So it is the time of year to give thanks for last year and to make New Year’s resolutions for this year. These exercises keep me grounded. As Gandhi stated, “There is more to life than simply increasing its speed.” It sure seems like life flies past faster and faster, and it reminds me of Fermat’s Principle: “Light takes the path of least time.” I am glad that Fermat’s Principle replaced one of the previous ideas that “light takes the path of least distance.” My life is certainly taking the path of least time and not the path of least distance. I know this because I have had some huge ups and downs (a crooked path) in the past five years and this past year has held true to the pattern.

We present an overview of our recent progress and the current state-of-the-art techniques of color image fusion for night vision applications. Inspired by previously developed color opponent fusing schemes, we initially developed a simple pixel-based false color-mapping scheme that yielded fused false color images with large color contrast and preserved the identity of the input signals. This method has been successfully deployed in different areas of research. However, since this color mapping did not produce realistic colors, we continued to develop a statistical color-mapping procedure that would transfer the color distribution of a given example image to a multiband nighttime image. This procedure yields a realistic color rendering. However, it is computationally expensive and achieves no color constancy since the mapping depends on the relative amounts of the different materials in the scene. By applying the statistical mapping approach in a color look-up-table framework, we finally achieved both color constancy and computational simplicity. This sample-based color transfer method is specific for different types of materials in a scene and can be easily adapted for the intended operating theatre and the task at hand. The method can be implemented as a look-up-table transform and is highly suitable for real-time implementations.

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We address design considerations and outline requirements for space telescopes with capabilities for high contrast imaging of exoplanets. The approach taken is to identify the span of potentially detectable Earth-sized terrestrial planets in the habitable zone of the nearest stars within 30 parsecs and estimate their inner working angles, flux ratios, SNR, sensitivities, wavefront error requirements, and sensing and control times parametrically versus aperture size. We consider 1, 2, 4, 8, and 16-m diameter telescope apertures. The achievable science, range of telescope architectures, and the coronagraphic approach are all active areas of research and are all subject to change in a rapidly evolving field. Thus presented is a snapshot of our current understanding with the goal of limiting the choices to those that appear currently technically feasible. We describe the top-level metrics of inner working angle, contrast and photometric throughput and explore how they are related to the range of target stars. A critical point is that for each telescope architecture and coronagraphic choice, the telescope stability requirements have differing impacts on the design for open- versus closed-loop sensing and control.

The James Webb Space Telescope (JWST) is an infrared space telescope designed to explore four major science themes: first light and reionization, the assembly of galaxies, the birth of stars and protoplanetary systems, and planetary systems and origins of life. JWST is a segmented architecture telescope with an aperture of 6.6 m. It will operate at cryogenic temperature (40 K), achieved via passive cooling, in an orbit about the Earth-Sun second Lagrange point (L2). Passive cooling is facilitated by means of a large sunshield that provides thermal isolation and protection from direct illumination from the Sun. The large size of the telescope and spacecraft systems require that they are stowed for launch in a configuration that fits the Ariane 5 fairing, and then deployed after launch. Routine wavefront sensing and control measurements are used to achieve phasing of the segmented primary mirror and initial alignment of the telescope. A suite of instruments will provide the capability to observe over a spectral range from 0.6- to 27-μm wavelengths with imaging and spectroscopic configurations. An overview is presented of the architecture and selected optical design features of JWST are described.

The Space-based Telescopes for Actionable Refinement of Ephemeris (STARE) program will collect the information needed to help satellite operators avoid collisions in space by using a network of nanosatellites to determine more accurate trajectories for selected space objects orbiting the Earth. In the first phase of the STARE program, two pathfinder cube-satellites (CubeSats) equipped with an optical imaging payload are being developed and deployed to demonstrate the main elements of the STARE concept. We first give an overview of the STARE program. The details of the optical imaging payload for the STARE pathfinder CubeSats are then described, followed by a description of the track detection algorithm that will be used on the images it acquires. Finally, simulation results that highlight the effectiveness of the mission are presented.

The performance of a segmented space telescope depends in part upon the ability to maintain the alignment and phasing of its primary mirror segments. Failures of segment control actuators pose a threat to mission success, but their effects can be mitigated by using the remaining segment actuators to optimize the pose of each affected segment. This paper considers the effect of actuator failures on the final wavefront error of a segmented space telescope whose primary mirror consists of 18 hexagonal segments, each controlled by a 3-6 hexapod. Optimization algorithms that minimize the wavefront error for single- and multiple-failure cases are developed, and simulation results are presented. When one actuator fails, the affected segment can still attain a pose with zero wavefront error by exploiting the rotational symmetry of the primary. When two actuators fail, the resulting wavefront error depends upon which hexapod legs fail and at what lengths; cases where both legs of a bipod fail are an order of magnitude worse than other cases. Finally, Monte Carlo simulations of many failures randomly distributed across an initially well-phased segmented primary show that more than 10% of the actuators must fail before the root-mean-square wavefront error degrades significantly.

The design considerations for astronomical space telescopes cover many disciplines but can be simplified into two overarching constraints: the desire to maximize science while adhering to budgetary constraints. More than ever, understanding the cost implications up front will be critical to success. Science performance can be translated into a set of simple performance metrics that set the requirements for design options. Cost is typically estimated by considering mass, complexity, technology maturity, and heritage. With this in mind, we survey the many diverse design considerations for a space telescope and, where appropriate, relate them to these basic performance metrics. In so doing, we hope to provide a roadmap for future space telescope designers on how best to optimize the design to maximize science and minimize total cost.

The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for an 8- to 16-m ultraviolet optical near infrared space observatory for launch in the 2025 to 2030 era. ATLAST will allow astronomers to answer fundamental questions at the forefront of modern astrophysics, including: Is there life elsewhere in the Galaxy? We present a range of science drivers and the resulting performance requirements for ATLAST (8- to 16-marcsec angular resolution, diffraction limited imaging at 0.5-μm wavelength, minimum collecting area of 45  m², high sensitivity to light wavelengths from 0.1 to 2.4 μm, high stability in wavefront sensing and control). We also discuss the priorities for technology development needed to enable the construction of ATLAST for a cost that is comparable to that of current generation observatory-class space missions.

The Spitzer Space Telescope, which has operated very successfully since 2003 in its unique Earth-trailing solar orbit, is NASA's Great Observatory for infrared astronomy. We provide a quick overview of the optical characteristics of Spitzer and review the observatory design. The main emphasis is on two unique on-orbit activities used to optimize the scientific return from Spitzer: 1. an unusual approach to focusing the telescope that minimized the use of the cryogenic focus mechanism, and 2. a methodology for extending the cryogenic lifetime of Spitzer by actively controlling the telescope temperature.

