I usually start editorials by joking around or using the "hook" as taught to me by a well-known newspaper writer in Washington, DC. However, I want to set a tone for this editorial that is serious, as my request to many of you is just that, serious and important. I want to discuss with you a matter regarding the future of Optical Engineering.

Since the time of Newton and Hershel, humans have understood that light can communicate beyond what can only be seen, and over the next 300 years, remote sensing of spectroradiometric information has been perfected by astronomers. In the last 50 years, those methods and techniques have been turned nadir, to better understand the inner space of earth. Compared to astronomy, hyperspectral remote sensing for earth science is in its infancy, but the rate at which it has accelerated our knowledge of forestry, agriculture, bathymetry, and geology, to name a few, will continue to grow exponentially as the challenges facing mankind require more optimal uses of natural resources.

The snapshot advantage is a large increase in light collection efficiency available to high-dimensional measurement systems that avoid filtering and scanning. After discussing this advantage in the context of imaging spectrometry, where the greatest effort towards developing snapshot systems has been made, we describe the types of measurements where it is applicable. We then generalize it to the larger context of high-dimensional measurements, where the advantage increases geometrically with measurement dimensionality.

Analysis of coastal marine algae communities enables us to adequately estimate the state of coastal marine environments and provides evidence for environmental changes. Hyperspectral remote sensing provides a tool for mapping macroalgal habitats if the algal communities are spectrally resolvable. We compared the performance of three classification approaches to determine the distribution of macroalgae communities in the rocky intertidal zone of Heligoland, Germany, using airborne hyperspectral (AISAeagle) data. The classification results of two supervised approaches (maximum likelihood classifier and spectral angle mapping) are compared with an approach combining k-Means classification of derivative measures. We identified regions of different slopes between main pigment absorption features of macroalgae and classified the resulting slope bands. The maximum likelihood classifier gained the best results (Cohan's kappa = 0.81), but the new approach turned out as a time-effective possibility to identify the dominating macroalgae species with sufficient accuracy (Cohan's kappa = 0.77), even in the heterogeneous and patchy coverage of the study area.

Original spectral features contain information pertinent to certain target spectral features. Without an efficient spectral feature extraction method, the target detection performance might be degraded. We present spectral feature extraction techniques based on the Fourier domain for use in target detection. These feature extraction methods are the Fourier magnitude (FM), Fourier phase (FP), and Fourier coefficient selection (FCS) methods. In our target detection experiments, we compared the proposed methods to the principle component analysis (PCA) and independent component analysis (ICA) methods and the original spectral features. The experiment results show that the FCS target detection accuracy is 95.75%, whereas the accuracies of the FM, FP, PCA, ICA methods, and the original spectral features are 86.76%, 36.28%, 84.51%, 74.49%, and 78.92%, respectively. The average feature extraction times of the proposed methods are 223% faster than that found for the PCA and 304% faster than the ICA methods.

We propose a novel method to estimate the first- and second-order statistics of the residual misregistration noise (RMR), which severely affects the performance of anomalous change detection techniques. Depending on the specific distribution of the RMR, the estimates allow for precisely defining the size of the uncertainty window, which is crucial when dealing with misregistration noise, as in the local coregistration adjustment approach. The technique is based on a sequential strategy that exploits the well-known scale-invariant feature transform (SIFT) algorithm cascaded with the minimum covariance determinant algorithm. The SIFT procedure was originally developed to work on gray-level images. The proposed method adapts the SIFT procedure to hyperspectral images so as to exploit the complementary information content of the numerous spectral channels, further improving the robustness of the outliers filtering by means of a highly robust estimator of multivariate location. The approach has been tested on different real hyperspectral datasets with very high spatial resolution. The analysis highlighted the effectiveness of the proposed strategy, providing reliable and very accurate estimation of the RMR statistics.

The Aerospace Leap-frog Imaging Stationary interferometer for Earth Observation (ALISEO) is a hyperspectral imaging interferometer for Earth remote sensing. The instrument belongs to the class of Sagnac stationary interferometers and acquires the image of the target superimposed to the pattern of autocorrelation functions of the electromagnetic field coming from each pixel. The ALISEO sensor together with the data processing algorithms that retrieve the at-sensor spectral radiance are discussed. A model describing the instrument OPD and interferogram center is also discussed, improving the procedures for phase retrieval and spectral estimation. Images acquired by ALISEO are shown, and examples of retrieved reflectance spectra are presented.

Remotely sensed spectral imagery of the earth's surface can be used to fullest advantage when the influence of the atmosphere has been removed and the measurements are reduced to units of reflectance. Here, we provide a comprehensive summary of the latest version of the Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes atmospheric correction algorithm. We also report some new code improvements for speed and accuracy. These include the re-working of the original algorithm in C-language code parallelized with message passing interface and containing a new radiative transfer look-up table option, which replaces executions of the MODTRAN® model. With computation times now as low as ~10  s per image per computer processor, automated, real-time, on-board atmospheric correction of hyper- and multi-spectral imagery is within reach.

