This PDF file contains the editorial “Fellow of the SPIE” for OE Vol. 37 Issue 10

We present an energy matrix representation for multiband images that captures spatial and spectral properties. Using a physical model for spectral reflectance, we derive a pseudoinverse method for the comparison of energy matrices that is invariant to the spectral properties of the scene illumination. At the same time, this method determines the illumination change matrix, allowing direct comparison of images obtained under different illumination conditions. We demonstrate the performance of the method for both illumination-invariant recognition and illumination correction on a large set of multiband images. The energy matrices are generated using a small set of oriented steerable filters. We also demonstrate that a related set of rotationally symmetric filters can be used for recognition invariant to both illumination and rotation and that subsequent processing can be used to recover the rotation angle of a recognized object.

Two types of direct-detection Doppler lidars are described: the multichannel spectral resolving approach and the edge technique approach. The two methods are compared in terms of fundamental system characteristics. The equations necessary to model the instruments and predict noise-limited performance are developed in forms that enable an easy comparison of the methods. Using those equations, simulation results are presented to compare the performance of the receiver systems. Results are shown for both aerosol Doppler and molecular Doppler systems. Instrument design considerations are discussed to clarify the choice of realistic values for the model parameters.

We explore the use of a tilted fiber phase grating to diffract modulated rf optical signal out of the fiber. A mathematical model based on perturbation analysis is derived and used to describe the radiation mode behavior, including scattering direction and radiation power. Simulation results for a system based on a 2-cm-long, fiber phase grating tilted 45 deg are presented.

We report a Tm3+ doped fluorozirconate fiber laser suitable for the first telecommunications window. We present a mathematical model and experimental measurements. The cw, low threshold pump power of 15 mW, pumped by a Ti:sapphire laser at 778 nm, and a 85 mW maximum output power around 810 nm with a 85% slope efficiency against launched pump power are achieved. This represents a conversion efficiency of ~95%, which is the highest reported to date for any laser. Visible up-conversion fluorescence is also observed. We describe two different oscillator configurations.

Recent advances in high powered laser diodes and fiber optic coupling enable efficient integration of laser systems into existing gimballed systems. A high power, divergent beam is used to illuminate a scene providing enhanced performance in poor weather, the recording of (ship, aircraft or automobile) registry and augmentation to existing night vision devices. Ground tests are conducted by observing alphanumeric characters at 200, 400, 600, 800, 1100 and 1300 m and results are presented.

The visualization of a quasi-stable flow field with full 3-D meaning must be provided with 2-D projections. In flow field interferometric tomography, the conventional method of fringe tracking, by which a few solitary 1-D projections are obtained, can evaluate only the 2-D distribution of the field on a limited number of cross sections. A new method that combines Fourier analysis and modified multigrid iteration is proposed to extract 2-D projections from interferograms of the measured field in various directions. On the basis of 2-D projections, the real 3-D field reconstruction can be realized. An experiment with an asymmetric temperature field measurement using a rotary Fabry-Pe´ rot (F-P) interferometer is reported and some cross sections of the reconstructed temperature field are given to prove that the methods of sampling, processing and reconstruction of the algorithm illustrated are effective.

By incorporating a prism pair in an optical system for multiplex holography, the 2-D image for holographic recording can be compressed in one direction with respect to the other direction. Hence, a cylindrical lens with smaller aperture can be used. The effects of the prism pair on the image of the original object and on the real image of the illuminating source point are analyzed. The aspect ratio of the image for hologram recording can be continuously varied with the least root mean square error of the object. Experimental results confirming the results of computer simulation are also provided.

We propose a new iterative algorithm for the generation of a codebook in vector quantization. The algorithm starts with an initial codebook that is improved by a combination of merge and split operations. By merging small neighboring clusters, additional resources (codevectors) are released. These extra codevectors can be reallocated by splitting large clusters. This process can be iterated until no further improvement is achieved in the distortion of the codebook. Experimental results show that the proposed method performs well in comparison to other tested methods, including the generalized Lloyd algorithm (GLA) and two hierarchical methods.

