In keeping with an Optical Engineering tradition, I want to report on the state of the journal at the end of 1999. The most remarkable aspect of this year’s production was probably noticed by most readers—it’s thinner...a lot thin-ner. The number of pages and papers has dropped by a third. In an era of ever-increasing numbers—at least if you listen to the financial news these days—this result would be announced in the gravest tones. Down is bad. For Op-tical Engineering, I believe that the reduced page and paper counts were the result of a change in approach to editing the journal.

Brightness calibration of vision sensors is an important step in developing machine vision applications, yet it is often ignored and overlooked. It enables the accurate representation of image intensity readings with respect to a common linear brightness scale that is proportional to the scene irradiance. We present a brightness calibration procedure for CCD camera systems. We also describe the characteristics of today's CCD cameras, which are key to their effective use as well as the visual brightness sensory information in industrial applications. Aspects of brightness measurement are discussed. Results from calibrating a stereo CCD camera system and testing the calibrated system are also presented and discussed.

Accurate spectral and radiometric calibrations of IR cameras are needed to interpret infrared imagery properly, to monitor camera performance over time, and to evaluate new imaging radiometers. In this paper, the physical basis for calibrating IR cameras is derived from first principles, and a laboratory setup used to perform both radiometric and spectral calibrations is described. The calibration procedures used with this setup are then demonstrated on a midwave IR focal plane array camera, a midwave IR scanned camera, and a longwave IR scanned camera. The system spectral response and radiometric response of each camera is given and analyzed. An error analysis of approximating a camera's spectral response by an equivalent top-hat responsivity is also given.

The interactions of polarized light with an optically active (chiral), multiply scattering medium are investigated using a relatively simple experimental system incorporating polarization modulation and synchronous detection techniques. The polarization properties of diffusely scattered light are studied as a function of scatterer particle concentration, chiral molecule concentration, and detection direction. A newly derived method for simultaneous extraction of the total degree of polarization, and optical rotation of the linearly polarized fraction, is theoretically discussed and experimentally implemented, using optically thick turbid media with the presence of one chiral component. The method requires measurements at several orientations of the analyzing linear polarizer, followed by data fitting to yield the unknown sample polarization properties. The accuracy and robustness of this method in the cases of weak signals and noisy data are superior to previous two-point approaches of data analysis. The measurable polarization preservation on multiple scattering, affected by the chirality and turbidity of the medium and by the detection geometry as described, provides a useful tool with which to probe the properties of multiply scattering media.

Surface plasmon resonance (SPR) is a suitable technique to optically characterize thin layers. It has often been stated that SPR cannot determine simultaneously both the thickness and the dielectric constant (possibly complex) of the layer. We demonstrate that this idea arises from an error caused by the method used in the simulation of the reflectivity curve. So we do not have to design complex systems to solve this problem as did previous authors. In this paper, we report on a simulation based on the Fresnel equations to calculate the reflectivity curve from the critical angle (?c ) to cover a wider range of ? values. With a matrix formalism, we can pick the layers we want very easily. With our process, results are excellent for all kind of noise distributions even at high noise levels. A metallic layer was first characterized; then an ultrathin (12 Å) dielectric layer was added. We also calculated the standard deviations for all cases to prove that the SPR technique is a very sensitive probe. In all studies, the results showed very good agreement between the true values of the parameters and the simulated ones, as well as small standard deviations.

An integrated on-line cable-monitoring technique for hybrid fiber/coaxial (HFC) networks is proposed and experimentally demonstrated. The in-service monitoring of fiber optic cable and coaxial cable is achieved simultaneously by an optical time-domain reflectometer (OTDR) and the frequency domain analysis (FDA) method, respectively, where the FDA results are encoded in the additional dummy fiber through digitally modulated fiber benders. This technique can be easily developed into an automated in-service surveillance system to provide real-time monitoring to enhance HFC network reliability.