An anaerobic digestion process, finalized to biogas production, is characterized by different steps involving the variation of some chemical and physical parameters related to the presence of specific biomasses as: pH, chemical oxygen demand (COD), volatile solids, nitrate (NO₃−) and phosphate (PO₃−). A correct process characterization requires a periodical sampling of the organic mixture in the reactor and a further analysis of the samples by traditional chemical-physical methods. Such an approach is discontinuous, time-consuming and expensive. A new analytical approach based on hyperspectral imaging in the NIR field (1000 to 1700 nm) is investigated and critically evaluated, with reference to the monitoring of wine waste anaerobic digestion process. The application of the proposed technique was addressed to identify and demonstrate the correlation existing, in terms of quality and reliability of the results, between "classical" chemical-physical parameters and spectral features of the digestate samples. Good results were obtained, ranging from a R² = 0.68 and a RMSECV = 12.83  mg/l for nitrate to a R² = 0.90 and a RMSECV = 5495.16  mg O₂/l for COD. The proposed approach seems very useful in setting up innovative control strategies allowing for full, continuous control of the anaerobic digestion process.

Hyperspectral imagery has been widely used in terrain classification for its high resolution. Urban vegetation, known as an essential part of the urban ecosystem, can be difficult to discern due to high similarity of spectral signatures among some land-cover classes. In this paper, we investigate a hybrid approach of the genetic-algorithm tuned fuzzy support vector machine (GA-FSVM) technique and apply it to urban vegetation classification from aerial hyperspectral urban imagery. The approach adopts the genetic algorithm to optimize parameters of support vector machine, and employs the K-nearest neighbor algorithm to calculate the membership function for each fuzzy parameter, aiming to reduce the effects of the isolated and noisy samples. Test data come from push-broom hyperspectral imager (PHI) hyperspectral remote sensing image which partially covers a corner of the Shanghai World Exposition Park, while PHI is a hyper-spectral sensor developed by Shanghai Institute of Technical Physics. Experimental results show the GA-FSVM model generates overall accuracy of 71.2%, outperforming the maximum likelihood classifier with 49.4% accuracy and the artificial neural network method with 60.8% accuracy. It indicates GA-FSVM is a promising model for vegetation classification from hyperspectral urban data, and has good advantage in the application of classification involving abundant mixed pixels and small samples problem.

An imaging spectrometer was used to acquire hyperspectral images of 120 strains of wheat ears and seeds under four different watering treatments. Whether wheat preharvest sprouting occurred could be reflected by spectral characteristics. Therefore, it was possible to judge whether wheat ears sprouted according to changes of spectral curve at 675 nm. According to principal component analysis of mean spectral reflectivity values of wheat seeds, it was found that wheat seeds watered three times every day and wheat seeds watered once every day were significantly different from nonsprouting wheat seeds soaked all day and original dry seeds due to significant sprouting situations, suggesting that imaging spectra can differentiate different extent of wheat preharvest sprouting. Glume had an influence on the hyperspectral images of wheat ears, therefore the hyperspectral images of wheat ears could be used to measure sprouting only when serious sprouting occurred. At an early stage of sprouting, only the hyperspectral images of wheat seeds could be used to analyze the sprouting of wheat.

Image mapping spectrometry (IMS) is a hyperspectral imaging technique that simultaneously captures spatial and spectral information about an object in real-time. We present a new calibration procedure for the IMS as well as the first detailed evaluation of system performance. We correlate optical components and device calibration to performance metrics such as light throughput, scattered light, distortion, spectral image coregistration, and spatial/spectral resolution. Spectral sensitivity and motion artifacts are also evaluated with a dynamic biological experiment. The presented methodology of evaluation is useful in assessment of a variety of hyperspectral and multi-spectral modalities. Results are important to any potential users/developers of an IMS instrument and to anyone who may wish to compare the IMS to other imaging spectrometers.

A new algorithm is described for estimating the noise model parameters in hyperspectral data when neither noise components variance nor noise spatial/spectral correlation priors are available. A maximum likelihood (ML) technique is introduced for checking the noise spatial correlation hypothesis and estimating the spatial correlation function width alongside with estimating signal-independent and signal-dependent noise components variance. The hyperspectral image is assumed to match a limited set of assumptions. A three-dimensional (3-D) fractional Brownian motion (fBm) model is introduced for describing locally the texture of the 3-D image noisy textural fragment. Nonstationarity of the useful image signal is taken into account by performing the estimation locally on a 3-D block-by-block basis. The accuracy of the proposed algorithm is first illustrated for synthetic images obtained from either pure fBm or almost noise-free AVIRIS hyperspectral images artificially degraded with spatially correlated noise. The results obtained for synthetic images demonstrate appropriate accuracy and robustness of the proposed method. Then results obtained for real life AVIRIS hyperspectral data sets confirm the noise spatial uncorrelation hypothesis for images acquired by the AVIRIS sensor. Conclusions and open problems are outlined.

Hyperspectral imaging provides us with high-dimensional, scene-independent color information but faces problems such as long image acquisition time and severe lighting and focusing conditions. To achieve efficient spectral imaging, this study presents an extended method of Bayesian image superresolution. The proposed method increases both the spatial and the wavelength resolution of input images and enables the processing of hyperspectral images to a higher resolution from easily acquired low-spatial-resolution multispectral images. In an experiment using acquired multispectral images of a Japanese traditional painting, visible and near-infrared hyperspectral images were produced, and the obvious effect of superresolution was validated.

