This PDF file contains the editorial “2007 in Review” for OE Vol. 47 Issue 02

We propose and investigate a new ring-based power-splitting passive optical network (PS-PON) with a self-healing mechanism that prevents fiber fault. Using our proposed Y-type passive component with bidirectional function in each remote node (RN), the proposed ring-based PS-PON can be retrieved directly under single fiber failure.

An optical pumping device consisting of pigtailed diode lasers and a paraboloidal mirror is presented. The pigtailed diode lasers are mounted on a circular plate in radial position in front of the mirror, and the reflected beams are then launched into a 200-μm-diam undoped silica fiber with silicone cladding, with up to 75% coupling efficiency. The implementation of the device is simple and can be used to scale the power in fiber laser systems.

A few competitive models for lens distortion are presented and their accuracy is considered. Effectiveness of these models is tested comparatively against ray-tracing grid distortion data. Emphasis is made on retrofocus lens design typically occurring in low-cost camera systems. Theoretical conclusions are supported with practical camera calibration data.

A new approach for the fabrication of continuous-relief diffractive phase patterns is presented. The approach is based on a maskless lithography system with reflective liquid crystal displays that is able to expose continuous and binary reliefs in photoresist with a resolution of 3.4 μm. Due to a spatial frequency analysis of the entire exposure system, a compensation transformation may be applied to the input data, which results in constant structure depths independent of spatial frequencies.

We report the results of testing samples made of glass ceramics with a zero thermal expansion coefficient. The samples consist of two parts, joined by a new technology of solid-phase sintering polished parts with vacuum-deposited aluminum coating of nanosized thickness. Also reported are data on the stability of these samples after exposure to extreme factors such as cryogenic temperature (temperature of liquid nitrogen), high temperatures of 400 and 1000°C, laser radiation, etc. The test results show that the suggested technology can be used for producing light-weight astronomical telescope mirrors of Zerodur glass ceramics. In our opinion, the suggested design of a light-weight astronomical telescope mirror with two parts joined by the new technology [the bottom part is silicon carbide (SiC) and the upper is an optical layer of glass ceramics with a thermal expansion close to that of SiC in value] is promising.

3-D triangulation measurement systems with a fixed geometrical configuration have practical limitations that make them inappropriate for a wide variety of applications. The reason is that the ratio between the depth recovery error and the lateral extension is a constant that depends on the geometrical setup. Therefore, with a fixed triangulation setup, there is a tradeoff between field of view and depth resolution. As a consequence, measuring large areas with low depth recovery error necessitates the use of multiresolution techniques. In this work, we propose a multiresolution technique based on a camera-projector system previously calibrated and a second auxiliary camera that can move freely. The method consists of making first a measurement with a large field of view (coarse measurement). Afterwards, the geometrical configuration of the 3-D rig is changed to acquire a small field of view (fine measurement) that is referred to the original reference system and calibration parameters by means of the auxiliary camera. Using this method, a multiresolution reconstruction is possible without any optimization, registration, or recalibration process. Experimental results, which show a decrease of approximately one order of magnitude in the depth recovery error between fine and coarse measures, demonstrate the feasibility of the proposed method.

On-line noncontact surface inspection with high precision is still an open problem. Usual methods are, in general, not applicable in hostile environments or not adequate for on-line measurement, as they are either slow in nature or need to work from very short, unsafe distances, providing small depths of field and apertures. The ongoing work toward the development of a noncontact optical profile measuring sensor that could be used for submicron measurements in on-line applications is presented here. Our approach is based on conoscopic holography and triangulation, and uses a very simple method for removing speckle noise, which is key for obtaining high precisions from safe distances (several centimeters).

We present the imaging polarimetry method with phase shifting. The use of a liquid crystal modulator makes this method equally as quick as the one of imaging polarimetry with carrier frequency. This work presents a simple optical arrangement, together with the liquid crystal (LC) calibration procedure and experimental results confirming the correctness of the method and its accuracy.

