The mail in whatever form is a relentless constant in the life of any journal editor. The U.S. mail delivers six days a week plus special deliveries on occasion. Other special delivery vans seem to be in and out of my driveway on a regular basis. And then there is e-mail (that I don’t have) and fax mail (that I do have), not to mention phone mail, of course.

When a large aperture is used to collect light propagated through the atmosphere, it performs an average operation on the irradiance fluctuations, resulting in collected-power fluctuations that are not as large as those that could be obtained from a point receiver. We present an expression for the aperture-averaging factor of optical scintillation using multiaperture architectures on the receiver configuration. That expression is used to assess the decrease in the total collected power fluctuations for several multiaperture receiver configurations.

We treat the generation of flat-top intensity distributions, as required for laser applications at short wavelengths. To obtain high fill factors and almost arbitrary shapes, arrays of diffractive Fresnel zone plates at the fabrication limit are investigated. The angular power spectrum noise due to the binarization of the transmission phase function is smoothed using an incoherent source. The remaining zeroth order is ommited by the addition of a constant offset phase to the transmission phase function of the array. An analysis of etch-depth errors as well as an investigation of multilevel elements is appended. Simulation results, obtained by a 2-D analysis for radial symmetry, are compared to measurements.

A wavelength insensitive fiber optic strain sensor configuration is presented. It consists of two variable ratio couplers in series: a reference and a sensing element. Difference-over-sum processing yields linear outputs that are insensitive to fluctuations in optical intensity. By subtracting the reference from the sensor output, wavelength compensation is achieved. The wavelength properties of this sensor were determined experimentally and the results compared to computer simulations. Theoretical and experimental results show good agreement. The compensation technique is suitable for any variable ratio coupler sensor and is not limited to axially strained fused tapered couplers.

Generally tilted in-core fiber gratings are modeled by an equivalent inhomogeneous optical thin film. Its reflectance spectrum is evaluated using the multilayer and optical-path approximations. The results are shown to be similar to those obtained using the exact localnormal mode method for the case of weak gratings. A fiber grating synthesis procedure is also introduced based on the methods advanced in this paper.

Sensitivities, displacement range, and accuracy of two types of optical vibration sensors, one fiber optic with a light-emitting diode source (LED/FO) and the other with a laser diode source and small (~1 mm) optics (LD/SO) were designed, assembled, tested, and compared. For the configurations adopted, sensitivity of the LED/FO with a 400- ?m aperture was found to be about 1.13 mV/?m over a 0.2- to 1.0-mm range and 20.37 mV/? over a 1.5- to 2.5-mm range. LD/SO sensitivities were 22.28 mV/?m over a 2.0- to 3.0-mm range for the f /2 design and about 21 mV/?m over a 0.1- to 10-mm range for the f /5 design. Although the LD/small-optics arrangement is capable of yielding greater sensitivities over longer ranges, the lower cost yet still precise and accurate LED/FO configuration is more rugged and therefore better suited to the field and related in situ and embedded applications.

An analysis is performed of reflective waves and their mixing during the holographic exposure of a photoresist film. It is shown that the resulting irradiance depends strongly on the reflectivity of the film/ substrate interface and on the optical thickness of the photoresist film. From these results it is possible to find the conditions where a synchronous detection system can be used to monitor and stabilize the recording process on photoresist films on nontransparent substrates. The operation of a negative feedback system to correct fringe perturbations in real time is analyzed for substrates of three different reflectivities. Although only photoresist film (Shipley AZ 1400) is studied, the general results can be applied to all types of photosensitive films or similar systems.

