An Editorial by the Editor-in-Chief, Don O'Shea.

Angular selectivity, where the geometry of the diffraction pattern depends on the incident direction of the readout beam, is observed in a computer-generated hologram synthesized with a photorefractive Fe-doped LiNbO3 single crystal. This angular selectivity is used to enhance the higher order diffraction patterns. Reconstruction of the strong second-order diffraction enables us to enlarge the effective reconstruction area of a Fourier-transformed computer-generated hologram.

Transparent indium tin oxide (ITO) films have many applications as electrodes in Liquid Crystal displays and EMI/RFI shielding. We have compared two processes for obtaining ITO thin films with low resistivity (below 15B/sq) and high transmittance (above 90%) in the visible region. The first process was deposition using electron beam gun evaporation. The second process was using Ion Assisted Deposition (lAD) of low energy oxygen ions from an end-Hall ion source. In both cases the conductive layer was overcoated with 50-250 nm thickness of a MgF2 layer to enhance the transmittance. When ITO produced by IAD was overcoated with a MgF2 layer, the surface was found to be conductive. The surface was analyzed using the Auger Electron and Second Ion Mass Spectroscopy methods. Traces of indium were found on the MgF2 layer. We speculate that indium that diffused through the overcoat layer gives assistance to the conductivity and enables the measurement of the resistivity from the top surface of the coating. This effect occurred only when the ITO was deposited using IAD. This is an advantage in manufacturing of optical conductive windows. Otherwise there is a need to leave exposed areas of ITO for conductive contacts. The diffusion process was not observed with oxide layers. Atomic Force Microscopy scans show that the IAD process decreased the average roughness of the surface.

A grating interferometer for high-resolution displacement measurements is analyzed. To decrease interferometer sensitivity to inaccuracy of the grating guide, a laser diode beam is focused on the grating surface. The effect of the interferometer geometry on the direction and period of the fringes is analyzed. In addition, the influence of the system geometry on the optical path difference is evaluated. Methods of adjustment of the fringe direction and period and also the zero value of the optical path difference in the interferometer are proposed. The theoretical analysis is verified experimentally by analyzing separately the influence of selected geometrical parameters on fringe direction and fringe constant. The experimental results are compared with regression models obtained by theoretical analysis. In all the analyzed cases, more than 92% of fringe direction and constant variability is caused by the theoretically predicted model of functions.

Metrological feasibilities of the prototype of a high-resolution displacement encoder with a laser diode light beam focused on the scale surface are investigated. Resolution of 0.01 µm has been obtained. The repeatability of the system ranges from 0.02 to 0.03 µm. A new simple reference point detection method that uses a scale grating edge as a reference point has been proposed. We suggest two possible ways of implementation of this method: analog by dc signal component extraction and digital by signal amplitude extraction. The proposed reference point detection technique allows significant reduction of nonlinearity errors of the measuring system. Nonlinearity of the prototype device does not exceed 0.1 µm in the 48-mm measuring range. Due to the application of a focused laser beam, the proposed optical system is extremely insensitive to disturbing shifts and tilts of the scale. The acceptable tilts of the encoder detection head relative to the grating in the prototype device reach about 0.5 arcdeg in all directions. The tolerance of the distance between detection head and the grating is approximately equal to 0.1 mm.

In this work, a Fourier transform technique for automatic analysis of moire´ deflectograms is presented. A squared grating is used to multiplex the information of the deflection in two orthogonal directions in one image. This procedure avoids the necessity of rotating the gratings to obtain the complete deflection information. With this method only two fringe patterns, reference and distorted, are needed to determine the complete deflection information. To deal with irregularly shaped processing areas, a Gerchberg extrapolation method is used. The automatic determination of the carrier as well as the size and position of the reconstruction windows permit the complete and automatic measurement of the deflection produced by an ophthalmic lens in two orthogonal directions. Afterwards, the refractive power maps can be obtained. Experimental results obtained with a progressive addition lens are presented and comparison with measurements obtained with a commercial focimeter are shown showing a good agreement.

A new Fourier transform spectrometer is presented. The novelty of this work comes from the interferometer designed with two identical Wollaston prisms. Thus, the interferogram, formed at infinity in the spatial domain, is independent of the size of the source and of its position. In order to know the characteristics of the apparatus and especially its resolution, we propose the complete calculation of the optical path difference introduced by such an interferometer. Then, by associating the birefringent interferometer with a lens and a linear CCD sensor, we realize a spectrometer with a theoretical resolution about 230 cm-1. Finally, an experimental result is presented, proving the feasibility of the system.

An edge-based wavelet transform is proposed for image compression. In the encoder, first the dominant edges of an image are detected and coded as side information. Then, the wavelet transform (WT) is carried out in such a way that no filtering over previously detected edges is performed. Compression examples show that the edge-based WT achieves good reproduction of sharp edges?even at very low bit rates. Because of the additional side information, the PSNR is typically slightly lower than for standard wavelet coders. But the picture quality scale, an objective quality measure that better reflects the subjective impression, shows superior results for the proposed coder.