Conventional measurement methods for large flat mirrors are generally difficult and expensive. In most cases, comparison with a master or a reference flat similar in size is required. Using gravity, as in modern pendulum-type electronic levels, takes advantage of a free reference to precisely measure inclination or surface slopes. We describe using two electronic levels to measure flatness of large mirrors. We provide measurement results on a 1.6-m-diameter flat mirror to an accuracy of 50 nm rms of low-order Zernike aberrations.

The effect of oil vapor contamination on sol-gel porous silica antireflection (AR) coatings deposited on optics used in vacuum spatial filters of high-power lasers is experimentally studied. The contamination results in the reduction of laser-induced damage threshold (LIDT) and the increase in reflectivity of the AR coatings. In comparison, the silica coatings treated with ammonia and hexamethyl-disilazane (HMDS) show almost no increase of reflectivity, and their LIDT value reduces only marginally at the wavelength of laser operation. It is found that the decrease in LIDT of the coatings exposed to oil vapors occurs due to higher absorption of the laser light, as evidenced from the increase in the imaginary part of the refractive index of the coatings.

The relationship between flicker and a common voltage (Vcom), which directly affects the image sticking problem of liquid crystal displays, is explained. A simple symmetry of flicker with respect to Vcom is introduced. A new circuit utilizing a digital interface to generate Vcom is proposed. The circuit easily controls Vcom through the digital interface, enabling automation of the Vcom optimization. The development of an automatic Vcom-tuning system plus the Vcom optimization algorithms using the symmetry of flicker is presented. The total tuning time was 0.35 seconds regardless of screen size.

The output of an external cavity diode laser (ECDL) is frequency stabilized to a water (H₂O) vapor absorption line at 935 nm using wavelength modulation spectroscopy (WMS) by means of a dual-feedback locking loop. A novel mode-referencing technique is presented that, in conjunction with the feedback locking mechanism, helps improve the overall frequency-locking system. The mode-referencing enables the device output to maintain its locked frequency in the presence of environmental and other effects, which may cause the operational characteristics of the laser to drift.

Laser shock forming (LSF) of sheet metal is a new technique realized by applying an impulsive pressure generated by a laser-induced shock wave on the surface of metal sheet. Our objective is to examine the deformation and the surface quality of LSF. LSF of a brass metal sheet is investigated using a Q-switched Nd:YAG laser with an energy per pulse of 15 to 50 J. The microhardness, roughness, and microstructure of the processed brass specimen are examined. ABAQUS software is employed to simulate the LSF process. The central displacement of the shocked region is measured and compared with the simulation. The results reveal that the microhardness of the brass specimen increases by about 20% because of the LSP treatment, and the surface quality and the microstructure has no visible change: LSF is a mechanical process, not a thermal process, and no remarkable ablation is observed. The higher the pulse energy, the higher is the central displacement of the shocked region obtained. The deformation of the simulation matches the experiment quite well.

A sensing fiber that has a gradually increasing Brillouin gain-coefficient g_B/A_eff along its length and that can keep the received Brillouin Stokes power constant in a Brillouin fiber-optic sensor is proposed. This method can be an additional way to further extend the sensing distance of the distributed Brillouin fiber-optic sensor.

Modeling the process of ion exchange in glass requires accurate knowledge of the self-diffusion coefficients of the incoming and outgoing ions. Furthermore, correlating the concentration profile of the incoming ions to a change in refractive index requires knowledge of the correlation coefficient. A novel method of a neural network based on a particle swarm optimization algorithm is considered. In the range of training, the performance parameters of ion-exchanged waveguides in any arbitrary experiment condition can be obtained easily and quickly. This method has the advantages of reliability, accuracy, and time efficiency, which are identified by simulation. Therefore, it has promise in both fields of investigation and applications.

We present a reliable, nondestructive, and real-time technique for characterization of propagation properties of planar optical waveguides based on accurately imaging the scattered light from the optical waveguide using a sensitive charge-coupled device (CCD) camera with built-in integration functionality. This technique can be used for real-time investigation of the propagation properties (loss, mode profile, bending properties, etc.) as well as the fabrication quality of planar optical waveguides. With this technique, we evaluate high-definition polymer optical waveguides on printed circuit board (PCB) substrates with a very low loss of 0.065 dB/cm at a wavelength of 850 nm, and measurement accuracy is less than 0.01 dB/cm. We expect this technique with the given CCD camera to be suitable for reliably measuring loss coefficients well below 0.1 dB/cm.

