Publications

Refine Results

(Filters Applied) Clear All

High-efficiency large-angle Pancharatnam phase deflector based on dual-twist design

Summary

We have previously shown through simulation that an optical beam deflector based on the Pancharatnam (geometric) phase can provide high efficiency with up to 80° deflection using a dual-twist structure for polarization-state control [Appl. Opt. 54, 10035 (2015)]. In this report, we demonstrate that its optical performance is as predicted and far beyond what could be expected for a conventional diffractive optical device. We provide details about construction and characterization of a ± 40° beam-steering device with 90% diffraction efficiency based on our dual-twist design at a 633nm wavelength.
READ LESS

Summary

We have previously shown through simulation that an optical beam deflector based on the Pancharatnam (geometric) phase can provide high efficiency with up to 80° deflection using a dual-twist structure for polarization-state control [Appl. Opt. 54, 10035 (2015)]. In this report, we demonstrate that its optical performance is as predicted...

READ MORE

Optical phased-array ladar

Published in:
Appl. Opt., Vol. 53, No. 31, 1 November 2014, pp. 7551-5.

Summary

We demonstrate a ladar with 0.5 m class range resolution obtained by integrating a continuous-wave optical phased-array transmitter with a Geiger-mode avalanche photodiode receiver array. In contrast with conventional ladar systems, an array of continuous-wave sources is used to effectively pulse illuminate a target by electro-optically steering far-field fringes. From the reference frame of a point in the far field, a steered fringe appears as a pulse. Range information is thus obtained by measuring the arrival time of a pulse return from a target to a receiver pixel. This ladar system offers a number of benefits, including broad spectral coverage, high efficiency, small size, power scalability, and versatility.
READ LESS

Summary

We demonstrate a ladar with 0.5 m class range resolution obtained by integrating a continuous-wave optical phased-array transmitter with a Geiger-mode avalanche photodiode receiver array. In contrast with conventional ladar systems, an array of continuous-wave sources is used to effectively pulse illuminate a target by electro-optically steering far-field fringes. From...

READ MORE

Comparisons between the extended Kalman filter and the state-dependent Riccati estimator

Summary

The state-dependent Riccati equation-based estimator is becoming a popular estimation tool for nonlinear systems since it does not use system linearization. In this paper, the state-dependent Riccati equation-based estimator is compared with the widely used extended Kalman filter for three simple examples that appear in the open literature. It is demonstrated that, by simulation, the state-dependent Riccati equation-based estimator at best has comparable results to the extended Kalman filter but is often worse than the extended Kalman filter. In some cases, the state-dependent Riccati equation-based estimator does not converge, even though the system considered satisfies all the mathematical constraints on controllability and observability. Sufficient detail is presented in the paper so that the interested reader cannot only duplicate the results but perhaps make suggestions on how to get the state-dependent Riccati equation-based estimator to perform better.
READ LESS

Summary

The state-dependent Riccati equation-based estimator is becoming a popular estimation tool for nonlinear systems since it does not use system linearization. In this paper, the state-dependent Riccati equation-based estimator is compared with the widely used extended Kalman filter for three simple examples that appear in the open literature. It is...

READ MORE

Bioinspired resource management for multiple-sensor target tracking systems

Summary

We present an algorithm, inspired by self-organization and stigmergy observed in biological swarms, for managing multiple sensors tracking large numbers of targets. We devise a decentralized architecture wherein autonomous sensors manage their own data collection resources and task themselves. Sensors cannot communicate with each other directly; however, a global track file, which is continuously broadcast, allows the sensors to infer their contributions to the global estimation of target states. Sensors can transmit their data (either as raw measurements or some compressed format) only to a central processor where their data are combined to update the global track file. We outline information-theoretic rules for the general multiple-sensor Bayesian target tracking problem. We provide specific formulas for problems dominated by additive white Gaussiannoise. Using Cramer-Rao lower bounds as surrogates for error covariances, we illustrate, using numerical scenarious involving ballistic targets, that the bioinspired algorithm is highly scalable and peforms very well for large numbers of targets.
READ LESS

Summary

We present an algorithm, inspired by self-organization and stigmergy observed in biological swarms, for managing multiple sensors tracking large numbers of targets. We devise a decentralized architecture wherein autonomous sensors manage their own data collection resources and task themselves. Sensors cannot communicate with each other directly; however, a global track...

