This PDF file contains the editorial “Print” for OE Vol. 48 Issue 11

Interference filters have a defect layer incorporated within a photonic crystal structure and generate a narrow transmission notch within a wide stop band. In this paper, we propose and demonstrate wavelength-tunable spatial filters by introducing diffractive optical elements in the defect layer. The spectral transmission through the device was a function of the local defect layer thickness under broadband illumination. For each wavelength, the spatial transmission followed the contours of equal defect layer optical thickness. The devices were implemented by depositing a one-dimensional photonic crystal with a centrally integrated defect layer on a silicon substrate using plasma-enhanced chemical vapor deposition. The defect layer was lithographically patterned with charge 2, 8-level vortex structures. The spectral transmission peak and linewidth was characterized by separately illuminating each zone of diffractive element using a tunable laser source and compared with model simulations. The spatial transmission through the device was imaged onto a CCD camera. Triangular wedge-shaped zones with wavelength-dependent orientations were observed. These novel devices with spectrally tunable spatial transmission have potential applications in pupil filtering, hyperspectral imaging, and engineered illumination systems.

We present an adaptive quarter-pel (Qpel) motion estimation (ME) method for H.264/AVC. Instead of applying Qpel ME to all macroblocks (MBs), the proposed method selectively performs Qpel ME in an MB level. In order to reduce the bit rate, we also propose a motion vector (MV) encoding technique that adaptively selects a different variable length coding (VLC) table according to the accuracy of the MV. Experimental results show that the proposed method can achieve about 3% average bit rate reduction.

The development of high-energy lasers has focused attention on the requirement to assess the mechanical strength of optical components made of fused silica or fused quartz (SiO₂). The strength of this material is known to be highly dependent on the stressed area and the surface finish, but has not yet been properly characterized in the published literature. Recently, Detrio and collaborators at the University of Dayton Research Institute (UDRI) performed extensive ring-on-ring flexural strength measurements on fused SiO₂ specimens ranging in size from 1 to 9 in. in diameter and of widely differing surface qualities. We report on a Weibull statistical analysis of the UDRI data-an analysis based on the procedure outlined in Proc. SPIE 4375, 241 (2001). We demonstrate that (1) a two-parameter Weibull model, including the area-scaling principle, applies; (2) the shape parameter (m~=10) is essentially independent of the stressed area as well as the surface finish; and (3) the characteristic strength (1-cm² uniformly stressed area) obeys a linear law, C (in megapascals) ~=160-2.83×~¯PBS(in parts per million per steradian), where ¯PBS characterizes the surface/subsurface "damage" of an appropriate set of test specimens. In this light, we evaluate the cumulative failure probability and the failure probability density of polished and superpolished fused SiO₂ windows as a function of the biaxial tensile stress, for stressed areas ranging from 0.3 to 100 cm².

We present a method in which we stabilize mechanically an optical tweezer setup over a period ranging up to 30 min. A feedback loop is used to correct the mechanical and thermal drifts. The position of a fixed object on the sample surface is measured with a CCD device and its fluctuations analyzed and used to maintain its position fixed with three piezoelectric devices. With this setup, we obtain a spatial stability of 1.5 nm in the radial direction and 5 nm in the axial direction. This method opens the route for real-time measurements of kinetics of macromolecules association, at a single molecule level, on very long time scales.

We offer new equations for phase evaluation in measurements. Several phase-shifting equations with an arbitrary but constant phase shift between captured intensity signs are proposed. We show a mathematical model that seeks new equations by minimizing the uncertainty in measurements. The equations are similarly derived as the so-called Carré equation. The idea is to develop a generalization of the Carré equation that is not restricted to four images. Errors and random noise in the images cannot be eliminated, but the uncertainty due to their effects can be reduced by increasing the number of observations. An experimental analysis of the mistakes of the technique was made, as well as a detailed analysis of mistakes of the measurement. The advantages of the proposed equation are its precision in the measures taken, speed of processing, and the immunity to noise in signs and images.