A novel all-optical header and payload separation technique that can be utilized in unslotted optical packet switched networks is presented. The technique uses a modified terahertz optical asymmetric demultiplexer (TOAD) for packet header extraction with differential modulation scheme, and two semiconductor optical amplifiers (SOAs) that perform a simple XOR operation between the packet and its self-derived header to get the separated payload. The main virtue of this system is its simple structure and that it does not need any additional continuous pulses. Through numerical simulations, the operating characteristics of the scheme are illustrated. In addition, the parameters of the system are discussed and designed to optimize the operation performance.

The filtering and multiplexing of microwave signals in the frequency range of 0.01 to 4 GHz is experimentally demonstrated. Filtering is obtained by the spectral characteristics of a 1.5-μm multimode laser diode (MLD) and the chromatic fiber-dispersion parameter. Multiplexing is based on the use of appropriated optical delays generated by the use of a Michelson interferometer that allows a very precise adjustment of the free spectral range (FSR) of the MLD used. Experimental results are validated by means of numerical simulations. To show potential applications in the area of optical communications, a filtered microwave signal is used as a microwave electric-carrier transmitting TV-video signal on a long-distance optical telecommunication system. This is achieved by using an external modulation technique over 28.3 km of a single-mode standard fiber, and using an MLD diode emitting at an optical wavelength around 1.5 μm.

The effect of an interpixel gap on light leakage in a free-space liquid-crystal-based dynamic channel blocker/equalizer is studied. The electric field components along the driving electric field within the liquid crystal interpixel gap are numerically calculated. The results show nonuniform distributions in both width and thickness. The numeric results on the relation between gap width and electric field distribution are also presented. A 20-channel, 200-GHz channel-spacing blocker/equalizer on the C band with flat tops and a 40-dB extinction ratio is fabricated and examined.

The biggest concern in the use of radio-over-fiber (ROF) links in wireless access is the limited dynamic range due to nonlinear distortion (NLD). We introduce the configuration of the ROF system, then the Volterra series, a higher-order adaptive-filter-based nonlinearity compensation scheme, is proposed to model the system and compensate the NLD. The adaptive algorithms of least mean square (LMS) and recursive least squares (RLS) for identifying Volterra kernels are both studied. The simulated results based on the measured results show that both Volterra LMS and Volterra RLS can be used to model the system, and gradually saturating amplitude nonlinearity can be adequately linearized by the latter.

An optical transmitter system-on-packaging (TxSoP) with an electro-absorption modulator (EAM) was developed for 60-GHz band rf with radio-over-fiber (rf/RoF) uplink. An analysis to develop the TxSoP with a small noise figure was performed so that the noise figure of the modified TxSoP decreased by 15 dB. The rf/RoF uplink with the modified TxSoP was established, and the error vector magnitude (EVM) and the signal-to-noise ratio (SNR) of the link were measured between 2.2% and 3.2% and between 26 dB and 29 dB from 140 MHz to 800 MHz, respectively. Digital CATV signals corresponding to 86 channels were transmitted through the link, and total throughput of the link was 2.6 Gbps.

Standard photonic crystal (PC) waveguide gratings show a stopband only in reflection. By incorporating single or multiple phase-shift regions into the PC waveguide gratings, an extremely narrow transmission peak opens up in the reflection band. Using coupled-mode theory together with transfer-matrix formalism, it is shown that by properly choosing the magnitudes of the phase shifts, the transmission spectrum can be tailored into a nearly rectangular line shape. As a specific application, the designed phase-shifted PC waveguide gratings can be used as a filter in dense wavelength-division-multiplexed (DWDM) optical communication systems with a 100-GHz channel spacing. The theoretically calculated results are numerically verified by using two-dimensional (2-D) finite-difference time-domain (FDTD) method.

