This PDF file contains the editorial “Editorial: Coupling technology to national needs” for OE Vol. 32 Issue 04

This PDF file contains the editorial “Guest Editorial: Emerging Optoelectronic Technologies” for OE Vol. 32 Issue 04

Photo-induced cross-linking polymers offer excellent properties, such as ease of handling, low cost, and real-time recording, for the application of holography and nonlinear optics. A vinyl polymer, namely, polyvinyl alcohol (PVA), has been chosen as a host matrix and is employed for holographic recording and nonlinear optics. Significant results of our experimental investigations on recording media fabricated by doping PVA with azo dyes and rhodamine 6G for real-time holographic recording and nonlinear optics are reported. The evaluation of third-order nonlinearities of azo dye/PVA systems and the characteristics of chrysoidine/PVA as a nonlinear waveguide are presented. Also, degenerate four-wave mixing experiments using a novel geometry have been carried out in rhodamine 6G/PVA films.

Volume transmission holograms have been recorded in dichromated poly(vinyl alcohol) (DCPVA), dichromated poly(acrylic acid) (DCPAA), and ferric chloride poly(vinyl alcohol) (FePVA) films using a 488-nm light (from an argon-ion laser), and the hologram development has been monitored in real time using a 647-nm line of the krypton laser. The influence of different chemical parameters (e.g., pH and electron donor) on the holographic efficiency has been determined, and an efficiency value as high as 70% was achieved in all three recording media. Further, the possible primary photoprocesses responsible for the hologram formation are tentatively identified and discussed

Growth of Hg_1-xCd_xTe mercury cadmium telluride (MCT), by liquid phase epitaxy (LPE) is the most important technology for the fabrication of IR detectors for imaging. We present in detail the LPE growth of MCT from Te-rich solutions using a dipping technique. The physical parameters such as surface morphology, composition, thickness, and the electrical properties of the undoped epilayers are given. Effects of substrate rotation on surface morphology have been studied. The conditions for obtaining good uniform epilayers in 8 to 14 μm are discussed. The LPE layers have been annealed in the Hg atmosphere. The results of Hg diffusion into the p-type layer as a function of annealing temperature are also discussed.

Photorefractive single crystals of bismuth silicon oxide (Bii2SiO2o) and bismuth germanium oxide (Bi12GeO2o) have been grown using the Czochralski technique. The experimental results are explained with the existing theoretical models. The grown crystals are characterized by x-ray, differential thermal analysis, scanning electron microscopy, IR transmission spectrum, and electron-probe microanalysis.

When radiation is allowed to fall on the spacing between the source and gate and the gate and drain of a AlGaAs/GaAs high electron mobility transfer device, a photovoltage develops across the heterojunction. This significantly enhances the device characteristics.

The design and performance of a fiber optic sensor, working on the principle of evanescent wave absorption, are described. Using this sensor, the rate of a standard chemical reaction is determined. The measured value is compared with that obtained using a spectrophotometer

A new numerical technique for the propagation of optical pulses through nonlinear dispersive media is presented. The method is based on the collocation principle and is numerically more efficient than the split-step Fourier method. The accuracy and efficiency of the new method is demonstrated and several numerical examples are presented.

A study of the erbium-doped multicomponent glass fiber laser pumped by an argon ion laser is presented. Simultaneous laser oscillation in (a) the 1535- and 1550-nm bands and (b) 1550- and 1565-nm bands were observed, and the results indicate the possibility of achieving laser oscillations simultaneously at all three wavelength bands-of interest in telecommunications. Frequency shifts were observed by varying fiber lengths, and the relative intensity of the laser oscillations was found to depend on the input pump power.

An analysis of the asymmetric response from the opposite device facets is performed. Attention is devoted to those mechanisms and their microscopic origins that make the feedback adversely affect differential quantum efficiency in a single-mode laser. Similarities to a laser with a saturable absorber are shown, and instabilities related to the nonlinear behavior of the characteristic curve are discussed. A key is obtained to the description and control of the nonlinearity of the characteristic curve in the region just above threshold (kink), providing a feedback-driven bistability in the system.

Efficient second-harmonic generation from a pulsed parametric laser to 427 to 470 nm has been obtained in a KNbO₃ crystal only 1.5 mm in length by angular tuning at room temperature. The energy conversion efficiency is over 40%. Single pulse blue light output reaches 60 kW in peak power. The angular dependence of a phase matching wavelength, the relation between conversion efficiency and fundamental intensity, and acceptable angular phase mismatch are studied and discussed.

