Angus P. Andrews

Miniaturized micro-optical scanners

Optical beam scanners are critical components for airborne and space-based laser radar, on-machine-inspection systems, factory automation systems, and optical communication systems. We describe here a laser beam steering system based on dithering two complementary (positive and negative) microlens arrays. When the two microlens arrays are translated relative to one another in the plane parallel to their surfaces, the transmitted light beam is scanned in two directions. We have demonstrated scanning speeds up to 300 Hz with a pair of 6-mm-aperture microlens arrays designed for input from a HeNe laser. The output beam covers a discrete 16 x 16 spot scan pattern with about 3.6 mrad separation and only 400 μrad of beam divergence, in close agreement with design predictions. This demo system is relatively compact; less than 2 in. on a side. We also describe several near-term applications, some critical design trade-offs, and important fabrication and design issues.

Development of micro-electro-mechanical optical scanner

Rockwell is working on the development of a micro-electromechanical optical scanner based on bimorph microactuators. This scanner is lightweight, is small, and has superior scanning performance. The scanner is a low-power (<1 W) device that has large scan angles (?20 deg) and scan rates in the range of 100 to 2000 Hz. It works for all wavelengths and offers the potential for monolithic integration with both electronics and optics for on-chip signal processing and control. The optical scanner consists of two main components—actuator and mirror— which are fabricated on a silicon cantilever beam. The actuator is comprised of a bimorph layer covered with two metal layers, which function as top and bottom electrodes. The mirror can be as large as 12 mm2 in area, is placed at the end of the cantilever beam, and is designed for maximum optical flatness. The optical efficiency of the device is very high and can exceed 90% on proper metallization of the mirror area. The scan angle is a function of beam thickness, power efficiency of the bimorph, and many other design criteria. Through many improvements in these design parameters, a scan angle greater than 20 deg is expected to be achieved with high yield.

MOEM scan engine for bar code reading and factory automation

Rockwell is in the state of technology transfer to manufacturing of a micro-opto-electro-mechanical scan engine with superior scanning performance for bar code reading and factory automation. The scan engine consists of three main components: actuator, mirrors, and control electronics. The first two components are fabricated on a silicon cantilever beam while the control electronics are presently hybrid. The actuator comprises of a bimorph layer covered with two metal layers. The mirror has a large area (several mm2) and it is micromachined with a surface flatness better than (lambda) /2. Actuator scan-angles greater than 22 degree(s) with high repeatability in performance are achieved. The scan engine was integrated with an existing Rockwell commercial bar code reader/decoder and successfully proven to read a two-character code 39 bar code. The system was capable of decoding the 13-mil label at 360 scans per second with a 100% successful read performance. Environmental testing of the device indicates that the scanner can operate at elevated temperatures up to 70 degree(s)C with minor fluctuations in frequency and scan angle. The scanner has also gone through a lifetime cycle test and it has survived more than 8 billion cycles during a period of 18 months. To increase the yield and the performance level of the device, theoretical study as well as dynamic simulation by finite elements modeling have been investigated and will be reported separately.

An introduction to the kalman filter

This is a list of errors in the book Optimal State Estimation, John Wiley & Sons, 2006. The main web site for the book is at http://academic.csuohio.edu/simond/estimation. My email address is listed on my home page at http://academic.csuohio.edu/simond. I enthusiastically welcome feedback, comments, suggestions for improvements, and corrections. I also gratefully acknowledge those who have pointed out many of the errata that are documented here: Ali Javadi, Juan Luque, Ibrahim Abdel Hameed, Rick Rarick, Memo Ergezer, David Schwartz, Jeff Gove, Kevin Sharp, Stephan Busch, Yeoh WeeSoon, Michael Haralambous, Ville Kyrki, George Dontas, Felix Monasterio-Huelin, Cagdas Ozgenc, Cheng Zhong, Ning Lei, Roberto Rigamonti, Vincent Sircoulomb, Sami Fadali, Max Medvetsky, Jonathan How, Ismar Masic, Arthur Menikoff, Nedzad Arnautovic, Gabriel Zigelboim, Antje Westenberger, Laurent de Vito, Warner Losh, HunCheol Im, Martin Grossman, Christof Voemel, Bill Jordan, Bruno Stratmann, Philipp Warode, John McFarland, and James Tursa.In 1960, R.E. Kalman published his famous paper describing a recursive solution to the discrete-data linear filtering problem. Since that time, due in large part to advances in digital computing, the Kalman filter has been the subject of extensive research and application, particularly in the area of autonomous or assisted navigation. The Kalman filter is a set of mathematical equations that provides an efficient computational (recursive) means to estimate the state of a process, in a way that minimizes the mean of the squared error. The filter is very powerful in several aspects: it supports estimations of past, present, and even future states, and it can do so even when the precise nature of the modeled system is unknown. The purpose of this paper is to provide a practical introduction to the discrete Kalman filter. This introduction includes a description and some discussion of the basic discrete Kalman filter, a derivation, description and some discussion of the extended Kalman filter, and a relatively simple (tangible) example with real numbers & results.

Micro-optic laser beam scanner

Laser beam scanners are used to modulate the direction of laser light, and are critical components of airborne and space-based LIDAR and optical communications systems. We report here a laser beam steering device design based on dithering two complementary (positive and negative) binary optic microlens arrays. When the two microlenses are translated relative to one another in the plane parallel to their surfaces, a light beam can be scanned and controlled in two directions. The first demonstration of this device concept was reported by Lincoln Laboratory. We have demonstrated a miniaturized version of this concept consisting of a pair of 6-mm-aperture binary optic microlens arrays designed for HeNe laser wavelength.

Parallel time-frequency analysis

Conventional time-frequency analysis methods are generally too computationally intensive for real-time implementation. A relatively new method based on a dynamic state-space model is inherently a real-time method and can be implemented in parallel processing. It has O(n) computational complexity per signal sample, where n is the number of frequencies in the analysis. Its offered concurrency allows only sublinear speedup with parallel digital implementations, but linear speedup with a partially analog implementation.<<ETX>>

Silicon micromachined piezoelectric ZnO bimorphs as micromirrors for display applications

Cantilever beams of piezoelectric heterogeneous bimorphs (ZnO-on-Si3N4 bimorphs) have been designed and fabricated on silicon wafers for applications as micro-mirrors. The bimorph is a composite beam comprised of a bottom layer of Si3N4 and a top layer of ZnO which has been metallized with Au/Cr film on both surfaces. A metallized rectangular pad near the tip of the bimorph has been designed to serve as a deflecting micro-mirror. The fabrication procedures of the bimorphs using surface-machining method with ZnO as the sacrificial layers are presented in the paper. Measurement of the deflection of the bimorph as a function of dc voltages showed two different regimes of voltage dependence. For voltage magnitude less than 1 volt, small and linear deflection was obtained which was consistent with the theoretical prediction. At voltage magnitude larger than 1 volt, large deflection was obtained with quadratic dependence on the magnitude of the applied voltage. The large deflection can be attributed to joule heating effect due to current conduction in the semiconducting ZnO. The fundamental resonance frequency of the bimorph has been measured and is in close agreement with the predicted value obtained from the Euler-Bernoulli beam equation. Because of the quadratic dependence on the voltage, resonance can be obtained even though the frequency of the driving signal was only at half of the true resonance frequency. Air damping was observed which led to a reduction of the Q-factor. To test the bimorph for micro-mirror display applications, a HE-Ne laser beam has been directed at a metallized pad at the tip of the bimorph. A sinusoidal signal superimposed with a dc bias has been applied to the bimorph. The scanning range of the reflected laser beam is reported and discussed in the presentation.