This PDF file contains the editorial “Editorial: What Is a Reference?” for OE Vol. 34 Issue 07

This PDF file contains the editorial “Guest Editorial: Optics in Switzerland, Part 1: Federal Institutes of Technology” for OE Vol. 34 Issue 07

A new type of 2-D polarimeter is developed for use in high-resolution observations of solar magnetic fields. Two piezoelastic polarization modulators are used in combination with charge-coupled-device (CCD) image sensors to simultaneously record all four Stokes parameters. Demodulation of the fast 50 and 100 kHz intensity modulations produced by the piezoelastic modulators is achieved by CCD sensors used as synchronous integrators sensitive to a single frequency. The temporary buffer storage needed to separate the charges generated during the two modulation half periods is obtained by covering every second row of the CCD sensors with an opaque mask. The charges are shifted back and forth between the photosensitive uncovered and the adjacent storage rows in phase with the modulation. The polarization signal is calculated from the difference between the charges accumulated in two adjacent rows. A separate CCD sensor is needed for each normalized Stokes parameter Q/I, U/I, or V/I. Because the high modulation frequency lies well above the seeing frequencies occurring in solar observations, precision polarimetry becomes possible. We have demonstrated the capability of this new type of instrument to achieve a polarimetric sensitivity below 10^-3 in a single frame. By frame averaging the noise level in the fractional polarization can be reduced to the order of 10^-5.

Starting with the basic equation of holographic interferometry for arbitrary deformations, a generalization of the real-time technique with modification in the case of large deformations is laid out. Ultimately, the problem of recovering previously invisible fringes when reconstructing and the following fringe analysis is discussed. In the past, necessary equations derived from two first derivatives have been established to ensure a proper spacing and a sufticient contrast of these fringes, by a careful choice of the modification parameters at least locally around some point for such a general setup. To make the fringes visible not only locally but also in a larger domain, further equations resulting from the second derivatives of the optical path difference must be considered; in other words, the remaining modification parameters must be determined in such a way that the optical path difference becomes quasi-stationary in an extended domain. This second derivative reveals a particular relation to the aberration theory of the holographic image. It is composed of a mechanical deformation term containing the curvature change of the object surface, a completely dual term of the virtual optical deformation because of the modification, also implying the astigmatism of the image points, and finally a mixed term that is dual to itself. Two illustrative examples of the application of this second-derivative expression are discussed. First, with a small shift of the reference source but no object deformation, a previous result is confirmed, which also shows explicitly how to alter the fringe curvature. Second, the standard case of small isometric object surface deformation without modification reveals a result which allows the determination of the curvature change of Kolter-Sanders of the object surface.

The projection moiré technique enables quantitative measurements of the shape of an opaque curved object surface in space. In contrast to the actual literature, where the interpretation of moiré fringes is mostly limited to particular geometrical configurations, we present a strong mathematical tool that makes it possible to accurately analyze more general and complicated geometrical cases. We therefore introduce a mathematical model based on the calculation with projectors and use tensor calculus to deduce the general equations of projection moiré. Emphasis is put on relative moiré, which is used in most experiments, and on difference moiré, which is generally used to calibrate optical systems. The concept of a sensitivity vector, which comes essentially from holographic interferometry, is also introduced. Using a computer-based image processing system, a numerical experimental verification of the obtained theoretical tensor equations is performed. Simultaneously, we describe how to calibrate an optical setup and gain evidence of a few nonlinear effects. This shows which parameters of the setup are of importance and should be carefully controlled. Moreover, we treat some well-known special cases to demonstrate the agreement with the existing literature.

We present a study concerning the realizability of a syntactical image coding scheme for the modeling of brightness perception. This scheme is based on a multiscale Gabor analysis, a symbolic line and edge representation, additional low-pass channels, and nonlinear amplitude transfer functions. It is shown that this scheme, although not optimized, can already predict various brightness effects such as illusions. Although only studied in the 1-D static case, and without going into details concerning quantization effects, we argue that such a brightness model may be advantageous in digital image coding applications.

A novel in-line multiplexing scheme for optical displacement and temperature sensors based on low-coherence interferometry is presented. It allows the measurement of deformations with a resolution of 10 μm and temperatures with a resolution of 1°C m. The multiplexing of two displacement sensors and one temperature sensor along the same fiber line is demonstrated experimentally, and a theoretical calculation for a system with 10 sensors is presented. This type of sensor would be especially useful for the long-time monitoring of large structures.