In a color-mapped (pseudo-color) image, pixel values represent indices that point to color values in a look-up table. Well-known linear predictive schemes, such as JPEG and CALIC, perform poorly when used with pseudo-color images, while universal compressors, such as Gzip, Pkzip and Compress, yield better compression gain. Recently, Burrows and Wheeler introduced the Block Sorting Lossless Data Compression Algorithm (BWA). The BWA algorithm received considerable attention. It achieves compression rates as good as context-based methods, such as PPM, but at execution speeds closer to Ziv-Lempel techniques. The BWA algorithm is mainly composed of a block-sorting transformation which is known as Burrows-Wheeler Transformation (BWT), followed by Move-To-Front (MTF) coding. We introduce a new block transformation, Linear Order Transformation (LOT). We delineate its relationship to Burrows-Wheeler Transformation and show that LOT is faster than BWT transformation. We then show that when MTF coder is employed after the LOT, the compression gain obtained is better than the well-known compression techniques, such as GIF, JPEG, CALIC, Gzip, LZW (Unix Compress) and the BWA for pseudo-color images.

A fractal image compression scheme is presented which incorporates the vector quantizer (VQ) to reduce the computational complexity in the encoding phase. The high-detail blocks of an input image are approximated by a fast fractal coding, and the low-detail blocks are encoded by the VQ technique. In fractal image coding, most of the time is spent on finding a close match between a range block and a large pool of domain blocks. We propose a two-stage search algorithm to reduce the search space of the domain pool. First, a fast and simple binary pattern matching algorithm is proposed to extract a small pool of candidate domains, and then the gray-level-matching algorithm is used to find the best match from the candidates. In addition, a variable block-size segmentation method is used in our coding system to further improve the image quality. It is shown that the average encoding time is short, and the average speedup factor of 45 is achieved, as compared to the full search fractal coding. Simulation results also show that the proposed scheme can achieve better image quality and higher compression ratio than other fast fractal-based coding schemes.

The optical detection of the in-plane displacements on a scattering aluminum metal sample, produced by laser-induced ultrasound, is reported. The experiments were performed with a GaAs adaptive photodetector operating at l5532 nm using a speckle-based referenceless configuration. In-plane displacements produced by shear and longitudinal ultrasound waves were observed and the estimations of their propagation velocities correspond well to the known data.

A modified double-interaction model is applied to the study of backscattering from metallic particles on conducting substrates. Polarization parallel or perpendicular to the plane of incidence is considered. The agreement with the experiment is successfully checked for metallic spheres of two different diameters and for a metallic cylinder on a flat conducting substrate. Using the model this enables a systematic study of some features of the backscattering patterns and, in particular, the angular positions of the minima, strongly dependent on the size. Some applications of this dependence are proposed, in particular, the possibility of distinguishing the size of the particle on the substrate and the distance from its center to the substrate.

Low-cost power splitting and star-coupling using large-core polymer optical fibers (POFs) are studied. Tapered and untapered mixing rods are used to form 1 x 7 and 7 x 7 couplers. Excess loss and coupling uniformity of a 15 cm length tapered mixing-rod based 1 x 7 coupler are measured to be 1.72 dB and 1.0 dB. The average excess loss and uniformity for a 18 cm mixing-rod length 7 x 7 star-coupler are 1.38 dB and 1.91 dB, respectively.

The phase error caused by sampling the fringe patterns in practical Fourier transform profilometry is discussed. In the fTp method, a grating pattern is projected onto an object surface and the deformed fringe is Fourier-transformed and processed in its spatial frequency domain as well as in its space-signal domain. it has been stated that the fundamental spectrum must separate from zero and higher order spectra, because only the fundamental component is needed for phase retrieval. Here we discuss another kind of spectrum overlapping that is caused by the discrete Fourier transform (DFT). The DFT of a digitized fringe pattern results in periodically equi-spaced frequency islands in the spectrum domain. The higher order spectra from adjacent islands may overlap the fundamental spectrum that is filtered out for phase reconstruction. This kind of overlapping also introduces noise into the reconstructed phase. The conclusion is that to obtain a correct reconstruction of the measured object, the fundamental spectrum does not alias with zero order or higher order spectra in the same frequency island nor with the higher order spectra from adjacent frequency islands. Theoretical analysis is given and the criteria of selecting sampling frequency are discussed. Computer simulations and experiments verified our theories.

This paper describes a high-speed surface measurement system for in-line semiconductor package inspections. The system features the following three points in construction. One is an optics for con- focal imaging. We call the optics a nonscanning multiple-beam confocal microscope. The microscope can get a confocal image in a short time because XY-scanning, which is required in conventional confocal microscopes, is not needed. Two is the algorithm that performs accurate reconstruction of the object surfaces from a few confocal images. The last is a mechanism that performs shifts of the focused plane of the microscope quickly. The experimental system can cover the measurement area of 9.6x9.6x0.64 mm and can measure that area in less than 0.4 s with an accuracy of about 1 µm.