READ MORE

Time delay integration and in-pixel spatiotemporal filtering using a nanoscale digital CMOS focal plane readout

Summary

A digital focal plane array (DFPA) architecture has been developed that incorporates per-pixel full-dynamic-range analog-to-digital conversion and orthogonal-transfer-based realtime digital signal processing capability. Several long-wave infrared-optimized pixel processing focal plane readout integrated circuit (ROIC) designs have been implemented, each accommodating a 256 x 256 30-um-pitch detector array. Demonstrated in this paper is the application of this DFPA ROIC architecture to problems of background pedestal mitigation, wide-field imaging, image stabilization, edge detection, and velocimetry. The DFPA architecture is reviewed, and pixel performance metrics are discussed in the context of the application examples. The measured data reported here are for DFPA ROICs implemented in 90-nm CMOS technology and hybridized to HgxCd1-xTe (MCT) detector arrays with cutoff wavelengths ranging from 7 to 14.5 m and a specified operating temperature of 60 K-80 K.
READ LESS

Summary

A digital focal plane array (DFPA) architecture has been developed that incorporates per-pixel full-dynamic-range analog-to-digital conversion and orthogonal-transfer-based realtime digital signal processing capability. Several long-wave infrared-optimized pixel processing focal plane readout integrated circuit (ROIC) designs have been implemented, each accommodating a 256 x 256 30-um-pitch detector array. Demonstrated in this...

READ MORE

Design approaches for digitally dominated active pixel sensors: leveraging Moore's law scaling in focal plane readout design

Summary

Although CMOS technology scaling has provided tremendous power and circuit density benefits for innumerable applications, focal plane array (FPA) readouts have largely been left behind due to dynamic range and signal-to-noise considerations. However, if an appropriate pixel front end can be constructed to interface with a mostly digital pixel, it is possible to develop sensor architectures for which performance scales favorably with advancing technology nodes. Although the front-end design must be optimized to interface with a particular detector, the dominant back end architecture provides considerable potential for design reuse. In this work, digitally dominated long wave infrared (LWIR) active pixel sensors with cutoff wavelengths between 9 and 14.5 um are demonstrated. Two ROIC designs are discussed, each fabricated in a 90-nm digital CMOS process and implementing a 256 x 256 pixel array on a 30-um pitch. In one of the implemented designs, the feasibility of implementing a 15-um pixel pitch FPA with a 500 million electron effective well depth, less than 0.5% non-linearity in the target range and a measured NEdT of less than 50 mK at f/4 and 60 K is demonstrated. Simple on-FPA signal processing allows for a much reduced readout bandwidth requirement with these architectures. To demonstrate the potential for commonality that is offered by a digitally dominated architecture, this LWIR sensor design is compared and contrasted with other digital focal plane architectures. Opportunities and challenges for application of this approach to various detector technologies, optical wavelength ranges and systems are discussed.
READ LESS

Summary

Although CMOS technology scaling has provided tremendous power and circuit density benefits for innumerable applications, focal plane array (FPA) readouts have largely been left behind due to dynamic range and signal-to-noise considerations. However, if an appropriate pixel front end can be constructed to interface with a mostly digital pixel, it...

READ MORE

The digital focal plane array (DFPA) architecture for data processing "on-chip"

Published in:
2007 Meeting of the Military Sensing Symposia (MSS) Specialty Group on Camouflage, Concealment & Deception; Passive Sensors; Detectors; and Materials, 5-9 February 2007.

Summary

The digital focal plane array (DFPA) project seeks to develop readout integrated circuits (ROICs) utilizing aggressively scaled and commercially available CMOS. Along with focal plane scaling and readout robustness benefits, the DFPA architecture provides a very simple way to implement processing algorithms directly on image data, in real-time, and prior to read-out of the data to an external digitizer or computer. In principle, almost any linear image processing filter kernel can be convolved with the scene image prior to readout. The useful size of the filter kernel is only limited by the size of the DFPA. Time domain filters can also be implemented on the ROIC to accomplish digital time domain integration (TDI) or change detection algorithms. The unique architecture can achieve the processing capability without the use of traditional digital adders or multipliers, like those used in most signal processors. Instead, a DFPA manipulates sequential digital counters under every pixel in a unique way to achieve the desired functionality. A non-addressable readout scheme is used for data transfer in four possible directions across the array. Although we are currently targeting longwave infrared (LWIR) applications, the approach can be potentially applied to any imaging application in any band.
READ LESS

Summary

The digital focal plane array (DFPA) project seeks to develop readout integrated circuits (ROICs) utilizing aggressively scaled and commercially available CMOS. Along with focal plane scaling and readout robustness benefits, the DFPA architecture provides a very simple way to implement processing algorithms directly on image data, in real-time, and prior...