Small-tilt micromirror-based 2x2 fiber optic switch array structures are proposed using fixed mirrors and fiber interconnections. A multiwavelength 2x2 fiber optic switch based on this small-tilt micromirror is experimentally demonstrated. The key innovation in this architecture is the use of a specially located fixed mirror to form a symmetric 2x2 retroreflective switching structure. These 2x2 fiber optic switch structures can also provide a fault-tolerant design using a macropixel approach. A two-dimensional digital micromirror device (2D-DMD) from Texas instruments (Ti) designed to operate in the visible band is used to represent the small-tilt micromirrors in our experimental demonstration. Multiwavelength switch operation is characterized by changing the operating wavelength of the tunable laser. The measured average optical coherent crosstalk is -22 dB with ±0.9 dB fluctuation over 40 nm, limited by the on-off ratio of the 2D-DMD. The measured average optical loss is 14.8 dB at a 1.55?m operating wavelength, limited by the visible wavelength design TI 2D-DMD, three-port optical circulators, fiber adapters, and free-space-to-fiber coupling efficiency.

A collective micro-optics is developed for coupling laser diode arrays to single-mode-fiber ribbons. The arrangement consists of graded-index multimode fiber ribbons and coreless silica fiber ribbons of calibrated lengths that are spliced and cleaved collectively. Coupling losses of 1.07±0.11 dB with a working distance of 30.4± 1.2 xm are achieved. A theoretical model that predicts the coupling efficiency as a function of the lengths of the sections is also established.

The phase correction process is usually necessary in the calculation of the Fourier transform spectrum. We propose one improved method to calculate the phase-corrected Fourier transform spectrum. By omitting the interpolation calculation and reducing two fast Fourier transform (FFT) operations to only one, high computation efficiency and concise algorithm structure are achieved.

We address the size of space-invariant patches in a large- field-of-view diffraction-limited imaging system. Given the coordinates of a point in the image plane, we derive the size of the space-invariant patch around it. Rather than in conventional radial and tangential directions, the size is calculated and expressed in the same rectangular coordinates as those of the image point. The presented formulas to calculate the size of the space-invariant patches are convenient to use to divide the space-variant large field of view field into the numbers of space-invariant fields.

The multistage holographic optical random access memory (HoRAM) system reported recently by Liu et al. provides a new degree of freedom for improving storage capacity. we further present a theoretical and practical analysis of the HoRAM system with experimental results. our discussions include the system design and geometrical requirements, its applications for multichannel pattern recognition and associative memory, the 2-D and 3-D information storage capacity, and multichannel image storage and retrieval via VanderLugt correlator (VLC) filters and joint transform holograms. A series of experiments are performed to demonstrate the feasibility of the multichannel pattern recognition and image retrieval with both the VLC and joint transform correlator (JTC) architectures. The experimental results with as many as 2025 channels show good agreement with the theoretical analysis.

A wavelet packet transform algorithm for color still images is presented and we show how and with what performances the transformed image tree can be pruned and the imagets altered to obtain a compression/decompression algorithm respectful of human psychovisual image perception. The basic assumptions for human vision on which the algorithm has been constructed are presented; and we deal with the color transformation used before applying wavelet packet transform. We also point out that a quasi-lossless compression/ decompression scheme can be easily obtained with a compression ratio up to 1:10 (quantization step was not considered here). Finally, a new quality criterion based on the results of tests on human sensitivity to various scale and color image details is proposed. This figure of merit can be considered a multiresolution release of the most commonly used peak SNR (PSNR) criterion.

The goal of this paper is to analyze a new notion of visual pattern that captures the primary details for the task of quantifying the visual distinctness of targets in complex natural scenes. We show that given an objective function, which is defined as the mean of the fraction of correctly classified targets across a number of datasets and whose maximization is desired, the optimal notion of visual pattern in a complex natural background can be defined as congruence in a certain statistical structure at attentional points across a range of 2-D frequency bands. We draw this conclusion from several experiments in which the best definition of visual pattern is estimated based on the relation between the visual target distinctness measured by human observers and a computational distance that applies a simple decision rule to the differences between segregated visual patterns.

