This PDF file contains the editorial “Editorial: A tribute to Rudolph Kingslake on his 90th birthday” for OE Vol. 32 Issue 08

This PDF file contains the editorial “Guest Editorial: Special Section: A Tribute to Rudolf Kingslake” for OE Vol. 32 Issue 08

Practical solutions for most optical system designs require small third-order aberrations. True global optimization requires repeated searches based on experience. Ready acceptance of a final solution can lead to problems.

Lens design is one of the most basic activities in optical engineering. The subject requires an active working knowledge of all aspects of optics, and is a profession changing with the rise of new techniques in modern optics. The approach to teaching the subject is discussed, and the changes that have taken place over the past few decades are described.

New computer technology is changing lens design from a unique profession to a branch of optical engineering. However, the fundamental problem of optical design remains: the construction of a suitable merit function (mathematical or otherwise) to specify the properties of the optimal design. As the scope of optical design expands, the number and variety of data to be included grow correspondingly. The conventional image quality specifications of an optical design are too simplistic to characterize a lens: tolerances, operating conditions, and manufacturing data must also be included. It is useful to think of optical design as a process of documentation preparation, in which the document consists of the lens data and all the other data needed to construct the merit function.

A brief discussion of lens design is given. The future of lens design is in computer programs that analytically solve equations for the best starting solution, which is preferred to global optimization techniques.

The special properties of lens design as an optimization problem are discussed and are related to the properties of the Levenberg-Marquardt (damped least-squares) optimization method. Several variations of the basic method are discussed and compared. Some examples are given to illustrate the effectiveness and limitations of the method.

The advent of computers and the resultant use of programs for the design and optimization of optical systems are sometimes seen as a revolutionary turning point in the history of optics. In the last few years, there has been a growing tendency to believe that the use of software and hardware will automatically provide the best possible lenses at the mere press of a button. Even the latest advances made in software development-the programs for so-called global optimization-cannot make this misconception a reality. A review of global optical design is presented, with emphasis in the optical systems of lenses, the structure of which ultimately determines image formation and, hence, image quality. The structural analysis of optical systems using the theory of aberrations is a suitable means of explaining how optical systems work. This analysis also highlights design affinities and analogies and, hence, defines regions of solutions. From the standpoint of global optical design, I not only discuss lenses from the golden age of optical design, but also recent and less recent lenses from the age of computers.

Global optimization is examined from the viewpoint of lens design for commercial production optics and is found to be unsatisfactory in its present state because of the need of the lens designer to remain involved in rather than divorced from the work. A genetic algorithm based on the use of nearly zero power operators that perform structural changes to a Gaussian optics system design is proposed. The algorithm selects operators that improve system performance or fitness using procedures of mating and random crossover and breeds succeeding generations of new operators that, when applied to the starting Gaussian optics system and then optimized, yield an improved lens design. The algorithm is efficient, robust, and allows lens designers to relate to designs in terms of aberration correcting means.

The direct-view CRT, because of its readily available technologies, is considered one of the most viable approaches for high-definition television (HDTV) displays. The advantages of using a direct-view CRT include its brightness, contrast, resolution, viewing angles, etc. However, because the engineering requirement for a HDTV display is much higher than that for a standard TV, improvements in all these areas are needed. A review of the current status and the potential for further improvements are discussed in detail.

Modeling of a liquid crystal display (LCD) includes two parts: one is the calculation of the LC director deformation profile inside the cell and the other is the LCD optics computation. For the LC director deformation profile calculation, it is usually assumed that all the LC molecules within a pixel respond together uniformly to a driving voltage. This one-dimensional (l-D) simulation is a good approximation for most cases. However, due to the finite size of the pixel, the pixel fringe field may drive the LC molecules near the pixel edge to tilt in a direction different from those in the center of the pixel. To understand the detailed LC director structures inside the pixel and their effect on the display performances (especially for the small pixel), the two-dimensional (2-D) or sometimes the three-dimensional (3-D) simulation is required. The l-D, 2-D, and 3-D simulations of the LC director deformation profile are reviewed. For the LCD optics, besides the 4 x 4 matrix method, an alternative method is also discussed. Finally, examples using the 1 -D, 2-D, and 3-D LCD simulations for improving the display optical performances are illustrated.

Two kinds of liquid crystals are selected with the aid of computer simulation for the fabrication of high-contrast liquid crystal displays (LCDs). One is suitable for the first minimum operation of a twisted nematic LCD and the other is suitable for the second minimum operation. The contrast ratios in the normally white mode of the first minimum operation and the contrast ratio in the normally black mode of the second minimum operation are both higher than 100:1 . These LCDs can be used in direct view and projection applications.