A new technique for measuring the accumulated chromatic dispersion in single-mode fibers is presented. The proposed simple and tunable technique uses the null frequency of the optical beating signal between pump, probe, and four-wave-mixing conjugated signals as the pump and probe frequency separation is changed. The null frequency of the optical beating signals varies with the accumulated chromatic dispersion in the single mode fiber. A full mathematical model of the measurement technique is developed and is supported by experimental results. The technique is successfully demonstrated experimentally using a semiconductor optical amplifier as a phase conjugator to achieve a null frequency variation of 1.2 GHz for a difference of 960-ps/nm accumulated chromatic dispersion.

Receiver architectures are suggested for the detection of optical field using avalanche photodiode (APD) arrays. It is assumed that optical field is modulated using either binary pulse-position modulated (BPPM) or on-off keying (OOK), and that direct-detection is used to recover the optical signal. It is further assumed that the optical field is exposed to weak atmospheric turbulence. Receivers motivated by the maximum a posteriori (MAP) rule for OOK and BPPM communications are suggested. Due to the complexity of the suggested receivers, suboptimum combining schemes are presented. In one scheme, a simple summation of the output of APDs is utilized to render a decision. In alternate schemes, for BPPM and OOK scenarios, weighting mechanisms that combine the output of detectors in an optimum manner are suggested. For binary PPM signaling, the proposed weighting mechanism maximizes the signal-to-noise ratio (SNR). For OOK signaling, the weighting mechanism is an improvised optimization of the linear summation of the outputs of the APDs. Simulation results are presented to underscore the superiority of the weighted combining methods as compared to the simple summation algorithm.

In amplified wavelength-division-multiplexed (WDM) networks, the performance of a low-frequency (⪅100 kHz) pilot-tone-based monitoring technique could be deteriorated by the slow dynamic properties of erbium-doped fiber amplifiers (EDFAs). We develop a simple model to describe this effect and estimate the maximum size of WDM network that the pilot-tone-based monitoring technique could support. The result shows that 100-kHz pilot tones could be used for the cost-effective monitoring of metro optical networks (32 channels, 320-km transmission).

A novel scheme to deploy a point-to-multipoint optical wireless communication network is proposed. The master node provides hemispherical field-of-view (FOV) acquisition via a fisheye lens to achieve the automatic establishment of optical links with user nodes. We present an effective distortion-correcting algorithm based on two-ary piecewise bicubic spline interpolation to correct the large optical distortions of the fisheye lens. Using this algorithm, the angles of the incident beams are accurately calculated according to the laser spot position on the CCD (charge-coupled device) sensor with the maximum error of 0.027 deg. In addition, the strong background radiation from such an ultrawide FOV also leads to significant degradation of the angle detection accuracy under the condition of weak received optical power. A Voigt anomalous dispersion optical filter with ultra-narrow-pass bandwidth is adopted to resist the background radiation. The numerical simulation results show that the total angle detection error caused by the optical distortion and the background radiation is within 0.06 deg. Considering the extra gimbal pointing error and the angle-of-arrival fluctuations due to atmospheric turbulence, the pointing error of the master node is less than 0.079 deg, which meets the high-accuracy requirement of pointing for the automatic optical link establishment.

A wavelength division multiplexing (WDM)-based optical backplane architecture is introduced. It is a tunable transmitter fixed receiver (TT-FR) architecture incorporating an N×N arrayed waveguide grating (AWG) element for passive data routing between the nodes, which in conjunction with star couplers, offers both unicast and multicast capabilities. The data and control plane of the network are implemented on a high-speed field programmable gate array (FPGA), and a four-node demonstrator is built up. Three different types of AWG routing elements implemented in different technologies are employed, and bit error rate (BER) versus incident power on the receiver measurements are presented for a data rate of 10 Gbps per link. A total switching time as low as 500 ns is achieved, permitting packet switching operation with more than 95% efficiency when the packet length is greater than 10 kbytes.

A cost-effective and reliable liquid crystal spatial light modulator (SLM) system is developed for light modulation and holographic recording of variable data in photopolymer material. It is made by reverse engineering a mobile phone with a liquid crystal display (LCD) of resolution 84×48 pixels. The SLM is based on a detached LCD panel with drivers, a personal computer system, an interface to provide data, and the software for uploading data. The SLM works well in the transmissive mode, and the transmitted laser beam is modulated according to the electronic data input to the panel from a personal computer. The SLM is implemented with good transmission efficiency and image contrast for holographic data recording and related experiments, and is observed as a very cost-effective option for light modulation.

