This PDF file contains the editorial “Guest Editorial: To Change, or Not to Change; That is the Question” for OE Vol. 29 Issue 04

This PDF file contains the editorial “Book Rvw: Optical Fiber Sensors, Volume I: Principles and Components and Volume II: Systems and Applications," edited by Brian Culshaw, Alan Rogers and Richard Weiss for OE Vol. 29 Issue 04

This PDF file contains the editorial “Book Rvw: Quantum Electronics, Third Edition," by Amnon Yariv for OE Vol. 29 Issue 04

This PDF file contains the editorial “Book Rvw: Photorefractive Materials and Their Applications I: Fundamental Phenomena," edited by P. Gunter and J.-P. Huignard for OE Vol. 29 Issue 04

The restoration of the depth map of a three-dimensional object is formulated as an image-restoration problem. The object is modeled as an opaque discrete visible surface (DVS) in 3-D space. The projection of the radiance and depth information of the DVS onto a two-dimensional image yields an underdetermined system of equations. The 3-D imagerestoration problem seeks to recover the depth information of the DVS from the 2-D image. To uniquely specify a solution, constraints on the estimates of the DVS must be introduced. In this paper an in-focus image is used to provide radiance information. Further, the size of the problem is significantly reduced by limiting the range of possible depths to lie within a fixed interval of the depth values given by an independent coarse depth recovery method. It is shown that additional constraints on both the radiance and the geometry can easily be accommodated by the methods described. The use of three different methods of constrained optimization are investigated for solving the problem. A method based on simulated annealing is shown to offer the best performance. Results of applying the algorithms to test objects using both a simulated and a laboratory optical system are presented.

The restoration of images degraded by a stochastic point spread function and additive detection noise is examined. Previously, the optimization criterion of the Wiener technique was applied successfully to this problem. However, when the strengths ofthe noise sources are not small, the restoration results of this method become noisy, albeit the deblurring results are of good quality. First, to obtain smoother restoration, the constrained least squares deconvolution method was developed. The objective function chosen was the one which yields smooth restoration. The restoration results of this filter were very smooth, as expected, but the deblurring was not as effective as that of the Wiener technique. Then, a geometrical mean filter that combines both the Wiener and the constrained least squares criteria was developed. This resulted in restored pictures that were both smooth and deblurred. The two filters developed are computationally inexpensive since they both can be implemented in the Fourier domain using the circulant matrix approximation.

High-resolution signal parameter estimation is a problem of significance in many signal processing applications. Such applications indude direction-of-arrival estimation, system identification, and time series analysis. A novel approach to the general problem of signal parameter estimation is described. Although discussed in the context of directionof- arrival estimation, ESPRIT can be applied to a wide variety of problems. It exploits an underlying rotational invariance among signal subspaces induced by an array of sensors with a translational invariance structure. The technique, when applicable, manifests significant performance and computational advantages over previous algorithms such as Burg's maximum entropy method, Capon's maximum likelihood method, and Schmidt's multiple signal classification.

A hybrid optical/digital system for tracking an object in a sequence of images is described. Since a joint transform correlator does not require a matched spatial filter in the correlation process, object tracking can be carried out by continuously updating the reference image with the object image in the previous frame. This adaptive property of a joint transform correlator, together with the parallelism and high processing speed of an optical system, ensure high correlation between objects in two sequential frames. The relative position of the object can then be determined based on the location of the correlation peak. System performance is evaluated and experimental demonstrations are presented.

A new general theory of the dependence of strain on crystal size L for defect-free cubic materials bounded by {100} faces is presented. While current theories predict a (?/L) dependence, this work suggests a (F/L)½ dependence by considering both surface tension (?) and surface free energy (6FL2) effects. Since small crystals, especially if very fresh or not annealed, may contain a large fraction of point defects, the sizedependent strain must be separated from the defect-induced strain. The theory is verified by reinterpreting three experimental studies reported in the literature and based on the techniques of electron microscopy, x-ray diffraction, and nuclear magnetic resonance. The theory offers a straightforward explanation for the extra longitudinal strain in superlattices, as detected by Raman spectroscopy.

Carrier activation and mobility were studied by Raman spectroscopy and the Hall effect in pulsed laser annealed samples of GaAs implanted with doses of Si and Se from 2.2x 1012 to 6.Ox 1014 cm-2. The samples were annealed using a pulsed XeCl excimer laser (? = 308 nm) and a pulsed dye laser (? = 728 nm) with energy densities from 0.06 to 0.9 J/cm2 and pulse durations of about 10 ns. Very high carrier concentrations of 3x1019 and 1.5x 1019 cm-3 were obtained for the best n-type GaAs samples annealed with the dye and excimer lasers, respectively. The dye laser consistently produced higher activation than excimer laser annealing. A transient reflectivity signal was used to identify the GaAs melt threshold and the melt phase dynamics of the GaAs under the nitride cap. The threshold energies for cap damage were 0.34 and 0.12 J/cm2 for the excimer and dye lasers, respectively. Raman spectroscopy was used to identify the threshold energies for the GaAs implant layer recrystallization and for optimum carrier activation. Four major peaks were observed on the photoinduced current transient spectra in the temperature range of 60 to 400 K, corresponding to traps with activation energies between 0.06 to 0.80 eV.

