Dana Pyburn

Photoconductive optically driven deformable membrane for spatial light modulator applications utilizing GaAs substrates.

The fabrication and characterization of an optically addressable deformable mirror for a spatial light modulator is described. Device operation utilizes an electrostatically driven pixellated aluminized polymeric membrane mirror supported above an optically controlled photoconductive GaAs substrate. A 5 microm thick grid of patterned photoresist supports the 2 microm thick aluminized Mylar membrane. A conductive ZnO layer is placed on the back side of the GaAs wafer. A standard Michelson interferometer is used to measure mirror deformation data as a function of illumination, applied voltage, and frequency. A simplified analysis of device operation is also presented.

Mapping approach for image correction and processing for bidirectional resonant scanners

We have developed a mapping algorithm for correcting sinusoidally scanned images from their distortions. Our algorithm is based on the close relationship between linear and sinusoidal scanning. Straightforward implementation of this algorithm showed that the mapped image has either missing lines or redundant lines. The missing lines were filled by fusing the mapped image with its median-filtered or interpolated version. The implementation of this algorithm shows that it is possible to retrieve up to 98% of the original image (depending on the algorithm used for data fusion) as measured by the recovered energy. Excellent correction was obtained for both simulated scanned images and actual images from a scanning laser radar system.

A mapping approach for distortion correction in sinusoidally scanned images

We have developed a mapping algorithm for correcting sinusoidally scanned images from their distortions. Our algorithm is based on an approximate relationship between linear and sinusoidal scanning. Straightforward implementation of this algorithm showed that the mapped image has either missing lines or redundant lines. The missing lines were filled by fusing the mapped image with its median filtered version. The implementation of this algorithm shows that it is possible to retrieve up to 96.43% of the original image, as measured by the recovered energy.

Real-time holographic deconvolution for one-way image transmission through distorting media

We propose and demonstrate a photorefractive real-time holographic deconvolution technique for adaptive one-way image transmission through aberrating media. In contrast with preceding methods, which have typically required various coding of the exact phase or two-way image transmission for correcting phase distortion, our technique relies on one-way image transmission using exact phase information. Our technique can simultaneously correct both amplitude and phase distortions. We demonstrate our results through both experiment and computer simulation for different aberrators.

Photoconductive optically driven deformable membrane for spatial light modulator applications utilizing GaAs and InP substrates

The fabrication and characterization of an optically addressable deformable mirror for spatial light modulator is described. Device operation utilizes an electrostatically driven pixellated aluminized polymeric membrane mirror supported above an optically controlled photoconductive GaAs substrate. A 5-μm thick grid of patterned photoresist supports the 2-μm thick aluminized Mylar membrane. A conductive ZnO layer is placed on the backside of the GaAs wafer. Similar devices were also fabricated with InP. A standard Michelson interferometer is used to measure mirror deformation data as a function of illumination, applied voltage and frequency. A simplified analysis of device operation is also presented.

Resolution limits in imaging LADAR systems

In this paper, we introduce a new design concept of laser radar systems that combines both phase comparison and time-of-flight methods. We show from signal to noise ration considerations that there is a fundamental limit to the overall resolution in 3-D imaging range laser radar (LADAR). We introduce a new metric, volume of resolution (VOR), and we show from quantum noise considerations, that there is a maximum resolution volume, that can be achieved, for a given set of system parameters. Consequently, there is a direct tradeoff between range resolution and spatial resolution. Thus in a LADAR system, range resolution may be maximized at the expense of spatial image resolution and vice versa. We introduce resolution efficiency, ηr, as a new figure of merit for LADAR, that describes system resolution under the constraints of a specific design, compared to its optimal resolution performance derived from quantum noise considerations. We analyze how the resolution efficiency could be utilized to improve the resolution performance of a LADAR system. Our analysis could be extended to all LADAR systems, regardless of whether they are flash imaging or scanning laser systems.

An FPGA-based method for a reconfigurable and compact scanner controller

An essential part of a LADAR system is the scanner component. The physical scanner and its electrical controller must often be as compact as possible to meet the stringent physical requirements of the system. It is also advantageous to have a reconfigurable electrical scanner controller. This can allow real-time automated dynamic modifications to the scanning characteristics. Via reconfiguration, this can also allow a single scanner controller to be used on multiple physical scanners with different resonant frequencies and reflection angles. The most efficient method to construct a compact scanner with static or dcynamic re-configurability is by using an FPGA-based system. FPGAs are extremely compact, reconfigurable, and can be programmed with very complex algorithms. We show here the design and testing of such an FPGA-based system has been designed and tested. We show here this FPGA-based system is able to drive scanners at arbitrary frequencies with different waveforms and produce appropriate horizontal and vertical syncs of arbitrary pulse width. Several programmable constants are provided to allow re-configurability. Additionally we show how very few essential components are required so the system could potentially be compacted to approximately the size of a cell phone.

Sinusoidal to linear scanning correction using a diffraction grating

Mechanical limitations dictate that high speed oscillating scan mirrors, required for video rate scanning, must be driven sinusoidally rather than at constant velocity. We have designed a diffractive corrector element that removes the resultant distortion in the scan field by optically converting the sinusoidal scan into a linear one

Photorefractive nonlinear deconvolution for one-way image transmission through aberrating media

We propose and demonstrate a photorefractive real-time holographic deconvolution technique for adaptive one-way image transmission through aberrating media. In contrast with preceding methods, which have typically required various coding of the exact phase or two way image transmission for correcting phase distortion, our technique relies on one-way image transmission through using exact phase information. Our technique can simultaneously correct both amplitude and phase distortions and provide substantial noise filtering. The nonlinearity of the photorefractive medium also helps to enhance the signal-to-noise ratio (SNR). And is thus superior to previous methods. We demonstrate our results through both experiment and computer simulation for different aberrators.

Low-power portable scanning imaging ladar system

We propose and are in the process of progressively implementing an improved architecture for a laser based system to acquire intensity and range images of hard targets in real-time. The system design emphasizes the use of low power laser sources in conjunction with optical preamplification of target return signals to maintain eye safety without incurring the associated performance penalty. The design leverages advanced fiber optic component technology developed for the commercial market to achieve compactness and low power consumption without the high costs and long lead times associated with custom military devices. All important system parameters are designed to be configured in the field, by the user, in software, allowing for adaptive reconfiguration for different missions and targets. Recently we have started our transition from the initial test bed, using a laser in the visible wavelength, into the final system with a 1550nm diode laser. Currently we are able to acquire and display 3-D false-color and gray-scale images, in the laboratory, at moderate frame rates in real-time. Commercial off-the-shelf data acquisition and signal processing software on a desktop computer equipped with commercial acquisition hardware is utilized. Significant improvements in both range and spatial resolution are expected in the near future.