This PDF file contains the editorial “Editorial: ‘‘Not Wrong’’ Papers” for OE Vol. 44 Issue 04

We report, for the first time to our knowledge, the detection and localization of a loss-inducing perturbation along more than 20-km-long test fiber based on the analysis of transmitted and Rayleigh backscattered powers of an unmodulated continuous-wave light source. Localization of a strong disturbance with an estimated accuracy of 1 m near the source end and 7.5 m near the remote end of the 21.067-km-long single-mode sensing fiber is demonstrated.

A theoretical and experimental study of radio-frequency ring resonators (RR) for referencing and improving the sensitivity of fiber-optic intensity sensors (FOS) is reported. The separation between lead and transducer losses in the FOS is solved by converting the light intensity fluctuations to be measured into RR losses that produce high amplitude variations in the proximity of the RR resonance frequencies. Two different self-referencing techniques are developed. Via the definition of the measurement parameter R_M, sensor linearity and sensitivity are analyzed. A calibration using an optical attenuator is reported to validate the model.

A periodic optical filter based on a Michelson interferometer with a three-mirror Gire-Tournois resonator in one of the two arms is analyzed. We derive the general condition for the occurrence of flattop spectra. The results show that flattop spectra can be obtained by suitably choosing the reflective coefficients of individual mirrors.

Two types of silicon-on-insulator thermo-optic variable optical attenuators (VOAs) based on a Mach-Zehnder interferometer and a multimode-interference coupler are fabricated, one with thermal isolating grooves to improve heating efficiency and the other without. Comparison of optical and electrical properties, such as insertion losses, the maximum attenuation levels and the corresponding power consumptions, and the response times, is carried out between the two types of VOAs. The comparison results indicate that use of thermal isolating grooves leads to better values for most characteristics and is an effective way to improve the performance of Mach-Zehnder interferometer-type thermo-optic devices.

This PDF file contains the editorial “Editorial: Advances in UV Ground- and Space-based Measurements and Modeling II” for OE Vol. 44 Issue 04

Spectral measurements of solar ultraviolet (UV) radiation have been made at several ground-based locations and for more than 10 yr at some sites. These measurements are important for two main reasons. First, the measurements combined with results of radiative transfer models contribute toward our understanding of the many complicated radiative transfer processes in the atmosphere and at the Earth's surface. These processes include absorption of radiation by atmospheric gases such as ozone and sulfur dioxide, scattering by atmospheric aerosols and clouds, and scattering from the earth's surface. Knowledge of these processes is required for operational applications such as the estimation of surface UV radiation from satellite data and the forecasting of the UV index. Also, our ability to estimate UV climatology in the past, as well as in the future, requires thorough knowledge of the UV radiative transfer processes. The second reason for making systematic ground-based measurements of UV radiation is to determine whether long-term changes are occurring as a result of ozone depletion or climate change and to identify specific causes. Examples of how long-term ground-based data records have contributed to our understanding of surface UV radiation are presented.

Successful retrieval of surface properties from space is hampered by the presence of atmospheric aerosol particles that contribute significantly to the measured signal. Our ability to obtain reliable information about surface properties depends to a large extent on how well we can account for the influence of aerosols. The problem is complicated by the fact that aerosols often consist of a multicomponent mixture of particles with different chemical compositions and different affinities to water. For example, to predict how the optical properties of such particles change with increasing humidity, we must make assumptions about how the particles grow, change their refractive indices, and mix as a function of humidity. We discuss possible strategies for reliable atmospheric correction over dark as well as bright surfaces. Also, we discuss the role of realistic simulations of the radiative transfer process in the coupled atmosphere-ocean system in the solution of the inverse problem required to retrieve surface properties is also discussed.

