In prior work, we demonstrate optical correlation via dynamic range compression in two-beam coupling using
thin-film organic materials. In this paper, we continue the effort; characterize the performance of this correlator
for variety of input. We successfully demonstrated correlation results almost free of cross- correlation and noise
for extremely complicated noisy image were the signal image consist of several targets and reference image
superposed of many templates.
In prior work, we exploited the nonlinearity inherent in four-wave mixing in organic photorefractive materials for
adaptive filtering. In this paper, we extend our work further and demonstrate new applications which involve:
dislocation, scratches and defect enhancement. With the availability of the organic photorefractive materials with
large space-bandwidth product, it should open the possibility of using the adaptive filtering techniques in quality
control systems.
In this paper, we propose a plasmonic parametric oscillator. The device is based on coupling between optically generated
and electrically induced surface plasmon waves. The device can be used for a variety of applications involving spectrum
analysis, widely tunable electromagnetic emitters, heterodyne detection, and amplification. We developed Maxwell's
equations based on the theoretical model of the coupling between plasmons and electrically induced plasmons.
Electrically induced plasmons are generated when a current is injected in the vicinity of a metallic grating. The coupling
between the two kinds of plasmon bands is dependent on the skin depth of each. The skin depth of an optically generated
plasmon is well known, while the skin depth of an electrically induced plasmon vanishes as the grating frequency
becomes small or the injected current becomes large.
In this paper we designed a highly tunable laser with a corrugated metallic nano-grating. The design leverages the free
electron laser design based on either the transit of an e-beam in the vicinity of a metallic grating or the transit of an ebeam
through a periodic, transverse magnetic field produced by arranging magnets with alternating poles. Our design
consists of a nano-film that is evaporated over a PMMA nano-grating. Current is injected into the nano-grating thin film.
The electrons in the injected current experience an oscillating motion due to the corrugated grating structure. If the mean
free path of the electrons within the nano-grating is long enough compared to the nano-grating spacing, the electron
wave emits electromagnetic radiation. We developed the electromagnetic emission theory by solving Maxwell's
equations for a current injected into a nano-wave grating, taking into consideration the electron mean free path. A
corrugated nano-grating device with an area of 300 μm × 300 μm and a 30 nm grating spacing was fabricated.
In this paper, we present simulation results pertaining to our broadband solid-state optically and electrically pumped THz
source design. Our design consists of a thin layer of dielectric sandwiched between a nano-grating and a thin film, such
as metal, semiconductor, or high electron mobility material. By passing a DC current through the lower layer, a THz
emission will be radiated from the nano-grating. We demonstrate preliminary current injection effects on surface
plasmons propagating on this device utilizing known analytical surface plasmon formulas and COMSOL Multiphysics
finite element analysis software.
In this paper, we demonstrate optical correlation via dynamic range compression in two-beam coupling using thin-film
organic materials. In contrast to the first demonstration, in which it was not possible to demonstrate correlation with
complicated input, here we demonstrate correlation with extremely challenging cases involving finger prints, images in
clutter, and SAR images. Our correlation results outperform many correlation results, including ones based on optimal
filters.
Imaging in atmospheric turbulence and target recognition in cluttered environments have been research topics for many
years. Currently, there are some well-established techniques for image restoration and recognition; however, if the
atmospheric turbulence becomes a severe scattering medium and the surrounding environment is very cluttered, most
conventional methods, such as inverse filtering and Wiener filtering, will be inadequate for correcting and recognizing
the captured images. In this paper, we experimentally demonstrate nonlinear dynamic range compression techniques for
image restoration and correlation via two-beam coupling and four wave mixing in organic photorefractive films.
In this paper, we exploit the nonlinearity inherent in four-wave mixing in organic photorefractive materials and demonstrate edge enhancement, contrast conversion, and defect enhancement in a periodic structure. With the availability of these materials, which have large space-bandwidth products, edge enhancement, contrast conversion and defect enhancement are possible. Some simulation results also are provided.
