agreement with experimental results

CMOS receiver array with 100 channels on 1 mm(2) chip area based on self-calibrating self-regenerative sense-amplifiers operating at 200 Mbit/s/channel

Parallel optical interconnects may become the communication method of choice to achieve future high bandwidth data transfer between chips or MCM's. For this purpose, an integrated CMOS detector approach is favorable at the light-reception side, so Flip-chip of detectors is no longer required. In this paper we present an integrated differential CMOS detector layout which gives a flat frequency response of 0.1A/W with a -3dB bit rate over 450Mbit/s/ch (wavelength of 860nm) in standard 0.6 mu technology. The detector works following the Spatially Modulated Light detector (SML-detector) principle. Based on this SML-detector we fabricated a dense detector/receiver array consisting of 100 channels on one square mm Si area in 0.6 mu standard CMOS. The detector area is 50x50 mu(2). The detector signal is amplified and latched by a self-regenerative sense-amplifier, which is self-calibrating for increased array homogeneity and receiver yield. The power consumption per receiver channel is as low as 1.1mW and the received light power at 200Mbit/s is 25.1 mu W (at a BER<1e(-12)). Measured standard deviation on the output jitter is 96ps and the measured worst case channel to channel output delay variation is 200ps. Future CMOS technology will improve the maximum detector/receiver bit-rate as well as the attainable sensitivity.status: publishe

Mushroom microlenses: Optimized microlenses by reflow of multiple layers of photoresist

A novel type of photoresist microlenses is conceived. The characteristic of these lenses is their mushroom shape: the lens dome is located at a certain controllable distance from the substrate, and the curvature of the lens is larger than that of traditional truncated-sphere lenses. These mushroom microlenses are equilibrium-state, stable products of reflow that are obtained when starting from a multilayer photoresist stack. Integration on light-emitting diodes results in enhanced output efficiency and directivity: a vertical-to-surface emission enhancement of up to a factor of 8 has been achieved.status: publishe

A User-Triggered Checkpointing Library for Computation-Intensive Applications

: We propose a method to incorporate coordinated checkpointing and rollback in high performance computing applications on massively parallel computers. A library allows the user to specify which data-items (including files) belong to the contents of the checkpoint, and to trigger the checkpointing in the application. The recovery-line management on the distributed disk system takes care of which recovery-lines are valid, (and may be used for rollback), and of which are obsolete (and may be deleted). This flexible approach provides a frame to incorporate non-blocking, continuebefore -validate checkpointing in the application. Besides, the main advantages are the hardware independence and flexibility. Keywords: fault tolerance, checkpointing, backward error recovery, massively parallel systems 1. Introduction Many scientific and commercial applications (simulations, solutions of computational complex problems, ...) require long execution times: they run for days or weeks before the re..