Refractive indices of two nematic liquid crystals, 5CB and 5PCH, were measured from the 400- to 800-nm region at various temperatures. Results fit the three-band model well. Through comparisons, the contributions of σ and π electrons to the refractive indices and birefringence of uniaxial liquid crystals are evaluated quantitatively. These physical insights are useful for tailoring liquid crystal molecules with proper refractive indices.

We describe the polymer-dispersed liquid crystal light valve (PDLCLV) using a polymer-dispersed liquid crystal (PDLC) film and a Bi₁₂SiO₂₀ (BSO) photoconductive crystal. The PDLCLV has many features suitable for large screen displays, such as no polarizer requirement, a high transmittance (72 to 78%) and high extinction ratio (146:1 to 178:1) in the entire visible wavelength, short rise/decay times (3/5 to 14/15 ms), and a high resolution (34 lp/mm). We discuss the light scattering and modulation characteristics of the PDLC film; photoconductive characteristics of the BSO crystal; and the design, fabrication method, and optical input/output characteristics of the PDLCLV. We also describe the configuration and image display characteristics of a monochrome projection-type display consisting of the PDLCLV as an image converter, an active matrix liquid crystal panel with thin film transistors as an image source, and a 1-kW xenon arc lamp as a reading light source.

Several fluorinated diphenyldiacetylene and tolane liquid crystals are synthesized and their physical properties evaluated. These liquid crystals exhibit a high resistivity, high birefringence, low viscosity, and modest dielectric anisotropy. Some difluoro compounds show a relatively low melting temperature and small heat fusion enthalpy and are useful for formulating eutectic mixtures. The mixtures consisting of these fluorinated compounds are particularly useful for active matrix, photoactivated light valve, and polymer-dispersed liquid crystal displays.

Polycrystalline silicon (poly-Si) thin-film transistors (TFTs) with thin oxide/nitride (O/N) structures as gate dielectrics are fabricated. Various gate dielectrics, i.e., high-temperature thermal oxides with different thicknesses, low-pressu re chemical-vapor-deposited silicon nitrides, and different combinations of O/N structures with various thicknesses, are performed to study their effects on poly-Si TFTs. The effective carrier mobility of devices with thin gate oxides is several times larger than of those with thick gate oxides. However, the breakdown voltages of thin gate oxides are too low to satisfy the requirements of TFT applications. Silicon nitrides can be substituted because of the high breakdown voltage and the smooth dielectric/poly-Si interfaces. A problem in adopting silicon nitride is the large interface stress between the silicon nitride and the poly-Si. A thin thermal pad oxide beneath the silicon nitride is therefore grown to reduce the high interface stress. Finally, the equivalent oxide thickness effect of the O/N gate structures on the electrical characteristics of TFTs is systematically investigated.

To evaluate the interface properties of a thin-film electroluminescent (EL) stacked-layer insulator structure, four kinds of samples with different insulating layers are prepared. We found that by using insulating layers with a low resistivity and a high dielectric constant adjacent to the active layer, we can greatly improve the emission characteristics. We also found that the EL device with a glass/indium tin oxide/BaTiO₃/ZnS:TbF₃/HfO₂/Ta₂O₅/HfO₂/Al structure exhibited higher brightness and higher efficiency than the other devices. The highest luminous efficiency η and brightness of 0.9 lm/W and 1000 cd/m² were obtained, respectively, by applying a 1-kHz sinusoidal wave voltage.

A novel method to combine a microscope and an optical multichannel analyzer (OMA) into a microspectrophotometer (MSP) system is presented. In this system, an optical fiber was mounted into the image plane of the microscope both to collect light from the microscope and transmit it to the OMA for spectral analysis, as well as to conduct light in the reverse direction into the microscope for alignment purposes. The system is easy to construct, is simple to use, and has a higher spectral resolution than conventional MSPs without increasing the acquisition time. Its sensitivity depends on the photodetector used in the OMA. For the two application examples presented, (1) absorbance spectrum measurements of cytoplasm and nuclear areas of Papanicolaou-stained cervical cells and (2) autofluorescence spectrum measurements of different locations of unstained and unfixed skin tissue sections, this system was found to possess adequate sensitivity.

We present a new algorithm for computer color matching that combines effectively spectrum matching with tristimulus matching. The result is of great value in practice.

We describe a simple technique for aligning optical fibers prior to fusion splicing. The technique relies on the fact that well-cleaved fiber ends have extremely sharp edges. By making the narrow pencil of light emerging from one fiber scan laterally over the entrance face of a second fiber, and by monitoring the light diffracted past its sharp edges, we can locate precisely the geometric center of the output fiber. With this technique, we have aligned fiber cores with a mean lateral offset of 0.81 μm, the major part of this offset caused by the eccentricity of the core relative to the cladding's circular perimeter.