In this paper, we present a design for a widely tunable solid-state optically and electrically pumped THz laser based on
the Smith-Purcell free-electron laser. In the free-electron laser, an energetic electron beam pumps a metallic grating to
generate surface plasmons. Our solid-state optically pumped design consists of a thin layer of dielectic, such as SiNx,
sandwiched between a corrugated structure and a thin metal or semiconductor layer. The lower layer is for current
streaming, and replaces the electron beam in the original design. The upper layer consists of one micro-grating for
coupling the electromagnetic field in, another for coupling out, and a nano-grating for coupling with the current in the
lower layer for electromagnetic field generation. The surface plasmon waves generated from the upper layer by an
external electromagnetic field, and the lower layer by the applied current, are coupled. Emission enhancement occurs
when the plasmonic waves in both layers are resonantly coupled.
In this paper, we propose a design for a widely tunable solid-state optically and electrically pumped THz source based
on the Smith-Purcell free-electron laser. Our design consists of a thin dielectric layer sandwiched between an upper
corrugated structure and a lower layer of thin metal, semiconductor, or high electron mobility material. The lower layer
is for current streaming, which replaces the electron beam in the Smith-Purcell free-electron laser design. The upper
layer consists of two micro-gratings for optical pumping, and a nano-grating to couple with electrical pumping in the
lower layer. The optically generated surface plasmon waves from the upper layer and the electrically induced surface
plasmon waves from the lower layer are then coupled. Emission enhancement occurs when the plasmonic waves in both
layers are resonantly coupled.
In this paper we demonstrate image restoration via photorefractive two-beam coupling. Our restoration is based on
coupling between the joint spectra of the distortion impulse response and the distorted image, and the clean reference
beam. The image restoration is used to demonstrate one-way image transmission in an aberrating medium. Our
experimental demonstration is supported by theoretical modeling of the restoration process and by computer modeling.
In this paper, we exploit the nonlinearity inherent in four-wave mixing in organic photorefractive materials and
demonstrate edge enhancement, contrast conversion, and defect enhancement in a periodic structure. With the
availability of these materials, which have large space-bandwidth products, edge enhancement, contrast conversion and
defect enhancement are possible.
In this paper, we present a design for a widely tunable solid-state optically and electrically pumped THz laser based on
the Smith-Purcell free-electron laser. In the free-electron laser, an energetic electron beam pumps a metallic grating to
generate surface plasmons. Our solid-state optically pumped design consists of a thin layer of dielectic, such as SiNx,
sandwiched between a corrugated structure and a thin metal or semiconductor layer. The lower layer is for current
streaming, and replaces the electron beam in the original design. The upper layer consists of one micro-grating for
coupling the electromagnetic field in, another for coupling out, and a nano-grating for coupling with the current in the
lower layer for electromagnetic field generation. The surface plasmon waves generated from the upper layer by an
external electromagnetic field, and the lower layer by the applied current, are coupled. Emission enhancement occurs when the plasmonic waves in both layers are resonantly coupled.
We have developed a differential interpolation method for correcting sinusoidally scanned distorted images. In our
approach, the scanned image is processed by a line-by-line interpolation technique based on differentiation. As a natural
consequence of the method, the image can be divided into four domains/zones perpendicular to the scan direction. The
domain boundaries are set by our interpolation algorithm. Each domain is corrected using its specific algorithm;
corrected domains are reassembled to construct the corrected image. The implementation of this algorithm shows that,
for our 100 pixel wide test image, it is possible to retrieve at least 97.45% of the original image, as measured by the
recovered energy, which is superior to the established methods we have applied to this problem.
We are in the process of developing an all optically driven, deformable mirror device through the
integration of an array of photodetectors with an array of MEMS deformable mirror devices. In this
paper we demonstrate the optical actuation of a single-pixel, deformable-mirror MEMS device
through a direct cascade with a photodetector. Deformation is quasilinear at low light intensities, and
saturates at higher intensities. We also describe the fabrication of an integrated device consisting of
an all optically addressed deformable-mirror MEMS suspended over a p-i-n photodetector. Initial
demonstration of optical actuation of the deformable mirror using the newly integrated device is also
presented. We have fabricated several membrane materials, membrane structures, and photodetector
arrays.
Nonlinear information processing via two-beam coupling using thin-film organic
photorefractive material is demonstrated. The organic material is found to possess superior response
time and resolution compared to photorefractive bulk material. The possibility of designing dynamic
range compression deconvolution for restoring blurred images embedded in a noisy environment is
also demonstrated.