A formulation for min-max clairvoyant fusion (also known as continuum fusion) is developed that exploits the invariance of hypothesis testing statistics to monotonic transformations. In addition to generalizing an earlier formulation based on manipulated thresholds, the new formulation leads to efficient algorithms for two of the most widely advocated fusion "flavors:" one based on combining detectors with the same false alarm rate, and another based on constant detection rate. These algorithms are used to investigate and compare the performance of different detectors for a class of problems that arises from detecting small or weak targets in hyperspectral imagery. The experiments are performed on simulated data from well-defined distributions so as to isolate the effect of different flavors of fusion from the effects of model mismatch.

Band clustering and selection are applied to dimensionality reduction of hyperspectral imagery. The proposed method is based on a hierarchical clustering structure, which aims to group bands using an information or similarity measure. Specifically, the distance based on orthogonal projection divergence is used as a criterion for clustering. After clustering, a band selection step is applied to select representative band to be used in the following data analysis. Different from unsupervised clustering using all the pixels or supervised clustering requiring labeled pixels, the proposed semi-supervised band clustering and selection needs class spectral signatures only. The experimental results show that the proposed algorithm can significantly outperform other existing methods with regard to pixel-based classification task.

Imaging static Fourier transform spectrometers are well-adapted instruments for remote sensing. However, the path from the raw images to the spectral images is quite long, thus multiplying the potential noise sources. In this article, we propose to review these perturbation sources. We first recall how detector or photon noise on the interferogram affects the estimated spectrum. Then, we focus on inhomogeneities of the focal plane array. Although these inhomogeneities are deterministic, they generate noise when they are ill-corrected. Finally, we describe defects due to errors that may occur during the image processing step. We also give some avenues to limit the impact of these noises.

Remote gas detection and visualization provides vital information in scenarios involving gas leaks, environmental monitoring, chemical accidents or attacks. Imaging systems based on Fourier transform spectrometers with single detector elements have been applied for several years by emergency response forces for gas identification and quantification. In this work a hyperspectral imager employing a Michelson interferometer and an infrared focal plane array detector is characterized. The system provides spatially resolved spectral information about the measurement scene. The performance of the system is evaluated by laboratory measurements. Results of gas detection in the field are presented and discussed. The gas detection algorithm is based on a physical model for the measured radiance. In this model the atmosphere is divided into multiple homogenous layers of constant temperature. The signatures of the gases present in these layers are then compensated in the measured spectrum. No information about the signature of the background is required. Moreover an algorithm that combines spectral and spatial information is presented. This algorithm enhances the signal to noise ratio of the spectra and thus improves the detection limits. Using these algorithms it is possible to identify, visualize, and track gas clouds in real time.

The continuum fusion (CF) methodology produces new classes of multivariate detection algorithms, some of which have been used in spectral applications. CF principles apply to model-based problems in which not all parameter values are known, a common circumstance in hyperspectral operations. We reviewed the principal theoretical and applied CF results devised to date, summarized recent experimental results, and discussed in detail an important class of algorithms that illustrate the design freedom CF affords. Finally, we reviewed the fundamental CF principles as applied to a new category of model parameters only recently considered, involving a distinction in the form of a constraint that is not recognized by older methods.

The quick atmospheric correction (QUAC) code performs atmospheric correction on multi- and hyperspectral imagery spanning all or part of the visible and near infrared-short wave infrared spectral range, ∼ 400−2500  nm. It utilizes an in-scene approach, requiring only approximate specification of sensor band locations (i.e., central wavelengths) and their radiometric calibration; no additional metadata is required. Because QUAC does not involve first principles radiative-transfer calculations, it is significantly faster than physics-based methods; however, it is also more approximate. We present a detailed description of the QUAC algorithm, highlighting recent accuracy improvements. Example results for several multi-and hyperspectral data sets are presented, and comparisons are made to more rigorous correction approaches.

A new approach for the design and fabrication of a miniaturized hyperspectral imager is described. A unique and compact instrument has been developed by taking advantage of light propagation within bonded solid blocks of optically transmitting glass. The resulting series of micro-hyperspectral imaging (microHSI™) spectrometer has been developed, patented, and built as a visible near-infrared (VNIR) hyperspectral sensor capable of operating in the 400- to 1000-nm wavelength range. The spectrometer employs a blazed, convex diffraction grating in Offner configuration embedded within the optical blocks for ruggedized operation. This, in combination with fast spectrometer operation at f/2.0 , results in high optical throughput. The resulting microHSI™VNIR spectrometer weighs 0.54 kg, including foreoptics and camera, which results in a 2× decrease in spectrometer volume compared with current air-spaced Offner spectrometers. These instruments can accommodate custom, ruggedized foreoptics to adapt to a wide range of field-of-view requirements. These fast, telecentric foreoptics are chromatically corrected for wideband spectral applications. Results of field and laboratory testing of the microHSI™ spectrometers are presented and show that the sensor consistently meets technical performance predictions.