A procedure based entirely on computer simulation is developed for testing the quality of computer-generated holographic optical elements (CGHOEs). This new testing method may be of help in optimization techniques in the future. We introduce a mathematical quantity, the correlation, to characterize the performance of the studied CGHOE. Our procedure examines how the correlation between the object and the reconstructed image depends on various parameters of the CGHOE, such as the reference amplitude, the location and number of the object points, the number of gray levels used, and the pixel size on the hologram. To reduce computer running time, we introduce a new method for modeling the reconstruction of a computer-generated hologram (CGH): instead of using the whole information stored on the CGH, we use randomly chosen pixels (square-shaped slits) of the CGH. In this way, computer running time becomes smaller by two orders. A postquantization procedure is developed that, under certain conditions, improves the quality of the CGHOE. Our model uses amplitude holograms and 2-D objects, but in principle, there are no difficulties in extending it to phase holograms and 3-D objects.

The design method and the performance of two types of concave gratings for operation as multiplexers/demultiplexers, with 10 nm/mm reciprocal linear dispersion, required to multiplex/demultiplex channels separated by 0.5 nm in wavelength, are presented. The first type of grating is designed in such a way that the principal ray of the central wavelength in the spectrum is diffracted at normal angles to the image field. The second type of grating is a Rowland circle mount. In each case, two recording configurations are obtained. The performances of the mounts are almost identical. In the first configuration, the coupling loss is less than 22.7 dB and the optical isolation is better than 237 dB. In the second configuration, the losses are less than 21.8 dB and the optical isolation is better than 243 dB. Finally, a Rowland circle grating with 4 nm/mm reciprocal linear dispersion, which can multiplex/ demultiplex at least 175 channels with loss less than 22.6 dB and crosstalk better than 228 dB, is presented. These spectrographs can be used for wavelength routing applications in wavelength division multiplexing (WDM) networks.

An iterative method is introduced for determining the exposure schedule for multiplexing holograms in saturable recording materials, such as photopolymers. This method is designed to share all or part of the available dynamic range of the recording material among the holograms to be multiplexed. Using exposure schedules derived from this method, the authors find that the diffraction efficiency of DuPont’s HRF- 150 38- and 100-?m photopolymer scale is (2.2/M)2 and (6.5/M)2 respectively, where M is the number of holograms recorded. Finally, 1000 holograms were multiplexed at a single location in the 100-mm thick photopolymer using an exposure schedule derived with this method.

Two techniques for implementing symbolic substitution (SS) using one-of-many coding are presented. Both techniques involve simultaneous recognition of multiple rules and hence reduce the complexity of SS implementation. Based on these new implementations, some factors that influence simultaneous recognition of rules are identified. It is shown using illustrations that the one-of-many coding is an optimal coding technique in terms of complexity of implementation.

Our study of a novel technique for adaptive image sequence coding is reported. The number of reference frames and the intervals between them are adjusted to improve the temporal compensability of the input video. The bits are distributed more efficiently on different frame types according to temporal and spatial complexity of the image scene. Experimental results show that this dynamic group-of-picture (GOP) structure coding scheme is not only feasible but also better than the conventional fixed GOP method in terms of perceptual quality and SNR.

The method of analysis and reconstruction of the structure for a 1-D nonregular grating composed of N identical apertures is discussed. The transmittance function of the grating is expressed as the sum of transmittance functions of pairs of the apertures, and the classes of these pairs are determined through their separation. Applying the autocorrelation technique to the function of intensity distribution in the far field of such a grating’s transmittance, it is possible to determine grating autocorrelation function. This function contains complete information concerning the actual structure of the grating itself, i.e., classes of the pairs of the apertures and their populations. With such information, it is possible to reconstruct the structure of the object.

A method is presented for the design of a single Gabor filter for the segmentation of multitextured images. Earlier methods were limited to filters designed for one or two textures or to filters selected from a predetermined filter bank. Our proposed method yields new insight into the design of Gabor filters for segmenting multitextured images and lays an essential foundation for the design of multiple Gabor filters. In the method, Rician statistics of filtered textures at two different Gabor-filter envelope scales are used to efficiently generate probability density estimates for each filtered texture over an extensive set of candidate filter parameters. Variable degrees of postfiltering and the accompanying effect on postfilter output statistics are also included in the design procedure. The result is a unified framework that analytically relates the texture power spectra, Gabor-filter parameters, postfiltering effects, and image-segmentation error. Finally, the resulting filter design is based on all constituent textures and is not constrained to a limited set of candidate filters.

