This PDF file contains the editorial “Keeping It Close to the Vest” for OE Vol. 41 Issue 09

We proposed a novel method to realize the readout of super-resolution pits by using a super-resolution reflective film to replace the reflective layer of the conventional ROM. At the same time, by using Sb as the super-resolution reflective layer and SiN as a dielectric layer, the superresolution pits with diameters of 380 nm were read out by a setup whose laser wavelength is 632.8 nm and numerical aperture is 0.40. In addition, the influence of the Sb thin film thickness on the readout signal was investigated, the results showed that the optimum Sb thin film thickness is 28 to 30 nm, and the maximum CNR is 38 to 40 dB.

This PDF file contains the editorial “Remote Sensing Technology and Applications” for OE Vol. 41 Issue 09

Commercial observation satellites promise to broaden substantially the sources of imagery data available to potential users of geospatial data and related information products. We examine the new trend toward private firms acquiring and operating high-resolution imagery satellites. These commercial observation satellites build on the substantial experience in Earth observation operations provided by government-owned imaging satellites for civilian and military purposes. However, commercial satellites will require governments and companies to reconcile public and private interests in allowing broad public access to high-resolution satellite imagery data without creating national security risks or placing the private firms at a disadvantage compared with other providers of geospatial data.

Imaging satellite systems represent a high capital cost. Optimizing the collection of images is critical for both satisfying customer orders and building a sustainable satellite operations business. We describe the functions of an operational, multivariable, time dynamic optimization system that maximizes the daily collection of satellite images. A graphical user interface allows the operator to quickly see the results of what if adjustments to an image collection plan. Used for both long range planning and daily collection scheduling of Space Imaging's IKONOS satellite, the satellite control and tasking (SCT) software allows collection commands to be altered up to 10 min before upload to the satellite.

A new method is presented to optimize atmospheric correction for hyperspectral thermal imaging for object detection and recognition. The spectral similarity scale (SSS) is utilized to quantify the "goodness of fit'' for spectral emissivity output from atmospheric correction. The in-scene atmospheric correction (ISAC) method is enhanced with the SSS metric and applied to a MODTRAN 4 perturbed SEBASS sensor scene. Outputs of this process include the spectral emissivity for each pixel of the test scene image consisting of input spectral radiance. Atmospheric perturbations for long slant ranges are found to shift the required reference wavelength significantly from the commonly fixed reference either to the long or short side, dependending on the atmospheric parameters. This shift significantly impacts proper scaling of the corrected image data. Initial evaluation of the new method utilizes measured emissivity spectra of nonblackbody pixels for the ground truth reference to compare with the solved ISAC emissivity spectra. A scene-based receiver operating curve (ROC) metric is applied for minimized values of the SSS to demonstrate levels of improved object recognition for different range values of atmospheric path transmittance and radiance. We also determine future work, which offers the capability to significantly improve the fundamental method for identifying in-scene blackbody pixels, which are required for the ISAC methodology. Finally, the emissivity- based SSS comparison matrix demonstrates the capability to relate the differences in the ROC results to differences in the magnitude of the target spectral similarity.

Storage and transmission requirements for hyperspectral data sets are significant. To reduce hardware costs, well-designed compression techniques are needed to preserve information content while maximizing compression ratios. Lossless compression techniques maintain data integrity, but yield small compression ratios. We present a slightly lossy compression algorithm that uses the noise statistics of the data to preserve information content while maximizing compression ratios. The adaptive principal components analysis (APCA) algorithm uses noise statistics to determine the number of significant principal components and selects only those that are required to represent each pixel to within the noise level. We demonstrate the effectiveness of these methods with airborne visible/infrared spectrometer (AVIRIS), hyperspectral digital imagery collection experiment (HYDICE), hyperspectral mapper (HYMAP), and Hyperion datasets.