X-ray Multi-mirror Mission (XMM-Newton) has been one of the most successful astronomy missions launched by the European Space Agency. The mission exploits innovative use of replication technology for the x-ray reflecting telescopes that has resulted in an unprecedented combination of effective area and resolution. Three telescopes are equipped with imaging cameras and spectrometers that operate simultaneously, together with a coaligned optical telescope. The key features of the payload are described, and the in-orbit performance and scientific achievements are summarized.

With grazing incidence telescopes, x-ray astronomy became a major branch of astrophysics. They are an indispensable tool in the study of >10⁶  K thermal and non-thermal high energy phenomena occurring in objects from the solar system to the most distant sites in the universe. They have shed light upon dark matter and dark energy. Four cosmic missions with focusing grazing incidence x-ray telescopes based upon the Wolter 1 geometry are currently in space. They include two observatory class facilities launched in 1999, NASA's high resolution x-ray and ESA's high throughput XMM-Newton. Two others are Japan's Suzaku, performing a variety of studies, and the Swift XRT, which finds precise positions for the x-ray afterglows of gamma-ray bursts. Four new cosmic missions with Wolter-like focusing telescopes are scheduled for launch. They will provide much broader bandwidth (NuSTAR and Astro-H), perform a new sky survey with more exposure time and a broader energy range than previous surveys (eROSITA), have an imaging detector with much better energy resolution (Astro-H), and measure polarization (GEMS). The Kirkpatrick-Baez and the lobster-eye are two types of potentially useful grazing incidence telescopes that have not yet been in orbit. It may not be possible to improve upon Chandra's 0.5 arcsec resolution without new technology.

The Hubble Space Telescope's mission is summarized, with special emphasis placed on the Space Telescope Science Institute's unique experience with Hubble's behavior as an astronomical telescope in the environment of low earth orbit for over two decades. Historical context and background are given, and the project's early scientific expectations are described. A general overview of the spacecraft is followed by a more detailed look at the optical design, both as intended and as built. Basic characteristics of the complete complement of science instruments are also summarized. Experience with the telescope on-orbit is reviewed, starting with the major initial problems, solutions, human servicing missions, and the associated expansion of the observatory's capabilities over this time. Specific attention is then given to understanding Hubble's optical quality and pointing/jitter performance, two fundamental characteristics of a telescope. Experience with-and the important mitigation of-radiation damage and contamination is also related. Beyond the telescope itself, the advances in data reduction, calibration, and observing techniques are briefly discussed, as well as the subsequent emergence of highly accessible high-level archival science products. Hubble's scientific impact concludes the discussion.

The Fermi Gamma-ray Space Telescope, launched in June 2008, is an observatory designed to survey the high-energy gamma-ray sky. The primary instrument, the Large Area Telescope (LAT), provides observations from 20 MeV to greater than 300 GeV. A second instrument, the Gamma-ray Burst Monitor (GBM), provides observations of transients from less than 10 keV to 40 MeV. We describe the design and performance of the instruments and their subsystems, the spacecraft and the ground system.

Significant advances in science always occur when the state of the art in instrumentation improves dramatically. NASA's Chandra X-ray Observatory represents such an advance. Launched in July of 1999, Chandra is an observatory designed to study the x-ray emission from all categories of astronomical objects-from comets, planets, and normal stars to quasars, galaxies, and clusters of galaxies. At the heart of this observatory is the precision x-ray optic that has been vital for Chandra's outstanding success and that features an angular resolution improved by an order of magnitude compared to its forerunners. The Chandra mission is now entering its thirteenth year of operation, which, given that the observatory was designed for a minimum of three years of operation, testifies to its robust and carefully thought-out design. We review the design and construction of the remarkable telescope, present examples of its usage for astronomy and astrophysics, and speculate on its future.

Phase retarders usually exhibit strong wavelength dependence. For this paper, the design and characteristics of an achromatic cascaded system of birefringent plates were studied. The combination of three retarders in a series had been previously proposed by Pancharatnam, and he discussed the possibility of fabricating reasonably good achromatic quarter-wave plates with a suitable level of retardance. This combination, however, still shows substantial variation in terms of retardance within 500 to 700 nm. Here, the combination of four plates for the construction of an almost achromatic quarter-wave plate, which has a variation of only ± 1 degree over the wavelength spectrum of 500 to 700 nm, is proposed. Moreover, spherical trigonometric considerations have been used by Pancharatnam for obtaining the transmission characteristics of a cascaded system. We, however, used the succinct and relatively simple Jones matrix formalism to derive a general expression for the equivalent retardation of this combination. The proposed arrangement of four birefringent plates promises better achromatic combinations.

A Fourier transform spectrometer (FTS) acquires interferogram data for spectral measurements. Conventional FTS instruments incorporate Michelson interferometers. However, limitations of the Michelson for imaging applications have produced interest in alternative interferometer configurations. Common path interferometers, such as birefringent interferometers, offer advantages for remote sensing applications. To ensure the best possible signal-to-noise ratio, the fringe contrast provided by the interferometer should be maximized. Unfortunately some birefringent interferometers, such as those that utilize Wollaston prisms (WPs), require stringent tolerances in order to ensure high fringe contrast across even a modest field of view (FOV). Fabricating an interferometer to meet these tolerances adds fabrication cost and time to the development of an instrument. We present how the introduction of additional birefringent elements into birefringent interferometer can be used to compensate for a decrease in fringe visibility due to manufacturing errors. These components form a variable angle WP (VWP), which can be used to vary the fringe visibility across the FOV. Experimental results confirming the ability of the VWP to vary the fringe visibility of a birefringent interferometer are included. These results are compared to polarization raytrace simulations for the system.

We describe a high-throughput (5×10^-4cm² sr) imaging spectrograph that uses an echelle grating operating at a high dispersion order (24 to 43) to observe extended sources such as atmospheric airglow and diffuse proton aurora at high spectral resolution (approximately 0.02 nm). Instead of using a traditional single slit, the implementation of the instrument described here uses four (50 µm × 25 mm) slits through which the radiation enters the spectrograph. The field of view is selected using appropriate foreoptics: the present implementation is a long, narrow configuration of 0.1 × 50 deg. By placing interference filters in the beam path, the instrument can simultaneously observe several spectral features located anywhere in the visible band (approximately 300 to 1000 nm) at high resolution. This design allows a single echelle grating and a single detector (a CCD in the present implementation) to view the same scene. The design is flexible; the number of slits and the slit dimensions can be tailored to the trade-offs between resolution, throughput, and number of spectral features depending upon the measurement need. While the implementation described here covers only the visible range, the use of different combinations of detector and filter sets can extend its operation to other wavelength regions.