A software tool for end-to-end simulation of data products of spaceborne and airborne visible, near-infrared and short-wave infrared imaging spectrometers, starting from either synthetic or airborne hyperspectral data, has been developed and tested. Such a simulator is conceived as a preliminary aid tool (during phase 0/A ) for the specification and early development of new Earth observation optical instruments, whose compliance to user's requirements is achieved through a process of cost/performance trade-off. The proposed simulator is based on three different core modules: the reflectance scenario simulator, the atmospheric simulator, and the instrument simulator.The main novelty of this paper is that the modeling adopted for the simulator is validated and assessed through the matching of synthetized spectra, both radiance and reflectance, to true spectra measured on an agricultural clay bare soil by means of a hand-held point spectrometer and an airborne instrument developed and manufactured by Selex Galileo S.p.A. Both pure and mixed spectra show a high degree of matching between true and synthetic data, thereby establishing the validity of the underlying linear spectral mixing model. Furthermore, a validation of an application test has been performed for clay soil mapping at ground and airborne level. Eventually,a satellite instrument simulation of the same clay map has demonstrated a more than acceptable agreement notwithstanding the low spatial resolution.

The multitarget compounding technique is key in an infrared hardware-in-the-loop simulation system. In this study, the beam-broadening theory and carefully designed experiments are presented to analyze a multitarget compounding system based on a dimpled mirror. By paraxial approximation of geometrical optics, the expression of broadened beamwidth of a dimpled-mirror two-mirror three-reflection concentric system was obtained as the function of system parameters. A multitarget compounding setup was designed and experiments were performed. Excellent matching results were achieved between the beamwidth theory and the experiments. Experimental results demonstrated that the beam-broadening theory is creditable and suitable to design the multitarget compounding system. The theory and experiments are beneficial to the future development and implementation of multitarget compounding technique.

A direct linear transformation (DLT) model is derived to describe the scan imagery of a line scan camera undergoing a uniform rectilinear motion. When more than five points on scan image and their corresponding three-dimensional space points are substituted in the DLT model, 11 coefficients are settled directly and linearly without any approximations. After that, the 11 physically meaningful line scan camera parameters are worked out from the 11 DLT coefficients through a group of analytical operations. The performance is tested and verified by both simulated experiment and demonstration of a real line scan camera.

In a computed radiography (CR) system, there are a number of different mechanisms that cause blurring. The aim of this study was to analyze intrinsic system factors of CR systems that could affect the modulation transfer function (MTF), such as afterglow during readout and the anti-alias filter before analog to digital converter. Methods and Materials: Mathematical slit and edge images were generated from analytical functions. These images were arranged perpendicularly to the laser scan and the plate scan directions, respectively. The influence of afterglow and the anti-alias filter was simulated by using Microsoft Excel. The MTF values calculated from those simulation images were compared with the theoretical MTF values obtained analytically. Results: MTF values in the laser scan direction measured with the slit and edge methods were significantly lower than MTF values in the plate scan direction. The degree of influence on MTF with respect to afterglow and the anti-alias filters was different depending on the measurement method and the scan directions of CR systems. The influence of the anti-alias filters mainly contributed to the differences between MTF values with the slit and edge methods in the laser scan direction.

An enhanced surface tracking system based on optical coherence tomography (OCT) modality has been developed and tested for use in a surgical guidance system. A surface detection algorithm based on a Savitzky-Golay filter of A-scan data and thresholding was applied to real-time depth tracking. The algorithm output controlled a motorized stage to adjust the probe position according to the sample's topological variance in real-time. As a result, the root mean square error (RMSE: 4.2 μm) of our algorithm was relatively lower than the conventional method (RMSE: 16.6 μm). Also, OCT images obtained using the algorithm showed a significantly extended imaging range and active surface tracking in real time. Consequently, the devised method demonstrated potential for use in systems for guiding surgical robots and endoscopic OCT.

An analysis of a novel unit destined for measuring roughness of smooth and isotropic surfaces as well optimization of its parameters has been presented. The unit is functioning on the measurement of the total integrated scatter parameter using a flat photodiode integrator rather than a conventional optical sphere or hemisphere. By that means, one can obtain much less expensive and smaller instruments than the traditional ones. Unfortunately, a decrease of the integrator dimensions could reduce its spatial frequency bandwidth causing measurement errors. Therefore, an analysis of this factor utilizing the results of the Rayleigh-Rice vector perturbation theory has been performed. For the case when smooth surfaces are investigated, the lower limit of the angle range is particularly critical and should be diminished as much as possible. This is in contradiction with the demand of a broader upper limit to have a greater roughness measuring range. Therefore, a way of optimization of unit parameters has also been described. Results of experiments concerning the validity of assumptions confirmed in the analysis as well as results of roughness measurements obtained using a tentative measuring unit are also given.

A recent study found that it is very difficult to use the squared binary defocusing technique to eliminate the influence of third-order harmonics without compromising fringe quality, and thus it is challenging to utilize Fourier transform profilometry to achieve high-quality three-dimensional measurement. A novel approach is presented to effectively eliminate the third-order harmonics by modulating the squared binary structured patterns. Both simulation and experiments are presented to verify the performance of the proposed technique.