The application of laser photoacoustics to two different areas is discussed. First, laser-induced spallation and interferometric detection of transient surface displacements is proposed as a powerful noncontact tool for the investigation of adhesion properties of solid surface coatings. Results for nickel and plasma-sprayed ceramic coatings are presented. Delamination processes at the interface between substrate and coating could be detected with excellent spatial and temporal resolution and adhesion strengths in the 0.2 to 2 GPa range be determined. Second, laser photoacoustic spectroscopy is applied to trace gas monitoring. An automated mobile CO₂ laser photoacoustic system is employed for in situ air monitoring with parts per billion sensitivity in industrial, urban, and rural environments. An improvement in detection selectivity for multicomponent gas mixtures is achieved with a continuously tunable highpressure CO₂ laser with a narrow linewidth of 0.017 cm^-1. A CO laser photoacoustic system previously used for the analysis of motor vehicle exhausts is now employed for studying dimerization phenomena in fatty acid vapors. Finally, emphasis is put on the development of widely tunable, narrow-band, mid-IR laser sources based on optical parametric oscillation or difference frequency generation employing tunable diode lasers and AgGaSe² as nonlinear material.

Comparative holography solves a key problem of nondestructive evaluation: the comparison of the mechanical behavior of two nominally identical specimens subjected to the same loads. The method provides contours of equal differences in displacements of two stressed objects. This feature makes the method particularly attractive in flaw detection. The aim is to briefly outline the principles and practice of comparative holography with an emphasis on recent developments.

Characterization and optimization of KNbO₃ crystals for photorefractive applications over an extended spectral range is described. Intrinsic properties are used to describe the refractive index response to space-charge field gratings. Extrinsic properties that are important for the photorefractive effect, such as absorption, photoconductivity, charge transport, and trapping, are discussed. Some results on the extended IR response of crystals doped with Fe, Ni, Cu, Ce, Mn, and Co are presented. Post growth annealing at temperatures of 400 to 900°C in a controlled atmosphere is shown to modify the charge-transport parameters, therefore also modifying the response time of photoinduced refractive index changes.

We have developed a new integrated narrowband spectral filter, which consists of a planar waveguide covered with a thin polymer film containing molecules, which undergo persistent spectral hole burning at liquid helium temperature. We show that such a device performs as a miniature programmable narrowband spectral filter, with a transmission bandwidth less than 1 GHz. In such a filter the frequency resolution is limited by the width of the homogeneous zero-phonon lines of the chromophore molecules, and not by the geometrical dimensions of the device. Experimental measurements in the time domain using a picosecond dye laser, and in the frequency domain using a single-mode diode laser, are presented.

The spontaneous and stimulated emissions of strongly excited GaAs/(Ga,Al)As quantum wells are investigated in the one-dimensional optical amplifier geometry, using the variable-stripe-length method. The optical amplification and its saturation are studied by monitoring the spectra of spontaneous and amplified luminescence as a function of the position on the stripe. The deduced experimental spatial dependences of carrier and luminous densities are found to agree in a semiquantitative way with the numerical solutions of the amplifier equation, obtained by assuming steady state and thermal carrier distributions. Saturation of optical amplification is caused by two effects: (1) carrier depopulation through stimulated recombination of electron-hole pairs, and (2) loss of light caused by scattering at sample defects and by imperfect wave guiding.

We present new experimental results on second-harmonic generation in highly conjugated organic molecules and molecular crystals recently developed in our group, as well as on electro-optic eftects in thin-film polymers. A large value of the molecular hyperpolarizability of a new hydrazone-type molecule crystallizing in a noncentrosymmetric point group is reported. Large nonlinear optical coefticients of up to 840 ± 200 pmN were measured in crystals of 4'-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST). The new experimental results are compared with theoretical calculations of limiting values of nonlinear optical coefticients. Computer modeling of crystal structures shows good agreement with experimental results. Measurements on electro-optic polymers with high thermal stability are presented.

This article presents a way of scanning three-dimensional (3-D) objects using noninvasive and contact loss techniques. The principle is to project parallel fringes on an object and then to record the object at two viewing angles. With an appropriate treatment one can reconstruct the 3-D object even when it has no symmetry planes. The 3-D surface data are available immediately in digital form for computer visualization and for analysis software tools. The optical setup for recording the object, the data extraction and treatment, and the reconstruction of the object are reported and commented on. Application is proposed for reconstructive/cosmetic surgery, CAD, animation, and research.

