This PDF file contains the editorial “2005 in Review” for OE Vol. 45 Issue 02

Two novel methods are demonstrated to build up a band-selective amplified spontaneous emission (ASE) broadband light source that can operate in the selective conventional band (C-band, 1525~1565 nm) or long-wavelength band (L-band, 1565~1605 nm) region using a 1×2 optical switch. With the backward ASE feedback technique, an output power of 27.6 mW for the C-band ASE and 11.8 mW for the L-band ASE are obtained while with the compound pump technique, a power of 24.5 mW for L-band ASE and 27.2 mW for C-band ASE are obtained both with a fixed total pump power of 100 mW. The advantage of using the backward ASE feedback technique is that the ASE source design is simpler whereas the power of L-band ASE is lower, and the notable advantage of using the compound pump technique is that the output powers of the two selective bands (C- or L-band) are balanced though the configuration is a little complicated.

We propose a new optical compensator for both first-order and higher-order polarization mode dispersion (PMD) effects in an optical fiber channel. The compensation scheme needs just one more polarization controller and one more variable differential group delay (DGD) element than first-order optical compensators with adjustable DGD elements. And the control algorithm for this compensator is easier and more stable than that for the typical higher-order optical polarization mode dispersion compensators. By an advised control method, the proposed compensator can always have better performance than first-order optical compensators. Numerical results are given to prove the efficiency of the proposed compensation scheme.

A kind of novel power splitter built with two-dimensional photonic crystals based on directional coupling is proposed. Different output power levels are achieved by changing the coupling length. The distribution of light intensity in the coupling waveguides is investigated and the dependence of transmission on coupling length is provided. A good agreement between the theoretical and experimental output transmissions is shown. With the low-loss bends, a total transmission up to ~0.96 is achieved. The power in each branch can be easily further split.

In the past few years, the computer vision and pattern recognition community has witnessed the rapid growth of a new kind of feature extraction method, the manifold learning methods, which attempt to project the original data into a lower dimensional feature space by preserving the local neighborhood structure. Among them, locality preserving projection (LPP) is one of the most promising feature extraction techniques. Based on LPP, we propose a novel feature extraction method, called uncorrelated locality preserving projection (ULPP). We show that the extracted features via ULPP are statistically uncorrelated, which is desirable for many pattern analysis applications. We compare the proposed ULPP approach with LPP and principal component analysis (PCA) on the publicly available data sets, FERET and AR. Experimental results suggest that the proposed ULPP approach provides a better representation of the data and achieves much higher recognition accuracies.

We present four preliminary designs for a telecentric optical train supporting the Advanced Technology Solar Telescope (ATST) multiple Fabry-Pérot interferometer (MFPI), which is to be used as an imaging spectrometer and imaging spectropolarimeter. The point of departure for all three designs is the F/40 telecentric image at the Coudé focus of the ATST. The first design, representing the high-spectral-resolution mode of operation, produces an intermediate F/300 telecentric image within the triple étalon system and a 34-arcsec field of view (FOV). The second design, intermediate between high- and low-spectral-resolution modes of operation, produces an intermediate F/150 telecentric image at the étalons and a 1.1-arcmin FOV. The third and fourth designs each represent a low-resolution mode of operation, producing an F/82 telecentric image at the étalons and a 2-arcmin FOV. Each design results in good telecentricity and image quality. Departures from telecentricity at the intermediate image plane cause field-dependent shifts of the bandpass peak, which are negligible compared to the bandpass FWHM. The root mean square (rms) geometric spot sizes at the final image plane fit well within the area of a camera pixel, which is itself in accordance with the Nyquist criterion, half the width of the 28-µm-wide resolution element (as determined from the diffraction limit of the ATST). For each configuration, we also examine the impact that the Beckers effect (the pupil apodization caused by the angle-dependent amplitude transmittance of the MFPI) has on the image quality of the MFPI instrument.

The impact response of an impact hammer is evaluated by means of an optical method. In the method, an object is first levitated using a pneumatic linear bearing, so that it encounters negligible friction, and is then made to collide with the impact hammer under test. The total force acting on the levitated mass (i.e., the product of the mass and acceleration) is measured highly accurately by measuring the Doppler frequency shift of a laser beam reflected from the colliding mass. The velocity, position, acceleration, and inertial force of the mass are then numerically calculated from the measured time-varying Doppler frequency shift. The output signal of a force transducer embedded in the hammer and the measured total force acting on the levitated mass are compared. The future prospects of the proposed method are discussed.