The application of dual-grating moiré fringe is introduced in lithography alignment. Minute angular displacement between the two alignment marks will lead to the tilt of moiré fringe, which has an influence in high-accuracy alignment. Proposed is a novel measurement method of angular displacement based on the phase of moiré fringe. The relationship between phase of moiré fringe and angular displacement is analyzed. Both simulation and experiment indicate that an angular displacement can be determined to achieve a linear displacement measurement with error of nanometer level.

A method for effective focal length measurement using imaging conjugates is discussed and demonstrated. This method is used to determine the effective focal length of an objective lens with precision and without the need to know the exact position of the principal planes by measuring relative distances of imaging conjugates. Focal length determination was done with the aid of an interferometer and with a precision of ±0.054%. A discussion of the method is presented and an error analysis discussed. This method can be used for characterizing optical systems with a wide range of focal lengths because of its simple experimental configuration.

Surface defects that affect the quality of metals are an important factor. Machine vision systems commonly perform surface inspection, and feature extraction of defects is essential. The rapidity and universality of the algorithm are two crucial issues in actual application. A new method of feature extraction based on contourlet transform and kernel locality preserving projections is proposed to extract sufficient and effective features from metal surface images. Image information at certain direction is important to recognition of defects, and contourlet transform is introduced for its flexible direction setting. Images of metal surfaces are decomposed into multiple directional subbands with contourlet transform. Then features of all subbands are extracted and combined into a high-dimensional feature vector, which is reduced to a low-dimensional feature vector by kernel locality preserving projections. The method is tested with a Brodatz database and two surface defect databases from industrial surface-inspection systems of continuous casting slabs and aluminum strips. Experimental results show that the proposed method performs better than the other three methods in accuracy and efficiency. The total classification rates of surface defects of continuous casting slabs and aluminum strips are up to 93.55% and 92.5%, respectively.

A two-dimensional circular photonic crystal ring resonator (PCRR)-based add-drop filter (ADF) is designed for ITU-T G.694.2 eight-channel coarse wavelength division multiplexing systems. The resonant wavelength and pass-band width of the ADF are 1491 and 13 nm, respectively. Close to 100% of coupling and dropping efficiencies and a 114.69 quality factor are observed through simulation. Then the coupled mode theory (CMT) analysis of circular PCRR-based ADF is attempted to compare obtained CMT response into simulated finite difference time domain method response. The overall size of the device is much smaller; that is, 11.4×11.4 μm, which is highly suitable for photonic integrated circuits and all optical photonic network applications.

We propose a liquid prism based on electrowetting for wide-angle beam tracking and steering. Two transparent cubic cells which are filled with two immiscible liquids are stacked together to form the device. The two cubic cells function as two optical prisms. Via eletrowetting, we successfully control the liquid–liquid interface by changing the applied voltage on the opposite sidewalls. The device is capable of wide-angle beam tracking and steering. The experiment shows that the device can deflect and steer the light through an angle of ∼19.9  deg (+10.4  deg to −9.5  deg), and the total response time is ∼202  ms. The proposed liquid prism has a potential application such as free-space optical communications and laser detection electrowetting solar cells.

Measurements of birefringence induced in K₉ and fused silica specimens by cracks produced by 1064 nm Nd : YAG laser have been presented. The Birefringence data is converted into the units of stress, thus permitting the estimation of residual stress near crack. The intensity of residual stress in K₉ glass is larger than that in fused silica under the same condition. The similarity of residual stress distribution along the y-axis reveals that the nature of shock wave transmission in optical materials under 1064 nm laser irradiation is the same with each other. The value of residual stress can be influenced by laser parameters and characterization of optical material. Simulation based on a theoretical model giving the residual stress field around a crack is developed for comparison with experiment results. The probability of initial damage and the direction of the energy dissipation in cracks determine the residual stress distribution. The thermal stress coupling enlarges the asymmetry of residual stress distribution. Residual stress in optical material has a strong effect on fracture and should be taken into account in any formulation that involves the enhanced damage resistance of optical components used in laser induced damage experiments.

A switchable mode-locking fiber laser is proposed by means of fiber Bragg grating (FBG). The FBG plays two key roles, the switchable wavelength operation and the spectral filtering effect, on the proposed laser. The switchable single-wavelength mode-locking operation, lasing at either 1545.25 or 1548.34 nm, corresponding to the central wavelengths of the FBGs, is obtained by appropriately rotating the polarization controllers (PC). In addition, the dual-wavelength mode-locking operation is observed with proper PC state. The switchable mode-locking operation attributes to the wavelength-dependent loss mechanism and the spectral filter formed by PCs and FBGs.

This paper presents a purification process of hydrogen bromide (HBr) gas by fractional distillation technique and its use for performance enhancement of copper-HBr laser (Cu-HBrL). The residual impurities in HBr were suppressed by a two-step distillation process at temperatures of - 196°C and - 20°C. The lowering of the impurities was confirmed by comparing the mass spectrograph of the HBr gas before and after distillation, using a quadrupole mass spectrometer. The effect of the purified HBr gas on the performance of Cu-HBrL average output power as well its electrical discharge characteristics were studied. More than 37% improvement in the laser average output power (40 to 55 W) was observed with the use of this distilled HBr gas compared to undistilled gas. The underlying mechanism of the enhancement was analyzed by comparing electrical discharge characteristics in the two cases. The improvement in Cu-HBrL performance with distilled HBr gas was attributed to lowering of bromine and hydrogen concentration, mainly manifested as increased average electrical energy coupling to the discharge. This resulted in increased laser gain as well as gain volume, which were reflected in increases in laser output power and beam diameter.

