I wrote many years ago that I felt physicists and photonics scientists were like Spock on Star Trek and that optical engineers were like Scotty. Spock would always understand the physics behind the problems and would usually save the day through some ground-breaking discovery that, on earth, would win the Nobel Prize. Scotty, in the meantime, would use what Spock had discovered to kluge together an effective way to power or protect the ship.

A new approach to locating gas and vapor plumes is proposed that is entirely passive. By modulating the transmission waveband of a narrow-band filter, an intensity modulation is established that allows regions of an image to be identified as containing a specific gas with absorption characteristics aligned with the filter. A system built from readily available components was constructed to identify regions of NO₂. Initial results show that this technique was able to distinguish an absorption cell containing NO₂ gas in a test scene.

Three-dimensional laser scanned surface segmentation is an important step for computer-aided broken objection patching. Current methods still have high time consuming problem in practical applications. In order to solve this problem, we propose the rapid three-dimensional (3-D) surface segmentation based on region dilation. The procedure includes three steps of point cloud meshing, candidate region generating, and insignificant region eliminating. Some experiments are implemented on the 3-D surface with a Roland LPX-250 3-D laser scanner to testify the feasibility and performance of the proposed algorithm compared with other methods.

A compact, low-cost semiconductor laser diode producing 40 ps full width at half maximum (FWHM) single-spike lasing pulses with 6 Watts peak power from a 20 μm stripe width is realized in the form of a simple single-heterostructure, grown by metal-organic chemical vapor deposition. The structure possesses a linearly graded doping profile extending from the p⁺ and n⁺ sides towards the p-n junction. This laser diode is operated under room temperature conditions and applies pumping current pulses (roughly 10 to 20  A/2 to 3 ns FWHM) achievable with a commercially available silicon avalanche transistor as an electrical switch.

We propose a novel all-fiber vibration sensor without any bulk optical element by employing an in-line nano-wire grid (NWG) fiber polarizer. The NWG is directly fabricated on tip of a single mode fiber (SMF) by focused ion beam technology. According to effective medium theory, the sub-wavelength NWG has strong polarization properties. In our experiment, the reflection contrast between transverse electric and transverse magnetic modes reaches 14 dB, which is sensitive enough to monitor polarization change induced by photoelastic effect. We apply a sinusoidal vibration signal generated by a piezoelectric transducer onto the fiber. The output light signal from the SMF coincides well with the vibration source. The frequency response of the sensor is measured from 20 Hz to 4 kHz showing great consistency.

We present a study of parameters that affect the accuracy of a reflectance spectrum recovery from the compressed data obtained in a multispectral imaging (MSI) system consisting of a computer-controlled set of light-emitting diodes (LEDs) synchronously switched with a digital monochrome camera. The system allows recovery of a two-dimensional distribution of reflection spectra in a wide spectral range (400 to 700 nm) just from a few captured frames. It is shown that the MSI system designed and assembled by students in a University laboratory is capable of measuring of absolute values of smooth reflectance spectra with an error smaller than 3%. Further, the increasing of the system accuracy could be achieved by providing higher spatial uniformity and higher overlapping of object illumination by all the LEDs.

White blood cells (WBC) are comparatively significant components in the human blood system, and they have a pathological relationship with some blood-related diseases. To analyze the disease information accurately, the most essential work is to segment WBCs. We propose a new method for pathological WBC segmentation based on a hyperspectral imaging system. This imaging system is used to capture WBC images, which is characterized by acquiring 1-D spectral information and 2-D spatial information for each pixel. A spectral information divergence algorithm is presented to segment pathological WBCs into four parts. In order to evaluate the performance of the new approach, K-means and spectral angle mapper-based segmental methods are tested in contrast on six groups of blood smears. Experimental results show that the presented method can segment pathological WBCs more accurately, regardless of their irregular shapes, sizes, and gray-values.