A digital elevation model (DEM) can be extracted automatically from stereo satellite images. During the past decade, the most common satellite data used to extract DEM was the across-track SPOT. Recently, the addition of along-track ASTER data, which can be downloaded freely, provides another attractive alternative to extract DEM data. This work compares the automated DEM extraction results using an ASTER stereo pair and a SPOT stereo pair over an area of hilly mountains in Drum Mountain, Utah, when compared to a USGS 7.5-min DEM standard product. The result shows that SPOT produces better DEM results in terms of accuracy and details, if the radiometric variations between the images, taken on subsequent satellite revolutions, are small. Otherwise, the ASTER stereo pair is a better choice because of simultaneous along-track acquisition during a single pass. Compared to the USGS 7.5-min DEM, the ASTER and the SPOT extracted DEMs have a standard deviation of 11.6 and 4.6 m, respectively.

We discuss a fully automatic technique for extracting roads in urban environments. The method has its bases in a vegetation mask derived from multispectral IKONOS data and in texture derived from panchromatic IKONOS data. These two techniques together are used to distinguish road pixels. We then move from individual pixels to an object- based representation that allows reasoning on a higher level. Recognition of individual segments and intersections and the relationships among them are used to determine underlying road structure and to then logically hypothesize the existence of additional road network components. We show results on an image of San Diego, California. The object-based processing component may be adapted to utilize other basis techniques as well, and could be used to build a road network in any scene having a straight-line structured topology.

Earth observation missions have recently attracted a growing interest, mainly due to the large number of possible applications capable of exploiting remotely sensed data and images. Along with the increase of market potential, the need arises for the protection of the image products. Such a need is a very crucial one, because the Internet and other public/private networks have become preferred means of data exchange. A critical issue arising when dealing with digital image distribution is copyright protection. Such a problem has been largely addressed by resorting to watermarking technology. A question that obviously arises is whether the requirements imposed by remote sensing imagery are compatible with existing watermarking techniques. On the basis of these motivations, the contribution of this work is twofold: assessment of the requirements imposed by remote sensing applications on watermark- based copyright protection, and modification of two well-established digital watermarking techniques to meet such constraints. More specifically, the concept of near-lossless watermarking is introduced and two possible algorithms matching such a requirement are presented. Experimental results are shown to measure the impact of watermark introduction on a typical remote sensing application, i.e., unsupervised image classification.

The immense size and scope of the rescue and clean-up of the World Trade Center site created a need for data that would provide a total overview of the disaster area. To fulfill this need, the New York State Office for Technology (NYSOFT) contracted with EarthData International to collect airborne remote sensing data over Ground Zero with an airborne light detection and ranging (LIDAR) sensor, a high-resolution digital camera, and a thermal camera. The LIDAR data provided a threedimensional elevation model of the ground surface that was used for volumetric calculations and also in the orthorectification of the digital images. The digital camera provided high-resolution imagery over the site to aide the rescuers in placement of equipment and other assets. In addition, the digital imagery was used to georeference the thermal imagery and also provided the visual background for the thermal data. The thermal camera aided in the location and tracking of underground fires. The combination of data from these three sensors provided the emergency crews with a timely, accurate overview containing a wealth of information of the rapidly changing disaster site. Because of the dynamic nature of the site, the data was acquired on a daily basis, processed, and turned over to NYSOFT within twelve hours of the collection. During processing, the three datasets were combined and georeferenced to allow them to be inserted into the client's geographic information systems.

As new remote sensing data and geographic information system (GIS) technology becomes available, it is increasingly possible to develop and provide effective products, services, and tools to the emergency management community. GIS technology has become increasingly affordable and provides the ability to capture, organize, manipulate, display, and analyze complex collections of geographic data and information. The Pacific Disaster Center (PDC) has historically provided decision support products and services to local, state, federal, and regional emergency managers in the Pacific Region to assist in all four phases of disaster management: mitigation, preparation, response, and recovery. The PDC’s current mission includes the integration of scientific knowledge, remote sensing data and tools, modeling and simulation technology, weather analysis, digital and information technology, and systems engineering processes in support of the disaster management community. Current activities and methods are presented in this paper.

We address hyperspectral imaging (HSI) technology and its attendant key issue of spectral libraries to enable the exploitation of hyperspectral images for transportation applications. Five key applications are reviewed here: detection/identification of submerged aquatic vegetation in navigable waterways, detection/tracking of oil spills, extracting/ assessing road characteristics, mapping impervious surfaces, and the detection/identification of vehicles. Central to all these applications is the need for a comprehensive spectral library in which various reflective spectra are correlated with physical surfaces and environments encountered in transportation. Much of this critical work is being funded by the Department of Transportation through four university consortia, each specializing in one of the key transportation areas of: transportation flows; infrastructure; environmental assessment; and safety, hazards, and disaster assessment for transportation lifelines.