Microscope images of thin marble sections can be used to determine their geographical origin by means of the shape, size, and spatial distribution of their grains. We present a method that is the first step toward the automatic origin determination, namely, the segmentation of grains in digital images of thin marble sections. Each grain has a preferred direction, different from that of its neighbors, which rules its behavior when it is illuminated with polarized light. First, we perform an oversegmentation of the image with a filter based on a partial wavelet reconstruction followed by a watershed transformation. Afterward, from a sequence of images of the same sample obtained by means of polarized light we compute, for each region, two parameters that depend on the preferred direction of that region’s grain. Finally, the set of parameter values for all the regions is the input to a region-merging procedure that achieves the final segmentation. We present the results for samples from six quarries, each with different visual features.

An intelligent radical-based on-line Chinese character recognition (OLCCR) system is proposed. We make use of the characteristic that most Chinese characters possess radicals and develop a radicalbased preclassification technique. In the procedure of recognizing radicals, potential candidate radicals are identified from an input character first and then matched with radical templates. Based on the matched radicals, corresponding candidate characters with a smaller matching distance are thus identified. Postprocessing, which utilizes the information of the first and last stable line segments, is incorporated to improve the recognition accuracy. Experiments are carried out to evaluate the performance of the proposed OLCCR system and the average recognition rate is improved from 96.06 to 96.52% if only the first winner is selected and the average recognition time is shortened by about 44%.

A novel multilevel adaptive pixel classification and detection (AMLCD) method for detecting pixel and subpixel-size targets for multispectral images is presented. The AMLCD method takes into account both spectral and spatial characteristics of the data. In the first level of processing, the principal background end members are obtained using the K-means clustering method. Each pixel is examined next for classification using a minimum-distance classifier with the principal end members obtained in the previous level. In the second level, the neighborhood of each unclassified pixel is analyzed for inclusion of candidate end members in an unmixing procedure. If the list of candidate background classes is empty, the conditions for their inclusion are relaxed. The fractions of neighborhood and target signatures for the unclassified pixels are determined by means of a linear least-squares method in the third level. If the results of unmixing are not satisfactory, the list of candidate clusters is renewed. Target detection within each pixel is performed next. The last processing level determines the size and location of detected targets with a clustering analysis methodology. Target size and location are estimated on the basis of the sum and weighted vector mean, respectively, of the mixing fractions of the neighboring pixels. The AMLCD method was successfully applied to both synthetic and Airborne Visible/ Infrared Imaging Spectrometer (AVIRIS) hyperspectral imagery data sets.

When detecting in low-light-level conditions, the dead time that appears in actual intensified image detectors increases both the systematic and the statistical error in the centroid estimate. We develop a simple technique to reduce these errors. This technique enables extending, with a good level of accuracy, the applicability of experimental methods involving the centroid measurement to those fields dealing with faint light sources.

The restoration of images blurred as a result of image motion or vibration is discussed. The key to the success of the restoration algorithm is accurately determining the optical transfer function (OTF) representing the image motion degradation in the spatial frequency domain. The basic method of obtaining the OTF from the measured function of relative displacement between the camera and the object using a motion sensor has been developed recently and is discussed elsewhere (Sezan and Lagendijk, 1993). The motion function is derived instead from an analysis of a sequence of consecutive images. The first step is to obtain the image motion information from the sequence of images according to two well-known algorithms—the block-matching algorithm (BMA) and the edge trace tracking (ETT). The basis for these two methods consists of tracking a block or an edge through a sequence of several consecutive images. Results of these two methods were fitted to a sinusoidal vibration function and compared; there was excellent agreement between them. Finally, the image is restored using the OTF estimated via the tracking method.

