This PDF file contains the editorial “Preview of Coming Attractions” for OE Vol. 36 Issue 09

Processing of color image data using directional information has received increased attention lately due to the introduction of the vector directional filters. These rank-ordered type filters utilize the direction of color vectors to enhance, restore and segment color images. First, the different vector directional filters already in use are presented, focusing on their similarities and differences and, second, new adaptive vector directional filters are introduced. Fuzzy as well as nearest neighbor structures are utilized to determine the weights in the proposed adaptive filters. Simulation studies involving color images are used to assess the performance of the different vector directional filters and to compare them with other commonly used nonlinear filters. The simulation studies reported indicate that the new adaptive filters are computationally attractive and have excellent performance.

One of the oldest and simplest techniques for the determining the thickness of a thin transparent film is based on the evaluation of the interference colors produced by the film. Though its accuracy is limited and the technique itself has been superseded by many advanced techniques, it still plays an irreplaceable role in observing moving thin fluid lubricant films. A computer-aided system for the reconstructing the shape of a thin fluid film from chromatic interference fringes is presented conceptually, and parts of the system are demonstrated. Quasistatic fluid films were generated in an experimental apparatus operating as a twolayer Fizeau interferometer. Chromatic patterns produced by the Tolansky method were photographed and digitized. The CIELAB color difference equation was used for comparing interferograms with the digital color chart to determine the film thickness. Three-dimensional mesh surface plots of the film shape with high thickness resolution were generated using techniques of image processing and computer graphics. The limitations and accuracy of the proposed system are discussed, and its validity was checked by observing a lubricant’s ability to create a coherent film under various conditions.

We report the first experimental realization of the incoherenterasure joint-transform correlator operating on the erasure nonlinearities of degenerate four-wave mixing in a real-time holographic medium. Our experiment used the joint-transform spectrum produced on a shorterwavelength laser beam to erase a longer-wavelength four-wave mixing hologram in Bi12GeO20. We demonstrate a transition from matched-filter correlation to phase-extraction correlation by increasing the erasure beam intensity, in quantitative agreement with the weak-coupling photorefractive model and simulation results.

A robust technique for achieving nearly diffraction-limited imaging through the Earth’s atmosphere is developed, which makes it possible to approximate the angular Fourier spectrum of any desired object without any recursion procedure for reconstruction of the phase spectrum. The proposed method is based on the fact that the N’th-order spectrum at certain two-dimensional subplanes in (N-1)-dimensional frequency space may be considered as a result of low-pass filtering of the object. It is significant that the filter band becomes much wider than the object frequency band and also that the filter characteristic becomes real with increase in the order N. Undistorted high-order spectra within one of the subplanes can be measured by pupil-plane interferometry technique. Analytical results have been verified by numerical simulation.

We show how phase-only filters can be used in incoherent optical correlators for security applications such as access control, identification, or authentication. As a specific example, a biometric signature, a fingerprint, is encoded in a phase-only representation. The phase encoding is accomplished with the method of generalized projections onto constraint sets implemented by an iterated Fourier transform algorithm. The operation of an incoherent optical security system using both a phase-only filter generated with the generalized projections algorithm and a phase-only matched filter is simulated. The results demonstrate that the selected access pattern was accepted while a false pattern was rejected by the security system and that better recognition and discrimination performance was attained with the phase-only filter produced by the generalized projections algorithm.

A new pipelined time-division multiplexing optical bus for implementing a linear-array parallel computer architecture is proposed. In this system, switches are introduced on the receiving segment of the bus to control the signal delays on the optical waveguide. The states of switches are dynamically programmable under the control of processors according to computation needs. In conjunction with coincident pulse processor addressing technique, the reconfigurability of signal delays becomes an integral part of parallel computation, as demonstrated by parallel algorithm design examples. The linear processor arrays based on such buses can be used as building blocks to construct parallel architectures of higher dimensions to achieve improved scalability and performance.

Based on a recently prescribed simple and novel approximation of the fundamental mode, we present analytic expressions for the Petermann II spot size, suitable for evaluating the dispersion parameters of single-mode graded-index fibers. With these expressions, we calculate the group delay dispersion factor and also the normalized waveguide dispersion coefficient. On comparison, our formulation is shown to be superior to the Gaussian approximation and predicts the parameters identically with the exact numerical techniques for step and parabolic index profiles.