A method is proposed for accurately measuring a sectional profile of a metal cylinder. In this method a sinusoidally vibrating sinusoidal interference pattern is used to generate an exact spatial scale along one direction. Light from top points of a metal cylinder surface is extracted by spatial filtering in an afocal imaging system to form an image of the top points. A time-varying signal is detected in the image, and a sectional profile of the metal cylinder is measured from the phase of the detected signal on a position where the amplitude of the signal has a maximum value. Detection of the amplitude and the phase is carried out easily and exactly with sinusoidal phase-modulating interferometry.

A method of lens distortion correction is proposed in order to improve the measurement accuracy of digital image correlation for two-dimensional displacement measurement. The amounts of lens distortion are evaluated from displacement distributions obtained in a rigid body in-plane translation or rotation test. After detecting the lens distortion, its coefficient is determined using the method of least squares. Then, the corrected displacement distributions are obtained. The effectiveness of the proposed method is demonstrated by applying the correction method to an in-plane translation test and tension tests. The experimental results show that the proposed distortion correction method eliminates the effect of lens distortion from measured displacements.

A new method for 3-D shape registration of prismatic objects is presented. The term prismatic object denotes any object with sharp boundaries on its surface. These kinds of objects cannot be correctly registered with typical existing methods, which require smooth overlapping of the whole surface. The method presented here is based on the use of reference marks, placed on a planar glass plate that is attached to the prismatic object. Two 3-D range measurements of the object are then acquired, before and after rotating the object by approximately 180 deg. Using the reference marks on the glass and two different calibrations of the 3-D range scanning system, these two range measurements can be correctly merged to provide a full 3-D range scan of the prismatic object.

Basing ourselves on a novel segmentation algorithm for multispectral images, we consider how to detect multipixel anomalous objects in image cubes where spectral information is available. In particular, we have developed several morphological filters to compensate for noise that may be present in the initial cube. We show that for different types of noise (Gaussian and speckle), a modification of our morphology technique allows us to better detect targets without an enhanced false-alarm result.

It is known that the beamsplitter in interference ellipsometers is one of the possible sources of inaccuracy. In the general case, the polarizing effect of the beamsplitter adds systematic error to measurement results. Moreover, accurate measurements require such preliminary steps as precise determination of test specimen polarization axes and their alignment relative to the ellipsometer axes. We propose a new retardance measurement method that is free from these disadvantages. This becomes possible due to specimen rotation around the axis and constant interference signals tracking.

Color filters are key components in an optical engine projection display system. In this paper, a new admittance-matching method for designing and fabricating the high performance filters is described, in which the optimized layers are limited to the interfaces between the stack (each combination of quarter-wave-optical-thickness film layers is called a stack) and stack, or between stack and substrate, or between stack and incident medium. This method works well in designing filters containing multiple stacks such as UV-IR cut and broadband filters. The tolerance and angle sensitivity for the designed film stacks are analyzed. The thermal stability of the sample color filters was measured. A good result in optical performance and thermal stability was obtained through the new design approach.

We present explicit expressions for the reflection and transmission coefficients of an anisotropic thin film. In the general case, the optical axis and the incident ray are in arbitrary directions. Multireflected ordinary rays and extraordinary rays in the thin film are coupled to each other at the interface. The degrees of polarization conversion for reflected and transmitted light from the anisotropic thin film are calculated. The transmittance and reflectance are measured by rotating the polarization of the normal incident ray, and the columnar growth plane and film thickness are thus determined.

We derive the phase difference equation between the p- and s-polarizations of reflection light based on the Kretschmann-Raether configuration. This phase difference equation is used to examine the relationship of the incident angle and metal film thickness versus the phase differences under a small refractive index variation. For a fixed incident angle, the phase difference has a higher measurement sensitivity than the reflectivity change. At the critical angle, there is a higher sensitivity when the metal film thickness is smaller than the skin depth. The surface plasmon resonant (SPR) angle dominates when the metal film thickness is greater than the skin depth. The phase measuring sensitivity at the SPR angle is higher than that at the critical angle by 1 order.