We report a method of measuring workpiece position in laser material processing and machining that uses a fiber optical beam delivery system. The method is based on a measurement of the power propagating in the cladding of the optical fiber in the direction from the workpiece to the laser. The power reflected from the workpiece and coupled into the cladding is shown to be a function of the position of the workpiece relative to the beam waist formed by the output optics of the beam delivery system.

The simultaneous measurement of the spectrally and spatially variant transmittance of a linear variable order-sorting filter in a manner that closely resembles its conditions of actual use is described. The transmittance of a prototype order-sorting filter was measured in the 400- to 880-nm wavelength region by illuminating it with the output beam of a spectrophotometer while the filter was attached to the front of a 30 x 32 pixel silicon array detector. The filter was designed to be used in the output beam of a grating spectrometer to prevent the dispersal of higher diffracted orders onto an array detector. Areas of the filter that were spatially matched to the corresponding detector pixel column had measured peak transmittances of about 90% that were uniform to within ±1.5% along a given column. Transmittances for incident wavelengths shorter than the desired bandpass, corresponding to the order overlap region, were measured in the 3 x 10^-3 range. Line spread function measurements made with the array detector indicated no significant beam spreading caused by inserting the filter into the beam.

Polarizing computer-generated holograms (PCGH) may be useful combining different optical functions such as polarizing, imaging, beam shaping, and beamsplitting in one element. We propose the fabrication of PCGHs based on microstructuring of polarizing or birefringent materials. A simple and useful method of production of binary and grayscale-amplitude PCGHs by laser beam bleaching of polarization foil is shown. Experimental results are presented.

A detailed characterization of the Du Pont photopolymer holographic film (HRF-150-38) for thick transmissive holograms is described. Several aspects important for angularly multiplexed holographic memories have been considered. Emphasis is on development methods and shrinkage. The two plane wave case as well as the converging object wave case are described in detail.

We describe a compression scheme that aims at improving the fidelity of reconstructed images through the parallel application of both lossless and lossy compression techniques. The purpose of the scheme is to obtain compression ratios higher than those obtained by lossless compression schemes and at the same time produce reconstructed images with better fidelity than those normally obtained with lossy techniques. The straightforward (nonoptimized) application of this scheme consistently improves the fidelity of reconstructed images compared to a raw discrete cosine transform (DCT) algorithm. Using standard lossless compression utilities, the integrated scheme gives better fidelity (up to 62% improvement in mean square error) than the raw DCT algorithm under equal compression ratios. Further research is needed to optimize the integrated method, adapt it to the Joint Photographic Experts Group and other equivalent schemes, and evaluate the resulting performance. A discussion of ways that can further improve the efficiency of the integrated approach is given.

Correction of photoresponse nonuniformity in IR staring sensors is investigated. Spatial noise expressions for uncorrected, one-point corrected, and two-point corrected imaging are developed. These theoretical results take into account the properties of the IR source, sensor constants, and spatial variations in the IR imaging device. To demonstrate the application of these results, both theoretical and actual spatial noise curves for a platinum silicide IR sensor are presented.

A polarizing grating beamsplitter working in reflection at the 10.6-μm wavelength is presented. The grating was designed using rigorous diffraction theory. The incident TM-polarized light is not diffracted but reflected as the zero order, and the TE-polarized light is mainly diffracted into the + 1 and - 1 diffraction orders. The grating is a surface relief with a metal coating. It consists of V-grooves and is fabricated in silicon using photolithography and a combination of dry and wet chemical etching. The measured diffraction efficiencies agree with the theoretical predictions. The sum of the measured diffraction efficiencies of the + 1 and the - 1 orders is 90% for TE polarization and 6% for TM polarization. If the grating is in a conical mount, it can be used as a beam attenuator or a three-way beamsplitter.

The calculation results in a one-dimensional (1-D) interconnection system are proposed. The method of preparing phase-only masks with reactive ion etching is introduced. The masks are applied to a 1-D interconnection experiment. The experimental results are consistent with the theory.

The design, assembly, and testing details of an objective lens used to image an array of 4096 beams are discussed. The main characteristics of the lens are a 15-mm focal length, a speed of f/1.5, diffraction-limited quality, telecentricity, f-sin(θ) mapping, an external stop, and a simplicity of fabrication.