Texas Instruments’ new single-chip multiprocessor, TMS320C80, is a powerful programmable digital signal processor with many unique features optimized for multimedia, image processing and computer graphics applications. The performance of a TMS320C80- based multimedia system for image processing and computer vision tasks is evaluated using the Abingdon Cross benchmark. The result shows that the TMS320C80-based system outperforms most of 1980s specialized parallel image computers at a fraction of the system cost.

Fuzzification is introduced into gray-scale mathematical morphology by using two-input one-output fuzzy rule-based inference systems. The fuzzy inferring dilation or erosion is defined from the approximate reasoning of the two consequences of a dilation or an erosion and an extended rank-order operation. The fuzzy inference systems with numbers of rules and fuzzy membership functions are further reduced to a simple fuzzy system formulated by only an exponential two-input oneoutput function. Such a one-function fuzzy inference system is able to approach complex fuzzy inference systems by using two specified parameters within it—a proportion to characterize the fuzzy degree and an exponent to depict the nonlinearity in the inferring. The proposed fuzzy inferring morphological operators tend to keep the object details comparable to the structuring element and to smooth the conventional morphological operations. Based on digital area coding of a gray-scale image, incoherently optical correlation for neighboring connection, and optical thresholding for rank-order operations, a fuzzy inference system can be realized optically in parallel.

We present an efficient codebook search algorithm in a vector quantization (VQ)-based system that searches only through a window of consecutive codewords on the preordered codebook, rather than all codewords in the codebook, and achieves full-search-equivalent performance. The ordering technique used to rearrange the positions of codewords in the codebook utilizes the scattering orientation of codewords in the k -dimensional space or the compactness property of signal energy on the transform domain. The procedure for determining the search window on the ordered codebook relies on the geometric relations among input vector and codewords to eliminate those codewords that are certain not to be the closest codeword to the input vector. Finally, the closest codeword to an input vector is selected from the determined search window by an improved partial distortion search algorithm. In comparison with other existing fast algorithms, the proposed algorithm requires the least number of multiplications and the least total number of distortion measurements.

We have developed active interferometers in which fringes are stabilized by detecting their movement induced by external perturbations such as mechanical vibration or air flow with a spatial filtering detector and by feeding back the signal to a piezoelectric mirror of the interferometer. We also extended the system to active phase-shifting interferometers by which the fringe shifts are monitored in real time to be delivered accurately for automatic analysis even in the presence of external perturbations or temperature drift of the piezoelectric element. By applying these feedback controls to a Twymann-Green interferometer placed on a wooden desk we could measure the flatness of a mirror with almost the same peak-to-valley and root-mean-square values as measured on an optical bench. Only their repeatability was worse, by three times. We also applied the method to a dual-beam speckle interferometer and could measure in-plane displacement even in the presence of air flow generated by a fan, which prevented measurement without feedback. It has proved to be especially useful for measurement of large displacement by integrating incremental displacements.

Using a grazing incidence interferometer, the interferoscope, an automatic absolute measurement of a test object surface height can be made by counting the number of interference fringes when varying the surface incident angle. This is accomplished by combining the interferoscope with a computer-controlled stepping motor along with an image processing system. By transforming the equations describing the interferoscope, the sought depth can be regarded as a ‘‘frequency,’’ which can be attained using Fourier transforms or other frequency evaluation algorithms.

We develop a general formalism for describing the polarization effects in stellar interferometers. We show that celestial field rotation and phase delays between the s and p fringe patterns are first order effects. Experiments in laboratory partially check our modeling and thanks to these measurements we optimize a field rotator to compensate the visibility losses due to celestial field rotation. Then we predict the visibility functions of the Grand Interférométre á 2 Télescopes (GI2T) of the Observatoire de la Cóte d’Azur with its present beam combiner and with the future Recombinateur pour Grand Interférométre (REGAIN): the field rotator enables an increase in the observation time by more than 3 hours. Finally, we compare our results to observations done with the GI2T and we emphasize the importance of such calibrations with a polarimetric mode whose principle is validated.