A generic nonlinear dynamic range compression deconvolver (DRCD) is proposed. We have performed the dynamic
range compression deconvolution using three forms of nonlinearities: (a) digital implementation- A-law/μ-law, (b)
hybrid digital-optical implementation- two-beam coupling photorefractive holography, and (c) all optical
implementation- MEMS deformable mirrors. The performance of image restoration improves as the saturation
nonlinearity increases. The DRCD could be used as a preprocessor for enhancing Automatic Target Recognition (ATR)
system performance. In imaging through atmosphere, factors such as rain, snow, haze, pollution, etc. affect the received
information from a target; therefore the need for correcting these captured images before an ATR system is required. The
DRCD outperforms well-established image restoration filters such as the inverse and the Wiener filters.
KEYWORDS: Scattering, Image enhancement, Signal to noise ratio, Image compression, Synthetic aperture radar, Interference (communication), Laser scattering, Energy efficiency, Signal detection, Signal processing
Synthetic radar image recognition is an area of interest for military applications including automatic target recognition,
air traffic control, and remote sensing. Here a dynamic range compression two-beam coupling joint transform correlator
for detecting synthetic aperture radar (SAR) targets is utilized. The joint input image consists of a pre-power-law,
enhanced scattering center of the input image and a linearly synthesized power-law enhanced scattering center template.
Enhancing the scattering center of both the synthetic template and the input image furnishes the conditions for achieving
dynamic range compression correlation in two-beam coupling. Dynamic range compression: (a) enhances the signal to
noise ratio, (b) enhances the high frequencies relative to low frequencies, and (c) converts the noise to high frequency
components. This improves the correlation peak intensity to the mean of the surrounding noise significantly. Dynamic
range compression correlation has already been demonstrated to outperform many optimal correlation filters in detecting
signals in severe noise environments. The performance is evaluated via established metrics, such as peak-to-correlation
energy (PCE), Horner efficiency and correlation peak intensity. The results showed significant improvement as the
power increased.
We propose using the smart antenna principle as the basis of a new design for smart optical receivers in LADAR
systems. This paper demonstrates the feasibility of designing a LADAR system with a receiver consisting of an array of
photodetectors, which leads to field-of-view enhancement and beamforming by fusing streams of video information
received from the detectors. As a proof of concept, we demonstrate this design by fusing several video information
streams from different fields of view using our Mathworks Simulink® model. The fusion algorithm uses the fuzzy logic
maximum operation on the data output from the cameras.
A power-law correlation based on an inverse filter Fourier-Radon-transform synthetic discriminant function (SDF) for
facial recognition is proposed. In order to avoid spectral overlap and nonlinear crosstalk, superposition of rotationally
variant sets of inverse filter Fourier-transformed Radon-processed templates is used to generate the SDF. For the inverse
filter, the Fourier transform of M projections (Radon Transform) from one training image is combined with (N-1) M
Fourier transform of M projections taken from another N-1 training image. This synthetic SDF filter has a very high
discrimination capability; however, it is not noise robust. To overcome this problem, a power-law dynamic range
compression is added to the correlation process. The proposed filter has three advantages: (1) high discrimination
capability as an inverse filter, (2) noise robustness due to dynamic range compression, and (3) crosstalk-free nonlinear
processing. The filter performance was evaluated by established metrics, such as peak-to-correlation energy (PCE),
Horner efficiency, and correlation-peak intensity. The results showed significant improvement as the power-law filter
compression increased.
A generic nonlinear dynamic range compression deconvolver (DRCD) is proposed. We have performed the dynamic
range compression deconvolution using three forms of nonlinearities: (a) digital implementation- A-law/μ-law, (b)
hybrid digital-optical implementation- two-beam coupling photorefractive holography, and (c) all optical
implementation- MEMS deformable mirrors. The performance of image restoration improves as the saturation
nonlinearity increases. The DRCD could be used as a preprocessor for enhancing Automatic Target Recognition (ATR)
system performance. In imaging through atmosphere, factors such as rain, snow, haze, pollution, etc. affect the received
information from a target; therefore the need for correcting these captured images before an ATR system is required. The
DRCD outperforms well-established image restoration filters such as the inverse and the Wiener filters.
In this paper, the fabrication, modeling and characterization of an all optically addressed spring patterned silicon-nitride
deformable mirror Micro-Electro-Mechanical-System (MEMS) device is reported. This device is biased through
combinations of high frequency AC and DC voltages. The experimentally verified theoretical modeling for this device
shows mirror deflection saturation as a function of light intensity appropriate for dynamic range compression
deconvolution. It was experimentally verified that the spring MEMS deformable mirror device has response up to 10
MHz, which opens the possibility of correcting supersonic turbulence as well as atmospheric turbulence.
