This PDF file contains the editorial “The Dead Tree Strategy” for OE Vol. 37 Issue 09

A model for numerical simulations of the dynamical behavior of the Large Earth-based Solar Telescope is described. The model includes the various subsystems of the telescope optics and mechanics, as well as its live optics system. The live optics system consists of subsystems for active optics, for adaptive optics, and for automatic alignment and guiding. The model also includes various kinds of disturbances, such as atmospheric turbulence and wind gusts. The modeling of the disturbances is also described. The dynamics of the telescope is analyzed using the numerical model. The simulation results confirm the fundamental importance of the live optics system of the telescope. The amount of atmospheric turbulence is found to be critical to telescope performance, although during favorable seeing conditions other sources of image degradation limit the performance. Wind gusts are of little concern during normal weather conditions, especially when the live optics system is used. In addition to the numerical time-domain model, a statespace model is used for frequency-domain analysis and for verification of the time-domain model. The results from the state-space model show that the image motion in the final focus is significantly reduced at frequencies below the eigenfrequency of the fast tip-tilt mirror.

To realize the cyber space that exists only in the computer, a geometric method for a holographic stereogram is proposed. In the calculation of the binocular parallax angle, some additional distance that is not real is considered. Considering the magnification of the projected images, the binocular parallax angle is calculated and horizontalparallax- only (HOP) holograms are made. This method is applicable to both flat and cylindrical stereograms.

The attenuation and input end heating of hollow-glass waveguides are greatly affected by the way in which the input laser energy is coupled into the guides. A theoretical discussion of coupling conditions is related to waveguide loss and local heating, which can occur when the coupling is not optimized. Our results indicate that the optimum coupling for maximum transmission is not necessarily equivalent to optimum coupling to the lowest order HE11 mode. Additionally, it is shown that the input end heating of these waveguides can be reduced substantially with minimal effect on transmission if the waveguide bore size is large.

The authors present a new concept for a spectrometer adapted to low light level, high-speed operation and low spectral resolution. It is based on a spatially modulated Mach-Zehnder Fourier transform interferometer, with a new arrangement to record the fringes. The interferogram is sensed by the use of a focal plane array tilted with respect to the fringe axis. This technique allows oversampling of the fringe pattern, which eliminates spectral aliasing that occurs with the conventional configuration. It extends the free spectral and dynamic range.

Based on the propagation properties of Gaussian beams, a new scheme for an instrument for collimating and expanding (ICE) Gaussian beams for underwater laser imaging systems is proposed, as well as a method for its optimal design. The aberration of a Gaussian beam passing through the ICE is calculated approximately. A design example of the aligning system for the underwater laser imaging system with synchronous scanning is presented.

Image interpolation based on median-type filters is investigated. We study this problem for two decimation schemes that are most commonly used in practice: (1) quincunx lattice and (2) rectangular lattice. For each decimation lattice, we propose a number of interpolation structures that are based on some median or finite impulse response (FIR)-median hybrid filters. Extensive simulations show that the proposed median-based interpolators outperform significantly as compared with linear schemes. To further verify the effectiveness of these medianbased interpolators, we compare them with multilayer neural networks designed through a training process, and still show a preference for the median-based interpolators. As an application, they are used in an interpolative Joint Photographic Experts Group (JPEG) coding scheme to suppress blocking artifacts at very low bit rates.

A color image compression method based on a genetic algorithm and absolute moment block truncation coding (BTC) is proposed. Color images comprise three planes: red, green, and blue. There are very high correlations between the images in these planes. This motivates the use of one common bitmap to represent all three color bitmaps. In order to generate such a bitmap so that the average mean squared error between original and reconstructed images is a minimum, the genetic algorithm is applied. Comparison of results with various methods have verified that the proposed method has higher performance than the other schemes for single bitmap BTC coding of color images.