Highly sensitive and stable detection of minute ac and pseudo-dc (i.e. , very low frequency) vibrations is performed by means of a differential fiber optic Michelson interferometer. Any residual instabilities are eliminated by means of an ac feedback control loop. The stabilization technique is not affected by the variations in the reflectivity of the sample and by launch inefficiencies into the fiber. This approach also provides a simple, quantitative method for calibrating sample vibrations. Results are presented on the operation of the system in stabilizing its output as well as on the detection of the vibration of a silicon sample.

Phase-shift interferometry suffers from periodic systematic errors caused by erroneous reference phase adjustments and instabilities of the interferometer. A new method is described that uses only four interferograms and eliminates the errors caused by linear adjustment deviations of the reference phase or the mean phase in the interferometer. Test results confirm the theoretical predictions.

We investigate the optimal designs of binary phase and amplitude filters (BPAF5) for the key correlation metrics of peak intensity, peak-to-correlation energy, SNR, and discrimination. These filters may be implemented on binary polarization-rotating spatial light modulators. We present simulation results comparing performance to conventional binary phase-only filters (BPOFs) and illustrating trade-offs between the different performance criteria in terms of the filter design parameter. We also extend the generalization to three-level phase and amplitude filters with a nonzero region of support and demonstrate that optimal three-level BPAFs can provide clearly superior performance to optimal three-level BPOFs.

Based on the theory of partially coherent light, an analytical scheme is established to determine the radiative properties of multilayer thin films. Accurate knowledge of the magnitude of interference effects is absolutely indispensable when measurements of the spectral transmissivity and reflectivity of thin films are used to derive optical constants of the film material. As illustrated by experiments, in many cases of practical interest neither a geometrical nor a wave-optics model gives satisfactory results. A general formulation is introduced that covers this intermediate partially coherent regime as well as the limiting cases of geometrical and wave optics. The complex degree of coherence provides a direct measure of the varying influence of interference effects on spectral measurements. An analytical approximation of the numerical approach is developed that gives a good physical understanding of the occurring phenomena. Experiments on the transmissivity of a one-layer glass film using a Fourier transform infrared spectrometer in the medium infrared range (λ = 2 to 20 μm) confirm the theoretical approach and the relevance of the addressed issue.

An optoelectronic device for generating random numbers at high flow rates is presented. Such a device can be exploited for implementating massive arrays of stochastic decision-making elements encountered in simulated annealing and in Boltzmann machine algorithms. It is comprised of an optical random number generator and an array of electronic neuron elements. The random number arrays are derived from the continually changing modal noise of a step-index optical fiber, and the neuron elements include photodiodes and a few associated electronic components. To demonstrate the feasibility of large arrays of neuron elements, a circuit with three neurons has been implemented and tested. The results reveal that 10⁴ neuron elements can be integrated into 1 cm² and that flow rates of 10¹⁰ random numbers per second are possible.

A method is discussed for determining range using an image blurred by lateral translation of the camera optical axis. We describe a system consisting of rotating and stationary mirrors that accomplish optical axis translation without actual motion of the camera. Three different methods for determining the range from motion blur are presented. Experimental results for both synthetic images and images using the rotating mirror apparatus are discussed. It is concluded that the optical apparatus performs adequately and that two of the computational schemes are appropriate for further study using more complex images.

In our work with the phthalocyanines and perylenes, we have formulated a hierarchy of placement of dyes in p-n heterojunction devices to optimize the short-circuit current density. Computer modeling of Schottky barrier cells, with parameters fit to experimental results and incorporating field-dependent carrier generation, were used to optimize the power efficiency. The model predicts an optimum carrier concentration density and suggests different hierarchies for utilization of Förster radiationless energy transfer. Synthesis and purification of materials is also discussed. In terms of purity, most materials used in the literature are shown to have been quite below solar grade. A newly devised purification technique is introduced. A hydration mechanism is shown to exist for chloroaluminum phthalocyanine, previously thought immune to hydration. The latter mechanism had been mistaken before for a simple phase transformation and can be induced by various different treatments with organic nonsolvents for chloroaluminum phthalocyanine. Testing of p-n and Schottky barrier cells is also discussed. The different capacitance versus voltage (C-V) spectroscopies are compared, and the case for the small-signal method is argued over the triangular voltage sweep. Several cautions on the interpretation of the C-V curves are noted.