This paper investigates binary wavefront control in the focal plane to compensate for atmospheric turbulence
in fiber-coupled free-space laser communication (LaserCom) systems. Traditional approaches to turbulence
compensation (i.e., adaptive optics) modify optical phase in the pupil plane to improve the focal plane image
or increase energy on target in the far field. For high-energy laser applications, focal plane phase modulation is
problematic due to high power densities and device damage thresholds. However, LaserCom systems aim to use
minimal power for reasons such as eye safety and covert communication. Thus, focal plane wavefront control is
a reasonable approach for this application. Numerical results show that in an air-to-air scenario, binary phase
modulation provides mean fiber coupling efficiency nearly identical to that resulting from ideal least-squares
adaptive optics, but without the requirement for direct wavefront sensing. The binary phase commands are
derived from a single imaging camera and an assumption about the nature of spot breakup. The use of binary
wavefront control suggests that existing ferro-electric spatial light modulator technology may support real-time
correction. Coupling efficiency results are also compared to those for the Strehl ratio, highlighting the importance
of metric-driven design.
We propose dynamic range compression deconvolution by a new nonlinear optical limiter micro-electro-mechanical system (NOLMEMS) device. The NOLMEMS uses aperturized, reflected coherent light from optically addressed, parabolically deformable mirrors. The light is collimated by an array of micro-lenses. The reflected light saturates as a function of optical drive intensity. In this scheme, a joint image of the blurred input information and the blur impulse response is captured and sent to a spatial light modulator (SLM). The joint information on the SLM is read through a laser beam and is Fourier transformed by a lens to the back of the NOLMEMS device. The output from the NOLMEMS is Fourier transformed to produce the restored image. We derived the input-output nonlinear transfer function of our NOLMEMS device, which relates the transmitted light from the pinhole to the light intensity incident on the back side of the device, and exhibits saturation. We also analyzed the deconvolution orders for this device, using a nonlinear transform method. Computer simulation of image deconvolution by the NOLMEMS device is also presented.
In this paper the A-law/μ-law Dynamic Range Compression algorithm used in telecommunication systems is proposed
for the first time for nonlinear Dynamic Range Compression image deconvolution. In the proposed setup, a joint image
of the blurred input information and the blur impulse response are jointly Fourier-transformed via a lens to a CCD
camera which acts as a square-law receiver. The CCD camera is responsible for mixing the Fourier transforms of the
impulse response and the distorted image to compensate for the phase distortion and then the A-law/μ-law nonlinear
transformation is responsible for enhancing both the high frequencies and the signal-to-noise ratio. The proposed
technique is supported by computer simulation.
We have developed a spatial demultiplexing/multiplexing algorithm for correcting sinusoidally scanned distorted images. In our approach, the scanned image is demultiplexed into equal spatial slots (strips) perpendicular to the scan direction. Each spatial slot is interpolated through either an oversampling or an undersampling algorithm, depending upon its location. The interpolated spatial slots are multiplexed to reconstruct the corrected image. The implementation of this algorithm shows that, for our 100-pixel-wide test image, depending upon the slot size, it is possible to retrieve at least 99% of the original image, as measured by the recovered energy.
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.
We propose a design of diffractive and refractive optical corrective elements with zooming capability for linearizing the angular scan of a resonant mirror scanner. Considering the symmetry requirements of the refractive element a graded index of refraction and its binary amplitude version are designed based on phase lag (beam retardation due to propagation through an inhomogeneous media). The design takes the beam diameter into consideration making it robust against beam fanning.
In this paper we demonstrate the first optical actuation of a single-pixel, deformable-mirror MEMS device through a
direct cascade with a photodetector. Photovoltaic, p-i-n, and avalanche photodetectors were successfully utilized. Mirror
deformations were monitored by interferometry. Deformation is quasilinear at low light intensities, and saturates at
higher intensities. Actuation at picowatt light intensities has been accomplished by cascading with an avalanche
photodetector. We also describe the fabrication of an integrated device consisting of an all optically addressed
deformable-mirror MEMS suspended over a p-i-n photodetector. Initial demonstration of optical actuation of the
deformable mirror using the newly integrated device is also presented.