A system composed of laser sensor and 6-DOF industrial robot is proposed to obtain complete three-dimensional (3-D) information of the object surface. Suitable for the different combining ways of laser sensor and robot, a new method to calibrate the position and pose between sensor and robot is presented. By using a standard sphere with known radius as a reference tool, the rotation and translation matrices between the laser sensor and robot are computed, respectively in two steps, so that many unstable factors introduced in conventional optimization methods can be avoided. The experimental results show that the accuracy of the proposed calibration method can be achieved up to 0.062 mm. The calibration method is also implemented into the automated robot scanning system to reconstruct a car door panel.

The fabrication of optoelectronic devices such as light-emitting diodes (LEDs) typically involves photolithography steps, requiring specific lithography masks. This approach is expensive, inflexible and time consuming, in particular for prototyping. Therefore it would be attractive to replace these steps by direct writing techniques such as laser processing, which would speed up, for example the development and prototyping of new devices. Picosecond lasers provide a universal tool for material processing. Due to the short pulse length, material is removed by a process called "cold ablation," with minimal thermal damage to neighboring regions. As a result, better-defined structures with smoother and cleaner side walls can be fabricated compared to nanosecond-pulsed laser-based processing. We report on fully laser-processed planar gallium nitride-based LEDs fabricated using only ps laser processing for pattern definition and material removal. On the bare semiconductor wafer, isolation trenches and mesa structures are formed directly by ultraviolet ps laser pulse writing. For the direct deposition of patterned ohmic contact metallizations, the ps laser fabrication and subsequent use of high-resolution shadow masks is presented. Finally, the ps laser-processed LEDs are electrically and optically characterized and their characteristics compared with those of conventionally fabricated mesa LEDs.

Unidirectional light transmission through composite structures, consisting of a square lattice of square metals with different sizes, is studied by the finite-difference time-domain method. Through adding two metallic slices into the lateral boundaries of the composite structures, the lateral light energy leak is avoided and unidirectional light propagations towards two opposite directions are obtained within two separate frequency regions based on the directional band gaps. Through the design of arranging metallic rods at the interface of two photonic crystals, the unidirectional light propagation, based on the different refractive and reflective behaviors at the frequencies within the pass bands, is also obtained.

A polymer electro-optic (EO) waveguide beam-steering device with deoxyribonucleic acid (DNA) biopolymer conductive cladding layers and a core layer of the commercially available EO polymer SEO100 is demonstrated with 100% relative poling efficiency. This demonstration device exhibits a deflection efficiency of 99  mrad/kV with a corresponding in-device EO coefficient r33 of 124  pm/V at 1550 nm. When the DNA biopolymer bottom cladding layer is replaced by the commonly used cladding polymer UV15, the deflection efficiency and in-device r33 drop to 34  mrad/kV and 43  pm/V, respectively.

Novel index-guiding photonic crystal fibers (PCF) with rings of cladding holes (circularly or elliptically shaped) arranged in the Fibonacci series are proposed. The dispersion, confinement losses, and generated birefringence in PCFs are evaluated for light signal at 1.55-µm wavelength, by employing alterations in various design parameters. Full-vector analysis using anisotropic perfectly matched layers is performed to validate the accuracy of the modeled PCFs in a finite-difference time-domain environment. For such PCF modeling, the lower value of dispersion is found to be 7.311  ps nm⁻¹ km⁻¹, and the zero-dispersion wavelength is shifted to lower infrared region in accordance with variation in the hole diameter-to-pitch ratio.

An incoherent microwave photonic filter (MPF), based on multiwavelength phase modulation (PM) and a WaveShaper, is proposed and investigated. The multiwavelength erbium-doped fiber laser provides multiple taps, while the WaveShaper and a dispersive device perform PM to amplitude modulation (AM) conversion. The WaveShaper can also induce both spectral shaping effect for the taps and a different phase for radio-frequency signal during the PM-to-AM conversion. Principle analysis of MPF based on PM-to-AM conversion is discussed. Simulation is carried out to investigate the influence of WaveShaper parameters on the frequency response of the MPF. Through adjustment of the WaveShaper, MPFs with positive, negative, or complex coefficients are also obtained in the experiment. Experimental observations agree well with the simulation results and discussions are given.

Star L quadrature amplitude modulation (SLQAM, L representing the number of constellation points) modulated orthogonal frequency division multiplexing (OFDM) is applied to the optical domain for the first time. Numerical simulations are conducted between an S16QAM and a square 16QAM modulated optical OFDM system to compare the tolerance toward various transmission penalties in a 30.2-Gbit/s coherent optical OFDM (CO-OFDM) system over 640, 720, and 800 km. After 640-km transmission, the optimal launch power and corresponding Q² factor of an S16QAM modulated optical OFDM signal are 2 and 0.6 dB higher, respectively, than the square 16QAM modulated OFDM signal in a 30.2-Gbit/s single-channel single-polarization CO-OFDM system, while in a 5×30.2-Gbit/s wavelength-division multiplexing single-polarization CO-OFDM system, the optimal launch power and corresponding Q² factor of an S16QAM modulated optical OFDM signal are 1 and 0.7 dB higher than with a square 16QAM modulated OFDM signal, showing increased tolerance toward nonlinearity such as SPM and XPM.