A novel structure of illumination system based on laser sources and gradient-index (GRIN) lens arrays for single-plate digital light processing (DLP) projector is proposed. Under the evaluation of light collection efficiency and illumination uniformity, we designed two different architectures of GRIN lens arrays: the unit lens cross section being either square or circular. Also, we designed the one-to-one coupling mechanism between GRIN lens array and Gaussian beam array. By means of three-dimensional modeling and ray tracing, we simulated the optical characteristics of illumination system, and the optical parameters are evaluated. Results show that the total light collection efficiency is 37.9%, the illumination uniformity is 89.7% and the volume is only 12.4 cm³. Thus we improved optical characteristics and reduced the physical dimension of DLP optical engine.

A practical omnidirectional vision sensor, consisting of a curved mirror, a mirror-supporting structure, and a megapixel digital imaging system, can view a field of 360 deg horizontally and 135 deg vertically. The authors theoretically analyzed and evaluated several curved mirrors, namely, a spherical mirror, an equidistant mirror, and a single viewpoint mirror (hyperboloidal mirror). The focus of their study was mainly on the image-forming characteristics, position of the virtual images, and size of blur spot images. The authors propose here a practical design method that satisfies the required characteristics. They developed image-processing software for converting circular images to images of the desired characteristics in real time. They also developed several prototype vision sensors using spherical mirrors. Reports dealing with virtual images and blur-spot size of curved mirrors are few; therefore, this paper will be very useful for the development of omnidirectional vision sensors.

While Alvarez lens prototypes have recently been manufactured and tested for visible wavelengths, there is little discussion of these types of components for infrared applications in the published literature. We present and characterize a germanium Alvarez lens for infrared imaging. Mathematical analysis for determining the required cubic surfaces is presented, and ray-based and wave-based optical simulations are performed to confirm and refine the expected variable-focus behavior. As part of the design study, we examine the effects of effective f-number of the Alvarez lens and gap between the freeform surfaces on image quality, modulation transfer function, and Strehl ratio. The germanium Alvarez lens pair is fabricated through freeform diamond micro-milling, and characterized using a custom-built imaging test station in the mid-infrared. The variable-focus and imaging capabilities of this lens are demonstrated experimentally and compared to predicted results with good agreement.

Development of a phased-array-grating compressor is a crucial issue for high-energy ultrashort pulse petawatt lasers. To achieve tiled array gratings and increase stability of tiled-grating frames, a new tiled grating frame is designed. In the tiled-grating frame, an integrated support structure is adopted to increase the natural frequency of the tiled-grating and the flexible hinges are used rather than the spring to increase the joint stiffness between the grating and the support frame. The experiment indicates that stability of the tiled-grating can be maintained for more than 1 h and the standard deviation of the tiling error is 35.7 nm, which satisfies the design requirement.

Albedo estimation has traditionally been used to make computational simulations of real objects under different conditions, but as yet no device is capable of measuring albedo directly. The aim of this work is to introduce a photometric-based color imaging framework that can estimate albedo and can reproduce the appearance both indoors and outdoors of images under different lights and illumination geometry. Using a calibration sample set composed of chips made of the same material but different colors and textures, we compare two photometric-stereo techniques, one of them avoiding the effect of shadows and highlights in the image and the other ignoring this constraint. We combined a photometric-stereo technique and a color-estimation algorithm that directly relates the camera sensor outputs with the albedo values. The proposed method can produce illuminant-free images with good color accuracy when a three-channel red-green-blue (RGB) digital camera is used, even outdoors under solar illumination.

This work offers a comparison of broadband shortwave infrared, defined as the spectral band from 0.9 to 1.7 μm, and hyperspectral shortwave infrared imagers in a marine environment under various daylight conditions. Both imagers are built around a Raytheon Vision Systems large format (1024×1280) indium-gallium-arsenide focal plane array with high dynamic range and low noise electronics. Sample imagery from a variety of objects and scenes indicates roughly the same visual performance between the two systems. However, we show that the more detailed spectral information provided by the hyperspectral system allows for object detection and discrimination. A vessel was equipped with panels coated with a variety of paints that possessed spectral differences in the 0.9 to 1.7 μm waveband. The vessel was imaged at various ranges, states of background clutter, and times of the day. Using a standard correlation receiver, it is demonstrated that image pixels containing the paint can be easily identified. During the exercise, it was also observed that both bow waves and near-field wakes from a wide variety of vessel traffic provide a spectral signature in the shortwave infrared waveband that could potentially be used for object tracking.

In the modern world, we need high-resolution images for many applications, but the resolution of the imaging system can be degraded due to many factors, mainly the optical and geometrical components. The resolution limit for the optical system is set by diffraction, called diffractive superresolution. The resolutions of the imaging system are reduced not only by the optical components, but also by the geometrical components, which we call charge couple devices (CCDs). A CCD is an array of infinitesimal pixels (photodetectors). The resolution limit set for the imaging system due to the shape, size, and pitch of the sampling pixels (i.e., the distance between the centers of the consecutive sampling points) is called gometric superresolution. We are trying to overcome resolution limitations put on the imaging system by the CCD. With this technique we consider an infinitesimal delta function for the pixels of the CCD and an optical rectangular mask in which each pair (line/mm) has a specific width to make the optical rectangular mask more practical. Here we consider a 4-f optical imaging system; the spectrum of the input object falls on the optical rectangular mask, which is located at the back focal plane, and an inverse Fourier transform provides the image of the input object at the CCD plane. This image is sampled by the infinitesimal point pixels of the CCD and the Fourier transform gives the multiple spectrum of the input object overlapped to half of the next spectrum on either side. Then the overlapped spectrum is multiplied with the decoding optical rectangular mask (the same as encoding optical rectangular mask) that makes the overlapping effect disappear, and a train of completely separated spectrums is obtained; filtering gives a single spectrum matched to the spectrum of the original input object.

We propose a new phase contrast filtering technique based on a combination of a focused and a defocused point-spread-function. This way, an axial shear is introduced in the imaging system. Compared to conventional differential interference contrast, an isotropic behavior is achieved. The lateral resolution is improved compared to conventional defocusing. Furthermore, the digital combination of multiple images leads to strongly enhanced visualization of small structures. We show simulated results as well as experimental results using a spatial-light modulator-based microscope.

Ion beam figuring (IBF) Technology to fabricate optical materials with a high thermal expansion coefficient, such as BK7, we were aware that the thermal effect is a troublesome problem that generates high thermal stress. If the thermal stress is over the component mechanical stress limit, the component may crack or break. We discuss this problem in detail and set up a thermal model. Using this model, we gain the machined component temperature field and its corresponding thermal stress field. A filtered IBF method is created to correct the thermal stress field which that gain a more even thermal stress distribution and decrease the thermal stress about 20%.