Photovoltaic narrow-gap IV-VI (lead chalcogenide) infrared sensor arrays on Si substrates have the potential for low-cost infrared focal-plane arrays. The arrays can be bump bonded to readout multiplexers, or be grown on prefabricated active Si substrates containing the whole readout circuits. Sensitivities are similar to that of Hg_1-xCd_xTe, but processing procedures are much less demanding. This is because the structural quality of even heavily lattice-mismatched IV-VI layers is adequate to fabricate devices with good sensitivities, because 2- to 4-μm layer thickness suffices, and because good homogeneity in ternary Pb_1-xSn_xSe for the 8- to 12-μm range is much easier to obtain than in Hg_1-xCd_xTe. New results are presented on the molecular beam epitaxal growth of the layers, including a very thin CaF₂ buffer needed for compatibility reasons, and a new photolithographic patterning technique suited for full wafer processing has been developed to fabricate the sensor arrays. First thermal images using these chips are demonstrated.

Two different photogrammetric techniques for the determination of high-resolved simultaneous 3-D velocity fields in flows are outlined and compared: a technique based on the discrete visualization of a flow with tracer particles and recording of image sequences by multiple CCD cameras, and a technique based on scanning an observation volume of a flow marked with dye by a laser Iightsheet and tracking of flow patterns by 3-D least-squares matching in sequences of voxel datasets. The article shows the principles of both methods, hardware configurations for data acquisition, application fields, and results achieved.

The method used for ground-based total ozone observations and the design of two instruments used to monitor atmospheric total ozone at Arosa (Dobson spectrophotometer and Brewer spectrometer) are briefly described. Two different procedures of the calibration of the Dobson spectrometer, both based on the Langley plot method, are presented. Data quality problems that occurred in recent years in the measurements of one Dobson instrument at Arosa are discussed, and two different methods to reassess total ozone observations are compared. Two partially automated Dobson spectrophotometers and two completely automated Brewer spectrometers are currently in operation at Arosa. Careful comparison of the results of the measurements of the different instruments yields valuable information on possible small long-term drifts of the instruments involved in the operational measurements.

Light-emitting diodes (LED5) based on organic semiconductors have received much attention recently due to their promise as cheap, novel light sources for electro-optical applications. Unlike conventional diodes, light emission from these organic LEDs is achieved by double injection of electrons from a low-work-function electrode and holes from a high-work-function electrode into the organic polymer light-emitting layer. By appropriately engineering the polymer backbone, emission of various visible colors has been demonstrated. Our work in this field has concentrated on organic block copolymers as the active light-emitting materials. We demonstrate that the use of copolymer systems leads to large enhancement of device performance.

We report on the realization of InGaAs-InGaAsP separate confinement heterostructure multiple quantum well lasers grown by chemical beam epitaxy. We discuss key growth parameters and characterization by secondary-ion mass spectroscopy, transmission electron microscopy, electron-beam-induced current, and x-ray diffraction. Threshold current densities as low as 450 Acm² are obtained on lasers with five strained InGaAs quantum wells, along with internal quantum efficiencies of 90% and optical losses of 5 cm^-1.

The authors describe the realization of a single-longitudinal-mode high-pressure CO₂ laser with a plasma shutter. Single-mode operation is achieved with a three-mirror resonator with etalon. The resonator includes a subcavity, which protects the temperature-controlled etalon from destruction by high radiation intensities. In particular we have investigated two subcavity configurations, which use different etalons and grating arrangements. The maximal pulse energy of about 140 mJ was achieved with a grating that is employed in grazing incidence. A theoretical model has been developed, which illustrates the nonlinear frequency-tuning behavior of the three-mirror resonator and explains how the subcavity has to be adjusted to optimize the mode discrimination of the resonator. With the help of a plasma shutter we have produced tunable truncated 10-μm laser pulses. These pulses were employed to generate 100-ps pulses by optical free induction decay (OFID). With our system we produced for the first time OFID pulses 15 GHz off a CO₂ laser line center and investigated the effects of a frequency detuning between the laser frequency and the absorption line of the spectral filter in an OFID system.

The author presents an optoelectronic system called CREHOS: a high-speed, high-resolution, and large-area laser scanner for the fully automated detection of narrow cracks in large rough surfaces. The main application is the survey of road pavements (a 4-m-wide lane at 80 km/h, 1 x 2-mm resolution). The system includes two original elements: a large multifacet holographic light collector and a custom parallel processor for real-time recognition of cracks. A prototype has been built. The author presents the general concept of CREHOS, the principle of the holographic collector, and the robot that has been built to record this special hologram. The electronic device is also sketched.