In an attempt to mitigate the effects of the atmosphere on the coherence of an optical (laser) beam, interest has recently been shown in changing the beam shape to determine if a different power distribution at the transmitter will reduce the effects of random fluctuations in the refractive index. Here, a model is developed for the field of a flattened Gaussian beam as it propagates through atmospheric turbulence, and the resulting effects on the scintillation of the beam and beam wander are determined. A comparison of these results is made with the like effects on a standard TEM₀₀ Gaussian beam. The theoretical results are verified by comparison with a computer simulation model for the flattened Gaussian beam (FGB). Further, a determination of the probability of fade and of mean fade time under weak fluctuation conditions is determined using the widely accepted lognormal model. Although this model has been shown to be somewhat optimistic when compared to results obtained in field tests, it has value here in allowing us to compare the effects of atmospheric conditions on the fade statistics of the FGB with those of the lowest order Gaussian beam.

Laser imaging through atmospheric turbulence is a challenging problem due primarily to turbulence near the aperture. Amplitude measurements of the return beam in the aperture plane are less sensitive to near-field turbulence, but contain limited information about the Fourier phase of the target image. We propose a method of using deconvolution of laser speckle degraded imagery, together with pupil plane techniques, to produce coherent image reconstructions with spatial resolution not limited by the atmospheric conditions. The technique is demonstrated using computer simulation.

It is well know that free-space laser system performance is limited by atmospheric turbulence. Most theoretical treatments have been described for many years by Kolmogorov's power spectral density model because of its simplicity. Unfortunately, several experiments have been reported recently that show that the Kolmogorov theory is sometimes incomplete to describe atmospheric statistics properly, in particular, in portions of the troposphere and stratosphere. We present a non-Kolmogorov power spectrum that uses a generalized exponent instead of constant standard exponent value 11/3, and a generalized amplitude factor instead of constant value 0.033. Using this new spectrum in weak turbulence, we carry out, for a horizontal path, an analysis of long-term beam spread, scintillation index, probability of fade, mean signal-to-noise ratio (SNR), and mean bit error rate (BER) as variation of the spectrum exponent. Our theoretical results show that for alpha values lower than α=11/3, but not for alpha close to α=3, there is a remarkable increase of scintillation and consequently a major penalty on the system performance. However, when alpha assumes a value close to α=3 or for alpha values higher than α=11/3, scintillation decreases, leading to an improvement on the system performance.

The performance of electro-optical systems can be substantially affected by aerosol particles that scatter and absorb electromagnetic radiation. While molecular extinction can be calculated using propagation codes such as MODTRAN (Berk et al., 1989), the influence of aerosols is much less easy to account for. However, concentrations and optical properties of aerosol particles in the atmosphere are quite variable both in time and space. Very few relevant models for the aerosol size distributions have been published during the last decades. One of the most used is the Navy aerosol model (NAM, Gathman, 1983), which is currently being upgraded to the advanced Navy aerosol model (ANAM, van Eijk and Merritt, 2006). NAM and ANAM are dedicated to open ocean, while coastal areas induce specific processes (Piazzola et al., 2000, and Bendersky et al., 2004). To include coastal effects for the prediction of aerosol concentrations and their effects on the extinction, Piazzola et al. (2003) proposed the aerosol extinction code MEDEX. We deal with the extension of the predictions of MEDEX on a regional scale. To achieve it, MEDEX is forced by the regional mesoscale meteorological model RAMS (Cotton et al., 2003) to account for the fine details of the coastal orography. Simulations are then compared to aerosol size distributions recorded in the Mediterranean. The results show a nonhomogeneous spatial coverage of the aerosol concentrations over the northern Mediterranean. In addition, we show the least performance of the coupling for unsteady conditions of the wave field.