New methods for inverting Compton camera data have recently been developed. In particular, an inversion method was developed for each of the two models of Compton camera data that have been proposed in the literature. These methods make it possible to produce a parallel projection as well as a "voxel-wise" reconstruction of a distribution of radioactivity. An objective of the computer simulations presented here is to demonstrate these methods' ability to produce parallel projections and voxel-wise reconstructions. The results of the simulations indicate the new inversion methods can produce reasonable images and projections, at least when noiseless simulated data is used. Furthermore, the minimum sets of data needed to use these inversion methods were also recently determined. Presumably, incorporating more measurements into the reconstruction process than the minimum needed will improve the quality of the reconstructions that result. Methods for doing this are developed here as well.

In order to make full use of the characteristics of parallelogram and calibrate the camera online, on the basis of studying the projective properties of a parallelogram, a camera calibration method based on parallelogram similarity invariants is presented. At least three images of the space parallelogram taken from different angles were used to establish the constraint equations on the image of the absolute conic and parallelogram similarity invariants, and the camera's intrinsic and extrinsic parameters were computed by solving the constraint equations. The first two parameters of radial distortion were also estimated according to the projective property of straight line. Experimental results on simulated data and real images demonstrate that the proposed algorithm is effective and flexible.

A novel line-scan camera calibration method in close-range photogrammetry is proposed. Since the line-scan camera is only sensing in one dimension, it's hard to recognize the space points from the linear data captured in static state. To address this problem, the camera is fixed to a programmable linear stage. With the help of the linear stage, a scan image of the pattern is grabbed by the line-scan camera in uniform rectilinear motion state. Therefore, the image points are definitely matched with the space points on the pattern. A pair of projective equations is established to describe this dynamic imaging model, which is determined by six extrinsic camera parameters, five intrinsic camera parameters and three other motion parameters. All the fourteen parameters are estimated approximately by using the direct linear transformation of a reasonably simplified camera model firstly, and then the results are further refined by non-linear least square mean (LSM). Both computer simulated data and real data are used to test our calibration method. The robustness and accuracy are verified by lots of simulated experiments, and for the real data, the root mean square error of re-projected points is less than 0.3 pixels.

Here, we report for the first time the optical testing of modern 1.3, 5, and 8 megapixel panoramic lenses available on the market for security and surveillance applications. Our first test focused on the measurement of the image mapping and more particularly on the inverse of the instantaneous field of view expressed in pixels/degree (IFOV−1). This kind of measurement provides a valuable comparison parameter for the user community. The second test was a measurement of a modulation transfer function (MTF) system. All tested lenses were coupled with the same camera in order to measure the MTF system using the edge response. While this measurement is not a measurement of the MTF of the lens, it provides a basis for comparison between the different lenses. Our measurement shows that the IFOV is more robust than the MTF to manufacturing and assembly errors. This provides robustness to the unwrapping image post-processing. The MTF measurements show that all the tested lenses have an on-axis MTF of 35% at Nyquist frequency over 2 (Ny/2) for a 2.2 μm pixel pitch.

The measurement of holes in the engine block top surface determines the general coupling effect of the engine. All of these holes are strictly restricted by the requirements of the dimensional tolerance and the geometrical tolerance, which determines the final engine quality. At present, these holes are measured mostly by the coordinate measuring machine (CMM) in the production line, and meeting the industry demands of automation, rapidity, and online testing with the method is difficult. A new rapid solution measuring the holes in the engine block top surface is proposed, which is based on the combination of multiple visual sensors. The flexible location method of the block is designed, and the global data fusion model based on multiple visual sensors is studied. Finally, the unified correction model of the lens distortion and the system inclination is proposed, and a revised system model with more precision is researched. The CMM measures the holes sizes and the spatial relationship between holes, and the data obtained are substituted into the global data fusion model to complete the system on-site rapid calibration. The experimental results show that the scheme is feasible. The measurement system can meet the production line needs of intelligence, rapidity, and high precision.

Based on the recently proposed time-dependent coupled mode theory (TD CMT) for parallel waveguides, we present an analysis of three advanced photonic micro-devices: micro-interferometer, 90-deg bent, and a tunable beam splitter. An accurate analysis of these devices with commercial software may take many hours, whereas the TD CMT needs only minutes with little sacrifice of accuracy.