READ MORE

Using filter banks to improve interceptor performance against weaving targets

Author:
Published in:
AIAA Guidance, Navigation, and Control Conf., 21-24 August 2006.

Summary

It is well known that interceptor performance against a weaving or spiraling target can be improved by use of a special purpose weave guidance law. However the weave guidance law requires knowledge of the target weave frequency. When the target weave frequency is unknown an extended Kalman filter is usually considered for the problem because it can be used to estimate the target weave frequency. However, the performance of the extended Kalman filter is sensitive to initialization errors. This paper offers an unusual linear Kalman filter bank approach, where each filter is tuned to a different target weave frequency, as a potential solution for estimating the target weave frequency. Rather than combining individual filter outputs in some probabilistic sense, a straightforward algorithm is presented for choosing the filter that is most closely tuned to the actual target weave frequency. This paper demonstrates that this filter bank approach is superior to that of the extended Kalman filter for the weaving target problem.
READ LESS

Summary

It is well known that interceptor performance against a weaving or spiraling target can be improved by use of a special purpose weave guidance law. However the weave guidance law requires knowledge of the target weave frequency. When the target weave frequency is unknown an extended Kalman filter is usually...

READ MORE

Normalized analysis of interceptor missiles using the four-state optimal guidance system

Author:
Published in:
J. Guid. Control Dyn., Vol. 26, No. 6, November-December 2003, p. 838-845.

Summary

Performance prediction of miss distance due to sensor measurement errors and random target manuevers for missiles using proportional navigation guidance has been analyzed using the adjoint technique; a normalization technique has been usedto reduce the solution of the set of differential equations describing the proportional navigationguidance problemto a set of algebraic equations using normalized steady-state adjointmiss distance coefficients. The four-state optimalguidance system is generally accepted to yield superior miss distance performance to that of proportional navigation guidance. The previously mentioned normalization technique is described and extended to the four-state optimal guidance system to calculate a new set of values for the normalized steady-state adjointmiss distance coef. cients for this con. guration. Plots of these normalized coefficients as a function of a normalized tuning parameter provide designers with insight into system performance sensitivities to design parameter and intercept parameter variations. The advantage of this technique is that the results are closed-form equations, and the analyst neither needs to perform simulations nor even to solve the adjoint differential equations. In addition, optimalguidance system results formiss distance due to target spiral maneuver are presented asmiss distance normalized to the target maneuver spiral radius, thus providing valuable insights into interceptor performance.
READ LESS

Summary

Performance prediction of miss distance due to sensor measurement errors and random target manuevers for missiles using proportional navigation guidance has been analyzed using the adjoint technique; a normalization technique has been usedto reduce the solution of the set of differential equations describing the proportional navigationguidance problemto a set of...

READ MORE

Improving the high altitude performance of tail-controlled endoatmospheric missiles

Published in:
AIAA Guidance, Navigation, and Control Conf., 5-8 August 2002.

Summary

It is demonstrated that at high altitude the performance of a tail-controlled aerodynamic missile can degrade because of the existence of low frequency right-half plane zeroes in the airframe transfer function when either proportional navigation or optimal guidance is used. A new guidance law that accounts for the airframe zeroes is developed numerically and shown to have superior performance to existing guidance laws at the higher altitudes. Although no closed-form solution for the guidance law is presented, the resultant numerical values for the control gains of the guidance law can easily be stored as a multidimensional table in existing on-board flight control computers. Two methodologies for computing the guidance law control gains are presented.
READ LESS

Summary

It is demonstrated that at high altitude the performance of a tail-controlled aerodynamic missile can degrade because of the existence of low frequency right-half plane zeroes in the airframe transfer function when either proportional navigation or optimal guidance is used. A new guidance law that accounts for the airframe zeroes...

READ MORE

Showing Results

1-10 of 10