We investigate an optical waveguide system consisting of an unclad fiber core suspended at a constant distance parallel to the surface of a planar waveguide. The coupling and propagation of light in the combined system is studied using the three-dimensional explicit finite difference beam propagation method with a nonuniform mesh configuration. The power loss in the fiber and the field distribution in the waveguide are studied as a function of various parameters, such as index changes, index profile, and propagation distance, for the combined system.

A computer-controlled laser writing system for optical integrated circuits and data storage is described. The system is characterized by holographic (649F) and high-resolution plates. A minimum linewidth of 2.5 μm is obtained by controlling the system parameters. We show that this system can also be used for data storage applications

A quasi-feed-forward (QFF) linearization scheme for use with electro-optic modulators is presented. This scheme provides an increase in the intermodulation-free dynamic range of the modulator as well as substantial cancellation of laser relative intensity noise (RIN) of the cw source. The results of this investigation indicate that such a scheme is adequate for the transmission of 100 or more Canadian television channels transmitted in a vestigial sideband AM format using a cw source with a RIN of only - 130 dB/Hz. A tolerance analysis has been performed to predict the effects of a nonideal practical implementation.

An improved matrix method for the analysis and design of nonlinear directional couplers (NLDC) with Kerr-like coupling media is presented. The method represents an extension of the original matrix method that has been used to study linear waveguides with inhomogeneous refractive index profiles and three-layer nonlinear waveguides. The method is based on an iterative averaging algorithm that calculates the average values of the dielectric constant and the field amplitude in each stratified nonlinear layer. This numerical method is applied to compute the power-dependent characteristics of symmetrical and nonsymmetrical multiple quantum-well (MQW) NLDCs. Saturation of the refractive index in the MQW coupling medium is taken into account and, for a symmetrical structure, the numerical results are shown to be in agreement with published experimental data.

The usefulness of semiconductor lasers can be greatly limited when the laser is subjected to uncontrolled optical feedback (OFB). In particular, the laser intensity noise can be severely degraded when OFB is greater than 0.1%. Although the technique of high-frequency injection (HFI) can solve this problem, the proper modulation frequency and depth must be chosen empirically. We investigate this problem through cornputer simulations of the multimode stochastic rate equations, modified to include OFB and HFI. By providing the program with measurable laser and system parameters, the simulations predict the HFI modulation frequency and depth that optimize the laser behavior. The results of the simulations are compared with experiment, and good agreement is obtained.

Results of the theoretical investigation of light polarization changes during Bragg acousto-optic interaction are presented. It is shown that a linearly polarized light wave, entering an acoustic field, becomes elliptically polarized because of an additional phase shift effect. The polarization state can be controlled by varying power or frequency of the ultrasound. An effect of polarization nonreciprocity for two optical waves passing through the acoustic field in opposite directions is also studied.

A unified theory that relates optical phase changes to applied strain and temperature fields in structurally embedded interferometric optical fiber sensors of all types is developed through a careful consideration of basic assumptions and definitions. The theory is applied to Mach-Zehnder, Michelson, intrinsic and extrinsic Fabry-Pérot, polarimetric, dual-mode, and Bragg grating optical fiber sensors.

Using the unified theory that relates optical phase changes to applied strain and temperature fields in structurally embedded interferometric optical fiber sensors of all types, as applied to Mach-Zehnder, Michelson, intrinsic and extrinsic Fabry-Pérot, polarimetric, dual-mode, and Bragg grating sensors, with resistance strain gauge concepts and the theory of elasticity solutions, the response of optical fiber sensors that are embedded in transversely isotropic composite materials is theoretically explored. The concepts of transverse strain sensitivity and thermal apparent strain are carefully defined for embedded optical fiber sensors, and it is found that errors resulting from these effects completely dominate the desired sensor response for all sensors except the extrinsic Fabry-Pérot. Conditions that minimize these errors are presented. The theory of elasticity solutions used in this analysis encompasses six different thermomechanical loading conditions. Comparisons to Buffer and Hocker's model are also presented.

An accurate approximation is presented of the focal shift in the diffraction field of a Gaussian laser beam that is focused by a thin lens that fills a circular aperture of any prescribed radius. The limiting cases of beam truncation by the aperture are discussed and formulas for nontruncated Gaussian beams and for uniform beams are obtained. The proposed formulas provide a convenient means for circumventing the transcendental equations in the focal-shift problem.