We conduct an investigation into optical nanoantennas in the form of a strip dipole made from aluminum. With the finite-difference time domain simulation both optical input impedance and radiation efficiency of nanostrip antennas are addressed. An equivalent circuit is presented as well for the nanostrip antennas at optical resonances. The optical input resistance can be adjusted by varying the geometric parameters of antenna strips. By changing both strip area and strip length simultaneously, optical input resistance can be adjusted for matching impedance with an external feeding or loading circuit. It is found that the optical radiation efficiency does not change significantly when the size of a nanostrip antenna varies moderately.

Linear calculation models are proposed and demonstrated to evaluate the color rendering index (CRI) performance associated with the correlated color temperature (CCT) of a white light emitting diode with two phosphors. All the three proposed models are simple and easy, and the error in predicting the CRI is within 1, while the deviation of the CCT is around 300 K and less. Such models can be useful in evaluating the chromatic performance of a specific recipe with two phosphors.

The conventional speckle contrast measures only speckle severity, and is unable to characterize granularity and anisotropy in displayed images, which are easily picked up by human observers. Here, we propose a comprehensive method based on the power spectral density which allows the simultaneous measurement of three components of laser speckle-severity, granularity and anisotropy-as a superior way to evaluate both speckle and speckle reduction techniques.

We propose a new guidance system for the blind. An optical triangulation method is used in the system. The main components of the proposed system comprise of a notebook computer, a camera, and two laser modules. The track image of the light beam on the ground or on the object is captured by the camera and then the image is sent to the notebook computer for further processing and analysis. Using a developed signal-processing algorithm, our system can determine the object width and the distance between the object and the blind person through the calculation of the light line positions on the image. A series of feasibility tests of the developed blind guidance system were conducted. The experimental results show that the distance between the test object and the blind can be measured with a standard deviation of less than 8.5% within the range of 40 and 130 cm, while the test object width can be measured with a standard deviation of less than 4.5% within the range of 40 and 130 cm. The application potential of the designed system to the blind guidance can be expected.

Femtosecond lasers have been found suitable for maskless photolithography with submicron resolution, which is very attractive for solving the problem of high photomask cost. Direct femtosecond laser writing of lithographic patterns is reported with submicron feature width on thin positive photoresist film. We use a scanning electron microscope to investigate the feature sizes of femtosecond laser lithography, which are determined by the incident laser power, the number of scan times and the substrate materials. Submicron T-shaped gates have been fabricated using a two-step process of femtosecond laser lithography where the gate foot and head can be separately defined on positive AZ4620 photoresist film. This work has led to the stable fabrication of sub-300 nm T-gates on the samples of GaN on sapphire substrate and AlGaN/GaN on Si substrate.

This paper presents the project, optimization, design details, and fabrication of an optical chemical sensor based on a Mach-Zehnder interferometer (MZI), fabricated with metal-oxide semiconductor compatible processes and materials. The sensing material is hexamethyldissilazane (HMDS) plasma polymerized thin film, which exhibits hydrophobic characteristics, high resistance to acid or basic solution, and adsorption of polar and nonpolar organic compounds. Both reference and sensor arms of the fabricated MZIs are covered with HMDS thin film in order to keep the device balanced. Different substances, such as water, 2-propanol, and hexane vapors are investigated. The high sensitivity of the MZI structure, associated with refractive index variations of about 10−4, paves the way for a myriad of sensor applications, such as humidity, organic compounds, proteins, antibodies (antigens), enzymes, pesticides, and others. The minimum detectable measurements were 4.6  mg/min for n-hexane and 0.2  mg/min for 2-propanol.