Radiative transfer calculations of UV irradiance from total ozone mapping spectrometer (TOMS) satellite data are frequently overestimated compared to ground-based measurements because of the presence of undetected absorbing aerosols in the planetary boundary layer. To reduce these uncertainties, an aerosol UV absorption closure experiment has been conducted at the National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC) site in Greenbelt, Maryland, using 17 months of data from a shadowband radiometer [UV-multifilter rotating shadowband radiometer (UV-MFRSR), U.S. Department of Agriculture (USDA) UV-B Monitoring and Research Network] colocated with a group of three sun-sky CIMEL radiometers [rotating reference instruments of the NASA Aerosol Robotic Network (AERONET)]. We describe an improved UV-MFRSR on-site calibration method augmented by AERONET-CIMEL measurements of aerosol extinction optical thickness (τ_a) interpolated or extrapolated to the UV-MFRSR wavelengths and measurement intervals. The estimated τ_a is used as input to a UV-MFRSR spectral-band model, along with independent column ozone and surface pressure measurements, to estimate zero air mass voltages V₀ in three longer wavelength UV-MFRSR channels (325, 332, 368 nm). Daily mean ⟨V₀⟩, estimates and standard deviations are obtained for cloud-free conditions and compared with the on-site UV-MFRSR Langley plot calibration method. By repeating the calibrations on clear days, relatively good stability (±2% in ⟨V₀⟩) is found in summer, with larger relative changes in fall-winter seasons.

Compared to the visible spectral region, very little is known about aerosol absorption in the UV. Without such information it is impossible to quantify the causes of the observed discrepancy between modeled and measured UV irradiances and photolysis rates. We report results of a 17-month aerosol column absorption monitoring experiment conducted in Greenbelt, Maryland, where the imaginary part of effective refractive index k was inferred from the measurements of direct and diffuse atmospheric transmittances by a UV-multifilter rotating shadowband radiometer [UV-MFRSR, U.S. Department of Agriculture (USDA) UV-B Monitoring and Research Network]. Colocated ancillary measurements of aerosol effective particle size distribution and refractive index in the visible wavelengths [by CIMEL sun-sky radiometers, National Aeronautics and Space Administration (NASA) Aerosol Robotic Network (AERONET)], column ozone, surface pressure, and albedo constrain the forward radiative transfer model input, so that a unique solution for k is obtained independently in each UV-MFRSR spectral channel. Inferred values of k are systematically larger in the UV than in the visible wavelengths. The inferred k values enable calculation of the single scattering albedo ω, which is compared with AERONET inversions in the visible wavelengths. On cloud-free days with high aerosol loadings [τ_ext(440)>0.4], ω is systematically lower at 368 nm (<ω₃₆₈>=0.94) than at 440 nm (<ω₄₄₀>=0.96), however, the mean ω differences (0.02) are within expected uncertainties of ω retrievals (~0.03). The inferred ω is even lower at shorter UV wavelengths (<ω₃₂₅>~<ω₃₃₂>=0.92), which might suggest the presence of selectively UV absorbing aerosols. We also find that decreases with decrease in aerosol loading. This could be due to real changes in the average aerosol composition between summer and winter months at the Goddard Space Flight Center (GSFC) site.

Global atmospheric trends in ozone column amount have focused attention on the environmental risk of exposure to ultraviolet (UV) radiation. Monitoring UV irradiance in diverse and remote locations is necessary to understand the variability of exposure, dose rates, and resultant vulnerability of ecological systems. The U.S. Department of Agriculture (USDA) UV-B Monitoring Program maintains a wide network for ground-based continuous measurement of solar radiation in several wavelengths of interest for photosynthesis, plant growth, UV exposure to humans, and photochemistry. This network provides data for analysis of UV climatology and trends at those sites. A satellite-based method to produce mesoscale-resolution mapped distributions of UV spectral irradiance has been developed that utilizes this network data for verification. The methodology combines radiative transfer modeling, multispectral image pixel classification, cloud optical depth retrievals, and auxiliary remote sensing data. Retrieved parameters are compared with ground-based measurements from the USDA network instrumentation at two sites [Poker Flat Research Range, Alaska; 65.12 deg N, 147.43 deg W, 550 m mean sea level (MSL); and Storm Peak Laboratory, Colorado, 40.45 deg N, 106.73 deg W, 3220 m MSL]. The results are used to evaluate the effects of cloud distribution and surface albedo in determining mesoscale variability of UV exposure and photolysis rates in high-latitude and high-altitude environments.