We have successfully demonstrated that an appropriately designed semiconductor saturable absorber device, the antiresonant Fabry-Perot saturable absorber, can reliably start and sustain stable mode locking of solid state lasers such as Nd:YAG, Nd:YLF, Nd:Glass, Cr:LiSAF, and Ti:sapphire lasers. Especially for solid state lasers with long upper-state lifetimes, previous attempts to produce self-starting passive mode locking with saturable absorbers was always accompanied by self-Q-switching. We derive criteria that characterize the dynamic behavior of solid state lasers in the important regimes of Q-switching, mode-locked Q-switching, and continuous-wave mode locking in the picosecond and femtosecond range for the pulsewidth. We demonstrate that semiconductor absorbers can be designed to predetermine the dynamic behavior of a laser for a given solid state laser material and present an experimental verification. This allows for the development and design of robust, compact pico- and femtosecond solid state laser sources for scientific and industrial applications.

Analytical formulas for intermodulation- and harmonic-distortion products of a directly intensity-modulated laser diode are presented. The Volterra theory of nonlinear systems is applied to the single-mode rate equations of the modulated carrier and photon densities. This analysis takes gain saturation and noncoherent external optical feedback into account and provides expressions for the frequency-dependent intermodulation- and harmonic-distortion products. The single-mode analysis has been applied to a InGaAsP/InP Fabry-Perot laser diode, and the theoretical values of the second- and third-order intermodulation products at high modulation frequencies show good agreement with measurements. Thus, the formulas seem to provide a convenient and accurate means of predicting the laser-induced distortions in an analog optical transmission link over a wide frequency range.

We report on the investigation of a new configuration of an all-optical associative memory. The images to be recalled associatively are stored in a LiNbO₃ crystal via angular multiplexing. Thresholding of the reconstructed reference beams during associative readout is achieved by using a saturable absorber with an intensity-tunable threshold. We demonstrate associative readout and error correction for 10 strongly overlapping black-and-white images. Associative recall and full reconstruction is performed when only 1/500 of the image stored is entered.

We report new measurements on LiNbO₃ integrated optical circuits using two setups based on the use of a low-coherence light source. Fundamental limits of an all-fiber optical low-coherence reflectometry setup are outlined, and a complete analysis of the measured optical parameters of the circuits and their effects is presented. We also report measurements related to a polarization-axis misalignment of pigtailed LiNbO₃ components.

A precise method to determine the absorption and reduced scattering coefficients of turbid media from the spatial distribution of light has been developed. It allows in vitro local measurements on samples, and needs only one measurement performed by a linear CCD detector. The intensity profile of the scattered light is characterized by the maximum of the intensity and the full width at half maximum. These parameters have been related theoretically to the absorption and reduced scattering coefficients. The theoretical approach is based on Monte Carlo simulations, which are used to predict the intensity profile at the output surface. The boundary reflections and the source and detector characteristics have been taken into account. For a thickness lower than 6 transport mean free paths, significant differences have been found depending on whether a Mie or a Henyey-Greenstein phase function (with the same anisotropic factor) is used. This is of help in the determination of the validity range of the similarity relations. Very good agreement (error typically less than 5%, maximal 15%) has been found between simulations and experiments performed on microsphere suspensions.

The optical properties of various biological tissues have been investigated by the measurement of the maximum intensity M and the full width at half maximum ( FWHM) of the intensity profile of a scattered light beam. These two quantities have turned out to be highly discriminating parameters for the different tissues under scrutiny: muscle, liver, adipose, and gray and white brain matter. The inverse problem, i.e., the computation of the absorption and reduced scattering coefficients from M and FWHM, has been solved in the domains where Monte Carlo simulations have yielded possible values for M and FWHM. The accuracy is typically 5% for the reduced scattering coefficient and 20% for the absorption coefficient. This method is judged to be reasonably good for application to biological materials: it allows a good overall characterization of tissues. A scanning technique has been developed to evaluate the variability of the optical parameters at different locations in biological tissues. Whereas Monte Carlo simulation works well for tissues such as muscle or liver, it appears to be inappropriate in describing the optical properties of adipose and brain tissues. The reasons are still unclear and are probably related to the particular structural properties of such tissues.