This paper discusses an applicable fiber-optic accelerometer composed of a transmissive grating panel, a reflection mirror, and two optical fibers with a separation of quarter grating pitch as transceivers that monitor the low-frequency accelerations of civil engineering structures. This sensor structure brings together the advantages of both a simple sensor structure, which leads to simplified cable design by 50% in comparison with the conventional transmission-type fiber optic accelerometer, and a stable reflected signals acquisition with repeatability in comparison to the researched grating-reflection type fiber optic accelerometer. The vibrating displacement and sinusoidal acceleration measured from the proposed fiber optic sensor demonstrated good agreement with those of a commercial laser displacement sensor and a MEMS accelerometer without electromagnetic interference. The developed fiber optic accelerometer can be used in frequency ranges below 4.0 Hz with a margin of error that is less than 5% and a high sensitivity of 5.06 rad/(m/s)².

Here, the concentration of TNT was detected by using evanescent absorption method, U-shaped plastic optical fiber was used as sensor head and light transmit element. A high brightness blue light-emitting diode with spectrum centered at 470 nm was used as excitation source. The relationship between the transmitted light power of U-shaped sensor head and TNT concentration was linearly and the linear coefficient was 0.944. The system showed excellent reversibility when the sensor tested by alternately cycling between 0 and 25  mg/100  ml TNT solution in five cycles. The stability of the sensor head in 25  mg/100  ml TNT solution was also tested within two hours. The proposed sensor is a cost-effective alternative to traditional TNT sensors and provides a platform for other optically based sensors.

We theoretically analyze the effective indices of a horizontal slotted waveguide on SOI platform. Based on the analysis, both polarization independent and strongly birefringent waveguides can be constructed in our proposed waveguide geometry. Utilizing the strongly birefringent waveguide, an ultra-compact polarization splitter based on a directional coupler (DC) was proposed and subsequently optimized by 3D-beam propagation method. The simulation results suggest that the coupling length of the DC could be less than 18 μm, and the maximum polarization crosstalk less than −47 and −37  dB for the cross and bar ports, respectively. Around the 1550 nm operating wavelength, a bandwidth of 30 nm is obtained for the crosstalk less than −20  dB. Finally, the tolerance of the splitter is discussed.

A fiber transmission filter is proposed and experimentally explored. The bandwidth of the filter is less than 0.1 nm, the loss and back-reflection index is 1.84 dB/18.60 dB for one direction and 1.57 dB/20.78 dB for the other direction, figures which exhibit a great value for ring-laser gyros. By utilizing this filter, a bidirectional laser wave carrying a beating signal can be obtained in a homogeneously broadened gain medium. Finally, a ring-laser gyro with its lock-in area less than 10 deg sec^-1 is obtained and presented.

Modelling of a compact and completely non-blocking 4×4 optical switch utilizing integrated multi-mode interference (MMI) waveguides with a channel profile of Ti-indiffused Lithium Niobate is described. Design novelty lies in its satisfactory operation for two wide optical windows (100 nm each), with center wavelengths (λ_centre) of 1.3 and 1.55 µm, possessing low losses. For either of these windows, the average value of propagation losses are maintained lower than 1 dB with a vacillation of extremely low polarization dependent losses ( ≤ 0.15 dB). Index tuned regions are optimized to achieve average crosstalk levels better than -19 and -12 dB for its operation in the wavelength range of 1.25 to 1.35 µm and 1.50 to 1.60 µm, respectively. It is also observed that switch possess absolute loss uniformity (of the range of 0.5% to 1.6%) with a maximum of ±2.5% tolerance in the structural parameters.

We investigate the possibility of forming spatiotemporal vortex solitons (optical vortex bullets) in inhomogeneous dispersive nonlinear optical fibers using a graded-index Kerr medium as an example. We use a variational approach to solve the multidimensional inhomogeneous nonlinear Schrödinger equation and show that vortex solitons can be stabilized under certain conditions in self-defocusing Kerr medium. Optical vortex results from the phase singularity in a light wave, which the energy flow rotates around the vortex core in a given direction. However, we show that vortex solitons become bistable in self-focusing Kerr medium, depending on pulse energy.