Surface scatter effects from residual optical fabrication errors can severely degrade optical performance. The total integrated scatter (TIS) from a given mirror surface is determined by the ratio of the spatial frequency band-limited "relevant" root-mean-square surface roughness to the wavelength of light. For short-wavelength (extreme-ultraviolet/x-ray) applications, even state-of-the-art optical surfaces can scatter a significant fraction of the total reflected light. In this paper we first discuss how to calculate the band-limited relevant roughness from surface metrology data, then present parametric plots of the TIS for optical surfaces with arbitrary roughness, surface correlation widths, and incident angles. Surfaces with both Gaussian and ABC or K-correlation power spectral density functions have been modeled. These parametric TIS predictions provide insight that is useful in determining realistic optical fabrication tolerances necessary to satisfy specific optical performance requirements.

To overcome inherent problems with conventional three-dimensional profiling systems based on pattern-projection method, we propose incorporating a digital device, such as a single MEMS mirror in the projection optics. In this system, a projector is controlled to generate a projection pattern with an appropriate periodic structure and sinusoidal intensity distribution. The key aspect to this projection method is that sinusoidal signals are generated by a function generator; that is, the temporal sinusoidal intensity distribution is transformed from the time domain to the spatial domain. This flexible pattern-projection method permits phase-shifting techniques to be applied to industrial measurement and inspection. This apparatus is so compact as to have a dimensional size similar to a conventional digital camera [53  mm(H)×130  mm(W)×38  mm(D)]. Furthermore, it is lightweight (320 g) without a battery or circuit boards. Such a compact system can be used as a palm-top camera and potentially may be used in low cost measurement systems for three-dimensional profilometry.

We present an accuracy analysis of noncontact measurement applied for the evaluation of radial velocity and distance of a moving object. The principle of velocity and distance measurement is based on the Doppler effect. Described here are the radial velocity and distance measurement principle, as well as the approach based on the Doppler effect. The accuracy of radial velocity, and distance identification of a moving object, directly depends on the stability of a laser or other radiation source. Measurement results can also be influenced by deviations of radiation source parameters and atmospheric factors. Accuracy analysis evaluation is based on probability estimation of random mistakes methodology. Evaluated are the impact of a laser or other radiation source and atmospheric parameters crosscorrelating on the accuracy of moving object radial velocity and the distance.

In order to obtain more comprehensive three-dimensional (3-D) deformation data, improve the flexibility and precision of 3-D deformation measurement, and describe the real-time displacement of various points in the measurement scope, we researched speckle methods in this field. First, we expounded basic theories of speckle technique and elaborated on several important aspects of 3-D measurement, including camera calibration, images matching, and 3-D coordinate and displacement calculation. Then, we established the relevant mathematical models and developed a corresponding measurement and analysis software, XJTUDIC. Aided with the appropriate hardware devices, this software recorded and analyzed the whole process of tensile deformation. When compared with the results of the simulation analysis using ANSYS, this method achieved a relative error within ±0.75%, demonstrating the reliability, feasibility, and advantage of this method and its corresponding applied software and hardware.

We describe a methodology for identifying asymmetries in boat hull sections reconstructed from point clouds captured using a terrestrial laser scanner (TLS). A surface was first fit to the point cloud using a nonparametric regression method that permitted the construction of a continuous smooth surface. Asymmetries in cross-sections of the surface were identified using a bootstrap resampling technique that took into account uncertainty in the coordinates of the scanned points. Each reconstructed section was analyzed to check, for a given level of significance, that it was within the confidence interval for the theoretical symmetrical section. The method was applied to the study of asymmetries in a medium-sized yacht. Identified were differences of up to 5 cm between the real and theoretical sections in some parts of the hull.

A pixelated, wire-grid diffraction grating is designed, fabricated, aligned, and mounted on an active focal plane array of a camera operating in the visible. The resulting design of the pixelated wire-grid polarizer array eschewed the need for fine translational alignments and drastically reduced cross-talk between pixels detecting differing polarization states. Using common optomechanical elements in conjunction with a novel correlation-based alignment metric, we are able to achieve repeatable angular alignments to better than 0.004 deg between the focal plane array and the pixelated wire-grid polarizer array, both featuring 6.45 μm pixels. An on-chip, four-state, linear snapshot polarimeter is yielded in the detailed processes and raw image data from the instrument are presented.

We propose a precise circuit model to estimate transient optical responses of an active-matrix liquid crystal display (AMLCD). Liquid crystal (LC) molecules in the pixel is behaviorally modeled by using the first-order system that is described by Verilog-A. Capacitance-voltage (C-V) characteristics of a pixel determine the accuracy of the dynamic responses. Measuring C-V characteristics is impossible because pixels are driven by switching transistors in the AMLCD. We propose a method to obtain the C-V data from natural optical responses. Estimated optical responses based on the C-V data extracted by our proposal show more accurate results than those based on C-V data obtained by using transmittance-voltage data. It is demonstrated that our behavioral model enables us to predict very accurate transient responses, which makes it possible to design LCD products with lower costs.

Microdisplay technologies for near-to-eye applications mostly use a complementary metal-oxide semiconductor (CMOS) processing chip as backplane for pixel addressing, with extensive post-processing on top of the CMOS chip to deposit organic LED or liquid crystal layers. Here, we examine the possibility of integrating emissive microdisplays within the CMOS chip, with absolutely no post processing needed. This will dramatically reduce the manufacturing cost of microdisplays and may lead to new microdisplay applications. Visible electroluminescence is achieved by biasing pn junctions into avalanche breakdown mode. The most appropriate CMOS pn junction is selected and innovative techniques are applied to increase the light extraction efficiency from the CMOS chip using the metal layers of the CMOS process. An 8×64 dot matrix microdisplay was designed and manufactured in a 0.35-μm CMOS technology. The experimental results show that a luminance level of 20  cd/^m2 can be reached, which is an adequate luminance value in order to comfortably read data being displayed in relatively dark environments. The electrical power dissipation per pixel being activated is 0.9  mW/pixel. It is also shown that the pixels can be switched at a rate faster than 350 MHz.

A ceramic ytterbium:yttrium aluminum garnet (Yb:YAG) thin-disk laser is investigated at 15°C (288 K) and also at 80 K, where it behaves as a four-level laser. We introduce a new two-phase spray cooling method to cool the Yb:YAG. One system relies on R134a refrigerant while the other uses liquid nitrogen (LN₂). The use of two systems allows the same disk to be tested at the two temperatures. When the Yb:YAG is cooled from room to cryogenic temperatures, the lasing threshold drops from 155 W to near 10 W, while the slope efficiency increases from 54% to a 63%. A 277 W laser with 520 W of pump is demonstrated. We also model the thermal and structural properties at these two temperatures and estimate the beam quality.

