High-speed, polyimide-based semi-insulating planar buried heterostructures

We describe planar buried heterostructure lasers which have low capacitance (lpF), large bandwidth (19GHz), high power (>20mW/facet) and high temperature operation (100°C). These lasers are very suitable for long-distance, highspeed digital and analogue signal transmission.     

Polarization independent isolator using spatial walkoff polarizers

A novel type of polarization-independent optical isolator is described which utilizes the polarization walkoff provided by birefringent crystals. Isolation of 44 dB is measured at a wavelength of 1.3 mu m with single-mode fiber insertion loss of 1.5 dB. A temperature-independent scheme is also described that provides at least 39 dB of isolation over the temperature range of 25-75 degrees C.<>     

Computers for symbolic processing

A detailed survey on the motivations, design, applications, current status, and limitations of computers designed for symbolic processing is provided. Symbolic processing computations are performed at the word, relation, or meaning levels, and the knowledge used in symbolic applications may be fuzzy, uncertain, indeterminate, and ill represented. Various techniques for knowledge representation and processing are discussed from both the designers' and users' points of view. The design and choice of a suitable language for symbolic processing and the mapping of applications into a software architecture are then considered. The process of refining the application requirements into hardware and software architectures is treated, and state-of-art sequential and parallel computers designed for symbolic processing are discussed     

Refractive index profiling-state of the art

Problems associated with different calibration techniques and some instrumental effects that can determine instrumental accuracy are discussed. It is shown how transmission effects can be observed and used to generate a correction curve for refracted near-field instruments. High-quality fiber slices needed for axial interferometry were used to obtain refractive index differences on suitable fibers to ±1% with the measurements traceable to national standards. Interferometry was used to calibrate a multiple-step fiber which is available in 10-m lengths with a certificate of calibration. The limitations of the technique are discussed, and preliminary results of a study on the effects of residual stress and stress relief on measurements are given. Comparisons are made between measurements made by axial interferometry and refracted near field on a range of fibers. It is shown that commercial profilers can produce reliable measurements of refractive index difference, absolute refractive index, profile shape, and numerical aperture that agree well with measurements by other techniques     

Design and Experimental Characterization of Low‐Volume PM10/2.5/1.0 Trichotomous Sampler Inlet

This paper presents the development and laboratory evaluation of a PM10/2.5/1.0 trichotomous sampling inlet that consists of two main parts: a previously designed PM10 size‐selective inlet part and a PM2.5/1.0 two‐stage virtual impactor, which was newly fabricated and attached serially to the PM10 size selective inlet part. Particles are collected in three locations through the trichotomous sampling inlet to provide for not only particle concentration measurements of PM10, PM2.5 and PM1.0, but also those of PM2.5–10 and PM1.0–2.5.     

Characterization of GaAs layers grown on polycrystalline GaAs by LPE and current controlled LPE

It is the purpose of this paper to investigate the suitability and effectiveness of growth of thin GaAs layers on polycrystalline GaAs substrates by liquid phase epitaxy (LPE) and current controlled LPE (CCLPE). During each growth run LPE and CCLPE were used to grow thin GaAs layers on two large-grain polycrystalline GaAs substrates cut from the same wafer and simultaneously placed in the same growth system. The grain boundary was exposed by cleaving the samples perpendicular to the grain boundary. Notnarski contrast, SEM, C-V and Hall measurements were performed in order to determine the surface morphology, discontinuity of epilayer at the grain boundary, epilayer thickness unform-ity, resistivity (in directions parallel and perpendicular to the grain boundary), and dopant concentration. The CCLPE system was carefully designed so that growth would take place only by electrotransport in the absence of convection or Peltier cooling. The results indicate that CCLPE yields layers with improved surface morphology and thickness uniformity as compared to those grown by LPE. In some samples the epilayer was discontinuous at certain grain boundaries. Results are presented on CCLPE growth rate dependence upon grain orientation, current density, and continuity of the epilayer at the grain boundary.     

Modeling and compensation of asymmetry in optical recording

Asymmetry, also known as domain bloom, is a systematic imperfection caused by the writing process in optical or magneto-optical recording. At the reading end of the system, asymmetry causes shifts of adjacent signal transitions in opposite directions. We present a simple nonlinear model for the replay signal in the presence of asymmetry. The model is specified by a single parameter, which is proportional to asymmetry, and its accuracy is demonstrated by application to replay signals from digital video disk drives. Based on the proposed model, a maximum-likelihood sequence detector is designed for replay signals with asymmetry. Simple modifications of the proposed detector lead to significant reductions in complexity, while the attainable performance, evaluated both analytically and through error-rate simulations, is superior to that of conventional techniques.