Polarization fluctuation in polarization maintaining fiber (PMF) resonator is one of the major noise sources in resonant fiber optic gyroscope (R-FOG). 90-deg polarization-axis rotated splicing in R-FOG is an effective way to suppress the polarization-fluctuation induced noise. 90-deg polarization-axis rotated splicing error influences the noise suppression effect. Here, a polarization-coupling testing system based on white-light interferometry is designed to control 90-deg splicing error in double-coupler PMF resonator first time and a result of 0.37-deg splicing error is obtained for the first time. Then the resonant characteristics of the double-coupler PMF resonator are tested using the saw-tooth waveform scanning method. The finesse of this double-coupler PMF resonator is 24.0 and the phase interval of the two eigenstates of polarization (ESOPs) is π.

A simple, cost-effective, centrally controlled, self-protection, colorless wavelength division multiplexing passive optical network is proposed. By using an optical switch at the optical line terminal and an N×N arrayed waveguide grating at a remote node, it can provide 1∶1 protection for downstream traffic and 1+1 protection for upstream data, respectively. The scheme feasibility is verified with 1.25  Gb/s for upstream and 2.5  Gb/s for downstream data rates based on gain-saturated reflective semiconductor optical amplifier, in both normal working and protection modes. The network performance in terms of complexity and availability is also evaluated.

Optical RF Communications Adjunct Program flight test results provide validation of the theoretical models and hybrid optical radio frequency (RF) airborne system concepts developed by the Defense Advanced Research Projects Agency and the U.S. Air Force Research Laboratory. Theoretical models of the free-space optical communications (FSOC), RF, and network components accurately predict the flight test results under a wide range of day and night operating conditions. The FSOC system, including the adaptive optics and optical modem, can operate under high turbulence conditions. The RF and network mechanisms of Layer 2 retransmission and failover provide increased reliability, reducing end-to-end packet error rates. Overall the test results show that stable, long-range FSOC is possible and practical for near-term operations.

This communication describes some details of polarization modulation that are useful in phase-shifting interferometry when applied to phase profile measurements of phase objects. Since non-destructive optical techniques allow surface measurement with high accuracy, a Mach-Zehnder configuration coupled to a 4-f arrangement using phase gratings placed on the Fourier plane was implemented to analyze phase objects. Each beam of the interferometer goes through a birefringent wave plate in order to achieve nearly circular polarization of opposite rotations, with respect to each other. The interference of the fields associated with replicated beams, centered on each diffraction order, is achieved varying the spacing of windows with respect to the grating period. Experimental results are presented for cases of four and nine simultaneously captured interferograms.

Three-dimensional digital holographic microscopic phase imaging of objects that are thicker than the wavelength of the imaging light is ambiguous and results in phase wrapping. In recent years, several unwrapping methods that employed two or more wavelengths were introduced. These methods compare the phase information obtained from each of the wavelengths and extend the range of unambiguous height measurements. A straightforward dual-wavelength phase imaging method is presented which allows for a flexible tradeoff between the maximum height of the sample and the amount of noise the method can tolerate. For highly accurate phase measurements, phase unwrapping of objects with heights higher than the beat (synthetic) wavelength (i.e. the product of the original two wavelengths divided by their difference), can be achieved. Consequently, three-dimensional measurements of a wide variety of biological systems and microstructures become technically feasible. Additionally, an effective method of removing phase background curvature based on slowly varying polynomial fitting is proposed. This method allows accurate volume measurements of several small objects with the same image frame.

The goal of this work is to develop an algorithm to enhance the utility of three-dimensional (3-D) FLASH laser radar sensors through accurate ranging to multiple surfaces per image pixel while minimizing the effects of diffraction. With this algorithm it will be possible to realize numerous enhancements over both traditional Gaussian mixture modeling and single-surface range estimation. While traditional Gaussian mixture modeling can effectively model the received pulse, we know that its shape is likely altered by optical aberrations from the imaging system and the medium through which it is imaging. Additionally, only identifying a single surface per pulse may result in the loss of valuable information about partially obscured surfaces. This algorithm enables multisurface ranging of an entire image with a single laser pulse. Ultimately, improvements realized through this new ranging algorithm when coupled with various other techniques may make 3-D FLASH LADAR more suitable for remote sensing applications. Simulation examples show that the multisurface ranging algorithm derived in this work improves range estimation over standard Gaussian mixture modeling and frame-by-frame deconvolution using the Richardson-Lucy algorithm by up to 91% and 70% respectively.