We present a dynamic monitoring method and monitoring system of grating angle, referred to as the Precise Angle Monitor (PAM), at U4B, a soft x-ray spherical grating monochromator (SGM) beam line at the National Synchrotron Light Source (NSLS). In an SGM, a photon energy scan is accomplished by rotating the grating angle precisely. After several decades of service, the monochromator at U4B developed instabilities that severely impacted the experimental program. Over several hours, either the spectral shape experienced distortions or the spectral peak shifted. In order to directly monitor the grating motion during scans, the optical head of a portable long trace profiler (PTLTP) was installed on U4B as the PAM. We find that the grating rotational motion is not ideal: (1) the scan steps are not smooth and there are high-frequency step angle errors; (2) there is also a low-frequency angle error; and (3) an unstable thermal expansion produces extra rotational error. Measurements of dynamic monitoring are presented, including grating rotation repeatability and thermal instability. The results illustrate the utility of dynamic monitoring of monochromator motion during actual operation.

Optical three-dimensional shape measurement of live objects is becoming an important developing and research tool because of its nonintrusive nature and high measuring speed. The current methods are reaching truly high speed in one view configuration, but in the case of the entire object shape measurement, they are limited due to mutual interference between multiple measuring modules. The proposed method overcomes this limitation by using a laser multiple-line triangulation technique, where each of several measuring modules uses a unique laser wavelength. The measuring modules are positioned so that the entire surface of the foot is digitized. This prevents unwanted overlapping between adjacent light patterns. The calibration procedure for each measuring module and for the entire system is based on measurements of the surface of a reference object. The system parameters are determined using an iterative optimization algorithm. The precision of the system is better than ±0.3 mm. The system is capable of measuring objects in motion. The results of the shape of a foot rising on its toes are given as an example.

We developed a novel twisted nematic (TN) liquid crystal display (LCD) having wide viewing angle characteristics through the reduction of the residual liquid crystal phase retardation at oblique angles using an embedded diffusing unit. Compared to a conventional TN panel, this embedded approach provides extended isocontrast contours by more than ±10 deg at a contrast ratio of 100:1 along the horizontal direction and a wide region free of grayscale inversion by a factor of 2 along the vertical direction. Moreover, the off-axis image distortions in our novel LCD are improved by 50% compared to those in a film-compensated TN LCD.

Liquid crystal optical phased arrays are an enabling technology for a variety of photonic and electronic beam manipulation functions, including steering, control of polarization, and amplitude and phase modulation. For applications in the emerging field of space laser communications, such devices would need to survive in the space environment for 10 to 15 years. To assess suitability and identify potential issues, a series of experiments were conducted in which nematic liquid crystal devices were subjected to three radiation environments: total dose (gamma), prompt dose (x rays), and fast neutrons. Tests were conducted using simple phase retarder devices, which served as surrogates for beamsteering devices. Impacts to optical and electrical characteristics of the devices at 1.55 μm were measured after incremental exposure trials. Modest effects were observed, but none were deemed significant enough to impact performance of the devices for space communication beamsteering applications.

Orientation-patterned zinc selenide (OPZnSe) is a unique quasi-phase-matched nonlinear optical material for enabling frequency conversion from visible to long-wave infrared wavelengths. We have fabricated and tested OPZnSe devices over a wide spectral range. Single-crystal OPZnSe films of greater than 1 mm thickness were grown and characterized for optical loss showing an attenuation coefficient less than 0.05 cm^-1 from 1 to 12 μm. We demonstrated nonlinear frequency conversion in the near infrared, mid-infrared, and long-wave infrared in these devices through a variety of nonlinear optical mixing processes.

The waveguide second-harmonic generation is a reliable mechanism for frequency doubling of laser emission since light can be highly confined to a nonlinear waveguiding medium, besides being compatible with current present semiconductor and solid state lasers. An optimization is achieved based on designing the resonator mirror reflectivity at the fundamental and the second-harmonic wavelengths to obtain optimal trapping and optical losses of the fundamental and the second-harmonic waves inside the resonator.