An image processing method is presented that enables an efficient and robust separation of straight line-like structures from an isotropic background texture. The algorithm is based on a transform sequence mapping both image components onto two nearly disjoint and parameter invariant areas in the resulting transform domain. Applying a linear notch filter to the transformed image enables us to ascertain for each component of the discrete Fourier spectrum of the image, whether it contributes more to the line-like structures or more to the background. Based on this decision, the spectrum is split into two complementary and disjoint spectra, the inverse Fourier transforms of which are taken as estimates for both image components. In practical applications, the algorithm behaves robustly with respect to its parameters as well as to the assumptions made about the images.

We present a new method for processing the data in a nonlinear joint transform correlator (NJTC). The output of the NJTC is obtained after two steps. The first step consists of the acquisition of the joint power spectrum (JPS) of the images to be correlated. The JPS is in principle a bidimensional image. The second step is the calculation of the cross-correlation function. To do this, the JPS image is compressed to one dimension and a 1-D Fourier transform is performed. This significantly reduces the number of operations required to evaluate the crosscorrelation. To improve the cross-correlation sensitivity, a degree of nonlinearity is introduced using an illumination level above the saturation threshold of the camera used to acquire the JPS.

We demonstrate an all-optical programmable switch that can simulate the function of an XOR logic gate. This gate consists of a doped silica planar waveguide, a laser, and the means to couple two fundamental-frequency waves into different waveguiding modes, along with a second-harmonic wave coupled into one guiding mode. The measured SNR is 5.5 dB.

With uncoated optical surfaces, it is possible to use a Fizeau interferometer to make direct measurements of small-scale irregularities with very small amplitudes. However, problems arise with highly reflecting surfaces. Some optical systems that can be used for such measurements are described.

The optical characteristics of two commercially available UV curable epoxy resins are investigated using nondegenerate four-wave mixing. The materials assessed are optimized for use with a UV argonion laser. The holographic gratings were written at a wavelength of ? 5351.1 nm for an irradiance range 0.5 to 3.0 W/cm2 and read at ? 5632.8 nm to compare the reactivity, curing speed, shrinkage, and resolution of the resins. These experiments were carried out to prove the suitability of the photopolymerization systems for microstereolithography.

Highly concentrated sunlight has the power density required by many laser fiber optic surgical procedures. Thanks to recent progress in optical design, the means now exist to concentrate solar radiation in dielectrics to levels that exceed those at the surface of the sun, and to efficiently deliver it remotely. Since surgical power requirements are typically only several watts, the solar collection unit can be miniaturized. Although generating uncollimated radiation, solar surgery can serve as a low-cost alternative to laser fiber optic systems in treatments where wide-angle emissions are preferable. Even nominally monochromatic treatments such as photodynamic therapy can use highly concentrated sunlight because the power density within a typical wavelength window for these treatments (around 0.004?m) is adequate to the task. Scheduling of solar surgery should not pose difficulties in clear climates. Solar concentration is performed in two stages: a paraboloidal reflector dish and a second-stage nonimaging concentrator. Concentrated irradiation would be transported via low-attenuation silica optical fibers to the operating room. With power delivery typically emanating from a disk of diameter 0.6 mm, the dish diameter would be in the vicinity of 200 mm with an even smaller system depth. The system could deliver a flux density as high as 70 W mm-2 for contact surgery and 30 W mm-2 for noncontact surgery. Aside from lasers, sunlight is uniquely suited to the task, in contrast to today’s available light sources.

Accurate knowledge of the relative image irradiance is important in the design of some optical instruments, e.g., IR systems, where it determines the apparent temperature of the object, and camera systems employing irregular-shaped aperture stops or light-absorbing elements. We review the quick Hopkins method for calculating the relative image irradiance of systems with circular or elliptical stops and then describe a modification that enables it to be used for the less conventional systems mentioned. The new method is used to calculate the relative irradiance of a camera objective that includes a neutral density wedge. We also present a brief discussion of the often misunderstood cos4 law, which is of some importance in the design of optical instruments.