We have developed a reduced-order, physics-based model of gas cloud transport and combined it with an approximate formulation of the equation of radiative transport to enable efficient prediction of spectral irradiation for simulation of hyperspectral infrared sensors. The resulting combined model is easily implemented, providing a rapid and flexible in silico experimentation capability. The gas cloud model is based on the entrainment hypothesis and predicts cloud trajectories in three-dimensions, with elevation changes occurring primarily due to buoyancy effects and with spreading and accompanying dilution and cooling occurring due to a turbulence dominated growth mechanism. The radiation transport model is simplified through an approximate treatment of scattering that transforms the governing equation from an integro-differential equation to an ordinary differential equation. The conjugate model has been combined with a simple sensor model and has been validated through comparison to results from large-scale field tests. The utility of the simulations has also been demonstrated through inclusion in a larger algorithm development and analysis program, the chem/bio algorithm development kit.

Curved crystals, instead of flat mosaic crystals, can be used as optical elements of a Laue lens for hard x- and gamma-ray astronomy to increase the diffraction efficiency. We propose to achieve the bending of the crystals by a controlled surface damaging, which introduces defects in a layer of few tens nanometers in thickness undergoing a highly compressive strain. Several oriented silicon and gallium arsenide wafer crystals have been treated. The local and mean curvature radii of each sample have been determined by means of high resolution x-ray diffraction measurements in Bragg condition at low energy (8 keV). Silicon samples showed spherical curvatures, whereas GaAs-treated samples evidenced elliptical curvatures with major axes corresponding to the 〈110〉 crystallographic directions. Curvature radii between 3 and 70 m were easily obtained in wafers of different thicknesses. The characterization of GaAs samples performed in Laue geometry at gamma-ray energy of 120 keV confirmed the increase of the diffraction efficiency in the bent crystals.

This paper describes a new anisotropic diffusion method for removing ringing artifacts from deconvolution images. The characteristics of the deconvolution image ringing artifact are also analyzed. Unlike the previous anisotropic diffusion methods that use the global statistical value as the scale function, the proposed anisotropic diffusion defines a new scale function based on image local statistical characteristics to recognize the ringing artifacts. The proposed anisotropic diffusion performs well in terms of the images' detail preservation, error reduction, and improvement in visual quality in the presence of various levels of image ringing artifacts.

The traditional Fourier Mellin transform is applied to quaternion algebra in order to investigate quaternion Fourier transformation properties useful for color image registration in frequency domain. Combining with the quaternion phase correlation, we propose a method for color image registration based on the quaternion Fourier transform. The registration method, which processes color image in a holistic manner, is convenient to realign color images differing in translation, rotation, and scaling. Experimental results on different types of color images indicate that the proposed method not only obtains high accuracy in similarity transform in the image plane but also is computationally efficient.

At present, image retrieval has a great progress in indexing efficiency and memory usage, which mainly benefits from the utilization of the text retrieval technology, such as the bag-of-features (BOF) model and the inverted-file structure. Meanwhile, because the robust local feature invariants are selected to establish BOF, the retrieval precision of BOF is enhanced, especially when it is applied to a large-scale database. However, these local feature invariants mainly consider the geometric variance of the objects in the images, and thus the color information of the objects fails to be made use of. Because of the development of the information technology and Internet, the majority of our retrieval objects is color images. Therefore, retrieval performance can be further improved through proper utilization of the color information. We propose an improved method through analyzing the flaw of shadow-shading quasi-invariant. The response and performance of shadow-shading quasi-invariant for the object edge with the variance of lighting are enhanced. The color descriptors of the invariant regions are extracted and integrated into BOF based on the local feature. The robustness of the algorithm and the improvement of the performance are verified in the final experiments.