Several nonlinear effects (i.e., continuum generation, self-focusing, and material damage) were studied during femtosecond photodisruption. Numerical aperture dependence of white-light continuum generation and material damage were determined and a relation between the two effects was shown. We showed the possibility of reducing nonlinear side effects and at the same time ensuring precise cut by using lenses of a suitable numerical aperture for refractive surgery, cell surgery, and tissue dissection. Other side effects associated with optical breakdown in model substance were also discussed.

An optical fiber Fabry-Pérot tunable filter is constructed by fixing two microlensed mirror-coated fibers to the opposite ends of a piezoelectric transducer. A tunable filter with a free spectral range of 70 nm, a finesse of 175, an insertion loss of 1.05 dB, and a tuning frequency exceeding 1 kHz has been experimentally demonstrated. The filter is easy to construct at a low cost, and it is anticipated that it will be used in fiber-optic sensing systems, spectrometers, and tunable optical fiber lasers.

Artificial neural networks are studied for use in estimating strain in extrinsic Fabry-Pérot interferometric sensors. These networks can require large memory spaces and a large number of calculations for implementation. We describe a modified neural network solution that is suitable for implementation on relatively low cost, low-power hardware. Moreover, we give strain estimates resulting from an implementation of the artificial neural network algorithm on an 8-bit 8051 processor with 64 kbytes of memory. For example, one of our results shows that for 2048 samples of the transmittance signal, the presented neural network algorithm requires around 24,622 floating point multiplies and 35,835 adds, and where the data and algorithm fit within the 64-kbyte memory.

We report on an optical beam deflector capable of achieving a large beam deflection using a planar thermoplastic-based electro-optic (EO) polymer prism. By optimizing the prism's geometry, relative position, and incident angle of the input beam, the device shows that a large deflection angle can be achieved through a relatively small index change from a single EO polymer prism stage. In this paper, we present the design and fabrication of the deflector using a simple hot-embossing technique. Beam deflection experiments were conducted, and a maximum deflection angle of 5.6 deg was observed, in agreement with our predicted value.

As a special case of p cycles, a Hamiltonian cycle protection scheme is proposed to achieve fast failure restoration and simple management in fault-tolerant networks. We extend the idea of a Hamiltonian cycle protection scheme to fault-tolerant wavelength-division-multiplexing (WDM) optical fiber networks, and propose a new Heuristic Hamiltonian cycle protection algorithm (HHCPA) to tolerate the single-fiber failure. In the HHCPA, we consider the idea of differentiated protection for different-level demands, i.e., high-level demands with protection requirements and low-level demands without protection requirements. We also develop the link-cost function to achieve the load balancing and proper link selection in computing the light paths for each demand to effectively reduce the backup wavelength consumption. Simulation results show that, compared to conventional algorithm, the HHCPA can obtain significant performance improvement in resource utilization ratio and blocking probability.

We demonstrate a 1×2 optical switch using LiNbO3 modulators for optical packet switching. The switch can be used to construct N×N optical switches for optical packet-switched networks. The optical switch has a fast response time and high on/off switching ratio. The behavior of the switching device is investigated with numerical simulations and experimental measurements.

A new technique, using a cyclic path optical configuration, for generating two coherent, virtual point sources at the back focal plane of a corrected telescope objective, for producing a pair of mutually tilted collimated beams with linear orthogonal polarizations in a Fizeau interferometer cavity is presented. The orthogonal linear polarization components reflected from the reference and the test surfaces are utilized for introducing polarization phase shift between the reference and test waves. A method for elimination of the residual instrumental aberration due to a slight departure from strict on-axis operation is discussed. The result for a plane optical surface is presented. Because, in polarization phase shifting, it is possible to capture all the necessary phase-shifted interferograms simultaneously, the vibration susceptibility can be minimized and the present system could be applied for dynamic interferometry.