A new pattern generator, initially designed for ASIC fabrication, is employed for writing synthetic holograms and other micro-optical components. The specifications and limits of this machine are investigated. Test structures and synthetic holograms are shown. Arbitrary patterns with micrometer resolution, submicrometer positioning accuracy, large area patterns (up to 150 x 150 mm² possible), and good quality microprofiles are demonstrated.

A high-power frequency-doubled Nd:YAG laser using amplifiers in slab geometry has been developed to pump a dye laser as part of a spectroscopy experiment. The necessary fast synchronization within the experiment required a special pumping method that resulted in a more than four times higher average thermal load of the Nd:YAG crystals than it would be in a system with no synchronization requirements. Under these conditions, the laser was routinely operated at a repetition rate of 20 Hz, delivering about 600 mJ at 532 nm divided among four beams, which corresponds to a frequency conversion efficiency of more than 60%. Compared to a system with amplifiers in conventional rod geometry, the use of the slab geometry in the amplifiers made possible an increase of the repetition rate by a factor 4.

Field-of-view calculations are carried out on tunable birefringent filters designed for selective filtering of intrusive laser radiation. Two methods are used to analyze the problem-a rigorous 4 x 4 matrix method and an extended Jones matrix approximation. It is found that the extended Jones matrix approximation is sufficient to describe the filter characteristics. Using this method, the off-axis contrast ratios of low- and hig-horder filters are compared. The presented results show that although the field of view of these filters extends well beyond 10 deg, the contrast ratio in the high-order case is significantly degraded and in some cases falls below the desired value of 100:1. A proposed "wide-field" geometry improves the off-axis performance of the high-order filter.

A detailed chemical analysis was carried out on Spectralon, a highly Lambertian, diffuse reflectance material. Results of this investigation unambiguously identified the presence of an organic (hydrocarbon) impurity intrinsic to the commercial material. This impurity could be removed by a vacuum bake-out procedure and was identified as the cause of optical changes (degradation) that occur in the material when exposed to UV light. It was found that when this impurity was removed, the Spectralon material was photochemically stable and maintained its reflectance properties even after extensive solar UV exposure.

For the Multiangle Imaging SpectroRadiometer (MISR), currently under development for the Earth Observing System, we plan to use deployable diffuse reflectance panels to provide a flight calibration of its nine cameras. Near-lambertian reflectance characteristics are desirable to facilitate flat-field camera intercomparisons and to allow each camera to be calibrated under the same illumination levels. Panel spatial and spectral uniformity and stability with time are also required. Spectralon™, a commercially available diffuse reflectance material made from polytetrafluoroethylene (PTFE), has been baselined in the MISR design. To assess the suitability ofthis material, a series of environmental exposure tests were performed. No degradation of the optical properties was apparent following proton bombardment, and stability through UV illumination was satisfactory, provided simple cleaning and handling procedures were implemented. One surprise during the testing, however, was a buildup of several thousand volts of static charge, which developed while simulating a rare pass through an auroral storm. Such a potential for charge buildup is not unique to PTFE, but exists for many thermal control paints used to cover spacecraft exteriors. Further testing of the charged Spectralon failed to produce arcing to the metallic housing frame, and models indicate that charge neutralization will occur after passage through the storm. For these reasons we intend to fly Spectralon as per our original plan.

The hit-or-miss operator is used as the building block of optimal binary restoration filters. Filter design methodologies are given for general-, maximum-, and minimum-noise environments, the latter two producing optimal thinning and thickening filters, respectively, and for iterative filters. The approach is based on the expression of translation-invariant filters as unions of hit-or-miss transforms. Unions of hit-or-miss transforms are expressed as canonical logical sums of products, and the final hit-or-miss templates are obtained by logic reduction. The net effect is a morphological representation and estimation of the conditional expectation, which is the overall optimal mean-absolute-error filter.

Novel edge detection and line-fitting machine vision algorithms are applied for linewidth measurement on optical images of integrated circuits. The techniques are used to achieve subpixel resolution. The strategy employs a two-step procedure. In the first step, a neural network is used for edge detection ofthe image. Three neural network approaches are investigated: self-organizing, bootstrap linear threshold, and constrained maximization strategies. The weights of the neural networks are estimated using unsupervised learning procedures, the advantage of which is the ability to adapt to the imaging environment. Consequently, these proposed neural network approaches for edge detection do not require an a priori data base of images with known linewidths for calibration. In the second step, line-fitting methods are applied to the edge maps defined by the neural network to compute linewidth. Two methods are investigated: the Hough transform method and an eigenvector strategy. By employing this two-step strategy, the entire image is used to estimate linewidth as opposed to the use of just a single or a few line scans. Thus, edge roughness effects can be spatially averaged to obtain an optimal estimate of linewidth, and subpixel resolution can be achieved. However, the accuracy (or variance) of this estimate will, of course, be dependent on issues such as pixel size and the capability of the imaging system. The techniques are general and can be used on images from a variety of microscopes, including optical and electron-beam microscopes.