A new method of determining particle diameter from a farfield in-line hologram is proposed. The method is based on the following properties of an in-line hologram of small particles. The fringe interval of the hologram decreases with radius from the symmetrical axis. Therefore, the corresponding spatial frequency continuously increases with radius. The Fourier transformed (FT) pattern of the hologram preserves the properties similar to those of the original fringe pattern. In the FT plane, the uniform background and scattering term contribute only to the very low frequency region. The interference term, therefore, can be figured out, and it is the only contribution to the higher frequency region. It is shown that the FT pattern has a white ring zone, which corresponds to the zero point of the envelope function of the original fringe pattern. Since the position of the ring contains information on the particle diameter, it is demonstrated that measurement of the diameter of this ring provides a powerful and reliable way of obtaining particle diameter.

An extended analysis of the effects of uncompensated fiber dispersion on the fringe visibility of a fiber optic interferometer is developed, with particular emphasis on stellar interferometry. Both material and waveguide dispersion for single-mode, polarization-preserving fibers are considered. It is found that dispersion causes the fringe visibility curve to broaden, decrease in contrast, shift its centroid location, and in some cases become asymmetric. It is also shown that when the interferometer is operated at wavelengths near 1300 nm, cancellation of second-order material and waveguide dispersion significantly improves the fringe visibility. The theoretical results are verified experimentally at both 672 nm and 1307 nm using a fiber optic Mach-Zehnder interferometer.

Holographic microscopy for the simultaneous interferometric determination of all displacement components is described. The recording and the evaluation procedures are optimized by three illumination directions and conjugate reconstruction, respectively. Microscopic observation is completely separated from holographic recording. The holographic microscope performs maximum flexibility of magnification combined with high imaging accuracy. The phase-shift technique and Fourier analysis with a carrier frequency are applied for interferogram evaluation. Both methods are compared regarding the measurement range, accuracy, and handling. In-plane and out-of-plane displacement components can be measured simultaneously by both evaluation methods. A cantilever beam, a circular plate, and a surface-mounted microresistor are used to demonstrate the capabilities of the holographic microscope.

A novel demodulation scheme for the ranging of reflective markers is presented. This method is useful for implementing in-line multiplexing of displacement and temperature sensors based on lowcoherence interferometry. It allows the discrimination of reflective markers such as air-gap connectors or other partial reflectors spaced by as little as 0.1 m and the measurement of deformations occurring between two successive reflectors with a resolution of 2 ?m. The multiplexing of two displacement sensors is demonstrated experimentally. This type of sensor is especially useful for the long-time geometrical monitoring of large structures.

We present a noise reduction filter for the phase unwrapping of data from phase-shifting speckle pattern interferometry. This filter is effective in reducing the noise in wrapped phase maps without affecting the edges of the phase jumps, so that a simple and fast unwrapping algorithm can be used. We also discuss a data analysis strategy, including a routine for the recovery of unwrapping errors. The filter performance has been evaluated on real data from a fiber optic phase-shifting speckle interferometer, which we built for the analysis of out-of-plane deformations. The phase shifting is introduced by current modulation of the diode laser source. Some results relative to the analysis of very noisy phase measurements are presented.

We propose two methods to perform shearing in electronic speckle pattern shearing interferometry (ESPSI). These new methods of shearing make the setup compact and easy to align. The first system we propose consists of two parts: (1) the object is imaged onto an intermediate ground glass and (2) the image on the ground glass is in turn imaged onto the photosensor of a CCD camera. A holographic grating placed in front of the ground glass screen is used to shear the two images and to introduce phase stepping. The separation between the grating and the ground glass plate is used to control shearing. In the second method, two identical holographic gratings separated by a distance introduce shearing and the distance between two gratings can be used to control the size of shearing. Phase shifts to be employed for phase measurements are introduced by displacing the grating.

Two methods are described for absolute measurements of the deviations from flatness of optical surfaces using a Fizeau interferometer. The first method involves averaging measurements with a reference surface that is rotated in steps. Two sets of measurements are made, one with the test surface in the optical path and the other with the test surface removed. The errors of the test surface are then obtained directly from the difference of the two data sets. The second method, which is preferable where the highest accuracy is required, involves averaging the results of intercomparisons of three surfaces, taken two at a time, with the surfaces rotated in a series of steps. The errors of each of the surfaces are then obtained from the differences of these averages. Only simple calculations are required, and random errors are reduced significantly by the process of averaging.