A handheld gas detector is being developed that consists of a laser diode emitting light of wavelength equal to 1651 nm and an extended InGaAs detector. The IR laser beam is double-passed through a column of air via a folding mirror to a detector. The air column is in contact with the outside atmosphere so that low-relative-molecular-mass hydrocarbon gases, which diffuse into the air column, can be detected by the absorption of some of the IR light. The absorption at around 1651 nm is due to the overtones of C—H stretching vibrations and the limit of detection of the technique is at the parts per million level. One of the problems of using such a device in the field is that the operator cannot visualize the IR beam directly. Consequently, if the gas detection device fails to give a reading, the operator cannot be sure whether the laser is emitting light and the beam is correctly aligned. We describe the use of a novel phosphor screen to visualize the beam by converting the IR radiation into visible light. The properties of a number of phosphors that were developed and tested for the visualization of the beam are described. The merits of storage phosphors are compared to those of upconversion phosphors for use at this wavelength, which is longer than wavelengths previously visualized using upconversion phosphors.

We report the effect of buffer gas (neon) pressure on the spatiotemporal small signal gain evolution characteristics of a copper vapor laser (CVL). The CVL discharge tube of diameter 47 mm and length 150 cm is studied for neon pressure from 20 to 70 mbar. The gain evolution is mapped by a specially generated 6-ns, 510.6-nm probe pulse. The evolution of gain at the center and at the edge are found to be widely different for different gas pressures. At lower pressure (20 mbar), the gain at the edge is higher compared to that at the center, however, the situation is reversed at higher pressure (70 mbar). The increased laser-circuit impedance matching and the reduced discharge plasma skin effect with increase in buffer gas pressure are the possible mechanisms responsible for such a changeover.

A closed-form analytical model for the spatiotemporal processes giving rise to soliton pulse formation and compression in an additive-pulse mode-locked coupled-cavity fiber laser systems is presented. The model is based on a modified nonlinear Schrödinger equation for solitons. Perturbation techniques coupled with Fourier transform methods are employed to simplify the solution to the nonlinear Schrödinger equation. The contributions of Gaussian white noise, random noise, group velocity dispersion, and self-phase modulation to the mode-locking process and system performance are described. The model is used to analyze the temporal and spectral characteristics of a 1.55-µm mode-locked soliton fiber laser with a pulse width of 25 ps and a pulse repetition rate of 4 ns, accurately.

A steady state numerical model of wavelength conversion through cross-gain modulation in semiconductor optical amplifiers is developed. Increased understanding and accuracy over previous studies are achieved by including the spatial variations and wavelength dependence of the carrier density, gain coefficient, differential gain, and waveguide internal loss. The model is used to evaluate the performance of up-converters and down-converters for long and short device lengths. A comparison is made between the model developed in this work with other theoretical and experimental studies.

The effect of layer-by-layer electrostatic self-assembly processing parameters on resulting thin-film characteristics was determined in order to optimize the thin-film structure for optical biosensing. The use of long-period fiber gratings (LPFGs) requires careful control of the refractive index of the surrounding medium, which can be achieved by tuning the refractive index and thickness of an optical thin film deposited directly on the optical fiber surface. The high-sensitivity LPFG refractometry range falls in a window just below the effective index of the relevant cladding mode. We investigated five factors at two levels using variable-angle spectroscopic ellipsometry and analysis of variance. Salt concentration and pH were found to be critical parameters for refractive index control.

We develop an analytical model for the relationship between the strain measured by a fiber Bragg grating sensor and the actual structural strain. The values of the average strain transfer rates calculated from the analytical model agree well with available experiment data. Based on the analytical model, the critical adherence length of an optical fiber sensor can be calculated and is determined by a strain lag parameter, which contains both the effects of the geometry and the relative stiffness of the structural components. The analysis shows that the critical adherence length of a fiber sensing segment is the minimum length with which the fiber must be tightly bonded to a structure for adequate sensing. The strain transfer rate of an optical fiber sensor embedded in a multilayered structure is developed in a similar way, and the factors that influence the efficiency of optical fiber sensor strain transferring are discussed. It is concluded that the strain sensed by a fiber Bragg grating must be magnified by a factor (strain transfer rate) to be equal to the actual structural strain. This is of interest for the application of fiber Bragg grating sensors.