We extrapolated the lucky imaging technique, mostly used in astronomy, to the field of interferometry for displacement measurement. From the batch of interferograms generated by a Twyman-Green-type interferometer and acquired by a CCD camera, those with high overall contrast were selected and fitted to a sinusoidal function. The high-contrast interferograms showed a significantly lower dispersion and, consequently, a lower uncertainty of the measured displacement.

To investigate the benefits of multiband infrared sensor design for target detection, search and detection experiments were conducted in the midwave infrared (MWIR) and longwave infrared (LWIR) wavebands in both rural and urban battlefields. In each battlefield environment, real imagery was collected in both bands by a single sensor using the same optics for both bands, resulting in perfect co-registration of the imagery. In order to study the performance impact of the spectral content, and not diffraction or other sensor-specific differences, the images were processed as needed so that differences in resolution due to diffraction were mitigated. The results of perception experiments, including detection probabilities, search times, and false alarm data, were compared between the wavebands.

A random grid is a two-dimensional binary array in which entries, 0 or 1, are determined in 50% to 50%. A generalized random grid is also a 2-D binary array in which entries are determined but not necessarily 50% to 50%. Using generalized random grids for visual secret sharing, friendly meaningful transparencies, also called shares, can be generated, and the size of each share is the same with the secret image size. In the decoding phase, stacking at least two friendly meaningful shares together, the content of the secret image can be revealed without any computation, and the more shares stacked, the clearer the result. The proposed method can also be implemented for gray and color images.

Several factors during the scanning process, image reconstruction and geometry of an imaging system, influence the spatial resolution of a computed tomography imaging system. In this work, the spatial resolution of a state of the art flat panel detector-based cone beam computed tomography breast imaging system is evaluated. First, scattering, exposure level, voltage, voxel size, pixel size, back-projection filter, reconstruction algorithm, and number of projections are varied to evaluate their effect on spatial resolution. Second, its uniformity throughout the whole field of view is evaluated as a function of radius along the x-y plane and as a function of z at the center of rotation. The results of the study suggest that the modulation transfer function is mainly influenced by the pixel, back-projection filter, and number of projections used. The evaluation of spatial resolution throughout the field of view also suggests that this imaging system does have a 3-D quasi-isotropic spatial resolution in a cylindrical region of radius equal to 40 mm centered at the axis of rotation. Overall, this study provides a useful tool to determine the optimal parameters for the best possible use of this cone beam computed tomography breast imaging system.

Currently, most exposure fusion algorithms are put forward on the assumption that the source images are aligned prior to fusion. As a result, some artifacts, such as haloing, may be caused due to the slight misalignment in the source images. In order to reduce the influence induced by the misalignment, a novel shift-invariant and rotation-invariant steerable pyramid-based exposure fusion (SPBEF) algorithm is proposed. It can combine multiple color images of a scene with different exposures to one image with high quality. First, instead of processing of R, G, and B channels separately, the chrominance information of the scene is obtained by the average image of the median two images. The strategy can greatly reduce the computational complexity. Second, the luminance images of source images are then transferred to frequency domain and are fused to one luminance image using different fusion rules in different frequencies. In this process, fusion is performed in a hierarchical fashion. Last, the final color image is generated by combining the data of the fused luminance image and the chrominance information. Experiments show that SPBEF can give comparative or even better results compared to other exposure fusion algorithms, as well as other traditional pyramid-based fusion algorithms.

