Showing papers by "Neil Gordon published in 1998"

Optical concentrators for light-emitting diodes

Abstract: The incorporation of non-imaging optical concentrations in uncooled mid-IR LEDs is described. Novel micromachining methods are used to produce optical concentrators in the growth substrate of epitaxial InSb/InAlSb heterostructures. Resultant large area LED arrays, displaying both positive and negative luminescence, are shown to have optical gains of 3.5 over conventional mesas made form the same material. The LED technology shown also relies on the micromachined substrate being transparent to 3-5 micrometers radiation and to act as a low resistance common contact. The use of degenerate doping in InSb is described, resulting in a shift in the room-temperature transmission to the 3-5micrometers atmospheric window and providing high electrical conductivities.

Tracking in the presence of intermittent spurious objects and clutter

Abstract: The sampling based bootstrap filter is applied to the problem of maintaining track on a target in the presence of intermittent spurious objects. This problem is formulated in a multiple hypothesis framework and the bootstrap filter is applied to generate the posterior distribution of the state vector of the required target - i.e. to generate the target track. The bootstrap technique facilitates the integration of the available information in a near-optimal fashion without the need to explicitly store and manage hypotheses from previous time steps.

Effect of device processing on 1/f noise in uncooled, Auger-suppressed CdHgTe diodes

Abstract: Auger suppression reduces the leakage current in uncooled CdHgTe diodes to the point where the shot noise limited D* is significantly higher than for other uncooled detectors. However, Auger-suppressed diodes exhibit high levels of 1/f noise and so applications have initially been in devices operating at high frequency such as CO2 laser heterodyne detectors. In order to use Auger suppression in imaging devices, we need to reduce the 1/f noise and this paper describes a study of the effects of device processing on noise. We find that although some of the noise is associated with perimeter leakage currents, variations in the surface passivation treatment have little effect on the total noise. However, a post-passivation anneal can reduce the noise in some cases. We also find that CdTe passivated devices are more stable when baked than those passivated with ZnS.

A high-performance CO2 laser heterodyne detector operating at 250 K

Abstract: The design, construction and assessment of a CO 2 laser heterodyne receiver based on a Hg 1-x Cd x Te heterostructure is described. The structure has been designed to minimize the leakage currents at high temperatures while maintaining a high quantum efficiency. Measurements show that over 4 dB of shot noise can be obtained with the application of less than 1 mW of laser power. This result can be combined with the measured low-frequency quantum efficiency of 42% to give a noise equivalent power of 7.2 × 10 -20 W Hz -1 . The device is mounted on a single-stage thermoelectric cooler and coupled to an amplifier. It is hoped that the availability of high-performance detectors which do not need to be cooled to cryogenic temperatures will greatly improve the attractiveness of laser heterodyne systems.

Bayesian sensor resource allocation

Abstract: Many tracking and guidance problems may be formulated as a terminating stochastic game in which the distribution of outcomes is affected by the intermediate actions. Traditional technique ignore this interaction. In this paper we develop an information gathering strategy which maximizes the expected gain of the outcome. For example, the objective could be a function of the terminal miss distance and target identify with penalties for missing a valid target or attacking a friendly one. Several trade-offs are addressed: the increased information available from taking more measurements, the fact that an increased number of measurement may adversely affect change of success and the fact that later measurements may be more informative but also may be of little use since there my not be enough time available for reaction to this extra information. The problem is formulated so that we are required to choose, under uncertainty, an alternative from a set of possible decisions. This set has a discrete uncertainty as to the number of measurements to be taken and a continuous uncertainty as to where and when the measurements should be taken. Preferences over consequences are modeled with a utility function. We propose to choose as optimal the alternative which maximizes expected utility. A simulation based approximation to the solution of this stochastic optimization problem is outlined. This relies on recent developments in dimensions swapping Markov Chain Monte Carlo (MCMC) techniques. The use of MCMC methodology allow us to explore the expected utility surface and thus select a measurement strategy. The resulting algorithm is demonstrated on a simple guidance problem.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

4- to 10-um positive and negative luminescent diodes

Abstract: We describe uncooled mid-IR light emitting and negative luminescent diodes made form indium antimonide based III-V compounds, and long wavelength devices made from mercury cadmium telluride. The application of these devices to gas sensing, improved thermal imagers and imager testing is discussed.

A comparison of sample based filters and the extended Kalman filter for the bearings-only tracking problem

Abstract: In this paper1 we are concerned with the development and evaluation of effective filtering methods for the bearings-only tracking problem. For this problem we consider a stationary observer who only obtains measurements of the bearing of a moving object subject to noise. We assume a linear Gaussian evolution in the states describing the motion of the object. We develop new sample based methods for filtering for this extremely non-linear model. We compare the performance of these methods to existing sample based methods and to the extended Kalman filter. Simulated scenarios are considered for evaluating the relative efficiency of the methods considered. Finally, an actual scenario arising from recordings made on a civilian ship is considered.

Target acquisition/selection: a comparison between a Bayesian technique and the Munkres algorithm

Abstract: A Bayesian technique is applied to the target acquisition problem at handover from the fire control to the missile seeker. This is a multiple hypothesis scheme which includes an explicit model of the possible misalignment or bias between the fire control and seeker coordinate frames. This method is compared with a linear least cost assignment technique which may be implemented via the Munkres fast search algorithm.