Short spectral scan times of preferably less than 1 min in the UV region are an important prerequisite for modern spectroradiometers to reflect short-term solar irradiance radiation variations that can occur as a result of fast changes in cloud cover and/or cloud optical depth. Two different types of fast measuring spectroradiometers for solar UV irradiance are compared in a first field campaign: (1) the UV spectroradiometer on filter model basis (UV-SPRAFIMO) and (2) the modified version of the spectroradiometer SPECTRO 320D by Instrument Systems. The UV-SPRAFIMO instrument combines a filter radiometer with five narrowband (FWHM≈2.0 to 2.7 nm) filters centered at fixed wavelengths in the UV-B and UV-A regions with an advanced neural network-based model. Up to 5 measurements/s can be taken concurrently in the five wavelength channels. After averaging the measurements over preselectable time intervals, the measured irradiances are converted by the neural network model into a full spectrum from 280 to 450 nm at arbitrary wavelength steps (≥0.05 nm). The SPECTRO 320D spectroradiometer consists of a grating double monochromator with a cooled photomultiplier tube (PMT) receiver. The instrument version run by Deutscher Wetterdienst (DWD) is thermostatted and equipped with a Schreder type cosine diffuser as the entrance optics. A spectral scan from 290 to 450 nm with a selected 0.2-nm wavelength step takes less than 30 s. The two spectroradiometers are used in a field campaign at Izana (Tenerife Island) at a height of 2440 m above sea level (ASL) to compare measured spectral and integral values of solar irradiance. Results of that comparison and the instruments' characteristics are discussed. This first field comparison shows that due to the fast measurements regime, cloud effects on the measured spectra can be appreciably reduced. The campaign shows an acceptable agreement between the spectra measured by both instruments. It also reveals some issues for further improvements of the instrument design.

We present data describing various techniques that operators of Brewer spectrophotometers can use to monitor and maintain the long-term performance of their instrument. The National Ultraviolet Monitoring Center (NUVMC) at the University of Georgia (UGA) operates, under contract from the U.S. Environmental Protection Agency (EPA), 21 Brewer spectrophotometer instruments. Due to the remote location of the instruments, constant monitoring of instrument performance is required to ensure that the instruments' performance does not deteriorate, hence impacting on data collection and quality. These techniques are illustrated with data from the Brewer instruments in the UGA/EPA network.

Several ground-based ultraviolet (UV) monitoring networks exist in the United States, each of which is unique in the instrumentation employed for measurements. Two of these UV networks are the U.S. Environmental Protection Agency's (EPA's) Brewer Spectrophotometer Network and the U.S. Department of Agriculture's (USDA's) UV-B monitoring network, with a combined instrument total of 52 sites, with 32 sites located in the mainland United States. The Brewer records full sky spectra from 287 to 363 nm with 0.55-nm resolution, whereas the USDA instrument is a broadband device that measures broadband erythemally weighted UV data. To date, limited comparisons of data collected from these networks have been analyzed for comparative and quality assurance (QA) purposes. The data we use is taken from sites where instruments from each program are colocated, namely, Big Bend National Park, Texas, and Everglades National Park, Florida. To reduce the contribution of errors in the Brewer-based instruments, the raw data is corrected for stray light rejection, the angular response of the full sky diffuser, the temperature dependence of the instruments, and the temporal variation. This reduces the estimated errors of the absolute irradiance values of each Brewer spectral measurement to approximately ±5%. The estimated uncertainty of the USDA instruments is approximately ±6% with a systematic bias of (–13 to 5% depending on the total ozone) and is comprised of (1) standard lamp measurement errors, (2) spectral response determination, and (3) the angular response of the diffuser. We perform comparisons between the Brewer spectrally integrated and erythemally weighted UV irradiance measurements and the data collected by the broadband erythemal UV meters at colocated sites between 1997 through to 2002.

Recent technological advances have made measurements of UV doses and ozone column amounts with multichannel filter instruments not only possible, but also an attractive alternative to other more labor-intensive and weather-dependent methods. Filter instruments can operate unattended for long periods of time, and it is possible to obtain accurate ozone column amounts even on cloudy days. We present results from extensive comparisons of the performance of several Norwegian Institute for Air Research UV (NILU-UV) and ground-based (GUV) filter instruments against Dobson and Brewer instruments and the earth probe–total ozone mapping spectrometer (EP-TOMS) instrument. The data used in the comparisons are from four different sites where we have had the opportunity to operate more than one type of UV instrument for extended periods of time. The sites include the University of Oslo, Norway; Ny-Ålesund, Spitzbergen, Norway; the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center facilities at Wallops Island, Virginia, and Greenbelt, Maryland; and the University of Alaska, Fairbanks. Our results show that ozone column amounts obtained with current filter-type instruments have an accuracy similar to those obtained with the Dobson instrument. The mean difference between NILU-UV and Dobson direct sun measurements were 0.4±1.9% (1σ) in Oslo for the period 2000 to 2003. The difference between a GUV and the same Dobson was 1.7±1.4% for the same time period. The mean difference between GUV and TOMS in Ny-Ålesund 79 deg N and Oslo 60 deg N in the period 1996 to 1999 was <0.5±3% for days with noon solar zenith angles (SZAs)<80 deg.