A new method for enhancing the spatial resolution of lowresolution digital elevation models (DEMs) using a single higherresolution multispectral image is described. The method uses a nonlinear estimation algorithm to determine an empirical relationship between the spectral response of a pixel and the gradient or slope of its underlying elevation surface. This relationship is, in effect, the inverse of the reflectance map used in shape-from-shading to recover surface orientation from image brightness. However, unlike most shape-from-shading techniques, we do not assume constant albedo, nor do we assume a particular functional form for the reflectance map. A depth-from-gradient algorithm is used to generate high-resolution elevations from highresolution gradients using the low-resolution elevations as boundary values. Experimental results demonstrate the ability to generate enhanced resolution elevation maps from global 1-km DEMs and Landsat Thematic Mapper imagery.

An automatic object-oriented video segmentation and representation algorithm is proposed, where the local variance contrast and the frame difference contrast are jointly exploited for meaningful moving object extraction because these two visual features can indicate the spatial homogeneity of the gray levels and the temporal coherence of the motion fields efficiently. The 2-D entropic thresholding technique and the watershed transformation method are further developed to determine the global feature thresholds adaptively according to the variation of the video components. The obtained video components are first represented by a group of 4x4 blocks coarsely, and then the meaningful moving objects are generated by an iterative region-merging procedure according to the spatiotemporal similarity measure. The temporal tracking procedure is further proposed to obtain more semantic moving objects and to establish the correspondence of the moving objects among frames. Therefore, the proposed automatic moving object extraction algorithm can detect the appearance of new objects as well as the disappearance of existing objects efficiently because the correspondence of the video objects among frames is also established. Moreover, an object-oriented video representation and indexing approach is suggested, where both the operation of the camera (i.e., change of the viewpoint) and the birth or death of the individual objects are exploited to detect the breakpoints of the video data and to select the key frames adaptively.

The design and implementation of a computer-vision-based analysis system for dendrochronology are described. The primary issues covered are automatic focus detection, illumination distortion, spatial and radiometric registration of a sequence of images into a single mosaic, and edge detection and linking. These issues are not unique to the application, but are likely of interest to anyone developing automated image analysis systems. A modification of the Canny edge detection algorithm that adapts to the variable characteristics of tree-ring images is also described.

Three novel image compression schemes are proposed here for multimedia applications. The schemes are designed to combine the advantages of vector quantization and block truncation coding based on quadtree segmentation. A new vector quantization scheme, called subsampling VQ (SVQ), is proposed and used in the new schemes. The spatial correlation between neighboring image blocks and uniformity in variable-sized image blocks is exploited in these schemes. Simulation results show that the new schemes have succeeded in achieving better coding performance with subjective image quality at low bit rates.

A design of filters for pattern recognition is presented that have optimal trade-off for the criteria of noise robustness, peak sharpness, and Horner efficiency, when input scene noise is spatially disjoint (nonoverlapping) with the target. Three different criteria-signal-to-noise ratio, peak-to-output energy ratio, and light efficiency-are used to design the filter. Computer simulations for the various types of noise and parameters illustrate the performance of such filters for optical pattern recognition.

Integrated light scattering, from thin, transparent silicon wafers with different front and backside surface roughness is investigated. The measurements are made at near normal incidence in the IR wavelength region 5 to 20 xm using an integrating sphere. A method to separate the scattering contribution from each interface for measurements on transparent samples is introduced. Scalar scattering theory is used to calculate the effective root mean square roughness from reflectance and transmittance measurements, and these values are compared to profilo- meter data, correcting for the different bandwidth limits. Scattering measurements are performed with both the rough and the smooth surface of the wafer oriented toward the light source, which results in additional knowledge. The maximum ratio between the root mean square roughness and the wavelength of the light, to be used in scalar theory, is found to be considerably higher for the transmittance case than for the reflectance case. In agreement with theory, the calculated root mean square roughness is found to be proportional to the refractive index of incident medium in reflectance, and to the difference in refractive indices of incident and refracting medium for the transmittance case.