Endoscopes for use in ophthalmology can now be manufactured with overall intraocular diameters smaller than 0.89 mm. Endoscopes based on gradient-index lenses yield a higher resolution than those making use of ordered fiber bundles having the same diameter. Likewise, endoscopes with optical elements having a diameter of 0.50 mm yield a higher resolution than those with smaller diameter (0.35 mm). Thanks to the miniaturization, a working channel can also be integrated within the tube of the endoscope instead of being a part of the illumination bundle. This allows the design of new endoscopic devices including various surgical instruments. Preference is given to an endoscope with an integrated aspiration/irrigation system or with a fiber for laser therapy. The potential phototoxicity of these systems is briefly discussed.

A simple system for optical and microwave signals analysis based on the optical sampling technique is presented. It is novel in requiring only low-frequency detection and electronic components. This is made possible by the use of a commercially available L1NbO3 intensity modulator for processing the light wave. The ultimate performance of the system is discussed, and comparisons with standard detection systems are also made.

The resolution of time-gated breast transillumination images has been investigated both theoretically and experimentally. The resolution limit is quantified as the size of the smallest object visible on an image (the image quality index), which depends on such image parameters as the transfer function, the contrast, and the noise. The smallest diameter of a detectable carcinoma located in the breast has been determined on the basis of Monte Carlo simulation results as well as in vitro time-of-flight measurements on breast samples. The comparison of the Monte Carlo simulation of light propagation within biological tissues with the experimental data has been able to confirm the validity of the simulation. The simulation results, compared with measurements, suggest that the formation of time-resolved transillumination images of biological tissues can be adequately modeled in the near infrared. The enhancement of the transfer function by the introduction of time-gated detection is verified, and the limiting contribution of the noise at short integration times has been investigated. The estimated diameter of the smallest detectable sphere embedded on the front surface of a 20-mm-thick breast slab is around 3 mm. Extrapolated for a full-size breast, the estimate is still better by a factor of 2 than the resolution of classical diaphanography, which is commonly taken to be worse than 20 mm.

Two different methods are presented and discussed for the evaluation of the point spread function (PSF) in multicore fibers (MCFs) used as an image guide in microendoscopy. In the first method, the coupling intensities between the fiber cores in a MCF are measured at three different wavelengths (632, 520, and 488 nm) by scanning the input face of the MCF with an illuminated pinhole. In the second method, the intensity coupled into a fiber core from all the neighboring fiber cores is measured by obturating the fiber core and measuring the output light intensity. The nonnegligible contribution of leaky modes in the large intercore distance coupling is demonstrated. The two methods are fairly well correlated. The investigations have been carried out for two MCFs presenting well-differentiated characteristics. The major coupling mechanisms between fiber cores have been identified and their roles quantified as functions of the coupling distance. At short distance, crosstalk dominates, with a maximum coupling intensity of 15% at 632 nm for the nearest neighbor fiber core. At larger distances (ranging from 3.8 to 5 intercore distances), leaky modes play a predominant role in the coupling, which remains nonnegligible.

We present the design, construction, and characterization of a spherical-coordinate scanning, reflection-mode confocal laser microscope (SCSLM). Two system designs are presented, namely a conventional bulk optics object-scanning design and a preliminary optical-fiber-based two-axis optics/one-axis object scanning version. The bulk-optics design is characterized with respect to its optical sectioning property. Sample 3-D images acquired using the SCSLM are also presented, including a reconstruction of an ex vivo pig's cornea. The bulk optics design offers a higher light throughput, but it cannot be easily miniaturized for future integration in a microsurgical robot design. The fiber-based design has a reduced SNR but can be potentially made lightweight and small enough to be integrated as the imaging subsystem of a microsurgical robot.

Novel designs of programmable all-optical synchronous code-division multiple-access (CDMA) encoders and decoders are reported. They are based on cascades of optical delay lines and electro-optic switches. The operations of both optical encoders and decoders are illustrated with the well-known prime-sequence codes. Based on the proposed designs, these optical CDMA components can be constructed by integrated optics (i.e., the optical delay lines and switches are all fabricated on the same substrate). With the possibility of mass production and eliminating the fiber-waveguide interface power loss, better cost efficiency and lower power loss would be expected, as compared to the conventional designs.

We demonstrate the weakness of the real-time holographic associative memory implementation in addressing accuracy and describe a novel method to implement associative memory with accurate addressing. In this method, the memory images and their background images are stored in two common holographic memory systems, and the partial image and its background image are simultaneously used to address the two holographic memory systems. The experimental results have proved the system feasible. In addition, we describe a method of associative memory with accurate addressing in a common real-time holographic memory system using combinatorial memory images and combinatorial addressing images.

