This PDF file contains the editorial “How To Make Yourself Invisible” for OE Vol. 42 Issue 07

We show that three-dimensional orthoscopic real images can be produced in direct pickup one-step integral imaging. Impairment of the image resolution in direct pickup two-step integral imaging can be avoided with this approach.

We present a novel multiplexing storage technique for edge-lit volume holograms. Multiholograms are stored in a photorefractive plate using vertical shifting multiplexing and random phase encoding. The unpolished edge surface of a photorefractive plate serves as the random phase generator. The vertical shifting sensitivity is experimentally investigated.

The Space Interferometry Mission (SIM) is a space-based long-baseline optical interferometer for precision astrometry. One of the primary objectives of the SIM instrument is to accurately determine the directions to a grid of stars, together with their proper motions and parallaxes, improving a priori knowledge by nearly three orders of magnitude. The basic astrometric observable of the instrument is the path-length delay, a measurement made by a combination of internal metrology measurements that determine the distance the starlight travels through the two arms of the interferometer and a measurement of the white light stellar fringe to find the point of equal path length. Because this operation requires a nonnegligible integration time to accurately measure the stellar fringe position, the interferometer baseline vector is not stationary over this time period, as its absolute length and orientation are time-varying. This conflicts with the consistency condition necessary for extracting the astrometric parameters, which requires a stationary baseline vector. We address how the time-varying baseline is "regularized" so that it can act as a single baseline vector for multiple stars, and thereby establishing the fundamental operation of the instrument.

A linearly polarized light beam is incident on the boundary surface between the thin metal film of a surface plasmon resonance (SPR) apparatus and the tested solution. If the incident angle is very near to the resonant angle, then the phase difference between p- and s-polarizations of the reflected light is changed with the concentration of the solution. The phase difference can be measured accurately by heterodyne interferometry. Based on these effects, a method for measuring the concentration of a solution is presented. Because the reflected light is measured, only a small quantity of the solution is required. In addition, the method has the advantages of both common-path interferometry and heterodyne interferometry.

It has been well documented that microstructural effects cause ambiguities in strain measurement. Moreover, extreme sensitivity is required to measure strain in very thin structures. That it varies sharply across structural sections of interest and cannot be measured along the neutral plane of bending are additional reasons to reassess the suitability of strain as the usual measurand of choice for evaluation of structural deformation. We show that on all these accounts the alternative of measuring deformation curvature with a recently derived device called a curvature gauge offers conceptual advantages over the traditional practice of strain measurement.

The properties of a small-core high-numerical-aperture fiber are investigated using near-field scanning optical microscopy (NSOM). The microscopic structure of the fiber is also determined using a combination of etching and atomic force microscopy (AFM). Although the mode profile cannot be precisely predicted using AFM data alone, the measured profile is in extremely good agreement with that calculated using dimensional information provided by AFM and preform index data.

We describe the measurement of low differential group delay and fiber birefringence using a commercial polarization analyzer based on a free-space rotating quarter waveplate polarimeter. Stress-induced birefringence is isolated from the 60-cm fiber under test by placing it in a suitably designed fiber chuck. A referencing scheme is used to eliminate system birefringence. The suitability of this setup for the measurement of low polarization mode dispersion (PMD) is demonstrated. We also report results that demonstrate limitations of the recently proposed Jones matrix exponential expansion for first-order PMD measurement in devices with high second-order PMD.

We present a two-wavelength wavelength-division-multiplexing (WDM) externally modulated transport system that uses chirped fiber gratings (CFGs) to reduce the fiber dispersion and cross-phase modulation (XPM)-induced crosstalk simultaneously. In comparison to a two-wavelength WDM externally modulated transport system without CFGs, good performances of composite second-order (CSO) ≥ 67 dB and composite triple-beat (CTB) ≥ 65 dB distortions are obtained, accompanied by acceptable carrier-to-noise ratio (CNR) ≥ 50 dB value in our proposed system over a 100-km single-mode fiber (SMF) transport.

A compact and inexpensive optical fiber sensor for the measurement of dc and ac currents is demonstrated. The sensor consists of a fiber Bragg grating bonded on two joined pieces of metal alloys, one being Terfenol-D and the other MONEL 400. Because Terfenol-D has much stronger magnetostriction, a magnetic field applied along the two alloy bars stretches the two portions of the grating in different proportions and, thus, results in a split in the reflection spectrum of the grating, which can be measured with a simple technique using a single photodetector. On the other hand, because Terfenol-D and MONEL 400 have almost identical thermal expansion coefficients, a change in temperature does not cause the reflected spectrum of the grating to split and, therefore, does not affect the magnetic field measurement.