The effect of image patch size on phase difference determination by fringe pattern matching is discussed. The standard deviations based on the measurements from different sizes of image patches are derived from the statistical analysis of the fringe pattern matching process. The effect of image patch size on phase difference determination is examined by both computer simulation and experimentation. The background noise levels of interferograms are obtained by computer generated speckle noise, Gaussian noise and salt and pepper noise added to ideal fringe patterns, and the results from different sizes of image patches were acquired by fringe pattern matching in the simulation. The experimental results were also achieved from different sizes of image patches. The computer simulation and experimental results have shown that the larger image patches have a better accuracy in the presence of noise, which is in accordance with the results from theoretical analysis.

A new high-speed 2-D fringe analysis technique in the time domain using an electric circuit based on frequency demodulation is described. A 1-D fringe analysis system based on this new technique has already been built, and its performance and characteristics were reported. With that system, a 1-D fringe pattern could be processed every 10 ms. The accuracy was better than 1/20 fringe. The principle of 1-D fringe analysis is expanded to two dimensions. New electric circuits that can process the horizontal (X) and vertical (Z) directions simultaneously are built. The principles are proposed for the design of such circuits, which combine two outputs, one for the X direction and the other for the Z direction. A new 2-D fringe analysis system is then built using both analog and digital processing circuits. Using this new fringe analysis method, high-speed 2-D image processing can be achieved. The system can process 14 images/s. The characteristics of a laboratory prototype of this fringe analysis system are tested. The error sources of the system are checked with a computer simulation.

A laser diode interferometer that uses an optical fiber is proposed. The laser diode simultaneously functions as a light source, a phase modulator, and a phase compensator. Detection of the vibration and reduction of external disturbance are carried out using a feedback control for the injection current of the laser diode. Thus it can measure vibration accurately in real time with a simple signal processing circuit. The optical fiber not only functions as a flexible probe, enabling us to measure the vibration of an object that cannot be moved onto the optical bench, it also acts as a reference mirror, thereby simplifying the unit construction. The principle of the feedback control in laser diode interferometer is also described in detail.

The stabilization of a multiwavelength CO2 is very complex. The difficulty arises from the physical process inside the laser tube, which causes some uncertainty and/or imprecise factors in control. In this case, fuzzy logic control is more appropriate. A self-organized fuzzy controller is presented. By means of this fuzzy controller, a dualwavelength frequency-stabilized CO2 laser with high precision can be controlled effectively, and a satisfactory result is obtained.

The possibility of increasing the resolution and accuracy of the photomask fabrication process is discussed when using a laser pattern generator. The proximity effect is first taken into account in this technique. The redistribution of laser beam energy in photoresist, which results in pattern distortions, can be characterized and used for the distortion compensation. The method for measuring absorbed energy density in photoresist is proposed, and experimental results are obtained for conditions used for a standard-type of photomask manufacturing process.

We have designed a dual-beam magneto-optical (MO) storage system to test the dynamic storage properties of MO disks. The characteristics of this dual-beam system are demonstrated. Magnetic field modulated direct overwrite, which is a promising technique for highspeed MO storage, is realized on TbFeCo MO disks with this dual-beam MO system. The effect of light intensity, magnetic field intensity, and linear velocity of the disk and the modulating frequency variation on carrier-to-noise ratio is investigated.

A new method called four-map absolute distance contouring, based on the shadow moire´ technique, is described. In this system, the period of a sinusoidal grating is varied through its rotation, with the effect that the phase of the moire´ pattern is also changed. By selecting suitable rotation angles, four images at different grating positions are acquired, from which the absolute distance from the object to the grating can be determined. The theoretical analysis is presented for the method, which has been verified by suitable laboratory experimentation. The measurable range is directly proportional to the period of the grating and inversely proportional to the angles through which the grating is rotated. The results show that the method is fast and accurate.

The extremely high data rates of optical computing technology (100 Mwords/s and upward) present unprecedented challenges in the dynamic memory design. An optical fiber loop used as a delay line is the best candidate for primary, dynamic memory at this time. However, it poses special problems in the design of algorithms due to synchronization requirements between the loop data and the processor. We develop a theoretical model, which we call the loop memory model (LLM), to capture the relevant characteristics of a loop-based memory. An important class of algorithms, ascend/descend—which includes algorithms for merging, sorting, discrete Fourier transformation (DFT), matrix transposition, and multiplication and data permutation—can be implemented without any time loss due to memory synchronization. We develop both sequential and parallel implementations of ascend/descend algorithms and some matrix computations. Some lower bounds are also demonstrated.