An optical power splitter with one input and three output ports is proposed and demonstrated for near-infrared applications in the wavelength range of 2.3 to 2.5 µm. The device operates on the principle of directional coupling by introducing photonic crystal line-defect waveguides. Its functionality and performance have been numerically investigated and simulated by the finite-difference time-domain method. By cascading two 1×3-structure power splitters, a large-scale optical power splitter with one input and five output ports is achieved. The simulated results show that the 1×5 large-scale power splitter can also perform 1×2, 1×3, and 1×4 functions. The required optical power from each of the output waveguides can be easily controlled by adjusting the coupling length of interaction for photonic crystal line-defect waveguides. The total length of the 1×5 power splitter is 40 µm, which is significantly less than that of the conventional non-photonic-crystal power splitter. This is a promising device for future ultracompact and large-scale nanophotonic integrated circuits.

How to reduce the interdomain routing instability in multidomain optical networks is a burning issue of the day. An approach called active choke of interdomain routing (ACIR) is proposed to decrease the instability caused by temporary node overload. In this approach, when the network load increases to a certain value, the traffic requests without a minimum number of spanned domains are rejected directly or with a fixed or floating probability, while the rest are accepted. With the wavelength continuity constraint, numerical results on two network topologies demonstrate that the ACIR approach provides better blocking performance during heavy traffic and lower load at both nodes and domain controllers.

An all-optical controllable 4×4 photonic switch matrix is described. The switching mechanism is based on the selection of the light absorption or amplification characteristic of erbium-doped optical fibers controlled with 980-nm pumping light. Using this approach, 4×4 photonic switching without overall insertion loss has been demonstrated with millisecond switching time and minimum extinction ratio of 24.2 dB. The all-fiber-based device is packaged by fiber fusion splicing with no moving parts, to ensure long-term device reliability. The fabricated 4×4 photonic switch matrix can be potentially scaled up to enhance the network capacity in optical communication systems where nonblocking large-scale optical cross-connect switching is required.

Optical fiber offers many advantages over coaxial cable for the transmission of radio frequency (rf) signals in antenna-remoting applications, as well as cellular networks and cable television (CATV) signal distribution networks. Optical fiber shows significantly less loss, can support signals demanding much higher bandwidth, is immune to electromagnetic interference (EMI), and enables considerable size and weight savings when compared to coaxial cable. Free-space optics (FSO) communications is a technology that uses modulated optical beams to transmit information line of sight through the atmosphere. FSO can be deployed faster and cheaper when compared with optical fiber. Recently, FSO has been investigated by the telecommunications industry and research centers to transport digital signals for civilian "last mile" applications and military applications. We demonstrate the successful transport of modulated rf analog signals over an FSO link and compare key performance measures against a fiber optic link configured in an identical manner. Results of measurements of optical power, transmission response, reflection response, group delay that defines phase distortion, carrier-to-noise ratio (CNR), and dynamic range that defines nonlinear distortion are presented. Results from this comparative study indicate that FSO for rf applications is a suitable replacement for fiber optic transmission links over short distances.

A novel self-synchronization scheme is proposed that utilizes both cross gain modulation (XGM) and phase modulation, including self-phase modulation (SPM) and cross-phase modulation (XPM), in a semiconductor optical amplifier (SOA). The scheme consists of an SOA and a delay line interferometer. It is simple, integrable, and does not require any special marker pulses. With a proper design of the SOA parameters and interferometer delay time, a synchronization clock with an intensity contrast ratio of more than 20 dB can be obtained from return-to-zero (RZ) pseudorandom bit sequences (PRBSs) at different operation speeds.

A 50- to 60-GHz continuous wave (cw) millimeter wave (MMW) is generated by applying optical technology for optical-to-radio systems and ubiquitous communications. The generated MMW signals are radiated in a millimeter waveguide and detected through a dielectric cover on optical waveguide. The spectral linewidth of the MMW signals is less than 1 kHz. The power of the MMW signal obtained through alumina on an optical waveguide is larger than that detected from a strip-waveguide beyond 7 dBm at 55 GHz.

We demonstrate a translation-invariant VanderLugt correlator (VLC) for a set of images stored via holographic angle multiplexing of volume gratings in a polymeric substrate. The images read out from the volume gratings are optically correlated in a translation-invariant manner with a dc-suppressed holographic filter. The quality and efficiency of this correlator are observed to be nearly as good as that of another VLC with images directly from a spatial light modulator used as inputs. This experiment is the first step toward realizing a novel optical image recognition system capable of identifying a query image through an exhaustive search in a large database of filter images stored in an ultrahigh capacity superparallel holographic random access memory (SPHRAM). In this system, the identification of the query image is to be performed with a translation invariant, real-time VLC or a joint transform correlator (JTC).