Periodical perturbations along an optical fiber can cause power coupling between the core and cladding modes for the applications of spectral filtering and derivative operations. Such perturbations can be generated through periodical loading on fiber. By applying loading onto a fiber with two face-to-face, identical groove structures, it was found that the long-period grating effects were dependent on the relative phase of the two periodical corrugations. Particularly, when the relative phase was zero (crest to crest), spectral filtering effects disappeared completely. The comparisons of such results between the cases of jacketed and unjacketed fibers led to the conclusion that geometric deformation, instead of direct pressure-induced effects, was the dominating mechanism for generating spectral filtering functions in the double-sided loading configuration. The same conclusion can be applied to a single-sided loading device.

Principal component analysis is applied to the calculation of the power α of the 1/fα dependence of the power spectrum density of a sequence of frames affected by a 1/f noise and obtained from a focal plane array. This method provides an operational alternative of characterization of this type of noise that has been successfully applied to simulated and experimental data. The α parameter obtained by this method corresponds with a global characterization of the whole array. Besides, a calibration lifetime is calculated. This temporal parameter indicates when the 1/f noise begins to be more noticeable than the temporal noise in the images of the array.

The paper is concerned with the geometric calibration of infrared imaging systems with a view to use them in both photogrammetry and remote sensing applications. From the geometric point of view, three quite different types of infrared imagers can be distinguished: 1. the pyroelectric vidicon camera; 2. the CCD camera with 2-D areal array of solid-state detectors; and 3. the thermal video frame scanner (TVFS). These operate in different parts of the infrared spectrum. The special optical and detector technologies used in these different devices are first reviewed. On this basis, a special target plate is constructed with its own internal radiation source that allows all of these devices to be calibrated geometrically. The actual experimental and calibration procedures are described, as is the method used for the automated measurement of all the targets using image matching techniques. The subsequent data processing and analysis are then outlined. The results obtained from the successful calibration of a representative sample of CCD cameras and thermal video frame scanners are presented and discussed in detail. They provide much new and accurate information on the geometric characteristics of these imagers that can be used in military, medical, industrial, and environmental applications.

We describe a method for generating the color texture corresponding to a range image. Based on the projection of fringe patterns on an object, a color texture of the object's surfaces can be extracted from an original fringe image. Since the range image of the object is also obtained from the original fringe image, this method eliminates alignment problems during the texture mapping, and avoids the need for extra cameras to acquire the texture. Experimental results are given to illustrate the validity of color texture extraction using our proposed method.

As an extra option, fine grayscale data that exceed eight bits per pixel are encoded into pseudogray colors in 8-bit sRGB color space to be displayed on an 8-bit sRGB CRT monitor. The characteristics of the pseudogray are investigated in terms of the CIELAB color difference and a*b* coordinates.

By using a lifting scheme, we present a technique to construct compactly supported wavelets whose coefficients are composed of free variables that lie in an interval. By selecting the coefficients of the 9 to 7 wavelet filter and associated lifting scheme, an efficient approach via wavelets for image compression is developed. Furthermore, the rationalized coefficients wavelet filter that can be implemented with simple integer arithmetic is achieved, and its characteristic is close to the well-known original irrational coefficients 9 to 7 wavelet filters developed by Cohen, Daubechies, and Feauveau. Software and hardware simulations show that the new method has very low complexity, and simultaneously preserves a high quality of a compressed image.

Medical images must be compressed before transmission due to bandwidth and storage limitations. The set partitioning in hierarchical trees (SPIHT) algorithm is an efficient method for lossy and lossless coding of medical images. We propose some modifications to the SPIHT algorithm. It is based on the idea of the insignificant correlation of wavelet coefficients among medium- and high-frequency subbands. In this scheme, insignificant wavelet coefficients that correspond to the same spatial location in the medium subbands can be used to reduce the redundancy by a combined function proposed in associated with the modified SPIHT. In high-frequency subbands, the modified SPIHT proposes a dictator to reduce the interband redundancy. Experimental results indicate that the proposed technique improves the quality of the reconstructed medical image in terms of both the peak signal-to-noise ratio (PSNR) and the perceptual results over JPEG2000 and the original SPIHT at the same bit rate.