A methodology is described for parameter extraction from modeling for the determination of the appropriate figures of merit (FOMs) to be used for comparisons between different architectures of optical interconnects and their electrical counterparts. The key FOM selected for performance is that of data throughput, defined as the product of bitrate and interconnect length. Parameter extraction proceeds through modeling of a prototype optical transceiver introduced by GTE laboratories. Optical power budget modeling is performed as it applies to a simple basic optical interconnect, which can then be extended to the modeling of arrays, by incorporating channel crosstalk limitations. Through this modeling, the specific limitations to the data throughput are explored and several trade-offs such as those between gain and speed, power and delay-times, and power and bit error rate (BER) are quantified

Pulsed photothermal radiometry is a nondestructive technique for measurements of surface and subsurface thermal parameters of a wide variety of materials. A fiber optic pulsed photothermal radiometric system is constructed and its feasibility is demonstrated. The radiometric system includes a pulsed CO2 laser, an IR detector, and two IR transmitting silver halide optical fibers for delivering IR radiation to and from the sample. A weak laser pulse, absorbed by the sample, initially heats the sample surface. The time evolution of the transient emitted IR radiation is measured and analyzed. The results establish the feasibility of using the fiber optic pulsed photothermal radiometric system to measure coating thickness, to detect flaws, and to diagnose thermal damage in tissue. This fiber optic method would be useful for industrial and medical applications.

Thermal diffusivity measurements are carried out in certain organic liquids using the pulsed dual beam thermal lens technique. The 532 nm pulses from a frequency doubled Q-switched Nd:YAG laser are used as the heating source and an intensity stabilized He-Ne laser serves as the probe beam. Experimental determination of the characteristic time constant of the transient thermal lens signal is verified theoretically. Measured thermal diffusivity values are in excellent agreement with literature values.

Liquid refractometers are often used in the optical industry. Although there are some liquid refractometers available, such as, the Pulfrich refractometer,1 the Abbe refractometer,1 and the Hilger-Chance refractometer,1 all of them are based on the measurement of the critical angle or the deviation angle using a microscope or a telescope. The measuring process is tedious. Some other techniques for measuring the refractive index of a liquid include, for example, the interferometric method2,3 and the Brewster angle method.

Adaptive order statistic filters for noise smoothing in digital images are presented. Two classes of adaptive filters are studied, namely, the least mean squares (LMS)-based adaptive order statistic filters and the signal-adaptive filters. The filter structures in the first class require a noise-free image to be used as a reference image, whereas those in the second class do not require a reference image. Two filter structures from the former class are examined: the adaptive locationinvariant L-filter and the adaptive Ll -filter. A novel signal-adaptive filter, namely, the morphological signal-adaptive median (MSAM) filter is proposed in the second class. It employs an anisotropic window adaptation procedure based on mathematical morphology operations. The noisesmoothing capabilities and the computational complexity of the LMSbased adaptive order statistic filters studied serves as a baseline in the assessment of the properties of the proposed MSAM filter. Quantitative criteria (e.g., the SNR, the peak SNR, the mean absolute error, and the mean squared error) as well as qualitative criteria (e.g., the perceived visual quality of the processed images) are employed to assess the performance of the filters in various corruption cases by different noise models.

Region of interest (ROI) determination is a first and crucial step performed in an automatic target recognition (ATR) system. The goal of ROI determination is to identify candidate regions that may have potential targets. To be most effective, this initial detection (or focus of attention) stage must reject clutter (noise or countermeasures that provide target like characteristics), while ensuring that regions with true targets are not missed. We present a novel approach to ROI determination in synthetic aperture radar (SAR) images for ATR based on the premise that regions with targets would require a model with more free parameters to smoothly approximate the magnitude of the return. Toward that end, we use a sigmoidal multilayered feed-forward neural network with selected lateral connections between hidden layer neurons to approximate the return in disjoint square patches of the SAR image. This network probably uses as few neurons as possible to produce a desired approximation and thus enables the determination of the number of parameters used in approximating the return in an image patch. Those squares of the image that require a large number of neurons (more free parameters) are then labeled as ROIs. Results obtained with synthetic and real-world SAR images are used to demonstrate the effectiveness of the proposed method. A significant advantage of the proposed method is that it does not require the presence of a training data set, which, given the variability in SAR images and target signatures, is difficult to obtain.