This study investigates image processing using the radial imaging capsule endoscope (RICE) system. First, an experimental environment is established in which a simulated object has a shape that is similar to a cylinder, such that a triaxial platform can be used to push the RICE into the sample and capture radial images. Then four algorithms (mean absolute error, mean square error, Pearson correlation coefficient, and deformation processing) are used to stitch the images together. The Pearson correlation coefficient method is the most effective algorithm because it yields the highest peak signal-to-noise ratio, higher than 80.69 compared to the original image. Furthermore, a living animal experiment is carried out. Finally, the Pearson correlation coefficient method and vector deformation processing are used to stitch the images that were captured in the living animal experiment. This method is very attractive because unlike the other methods, in which two lenses are required to reconstruct the geometrical image, RICE uses only one lens and one mirror.

Image fusion is a process to combine multiple frames of the same scene into one image. The popular image fusion methods mainly concentrate on static image fusion and lack spatial-temporal adaptability. The conventional multi-resolution image fusion algorithms have not fully exploited the temporal information. To resolve this problem, we present a novel dynamic image fusion algorithm based on Kalman filtered compressed sensing. The fusion procedure characterized by estimation fusion is completed in state space. A parametric fusion model is proposed to learn and combine spatial and temporal information simultaneously. The experiments on the ground-truth data sets show that the proposed fusion algorithm offers a considerable improvement on the dynamic fusion performance and rivals the traditional multi-resolution-based fusion methods.

A new blind pixel-level self-repairing grayscale image authentication method, which is optimal under a minimax criterion of image-distortion reduction, is proposed. By dividing the grayscale range into bins, a three-bit bin code which provides the double functions of tampering localization and data repairing is generated as the authentication signal for each pixel in the cover image. The optimality in choosing three bits of a pixel as the authentication signal under a minimax criterion of minimizing the total maximum distortion resulting from authentication signal embedding and tampered pixel repairing is proved. Experimental results show the effectiveness of the proposed method.

The ability to image underwater is highly desired for scientific and military applications, including optical communications, submarine awareness, diver visibility, and mine detection. Underwater imaging is severely impaired by scattering and optical turbulence associated with refractive index fluctuations. This work introduces a novel approach to restoration of degraded underwater imagery based on a multi-frame correction technique developed for atmospheric distortions. The method represents synthesis of "lucky-region" fusion with nonlinear gain and optical flow-based image warping. The developed multiframe image restoration algorithm is tested on underwater imagery collected in a laboratory tank and in a field exercise. Reliance of image restoration on accuracy of the optical flow algorithm is revealed. The developed algorithm demonstrates significant resolution improvement of the restored image in comparison to any single frame or the mean of the underwater image sequence.

We introduce an automatic technique to stitch retinal images recorded with an adaptive optics confocal scanning laser ophthalmoscope (AOSLO). The AOSLO images whose field size is 1.5 deg are recorded while the fixation target is moving according to a square pattern so as to cover a wide field of view. Principal components analysis-scale invariant feature transform is used to extract and match point features of the retinal images. With the matched point features, the affine transformation is used to stitch the images to generate eight montaged images. Then, the eight images are stitched together to construct a wide-field image by a cross-correlation algorithm. An image blending algorithm is also developed to reduce seam artifacts. With the proposed algorithms, a montage whose field size is approximately 10.5×9.6 deg is constructed.

A new interpolation algorithm is proposed and demonstrated to perform automatic angle measurement of two-dimensional (2D) objects. The proposed algorithm works in conjunction with optical correlator neural network hybrid architecture (OCNN). The OCNN is trained with a combined algorithm of direct binary search and error back propagation. Input of the OCNN is presented with an image whose angle of rotation is to be measured, and output from the OCNN is fed into the proposed interpolation algorithm, which finally produces the rotation angle of the input image. Results of both computer simulation and experimental set-up are presented for an English alphabetic character as a 2D object. The experimental set-up consists of a real optical correlator using two spatial light modulators for both input and frequency plane representations and a PC based model of a single layer neural network. We obtained very low experimental mean absolute error of 3.18 deg with standard deviation of 2.9 deg.