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.
KEYWORDS: Scanners, Video, Field programmable gate arrays, Mirrors, Analog electronics, LIDAR, Control systems, Laser scanners, 3D scanning, Oscilloscopes
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.
In this paper we propose a new operational mechanism for an optically addressed deformable mirror device. The device consists of a pixilated metallized membrane mirror supported above an optically addressed photoconductive substrate. A conductive transparent conductive electrode is deposited on the backside of the substrate. A DC bias is applied between the membrane and the back electrode of the device accompanied with very high frequency modulated light. The membrane is deformed when light is shone from the backside of the device. This occurs due to impedance and bias redistribution between the two cascaded impedances.
In previous work we introduced a new metric for the image resolution volume that couples the spatial resolution with the range resolution. We showed from a quantum noise consideration that there is a constant volume resolution and that one can trade-off spatial resolution at the expense of range resolution, and vise-a-versa. This theory was developed for a heterodyne LADAR system. In this paper we extend our previous heterodyne LADAR system theory to develop a image resolution volume metric for time-of-flight LADAR system, where device parameters such as optical amplifier noise are included.
We describe a pose-invariant facial verification system for cooperative subjects for use in a controlled entry system. Facial images in several poses are acquired for template correlation to construct synthetic discriminate binary phase only filters (SDBPOF). SDBPOF is used to compensate for variances such as head rotation and tilt. Correlation accuracy is determined by SDBPOF construction. Subject identification based on facial appearance was performed with a digitally simulated 4-f optoelectronic correlator comparing performance between binary phase only filters (BPOFs) and SDBPOFs. Recognition accuracy and false positive rates were determined for each mode of operation.
During the last decade we have extended the implementation of companding techniques in communication theory to apply to improve image processing in several optical systems by using implementations using nonlinear optical media. In this paper we introduce a photorefractive two-beam-coupling deconvolution using spatially-variable dynamic spectral compression. Resolution recovery of blurred noisy images is demonstrated for several different type of image blur.
We introduce for the first time a novel and unique algorithm for a generalized form for a minimum mean-square-error image processing filter. This algorithm can be used to recognize or retrieve an image that is not only partially obscured by a constant disjoint background, but is also simultaneously blurred and overlaid with additive gaussian noise. Although this algorithm can be applied to many general filter forms that have never been considered before, we test the performance of this filter in four novel obscured-version operating modes: three recognition modes and one retrieval mode. These tests included varying the levels of the background illumination and of the additive white noise, as well as varying the amount of obscuration on the image. Our simulation results show that it is possible to recognize or retrieve images that are as much as 90% obscured, as well as blurred and noisy with a signal-to-noise ratio of 0.1. We also show that the background illumination of the obscuring object improves the performance of the filter in both its recognition or retrieval modes. This work should be a significant advance in the pattern recognition area for both automatic target recognition and machine vision.
We continue our study of the misregistered trade-off heterocorrelation filter (HCF), introduced in Part 1. Instead of using the matched filter, we use only the phases of the Fourier transforms of the functions constituting the filter, with our basic filter being the phase-only filter. We show that by adjusting the value of the trade-off factor it is possible to make the correlation pattern and intensities of the heterocorrelation peaks equal to those of the autocorrelation peaks; in effect, making the HCF a homogeneous filter. This means that it can equally recognize totally different objects that one designs it to recognize. These results (1) turn out to be independent of the amount of misregistration (i.e., shift) between the centers of the impulse responses of the functions making up the filter and (2) can also support the claim that a HCF is a totally new approach to generating synthetic discriminant filter functions. We also produce plots showing how the intensities, peak-to-noise ratios, and peak-to-secondary ratios of both autocorrelation and heterocorrelation peaks behave as a function of trade-off factor.