The ground-based optical interferometer with large apertures is a potential research tool for the study of stellar astrophysics and the synthesis of high-resolution stellar images. However, atmospheric turbulence can impose a significant limitation on the interferometer's performance. In order to reduce those degrading effects, we investigate the effectiveness of high-order adaptive optics in ground-based optical interferometry. The purposes of this paper are (1) to evaluate the performance with and without using high-order adaptive optics in a ground-based optical interferometer with large-aperture telescopes, and (2) to investigate the possibility of using the Strehl ratio to estimate visibility. The theoretical methodology and computer simulation results used to evaluate the performance of a ground-based stellar interferometer with high-order adaptive optics are presented, and a numerical computational method that uses the Strehl ratio to estimate the mean squared atmospheric coherence loss factor is developed.

The objective evaluation of the performance of pixel level fusion methods is addressed. For this purpose a global measure based on information theory is proposed. The measure employs mutual and conditional mutual information to assess and represent the amount of information transferred from the source images to the final fused gray-scale image. Accordingly, the common information contained in the source images is considered only once in the performance evaluation procedure. The experimental results clarify the applicability of the proposed measure in comparing different fusion methods or in optimizing the parameters of a specific algorithm.

We implement a binary differential joint-transform correlator for real-time single- and multiple-target recognition applications. In a real-time situation the input scene is captured using a CCD or thermal camera. The obtained joint power spectrum is first differentiated and then binarized. The subset median threshold method was used to get the threshold value for binarization. The binarized joint power spectrum is displayed over a ferroelectric-liquid-crystal spatial light modulator and is Fourier-transformed optically to obtain the correlation peaks. Differential processing of the joint power spectrum removes the zero-order spectra (dc) and hence improves the detection efficiency. Experiments taking single as well as multiple input images have been performed. The parameters for a performance measure have also been calculated. Single and multiple targets with added Gaussian noise have also been used to check the correlation outputs. Computer simulation and experimental results are presented.

We present new techniques for passive ranging with a dual-band IR search and track (IRST) sensor aboard a ship. Three distance estimation methods are described: the atmospheric propagation model, the apparent surface of the target, and target motion analysis (TMA). These methods are tested on the sensor output of real data during cold water trials (CWTs). They are evaluated by comparing with simultaneously obtained radar reference data at the test site. Results of these three passive ranging and three fusion processes, combining the preceding methods, are presented. This demonstrates the effectiveness of IR passive ranging techniques in the anti-air-warfare scenario. Majority voting fusion shows that improvement of the distance estimation is achieved in the CWT scenario when combining these three different methods. A range-error reduction of 41% is obtained, and a typical uncertainty of 5% is at a 8-km distance. During warm water trials (WWTs) the TMA algorithm was adapted to deal with a dynamic environment of the antisurface warfare scenario (ASuW). These WWTs prove that TMA in combination with an IRST system can extend the basic IRST functionality significantly for a dynamic ASuW scenario.

One of the most significant requirements for a useful watermarking system is strong resistance to a variety of common attacks. Accordingly, the watermark embedding is designed from the attack perspective in this paper. We attempt to develop a new just-noticeable distortion (JND) in the discrete cosine transform (DCT) domain, based on an attack simulation scheme that reversely derives the maximum modification amount embedded in the DCT domain under a condition of imperceptibility. A new location selection approach to watermark embedding is also addressed. We evaluate the fitness of the embedding location by considering the embedding capacity, i.e., the JND of the considered frequency component, in addition to the frequency and the spectral strength, which are usually adopted by the existing methods. Experimental results show satisfactory ability of our method to resist various common attacks such as JPEG compression, smoothing, sharpening, cropping, and noise attacks.

The successive elimination algorithm (SEA) has already proved successful in block motion estimation. This paper presents a simple and efficient algorithm called the threshold-based SEA as a search engine to take advantage of the simplicity of the SEA while avoiding its redundant computation. In addition, the threshold-based SEA utilizes a threshold adaptation mechanism to efficiently distribute the available computational power of the employed codec to blocks of video sequences. Since the threshold-based approach is performed at each search candidate block, it can be combined not only with the SEA but also with other fast algorithms, including the three-step search, the block-based gradient descent search, and the diamond search. Depending on the motion activity in the sequences, experimental results indicate that the threshold-based approach can uniformly achieve a quality improvement over the original SEA for the same computation.