Multichannel moderate-bandwidth ground-based ultraviolet (GUV) filter radiometers have recently been installed at several sites of the U.S. National Science Foundation's UV monitoring network where they complement high-resolution solar UV-100 (SUV-100) spectroradiometers. The five GUV channels are characterized for their spectral response and calibrated against SUV systems as well as irradiance standard lamps. Results indicate that accurate spectral characterization of GUV channels in the UV-B is crucial for obtaining high-quality UV measurements, in particular if instruments are calibrated with standard lamps. Using an inversion algorithm suggested by Dahlback (1996), total column ozone and approximately 30 different UV integrals and dose rates are routinely calculated from GUV measurements. For UV-A irradiance, GUV and SUV data agree to within ±5% for solar zenith angles (SZAs) up to 90 deg. A similarly good agreement can be achieved for the UV index if solar measurements are restricted to SZAs smaller than 78 deg. The agreement for data products that are dominated by wavelengths in the UV-B is generally worse, but can be substantially improved if GUV instruments are equipped with an additional channel at 313 nm. GUV total column ozone values agree on average to within ±5% with observations from the National Aeronautics and Space Administration's (NASA's) total ozone mapping spectrometer (TOMS) on board the earth probe satellite. GUV data products are disseminated via the website www.biospherical.com/NSF in near real time.

FastRT is a fast, yet accurate, UV simulation tool that computes downward surface UV doses, UV indices, and irradiances in the spectral range 290 to 400 nm with a resolution as small as 0.05 nm. It computes a full UV spectrum within a few milliseconds on a standard PC, and enables the user to convolve the spectrum with user-defined and built-in spectral response functions including the International Commission on Illumination (CIE) erythemal response function used for UV index calculations. The program accounts for the main radiative input parameters, i.e., instrumental characteristics, solar zenith angle, ozone column, aerosol loading, clouds, surface albedo, and surface altitude. FastRT is based on look-up tables of carefully selected entries of atmospheric transmittances and spherical albedos, and exploits the smoothness of these quantities with respect to atmospheric, surface, geometrical, and spectral parameters. An interactive site, http://nadir.nilu.no/~olaeng/fastrt/fastrt.html, enables the public to run the FastRT program with most input options. This page also contains updated information about FastRT and links to freely downloadable source codes and binaries.

We investigate the patterning accuracy limits of electron-beam lithography with different proximity-effect correction (PEC) methods applied to the fabrication of planar photonic crystal structures (PPCS). Energy-intensity distribution simulations reveal that conventional energy-equalization PEC techniques present a lower limit of the best attainable hole-radius variation of ≈1% for a generic PPCS, while a method proposed by Watson (midpoint-equalization PEC) should inherently account for beam broadening and theoretically can reach perfect accuracy. Simulation results are verified experimentally. Additionally, we introduce a new method to determine the beam-broadening parameter α. We compare energy-equalization PEC and midpoint-equalization PEC regarding the impact of geometrical key parameters of PPCS on achievable patterning accuracy, and show that proximity effects impose severe limitations on the patterning of structures with large fill ratios and/or small lattice constants. Furthermore, we perform a sensitivity analysis of both PEC methods on the proximity parameters and show that overestimation of the backscatter efficiency can actually improve the lithographic accuracy of the energy-equalization method and mimic the midpoint-equalization PEC method to a certain degree.

A two-grating interferometer for measurement of profiles of polished surfaces is proposed. The ±first-order beams diffracted by the first grating produce parallel fringes of about 50-µm spacing on an object surface. By using the second grating, we eliminate the parallel fringes and extract a phase distribution produced by the surface profile of the object. Moreover, the vibration of the second grating of a small size enables us to use the sinusoidal phase-modulating interferometry. Measurement resolution is higher than 0.3 µm at the equivalent wavelength of 35 µm.

