This PDF file contains the editorial “Editorial: From Russia--With Love” for OE Vol. 30 Issue 12

Far-field diffraction patterns of a glass cylinder are spatially sampled with a photodiode array. Three photometric signal processing methods are discussed. The first one is based on the analysis of fringes in the central lobe. It can be used for diameter monitoring, but not for a wide range of diameter measurements. The second method consists of best-fitting between the theoretical model of the irradiance distribution in the central fringe and the corresponding experimental data. The accuracy of this method (±1 μm, in the range 10 to 50 μm) is improved by introducing the optical transfer function (OTF) of the photosensitive area into the calculation. The third method uses a reliable estimation of the intensity at the center and the half-width of the central fringe in order to resolve the inverse problem by Newton's method. This method can be used for realtime measurements but must be improved by statistical approaches.

Speckle patterns can be used as natural surface markings that are printed by the high coherence of laser light. Speckle displacement caused by linear or rotary motion of a surface is detected with a linear image sensor whose output is analyzed by a real-time correlator. By using an image sensor of 15-μm pitch and 1024 elements, resolution of a micrometer and 1/1000 deg have been attained. The main advantages of the encoders are extreme simplicity in optical configurations and wide ranges of measurement.

The potential of silver halide emulsion as a low-cost material for noninterferometric recording of computer-generated phase holograms is evaluated by contact-printing binary-amplitude masks on this material. This process is found to result in a nonbinary surface-relief profile with appreciable overshoot in the vicinity of the intended phase jumps. Interestingly, the refractive-index modulation profile compensates for this effect, resulting in a nearly binary phase delay profile. Residual absorption in the emulsion and pattern transfer errors, most noticeable within small features, are found to limit the array size that can be achieved with a given period. The feasibility of the application of silver halide emulsion in recording holograms with a continuous profile is discussed.

A new definition of picture degradation error caused by the sampling-transferring process in image scanners is described. The aim of this new error definition is to characterize the whole image transfer process. A method is shown based on calculation ofthis similarity error (which could also be called spectral distortion error) to estimate the possible character recognition error rate related to the optical transfer functions and sampling performance of the scanner. The increase of the probable reading error can be sufficiently estimated by the similarity error. Theoretical and experimental results are in good accordance. The different character types, scanners, and printer outputs can be characterized by this method, as well.

An improved ray model for simulating the transmission of laser radiation through a metallic or metallic-dielectric multibent hollow cylindrical waveguide has been developed. It calculates the power transmission and the power density at any point along the curved waveguide, as a function of geometrical dimensions of the waveguide, coupling lens at the entrance, polarization (random, vertical, or perpendicular), and the 3-D trajectory of the waveguide. The theoretical calculations are compared with the experimental results.

The statistical behavior of irradiance over a ground-based IR sky image is dependent on the angle of elevation at which the image was made. Images made at different elevation angles cannot be compared unless a correction is made for the different viewing angles. The angle-dependent radiance caused by the difference in the optical path length over the field of view of the image must also be corrected, otherwise incorrect conclusions will result. Once the corrections have been made, the image can be analyzed and the true statistical parameters of the image can be obtained.

An algorithm has been developed to reconstruct the internal temperature distribution within a rising buoyant thermal from measurements of the radiances by an infrared imaging camera. The technique is applied to detonation of a stoichiometric mixture of methane and oxygen contained in a 3-m-diam mylar balloon. The temperature-time histories of the evolving fireball showed torus formation, followed by rapid cooling from entrained ambient air. Comparison of the temperature distribution with results of an Eulerian hydrodynamic computer code shows good agreement except at the center of the fireball. A possible explanation might be the lack of an entrainment mechanism in the hydrocode.

Aberrations introduced due to focus and tilt adjustments between the optical fiber cylindrical reference and line focus formed by a cylindrical optic in a Fizeau interferometer arrangement are examined.

The evaluation of the interference pattern of a prism interferometer by a phase-stepping technique is described. The required phase shift is achieved by moving the surface under test perpendicular to the hypotenuse of the prism. Limits of this phase-shifting technique are discussed. A calibration method of the phase shift between the interferograms for the adjustable sensitivity of the interferometer is shown. Finally measurements of technical surfaces are presented.

The modulation transfer functions (MTFs) of hexagonally sampled arrays with both rectangular and hexagonal pixel shapes are derived from spatial averaging considerations. In one direction, the hexagonal pixel shape is shown to provide a 13.6% improvement in MTF at the Nyquist bandlimit over an equivalent rectangular shape. For the orthogonal direction, the hexagonal shape has a slightly worse MTF, which is 4.8% less than the MTF of the rectangular shape at the Nyquist bandlimit.

An algorithm utilizing a syntactic approach and a criterion based on normalized moments is developed for the reliable, automatic, machine recognition of handwritten and printed Greek characters of any size and font. In this approach a binary image of the character in question is obtained initially; its skeleton is then produced by utilizing a standard thinning algorithm. The classification process then incorporates the topological features of the characters such as existence of closed curves, number of intersections, number and location of free ends, axial symmetry, and the criteria derived from normalized moments to uniquely identify each pattern. An alternate approach involving a mathematical (geometrical) modeling of each character is also proposed. In this method, each character is to be individually modeled to a standard geometrical shape and the least-mean-square method is used to form the best fit. Characters like alpha, beta, gamma, omega, theta, omicron, and rho have been modeled with standard geometrical shapes such as circles, lemniscates, cardioids, ellipses and lines. Experiments conducted for both approaches demonstrated a very high recognition rate.