We study and exactly evaluate the transmittance of microwave energy—below S-band—that goes through thick building walls covered by an external thin layer of rain. The incident radiation penetrates the wet walls at normal incidence, twice in their back-and-forth paths typical of sensing-through-the-wall (STTW) operations. The walls are responsible for most of the loss through the structure in view of their greater thickness, but the water layer contribution is significant, and it is quantitatively evaluated here. The properties of the water layer are expressed in terms of Debye's classical formulation, and those of the walls are obtained from available measurements. A simple homogenization technique is used to generate an "effective permittivity" of the double layer to be able to alternatively treat it as a single equivalent layer—an approximation to the exact values, which yields acceptable results. It is also found that the transmittance T and the reflectance R of a single and double layer could also be expressed in alternative and apparently novel forms that may simplify future calculations. Further, if either R or T were known as well as the layer(s) properties, then either one could be used to obtain the other. Finally, representative plots are displayed, quantitatively showing the (two-way) transmittance degradation that occurs when there is a rain layer on top of the various considered wall materials, and we explain a resonance effect observable in the transmittance plots that shows an oscillatory frequency behavior.

A novel algorithm, Gaussian mean shift registration (GMSR), is proposed for multisensor dynamic bias estimation. The sufficient condition for convergence of a Gaussian mean shift procedure is given, which extends the current theorem from a strictly convex kernel to a piece-wise convex and concave kernel. The Gaussian mean shift algorithm combined with the extended Kalman filter (EKF) is implemented to estimate the dynamic bias based on the measurements from a single target, which is an iterative optimization procedure. Monte Carlo simulations show that the new algorithm has significant improvement in performance with reducing root mean square (RMS) errors compared with the minimum mean square error (MMSE) estimator, based on multiple targets and multiple frames. The proposed estimator is close to the theoretical lower bound, i.e., it is more efficient in estimating the dynamic bias than other methods.

We generalize the spectral resolution model that was used for the Atmospheric Infrared Sounder (AIRS) instrument to account for the observed disparity between the predicted resolution and its measurement. The prelaunch-measured spectral resolution of the AIRS instrument was shown to be narrower or better than the prediction by 3% to roughly 14% with the narrowing increasing with wavelength across the AIRS infrared spectral band of 3.7 to 15.4 μm. The prediction was based on the common practice of using the slit as a secondary source, but with a tacit assumption of spatial incoherence for the slit illumination. We show that the narrowing of the spectral resolution is caused by partial coherence at the slit illumination, and is accounted for naturally by using the primary source and a system point spread function P, which includes the optical contributions of the preslit source optics or telescope in addition to that of the spectrometer. We model the disparity versus wavelength, and show a good comparison to that measured and reported in the literature.

As the demand toward a thin liquid crystal display accelerates, a backlight system must become thinner. Compact and efficient coupling of an LED to a thin light-guide is one of the key technologies. First, we consider simple face-down and prism coupling, and carry out experiments using a chip-type LED with a 2.4-mm-diam emission area and a 3.0-mm-thick light-guide. Face-down coupling guides only 12% of the LED output into the light-guide. With a right-angle prism, the efficiency is improved to 23%. We try to improve the coupling efficiency by altering the propagation direction of the light with an optical film. However, our experiments and simulations with off-the-shelf prism sheets and diffuser films show that the coupling efficiency decreases. Next, we carry out ray-tracing simulations for various input coupler designs. A chip-type LED with a 0.42-mm-diam emission area and a 0.1-mm-thick light-guide are assumed. Calculated efficiency greater than 50% is obtained by a square prism mounted obliquely on the light-guide, while the footprint of the coupler is about 1.3 mm. An input coupler based on an oblique cylinder improves the calculated efficiency to 73.5% at the expense of its footprint of 4.82 mm.

How to choose effective fusion frames and how to obtain effective fusion coefficients are key problems in image fusion. A novel image fusion scheme is presented based on multiscale decomposition and directional filter banks (DFBs). First, contrast pyramid (CP) decomposition is used for each level of each original image. Then, DFBs are constructed for filter each image. Furthermore, a kind of evolution computation method—the immune clonal selection (ICS) algorithm—is introduced to optimize the fusion coefficients for better fusion products. By applying this technique to fusion of infrared thermal and visual light images, simulation results clearly demonstrate the superiority of this new approach. Fusion performance is evaluated through subjective inspection, as well as objective performance measurements. Experimental results show that the fusion scheme is effective and the fused images are more suitable for further human visual or machine perception.