We describe a phase-shifting microscopic Mirau interferometer for measurement of surface roughness in which feedback control is implemented for shifter asymptotic adjustment. The actual height resolution of our instrument is of ~0.3 nm with a measurement accuracy of 0.5 nm. Comments on interferometer design, experimental examples, and error analysis are also given.

Sub-Nyquist interferometry (SNI) provides a method for measuring wavefronts with large departures from a reference sphere, such as those encountered when testing steep aspheric surfaces. SNI allows wavefronts with several hundred waves of departure to be recorded and analyzed. The theory of SNI is reviewed, its experimental implementation described, and limitations in the hardware and potential improvements are discussed. The importance of calibrating the interferometer for non-null testing is demonstrated.

Resolution-enhancement technologies such as alternatingtype phase-shifting masks (PSMs), half-tone PSMs, and the off-axis illumination method in optical lithography are necessary for manufacturing gigabit-scale ultra large scale integration (ULSI) devices. Because an alternating-type PSM is the most effective way to enhance resolution, we examine the resolution capabilities of KrF excimer laser lithography combined with the use of an alternating-type PSM through simulations. Our goal is to apply this technique to attain pattern delineation smaller than 200 nm. We simulate light intensity profiles for various types of PSMs in terms of the 3-D mask structure, and find that a PSM structure with a spin-on glass (SOG) phase shifter on a Cr layer that is thinner than in a conventional mask is one of the best choices for KrF excimer laser lithography. We examine potential problems such as the durability of the SOG phase shifters to KrF excimer laser irradiation exposure, and phase angle error due to the surface topography of the Cr aperture patterns. From our experimental results, we confirm that the optical characteristics of the PSM are not degraded, and the phase angle can be controlled with an accuracy sufficient for gigabit-scale ULSI device fabrication. Improved PSMs with a thin Cr layer and SOG phase shifters were successfully used to fabricate several layers of experimental 1-Gbit dynamic random access memory (DRAM) devices with sufficient resolution capability.

Reactive ion etching (RIE) is known as an effective technique for high precision anisotropic etching with a minimum loss of the critical dimensions provided by the photoresist or other masking materials. RIE can also be used to transfer continuous forms such as spherical resist microlenses into substrate materials (e.g., quartz glass or silicon). The form of the lenses can be considerably controlled by changing the etch rate ratio between resist and the substrate. This was achieved by varying the etch gas compound, especially the amount of oxygen, during the etching or by changing the applied power. Measured etch rates for silicon are given to demonstrate the possibilities of lens shaping. The surface roughness of the etched lenses was one of the main problems. The roughness could be minimized by adding helium to the etch gases for heat removal and by increasing the resist rinse time after the wet chemical development.

An external mode locking technique using RF modulation by an acousto-optic modulator and feedback from a phase-conjugate mirror is presented. A photorefractive BaTiO3 crystal is arranged in selfpumped phase-conjugator geometry. The setup is completely selfaligning and subnanosecond pulses are easily observed for He-Ne (632.8 nm), Ar+ (514.5 nm), and He-Cd (442 nm) lasers.

The modified signed-digit (MSD) number system satisfies the requirements of totally parallel addition using identical units and enables the addition of any two numbers in three sucessive steps. We show a simple and compact design of the parallel optical addition module based on MSD number representation using Boolean polarization-encoded logic algebra (BPLA). The four transforms of MSD addition are expressed mathematically and the realization of the transform module using liquid crystal devices (LCDs) are also given.

Plots of the index of refraction and of partial dispersion versus V-number have long been used as a standard tool in selecting glasses for chromatic correction. The change in the distribution of glasses on these plots for widely differing spectral regions has generally been ignored. Some sample plots demonstrate the adjustments in approach required for selecting glasses in alternative spectral regions.

An athermal chart, which plots chromatic dispersive power and thermal dispersive power on a Cartesian coordinate, is one of the graphical design methods for achromatized and athermalized optical systems. We expand the ideas of an athermal chart into a multilens system that is composed of thick lenses spaced apart by weighting the ratio of the paraxial ray heights at the lenses or the surfaces to the lens power, the chromatic dispersive power, and the thermal dispersive power of each lens or surface. We describe the methods for treating air space and lens thickness on the athermal chart with two-component optical systems. It is clarified that the proposed method is effective for athermalized optical system design through the evaluation of an IR optical system in the 8- to 11-?m wavelength band.