Edge detection is useful for locating objects of interest within an image and reducing the amount of processing required for the image analysis. Methods for edge detection usually involve convolving the image with an operator designed to have a relatively high output when an edge or gradient is present. In textured or noisy images, however, the edge-detection scheme must take into account the nature of random fluctuations throughout the image to limit erroneous detections. Two statistical tests for detecting edges in images corrupted by speckle are presented. The tests are based on the nonparametric Wilcoxon two-sample test and a parametric test derived from an exponential model for the speckle. These edge detectors are presented as null hypothesis tests for determining the presence of an edge based on significant changes in the location parameters (first-order statistics) between pixel neighborhoods. The null hypothesis test formulation allows for threshold determination based on desired false-alarm probabilities. Simulation results demonstrate the ability of the nonparametric test to maintain a constant false-alarm probability under variations in the skewness of the speckle statistics, whereas superior detection probabilities are achieved with parametric tests over a broad range of statistical variations. Examples of detector performance for ultrasonic images from breast tissue are also presented and interpreted in terms of the simulation results. Conclusions are presented outlining conditions for the successful application of parametric and nonparametric techniques for edge detection using first-order statistics.

The multiaperture overlap-scanning technique (MAOST) is a new method for large optics testing. We describe the mathematical model and the performance procedure of the transformation and connection of subapertures for MAOST. Computer simulation results show that the theoretical accuracy of a pair of two-subaperture connections tested with MAOST could be reached up to λ/600. The experimental test with a magnification ratio of 1.7 in a four-aperture overlap-scanning configuration is conducted and its result is analyzed in detail

Foucault knife-edge testing has been the classic qualitative test method for optical surface and wave-front quality measurement for more than one hundred years. We have developed an upgraded quantitative method, using off-the-shelf digital microprocessors and a solid state camera, to provide white-light evaluation of generalized optical surfaces with the precision and accuracy of computer-aided laser interlerometry. We describe a method that upgrades the knife-edge test from a qualitative test to a precise quantitative evaluation. The hardware is described and initial results for some aberrations are shown comparing the knife-edge test with interferometric measurements.

Interactive image-guided surgery is the synchronous display of surgical position on medical images during surgery. We have developed a technique for the dynamic display of surgical position on up to three independent sets of tomographic images. Each of these image sets may be composed of square images of any size and are limited only by the size of the disk in the system. In addition to the raster images, a graphic display is provided for visualization of relative position and surgical trajectory, or real-time intraoperative images may be used. This device allows for improved 3-D surgical navigation and lesion margin definition.

We use two-photon absorption of GaAs to realize the temporal shaping of single-longitudinal mode Q-switched pulses. The results of our experiment agree well with the numerical solutions.

Process fluids may be degraded by large concentrations of suspended particles, formations of gel slugs, the infiltration of air bubbles, and so on. The scattering of ultrasound is dependent on the relation of the wavelength and the scatterers' dimensions. Relatively large objects are easily detected because of their strong scattering in the short wavelength limit (SWL), but small ones may be missed because of their weak scattering in the long wavelength limit (LWL). When the object dimension is comparable with the wavelength of ultrasound (intermediate region), the approximations of both the SWL and the LWL do not apply. We experimentally investigated the scattering characteristics of particles in the intermediate region to estimate the size distribution of particles in some industrial fluids. Observed particle size distributions are studied and an exponential regression approach is proposed. The results demonstrate that moving scatterers detected by ultrasound are able to be recognized in real time by the system, and their sizes can be individually determined as well as their statistical distribution in each trial period. Finally, rules have been found to estimate the original distribution of particles from a derived system parameter and observed data.

The use of elastic bending to form the shapes of high-power x-ray mirrors for synchrotron radiation beamlines is considered. An approach in which the bending mechanism and the mirror are cut from the same monolithic block by electric-discharge-machining techniques is especially advocated. A discussion of the theory and practical design philosophies is given that includes circular and elliptical cylinder mirrors. The influence of gravity on the mirror shape is studied with emphasis on the optimum positions for the mirror supports that, for a uniform mirror, turn out to be at a spacing equal to the mirror length divided by root three.

The light emitted by electron avalanches in a parallel plate chamber can be used to image the tracks of photoelectrons liberated by the interaction of an incident x-ray with the gas filling the chamber. The differing morphologies of photoelectron tracks and high-energy charged particle tracks can be used for background rejection. The initial direction (before scattering) of the liberated photoelectron also contains information about the polarization of the incident radiation. We have built a small test chamber with which we have imaged photoelectron tracks using an intensified CCD camera. Our results show that optical imaging could be used in a hard x-ray imaging polarimeter useful for astronomy.

This PDF contains the communication on "Prospects of using germanium-dioxide-based glasses for optics."

The PDF contains the communication on "Variations of the effective refractive index of a particulate composite."

This PDF file contains the editorial “Book Rvw: Quantum Well Lasers," edited by Peter S. Zory, Jr. for OE Vol. 32 Issue 08