Modern techniques such as remote sensing have been one of the main factors leading toward the achievement of serious plans regarding coastal management. A multitemporal analysis of land use in certain areas of the Colombian Caribbean Coast is described. It mainly focuses on environmental impacts caused by anthropogenic activities, such as deforestation of mangroves due to shrimp farming. Selection of sensitive areas, percentage of destroyed mangroves, possible endangered areas, etc., are some of the results of this analysis. Recommendations for a coastal management plan in the area have also resulted from this analysis. Some other consequences of the deforestation of mangroves in the coastal zone and the construction of shrimp ponds are also analyzed, such as the increase of erosion problems in these areas and water pollution, among others. The increase of erosion in these areas has also changed part of their morphology, which has been studied by the analysis of SPOT images in previous years. A serious concern exists about the future of these areas. For this reason new techniques like satellite images (SPOT) have been applied with good results, leading to more effective control and coastal management in the area. The use of SPOT images to study changes of the land use of the area is a useful technique to determine patterns of human activities and suggest solutions for severe problems in these areas.

Bad pixels are defined as those pixels showing a temporal evolution of the signal different from the rest of the pixels of a given array. Principal component analysis helps us to understand the definition of a statistical distance associated with each pixels, and using this distance it is possible to identify those pixels labeled as bad pixels. The spatiality of a pixel is also calculated. An assumption about the normality of the distribution of the distances of the pixels is revised. Although the influence on the robustness of the identification algorithm is negligible, the definition of a parameter related with this nonnormality helps to identify those principal components and eigenimages responsible for the departure from a multinormal distribution. The method for identifying the bad pixels is successfully applied to a set of frames obtained from a CCD visible and a focal plane array (FPA) IR camera.

Thermally induced optical distortions severely degrade the quality of a laser beam, thus reducing the irradiance on the target. Procedures are formulated to evaluate the impact of spherical aberrations generated by actively cooled cylindrical components that transmit cw laser radiation. Specifically, we deal with edge- and face-cooled optical elements and examine how beam shape and cooling strength affect the performance. The heat-flow equation is formulated nondimensionally and solved analytically, thus demonstrating that (1) temperature gradients causing optical distortion scale with ?PIK, i.e., the power deposited per unit length and the thermal resistivity of the medium; (2) in most instances, fourth-order polynomials yield reasonably accurate temperature profiles; and (3) apodization can be very useful in mitigating the deleterious effects of thermal lensing. For edge-cooled components, the heat-transfer coefficient has no influence on the temperature profile, and the diameter does not affect the performance. The treatment of face cooling requires a more elaborate analysis; for weak cooling, the spherical aberration factors are similar to those associated with edge cooling, but Biot numbers ?10 are required to achieve a significant reduction of the distortion.

An improved approach is derived for the propagation of electromagnetic (EM) fields along a curved dielectric waveguide. The objective is to develop a mode model to provide a numerical tool for the calculation of the output fields also for intermediate radius of curvature (R~ 0.5 m). Therefore we take into account all the terms in the calculations, without neglecting the terms of the bending. The longitudinal components of the fields are developed into Fourier-Bessel series. The transverse components of the fields are expressed as functions of the longitudinal components in the Laplace plane and are obtained using the inverse Laplace transform. The separation of variables is obtained using the orthogonal relations. The metal boundaries of the waveguides are modeled as a lossy dielectric media. This model is applicable for hollow waveguide tubes where the wall of the bore is covered with a metal layer and dielectric overlayer.

We propose a nonlinear edge detection technique based on a two-concentric-circular-window operator. We perform a preliminary selection of edge candidates using a standard gradient and use the dualwindow operator to reveal edges as zero-crossing points of a simple difference function depending only on the minimum and maximum values in the two windows. Comparisons with other well-established techniques are reported in terms of visual appearance and computational efficiency. They show that detected edges are surely comparable with Canny's and Laplacian of Gaussian algorithms, with a noteworthy reduction in terms of computational load.