Amorphous silicon germanium (a-Si_1–xGe_x) thin films are prepared by low-frequency plasma-enhanced chemical vapor deposition (LF PECVD) on glass substrates, from SiH₄+GeF₄ and SiH₄+GeH₄. These films are deposited under capacitive discharge during 60 min, at a frequency of 110 kHz, substrate temperature of 300°C, pressure of 0.6 Torr, and power of 350 W. The germanium gas mixture composition, determined by X_Ge=[GeF₄]([GeH₄])/[SiH₄]+[GeF₄]([GeH₄]), is varied from 0 to 1. These films are deposited from a (1–X_Ge)SiH₄+(X_Ge)GeF₄(GeH₄) mixture, with H₂ dilution. The refractive index n and absorption coefficient α are determined from transmission spectra. The optical energy gap is also determined. The influence of gas sources on the optical parameters is discussed.

We present the design of a tunable wavelength filter based on an active arrayed waveguide grating (AWG). We show a novel layout and simulated performance of a tandem filter configuration that covers 43 nm in C band with 0.2-nm (25-GHz) channel spacing at –35-dB crosstalk level. Design of the device is based on Fourier-Fresnel formalism with special emphasis on tuning mechanisms. The Gerchberg-Saxton phase retrieval method is used to estimate phase errors and generate phase patterns required for device tuning. A polarization insensitive filter is presented with its main parameters and simulation results. The technological considerations of achieving nanoseconds-scale tunability by exploiting the electro-optical effect in LiNbO₃ crystals are discussed in detail. Such a filter may find various applications in packet-switched coarse and dense multiwavelength dynamic networks.

The sensitivity of SONET p-i-n photodiode receivers with transimpedance amplifiers (PIN-TIA) from OC-3 to OC-48 data rates, measured by using a standard bit-error-rate tester (BERT) and a novel sweep-frequency-modulation/intermixing (SMIM) technique, are compared. A threshold intermixed voltage below 15.8 mV obtained by the SMIM method corresponding to the sensitivity of the PIN-TIA receiver beyond –32 dBm determined by BERT for the SONET OC-48 PIN-TIA receivers with a required BER of better than 10^–10 is reported. The analysis interprets that the intermixed voltage for improving the PIN-TIA receiver sensitivity from –31 to –33 dBm has to be increased from 12.5 to 20.4 mV. As compared to the BERT, the SMIM is a relatively simplified, fast, and low-cost technique for on-line mass-production diagnostics for measuring the sensitivity and evaluating the BER performances of PIN-TIA receivers.

We study the performance of a simple computer-based control system for tuning and wavelength stabilization of an erbium-doped single-mode fiber laser. Tuning is achieved by stretching a fiber grating used as one of the mirrors for the laser cavity, while wavelength is monitored through an optical spectrum analyzer. The desired wavelength of emission is fed to the computer through a graphic computer interface, and an actuator stretches the grating to tune the fiber laser. Once the specified wavelength is achieved, the control systems stabilize the fiber laser by monitoring wavelength fluctuations due to parameters such as temperature variations. Accuracy for wavelength stabilization is limited only by the resolution of the optical spectrum analyzer (0.06 nm). Being a general purpose system, any other tuning methods or wavelength tracking devices such as etalons can be used. Thus, by using the proper devices, the computer-based system could be easily adapted for the tuning and stabilization of any other rare earth-doped optical fiber laser.

To understand mechanisms underlying laser-induced damage of BK7 and fused silica, we calculate the temperature field of the substrates with CO₂ laser irradiating at a given laser power and beam radius. We find that the two glasses show different thermal behaviors. A model is developed for estimating the time t to heat the surface of the substrates up to a particular temperature T with cw CO₂ laser irradiation. We calculate theoretically the duration t that the samples are irradiated, from the beginning to visual catastrophic damage, with the assumption of damage threshold determined by the critical temperature. The duration t that the samples are irradiated, from the beginning to visual catastrophic damage, is investigated experimentally as well. Here we take the melting point or softening point as the critical temperature, given the thermomechanical coupling properties, which is enough to cause damage for BK7. Damage features are characterized by the sound of visual cracks. Finally, we calculate stresses induced by laser heating. The analysis of stress indicates that the damage of BK7 is due to the stresses induced by laser heating.