We investigate the issue of efficient data organization and representation of the curved wavelet coefficients [curved wavelet transform (WT)]. We present an adaptive zero-tree structure that exploits the cross-subband similarity of the curved wavelet transform. In the embedded zero-tree wavelet (EZW) and the set partitioning in hierarchical trees (SPIHT), the parent-child relationship is defined in such a way that a parent has four children, restricted to a square of 2×2 pixels, the parent-child relationship in the adaptive zero-tree structure varies according to the curves along which the curved WT is performed. Five child patterns were determined based on different combinations of curve orientation. A new image coder was then developed based on this adaptive zero-tree structure and the set-partitioning technique. Experimental results using synthetic and natural images showed the effectiveness of the proposed adaptive zero-tree structure for encoding of the curved wavelet coefficients. The coding gain of the proposed coder can be up to 1.2 dB in terms of peak SNR (PSNR) compared to the SPIHT coder. Subjective evaluation shows that the proposed coder preserves lines and edges better than the SPIHT coder.

We present a new deinterlacing algorithm based on modularization by the local frequency characteristics of images. The input patterns of an image are divided into two regions—the edge region and the smooth region. Each region is assigned to one neural network. The local frequency characteristics of patterns are similar within each region, resulting in more accurate training for each network. The regional neural networks are composed of two modules. One is for the low-frequency components of the input pattern, and the other is for the high-frequency components. Both modules are combined in the output. Therefore, each module compensates for the drawbacks of the other. In simulation, the proposed algorithm showed better performances in both still images and video sequences than other algorithms.

We present a three-dimensional (3-D) hyperspectral image compression algorithm based on zero-block coding and wavelet transforms. An efficient asymmetric 3-D wavelet transform (AT) based on the lifting technique and packet transform is used to reduce redundancies in both the spectral and spatial dimensions. The implementation via 3-D integer lifting scheme enables us to map integer-to-integer values, enabling lossy and lossless decompression from the same bit stream. To encode these coefficients after the AT, a modified 3DSPECK algorithm—asymmetric transform 3-D set-partitioning embedded block (AT-3DSPECK) is proposed. According to the distribution of energy of the transformed coefficients, the 3DSPECK's 3-D set partitioning block algorithm and the 3-D octave band partitioning scheme are efficiently combined in the proposed AT-3DSPECK algorithm. Several AVIRIS (Airborne Visible/Infrared Imaging Spectrometer) images are used to evaluate the compression performance. Compared with the JPEG2000, AT-3DSPIHT, and 3DSPECK lossless compression techniques, the AT-3DSPECK achieves the best lossless performance. In lossy mode, the AT-3DSPECK algorithm outperforms AT-3DSPIHT and 3DSPECK at all rates. Besides the high compression performance, AT-3DSPECK supports progressive transmission. Clearly, the proposed AT-3DSPECK algorithm is a better candidate than several conventional methods.

In Europe, centrifugal spreading is a widely used method for agricultural soil fertilization. In this broadcasting method, fertilizer particles fall onto a spinning disk, are accelerated by a vane, and afterward are ejected into the field. To predict and control the spread pattern, a low-cost, embeddable technology adapted to farm implements must be developed. We focus on obtaining the velocity and the direction of fertilizer granules when they begin their flight by means of a simple imaging system. We first show that the outlet angle of the vane is a bounded value and that its measurement provides the outlet velocity of the particle. Consequently, a simple camera unit is used in the vicinity of the spinning disk to acquire digital images on which trajectory streaks are recorded. Information is extracted using the Hough transform, which is specifically optimized to analyze these streaks and to measure the motion of the particles. The optimization takes into account prior mechanical knowledge and tackles the problem of Hough space quantization. The method is assessed on various simulated images and is used on real spreading images to characterize fertilizer particle trajectories.