Sudden exposure to a supersonic flight environment subjects a missile window, or missile dome, to intense convective heat loads stemming from the rise in temperature of the boundary layer. The thermal response of the window then results in temperature gradients through the thickness, which generate transient stresses that may exceed the tensile strength of the material, thus causing thermal-shockinduced fracture. Since most of the materials that possess favorable optical properties in the infrared (IR) are relatively weak brittle solids, the problem of selecting window or dome materials and assessing their performance on a fly-out trajectory requires a careful evaluation of the window’s ability to withstand thermally induced shocks. In this context, it is essential to keep in mind that the transient stress intensity depends on the nature of the heat flow as characterized by the Biot number (Bi). The allowable heat flux depends not only on intrinsic material properties but also on the heat transfer coefficient, if the condition Bi>1 holds, or the thickness of the window, if the condition Bi>1 applies. In a first approximation, the thermal shock performance of a ‘‘thick’’ window is controlled by the figure of merit (FoM)Bi>1=RH , i.e., the Hasselman parameter for strong shocks; in a thermally thin regime, however, if ?f designates the flexural strength the appropriate figure of merit is (FoM)Bi<1=nfr'h with n=1/2 for flat plates and n=2/3 for hemispherical shells, and not the Hasselman parameter R H 8 for mild shocks. Judging from the results of thermal shock testing performed elsewhere, we conclude that in a laminar flow environment the allowable heat flux on a thermally thin IR dome can be expressed as follows: Qlim=2R'H/L, where L is the dome thickness. This expression provides a direct means of obtaining the Machaltitude failure line for a dome of given thickness and given radius, if the initial wall temperature is known. Furthermore, it then becomes straightforward to assess the thermal shock resistance capability of a thicknessoptimized IR dome in terms of either the allowable heat load or, more simply, the allowable stagnation temperature.

We investigate deformation of stainless steel and ceramic specimens with a precision of the order of tens of nanometers using a pulsed laser beam. Such a technique is useful, for example, in a process of removing distortions on magnetic head components to achieve a better contact between the magnetic disk head and the hard disk surface. Experiments are conducted to study the bending behavior of stainless steel and ceramics due to laser irradiation. A pulsed Nd:YLF laser beam is used to scan over the specimen to create out-of-plane deformation. The amount of deformation from each laser scan is correlated with laser and processing parameters. A theoretical model of the laser deformation process is presented based on thermo-elasticity-plasticity. The laser deformation process is explained as the result of the laser-induced nonuniform distribution of the compressive residual strain. Numerical simulations are carried out to estimate the laser-induced temperature field, the residual stress field, and the amount of deformation of the specimen. These theoretical studies help us to understand the complex phenomena involved in the pulsed-laser deformation process.

The reflection-transmission phenomena in sculptured thin films (STFs) of the ‘‘zigzag’’ type are considered. A finite layer of an STF is modeled as a stack of Motohiro-Taga interfaces. The boundary value problem for a plane wave obliquely incident on a single Motohiro-Taga interface is solved. This solution, incorporated into the generalized scattering matrices method, is used to evaluate the transmission and reflection coefficients of a finite layer. We show that the ordinary wave (TE polarized with respect to the plane containing the directions of inclinations of the columnar microstructures) is not reflected by the Motohiro- Taga interface. For the extraordinary (TM-polarized) wave the analysis gives zero reflection for all angles of incidence and nanocolumn inclination, while the transmission coefficients exceed the unit value under certain conditions. The result is therewith in agreement with the energy conservation statement.

We perform precise measurements of the x-ray transmission of the thin films comprising CCD gate structure, namely, phosphorus doped polysilicon, silicon dioxide, and silicon nitride. The x-ray transmission of these films shows large oscillations with small changes in energy in the vicinity of the following absorption edges: nitrogen K (400 eV), oxygen K (536 eV), silicon L and K (100 and 1840 eV, respectively). As a result, quantum efficiency of a CCD in the soft x-ray range deviates significantly from simple model predictions based on Henke et al. (1993) mass absorption coefficients. The measurements covered the range of energies from 60 to 3000 eV, using synchrotron beamlines at the Advanced Light Source (ALS; Berkeley), Physikalisch-Technische Bundesanstalt BESSY (Berlin), the Synchrotron Radiation Center (SRC; University of Wisconsin-Madison). Our model of the CCD response includes near edge x-ray absorption structure and predicts a very complicated shape of the energy dependence of the quantum efficiency around silicon and oxygen absorption edges. Experimental measurements of CCD quantum efficiency relative to a calibrated detector at the BESSY synchrotron confirmed our model predictions for both frontside and backside illuminated CCDs.

With increasing demand for LiNbO3 ~LN! optical intensity modulators for fiber communication systems, fine process control of LN device fabrication has become important to increase the fabrication yield and to supply low-priced modulators.