An innovative beam-shaping method for laser diode stacking is presented by employing a pair of reflective two-wedge-angle prism arrays. Each subprism with two variable wedge angles is designed for deflecting the partial emission from different bars to the dead spaces of the stack, according to the configuration of the real laser diode (LD) stack and the requirement of the system. The formula to determine the parameters of each subprism is deduced by way of geometrical analysis. A beam-shaping system for stack laser diodes with three bars is designed and simulated, and the results show that the stack laser beam is well transformed into a required distribution efficiently.

A stable and tunable fiber double-ring laser based on an erbium-doped waveguide amplifier (EDWA) is proposed and experimentally demonstrated. A widely tunable range from 1527 to 1567 nm, the side-mode suppression ratio (SMSR) of >45.6 dB/0.05 nm and the output power of >1.04 dBm in the operating range from 1535 to 1565 nm can be achieved for this ring laser. By applying the double-ring configuration, the ring laser is stabilized. The central wavelength variation of <0.02 nm and the power fluctuation of <0.03 dBm can therefore be retrieved.

A civil structure monitoring system based on fiber Bragg grating technology is presented. A complete set of new transducers, both for concrete and steel monitoring, is designed, fabricated, and successfully checked both in laboratory and in-field conditions.

We demonstrate that a multichannel fiber grating can be fabricated using a heating method based on differences in the thermal expansion of the phase mask and the fiber. The separation between two neighboring channels in a multichannel grating can be precisely tuned by means of temperature control. A three-wavelength-channel equal-spacing grating is implemented under three different temperatures of 25, 160, and 300°C, respectively. In addition, a chirp fiber grating is manufactured, whereby the temperature gradient is adjusted to obtain an increased, adjustable bandwidth, which can be used in optical filter applications.

A novel retrocommunication link utilizing reflective multiple quantum well (MQW) optical modulators and nonmechanical beam steering and tracking is demonstrated. Large aperture reflective MQW modulators using AlGaAs/GaAs are optimized and manufactured. The modulators exhibit a contrast ratio larger than 4:1 and a modulation bandwidth of 10 MHz. Nonmechanical beam steering and tracking are studied using nematic liquid crystal (NLC) spatial light modulators (SLMs). The communication link is comprised of a retromodulating array with four MQW modulators and a transceiver using a NLC SLM for beam steering and tracking. Transfer of audio, real-time image data and pseudorandom bit sequences over 100-m range while tracking the moving retromodulator is shown. The link is capable of transferring data at approximately 8 Mbps.

We analyze the turbulence affects on a quantum-key distribution (QKD) system and demonstrate them experimentally. We demonstrate a QKD scheme, in which we transform polarization states to time slots. This transformation to the time domain eliminates the need for numerous detectors or moving parts, and simplifies the system architecture by achieving a compact, lightweight, and reliable system. These attributes are broadly recognized as being important features of future mobile quantum communication applications that will be found in satellites and airplanes. We demonstrate the feasibility of our design.

We propose wavelength-division-multiplexing (WDM) networks with light splitting and wavelength conversion that can efficiently support multicast routing between nodes. Our iterative algorithm analyzes the original multicast routing network by decomposing it into multicast subgroups. These subgroups have the same wavelength, and the individual subgroup is combined to build a multicast tree. From the multicast tree, we can compute efficiently to multicast for short paths. Numerical results obtained for the ARPANET show that our algorithm can greatly reduce the optical blocking probability and the number of required wavelength conversions.

A novel measuring method, two-period interference fringes interferometry, is described. The principle of this method is different from that of the two-wavelength interferometry that is widely known. Two interference fringes, with a little difference between their spatial periods, are obtained by turning a binary step grating and produce a synthetic equivalent period much longer than either of the two periods. The interference fringes are produced by the ±first-order beams diffracted from the grating. The intensity distribution of the interference pattern is independent of the wavelength of the laser-diode light source used. The measuring range of this method is much larger than that of the two-wavelength interferometery. A sinusoidal phase modulating technique is easily applied to detect the phase distribution of interference pattern by vibrating the grating sinusoidally. The plane reflector of ~3 mm thickness is measured to verify this novel method.

A local histogram-data-orientated filtering algorithm is proposed to remove noise from the deformation phase map obtained by a phase stepping electronic speckle pattern interferometry (ESPI). The proposed filter can successfully eliminate any speckle-generated residues of a real dislocation free map. Since the filtered result is totally free from any phase inconsistency, a simple unwrapping rule, like Macy's method, can be applied for the correct phase retrieval. The motivation and theory of the proposed method is described. A simulated noisy wrapped map is employed to detail its implementation. An intercomparison of the present study and two well-known methods is performed to present the performance of the proposed method. In addition, several ESPI experiments are conducted to provide successful filtering of practical phase maps and to prove the effectiveness of the proposed method.