Adaptive optics and speckle imaging are common methods for improving Fourier domain signal-to-noise ratio (SNR) in astronomical images. These techniques may benefit from linear processing to deconvolve blurring due to the attenuation of high spatial frequencies in the compensated images. Typical linear deconvolution methods require an explicit estimate of the random atmospheric-optical system point spread function or optical transfer function (OTF). In addition, a priori knowledge of the object class and noise are not used in an optimal manner. We apply a vector Wiener filter to photon-limited images degraded by atmospheric turbulence to demonstrate the potential advantages of optimal deconvolution processing. This filter incorporates model-based information about object, OTF, and noise. To our knowledge, this is the first application of complete OTF correlation statistics to the reconstruction of turbulence-degraded images. Computer simulation of binary star images show the vector Wiener filter provides superior reconstructions when compared to the traditional scalar Wiener filter for non-wide-sense stationary objects. Much of this performance improvement can be attributed to variance reduction in the noisy Fourier data at spatial frequencies where the mean OTF is severely attenuated. However, vector Wiener filter performance is substantially degraded with respect to both mean square error and mean square phase error at spatial frequencies where the OTF SNR is less than unity.

A method to calibrate a nonlinear phase modulator is described that is based on the minimization of a function obtained from a sequence of interferometric images. The method is equally applicable to smooth wavefront and speckled wavefront interferometry, allowing convenient in situ calibration for a wide range of interferometer configurations. The main advantage over previous calibration methods is that both the linear and quadratic phase variation terms are measured. The performance of the proposed method is verified by experiments in which the phase shift is determined independently by a Fourier transform method.

Increasing demands for accuracy and speed in manufacturing and international standards of quality control require faster and more precise measurement techniques. Surface inspection and shape control of technical workpieces is commonly done by tactile profilometers. A faster alternative to this mechanical tool can be realized interferometrically. Grazing incidence of laser light onto the technical surface reduces speckle noise significantly. In our setup computer-generated holograms (CGHs) are used both as references for the technical surfaces to be tested and as beamsplitter or recombining element. Each class of workpieces requires specific CGHs, e.g., phase gratings for plane surfaces or diffractive axicons for cylindrical and conical surfaces. An ideally shaped workpiece will result in a zero fringe field. Deviations from the ideal shape will be indicated by interference fringes and fringe distortions. The sensitivity of the interferometer can be adapted to technical needs. The surface deviations of the workpiece are superimposed by adjustment aberrations which can be described mathematically with sufficient accuracy and eliminated by a least squares fit. This measurement technique is demonstrated with workpieces of different shape.

We develop a high-power Er:strengthened-glass laser emitting at the eye-safe 1.535 mm wavelength. To maximize the output parameters of an Er:glass laser, whose power supply must also be used with Nd:YAG, a two-lamp laser head with parallel power forming networks (PFNs) that could be fired with an internal delay is used. The system operates at a slope efficiency of 0.45%, yielding a maximum pulse energy of 330 mJ. Thermal effects are measured, indicating strong thermal lensing, of 16 diopter/kW and mild birefringence induced depolarization of 5% at 200 W electrical power. From this data we determine the radial-tangential average and birefringence elasto-optical coefficients, Cr ,Ø=0.075 ± 0.002 and CB=0.0094, respectively. A TEM00 beam is achieved for a hemispherical resonator configuration. Based on the measurements, a design is presented for improved high-power TEM00 performance using principles based on dynamic compensation of thermal focusing and birefringence correction using a reentrant resonator.

A laser writing lithography system is developed based on the 325-nm UV radiation of a helium-cadmium laser. A custom-built optical system with a modified microscope and computerized exposure and motion stages are the other main components of the system. The lithography system is able to process data input from industry-standard Caltech intermediate form (CIF) graphic files. We achieve a minimum linewidth resolution of 1.6 mm on a positive photoresist-coated silicon substrate written with a 103 UV objective lens of numerical aperture 0.20. Other processing parameters, such as the optimal writing speed and the amount of overlap for pattern generation, are also determined. Application of the laser lithography system is also demonstrated in the fabrication of a UV-detecting metal-semiconductor-metal diamond thin film photodetector and in the direct delineation of polythiophene polymer film.