Automatic inspection (locating and quality assessment) of centering marks engraved on ophthalmic lenses presents special difficulties. The scene is noisy and blurred, and the engraved marks are weak, low-contrast and partially occluded. To locate the marks, we take advantage of their binary-shaped characteristic to design a model that greatly simplifies the numerical computation of correlation without the need to binarize the scene. Three figures of merit are defined to ensure the robustness of the whole procedure: the contrast of the target against the background, the uniqueness of the correlation peak, and the similarity between target and model. By comparing these figures with suitable threshold levels, decisions can be reached based on existence, multiplicity, and completeness of the marks. The computational simplification enables a low-cost industrial implantation based on a CCD camera, a frame grabber, and a 486/33 PC. A precision of 0.1 mm in positioning is reached with a processing time of less than 1 s.

A simple technique is presented for estimating the thickness of a transparent plate. Using a laser source and detector, the transmitted light is measured as a function of angle of incidence. With prior knowledge of the refractive index of the plate at the laser wavelength, the observed fringes can be processed to estimate the plate thickness. The technique works with a modest degree of wedging, as long as fringes are discernible. Formal estimates of the error budget indicate the accuracy of this method is approximately 1 μm. If fringes are measured versus both angle and wavelength, it should be possible to estimate both thickness and refractive index.

We present a new scheme for an optical klystron harmonic freeelectron laser and analyze this novel free-electron laser using Madey's theorem. Theoretical analysis indicates that higher harmonic emission power density and gain can be enhanced greatly using this new structural wiggler.

Relative entropy thresholding techniques have been used for segmentation of objects from background in gray-level images. These techniques are related to entropy-based segmentations computed for the statistics of a spatial co-occurrence matrix. For detection of spectrally active targets such as chemical vapor clouds in multispectral or hyperspectral imagery, a spectral co-occurrence matrix is employed. Using the entropy of various regions of the matrix, thresholds can be derived that will segment an image family based on the spectral characteristics of the intended target. Experiments are presented that show the detection of a chemical vapor cloud in multispectral thermal imagery. Several manners of dividing the co-occurrence matrix into regions are explored. Thresholds are determined on both a local and global basis and compared. Locally generated thresholds are treated as a distribution and separated into classes. The point of class separation is used as a global threshold with improved results.

Optical systems with segmented mirrors require precision coalignment of their segments to attain the desired performance. A novel sensor for measuring piston over a ± 10 wave range by analyzing the image of a white light point source is described. The sensor combines a Young's two-slit aperture pair for coarse sensing with another set of apertures, which include a phase retardation portion for fine sensing. The course sensor has an accuracy of ± 0.25 wave over the full range. The fine sensor works within ± 0.5 wave of zero with ± 0.005 wave accuracy, and a repeatability of the order of ± 0.001 wave. Theoretical derivation and experimental results are provided.

Optical flow fields from parallel stereo cameras are analyzed to determine the 3-D motion of the camera platform with respect to objects in view and to establish stereo correspondence. A linear system of equations, whose coefficients consist of the moments of image velocities and coordinates in the stereo images, is solved to recover the 3-D motion components. This system of equations is derived under the assumption that all feature points have stereo matches (points without stereo matches are called drop-ins and drop-outs); however, point-to-point stereo correspondences are not required. No assumptions about the 3-D structure of the scene are made. Once the 3-D motion components are computed, stereo correspondence for a pair of potentially matching points is established by comparing three computed depth values: Z_l obtained from the monocular optical flow equations for the left image; Z_r, obtained from the same equations for the right image; and Z_s, obtained from stereo disparity. For correct matches these three depths must be nearly equal. The method is applied to numerically generated and laboratory image sequences with and without drop-ins and dropouts. In cases where the percentage of drop-ins and drop-outs is large, an iterative scheme is used to detect and eliminate the drop-ins and drop-outs, thus improving the motion estimates.

This PDF file contains the letter “Letter: Comment on the paper” for OE Vol. 34 Issue 07

This PDF file contains the editorial “Book Rvw: Spatial Light Modulator Technology: Materials, Devices, and Applications," edited by Uzi Efron for OE Vol. 34 Issue 07

This PDF file contains the editorial “Book Rvw: Elements of Signal Detection and Estimation," by Carl W. Helstrom for OE Vol. 34 Issue 07