A new method for generation of laser speckle, by using an integrating sphere, is investigated. This method is of particular interest in the production of speckle patterns for modulation transfer function testing of detector arrays and would be well suited in wavelength ranges for which a transmissive diffuser is not optimum. Attributes of the speckle field investigated in this paper include the degree of polarization and first- and second-order statistics. The speckle patterns generated by the integrating sphere method are seen to closely obey the theory for statistics of speckle generated by usual means.

This paper concerns the problem of describing and evaluating thermal lensing phenomena that occur as a result of the absorption of laser light in solid windows. The aberration function expansion method is applied for deriving the two optical distortion coefficients x+ and xthat characterize the degradation in light intensity at the Gaussian focus of an initially diffraction-limited laser beam passing through a weakly absorbing stress-birefringent window. In a pulsed mode of operation, the concept of an effective optical distortion coefficient Xeff, which properly combines the coefficients x+ and x- in terms of potential impact on focal irradiances, then leads to the definition of a figure of merit for distortion. The theory and calculations presented in this and earlier papers provide simple analytical tools for predicting the optical performance of a windowmaterial candidate in a specific system's environment.

A dynamic electrothermal model of the Earth Radiation Budget Experiment total, nonscanning channels has been formulated and implemented as a computer program. This model, which is a modification of an earlier version, is used to simulate two types of solar observations: those obtained through the solar port during solar calibration and those obtained during the satellite pitchover maneuver in which the sun is observed by the radiometer in its Earth-viewing configuration. New results of both simulations are compared with actual flight data. These results show an improved agreement between the simulated and observed radiometer response over previous simulations. The improvement in these severe cases justifies the modification to the model and establishes its accuracy. Thermal noise has been studied also, using a separate but related model, to evaluate its contribution to the radiative energy absorbed by the active cavity. This study has revealed that scattering of the collimated solar radiation contributes, on average, 0.071 mW during solar calibration and 0.207 mW during the pitchover maneuver. These values represent, respectively, 0.156% and 0.460% of the peak power that enters the cavity (?45 mW). On the other hand, the maximum amounts of diffuse power due to emission from the field-of-view limiter and the aperture plate are, respectively, 0.120 and 0.01 1 mW, which amount to 0.270% and 0.024% of the peak power. Finally, the cavity self-contamination contributes only 0.034 mW, or 0.071%, of the peak power absorbed by the active cavity radiometer. This study confirms the assumption that, due to the geometry of the radiometer assembly and the optical properties of its components, thermal noise is small and well within the range of previous estimates.

We present a novel, versatile optoelectronic neural network architecture for implementing supervised learning algorithms in photorefractive materials. The system is based on spatial multiplexing rather than the more commonly used angular multiplexing of the interconnect gratings. This simple, single-crystal architecture implements a variety of multilayer supervised learning algorithms including mean field theory, backpropagation, and Marr-Albus-Kanerva style algorithms. Extensive simulations show how beam depletion, rescattering, absorption, and decay effects of the crystal are compensated for by suitably modified supervised learning algorithms.

The use of two-wave mixing in photorefractive (PR) materials in a homodyne detection receiver structure is studied. The interaction between a strong local oscillator optical field and a weak signal optical field in the PR material results in the formation of a volume index of refraction phase grating. The grating automatically aligns such that it coherently couples the signal and local oscillator fields just like a fixed beamsplitter in a conventional homodyne receiver structure. The slow response of the PR material automatically compensates for slow changes in the angle of arrival of the signal beam but acts as a fixed grating with respect to rapid phase modulation of the signal beam. The performance of a homodyne receiver that uses a PR material as a beamsplitter, is shown to be up to 3 dB superior to the performance of a conventional homodyne receiver that uses a fixed 50-50 beamsplitter. Furthermore, a PR receiver can adjust and retain its optimal performance when changes in the received signal power occur, whereas a conventional receiver cannot.

A Y1/3,u',v' uniform color space is used to develop and evaluate a pseudocolor scale, the heated object spectrum, and an achromatic scale. The Y1/3,u',v' uniform color space is found to be more reliable, compared to the CIELUV and CIELAB uniform color spaces, when previously reported colorimetric data from self-luminous objects are modeled. The CIELUV and CIELAB uniform color spaces do not reliably predict the color thresholds from self-luminous objects due to the metric lightness of the uniform color scales and the method of combination for the orthogonal components. This implies that the Y1/3,u',v' uniform color space, rather than the CIELUV and CIELAB uniform color spaces, is more appropriate for developing uniform display scales for imaging with CRT displays. The heated object uniform display scale, compared to the achromatic uniform display scale, has a perceived display range that is 14% greater in the number of display scale values. Thus, the heated object uniform display has a greater contrast sensitivity range for the display/observer combination compared to the achromatic uniform display.

The principal noise sources of GaAs MESFETs are taken into account in order to completely characterize the equivalent circuit model that has been utilized in the design of a low-noise small-signal amplifier for optical receivers. The total input noise current of the amplifier, due to correlated gate and drain MESFET noise, has been estimated for evaluating the excess channel noise factor ? for different values of the photodiode capacitance. A method is demonstrated for easy identification of the matching network parameters and photodiode capacitance that mmimize the noise. Finally, the minimum noise gain, gain-frequency dependence, input and output voltage standing wave ratios, noise figure, and bandwidth of the amplifier are evaluated in the 8 to 12 GHz frequency range. A gain of 22.1 ± 1 dB and a noise figure less than 3 dB in a bandwidth larger than 4 GHz are obtained.