A novel numerical technique for temperature/strain profiles reconstruction based on Brillouin optical-fiber time-domain analysis (BOTDA) sensors is proposed. In this approach, we search directly for the temperature/strain profile along the fiber that matches the measured data. The algorithm is based on a harmonic expansion of the unknown profile, whose coefficients are determined by a multidimensional minimization. Several numerical simulations, even in presence of noise, prove the capability of the proposed algorithm to compensate for some systematic errors suffered by classical approaches based on the direct reading of Brillouin power spectra.

We describe several fundamental display properties of a flexible ferroelectric liquid crystal device containing polymer fibers between thin plastic substrates. The composite film of liquid crystal and polymer was created from a solution of liquid crystal and monomer materials between the plastic substrates under ultraviolet light irradiation. The dynamic electrooptic response to analog voltage pulses was examined with an incidence of laser beam light, and its light modulation property exhibited good linearity in continuous gray-scale capability. The excellent spatial uniformity of liquid crystal alignment formed between the flexible substrates resulted in high-contrast light modulation, although slight spontaneous bending of liquid crystal alignment in the device plane was recognized. When the laser light beam was obliquely incident on the flexible display device, the measured transmittance revealed that the device has a wide viewing angle of more than 100 deg without contrast reversal. This is considered to be caused by the molecular switching in the device plane and the thin electrooptic layer in the display device.

We present a way to measure the contrast of helmet- mounted displays. Standards exist for direct view flat panel displays and projection displays, but head-mounted displays do not seem to be covered by the standards yet. We start by discussing a basic setup (4-mm aperture, lens, detector) with the aperture residing in the exit pupil of the display. A 4 x4 checkerboard forms a contrast test image that is measured in all 16 rectangles by rotating the 4-mm aperture around a point 10.5 mm behind the aperture (to simulate the natural rotation of the eye). Subsequently, the relation between the measured contrast and the measurement field size is investigated. The data presented indicates that a measurement field size smaller than 1/12 the width and 1/12 the height of the image gives an error in the contrast measurement smaller than 5%. Next, we discuss that, for most cases, the detector can be placed in a fixed position even though this means that the image might be out of focus in the detector plane. Finally, a method is discussed to compensate for the error in the contrast measurement caused by stray light arising in the measurement device.

We present a novel method for scalable and robust image transmission over ATM networks. The algorithm is based on a scalable set partitioning in hierarchical trees (SSPIHT) coding scheme, in which the encoded image bit streams for packeting and transmission are divided into a number of layers. By accumulating different numbers of layers in the decoder side, images with different resolutions and distortions can be reconstructed. Decoders having different capacities therefore can share the same encoder. In addition, these layers have different degrees of significance so that transmission errors in insignificant layers will not cause severe degradation in performance for image reconstruction. Finally, we describe three basic schemes for the transmission of SSPIHT-encoded cells over ATM channels. Simulation results show that the algorithm is effective for the applications where robust and scalable transmissions are desired.

In an embedded wavelet scheme for progressive transmission, a tree structure naturally defines the spatial relationship on the hierarchical pyramid. Transform coefficients over each tree correspond to a unique local spatial region of the original image, and they can be coded bit-plane by bit-plane through successive-approximation quantization. After receiving the approximate value of some coefficients, the decoder can obtain a reconstructed image. We show a rational system for progressive transmission that, in absence of a priori knowledge about regions of interest, chooses at any truncation time among alternative trees for further transmission in such a way as to avoid certain forms of behavioral inconsistency. We prove that some rational transmission systems might exhibit aversion to risk involving "gambles" on tree- dependent quality of encoding while others favor taking such risks. Based on an acceptable predictor for visual distinctness from digital imagery, we demonstrate that, without any outside knowledge, risk-prone systems as well as those with strong risk aversion appear in capable of attaining the quality of reconstructions that can be achieved with moderate risk-averse behavior.