A new filtering scheme is investigated for the removal of speckle noise in the recorded fringe pattern by a digital speckle pattern interferometric technique (DSPI). The scheme consists of a preprocessing scheme i.e., averaging, sampling, thresholding, and again averaging, followed either by a symlet or biorthogonal wavelet filter. The preprocessing scheme improves the contrast between the dark and bright fringes, and the implementation of the biorthogonal wavelet filter, which is symmetrical and purely linear in phase, solves the problem of border effect and discontinuity. The developed scheme is implemented on recorded fringe patterns of a vibrating cantilever beam and vibrating square plate with all ends fixed. The performance and effectiveness of the proposed scheme in reducing speckle noise is evaluated and compared in terms of reduction in speckle index and the improvement of the signal-to-noise ratio (SNR) of speckle interferograms. The new scheme has the ability to improve the speckle index and SNR significantly.

We report on the experimental verification of an alternative method to the conventional least-squares fit method to obtain the phase of real interferograms. The proposed method performs an automatic polynomial fitting by solving an optimization problem, where an objective function is minimized and the solution to the irradiance equation is considered as an inverse problem. In this work, we consider fundamental concepts by comparing the performance of the least-squares fit method and the evolutionary algorithm. It is important to point out that the experimental verification of interferograms with the proposed method is applied to confirm the quality of some manufactured optical surfaces at the Instituto Nacional de Astrofísica, Optica y Electrónica.

We describe a new image fusion paradigm that provides an enhanced image from a set of source images that present regions with different spatial degradation patterns. The fusion procedure is based on the use of a new defocusing pixel-level measure. Such a measure is defined through a 1-D pseudo-Wigner distribution function (PWD) applied to nonoverlapping N-pixel window slices of the original image. The process is repeated to cover the full image size. By taking a low-resolution image as a reference image, which can be defined by blurring and averaging the two source images, a pixel-level distance measure of the defocus degree can be obtained from the PWD of each image. This procedure makes it possible to choose from a focusing point of view the in-focus pixels from each one of the given source images. The method is illustrated with different pairs of images of the same scene, which are partly focused and partly defocused in different regions. The image fusion approach that we propose here can work for any source of images available, and the comparison using evaluation measures such as mean square error or percentage of correct decisions shows that our framework can outperform the current approaches for the analyzed cases. One additional advantage of the present approach is its reduced computational cost when compared with other methods based on a full 2-D implementation of the PWD.

A new adaptive filter is presented, designed for the restoration of color images corrupted with an arbitrary noise model. The proposed filter is based on order-statistics restoration techniques and performs a linear combination of a number of difference measures to estimate the noise present in each pixel. To reduce color artifacts, the filtering is performed in a color space that decouples the intensity and color information. The choice of which color space is arbitrary; however, from experimentation it has been found that a spherical coordinate representation of the RGB pixel vectors provides the best results. As the results show, the proposed filter outperforms the current state of the art techniques for impulse, additive, and multiplicative noise types. In addition to the proposed filter, a new color performance measure is introduced based on the mean square error; however, it can be calculated using any error measure that employs differences between two input signals.

Perceptual problems of viewing topography on geoimages are caused by illumination from the southeast during data collection. This problem affects the majority of satellite images. The aim of this work is to obtain a stereoscopic effect of shaded relief in such images. Techniques available in commercial digital processing programs are used in the absence of a digital elevation model. The images used are taken by the Landsat TM and SPOT P satellites; the software used was the EASI-PACE and ACE programs (Canadian PCI Geomatics Group). The pseudoscopic effect is solved by using the first principal component obtained in a principle components analysis of the three channels, resulting from the weighted merging of the Landsat and SPOT data. The map obtained provides the observer a view with shaded relief.