We analyze an algorithm for the misregistered trade-off heterocorrelation filter (HCF) using nonlinear transformation methods. This HCF consists of a matched filter modified by a transmittance function that has been optimized for the metric peak-to-mismatched energy. We find that this algorithm employs a new form of the nonlinear synthetic discriminant function algorithm that generates multiple correlation peaks for both autocorrelation and heterocorrelation when the filter function is made up of functions misregistered (i.e., shifted) with respect to each other. By means of computer simulations we study the effect that the trade-off factor (), weighting the Fourier spectrum difference, has on the autocorrelation, heterocorrelation, and cross-correlations for centered inputs when the matched filter is used as the basic filter. We find that as increases, the difference between the autocorrelation and heterocorrelation peak intensities diminishes and reaches a minimum value when approaches 1. Furthermore, we find that for exactly registered (i.e., unshifted) images used to make up the HCF, there is only one order of autocorrelation peak and only one order of heterocorrelation peak; however, as the amount of misregistration increases, both the autocorrelation and heterocorrelation peaks split into many orders and their positions are displaced relative to each other. The amount of shift between successive autocorrelation and heterocorrelation peaks is equal to the amount of shift in the misregistered images used to make up the filter.
Recently surveillance and Automatic Target Recognition (ATR) applications are increasing as the cost of computing power needed to process the massive amount of information continues to fall. This computing power has been made possible partly by the latest advances in FPGAs and SOPCs. In particular, to design and implement state-of-the-Art electro-optical imaging systems to provide advanced surveillance capabilities, there is a need to integrate several technologies (e.g. telescope, precise optics, cameras, image/compute vision algorithms, which can be geographically distributed or sharing distributed resources) into a programmable system and DSP systems. Additionally, pattern recognition techniques and fast information retrieval, are often important components of intelligent systems. The aim of this work is using embedded FPGA as a fast, configurable and synthesizable search engine in fast image pattern recognition/retrieval in a distributed hardware/software co-design environment. In particular, we propose and show a low cost Content Addressable Memory (CAM)-based distributed embedded FPGA hardware architecture solution with real time recognition capabilities and computing for pattern look-up, pattern recognition, and image retrieval. We show how the distributed CAM-based architecture offers a performance advantage of an order-of-magnitude over RAM-based architecture (Random Access Memory) search for implementing high speed pattern recognition for image retrieval. The methods of designing, implementing, and analyzing the proposed CAM based embedded architecture are described here. Other SOPC solutions/design issues are covered. Finally, experimental results, hardware verification, and performance evaluations using both the Xilinx Virtex-II and the Altera Apex20k are provided to show the potential and power of the proposed method for low cost reconfigurable fast image pattern recognition/retrieval at the hardware/software co-design level.
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.
We introduce a new concept in pattern recognition that we call heterocorrelation. Contrary to standard approaches, heterocorrelation allows correlation of different images solely by modifying the filter's intensity transmissivity in the areas of greatest phase mismatch relative to the phase of the stored template. This approach can convert a single object recognition filter to a multiple object classification filter. We develop three algorithms and successfully test each of them for three completely different input cases: one that uses geometric input images with very little common edge information, one that uses these same images encoded with high spatial frequency information, and one that uses synthetic aperture radar (SAR) images that have almost no edge information. The third algorithm provides shift-invariant heterocorrelation with equalized in-class correlation peaks, and eliminates the possibility of any higher-order side peaks for the added in-class objects. We also demonstrate how the use of a heterocorrelation filter can improve the performance of conventional multiplexed filters, such as synthetic discriminant filters, as well as increase their template storage.
KEYWORDS: Optical correlators, Signal to noise ratio, Receivers, Signal processing, Computer simulations, Signal detection, Nonlinear optics, Interference (communication), Crystals, Four wave mixing
In this paper we summarize a new category of all optical companding nonlinear correlators developed by our group in
the last decade. All optical companding nonlinear correlators consist oftwo families: The first is based on energy transfer
between the joint spectra of reference and signal images. The second family is based on incoherent erasure of a grating
formed by coupled beams . Allof these correlators have similar features. Therefore, we take one representative case of
study, namely, the photorefractive two-beam coupling correlator. We perform theoretical analysis, computer simulations
and experimental demonstrations to predict the location of the best operating point of the two-beam coupling joint
transform correlator. From this study we determine the best operational condition for high speed and resolution, as well
as for optimal trade-off between correlation peak intensity, efficiency and noise performance. We also study the
performance of compansive correlators in analogy with the limiting square law receiver. It was found that the optimal
performing point corresponds to noise variance that is proportional to the transition from compression to expansion.
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.