We introduce a new generation of a semiautomated tree-ring image analysis system and new image analysis algorithms. System design, new tree-ring image registration, ring boundary identification, and average ring width and brightness profile measurement algorithms are described. By using a pyramid multiscale image registration algorithm, the program gains registration speed with little sacrifice of accuracy. For boundary identification, two new assumptions and associated nonring feature suppression, edge tracking, and fragment linking methods are proposed, such that most of the complicated ring boundaries can be identified successfully. To obtain more detailed information about the ring growth changes with time, an average brightness profile measurement algorithm is implemented. Additionally, automatic geometry warping is introduced to the average ring width and brightness profile measurement to handle abnormal ring cases. To allow manual override of the results, a new user intervention design is also implemented and described.

The JPEG baseline algorithm codes the dc of a block by giving its difference with the dc of the previous block. We propose to use ac coefficients for this purpose. Our method computes the difference of the sum of pixels of two boundary columns (or rows), one belonging to the current block and the other to a previous block, and then manipulates it in the direct cosine transform (DCT) domain so that the average of the coded differences for the whole image is near zero. Experimental results show that our method reduces the average JPEG dc residual by about 75% for images compressed at the default quality level. The reduction is even higher for unquantized DCT blocks.

We propose a novel deringing scheme based on the concept of a trilateral filter—an extension of the bilateral filter that consists of domain, range, and texture activity filters. The domain and range filters are used to measure image geometrical similarity and photometric similarity, respectively, while the texture activity filter helps to preserve image details during postprocessing. An image texture map is first computed with a dual-edge detection process. This texture map is then utilized to adjust the trilateral filter for effectively protecting the image detail from oversmoothing. Experimental results are provided to justify the algorithm.

In conventional super-resolution algorithms, a single scheme is usually adopted and applied for a whole image, regardless of region characteristics. Since an image consists of various regions having different characteristics, these algorithms may not provide equally good performance for all regions. To alleviate this fundamental drawback of the conventional approach, we propose a region-based super-resolution algorithm. In the algorithm, an image is first analyzed and segmented into smooth, intermediate, and edge regions. According to the region type, a different diffusion-based regularization term and different reconstruction parameters are then used. For regularization in edge regions in particular, we adopt directional smoothing based on adaptive anisotropic diffusion, rather than omni-directional smoothing, to restore the continuity and sharpness of edges and simultaneously reduce undesired noise. The reconstruction parameters are independently managed, depending on the region type, to maximize the visual quality of the whole image. Experimental results show that the proposed method improves the objective quality as well as the subjective visual quality of reconstructed high-resolution images.

We describe a new approach to fusion techniques in a multiple target tracking system for an infrared search and track (IRST) system operating in the mid- and long-wave infrared (IR) bands. The use of the two IR bands allows better performances in terms of detection probability, lower number of false tracks, and shorter time for track declaration. To properly merge data from the two sensors, an enhancement of the probabilistic data association (PDA) technique is introduced in the process. A simplification of the approach used brings back the algorithm to the well-known PDA, allowing its use in conjunction with the interacting multiple model (IMM) with increased tracking ability of the system.

We propose a fast and stable camera match-moving method aimed for real-time augmented reality applications. A known marker is used for fast and robust detection of marker points and for stable camera pose estimation. From the detected image points of a known marker on a single frame, we estimate the camera position and translation parameters. The entire pose estimation process is linear and initial estimates are not required. The most suitable reference point for the pose estimation is automatically chosen by investigating the depth variation. A planar marker is also allowed, since our linear method handles rank deficient cases. As an application of the proposed method, we implement a video augmentation system that replaces the marker in image frames with a virtual graphical object during the marker tracking. Experimental results show that the proposed camera tracking method is robust and fast enough for interactive video-based applications.