We report on three novel vertical-cavity laser (VCL) structures for 1.55-?m operation. Two of the structures utilize an n-type GalnAsP/ InP Bragg mirror combined with an Al(Ga)As/GaAs mirror using either wafer fusion or metamorphic epitaxial growth. The third employs two wafer-fused AlGaAs/GaAs mirrors, in which lateral current confinement is obtained by localized fusion of the p mirror. All three VCLs use strained GalnAsP quantum wells as active material and achieve continuous-wave (cw) operation at room temperature or above. The single fused VCL operates up to 17 and 101°C in continuous-wave and pulsed mode, respectively. The monolithic VCL-structure with a metamorphic GaAs/AlAs n-type mirror uses a reverse-biased tunnel junction for current injection. This laser achieves record high output power (1 mW) at room temperature and operates cw up to 45°C. The double fused VCLs with a 10x 10-?m2 active area operate cw up to 30°C with threshold current as low as 2.5 mA and series resistance of 30 H. The emission spectra exhibit a single lasing mode polarized with 30-dB extinction ratio and a spectral linewidth of 150 MHz.

A real-time two-color laser speckle-shift strain measurement system based on the technique of Yamaguchi was designed, built, and tested at room temperature. This noncontact 1-D system detects surface strain in a structural fiber as it is pulled in a tensile test machine. Interference or speckle patterns from the laser-illuminated fiber test specimen are recorded. As the fiber is pulled, its speckle pattern shifts in proportion to the strain, translational, and rotational components of the sample deformation. Shifting speckle patterns are detected using two linear CCD arrays with image processing performed in realtime by a hardware correlator. Surface strain is detected in fibers with diameters on the order of 100?m and can be resolved to 20 ?m/m. This system was designed to be robust and compact and generally does not require surface preparation of the structural fibers.

Two laser-based, optical techniques for drop-size measurement, which have been employed to obtain drop sizes in liquid-liquid pipe flow, are described. The measurement systems used are a laser diffraction technique (Malvern 2600 instrument) and a laser backscatter technique (Par-Tec 300C). The instruments are checked through measurement of a batch of glass beads suspended in water in a stirred cell. An image analysis technique and a phase doppler anemometer provide independent measurements of the size of the beads. The pipe, which is 0.063 m in diameter is installed on a liquid-liquid flow rig. The liquids used are kerosene (continuous phase) and aqueous potassium carbonate solution (dispersed phase). Special test sections are used to deploy the instruments. There are significant differences between the results from the two instruments.

A technique and apparatus for noncontact dynamic parameter measurement of micro- and macrodevices using an acousto-optic (AO) deflector for scanning is introduced. This system adopts an AO deflector to induce scanning in the laser beam rather than deflecting mirror or the movement of the X- Y stages to improve the positioning accuracy. The apparatus for incorporating a homodyne system in a laser scanning system is described. The system is composed of an interference technique by which the frequency shift induced in the scanning beam using the AO deflector is canceled out. Experimental results on measuring the dynamic parameter of the hard disk surface and the slider head on different scanning points are discussed.

A novel idea of utilizing a quarter-wave plate (QWP) to enhance the sensitivity of roll angle measurement is verified both theoretically and experimentally. The roll angle measurement is based on optical heterodyne phase detection and its sensitivity is enhanced by setting the polarizing angle, which produces elliptically polarized light. An experimental setup is described and the experimental results presented are considered with the theoretical predications. With this practical configuration, the resolution of roll angle is 0.6 arcsec.

The combined process of sampling and nonideal interpolation in imaging, which is not a shift-invariant process, is formulated in terms of a modulation transfer function (MTFs-i). This function is defined as the average envelope of the interpolated output at the sampling points, where the input is a sinusoid and the averaging is over the phase shift of the input relative to the sampler grid. This quantity can be useful in approximating spatial variant systems with the convenient notation of shift-invariant systems. The MTFs-i is derived as two cascaded MTFs: the first one, MTFs, accounts for the replicas of the sampled input that remains in the interpolated output, and the second, MTFi, corresponds to the attenuation of the original signal by the interpolation filter. Unlike the current assumption that MTFs is always a lowpass function, it is shown that at high frequency it has a distorted highpass characteristic. Following Michelson's definition for the visibility of fringes, an index of performance associated with the spatial variation of the process is suggested.