A high-resolution image is reconstructed from a sequence of subpixel shifted, aliased low-resolution frames, by means of stochastic regularized super-resolution (SR) image reconstruction. The Tukey (T), Lorentzian (L), and Huber (H) cost functions are employed for the data-fidelity term. The performance of the particular error norms, in SR image reconstruction, is presented. Actually, their employment in SR reconstruction is preceded by dilating and scaling their influence functions to make them as similar as possible. Thus, the direct comparison of these norms in rejecting outliers takes place. The bilateral total variation (BTV) regularization is incorporated as a priori knowledge about the solution. The outliers effect is significantly reduced, and the high-frequency edge structures of the reconstructed image are preserved. The proposed TTV, LTV, and HTV methods are directly compared with a former SR method that employs the L₁-norm in the data-fidelity term for synthesized and real sequences of frames. In the simulated experiments, noiseless frames as well as frames corrupted by salt-and-pepper noise are employed. Experimental results verify the robust statistics theory. Thus, the Tukey method performs best, while the L₁-norm technique performs inferiorly to the proposed techniques.

Shape from shading (SFS) has been a classical and important problem in the domain of computer vision. The goal of SFS is to reconstruct the 3-D shape of an object from its 2-D intensity image. To this end, an image irradiance equation describing the relation between the shape of a surface and its corresponding brightness variations is used. Then it is derived as an explicit partial differential equation (PDE). Using the nonlinear programming principle, we propose a detailed solution to Prados and Faugeras's implicit scheme for approximating the viscosity solution of the resulting PDE. Furthermore, by combining implicit and semi-implicit schemes, a new approximation scheme is presented. In order to accelerate the convergence speed, we adopt the Gauss-Seidel idea and alternating sweeping strategy to the approximation schemes. Experimental results on both synthetic and real images are performed to demonstrate that the proposed methods are fast and accurate.

We use image-locating techniques and a traditional whiteboard with two cameras to construct an electronic whiteboard (EWB) with a size of 88×176 cm corresponding to 1280-×1024-pixel resolution. We employ two strategies achieve the goal: (1) we develope a modified scale and bilinear interpolation (MSBI) method for pen locating and acceleration operation, and obtain high accuracy detection; and (2) a block parameter database (BPD) is created to improve the accuracy. For the BPD, we divide the whiteboard image into several blocks and record each block parameter (the X and Y coordinates) to follow pen position calculation. Experimental results demonstrate that the MSBI method can correctly calculate the pen position. Additionally, the BPD strategy is better than the traditional method as it improves the accuracy and decreases the maximum detection error from 6 to 3 pixels. The simulation results prove our method is an effective and low-cost EWB technique.

We present a novel approach for face recognition by combining a local binary pattern (LBP)-based face descriptor and the distinctive information of faces. Several studies of psychophysics have shown that the eyes or mouth can be an important cue in human face perception, and the nose plays an insignificant role. This means that there exists a distinctive information distribution of faces. First, we give a quantitative estimation of the density for each pixel in a fronted face image by combining the Parzen-window approach and scale invariant feature transform detector, which is taken as the measure of the distinctive information of the faces. Second, we integrate the density function in the subwindow region of the face to gain the weight set used in the LBP-based face descriptor to produce weighted chi-square statistics. As an elementary application of the estimation of distinctive information of faces, the proposed method is tested on the FERET FA/FB image sets and yields a recognition rate of 98.2% compared to the 97.3% produced by the method adopted by Ahonen, Hadid, and Pietikainen.

Wafer sawing performance must be closely monitored to ensure a satisfactory integrated circuits manufacturing yield. The inspection must allow the GO/NG decision to be fast and reliable, while also assuring that the training of the inspector is simple and not time consuming. The traditional neural-network approach to inspect images, while simple to implement, presents some disadvantages, including training efficiency and model effectiveness. Based on contour detection of the sawing lane, this work proposes a novel method combined with cross-center localization of sawing lanes, detection of sawing track, and four signatures to detect the abnormality of sawing effectively and timely. Our method does not need pretraining but runs faster and provides a better method with more effectiveness, higher flexibility, and immediate feedback to the sawing operation. An experiment using real data collected from an international semiconductor package factory is conducted to validate the performance of the proposed framework. The accurate acceptance rate and the accurate rejection rate are both 100%, while the false acceptance rate and false rejection rate are both zero as well. The results demonstrate that the proposed method is sound and useful for sawing inspection in industries.

