An aberrated laser beam will change shape as it propagates. We use this phenomenon to transform a collimated, uniform-intensity, round beam into a square beam with rounded corners and a fairly uniform intensity. The square beam can be recollimated because no rays cross each other. We found a similar transformation that turns a circular beam into a trapezoidal shape with rounded corners. These aberrating elements can be fabricated using binary optics technology.

Various methods developed to design phase gratings with specified diffraction patterns are systematized. In addition to differences with respect to the numerical technique applied, they differ in their structure modulation schemes. They are described and some of their characteristics, e.g., feature size in their structures, are compared. The finite precision of a fabrication device of phase elements is taken into account. The validity of the diffraction theory usually used for the calculation techniques of phase gratings is considered, dependent on the typical feature size, which results from a modulation scheme.

The potential of electro-optic techniques for application to the testing of high-speed digital electronics is explored. The generic problem of digital testing is discussed along with the requirements for a 2-GHz testing scenario. A testing procedure appropriate for high-speed digital testing is described and the motivation for investigating optical techniques is discussed. A generalized optical architecture for generating, setting, and providing the high-speed digital input data to the device under test (DUT) is presented along with two candidate optical techniques for generating high-speed pulses. This is followed by a description of an optical architecture that is appropriate for receiving and comparing the DUT output signals. Low-cost programmable, picosecond-type delay lines and programmable time-division fiber optic multiplexers necessary for controlling the rate and timing of the input/output data are also presented.

A technique for shape recognition that is invariant to scale and rotation is presented. This technique employs the number of bit quads, the basic 2 x 2 element of binary (0,1) imagery, of each object. The feature vector is a scaled version of the number of bit quads, which allows a distance to be defined between unknown objects and a collection of known prototypes. Recognition is accomplished by utilizing this distance metric as a classifier. An example is provided that recognizes an automobile shape from a set of six prototypes. Several experiments are performed that change the scale and relative rotation of the unknown. In all cases the correct automobile is identified from the set of six prototypes. A second example considers the effects of boundary noise on classification and points out the advantage of employing noise smoothing prior to feature extraction. The technique presented has the advantage of simplicity, pipeline implementation, and low storage requirements.

A new type of matched spatial filter referred to as the quasi phase-only filter (QPOF) has been recently introduced as an optical solution for the phase-only filtering concept. The high-efficiency attribute has been found to link the QPOFs and phase-only filters (POFs). Using computer simulation experiments, the properties of QPOFs are discussed in terms of a signal-to-noise ratio, a peak-to-sidelobe ratio, ability to discriminate, and also the general behavior of the output correlation signals.

The concept of the boundary value problem into image processing is introduced and an image modification technique is presented that works under the condition that the transformation function for a set of pixels is given a priori. For example, if adjoining pictures are taken separately under different illumination and then put together into a single picture, processing the whole picture uniformly can result in some artifacts along the seams, across which image features change abruptly. To resolve this problem, the image features of the border pixels should be transformed to be continuous with the neighboring pictures. Thus, the transformation function for such pixels should be set a priori to meet the above condition, and for the remaining pixels it should be adjusted accordingly. The same technique can be applied to a single picture. For example, if a picture is taken under nonuniform illumination, which causes some regions of the picture to be dark and others to be light, the ransformation function for those regions should be given as boundary conditions. Then the function at any pixel is interpolated from the boundary values. An interactive technique is discussed for giving the boundary conditions and for determining the image transformation function.

A neural-based optical image segmentation scheme for locating potential targets in cluttered FLIR images is presented. The advantage of such a scheme is speed, i.e., the speed of light. Such a design is critical to achieve real-time segmentation and classification for machine vision applications. The segmentation scheme used was based on texture discrimination and employed biologically based orientation specific filters (wavelet filters) as its main component. These filters are the well-understood impulse response functions of mammalian vision systems from input to striate cortex. By using the proper choice of aperture pair separation, dilation, and orientation, targets in FLIR imagery were optically segmented. Wavelet filtering is illustrated for glass template slides, as well as segmentation for static and real-time FLIR imagery displayed on a liquid crystal television.

A method for automating the analysis of images generated from the Fourier imaging (FI) process is described. Fourier imaging is used to observe the evolving topography of wafers as they are being etched in a reactive ion etcher. The focus of the research described in this paper is the segmentation and analysis of images generated from FI. A brief overview of the theory of FI is presented. Segmentation of a Fourier image is done in three steps; local maxima detection, Fourier component extent identification, and boundary tracking. Quantification descriptions for each component are then generated from the segmented image. The algorithm presented demonstrates how it is possible to obtain subpixel resolution automatically in image analysis to collect data that may be used to compute critical dimensions of the microtopography of the wafer substrate.

Computerized analysis of optical fringe patterns has become an accepted method of reducing the time and tedium associated with extracting quantitative data from phase encoded intensity distributions. The computing power of today's personal computers makes digital image processing of moire, holographic, photoelastic, and speckle interferometric fringe patterns both economical and efficient. We review several automatic and semiautomatic image processing algorithms that enable the reduction of both speckle and full-field fringe patterns to quantitative data. The speckle patterns are analyzed using morphological properties, while the full-field fringe patterns are analyzed using standard thinning and fringe order seeding, sinusoidal fitting, Fourier transform, and phasestepping techniques. The mapping that each fringe pattern experiences when being digitized is also discussed so that proper system calibration can be developed. Analysis of geometric moiré, moiré interferometric, photoelastic, and speckle interferometric fringe patterns are presented as examples of digital image processing based data reduction.