The results of investigation aimed at analysis of coordinate distributions for azimuths and ellipticity of polarization (polarization maps) in laser images of three types of phase-inhomogeneous layers are presented in this research, namely: rough, ground and bulk-scattering layers. Three groups of parameters: statistical moments of the first to fourth orders, autocorrelation functions, logarithmic dependences for power spectra related to distributions of azimuths and ellipticity of polarization inherent to phase-inhomogeneous layers laser images are suggested to characterize polarization maps for all the types of phase-inhomogeneous layers. The criteria for diagnostics and classification of phase-inhomogeneous layers optical properties are ascertained.

The applicability of a femtosecond KrF laser in absorbing film-assisted, laser-induced forward transfer of living cells was studied. The absorbing materials were 50-nm-thick metal films and biomaterials (gelatine, Matrigel, each 50 μm thick, and polyhydroxybutyrate, 2 μm). The used cell types were human neuroblastoma, chronic myeloid leukemia, and osteogenic sarcoma cell lines, and primary astroglial rat cells. Pulses of a 500-fs KrF excimer laser focused onto the absorbing layer in a 250-μm diameter spot with 225  mJ/cm2 fluence were used to transfer the cells to the acceptor plate placed at 0.6 mm distance, which was a glass slide either pure or covered with biomaterials. While the low-absorptivity biomaterial absorbing layers proved to be ineffective in transfer of cells, when applied on the surface of acceptor plate, the wet gelatine and Matrigel layers successfully ameliorated the impact of the cells, which otherwise did not survive the arrival onto a hard surface. The best short- and long-term survival rate was between 65% and 70% for neuroblastoma and astroglial cells. The long-term survival of the transferred osteosarcoma cells was low, while the myeloid leukemia cells did not tolerate the procedure under the applied experimental conditions.

In this study, an original scale-reduction rule without a drop in the sensitivity of a guided-wave optical pressure sensor was obtained using a micromachined diaphragm. The sensor has a rectangular diaphragm as a pressure-sensitive structure and a sensing waveguide across the diaphragm. Its sensitivity is theoretically known to be strongly dependent on the dimensions of the diaphragm. According to the theoretical results, the sensitivity can be kept constant even if the diaphragm dimensions are reduced as long as both the aspect ratio and the characteristic length of the diaphragm remain constant. Here, the characteristic length is introduced as the cube of either width or length of the rectangular diaphragm divided by the square of its thickness. Such a scale-reduction rule would be very useful for miniaturizing a sensor without reducing sensitivity, although it has not been experimentally confirmed. In this study, the scale-reduction rule was experimentally examined using three fabricated sensors with the same aspect ratio and the same characteristic length. The measured sensitivities of the three sensors were quite similar to each other, as theoretically predicted.

For in-process shape monitoring of rotating objects such as workpieces in a turning machine, contactless and compact sensors with high temporal resolution are necessary. For this challenging task, we developed a miniaturized and robust nonincremental interferometric fiber-optical distance sensor with dimensions of only 30×40×90 mm³, which enables attaching the sensor head directly to the mount of a turning tool bit. We present the results of in-process 3-D shape measurements of turning parts at a metal working lathe. To proof the accuracy of the measurement results, comparative measurements with tactile and optical sensors were performed. A maximal deviation between the different measurement methods of 2.2 μm was achieved for the determination of the mean height of a radial step.

Due to the Joule heating effect induced by the use of an assisting electric field, glass wafer temperature is experimentally found to increase synchronically with the flow of current during the process of field-assisted ion diffusion. A theoretical analysis demonstrates that the amplitude of the glass wafer temperature increase is dictated by competition between two factors, heat generation and heat dissipation. Heat generation and heat dissipation both become stronger as the glass wafer temperature increases. Studies have shown that the Joule heating effect can influence the waveguide manufacturing process profoundly, including aspects such as the stability of ion diffusion, theoretical modeling of the ion-diffusion process, and waveguide depth uniformity over the glass wafer.

Complying with security certifications in most harsh industrial areas is usually very expensive and sometimes hinders the industrialization of new technologies. Thus, we observe in the modern industry an increasing need for visual inspection and closed monitoring systems, either manual (direct and permanent observation of a supervisor) or automatic (usually through Computer Vision applications) to monitor hazardous environments. In such conditions, the use of incoherent optical fiber bundle (IOFB) for image transmission is probably the most appropriate solution. This option requires a prior calibration step to perform the reconstruction of the IOFB output image, where the reconstruction process is very efficient, according to the latest studies. It is of further interest to introduce and extend this technique in industrial applications, to make possible the portability of IOFB calibration. Indeed, a slight position shift of the system may corrupt the calibrated IOFB, consequently invalidating it for image transmission. We propose a new method to quickly and automatically solve this problem. Such an image acquisition and transmission system is very attractive for commercial introduction, since the IOFB can be pre-calibrated, and the calibration quickly recomputed any time it is needed without loss in image quality. The presented work has been submitted for patent.

This study demonstrates a broadband gain-clamped and gain-flattened dispersion-compensated Raman/erbium-doped fiber hybrid amplifier that recycles residual Raman pump power using a single fiber Bragg grating for wavelength-division multiplexing systems. The optimum gain-clamped wavelength was 1564 nm. A gain variation of less than 0.21 dB can be achieved from 1525 to 1625 nm, and the dynamic input power exceeds 18 dB, ranging from −20 to −2   dBm. Further, a gain ripple of ±1.75  dB can be achieved from 1530 to 1595 nm.

The superactivation of zero-capacity optical quantum channels makes it possible to use two zero-capacity optical quantum channels, with a positive joint capacity at the output. Here we show, that noisy Gaussian quantum channels with the help of entanglement and coherent optical devices, can be used to transmit quantum information perfectly. It will be demonstrated that using the superactivation effect, it is possible to develop efficient quantum repeaters with the elimination of the very inefficient and expensive purification process.

We use a commercially available 1.2 GHz bandwidth reflective semiconductor optical amplifier (RSOA)-based optical network unit (ONU) to achieve 10-gbits/s upstream traffic for an optical orthogonal frequency division multiplexing (OFDM) long-reach passive optical network (LR-PON). This is the first time the 64-quadrature amplitude modulation (QAM) OFDM format has been applied to RSOA-ONU to achieve a 75 km fiber transmission length. In the proposed LR-PON, the upstream power penalty of 5.2 dB at the bit error rate of 3.8×10−3 is measured by using a 64-QAM OFDM modulation after the 75 km fiber transmission without dispersion compensation.