An automated pavement inspection system consists of image acquisition and distress image processing. The former is accomplished with imaging sensors, such as video cameras and photomultiplier tubes. The latter includes distress detection, isolation, classification, evaluation, segmentation, and compression. We focus on wavelet-based distress detection, isolation, and evaluation. After a pavement image is decomposed into different-frequency subbands by the wavelet transform, distresses are transformed into high-amplitude wavelet coefficients and noise is transformed into low-amplitude wavelet coefficients, both in the high-frequency subbands, referred to as details. Background is transformed into wavelet coefficients in a low-frequency subband, referred to as approximation. First, several statistical criteria are developed for distress detection and isolation, which include the high-amplitude wavelet coefficient percentage (HAWCP), the high-frequency energy percentage (HFEP), and the standard deviation (STD). These criteria are tested on hundreds of pavement images differing by type, severity, and extent of distress. Experimental results demonstrate that the proposed criteria are reliable for distress detection and isolation and that real-time distress detection and screening is currently feasible. A norm for pavement distress quantification, which is defined as the product of HAWCP and HFEP, is also proposed. Experimental results show that the norm is a useful index for pavement distress evaluation.

We develop a simple and efficient algorithm for dynamic range compression and contrast enhancement of digital images in the compressed domain. The basic idea of our approach is to separate illumination and reflectance components of an image in the compressed domain. We adjust the amount of contribution of the illumination component to effectively compress the dynamic range of the image. For contrast enhancement, we modify the reflectance component based on a new measure of the spectral contents of the image. The spectral content measure is computed from the energy distribution across different spectral bands in a discrete cosine transform (DCT) block. The advantages of the proposed algorithm are (1) high dynamic range scenes are effectively mapped to the smaller dynamic range of the image, (2) the details in very dark or bright areas become clearly visible, (3) the computational cost is low, and (4) the compressibility of the original image is not affected by the algorithm. We evaluate the performance of the proposed algorithm with well-known existing methods, such as histogram equalization and α-rooting algorithm, using a few different enhancement quality metrics.

Formulas for description of center drift and for computing other geometric quantities of a binary object are derived for the purpose of estimating the location of the original object center, area of the object, and noise level in a noisy environment. Simulations support the theory. The coordinates of the object center estimated by the formulas are more accurate than those produced by median filtering. Consequently, more accurate object features are obtained. The formulas also lead us to conclude that when the object center coincides with the geometric center of the input plane, the object center does not drift, regardless of noise level. An optimal formation of concentric circles used for extraction of object features and for subpixel registration is also proposed.

Surface area and volume measurements provide important information for agriculture and food-processing applications. A machine vision system that uses a nondestructive method to measure volume and surface area of objects with irregular shapes is presented in this paper. The system first takes a series of silhouettes of the object from different directions by rotating the object at a fixed angular interval. The boundary points of each image are then extracted to construct a silhouette. A three-dimensional wire-frame model of the object can be reconstructed by integrating silhouettes obtained from different view angles. Surface area and volume can then be measured by means of surface fitting and approximation on the wire-frame model. System calibration and surface approximation were two major challenges for the design of this machine vision system. A unique centerline calibration method is introduced in this paper. Surface approximation and calculation are also discussed. Examples of applications in agriculture and food processing using this vision system for surface area measurement are included, and its accuracy is verified.

We present a method for manipulating individual sites in a 2-D optical lattice that enables the creation of defects within otherwise periodic light patterns. The modified optical lattice is created by interference of plane waves and spiral phase waves. Spiral phase modulation creates an optical vortex that is well suited for addressing single rows of the optical lattice owing to the localized wrap of the phase front. Local fringes can be split, annihilated, or have their size tuned by controlling the charge and location of the vortex cores. These properties provide a connection between dislocations in crystals, waves, and optical lattices.

The operating properties of the refractive-type optical limiting devices based on the self-focusing and defocusing phenomena are studied numerically, and the effects of both the installation position of the nonlinear refractive medium and the waist size of the incident Gaussian beam on the operating performance of the refractive-type optical limiters are examined. Our results show that the optical limiting curves of the refractive-type optical limiters exhibit a slowly attenuating oscillating waveform. The optical limiting threshold and the clamped output value of the optical limiters are dependant on the installation position of the sample and the convergence of the incident Gaussian beam to a great extent. When the sample position is given, the smaller the beam-waist radius, the better the optical limiting performance. When the beam-waist radius of the incident light is kept constant, an optimal position of the nonlinear sample can be found in the system. With fluctuating beam-waist size, however, the optimal location varies within a small range. For a self-focusing (self-defocusing) optical limiter, the optimal optical limiting effect can be obtained when the nonlinear medium is positioned at a certain location within half a Rayleigh range in the left (right) side of the focal plane.