An optical 3-D imaging system for autonomous vehicle and mobile robot navigation is presented. The system is based on a phase comparison range finder using a 30-mW laser diode modulated at a 5-MHz frequency, and a scanning mechanism, consisting of a nodding mirror and an eight-faced polygon and providing 30 X 30-deg total view with only 0.5-deg instantaneous fields of view for the receiver optics. A Si-avalanche photodiode (APD) optoelectric detector and low-noise preamplifier can detect very low levels of returned energy. With an integrated MC4044 circuit for phase comparison, pixel range information can be represented by gray level on the high-resolution video monitor. A 3-D range image is obtained in the experiment, and a range accuracy of 0.08 m at 10 m outdoors in sunlight is achieved.

Automatic inspection of woven textile fabric is discussed. A two-stage detection process is adopted, with the second stage involving set of novel contextual decision fusion techniques. Three significant problems are addressed: (1) texture feature extraction: Fourier transform features are found to be well matched to the spatially periodic nature of the woven pattern; (2) detection of localized flaw patterns: since prior probabilities are impossible to estimate, and we cannot hope to enumerate all defect classes, a Neyman-Pearson approach is adopted, i.e., flaw detection is via measured deviation from nominal; and (3) detection of extended flaw patterns: the most common flaws are characterized by linear or other cluster shaped patterns; although these are weakly detectable by local detectors, they may be ignored when local detector sensitivity is set to achieve tolerably low false-alarm rates; a localextended contextual decision fusion technique using morphological filtering enables us to achieve very low composite false-alarm rate. The performance of the system is evaluated on samples of denim fabric containing real defects. The predicted composite false-alarm rate is of the order 1 in 1013, or equivalent to 1 per 100 km of fabric roll. Experimental results demonstrate the compatibility of this favorable false-alarm rate with the reliable detection of flaws, which have been chosen for their subtlety and detection difficulty.

A low-cost imaging system capable of recognizing and counting semiconductor good dice is designed and is proven experimentally to be effective. The system utilizes a commercial scanner with the least modification of its inner optics by a beamsplitter-insertion method. Patterns on specular die surfaces therefore can be grabbed clearly, which results in the marks on defective dice being distinguishable. Also, a mask algorithm is developed to count the good dice on an adhesive tape, according to the gray-level histogram and the converted binary picture of the scanned image. The built-in software associated with the scanner, which is reliable and user-friendly, can also be incorporated into the designated algorithm without paying an additional price for system development.

A real-time method for object detection and tracking in outdoor environments where illumination can be very low and not constant is presented. A hierarchical (two levels) change detection method is employed to detect moving objects in the scene. At the first level, a focusof- attention stage is applied to individuate image areas containing moving objects; at the second level, each selected image area is inspected at higher accuracy to improve the detection probability and to obtain an accurate binary reconstruction of the object shape. A background updating procedure is used to adapt the background image to the changes in the scene. Then, an extended Kalman filter is applied to track multiple objects entering the scene. Results are reported on real scenarios in the presence of shadows, occlusions, light reflections, and bad environmental conditions.

This paper demonstrates a convenient experimental technique for measuring the resolution of a digital imaging system. The spatial frequency response of the system is obtained by deriving the modulation transfer function (MTF) from the measured contrast transfer function (CTF). Basic signal-processing techniques are used to establish a relationship between the MTF and the CTF. Experimental methodology is discussed with respect to avoidance of shift variation in the CTF. Discrete Fourier transformation is applied for a power-spectrum analysis of the MTF. Using the CTF as a measure of performance, a series of experiments were carried out to characterize an imaging system based on an integrated CMOS camera. The experimental results showed that this approach can be applied in general, for the assessment of spatial resolution for digital imaging systems.