We investigated Raman gain spectrum and its dependence on Stoke's shift for fiber Raman amplifiers (FRAs). We determined that the Raman gain spectrum is fairly broad with a gain variation of less than 1 dB from the pump wavelength of 1440 to 1460 nm with maximum gain at 1451.2 nm, which corresponds to a Stoke's shift of 13.4 THz for the input signal source at 1550 nm. Also, the effect of both a co-propagating and counter-propagating scheme on FRAs was studied without using any booster before the Raman fiber, and it was determined that a small signal gain in the case of the counter-propagating scheme is much higher than that of the co-propagating scheme. The impact of the Raman constant (f_r) on gain saturation is also illustrated. We have demonstrated that at high f_r (<0.18), gain saturation conditions worsen. This suggests that higher saturation input powers can be achieved by selecting an f_r value of 0.18 for small-signal gains of 20 dB and an input power of −20  dBm. We have numerically simulated the gain of a FRA for different Raman fiber lengths using varying pump powers. Gain saturation was observed when the input powers exceeded 5 dBm in an amplifier with a small signal gain of 20 dB, pump power of 1.2 W, and Raman fiber length of 8 km.

Bandwidth demand for transferring data among different consumer electronic products is increasing rapidly. Due to issues of high propagation loss, electromagnetic interference, and limited bandwidth-distance product of the present copper-based electrical cables, consumer electronic devices may not provide the bandwidth required for future high-capacity applications. The Intel Corporation has proposed Light Peak technology, allowing data transfer between electronic devices at 10  Gb/s in optical domain. To establish a reliable Light Peak connection, robust optical fiber is highly required. In this paper, we discuss the fabrication and characterization of a new type of 80-μm large-core optical fiber. We perform 10  Gb/s bit-error-rate measurements using 850 and 1550-nm transceivers. The results show that even though we have enlarged the fiber core diameter by 60% (from 50 to 80 μm) in order to increase the laser-to-fiber alignment tolerance, transmission bandwidth and distance required by Light Peak can still be achieved in this new type of large-core optical fiber.

The induced variations of complex third-order susceptibilities in bent single-mode fiber at the standard operating wavelengths, 1300 and 1550 nm, is studied using Fizeau interferometry for radius of curvature ranges from 5 to 11 mm. At λ = 1300  nm and at the minimum radius of curvature R = 5  mm, the cladding real (dispersive) third-order susceptibility Re|χ⁽³⁾| = 1.167×10⁻¹⁵±0.8% electrostatic unit (esu) on the tensile side, whereas on the compressed side it is 1.309×10−15  esu. On the tensile side, the cladding imaginary (absorptive) third-order susceptibility Im|χ⁽³⁾| = 2.089×10⁻¹⁸±0.8%  esu, whereas on the compressed side it is 2.118×10^-18esu. For λ = 1550  nm, the cladding Re|χ⁽³⁾| and Im|χ⁽³⁾| on the tensile side are 1.116×10^-15esu and 2.478×10^-18esu, whereas on the compressed cladding side they are 1.259×10^-15esu and 2.514×10^-18esu, respectively. At λ = 1300  nm and R = 5  mm, the core Re|χ⁽³⁾| is given by 1.318×10^-15esu on the tensile side and 1.324×10^-15  esu on the compressed side. The asymmetry in Im|χ⁽³⁾| is given by 4.687×10^-17  esu on the tensile side and by 4.89×10^-17esu on the compressed side. With λ = 1550  nm, the core Re|χ⁽³⁾| asymmetry is given by 1.267×10-15  esu on the tensile side and by 1.272×10^-15esu on the compressed side. For Im|χ⁽³⁾| its core asymmetry is provided by 5.561×10^-17esu on the tensile side and by 5.564×10^-17esu on the compressed side. The observed asymmetry in the measured complex third-order susceptibility components for bent fibers is attributed to the nonlinear response of Young's modulus of fiber material.

We propose and demonstrate a long-reach wavelength division multiplexed-passive optical networks (WDM-PON) based on reflective semiconductor optical amplifiers (RSOAs) with easy maintenance of the optical source. Unlike previous studies the proposed WDM-PON uses two RSOAs: one for wavelength-selected light generation to provide a constant seed light to the second RSOA, the other for active external modulation. This method is free from intensity-fluctuated power penalties inherent to directly modulated single-RSOA sources, making long-reach transmission possible. Also, the wavelength of the modulated signal can easily be changed for the same RSOA by replacing the external feedback reflector, such as a fiber Bragg grating, or via thermal tuning. The seed light has a high-side-mode suppression ratio (SMSR) of 45 dB, and the bit error rate (BER) curve reveals that the upstream 1.25-Gb/s nonreturn-to-zero (NRZ) signal with a pseudo-random binary sequence (PRBS) of length of 2¹⁵-1 has power penalties of 0.22 and 0.69 dB at BERs of 10^-9 after 55-km and 110-km transmission due to fiber dispersion, respectively.

This paper presents an improved direct binary search (DBS)-based algorithm for generating holograms to holographic optical tweezers. The simulations show that the improved algorithm greatly enhances computation speed while maintaining high hologram efficiency and high-intensity homogeneous target spots. The improved algorithm was applied to generate holographic optical tweezers in several experiments. The experiments demonstrate that real-time trap and manipulation can be realized with the improved algorithm if the number of trapped microparticles is small.

An optical tracking sensor that produces images containing the state of polarization of each pixel can be implemented using individual wire-grid micropolarizers on each detector element of a solid-state focal plane array. These sensors can significantly improve identification and tracking of various man-made targets in cluttered, dynamic scenes such as urban and suburban environments. We present electromagnetic simulation results for wire-grid polarizers that can be fabricated on standard imaging arrays at three different technology nodes (an 80-, 250-, and 500-nm pitch) for use in polarization-sensitive detector arrays. The degradation in polarizer performance with the larger pitch grids is quantified. We also present results suggesting the performance degradation is not significant enough to affect performance in a man-made vehicle-tracking application.

One of the fundamental challenges for a hyperspectral imaging surveillance system is the detection of sub-pixel objects in background clutter. The background surrounding the object, which acts as interference, provides the major obstacle to successful detection. One algorithm that is widely used in hyperspectral detection and successfully suppresses the background in many situations is the matched filter detector. However, the matched filter also produces false alarms in many situations. We use three simple and well-established concepts-the target-background replacement model, the matched filter, and Mahalanobis distance-to develop the matched filter with false alarm mitigation (MF-FAM), a dual-threshold detector capable of eliminating many matched filter false alarms. We compare this algorithm to the mixture tuned matched filter (MTMF), a popular approach to matched filter false alarm mitigation found in the ENVI® software environment. The two algorithms are shown to produce nearly identical results using real hyperspectral data, but the MF-FAM is shown to be operationally, computationally, and theoretically simpler than the MTMF.