A phase-measuring fiber optic electronic speckle pattern interferometer (ESPI) was recently constructed and demonstrated. In this arrangement, phase stepping is introduced by stretching the fiber wrapped around a piezoelectric transducer. Calibration of the phase step is critical in phase measurement techniques for obtaining good phase plots. Methods used for calibrating the stretcher are outlined and the drifts in the phase caused by fluctuations in temperature and mechanical stresses are discussed. Ways to minimize this drift are also presented.

Autonomous target recognition can be assisted by using CO₂ laser radar data. Of these data, range data provide 3-D geometric information and Doppler data detect boundaries of moving targets. A powerful 3-D feature extraction algorithm based on the Hough transform is used to obtain the orientations and dimensions of the target. This information is then utilized by an inference procedure that recognizes targets based on the available evidence from the sensory data. The experimental results using actual laser radar imagery are successful and the procedure can be used for the future development of a model-based expert system for target recognition.

A new type of optical isolator, the nonlinear isolator (NLI), was developed to replace polarization sensitive isolation devices in pulsed, solid state laser systems. The NLI was based on a high-reflectivity, stimulated Brillouin scatter (SBS) mirror configured as a Newtonian telescope. Transmission through the NLI was found to be limited to the SBS threshold power. Input powers tested were 50 to 100 times the threshold power. The NLI was operated in a 10-Hz repetition rate laser without introducing noticeable far-field distortion. Partial pulse compression could occur in the NLI. A single triple-pass phase-conjugated YAG amplifier that incorporated the NLI, plus a 2-mJ SLM oscillator, produced 0.83-J pulses of 2.5-ns duration.

In order to reactive ion etch (in a commercially available hex system) a feature in silicon dioxide leaving a vertical sidewall profile with no change in the resultant linewidth relative to the photoresist mask, it was found necessary to utilize a bilevel masking structure with polysilicon acting as the nonerodable hard mask. This hard mask prevents tapering and linewidth changes due to lateral photoresist erosion during the oxide etch. In addition, the etch was performed under conditions producing very little fluorocarbon polymer deposition to prevent lateral mask growth during the etch, and at very low pressure (≈5 mTorr) to reduce off-angle ion scatter-induced etching due to collisions in the plasma sheath. In a nonpolymer-depositing mode, the lack of sidewall passivation was found to promote lateral etching of the oxide at pressures where this scattering occurs. The same phenomena were found to be present when etching nonphotomasked oxide sidewall spacers. Etching spacers in a very nonpolymerizing chemistry at normal operating pressures (≈50 mTorr) caused significant lateral erosion of the spacers. Use of a low pressure, nonpolymerizing chemistry, or a higher pressure, polymerizing process gave spacer widths consistent with the deposited thickness of the spacer material.

A ray-tracing model was used to derive the light scattering Mueller matrix element curves for a dipole near a perfect surface as a function of incident angle, scattering angle, and surface refractive index. This system represents a fundamental system composed of a perfect plane surface and a perfect (Rayleigh) scatterer.

A spatial modulation display is described that permits the observation of a phantom or transparent image by several persons simultaneously and is suitable for medical imaging. The display uses spatial light modulators and large format convex lenses within a Schlieren optical system. The number of sectional images in a three-dimensional image is limited by the number of spatial light modulators. The display is electro-optical and requires no moving parts.

Application of holographic interferometry to nonintrusive temperature measurements in flames has been demonstrated as a viable means in engineering practices. However, the effect of composition changes on the previous investigations was often either neglected or assumed by a simpler relationship owing to lack of the distribution information of gas composition. This study investigates the effect of composition changes on temperature measurements using holographic interferometry by analyzing the composition of combustion gas using a gas chromatograph and measuring temperatures with a thermocouple to provide a comparison basis. Results are given for axisymmetric, laminar, premixed propane-air flames. Fuel-rich flame is found to have complex flame structure, and the effect of composition changes on the reconstruction of interferometric temperatures has to be taken into account. On the other hand, the flame structure in the fuel-lean case is much simpler, and using the linear distribution of molar refractivity in reconstruction of interferometric temperatures yields satisfactory results.

A novel single multifunctional holographic optical element is incorporated into a surface measurement system. As a result the system is lightweight, compact, and simpler than conventional ones. Numerical calculation reveals that submicron resolutions are possible both in the horizontal and vertical directions. Finally, experimental results demonstrate the feasibility of the approach.

A single-step technique for recording rainbow holograms is reported in which neither a lens is used nor is the object translated. The required real pseudoscopic image is produced by optical phase conjugation.

This PDF file contains the editorial “Book Rvw: International Trends in Optics," edited by Joseph W. Goodman for OE Vol. 31 Issue 02

This PDF file contains the editorial “Book Rvw: Acousto-Optic Signal Processing: Fundamentals & Applications," by Pankaj F. Das, Casimer DeCusatis, and Sergey V. Kulakov for OE Vol. 31 Issue 02