A novel realization method of the optical virtual private networks (OVPN) over multiprotocol label switching/optical packet switching (MPLS/OPS) networks is proposed. In this scheme, the introduction of MPLS control plane makes OVPN over OPS networks more reliable and easier; OVPN makes use of the concept of high reconfiguration of light-paths offered by MPLS, to set up secure tunnels of high bandwidth across intelligent OPS networks. Through resource management, the signal mechanism, connection control, and the architecture of the creation and maintenance of OVPN are efficiently realized. We also present an OVPN architecture with two traffic priorities, which is used to analyze the capacity, throughput, delay time of the proposed networks, and the packet loss rate performance of the OVPN over MPLS/OPS networks based on full mesh topology. The results validate the applicability of such reliable connectivity to high quality services in the OVPN over MPLS/OPS networks. Along with the results, the feasibility of the approach as the basis for the next generation networks is demonstrated and discussed.

The development of a 4-channel×10-Gbits/s optical interconnect module based on a silicon optical bench (SiOB) is presented. The 4-channel vertical-cavity surface-emitting laser (VCSEL) and photo diode (PD) arrays are flip-chip assembled onto the pedestals of SiOB using Au/Sn solder bumps to form an SiOB-based bi-directional optical sub-assembly (BOSA) configuration. The optical coupling of VCSEL-to-multi-mode fiber (MMF) and MMF-to-PD without adding coupled optics is -5.2 and -2 dB, respectively. The wide alignment tolerances of 1-dB power variation for the transmitting and receiver parts to be ±15 μm are achieved. The clearly open 10-Gbits/s eye patterns of transmitting part as well as the 10^-12-order bit error rate (BER) at the receiving part verify the proposed SiOB-based module is suitable for the application of 4-channel×10-Gbits/s optical interconnects.

Dispersion compensation with a wavelength selective switch-based reconfigurable optical add/drop multiplexer is experimentally realized in an optical transport network testbed. Through considering various dispersion compensation scenarios (including different fiber types, different wavelength ranges, and single- and multi-channel cases), we show that without deploying new optical components, a wavelength selective switch can successfully compensate for chromatic dispersion in its dispersion control range.

An all-fiber optical interleaver with almost rectangular wavelength response is developed using a new configuration. The device consists of a 2×2 directional fiber coupler and a fiber ring resonator; the general formulas are derived with the transfer matrix method, and explicit expressions for the power are given. The characteristic parameters, such as amplitude flatness, bandwidth, and phase group delay, are analyzed and optimized. The simulation indicates that the bandwidth of 0.5-dB passband and 25-dB stopband of proposed interleaver are simultaneously remarkably improved, which is much wider than those of the conventional Mach-Zehnder interferometer (MZI) and two-stage MZI (TS-MZI). Further analysis indicates that the influence of the propagation loss on extinction ratio can be effectively reduced compared with the interleaver based on an asymmetrical MZI with a ring resonator in one arm.

In this paper, a simple and practical method based on multimode fiber (MMF)-single mode chirped fiber Bragg grating (CFBG) structures for highly sensitive bending measurement is proposed. By employing the wide wavelength resonance of CFBG, enhanced backward cladding modes can be achieved through the coupling and recoupling between MMF and CFBG. Experiential results indicate that cladding modes with a large wavelength range can be effectively excited through the proposed sensor structure, and a comparatively highly sensitive and cost-effective bending measurement can be achieved by detecting deflection-induced intensity change of recoupled cladding modes.

Analytical models for optical channel crosstalk in short-range free space optical interconnect systems are proposed. The diffraction crosstalk noise is modeled as a function of many parameters of the interconnect system, including the interconnect distance, the interconnect spacing, and the photo-detector size. The dependence of crosstalk noise on different systems' parameters is discussed and evaluated using the proposed models. It is shown that optimum parameters for the optical system and the detectors array can be easily determined to optimize and improve the interconnect performance. The effect of high modes of vertical cavity surface emitting lasers (VCSELs), VCSEL aperture, and the incident angle of the VCSEL beam on crosstalk are also discussed.

Standard vacuum practices mitigate the presence of water vapor and contamination inside cryogenic vacuum chambers. However, anomalies can occur in the facility that can cause the accumulation of amorphous water ice on optics and test articles. Under certain conditions, the amorphous ice on optical components shatters, which leads to a reduction in signal or failure of the component. An experiment was performed to study and measure the deposition of water (H₂O) ice on optical surfaces under high-vacuum cryogenic conditions. Water was introduced into a cryogenic vacuum chamber, via a hydrated molecular sieve zeolite, through an effusion cell and impinged upon a quartz-crystal microbalance (QCM) and first-surface gold-plated mirror. A laser and photodiode setup, external to the vacuum chamber, monitored the multiple-beam interference reflectance of the ice-mirror configuration while the QCM measured the mass deposition. Data indicates that water ice, under these conditions, accumulates as a thin film on optical surfaces to thicknesses over 45 microns and can be detected and measured by nonintrusive optical methods which are based upon multiple-beam interference phenomena. The QCM validated the interference measurements. This experiment established proof-of-concept for a miniature system for monitoring ice accumulation within the chamber.