Multiclass geospatial objects detection within complex environments is a challenging problem in remote-sensing areas. In this paper we propose a novel, generalized kernel-based learning framework for the purpose of enhanced object detection. There are two novel areas. (1) Multisource information, including shape, feature points, and appearance, was extracted to give a comprehensive representation of the objects. We improved a shape descriptor and introduced a two-level spatial pyramid to represent appearance, both global and local. Therefore, basis kernels were formed, one for each feature. (2) In order to illustrate the effect of each kind of feature on each pyramid level, a generalized and weighted combination method was first used to combine all of the levels and then the features. The weights and the classifier model are based on the support vector machine framework for obtaining balance between all basis kernels. This classifier was transformed into a powerful detector by using a sliding window. The reported results are for the detection on high-resolution remote-sensing images. This study demonstrates that the proposed generalized and weighted combination of kernels can yield better performance compared with traditional single-kernel classifier and other combination methods.

A good photo is determined using various visual elements of photography and these elements have been implemented in mobile devices with functionalities including zooming, auto-focusing and auto-white-balancing. Although composition is an important element of a good photo and an interesting research topic, most composition-related functionalities have not been added to mobile devices. We propose a guide system for capturing good photos in mobile devices that considers composition elements. A photo composition mixture model (PCMM) is derived based on composition elements such as a Gaussian Mixture Model (GMM), and the best composition of current input is gradually determined by iterating the PCMM optimization. Experimental evaluations are conducted to show the usefulness of the proposed PCMM and its optimization performance. To show the efficiency of recomposition performance and speed, we compare our method with retargeting-based methods. By implementing our method in mobile devices, we show that our system offers valid user guidance for capturing a photo with good composition in realtime.

Traditional learning-based boundary extraction algorithms classify each pixel edge separately and then get boundaries from the local decisions of a classifier. However, we propose a supervised learning method for boundary extraction by using edgelets as boundary elements. First, we extract edgelets by clustering probabilities of boundary. Second, we use features of edgelets to train a classifier that determines whether an edgelet belongs to a boundary. The classifier is trained by utilizing edgelet features, including local appearance, multiscale features, and global scene features such as saliency maps. Finally, we use the classifier to decide the probability that the edgelet belongs to the boundary. The experimental results in the Berkeley Segmentation Dataset demonstrate that our algorithm can improve the performance of boundary extraction.

We introduces an efficient intra-field deinterlacing algorithm while considering both closeness and similarity between the interpolated pixel and the neighbor pixels. Instead of estimating the edge orientations via limited candidate directions as previous intra-field deinterlacing methods, we propose an adaptive spatial locality- and similarity-based deinterlacing method. Many deinterlacing methods described in the literature only consider the similarity between neighbor pixels and interpolated pixels; however, awareness of distance correlation and spatial locality has not yet been studied. Experimental results indicate that the proposed scheme outperforms a number of existing approaches, in terms of both the objective and subjective performance.

The Newton-Raphson (N-R) algorithm based on the sum of squared differences (SSD) function used in the digital image correlation (DIC) may obtain unreliable results in deformation measurements because light source variation is not taken into account. Here, a modified N-R algorithm that includes the effect of light source variations on the measurement results is presented. Instead of involving the mean value and square sum of the gray value of the object, variables were employed in the proposed algorithm. Thus, we refer to it as variables-based sum of squared differences (VSSD) function. VSSD has been validated by comparing the computer generated speckle images, which indicates that it could give rise to more accurate results in calculating deformation than SSD when the surrounding light source changes. In addition, VSSD is compared with the zero-normalized sum of squared differences (ZNSSD) function that is often used to remove the light source variation. The results show that VSSD can achieve the same accuracy within in less time compared to ZNSSD.

Natural scene classification is a challenging open problem in computer vision. We present a novel spatial pyramid representation scheme for recognizing scene category. Initially, each image is partitioned into sub-blocks, applying the technology of superpixel lattices segmentation according to a boosted edge learning boundary map, which makes the objects in each sub-block have the integrity-that is, the features in each sub-block are relatively consistent. Then, we extract the dense scale-invariant feature transform features of the images and form the contextual visual feature description. Finally, the image representations are performed by following the methodology of spatial pyramid. The feature descriptions we present include both local structural information and global spatial structural information; therefore, they are more discriminative for scene classification. Experiments demonstrate that the classification rate can achieve about 87.13% on a set of 15 categories of complex scenes.

We address the issue of human activity recognition by introducing the multiclass relevance vector machine (mRVM), the current state-of-the-art kernel machine learning technology given the multiclass classification problems (actually, activity recognition can commonly be viewed as a multiclass classification problem). Under our proposed recognition framework, the required procedure consists of three functional cascade modules: a. detecting the human silhouette blobs from the image sequence by the background subtraction method; b. extracting the shape and the motion features from the variation energy image (VEI); and c. sending the obtained features to the mRVM and recognizing the human activity. There are two types of mRVM: the constructive mRVM₁ and the top-down mRVM₂. We performed 10 times three-fold cross-validation on the Weizmann benchmark data set to examine the effectiveness of the proposed method. We also compared our method with other existing approaches, and the experimental results show that the proposed method offers superior performance. In summary, the mRVM, especially the mRVM₂, has advantages both in terms of recognition rate and sparsity, along with a simple feature extraction process. The mRVM also significantly simplifies the classification process, by comparison with traditional binary-tree style multiclass classifiers.

A robust and fast Hausdorff distance (HD) method is presented for image matching. Canny edge operator is used for extracting edge points. HD measure is one of efficient measures for comparing two edge images by calculating the interpixel distance between two sets of edge points, and does not require the point-to-point correspondence. However, high computational complexity is a common problem for HD measure because a large number of edge points could be extracted used to calculate HD. Further, a great many incorrect edge points will be extracted under the condition of occlusion and other ill conditions. A gradient orientation selectivity strategy is proposed to not only select available edges, but also reduce the number of edge points. Experimental results show that the proposed method has less computational cost, and has good robustness for object matching, especially under partial occlusion and other ill conditions.