A novel image compression scheme based on absolute moment block truncation coding (AMBTC) is proposed. The quadtree segmentation technique is employed in this scheme to exploit the variable-block-sized segmentation. In addition, the concept of using visual patterns to reduce the storage cost of the BTC bit plane is incorporated into this scheme. Finally, the bit plane omission technique is employed if these two quantization levels in each image block are quite similar. According to the experimental results, it is shown that the proposed scheme requires very little computational complexity. Besides, a good image quality of the compressed image can be obtained while the required bit rate is relatively low. In other words, the proposed scheme indeed provides a good approach to compress digital images with little computational cost at a low bit rate.

The purpose of this preliminary study is to segment the brain on magnetic resonance (MR) images by using a robust and fully automatic method. A 2-D T2-weighted MR sequence is used as a reference for imaging the brain. Our segmentation technique could segment the brain in each slice taken from different MR scanners using different image resolutions and MR sequences. This method is based on an integrated approach that uses image processing techniques and a priori knowledge. The originality of our work is to integrate the 3-D information of the sequence in the geometrical approach, to adapt this method for other MR imaging modalities, and to use only one MR sequence to segment the whole brain. This is a multistage process requiring the background noise to be removed, and the head mask is then obtained thanks to the combination of a recursive filling technique and geometrical properties of the brain. We describe the main features of the method, and give results for some brain studies.

A near-infrared waveguide photodetector in a Si-based ternary Si_1–x–yGe_xC_y alloy is analyzed theoretically and the simulation results are obtained for 0.85- to 1.06-μm wavelength fiber optic interconnection system applications. Two sets of detectors with active absorption layer compositions of Si_0.79Ge_0.2C_0.01 and Si_0.70Ge_0.28C_0.02 are designed. The active absorption layer has a thickness of 120 to 450 nm. The external quantum efficiency can reach ~3% with a cut-off wavelength of around 1.2 μm.

A novel 3-bit optical true-time delay module that can provide 64 time delays ranging from 0 to 443.03 ps is presented. The total insertion loss, including the propagation loss and the 1-to-64 fan-out loss is confirmed to be less than 20 dB. The crosstalk among channels is measured to be less than –40 dB. The bandwidth of the fully packaged module is determined to be as high as 539 GHz. This true-time delay module is employed to control an eight-element K-band phased array antenna system. Far-field patterns covering 18 to 26.5 GHz are measured and compared with the simulated results to verify this module's wide instantaneous bandwidth.

A simple spatial phase-shifting setup that uses a tiled mirror and a cat's-eye retroreflector is presented. It can be used in displacement measurement when high speed and accuracy are required. An experiment is carried out to demonstrate the feasibility of the method. A root mean square (rms) accuracy of better than 5 deg is obtained in ordinary circumstance. The system errors are also studied briefly.

A temporally modulated IR lamp is employed to heat the surface of a flawed plate and the resulting out-of-plane thermoelastic deflection is monitored using phase-shifted temporal speckle pattern interferometry. The speckle interferograms are continuously recorded by means of a high-speed digital camera with temporal phase shifting carried out by a Pockels cell synchronized with it. Temporal phase unwrapping through sequences of several hundreds of frames enables the determination of time-varying absolute displacement maps. Experimental results illustrate the possibilities of this novel nondestructive testing technique.

The clustering of satellites in cooperative fly formation constellations produces a lightweight, low cost, highly reliable and supraperformance space system. One way to communicate between the satellites is by a laser beam with a narrow divergence angle. To maintain line of sight between the transmitter and the receiver during the communication time, a steering device has to be incorporated into the communication system. We adopt a 2-D optical phased array (OPA) antenna. An OPA antenna is an attractive option for a steering device as it is lightweight, compact, and provides agile and inertia-free 2-D beam steering. We integrate two fields of study—OPA and laser communication theory—to attain a new perspective on communication system design. We theoretically analyze and model a laser intersatellite link using a 2-D OPA antenna and illustrate the model by a numerical simulation. The microsatellite antenna gain distribution statistics are derived from the OPA theory using the Monte Carlo method. We apply the results to evaluate system performance, particularly the effect of OPA phase errors.

We discuss the accuracy analysis of laser meters based on the Doppler effect and used in the measurement of automobile velocity. Usually, the systematic errors are assessed during calibration and are eliminated by instrumental means. Nevertheless, it is impossible to eliminate random errors. Their analysis is also important for such measurements, and this has been less extensively analyzed in scientific papers. A probabilistic method is used for error analysis assuming that only random errors are present. The accuracy of measurement by Doppler meters depends mostly on parameters of two kinds—laser source stabilization, measuring laser emission frequencies, and the errors in determining the emission speed in the atmosphere. Such analysis shows a value of the random error occurring during the measurement of automobile speed that also can be applied for assessment of other kinds of measurements of moving objects.