We present a novel statistical approach to unsupervised detection and localization of a chromatic defect in a uniformly textured background. The test images are probabilistically modeled using Gaussian mixture models, and consequently defect detection is posed as a model-order selection problem. The statistical model is estimated using a modified Expectation-Maximization algorithm that aids in faster convergence of the scheme. A test image is segmented only if a defective region/blob has been declared to be present, and this improves the efficiency of the entire scheme. This work places equal emphasis on defect localization; hence, an elaborate statistical multiscale analysis is performed to accurately localize the defect in the image. The underlying idea behind the multiscale approach is that segmented structures should be stable across a wide range of scales. The efficacy of the proposed approach is successfully demonstrated on a large dataset of stained fabric images. The overall detection rate of the system is found to be 92% with a specificity of 95%. All of these factors make the proposed approach attractive for implementation in online industrial applications.

A new approach is proposed for human behavior classification from MPEG compressed videos. Moving objects are first detected by subtracting the dc values in I frames from those in the background. In addition, the dc values of the background are also adapted to avoid noise and illumination change. The tracking process is then performed using the consecutive frames. Motion vectors extracted from P frames are used to predict the next position of moving objects. An overlapping table is constructed to determine relationships between moving objects, and the number of moving objects is updated. For analyzing human behavior, motion vectors and velocities of moving objects from P and B frames are extracted. These features are clustered to codewords using a codebook generated by vector quantization (VQ) for the input of discrete hidden Markov models (HMMs). By applying the HMM, four kinds of human behaviors are successfully identified from the human behavior sequences. The proposed approach is, furthermore, more accurate than the previous method based on conventional features.

We present a novel method to estimate the light source direction and relight a face texture image of a single 3-D model under arbitrary unknown illumination conditions. We create a virtual irradiance sphere to detect the light source direction from a given illuminated texture image using both normal vector mapping and weighted bilinear interpolation. We then induce a relighting equation with estimated ambient and diffuse intensity. We provide the result of a series of experiments on light source estimation, relighting, and face recognition to show the efficiency and accuracy of the proposed method in restoring the shading and shadow areas of a face texture image. Our approach for face relighting can be used for illuminant-invariant face recognition applications.

A simple focusing device is proposed for de Broglie matter waves—a diffractive lens, based on the optical effect of diffractive multifocal focusing of radiation. This matter-wave lens consists of two coaxial circular apertures in which the second aperture of smaller diameter is located where the Fresnel number of the first aperture is unity. It is shown that diffraction of a de Broglie matter wave by a system of two pinholes on an optical axis exhibits the multifocal focusing effect of matter waves in the near-field (Fresnel) zone, which creates a very intense, spatially localized beam of atoms. Theoretical predictions for the focusing efficiency of a neutral atomic beam by the diffractive lens are as follows. The spot diameter is ~0.1 μm, the ratio of focal and incident intensities is ~15, the focal length of the diffractive lens is in the range ~0.13 to 6 m, the focusing depth is in the range ~15 to 30 cm, and the energy transmitting efficiency is ~30 %. For the relatively large diameters of the pinholes, ≥5.0 μm, the proposed configuration acts as a matter-wave lens with a large focal length and a long focusing depth.

The wavefront of circular dark-hollow-beams with wavelength λ produces a helix of pitch m λ, where m is an integer. But the central phase singularity of such beams can also be generated reducing the pitch by using a modulo operation. When such a beam interferes destructively with an unmodified annular beam of the same order, an incomplete annular beam is produced. The final beam, generated using a standard computer-generated holographic procedure, retains its shape up to 1.5 cm. A potential use of such beams for manipulation of microorganisms has been indicated through a dynamic holographic procedure using a spatial light modulator.

The possibility of light manipulation at the nanoscale relies on the efficient coupling of the electromagnetic waves to surface excitations such as surface plasmon polaritons (SPPs). We expand on the work by Pendry, who put forward the idea of spoof surface plasmons in conducting films as a way to engineer SPP dispersion curves. We find that the surface texture and geometry can play an important role in determining the dispersion. We then compare the specific cases of circular versus rectangular textured surfaces and observe that the plasmon modes are less tightly bound in the former case. This dependence on geometry can also be used as a means for defect engineering or fine-tuning the regular plasmon dispersion.

This PDF file contains the errata for “OE Vol. 47 Issue 02 Paper 2841368” for OE Vol. 47 Issue 02