With the intention of precision profile measurement of aspheric surfaces, the Ronchi test is revisited to devise a special scheme of multiple-beam lateral shearing interferometry. A holographic sinusoidal grating is used instead of conventional rule gratings so that only 0 and ± 1 lower order diffraction beams induce necessary lateral shear with high quality. in addition, relative fringe phases of wavefront slopes are automatically obtained by applying phase shifts along two orthogonal directions in sheared interferograms. Finally an elaborate in-line calibration scheme is incorporated to identify the system scale factors with which the 3-D profiles of test surfaces are accurately reconstructed from the measured wavefront slopes. Experimental results prove that the proposed technique is useful, especially for aspheric surfaces with a short focal length.

A laser-diode array (LDA) side-pumped Nd:YAG slab ring laser is described that incorporates a prism-shaped acousto-optic modulator to enforce unidirectional operation and Q-switching. When pumped by the maximum power of 50 W, Q-switched energies of 3.6 mJ and 50 ns duration, corresponding to a peak power of 72 kW, are obtained.

We report on the characteristics of a newly developed high- resolution (640x480 pixels) parallel-aligned liquid crystal spatial light modulator (LCSLM) as a function of wavelength. phase-only operation over a range of 2? rad is easily achieved by operating at shorter wavelengths. We also measure an unexpected effect?the transmitted light intensity changes with applied voltage. Our experiments show that thin- film interference and pixel diffraction effects are responsible for this observed behavior. The diffraction effect is caused by a nonuniform electric field across each pixel. This nonuniform electric field introduces a blazing effect that changes the intensity distribution in the various diffracted orders as a function of applied voltage. These same kinds of effects have been observed with several other twisted-nematic LCSLMs. Because of the complicated polarization effects caused by these twisted-nematic liquid crystal devices, however, the diffraction and interference effects are more easily studied using the parallel-aligned LCSLM.

An optimization procedure for the optical implementation of correlation filters (CFs) in an optical-hybrid frequency plane correlator is presented. Our approach is based on mapping of the given calculated CF values to the values constrained by the available spatial light modulator (SLM) device to achieve the maximum intensity of the output correlation peak. The optimization is provided for the implementation of the CFs using a Sanyo liquid crystal display (SLCD). The commercially available SLCDs are characterized by the phase modulation curves that are (1) nonlinear, (2) of a smaller total phase change interval than desired (0,2?) interval, and (3) significantly disturbed by the coupled amplitude variations. For such a case, the optimization achieved by varying a phase shift parameter is explained theoretically, demonstrated numerically, and confirmed experimentally.

A color-encoded digital fringe projection technique is proposed for high-speed 3-D surface contouring applications. in this technique, a color fringe pattern whose RGB components comprise three phase-shifted fringe patterns is created by software on a computer screen and then projected to an object by a novel computer-controlled digital projection system. The image of the object is captured by a digital camera positioned at an angle different from that of the projection system. The image is then separated into its RGB components, creating three phase-shifted images of the object. These three images are used to retrieve the 3-D surface contour of the object through the use of a phase wrapping and unwrapping algorithm. Only one image of the object is required to obtain the 3-D surface contour of the object. Thus contouring speed, limited only by the frame rate of the camera, can be dramatically increased as compared to that of the traditional phase-shifting techniques. The technique is especially useful in applications where the object being contoured is going through quasi-static or dynamic changes. The principle of the technique is described and some preliminary experimental results are presented.

A three-dimensional (3-D) video system based on integral photography is proposed. In this system, real erect images of an object are formed by a gradient-index (GRIN) lens array as elemental images and are directly captured by a television camera. A large-aperture convex lens is introduced in front of the GRIN lens array to control the depth range of the reproduced image. The video signal of a group of elemental images is transmitted to a display device that combines a liquid crystal panel and an array of convex microlenses, producing a color 3-D image in real time. As a result, full-color and autostereoscopic 3-D images with full parallax can be observed. We confirmed the possibility of a 3-D television system.

We present optimized designs for two switchable achromatic phase shifters using a pair of ferroelectric liquid-crystal devices with retardations of a half-wave mounted between two quarter-wave retarders. The first system can be used with a linearly polarized beam to introduce phase shifts of 0°, 90°, and 270°, that are almost independent of the wavelength, over a wide range of wavelengths. The other system can be used to introduce phase shifts of 0° and ± 120° between two orthogonally polarized beams.

Roughness measurements of engineering surfaces are an important and interesting application for optical sensors. The increased speed, the ability to measure 3-D profiles, and the noncontact mode of optical sensors are of great interest for practical uses. A most challenging task is achieving comparability to the established methods, such as tactile stylus sensors, which are the most commonly used instruments in industry. We show that white-light interferometry is a useful method to measure in a microscopic range as well as with an extended field of view. The determination of the fringe contrast as a function of the focus position enables highly resolved data acquisition on engineering surfaces with a mean roughness of the order of a few nanometers to several micrometers. The measurements show that amplitude roughness parameters of engineering surfaces are not strongly affected by the spatial resolution. A good agreement between the results of a stylus sensor and the results of our optical method are demonstrated on different types of surfaces.