Images captured with wide-angle lenses suffer from spatial distortion, which prevents accurate measure and feature extraction. In this work, a mathematical model based on polynomial mapping is used to map the images from distorted image space onto the corrected image space. The model parameters include the polynomial coefficients, distortion center, and dot center. A new technique to estimate the distortion center based on the evaluation function is presented. In dot center estimation, a seed fill algorithm is used to traverse all pixels. The expansion polynomial was obtained by using cubic spline interpolation. With a field programmable gate array (FPGA), the real-time distortion correction is implemented, which is independent of a computer. The major benefit using FPGA is that the same circuit can be used for other circularly symmetric wide-angle lenses without being modified.

This work is devoted to the derivation of simple approximate equations, which can be used for studies of light reflection from various semiinfinite weakly absorbing turbid media. It is assumed that the probability of photon absorption in a single scattering event is small. The method used is largely based on the approximate summation of the MacLauren series for total light reflectance and other radiative transfer characteristics as functions of the probability of photon absorption. The main results comprise convenient analytical expressions for total light reflectance, plane albedo, reflection function, and degree of polarization of reflected light.

When an antiferroelectric liquid crystal (AFLC) cell is set between crossed polarizers for optical modulators or displays, it has low transmittance efficiency. This happens because AFLC materials have inherent tilt angles of typically 18 to 38 deg, not 45 deg. To improve the low transmittance efficiency, we propose a new optical configuration for antiferroelectric liquid crystal displays or devices, which also improves color dispersion. It consists of two crossed antiferroelectric liquid crystal cells. The characteristics of this dual-antiferroelectric liquid crystal display are simulated and experimented.

We use fluorescence optical microscopy to identify water stains on the surface of wet-cleaned silicon wafers. By using a commonly used confocal microscope, submicron resolution is routinely achieved, and both micro- and macroscopic distribution of water stains can be measured. The proposed technique is easy to implement, does not require any special conditions such as vacuum, and can serve as a powerful method in determining the optimal conditions for wet cleaning.

The fundamental concept of the visual range of a low-light-level imaging system is described. Based on a revised apparent distance detection equation, the relations of parameters that have an influence on system performance are analyzed. Combined with the research on CY-1 night vision goggle, the visual range under specific circumstances is estimated, proving the revised apparent distance detection equation is effective and the design of the system is feasible.

We propose the use of a multichannel optical correlator working with two spatial light modulators for texture classification. The architecture may implement any method based on frequency filtering in the Fourier domain. The addition of linear phases in each filter shifts the filtered image in the correlation plane and permits the implementation of several filters in parallel. To show the capacity of the system, we implement a particular case of texture classification method. The features used for the classification are the energy that falls in different frequency subbands. Six wedges and four rings in 24 frequency subbands divide the Fourier domain. By adding linear phases in different regions, it is possible to implement eight subbands simultaneously in the filter spatial light modulator. Then only three filters are necessary.

We propose a new method for optical interconnections between illuminating and receiving points. This method uses optical matrix structures (OMSs) to operate compact, simple, and cheap connections. Matrix structure elements can be reflective, refractive, or diffractive optical elements. The optical features of these elements must be determined one by one according to their light-redirection requirement. From the experiment results, this new OMS method performs better than the other conventional methods.

We examine the spatial resolution of pixelated-metal-mirror (PMM) ferroelectric-liquid-crystal (FLC) optically addressed spatial light modulators (OASLMs). To characterize the resolution of OASLM devices, their diffraction efficiency is measured as a function of the spatial frequency of the write image. The results show that aliasing is produced by the PMM devices, which correspond qualitatively with the predictions of sampling theory.

A new least-significant-bit (LSB)-based steganographic model providing high capacity is proposed. This model is based on the idea of statistical minimum mean square error (MSE) replacement and can be implemented in two schemes: the oblivious scheme and the cover escrow scheme. In both schemes, blockwise replacement is adopted in the hiding process based on the statistical characteristics of a cover image and a hidden image. Two operations, mean shifting and phase reversing, are used to modulate the subblocks of both the hidden and cover images, which contributes to minimizing the MSE introduced by LSB-based replacement. Examples are shown to demonstrate their effectiveness. Performance analysis is also done to provide the upper limits of the improvement by the two schemes in the ideal cases. Finally, experimental results with real images are presented to demonstrate the effectiveness of the proposed model.