We describe a postprocessing methodology for reconstructing undersampled image sequences with randomly varying blur that can provide image enhancement beyond the sampling resolution of the sensor. This method is demonstrated on simulated imagery and on adaptive- optics-(AO)-compensated imagery taken by the Starfire Optical Range 3.5-m telescope that has been artificially undersampled. Also shown are the results of multiframe blind deconvolution of some of the highest quality optical imagery of low earth orbit satellites collected with a ground- based telescope to date. The algorithm used is a generalization of multiframe blind deconvolution techniques that include a representation of spatial sampling by the focal plane array elements based on a forward stochastic model. This generalization enables the random shifts and shape of the AO-compensated point spread function (PSF) to be used to partially eliminate the aliasing effects associated with sub-Nyquist sampling of the image by the focal plane array. The method could be used to reduce resolution loss that occurs when imaging in wide-field-of-view (FOV) modes.

The light scattering characteristics of small ice particles modeled by polydisperse, randomly oriented, finite circular cylinders with different size distributions and different ratios of the length to diameter (L/D) at the visible (0.55 ?m), near-infrared (1.38 ?m), and some important infrared (IR) wavelengths up to 30 xm are investigated systematically using the exact T matrix approach. The effects caused by changes in effective variance of size distributions are addressed. The results show that scattering properties of small ice cylinders depend strongly on wavelengths, particle size distributions with different x(or re) and ve, and L/D. Some important facts are obtained that are significant in optical modeling and applications in remote sensing of cirrus clouds, and a new far-IR channel at the wavelength of 25 ?m is proposed.

polymeric microlenses play an important role in reducing the size, weight, and cost of optical data storage and optical communication systems. We fabricate polymeric microlenses using the microcompression molding process. The design and fabrication procedures for mold insertion is simplified using silicon instead of metal. PMMA powder is used as the molding material. Governed by process parameters such as temperature and pressure histories, the micromolding process is controlled to minimize various defects that develop during the molding process. The radius of curvature and magnification ratio of fabricated microlens are measured as 150 ?m and over 3.0, respectively.

A fiber-coupled laser-diode end-pumped passively Q-switched Nd:YVO4 laser with a Cr4 + :YAG saturable absorber is realized, providing pulse widths of 107 to 240 ns with pulse repetition rates ranging from 60 to 150 KHz. The dependences of pulsewidth, pulse energy, pulse repetition rate, and peak power on pump power are measured; meanwhile, the influences of different small-signal transmission T0 of a saturable absorber on Q-switched performances is compared. The rate equations are used to simulate the Q-switched process of the laser. The modified Q-switched criterion including the influence of pump power of this type laser is presented. The experimental results agree with the numerical solutions of the rate equations.

As the need for information storage media with high storage density increases, digital video disks (DVDs) with smaller recording marks and thinner optical disk substrates than those of conventional DVDs are being required. Therefore, improving the replication quality of land-groove or pit structure and reducing the birefringence distribution are emerging as important criteria in the fabrication of high-density optical disk substrates. We control the transcribability and distribution of birefringence by inserting an insulation layer under the stamper during injection-compression molding of DVD rAm substrates. The effects of the insulation layer on the geometrical and optical properties, such as transcribability and birefringence distribution, are examined experimentally. The inserted insulation layer is found to be very effective in improving the quality of replication and leveling out the first peak of the gapwise birefringence distribution near the mold wall and reducing the average birefringence value, because the insulation layer retarded the growth of the solidified layer.

We apply interference fringe scanning algorithms that are used in interference fringe analysis to an optical encoder as angle detection algorithms to disperse the influence of sinusoid wave distortion from the encoder's photodetector. We also evaluate these algorithms using the analytical system and techniques employed to obtain the same output signal as that of the actual encoder. This is accomplished using light intensity image data produced as the light permeates the slit disk of the encoder. As a result, we obtain about twice the angle precision by applying these algorithms to the optical encoder.

We propose a novel approximation of the fundamental modal field in single-mode graded-index fiber and present a variational analysis to investigate the propagation parameters of practical interest. Employing the formulated fundamental modal field, we prescribe analytical expressions for normalized Petermann I spot size, group delay, and modal dispersion parameter for single-mode graded-index fiber. With the examples of step- and parabolic-index fibers, we show that these parameters as evaluated by our formalism match excellently with the available exact ones over a wide range of V values. Particularly in the low V region, where the Gaussian approximation is not accurate, our results are found to predict the propagation characteristics accurately. Thus the validity of our formalism is justified. Much less computation is required than with previous methods. The approximation will be useful in the analysis of nonlinear and doped-fiber amplifiers.