It is known that error-correcting output codes (ECOC) is a common way to model multiclass classification problems, in which the research of encoding based on data is attracting more and more attention. We propose a method for learning ECOC with the help of a single-layered perception neural network. To achieve this goal, the code elements of ECOC are mapped to the weights of network for the given decoding strategy, and an object function with the constrained weights is used as a cost function of network. After the training, we can obtain a coding matrix including lots of subgroups of class. Experimental results on artificial data and University of California Irvine with logistic linear classifier and support vector machine as the binary learner show that our scheme provides better performance of classification with shorter length of coding matrix than other state-of-the-art encoding strategies.

We present a simple ellipse detector that accurately extracts the parameters of an ellipse based on randomized Hough transform (RHT). Ellipse detection by the conventional RHT method is challenging due to the huge calculation burden and voting complexity for the five parameters of one ellipse. To address this, we extracted formulas that separated these five parameters into two to three parameters and proposed a separated two-level voting scheme based on the RHT. The original image was first processed by edge detection, eight-zone distribution of its direction, and edge lists merging, and then the parameters were calculated and voted by the separated two-level voting scheme. Finally, an evaluation method was used to determine whether or not the detected ellipse existed in the image. We tested our method on various kinds of real images, and the experiments demonstrated that the proposed method provided a precise and efficient ellipse detection.

A static stereoscopic latent image (SSLI) created using photoaligned liquid crystal polymers is introduced. The image crosstalk and contrast are theoretically analyzed by adopting the Jones matrix method. The SSLI does not show any information for the naked eye, but displays a stereoscopic image using polarization spectacles. The image has three domains with even retardances but different optical axes directions with an angular separation of 45 deg. The two-eye view contrast is 0.6433 and the crosstalk is nearly zero, which agree with the theoretical results. This image is applicable to document security and information presentation, among others.

We propose context-based adaptive in-loop filters not only to reduce complexity but also to achieve coding efficiency by combining deblocking and in-loop filters. The proposed adaptive filters are designed based on contexts such as slice types, boundary strength values, pixel positions, and boundary directions in order to improve coding gain. The proposed method is also embedded with a deblocking filter to reduce complexity and to maintain subjective quality. Experimental results show coding gains of approximately 6.3% and 0.5% compared with the deblocking filter of H.264/AVC and the conventional block-based adaptive loop filter, respectively. Then the proposed method reduces complexity by about 20.8%.

A detailed model of diffraction of plane and Gaussian beams on plane uniform phase Bragg gratings based on a Kogelnik's theory of coupled waves is presented. The model describes reflecting gratings (Bragg mirrors) with arbitrary orientation in a plane-parallel plate having no material losses. It takes into account spectral width and angular divergence of laser beams. The results of modeling are compared with experimental data for Bragg mirrors in a photo-thermo-refractive glass.

In 2005, Stahl et al. published a multivariable parametric cost model for ground telescopes that included primary mirror diameter, diffraction-limited wavelength, and year of development. The model also included a factor for primary mirror segmentation and/or duplication. While the original multivariable model is still relevant, we better explain the rationale behind the model and present a model framework that may better account for prescription similarities. Also, we correct the single-variable diameter model presented in the 2005 Stahl paper with the addition of a leading multiplier.

A simple experimental setup for measuring the cleave angle of optical fiber facets by using a plano-convex cylindrical lens is presented. In this method, a laser beam is coupled to the perpendicularly cleaved input fiber facet and propagates up to the output end, where the fiber facet is cleaved at a certain angle. The divergent beam emerges from the output end fiber at an angle determined by the cleave angle and impinges at the cylindrical lens through a very narrow slit. The slit is placed in contact with the vertex of the convex side of the cylindrical lens and parallel to its axis. The slit-lens assembly is moved perpendicular to the optical axis of the lens so that the marginal rays of the incident beam pass through the slit. Using the output angles from marginal rays of the refracted beam by the cylindrical lens, it is possible to calculate the output angle of the principal ray and, by measuring this angle, the cleave angle can be estimated.

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