Both form and roughness of diamond-turned surfaces are simultaneously inspected by a method combining the angular deflection and light scattering techniques. A laser beam scans the sample under test. The reflected and scattered light from the sample surface is collected by a CCD array. The direction of the specularly reflected light gives information on the surface slope, which in turn results in surface form by an integration operation. Surface roughness information is encoded in the scattering and can be recovered. Based on this concept, it is possible to develop an instrument for inspecting the diamond turning process on the production line.

Measurements of aspheric surfaces by interferometry are possible but technically complicated. We present a simple laser-CCD camera setup based on the analysis of diffraction spectra for the surface form measurement. A slit is illuminated by a helium neon laser beam. A sample surface works as a mirror to direct the diffraction spectra of the slit to the CCD camera. The surface form of the sample redistributes the intensity of the diffraction spectra. This enables us to reconstruct the surface form from the measured diffraction spectra. This method has two particular features. First, no reference surface is necessary and therefore there is no special difficulty in measuring aspheric surfaces. Moreover, in comparison with the common focal plane light intensity measurement, we measure the light intensity distribution in the diffraction plane (the diffraction spectrum). It is not necessary to measure a very sharply dropping intensity distribution. In turn we do not need a detector with very broad dynamic range and very high special resolution.

By extension of the transfer-matrix technique from the real domain to the complex, complex expressions describing field distributions and eigenvalue equations are presented for both TE and TM modes of lossy periodic refractive index optical waveguides. In terms of the eigenvalue equation presented, mode propagation and loss characteristics of lossy periodic refractive index optical waveguides are analyzed. It is found that coupling interaction exists between the wells, and causes splitting of both the mode propagation constant and the mode loss coefficient; as a result, corresponding mode bands are formed. It is also found that the guided structural parameters strongly influence the coupling and the mode splitting as well as the bandwidth, so these effects are also discussed in relation to the period length, the thicknesses of the wells and the barriers, and the ratio of the well thickness to the period length.

The stimulated Brillouin scattering (SBS) reflectivity of bulk fused-silica glass is measured at the wavelength of 1.06 mm. At long pulse pumping using a longer focusing lens, a fused-silica glass shows high SBS reflectivity of approximately over 95% with no damage observation at a pumping energy of 380 mJ in a pulse duration of 15 ns. We have found that the laser-induced damage threshold at a high SBS reflectance condition is due to reduction of the transmitted power to focus. This makes it possible to operate with high performance in all solid state lasers using a phase-conjugated mirror with fused-silica glass.

A single half-wave retarder can be used to rotate the plane of polarization of a linearly polarized beam through any desired angle without any change in its intensity, but only with monochromatic light of the appropriate wavelength. We describe two simple combinations of birefringent retarders with a linear polarizer that can be used to produce a controllable rotation of the plane of polarization that is independent of the wavelength, with only minor variations in intensity.

A fringe analysis technique is proposed to automatically measure 3-D object shape. A grating pattern is projected onto an object, and the grating pattern deforms in accordance with the 3-D object. This deformed grating image is analyzed by means of the subfringe integration algorithm (SIA), in which the phase is retrieved using N bucket integration. Only one frame of the image is sufficient to obtain the phase distribution and the object shape at every pixel on measured object. Theoretical analysis, experimental results, and simulation calculations are presented.

Dynamic inspection of moving objects is a significant task in industrial machine vision systems. A CCD camera operating in time delay and integration (TDI) mode is equivalent to a digital drum camera, providing possibilities for dynamic inspection of moving objects (either rotating or translating on industrial platforms). We report some advances in the application of TDI cameras for the inspection and profiling of moving objects. The method is based on conventional light projection systems that are widely used in industry. The TDI system generates an on-line scanning moire´ display that could assist operators to identify defects on objects such as dents. Conventional projection systems use mechanical or interferometric types of fringe projections, which is not desirable in the industrial environment. The TDI system makes use of temporal modulation of a laser diode, which could be easily controlled by a PC or by the output ports in vision systems. In addition to the details of system implementation, we also describe two algorithms for unwrapping the deformation or shape profile of the test object based on the fast Fourier transform and sinusoidal fitting of the recorded patterns.