Clustering is one of the image-processing methods used in non-destructive testing (NDT). As one of the initializing parameters, most clustering algorithms, like fuzzy C means (FCM), Iterative self-organization data analysis (ISODATA), K-means, and their derivatives, require the number of clusters. This paper proposes an algorithm for clustering the pixels in C-scan images without any initializing parameters. In this state-of-the-art method, an image is sampled based on the rosette pattern and according to the pattern characteristics, and extracted samples are clustered and then the number of clusters is determined. The centroids of the classes are computed by means of a method used to calculate the distribution function. Based on different data sets, the results show that the algorithm improves the clustering capability by 92.93% and 91.93% in comparison with FCM and K-means algorithms, respectively. Moreover, when dealing with high-resolution data sets, the efficiency of the algorithm in terms of cluster detection and run time improves considerably.

We propose a novel face recognition method that represents and classifies face images in the feature space. It first assumes that in the feature space the test sample can be well expressed by a linear combination of the training samples, and then it exploits the obtained linear combination to perform face recognition. We also present the foundation, rationale, and characteristics of, as well as the differences between, our method and conventional kernel methods. The analysis shows that our method is a representation-based kernel method and works in the feature space. This method might be able to outperform the representation-based methods that work in the original space. The experimental results show that our method partially possesses the properties of "sparseness" and is able to reduce greatly the effects of noise and occlusion in the test sample.

In this paper, we propose a visual fatigue prediction method for stereoscopic video. We select visual fatigue factor candidates and determine the equations for each. The candidates are then classified into their principal components, and the validity of each is confirmed using principal component analysis. Visual fatigue is predicted using multiple regression with subjective visual fatigue. In order to determine the best model, we select the visual fatigue factors that have sufficient significance in terms of subjective fatigue according to the stepwise method. The predicted visual fatigue score is presented as a linear combination of the selected visual fatigue factors. Consequently, the proposed algorithm provides more reliable performance in terms of correlation with the subjective test results compared with a conventional algorithm.

Plane detection in 3-D space is a core function of the autonomous mobile robot. A representative technique for plane detection is the Hough transform method. The Hough transform is robust to noise and makes accurate plane detection possible. However, a common problem in methods based on the Hough transform is that too much time is required to calculate parameters, which adds computational cost and memory requirements for parameter voting to find the distribution of mixed multiple planes in the parameter space. Furthermore, real-time processing for sequential image sequences is challenging, because the whole process must be repetitively performed for the next detection. We extend the conventional self-organizing map by introducing a real-time clustering method and by detecting multiple planes through the creation, extinction, renewal, and merging of plane parameter data, which are input sequentially. The proposed method is also based on reliable plane detection through a planarity evaluation during data sampling. The results of experiments conducted under various conditions with an unmanned vehicle demonstrate that the proposed method is more accurate and faster than conventional methods.

We propose a wildfire smoke detection algorithm that uses temporospatial visual features and an ensemble of decision trees and random forest classifiers. In general, wildfire smoke detection is particularly important for early warning systems because smoke is usually generated before flames; in addition, smoke can be detected from a long distance owing to its diffusion characteristics. In order to detect wildfire smoke using a video camera, temporospatial characteristics such as color, wavelet coefficients, motion orientation, and a histogram of oriented gradients are extracted from the preceding 100 corresponding frames and the current keyframe. Two RFs are then trained using independent temporal and spatial feature vectors. Finally, a candidate block is declared as a smoke block if the average probability of two RFs in a smoke class is maximum. The proposed algorithm was successfully applied to various wildfire-smoke and smoke-colored videos and performed better than other related algorithms.

The Reeb graph provides a structure that encodes the topology of a shape, and it has been gaining in popularity in shape analysis and understanding. We introduce a spectral clustering method to compute the Reeb graph. Given a 3-D model embedded in the Euclidean space, we define the Morse function according to the connected components of the 3-D model in a spectral space. The spectral clustering formulation gives rise to a consistent Reeb graph over pose changes of the same object with meaningful subparts and yields a hierarchical computation of the Reeb graph. We prove that this method is theoretically reasonable, and experimental results show its efficiency.

The resonant frequency of triangle split resonant rings and metal wires (TSRRs-MWs) is analyzed. The simulated results show that the resonant frequency can be improved and the bandwidth widened by increasing the opening size of TSRRs and by contracting the substrate. Two samples are designed to implement the experimental measurement, and the experimental results show that the bandwidth of the resonant frequency becomes wider when the thickness of the substrate is reduced, and that the resonant frequency shifs from low frequency to high frequency. The experimental results show good agreement with the theoretical analysis.

We propose the analytic solution of cross-spectral density matrix (CSDM) of a partially coherent vortex beam while propagating. The solution to the propagation law is appropriate for a Gaussian Schell-model vortex beam to any order. It is found that the solution of CSDM of a Gaussian Schell-model beam revealed by Emil Wolf is a special instance. By this general solution, the intensity distribution, especially the degree of polarization and the mean-squared beam width of the partially coherent vortex beam, are investigated. It is found that the propagation character of the beam width is decided by the correlation-length, and that the topological charge affects only the value of the beam width.

An acousto-optic Bragg cell with first-order feedback, which exhibits chaotic behavior past the threshold for bistability, was recently examined for possible chaotic encryption and recovery of simple messages (such as low-amplitude periodic signals) applied via the bias input of the sound cell driver. We carry out a thorough examination of the nonlinear dynamics of the Bragg cell under intensity feedback for (i) dc variations of the feedback gain () and the phase shift parameter (0) and (ii) ac variations of 0,total under signal encryption, investigating both from two different perspectives: (i) examining chaos in view of the so-called Lyapunov exponent derived recently by Ghosh and Verma and (ii) examining chaos in terms of the familiar bifurcation maps of intensity plotted against the feedback gain and the effective bias. It is shown that overall, the nonlinear dynamical results using the two approaches broadly agree, both for dc (fixed-parameter) analyses and, more importantly, when applied to the case of ac signal encryption cases. This affirms the effectiveness of the nonlinear dynamical theory in predicting and tracking the actual physical behavior of this system for message signal transmission and recovery under complex chaotic encryption.

A novel photonic approach for measuring microwave frequency over a wide bandwidth, based on intensity-modulated link with output microwave interference detection, is proposed. In this simple measurement system, a tunable laser and a fixed-wavelength laser are used with a single-mode fiber as the dispersive medium. By scanning the wavelength of a tunable laser, the frequency of the modulated microwave signal can be obtained directly through analyzing the interference intensity of the microwave signal at the output of the photodetector. The proposed approach is demonstrated experimentally by obtaining the unknown microwave frequency in the range of 1 to 20 GHz with a measurement accuracy of several tens of MHz.

The smallest spot size of a laser diode beam is analyzed for various beam delivery distances after being collimated and focused. A simple way of calculating the spot size is found.