Bar code scanners are ubiquitous in supermarkets. As a bar code is passed over a scanner, a laser beam scans across the bar code. The scattered light is modulated by the reflectivity of the bars and spaces of the bar code. The bar code scanning process can be described as a 1-D convolution of the scanning laser profile and the bar code reflectivity function. The modulation transfer function (MTF) of bar code scanning is the Fourier transform of the marginal profile of the laser beam. The properties of the MTF of bar code scanning is similar to that of an incoherent imaging system. Measurements of the MTF of bar code scanning at one focal position are presented. The experimental results are then discussed.

Expressions describing field profile, dispersion relation, and propagation power are presented for nonlinear TE waves in a symmetric periodic refractive index structure with two nonlinear claddings beside the guide core. In terms of these formulas, the shape of the field profile of the symmetric nonlinear TE0 fundamental wave is investigated. We find that three shapes of the field profiles of the symmetric nonlinear TE0 fundamental wave exist in the symmetric periodic refractive index structure, and one of them has identical amplitudes in the guide core. The effects of the structural parameters on the amplitude-identical nonlinear TE0 fundamental wave are analyzed, and relative field profiles are illustrated. The results show that when the structural parameters (e.g., the core thickness, the well number, and the ratio of the well thickness to the periodic length) and the propagation power (and hence the effective refractive index) are selected at appropriate values, the amplitude-identical nonlinear TE0 fundamental wave can be formed in the symmetric periodic refractive index structure with two nonlinear claddings beside the guide core.

A method for the detection of small particles by a laser is presented. This method is based on the interaction of the particle with the field in the external cavity of the laser. The radiation scattered back by the moving particle into the laser resonator interferes with the field inside and causes changes in the pump current. The experimental device consists of a single-mode diode or gas laser with an external cavity. Information concerning the number, velocity and size of particles can be derived by processing the laser pump current pulses. This method is capable of detecting the movement of a single micrometer-diameter particle.

A memory matrix provides output vectors that are specified by the corresponding input vectors. If the input vectors represent input characters, the memory matrix performs character recognition. When the input characters contain noise, it is difficult to recognize the characters. To overcome this difficulty, we generate a new memory matrix by using singular value decomposition and manipulating the singular values. The effectiveness of the memory matrix is made clear by recognizing 26 alphabets characters containing noise with an optical recognition system.

A basic phenomenological model for photoinduced conductivity suitable for a wide variety of photosensitive and photoconductive materials is developed. The modulation of photoconductivity and creation of an internal electric field by spatially modulated light patterns in different materials are described. The moving gratings of photoconductivity and electric fields can be used for optical tweezing of harmful impurities in the liquid solutions.

A new method for position measurement with CCDs is presented. Two-dimensional position coordinates can be precisely measured in a short time with a special optical system having two linear array CCDs. The experimental setup with a signal-processing unit is described in detail. Experimental results are shown, and the sources of error are analyzed.

The ways in which an optical channel can be used to control the radiation divergence of a hot surface are investigated. The surface with the channel is a thermal beacon, which can be used for object tracking. A semiconical shape is used for this channel. The divergence is controlled by optimizing the channel parameters with respect to the cone angle 2? and the radius ratio of the two channels’ bases. This is to maximize the power radiation in a narrow range of directions about the surface’s normal vector. In contrast to popular computer simulation methods such as Monte Carlo, a mathematical model is used for this purpose. The channel is mapped onto a two-dimensional space, and then the optimization is carried out. It is shown that for a range of 20 deg and a radius ratio of 2, the optimized value for a is about 12 deg.

Good initial parameters are important for the application of adaptive wavelets to signal representation. An algorithm for the selection of good initial parameters is presented. The algorithm introduces negligible additional computational complexity into the signal representation process. Its effectiveness is demonstrated by numerical results on the representation of signals obtained from contours of coastlines.