Range-Doppler imaging is the basic method of inverse synthetic aperture radar, which is based on the uniform rotation of targets. Nonuniform rotation can occur to maneuvering targets, which produces smeared images. A constantly acceleratively rotating model is used here instead of the traditional uniformly rotating model. The generalized marginal integration along straight lines with varying slopes is calculated over the time-frequency plane. The imaging quality is improved by using the new method.

A new method to measure ultralow stray light in a double monochromator is proposed. This method can not only omit the linear checking of photoelectric testing system in large-order scale and the transmittance calibration of the neutral density filter, and improve the measured accuracy, but can also realize the measurement of ultralow stray light of any order. Roughly speaking, the testing limit of stray light is limited only by the power of the incident laser. A measured limit of the order of 10-14 and a ratio of relative light intensity are obtained, and the relative measured error can be reduced below 5%.

Wavelet transforms are currently being used for a number of applications such as cue feature and noise extraction from images and acoustic signals. This work describes and applies an algorithm that uses wavelets for finding the clutter in infrared (IR) and visual images. Once the clutter is found, the probability of detection (Pd) is calculated. Tidhar’s and Rotman’s probability of edge metric (POE) is extended to encompass the wavelet methodology for multiscale clutter metrics in IR images.

Today the great majority of target acquisition models within the Department of Defense (DoD) originate from two primary sources of empirical human observer data: the Blackwell-Tiffany visual perception experiments begun in World War II and the Army Night Vision Electrooptic Sensors Directorate (NVESD) field test trials with military observers. An extensive sensitivity analysis that compares the performance of several DoD acquisition models derived from these two extensive sets of data was carried out. A comprehensive analysis of each method and a detailed comparison of these different methodologies shows that they are in remarkably good agreement throughout their ranges of applicability. The authors show when the various modeling methodologies are applicable for a variety of military sensor and countermeasure scenarios.

The technology to fabricate and assemble many concentric, nested conical foil x-ray telescopes for high-throughput, moderateresolution, spectroscopic applications promises to be a cost-effective alternative to the grinding and polishing of conventional grazing incidence Wolter Type I telescopes. The three fundamental mechanisms that degrade achievable resolution for any imaging system are diffraction, geometrical aberrations (due to residual design errors, surface figure errors, and alignment errors), and scattering due to residual optical surface irregularities. A detailed parametric analysis of the image degradation due to each of these mechanisms is presented, with particular emphasis on the assembly and alignment errors for these tightly nested conical foil x-ray telescopes. A detailed error budget tree is then developed from which assembly and alignment tolerances can be derived. This error budget tree allows systems engineering trade-offs between foil surface tolerances, assembly and alignment tolerances, and the intrinsic resolution due to diffraction and residual design errors (the conical approximation to the ideal paraboloidal and hyperboloidal surface figure). Although the Danish Space Research Institute’s XSPECT conical foil x-ray telescope design parameters were used in this study, the methodology developed is applicable to any nested array of grazing incidence x-ray telescopes.

Mechanically based profilometers typically employ a scanning slit, either on a reciprocating mechanism or rotating drum. With the subject beam conveniently fixed in space, the slit is made to slice through the desired transverse plane of interest.

Semiconductor optics is probably the field in condensed matter physics that has been most intensely treated by a large number of scientists in recent decades. It offers to both evolve fundamental physical concepts and to develop a number of device ideas covering the most sophisticated uses in research laboratories and applications in daily life. One may think of telecommunication techniques, LEDs, or laser diodes for CDplayers, for example.

This PDF file contains the editorial “Book Rvw: Compact Sources of Ultrashort Pulses," edited by Irl N. Duling III for OE Vol. 35 Issue 10