In a previous publication we introduced a new photorefractive four-wave mixing deconvolution, FWMD, image correction approach for achieving one-way image transmission through an aberrating medium. In this paper we extend our work to include additional image degradations and more test cases. We characterize the performance as a function of the input beam ratios for four metrics: signal-to-noise ratio (SNR), normalized mean-square-error (NMSE), edge restoration (ER), and the peak-to-total energy ratio (PTE). In our characterization we color-code the best beam-intensity ratio 2D region(s) for each of the above metrics. Test cases are simulated at the optimal values of the beam-intensity ratios.
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.
This paper analyzes the operation of a new optically addressed deformable mirror device for applications in adaptive optics and optical signal processing. Device operation utilizes a pixellated metallized polymeric membrane mirror supported above an optically addressed photoconductive substrate. A grid of patterned photoresist supports the metallized membrane. A conductive ZnO layer is placed on the backside of the substrate. The device operates as an impedance distribution between two cascaded impedances between the deformable membrane and substrate and the substrate and back electrode. We develop a theoretical model to analyze the deformation as a function of the light intensity and electrical drive
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.
In previous work we introduced new algorithms for forcing two dissimilar patterns to correlate with each other with very high discrimination capability. In this work we analyze our algorithms mathematically using nonlinear-transform methods. In this analysis we distinguish what terms are responsible for the correlation and what terms are responsible for the heterocorrelation. Computer simulations supporting our mathematical analysis are presented.
In our previous paper "Theoretical analysis and simulation of heterocorrelation filter" we attempted to find the best conditions that makes the relative intensity of the autocorrelation to be equal to the heterocorrelation. Our theoretical modeling and computer simulation based on the theory developed in the previous papers showed that in order to make the autocorrelation equal to the heterocorrelation, it is essential to have phase-only based heterocorrelation.
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.
In this paper we introduce three weighting algorithms for performing shift-invariant heterogeneous phase-restricted correlation filters that are capable of identifying an object as belonging to a certain class while rejecting any object that is not a member of that class. We compare the performance of these highly discriminative filters to the performance of the phase-only filter, and the non- discriminative matched correlation filter, in similar circumstances. Even when the proposed filters achieved proper classification, the intensities of the correlation from heterogenous targets were much smaller than those from homogeneous targets. To increase the intensities of these hetero-correlation peaks relative to the autocorrelation peaks, we also introduced a fractional power law into the filter's transfer function, thereby controlling the rejection capability of the filter.
We develop a generalized minimum mean-square-error image processing filter for recognition and retrieval of noisy, blurred and obscured images. We examined the performance of this filter in four modes: (1) the well-known mean-square- error correlation filter; (2) the phase-only mean-square- error correlation filter; (3) the matched mean-square-error correlation filter, and (4) the image retrieving filter. Our simulation result show that it is possible to retrieve and recognize blurred images that are 90 percent obscured and whose signal-to-noise ratio is 0.1.
In this paper a 2D homodyne and heterodyne technique for imaging objects embedded in an opaque scattering medium is introduced. Our imaging approach is based on heterodyning of light with different Doppler shifts scattered from objects of two different textures or from an opaque object and a textured scattering medium. We report on the initial demonstration of pulling signals out of noise for an object hidden behind a scattering medium. Enhancements of signal- to-noise ratio of the order of 50 have been achieved utilizing a 2D holographic phase-sensitive detector.
We introduce a new type of integrated imaging sensor that detects multispectral and polarimetric signatures in an IR scene. The sensor is a stack consisting of an IR detector array, and an array of multispectral and polarimetric filters. In this first phase of the research, we fabricated multispectral filters for the 3-5 micron waveband don sapphire substrates and polarimetric filters on silicon substrates. These were characterized separately and in mechanical contact as a single unit. The transmission characteristics of both filters show excellent agreement with the theoretical result. Whenthe filters are integrated into an imaging sensor, such a sensor is anticipated to improve image contrast with sensor-fusion post processing. In addition, it will offer portability and robustness because of its integrated nature.
In this paper we introduce the mean-square-error correlation filter for obscured targets. We derive from this algorithm that the DC-blocked phase-only filter is the best practical approximation to this filter for recognizing SAR images with enhanced scattering centers for both inputs and templates. The performance of the DC-blocked phase-only filter is tested in the recognition of SAR images from the MSTAR data base under extended and non-extended operating conditions. The heterogeneous correlation filter algorithm used to correlate totally different images is utilized to correlate distorted images under extending operating conditions.