We demonstrate all-optical logic gates using bacteriorhodop- sin (bR) film. By studying the transmission of bR film, we advance an all-light-modulated transmission mechanism of bR film: complementary suppression-modulated transmission (CSMT). When a yellow beam (568 nm) and a blue beam (412 nm) illuminate bR film, the two transmitted beams suppress mutually. Based on this mechanism, we design an alloptical operating device in which we implement all 16 kinds of doublevariable binary logic operations. The intensity of an incident yellow or blue beam acts as the input to the logic gate and the transmission bears the output of the gate. We can turn this all-optical device into different states using different wavelengths and different intensity illuminations.

photorefractive two-beam coupling and energy transfer in BaTiO3 are studied at multiple wavelengths using He-Cd, He-Ne, and diode lasers. The photorefractive signal beam gain is measured as a function of the pump beam intensity, beam ratio intensity, spatial frequency of the grating, and angle between the grating vector and c axis of the crystal. The exponential gain coefficient is calculated from signal beam gain, and its dependence on the same parameters is studied. The dependence of the signal beam gain and exponential gain coefficient on spatial frequency are also evaluated theoretically and found to be in good agreement with the experimental data. Also, the signal beam gain is studied as a function of wavelength, and a very high value is obtained at 441.6 nm. Figure-of-merit parameters such as the maximum change in the refractive index, the space charge field at saturation, the trap density of the charge carriers, and the photorefractive sensitivity of the crystal are calculated from the experimental data. since the absorption in BaTiO3 varies strongly with wavelength, its influence has been included in the calculations of the figure-of-merit parameters. The results are discussed in the light of the present understanding of photorefractive phenomena in crystals.

Past investigations of membrane mirrors have led to the conclusion that they are not suitable for imaging in the visible. We reexamine this conclusion and discuss ways to circumvent the principal problems. A reanalysis of l'Garde measurements of a 6-^m-thick membrane mirror corrects earlier interpretations of the "W curve'' asymmetry. Correction of the classical Hencky aspheric shape of membrane mirrors is required to upgrade them for use in visible passbands. The theory of variable membrane thickness in a radial direction is presented. A numerical integration is done and a unique quadratic radial variation of thickness is found that corrects for the u4 Hencky term. Two methods to fabricate such a membrane are presented.

We study the problem of estimating the spacecraft attitude angular velocity using the signal of the spacecraft attitude angular sensors such as the IR horizon sensor, the star sensor, and the full attitude global positioning systems (GPS) sensor for the first time. A signal state model is established. Based on the linear least mean squares (LMS) error criterion, recursive Kalman filtering is developed for the direct estimation of angular velocity. Our algorithm requires relatively few computations and relatively small storage quantities. Finally, the new algorithm is applied to a set of physical simulated IR data, and the results have the advantages of smaller time lag, higher accuracy, and perfect smoothness.

A method for finding the attenuation coefficient of a planar or channel waveguide is described. Results for SiO2 and NdF3 waveguides were obtained, showing that the latter presents better attenuation characteristics. The influence of the prism shape on the measurements was also tested and found to result in variations in the measured attenuation coefficient. Two different locations of the waveguides were selected for the coupling, and again variations occurred, suggesting irregular thickness of the thin films. The method uses concepts based on the angle- limited integrated scattering technique and also on the well-known prism coupling method. It may be possible to make the system fully automatic.

The use of ion-exchanged waveguides to address the voxel emitters of a volumetric three-dimensional display promises to be a reasonable high-volume, high-resolution fabrication technique. We report on the fabrication and initial characterization of a first prototype of this novel display architecture.

Phase nonlinearity in polarization-coded interferometry is a systematic error that is periodic in nature and entirely optical in origin. Since its first appearance in the literature,1 there has been considerable effort in nonlinearity measurement and characterization2–8 and in theoretical modeling.

This PDF contains the communications section which includes "Self-aligned photoresist patterning for integrated optics".