We propose an optical method for detecting the displacement of an object in stereo images. Two images are displayed on two liquid crystal displays (LCDs), respectively, which are placed at a constant distance. Several plane waves of different propagating directions are illuminated to the LCDs. We can measure the displacement of the object by detecting which plane wave presents the strongest intensity after the plane waves pass through the LCDs. The method is applied to measuring the distance between cars from stereo images of a car.

In stereolithography, the most important procedure for improving the accuracy of modeling is to clearly identify the relationship between the method of laser irradiation and the solidification of photocuring resin. Thus, a theoretical analysis is made to find any effect on the solidification, namely the thickness and width of solidified resin influenced by laser power, laser beam diameters, laser scanning speeds, and properties of photocuring resin. These analytical results are compared with respective test results. The results can be summarized by the following. 1. The cured thickness of solidified resin can be represented by a function of the energy density at the center of laser, the attenuation coefficient, and the critical curing energy density of photocuring resin. 2. The cured width of solidified resin can be represented by a function of laser beam diameters, the energy density at the center of laser, and the critical curing energy density of photocuring resin. 3. Photocured models, which have been manufactured by controlling energy density at the center of laser, would have high manufacturing accuracy, and therefore can be applied as industrial design models.

Previous efforts have established models that relate IR and visible imaging sensor design and operating parameter values to measures of information extraction performance. The surveillance and reconnaissance community predicts National Imagery Interpretability Rating Scale (NIIRS) values using the general image quality equation (GIQE). The target acquisition community predicts probabilities of discrimination (detection, recognition, identification) using various minimum resolvable contrast/minimum resolvable temperature (MRC/MRT) models, and methods have been developed to link the two sets of predictions. No such models currently exist for the radar domain, although a radar NIIRS has been developed. We provide a basis for initial estimates of synthetic aperture radar (SAR) target acquisition performance. First, a conversion from radar to IR (and visible) NIIRS is provided. The IR NIIRS is then converted to probabilities of discrimination values. The two conversions together provide rough estimates of SAR target acquisition performance as a function of radar NIIRS values.

Imaging systems such as synthetic aperture radar collect band-limited data from which an image of a target scene is rendered. The band-limited nature of the data generates sidelobes, or spilled energy, most evident in the neighborhood of bright point-like objects. It is generally considered desirable to minimize these sidelobes, even at the expense of some generally small increase in system bandwidth. This is accomplished by shaping the spectrum with window functions prior to inversion or transformation into an image. A window function that minimizes sidelobe energy can be constructed based on prolate spheroidal wave functions. A parametric design procedure allows doing so, even with constraints on allowable increases in system bandwidth. This approach is extended to accommodate spectral notches or holes, although the guaranteed minimum sidelobe energy can be quite high in this case. Interestingly, for a fixed bandwidth, the minimum mean-squared-error image rendering of a target scene is achieved with no windowing at all (rectangular or boxcar window).

We develop a theory of target detection and classification from physics-based synthetic aperture radar (SAR) signatures. The target-return and clutter-return models are developed from electromagnetic theory. Both stripmap-mode and spotlight-mode SARs are treated. Adaptive-resolution processors, conventional SAR processors, and optimum likelihood-ratio target detectors are presented for multicomponent target detection, and their receiver operating characteristics are compared. Similarly, conventional and optimum likelihood-ratio processors are used for multicomponent target classification. We develop upper and lower bounds and present Monte Carlo simulations for the probabilities of correct classification.

Based on the adaptive importance sampling (AIS) method, an analyzing model examines the effect of coherent and incoherent crosstalk accumulation on the transmission performance of wavelength-division-multiplexed (WDM) networks. The expression of the average bit error probability of a wavelength channel is given. We study the probability distribution of power penalties, which are influenced by the network nodes number, the WDM wavelength number, and the crosstalk level of optical components.

Metal halide arc lamps have a number of advantages over state-of-the-art xenon arc lamp sources, including higher watts-to-lumens conversion efficiency, longer lifetime, and lower cost. However, metal halide source "white light" color, in terms of CIE xy color coordinates and color rendering index (CRI), is generally inferior to that of xenon arc lamp sources. We describe an approach that corrects the color of the characteristic spectral spikes in the metal halide lamp spectrum using a dual notch dielectric thin film filter, producing xenon arc equivalent performance in terms of both color temperature and CRI. Several novel design techniques are implemented, including high index ion-assisted deposition (IAD) dielectric materials and curved spherical filter substrates, to minimize angular spectral shifts in the fiber optically coupled light output. Results show the practical trade-offs that exist between color correction and filter notch depth.