In a previous report we developed optimization algorithms showing how optical correlation filters operating with obscured inputs were affected by disjoint constant background illumination. In this paper we extend these studies by upgrading our algorithms to include the theoretical treatment of zero-mean disjoint noise, as well as constant background illumination. Representative cases of computer simulations involving either noise clutter or background illumination are used to characterize the performance of our upgraded algorithms.
In this paper we theoretically analyze and demonstrate that a photorefractive correlator, originally proposed by D. M. Pepper and later implemented by J. O. White and A. Yariv as well as many others, can be used to realize adaptively a wide variety of optimal correlation filters such as the matched filter, the inverse correlation filter, the maximum discrimination correlation filter and several trade-off correlation filters.
In this paper we demonstrate that dc-blocked phase-only filter correlation, based on image sharpening algorithm of SAR images (using an MSTAR data base) for both input and its matching template, is significantly improved. Our approach is tested with a very complicated image using a binary input and a binary matching template. Prior to binarization an image sharpening algorithm is used to enhance the input image and the matching template.
In this paper we introduce a new algorithm for an encoded filter for heterogeneous correlation by enhancing the cross- correlation between selected different objects. The new algorithm should allow the expansion of the use of correlation systems from recognition to classification. We tested the feasibility of this approach using a data base of stored information.
A photorefractive nonlinear incoherent-erasure joint- transform correlator is presented and analyzed. The nonlinearity of this correlator can be tuned from the classical-matched filter to the phase-extraction limit by increasing the erasure beam intensity. Experimental results in Bi12GeO20 show a transition from matched-filter correlation to phase-extraction correlation by increasing the erasure beam intensity, in agreement with our theoretical results.
In this paper we discuss a new type of time integrative photorefractive device using self- pumped phase conjugation. This device can be used both for demultiplexing and phase sensitive detection.
Baseband demodulation, lock-in detection, noise reduction, compression/expansion nonlinearities, and correlation receivers are common subjects in communication theory. In this paper we use photorefractive materials to show how real-time holography can be used to implement these temporal electronic signal processing techniques as spatio-temporal optical signal processing on images.
We propose a phase coding technique for signal recovery of distorted images, and we demonstrate our results through computer simulations. In our demonstration we use two forms of distorted images: (1) a misfocused image and (2) a clean image distorted by passage through a thin aberrating medium. Our results show that even though only a portion of the distortion information was used, we can still recover the original image with a low level of additive noise. The proposed technique opens up the possibility of using all the available types of spatial light modulators for these purposes.
Several edge enhancement techniques are examined for improving the performance of binary phase-only filter pattern recognition devices. These include the linear techniques of blocking the lower Fourier orders and Laplacian filtering as well as the nonlinear techniques of phase extraction and phase binarization. The results indicate that the nonlinear techniques outperform the linear techniques when there is no distortion caused by aperturing the input information. However, when the input is apertured, both the linear and nonlinear techniques yield approximately the same peak-to-noise ratio.
An all optical nonlinear joint transform correlator is proposed and demonstrated. A hard- limiting quadratic nonlinearity is used in the Fourier plane to allow the first implementation of a phase only filter using photorefractive materials.
Nonlinear optical thresholding in the Fourier plane produces optically adaptive noise-cleaning masks that reduce additive signal-dependent noise, such as scalar multiplicative noise. We demonstrate the two-beam coupling artifact noise-reduction technique and achieve performance comparable to the Wiener filter.
Signal recovery from multiplicative complex noise is proposed and demonstrated. The recovery is achieved by using two phase conjugators in series to produce a photorefractive quadratic nonlinear processor.
An associative memory is implemented using a binary phase-only filter as the memory element. In the current architecture, if the input contains any part of the set of stored memories, then the entire set is retrieved at the output. In addition, the sharp autocorrelation peak and the high signal-to-noise ratio allows operation without necessitating a thresholding device.
The inactive areas of certain pixellated SLMs are transmissive rather than opaque, while their active areas modulate the optical phase or amplitude. Computer simulations of optical correlators are made for a continuous-input SLM and a filter SLM implementing either a classical matched, phase-only, or binary phase-only filter. The correlation peak and signal-to-noise ratio are studied as a function of dead-zone area in both the input and filter SLMs. These results are compared with those obtained from correlators whose SLMs have only opaque dead zones.
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