The systems considerations in implementing a bit serial optical computer using lithium niobate directional couplers and optical fiber is described. The three main problems in constructing such a computer, computation of fiber lengths, estimation of and compensation for power losses, and details of the physical construction of the machine, are discussed.

Optically switchable directional couplers can function as logically complete building blocks for constructing all-optical computational engines. Logically, such devices operate as all-optical five-terminal gates, where the two output signals are logical functions of two throughgoing input signals and a control input signal. Such an optically controlled exchange element is a promising functional unit for constructing general-purpose digital optical logic circuits. The implementation of such all-optical five-terminal gates using Ti:LiNbO₃ electro-optic directional couplers is described. These optical logic gates utilize mature technology developed for the telecommunications industry, facilitating construction of robust optical logic hardware. Single-mode optical fiber is used for all logical interconnections. Effectively dc-coupled control circuitry converts optical pulses into electrical pulses capable of switching the transfer state of low-voltage lumped electrode directional couplers. The use of such Ti:LiNbO₃ five-terminal optical logical gates in the construction of various simple circuits such as oscillators and divide-by-N circuits is shown. Such circuits demonstrate many of the issues arising in the construction of all- optical digital computing systems, and are fundamental subsections of an all-optical bit serial computer design currently under construction.

We describe a new type of bistable, optically addressed ferroelectric liquid-crystal spatial light modulator to be used as a binary spatial register. The good contrast ratio of the devices suggests their use in cascaded architectures or in optical feedback loops. We investigate these cascading abilities with a view to digital optical computing applications.

A theoretical analysis of a joint transform correlator that uses a phase-only spatial light modulator to input joint transform plane intensity data into the second Fourier transform system is presented. It is shown that this correlator produces signals that differ from, but are related to, the mathematical correlation between the test and reference input images. An undesirable characteristic of the correlator is that the form of the output signals depends on both the intensity-to-phase transfer characteristic of the phase modulator and the intensities of the input images. However, apodization of the joint transform intensity distribution by the reciprocal of the intensity distribution of the reference image Fourier transform can overcome this problem, and results in a correlator with narrow matching output peaks and high discrimination, in which the autocorrelation peak can be eliminated. Theoretical results are demonstrated by computer simulation.

We describe an optical fingerprint identification system that optically reads a latent fingerprint for correlation using a binary joint transform correlator. The fingerprint is read using the total internal reflection property of a prism. The system was built, tested, and the experimental results are presented.

In the next decades, we foresee the need for the fabrication of many large aspheric mirrors for space and astronomy applications. Itek Optical Systems has developed computer-controlled optical surfacing for rapidly fabricating such optics. Recently, these operations have been improved with the development of a sheaf of new processes based on a greatly increased understanding of the mechanics of glass surfacing. These improvements have already produced a reduction of large optics surfacing time by a factor of four, and the technology points toward a possible further reduction by a factor of two.

The results of an experimental investigation of the use of prismatic mirror arrays as a crossover interconnect are presented. Analysis of the precision with which it is necessary to fabricate and align the interconnect is discussed. This precision is found to be proportional to the mirror array size.

The problem of feeding and controlling the radiation pattern of phased-array radar has a novel solution involving the use of fiber and Fourier optics in the system originally proposed by Koepf in 1984. We give analytical descriptions of that system and introduce novel nonlinear optical techniques to address accuracy and alignment issues.

When a three-dimensional (3-D) object is imaged by means of an endoscope, only a two-dimensional (2-D) display is possible. In some medical diagnostics, the size and shape of the object under study need to be known. An effective method for reconstructing a 3-D object shape from a 2-D endoscopic image exploits the projected grating technique. This method is described and illustrated with some examples.

Analytical expressions and numerical methods are obtained for calculating the wave form, contrast, and frequencies of the optical output signal in amplitude- and frequency-modulating straight-spoked reticles when the optical input signal is assumed to be a Gaussian distribution of intensity. A comparative study of reticles with different numbers of spokes shows a similar behavior. A criterion is described for the design of the most sensitive reticle under small changes in the input signal.

An optical-digital technique for classifying rough surfaces that uses the irradiance moments extracted optically from the Hartley transform intensity of a rough sample is described. A set of discriminant features based on the lower moments is used to compute a discriminant function for the classification task. An example of application to classification of machined surfaces is also carried out.

A high-speed optical system capable of performing n-bit multiplication in a time proportional to log₂n is presented. The simultaneous generation and the optical regrouping of all the partial products and the pairwise addition of the partial products by means of a binary tree of adders capable of adding any two numbers in a single stage (by completely eliminating the carry propagation chain) are unique features of this multiplier. The input data to the multiplier can be in either a binary or a modified signed digit number system. The simultaneous generation and the pairwise addition of the partial products are accomplished by means of the principle of symbolic substitution logic that was originally proposed by Brenner.

One of the most important considerations in the design and manufacture of multilayer mirrors is material compatibility. Ideally, the materials selected should not chemically react or interdiffuse, thereby avoiding the formation of second phases, thus enhancing the smoothness of the layer interfaces and the reflectivity of the optic. The transparency of the spacing layers can therefore be augmented by materials of low absorption. Initial findings with B₄C layers indicate deposits that show smoother layering than those containing carbon, with the advantages of greater stability, lower absorption, and therefore greater reflectivity. The manufacture, microstructure, and reflectivity of W/B₄C multilayers are discussed.

This PDF file contains the editorial “Book Rvw: Optical Materials: A Series of Advances, Vol. 1," edited by Solomon Musikant for OE Vol. 30 Issue 12

This PDF file contains the editorial “Book Rvw: Image Recognition by Holography. G. I. Vasilenko and L. M. Tsibul'kin for OE Vol. 30 Issue 12