A newly developed sol-gel gel-glass based thermochromic material is studied from the point of view of its application to temperature sensors. This work shows the dynamic response of the thermochromic material both to temperature and to light radiation, exhibiting high repeatability. Also it is possible to store the maximum achieved temperature values.

The influences of TiO2 contents on the structural, optical, mechanical, and moisture resistant properties of CaF2-TiO2 composite films prepared by reactive ion-assisted codeposition are systematically investigated. The CaF2 films deposited at an ambient substrate temperature are found to have superior optical, mechanical, and moisture resistant properties with the addition of 10 at. % TiO2. The structure of this film changes from polycrystalline CaF2 to a mixed phase of amorphous TiO2 and polycrystalline CaF2. The hardness of composite films containing 45 at. % TiO2 is even higher than that of pure TiO2 and glass, which is attributed to the isolation of the crystalline CaF2 grains by the interconnection of the amorphous TiO2 dispersoids.

Thin film wave plates are constructed by the oblique deposition of dielectric material onto glass substrates. Two basic designs incorporating biaxial columnar thin films have been proposed. The singlecolumn- angle plate provides different sensitivities of retardance to angular tilting, but suffers from thickness (and hence retardance) wedging. The double-column-angle plate is relatively insensitive to tilt and substantially free of wedging. However, both basic designs are susceptible to the ingress of atmospheric moisture, which has the effect of reducing the retardance. In this paper we describe modifications to the basic designs that seal the wave plates against the uptake of atmospheric moisture. The modifications eliminate wedging in the singlecolumn- angle plate, but the characteristic angular sensitivities of the basic designs are retained.

The chief principles and properties of optical reflection and transmission guided-mode resonance (GMR) filters are presented. These devices are based on GMR effects in dielectric structures comprising gratings and homogeneous thin films. Detailed characteristics are calculated using rigorous coupled-wave analysis for bandpass filters operating in reflection and transmission for TE- and TM-polarized incident waves. High resonance efficiency with narrow or wide linewidths is achievable with near-zero reflectance or transmittance sidebands over extended wavelength ranges. To illustrate the potential of this technology, example GMR reflection and transmission characteristics are presented for filters operating in the visible spectral region. Excellent reflection-filter features are found when antireflection conditions prevail away from the resonance wavelength. Furthermore, long-range, low sidebands are found to be obtainable for a single-layer GMR reflection filter with a TM-polarized plane wave incident at the Brewster angle. The transmission filter is optimized when the structure is highly reflective off resonance. GMR filter fabrication tolerances are discussed with examples illustrating the sensitivity of the filter center wavelength to variations in layer thickness, grating shape, and incident angle. GMR filters are found to exhibit loss-dependent wavelength shifts such that the reflection peak occurs at a different wavelength than the corresponding transmission notch. However, under antireflection conditions, the resonance location becomes insensitive to loss. Finally, reflective GMR thinfilm structures that support multiple waveguide modes are studied. These devices exhibit unique characteristic angular and spectral signatures.

Dielectric microfilters are designed and developed providing different filter functions on 3-in. substrates. Combining several coating procedures, microlithographic techniques, and dry-etching processes, spectral properties of basic filters are modified within patterns with feature sizes down to 5 µm, resulting in large-area filter patterns (>5 cm2) with multiple spectral characteristics and vertical edge profiles. By applying these techniques within a three-step-iterative procedure red, green, and blue filters (RGB) are arranged edge to edge on one substrate to form a multispectral dielectric microfilter array for use as a key component in a local resolving color sensor. These microfilters are arranged in an array of 19 identical hexagons consisting of three rhombi each. The number of these arrays amounts to 81 on a single 3-in. substrate. A modular setup of a compact local resolving color sensor is presented, consisting of Si p-i -n photoelectric cells, dielectric microfilter arrays, an imaging lens, and a final glass cover plate with an IR-blocking filter.