A compact design of an acousto-optic high-speed infiniteimpulse- response filter for line enhancement or notch filtering is introduced. Such filters can find applications in communication systems for signal-processing tasks such as carrier and bit recovery, signal prefiltering for noise reduction, interference or jammer cancellation, and channel equalization. Stability of such filters is an important concern because of the feedback and the nonlinearity in the acousto-optic cell response. Stability conditions are derived. Theoretical analysis and numerical experiments show that an acousto-optic-cell-based infinite-impulseresponse filter can enhance the signal-to-noise ratio at the filter output by 15 to 30 dB or more, depending on the design.

A polarization control method is applied to suppress the e´ talon fringe, and experimental results are described. It is found that this method can suppress an e´ talon fringe of the order of 102-6 in terms of the equivalent absolute absorption value, 1/100 of the off-controlled condition. This technique enables our tunable diode laser absorption spectrometry (TDLAS) system to measure atmospheric methane of about 2 ppmv concentration with ambiguity within 102-4 ppmv (0.1 ppbv). This scheme is useful for the portable TDLAS systems because of its simplicity.

A complete forward-looking IR (FLIR) automatic target cuer/ recognizer (ATC/R) is presented. The data used for development and testing of this ATC/R are first generation FLIR images collected using a F-15E. The database contains thousands of images with various mission profiles and target arrangements. The specific target of interest is a mobile missile launcher, the primary target. The goal is to locate all vehicles (secondary targets) within a scene and identify the primary targets. The system developed and tested includes an image segmenter, region cluster algorithm, feature extractor, and classifier. Conventional image processing algorithms in conjunction with neural network techniques are used to form a complete ATC/R system. The conventional techniques include hit/miss filtering, difference of Gaussian filtering, and region clustering. A neural network (multilayer perceptron) is used for classification. These algorithms are developed, tested and then combined into a functional ATC/R system. Overall primary target detection rate (cuer) is 84% with a 69% primary target identification (recognizer) rate at ranges relevant to munitions release. Furthermore, the false alarm rate (a nontarget cued as a target) is only 2.3 per scene. The research is being completed with a 10 flight test profile using third generation FLIR images.

We describe the calibration and operation of a high-speed underwater scanning depth finder that has been designed for workspace sensing (that is, for ranges of 2 m or less). It uses standard components mounted in an underwater housing fitted with a planar viewing port. The use of a laser line forming element coupled with a single galvanometer mirror system enables fast data capture but introduces alignment problems with standard domed ports. Hence a planar interface is used. This results in the triangulation baseline varying as a function of scan angle. We present a simple but novel solution for the calibration and use of such a device. The effect of the varying baseline is modeled, and a calibration/depth calculation process is presented. Results obtained from using the device in a test tank demonstrate the performance of the system.

A self-contained diver-operated underwater instrument is developed to make in situ measurements of spectral fluorescence and reflectance of benthic marine organisms and substrates. The instrument, designated the benthic spectrofluorometer (BSF), is built around a single-board spectrometer with a 1024-element CCD array. Light input to the spectrometer is via a fiber optic cable. In fluorescence mode, the unit provides manual user-selectable excitation wavelength and measures fluorescence emission over the full visible spectrum. The BSF can also measure the spectrum of downwelling ambient light or of light reflected from surfaces of interest, enabling calculation of spectral reflectance. The instrument has been used successfully at several field locations, primarily for investigation of optical properties of coral reef organisms and in collecting baseline data in support of remote sensing systems. The instrument is described and representative data are presented.

There is currently great interest in determining optimal multiband sensor parameters for detection of tactical targets with known and unknown spectral signatures.1,2 Because many of the algorithms used to evaluate these parameters are iterative and computationally expensive, and generating receiver operating characteristics (ROC) curves requires that large amounts of data be processed at each parameter setting, it is desirable to have a quick and easy way to measure performance with a given set of parameters. The hope is that this performance metric will prove to have a direct relationship to ROC performance.

The value of any good reference book lies in the frequency of its use and the quality of the information it provides. In our laboratory, this book has already been extensively used by myself and others to support our work on nonlinear optical materials. The chapter ‘‘An Introduction to Photorefractive Polymers’’ provided an excellent background and key references, to which I referred as I began a new project in this area.