A mobile, semiautonomous vehicle with multiple sensors and on-board intelligence is proposed for performing preliminary scientific investigations on extraterrestrial bodies prior to human exploration. Two technologies, a hybrid optical-digital computer system based on optical correlator technology and an image and instrument data analysis system, provide complementary capabilities that might be part of an instrument package for an intelligent robotic vehicle. The hybrid digital-optical vision system could perform real-time image classification tasks using an optical correlator with programmable matched filters under control of a digital microcomputer. The data analysis system would analyze visible and multiband imagery to extract mineral composition and textural information for geologic characterization. Together these technologies would support the site characterization needs of a robotic vehicle for both navigational and scientific purposes.

An optical symbolic substitution using lenslet arrays is presented. By using the shift and the superposition properties of the lenslet array, the recognition and the substitution phases can be performed. The advantages of using the lenslet array for symbolic substitution are efficiency, cascadability, and high resolvability. Experimental demonstrations of the proposed symbolic processor are provided.

As very large scale integration technology advances toward higher complexity and density, future generation computing and communications systems will operate at speeds of several hundred megahertz or even gigahertz. In many cases, the capability of the interconnections within these systems to support the required speeds and densities will be a formidable challenge. Multichip-module (MCM) technology is one approach to overcome some of the interconnection bottlenecks, but even such an advanced packaging system has limitations, especially for very high speed complex systems. Optical interconnections offer the potential for improved performance in terms of large bandwidth, noise and crosstalk immunity, lower power dissipation, and large fan-out capability. We discuss the use of optical interconnections within multichip modules. We consider three specific applications-input/output access to the MCM, global signal distribution, and chip-to-chip interconnects-and discuss both free-space and guided-wave implementations of optical interconnects.

A method of recognizing human face profiles is proposed. Most conventional methods of recognizing human face profiles use fiducial marks, length of the line connecting the marks, angles between fiducial points, and other measures of profile outlines as the components of characteristic vectors. The P-Fourier descriptor developed by Uesaka can describe open curves fairly well, and it has many features of curves in the low-frequency range. We use the P-Fourier descriptor as a characteristic vector of a human face profile. We show that the P-Fourier coefficients in the low-frequency range are useful for human face profile recognition, that is, by using 31 P-Fourier coefficients, we obtained a correct recognition rate of 93.1 % for 130 subjects.

Speckle imaging is a statistical technique for achieving near-diffraction-limited imagery of astronomical objects with ground-based telescopes. The performance of this statistical postdetection processing technique is critically dependent on the signal-to-noise ratio (SNR) of the estimators used for various average spectra, which can be a strong function of detector characteristics. We discuss techniques for maximizing SNR under low-light conditions where so-called "read noise" becomes a factor in CCD detectors, and we derive an optimal exposure time for CCD detection when total viewing time limits the SNR. We also show that a properly optimized CCD can outperform a shot-noise-limited detector, in terms of the SNR, at much lower light levels than without optimization.

A segmentation-based video coding technique is presented. A change detector is used to find the regions of interest, i.e., moving areas, and then the moving areas are segmented based on the motion vector information. For the regions where the prediction error, defined by the difference between the original image and the motion-compensated image reconstructed by the motion vector, is large, the frame difference signal is used to supplement the segmentation results. Depending on the region characteristics, each region is represented by the motion vector and the frame difference signal. After postprocessing, the region information and the region boundaries are transmitted. Computer simulation with video sequences shows that the proposed algorithm reduces the trailing effect and gives better performance than the conventional method.

This PDF contains the Communications for the paper "Parameters for an infrared diffuse reflectance standard."

This PDF file contains the editorial “Book Rvw: Optics and Lasers, Including Fibers and Optical Waveguides," by M. Young for OE Vol. 32 Issue 04

This PDF file contains the editorial “Book Rvw: Opto-Mechanical Systems Design," by Paul R. Yoder, Jr. for OE Vol. 32 Issue 04