An architecture of an externally modulated NTSC AM-VSB 77-channel erbium-doped fiber amplifier (EDFA)-repeated system in the 1550-nm region, which uses a combination of reverse dispersion fibers (RDFs) and single-mode fibers (SMFs) as a dispersion compensation device, is proposed and demonstrated for the first time. Compared to the conventional externally modulated fiber optical CATV systems, with or without dispersion compensation fiber (DCF), excellent performances of carrier-to-noise ratio (CNR)?50.5 dB, composite second order (CSO)?76 dB and composite triple beat (CTB)?70 dB, were obtained after 40-km RDF and 40-km SMF transmissions.

Performance and compatibility of different partially new methods in optical topography measurement are discussed. By using autofocus sensing, an established measurement procedure, height data of the surface are delivered directly in the scanning modus. Via novel ellipso- topometry, the local slope angles of the surface are detected. Here, surface topography follows from the gradient data by integration. Two slope detection procedures are conceivable: scanning ellipsotopometry using a very thin measurement beam by focusing on the surface to be measured, and imaging ellipsotopometry applying a CCD sensor detecting an extended measurement beam. slope-based determination of topography is performed by optimal filtering algorithms based on the Gauss- Markoff estimation. This filtering takes advantage of inherent redundancy of the surface gradient data. For each of the two slope detecting procedures, we discuss the required algorithms to obtain optimal filtering. The performance of the data filtering is successfully demonstrated by measuring a sinusoidal surface standard. In comparison to nonredundant autofocus surface height measurement, ellipsotopometry applying optimal filtering can lead to significantly better results. The described filtering techniques can be transferred to other measurement procedures determining the surface gradients (e.g., Nomarsky interferometry, shearogra- phy), respectively.

Fulgide Aberchrome 670-doped polymer films are studied. The closed form of this chromophore presents a maximum of absorption centered at about 525 nm and is formed upon irradiation of its colorless open form at 365 nm. We have determined the photoreaction rate constants, kUV and kVIS, respectively, for the coloring and bleaching processes. It was found that photochemical fatigue of fulgide doped in the mixture of a cyanoacrylate adhesive with 10% of dioctoepoxy monomer is essentially absent after 40 UV/visible irradiation cycles. We thus report, for the first time, a simple and rapid preparation of dye-doped polymer films in a solvent-free process that shows significant improvements in fatigue behavior. Our previous investigation of conventional polymer matrices prepared by gravity deposition of dilute dye-polymer solutions found losses of 9, 11, 13, and 35% after only 8 UV/visible irradiation cycles, respectively, in polystyrene (PS), cellulose acetate (CA), poly(methyl methacrylate) (PMMA), and polyvinyl carbazole (PVK).

A relatively simple scheme for disk-type photopolymer high- density holographic storage based on angular and spatial multiplexing is described. The effects of the optical setup on the recording capacity and density are studied. Calculations and analysis show that this scheme is more effective than a scheme based on the spatioangular multiplexing for disk-type photopolymer high-density holographic storage, which has a limited medium thickness. Also an optimal beam recording angle exists to achieve maximum recording capacity and density.

Demonstration of short-range multispectral remote sensing, using 3 to 4-?m mid-infrared Sb semiconductor lasers based on codedivision multiplexing (CDM) architecture, is described. The system is built on a principle similar to intensity-modulated/direct-detection optical- CDMA for communications, but adapted for sensing with synchronous, orthogonal codes to distinguish different wavelength channels with zero interchannel correlation. The concept is scalable for any number of channels, and experiments with a two-wavelength system are conducted. The CDM-signal processing yielded a white-Gaussian-like system noise that is found to be near the theoretical level limited by the detector fundamental intrinsic noise. With sub-mW transmitter average power, the system was able to detect an open-air acetylene gas leak of 10-2 STPft3/hr from 10-m away with time-varying, random, noncooperative backscat- ters. A similar experiment detected and positively distinguished hydrocarbon oil contaminants on water from bio-organic oils and detergents. Projection for more advanced systems suggests a multi-kilometer-range capability for watt-level transmitters, and hundreds of wavelength channels can also be accommodated for active hyperspectral remote sensing application.