We propose a novel context-sensitive segmentation and recognition method for connected letters in Ottoman script. This method first extracts a set of segments from a connected script and determines the candidate letters to which extracted segments are most similar. Next, a function is defined for scoring each different syntactically correct sequence of these candidate letters. To find the candidate letter sequence that maximizes the score function, a directed acyclic graph is constructed. The letters are finally recognized by computing the longest path in this graph. Experiments using a collection of printed Ottoman documents reveal that the proposed method provides >90% precision and recall figures in terms of character recognition. In a further set of experiments, we also demonstrate that the framework can be used as a building block for an information retrieval system for digital Ottoman archives.

We present the use of phase-only filter-based correlation for fingerprint pattern identification. The main advantage of this approach is that it is distortion tolerant and can be realized in optical or electronic parallel hardware. Given that real-world fingerprints are almost never perfect, distortion tolerance can prove to be very important for this application. Our results indicate that the algorithm can identify prints with 58% of the data missing on average. With large fingerprint databases, identification can be a computationally challenging task. The high parallelism in the phase-only correlation filter makes it ideally suited to field programmable gate array (FPGA)-based hardware acceleration. We examine the FPGA-based acceleration of the fingerprint algorithm. On a Xilinx Virtex II Pro FPGA, we achieve speedups of about 47 times over an optimized C implementation of the algorithm on a 2.2-GHz AMD Opteron processor. Our FPGA implementation is optimized to allow efficient processing of large databases.

We propose a unified unimodal biometric system that is suitable for most individual modalities, e.g., face and gait. The proposed system consists of three steps: (1) preprocessing raw biometric data, (2) determining the intrinsic low-dimensional subspace of preprocessed data by local topology structure preserving projections (LTSPP), and (3) performing the classification in the determined subspace using the intraclass distance sum. In the proposed system, LTSPP is a novel subspace algorithm that focuses not only on the class information but also on the local topology structure. In terms of representing the separability of different classes, LTSPP projects the interclass margin data far apart. Meanwhile, LTSPP preserves the intraclass topology structures by using linear reconstruction coefficients. Compared with other subspace methods, LTSPP possesses more discriminant abilities and is more suitable for biometric recognition. In addition, both preprocessing each raw datum into unit and performing the classification using the intraclass distance sum are helpful to improve the recognition rates. We carry out various recognition experiments using the Yale and HumanID gait databases. The encouraging experimental results demonstrate the effectiveness of our unified unimodal biometric system, and the proposed LTSPP algorithm for this system can yield the best recognition rates compared to the other algorithms.

The traditional projector calibration always assumes that the reprojection errors on the projector image are independent and identically distributed and utilize the same method as the camera calibration. Actually, even if the measured points on the camera image are independent and identically distributed Gaussian variables, it is impossible to obtain the statistical characteristics of the reprojection errors on the projector image, because the relation between the original measurement error and the reprojection error is nonlinear. We propose a method to estimate the projector parameters according to the camera image reprojection error. It does not require us to know the statistical characteristics of the projector image point and makes full use of the background knowledge of the camera image noise, because our cost function does not concern the reprojection error on the projector image as is the case in the traditional method. The simulations and experiments affirm that this method has higher precision, even if the real noise is not normal.

Quality inspection of aluminum foil products plays an important role for aluminum foil manufactures. We present a method that uses input estimate (IE)-based chi-square detectors for defect detection in aluminum foil. It is assumed that the intensity of the aluminum foil image is Gaussian distributed, and the distribution of the defect intensity is different from the normal. Under these assumptions, Kalman filters with a constant velocity (CV) model are used to filter the image. We assume there is an unknown input in the CV model and the unknown input is estimated in the filtering process. The defects are determined by the chi-square test of the estimate of the unknown input. Experiments show that our technique is effective for most defects in aluminum foil.