Skin color can be an important feature when tracking skin-colored objects. Particularly this is the case for computer-vision-based human-computer interfaces (HCI). Humans have a highly developed feeling of space and, therefore, it is reasonable to support this within intelligent HCI, where the importance of augmented reality can be foreseen. Joining human-like interaction techniques within multimodal HCI could, or will, gain a feature for modern mobile telecommunication devices. On the other hand, real-time processing plays an important role in achieving more natural and physically intuitive ways of human-machine interaction. The main scope of this work is the development of a stereoscopic computer-vision hardware-accelerated framework for real-time skin feature identification in the sense of a single-pass image segmentation process. The hardware-accelerated preprocessing stage is presented with the purpose of color and spatial filtering, where the skin color model within the hue-saturation-value (HSV) color space is given with a polyhedron of threshold values representing the basis of the filter model. An adaptive filter management unit is suggested to achieve better segmentation results. This enables the adoption of filter parameters to the current scene conditions in an adaptive way. Implementation of the suggested hardware structure is given at the level of filed programmable system level integrated circuit (FPSLIC) devices using an embedded microcontroller as their main feature. A stereoscopic clue is achieved using a time-sequential video stream, but this shows no difference for real-time processing requirements in terms of hardware complexity. The experimental results for the hardware-accelerated preprocessing stage are given by efficiency estimation of the presented hardware structure using a simple motion-detection algorithm based on a binary function.

A hybrid edge detection method, using a combination of gradients and zero crossings to accurately locate the edges in an image, is proposed. By convolving the image with the gradient and second-order derivative operators deduced from a cubic facet model, computer experiments are carried out for extracting edge information from real images. Sharp image edges are obtained from a variety of sample images, without need of computation of the cubic facet coefficients. Under noisy conditions, impact of noise on the detected edge map represents isolated points or small clusters, which can be easily reduced by a postcleaning process. The hybrid edge detection technique, combined with a postprocessing method, results in comparable or better noise reduction than Canny. Compared with the Canny approach, the proposed algorithm has higher efficiency while providing a larger figure of merit.

As a lightwave having a Gaussian intensity profile passes through a tilted Fabry-Perot filter, the profile is distorted severely depending on the conditions of the parameters. This distortion has not been studied and reported in depth, though the propagation of a Gaussian wave itself has been discussed well in the literature. We show our results of quantitative calculation and discuss it, which we believe will help significantly design waveguides containing gratings or filters.

We propose an algorithm for reconstructing nonuniformly sampled interferograms when sampling locations are unknown. An optimization problem with multiple objective and constraint functions is designed based on the spatial and spectral characteristics of the data measurement. This problem is solved using an evolutionary approach, in which potential solutions are competing to be the fittest individual in a simulated natural environment.

The cerium target plasma flash x-ray generator is useful to perform high-speed enhanced K-edge angiography using cone beams, because K-series characteristic x-rays from the cerium target are absorbed effectively by iodine-based contrast mediums. In the plasma generator, a 200-nF condenser is charged up to 60 kV by a power supply, and flash x-rays are produced by the discharging. The x-ray tube is a demountable triode with a trigger electrode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Target evaporation leads to the formation of weakly ionized linear plasma, consisting of cerium ions and electrons, around the target, and intense flash x-rays are produced. At a charging voltage of 55 kV, the maximum tube voltage is almost equal to the charging voltage of the main condenser, and the maximum current is approximately 20 kA. When the charging voltage is increased, weakly ionized cerium plasma forms, and the K-series characteristic x-ray intensities increase. The x-ray pulse widths are about 500 ns, and the time-integrated x-ray intensity has a value of about 40 µC/kg at 1.0 m from the x-ray source with a charging voltage of 55 kV. In the angiography, we employ a filmless computed radiography (CR) system and iodine-based microspheres.

In the plasma flash x-ray generator, a 200-nF condenser is charged up to 50 kV by a power supply, and flash x-rays are produced by the discharging. The x-ray tube is a demountable triode with a trigger electrode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Target evaporation leads to the formation of weakly ionized linear plasma, consisting of copper ions and electrons, around the fine target, and intense Kα rays are produced using a 10-µm-thick nickel filter. At a charging voltage of 50 kV, the maximum tube voltage is almost equal to the charging voltage of the main condenser, and the peak current is about 15 kA. When the charging voltage is increased, the linear plasma forms, and the copper Kα intensities substantially increase. The Kα lines are quite clean and intense, and hardly any bremsstrahlung rays are detected at all. The x-ray pulse widths are approximately 700 ns, and the time-integrated x-ray intensity has a value of approximately 20 µC/kg at 1.0 m from the x-ray source with a charging voltage of 50 kV.