We propose a new phase calibration method, called the sensor-by-sensor phase calibration method (SSPC), which is applied for the phasing of a large segmented telescope mirror. Instead of making the entire segmented mirror in phase at one time and obtaining the desired sensor readings accordingly, we serially make the local areas in phase at each sensor location and thus obtain the desired sensor readings one by one. Then we run the telescope active control system to make the segments cophase. For the case of Keck telescopes, the SSPC method uses all the 168 phase measurements at 168 phase sensor locations; then we obtain 168 desired sensor readings for the segmented mirror active control system. The SSPC method is completely insensitive to the residual tilt errors from the segment alignment and the residual errors from the active control system. The validity of the SSPC method has been demonstrated in an active optics experimental system, which has three segments and a 500-mm-diam overall aperture. The accuracy of the SSPC method is better than 20-mm rms in this experimental system, and it is easy to obtain diffraction-limited images at a visible wavelength ?=650 nm over an aperture of 220 mm.

The modeling of single-mode distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers based on an index-coupled surface grating on the InGaAs/InGaAsP multiple-quantum-well (MQW) structures is carried out. Such lasers require relatively simpler grating fabrication processes without multistep-epitaxial growth or regrowth, as required in conventional devices. A key concern for surface grating is designing structure that can provide sufficient feedback to achieve single-mode operation and high laser performance. Bragg wavelength operation of the surface grating (SG) DFB and SG DBR lasers can be satisfied by etching deep and fine gratings on the surface of both side portions and along the top of the ridge stripe, respectively. The numerical results obtained enable optimization of grating and laser geometries to provide the desired feedback effect. The simulated laser design shows that single-frequency operation at a wavelength of 1.55 ?m with high a side-mode suppression ratio (SMSR) is attainable.

An optimization method is presented for the design of baffles for an axial two-mirror telescope. According to the specific criterion of baffles and the inequalities relating to baffles dimension and telescope parameters given in this work, the lengths and diameters of the baffles can be determined. The method overcomes the shortcomings of the graphing method, and it can be finished simultaneously with the optical design to obtain the optimization configuration of the telescope.

Titanium dioxide is extensively used as high index material for multilayer optical thin film device applications operating in the visible and near infrared region. The performance (high reflectance/transmittance and laser-induced damage) of the device is decided by the absorption in the films. The refractive index and extinction coefficient of TiO2 films is strongly influenced by the deposition parameters and stoichiometry of the evaporation material. In the present investigation, TiO2 films have been deposited by reactive electron beam evaporation of TiO, Ti2O3, and TiO2 in a neutral and ionized oxygen atmosphere. A Heitmann-type discharge source has been fabricated in the laboratory and used to ionize oxygen. Deposition parameters such as oxygen partial pressure (5 x 10-5 to 5x 10-4 torr), rate of deposition (60 to 210 Åmin-1), and substrate temperature (25 to 250°C) were varied during the preparation of the films. The optical constants of TiO2 films were estimated from the spectrophotometer data. In-situ optical monitoring of TiO2 films with suboxides as the starting material showed the presence of considerable absorption in the films deposited in neutral oxygen, even under favorable deposition conditions. Postdeposition heating was necessary to reduce the absorption in the films. TiO2 films with minimum absorption have been made using TiO2 starting materials. Absorption-free films have also been obtained using ionized oxygen with the starting materials, even at higher substrate temperatures. The observed variation in optical properties has been explained on the basis of mismatches between the film growth and rate of oxidation.

Two-photon absorption is evoked in a CdS crystal by laser excitation up to almost 200 GW/cm2 at 804 nm. Pulses with duration of 200 fs are used to achieve this high intensity. By means of a z-scan technique, the nonlinear absorption coefficient (?) is measured and the constant value of p= 6.9 cm/GW was found. Simultaneously, the two- photon excited emission is recorded. Examination of the photoluminescence data reveals that ? is not constant but decreases from 6.9 to 2.9 cm/GW with increasing excitation. The crossover between the ? values takes place at approximately 70% of the maximum intensity. The result shows that the two-photon excited photoluminescence is a very sensitive method to show saturation and intensity dependence of the nonlinear absorption coefficient.

In the late 1980s, a military avionics standard, called the MIL-STD-1773, was developed by the US Department of Defense to promote applications of sophisticated optical fiber technology to advanced military aircraft.1