A few holographic metallic (gold and silver) gratings with maximum diffraction efficiency (DE) in the 700 to 1100 nm wavelength range were designed. These designed diffraction gratings can be attractive for stretching and compressing pulses in chirped pulse amplification (CPA) technology. They were optimized for transverse magnetic polarized light in the first order (littrow mount). KPP1206 photoresist was used to model the final pattern on photoresist thin film. To obtain super Gaussian profiles, approximately identical exposure energy density intervals were used for optimizing grating profile. The optimized gold and silver gratings were compared in terms of DE, bandwidth and incidence angle range. Dependence of DE on the depth and duty cycle of super Gaussian gold and silver gratings showed that the silver grating had higher DE than the gold grating in 1064 nm. Fabricated silver grating based on modeling results had good agreement with experimental results.

Innovations in x-ray imaging are described to evaluate spatial and temporal dissipation and relaxation dynamics in materials. A system is constructed employing five sets of image planes orthogonal to the target, such that the centerline image-plane orthogonal axes are coplanar. Variable pulser firing sequences flash five x-ray tubes, capturing temporal sequences of interest, and controlled coincident firing sequences characterize ballistic impact events in three dimensions.

The quarter-pel motion vector accuracy supported by H.264/advanced video coding (AVC) in motion estimation (ME) and compensation (MC) provides high compression efficiency. However, it also increases the computational complexity. While various well-known fast integer-pel ME methods are already available, lack of a good, fast subpel ME method results in problems associated with relatively high computational complexity. This paper presents one way of solving the complexity problem of subpel ME by making adaptive motion vector (MV) accuracy decisions in inter-mode selection. The proposed MV accuracy decision is made using inter-mode selection of a macroblock with two decision criteria. Pixels are classified as stationary (and/or homogeneous) or nonstationary (and/or nonhomogeneous). In order to avoid unnecessary interpolation and processing, a proper subpel ME level is chosen among four different combinations, each of which has a different MV accuracy and number of subpel ME iterations based on the classification. Simulation results using an open source x264 software encoder show that without any noticeable degradation (by - 0.07 dB on average), the proposed method reduces total encoding time and subpel ME time, respectively, by 51.78% and by 76.49% on average, as compared to the conventional full-pel pixel search.

We present a near-real-time visual-processing approach for automatic airborne target detection and classification. Detection is based on fast and robust background modeling and shape extraction, while recognition of target classes is based on shape and texture-fused querying on a-priori built real datasets. The presented approach can be used in defense and surveillance scenarios where passive detection capabilities are preferred (or required) over a secured area or protected zone.

The problem of super-resolution and tracking for midcourse closely spaced objects (CSO) is examined using a space-based infrared sensor. Within a short time window, the midcourse CSO trajectories on the focal plane can be modeled as following a straight line with a constant velocity. Thus, the object's initial state (location and velocity on the focal plane) exclusively corresponds to its trajectory on the focal plane. Thereupon, the objects number, intensities and initial states, as well as the sensor noise variances, are considered random variables, and a Bayesian model is proposed which is utilized to define a posterior distribution on the joint parameter space. To maximize this distribution, reversible jump Markov chain Monte Carlo algorithm is adopted to perform the Bayesian computation. The proposed approach simultaneously used the multiple time-consecutive frame data to estimate model parameters. Compared with the single-frame method, it not only gains the super-resolution capability but also can directly estimate focal plane trajectories without using explicit data association techniques. Results show that the performance (estimation precision of objects number, focal plane locations, intensities and ballistic trajectories for the CSO, together with the computation load) of the proposed approach outperforms the conventional single-frame and multiframe approaches.

For visible and infrared color fusion images of three typical scenes, color harmony computational models are proposed to evaluate the color quality of fusion images without reference images. The models are established based on the color-combination harmony model and focus on the influence of the color characteristics of typical scenes and the color region sizes in the fusion image. For the influence of the color characteristics of typical scenes, color harmony adjusting factors for natural scene images (green plants, sea, and sky) are defined by measuring the similarity between image colors and corresponding memory colors, and that for town and building images are presented based on the optimum colorfulness range suited for a human. Simultaneously, considering the influence of color region sizes, the weight coefficients are established using areas of the color regions to optimize the color harmony model. Experimental results show that the proposed harmony models are consistent with human perception and that they are suitable to evaluate the color harmony for color fusion images of typical scenes.

Moving cast shadow detection plays an exceedingly important role in content-based analysis in surveillance videos. A novel integrated moving cast shadow detection method is proposed for accurate moving objects detection. Based on the analysis for shadow model, we first exploit color information sufficiently in hue, saturation, and value color space and texture similarity in texture space to separate moving cast shadows from the foreground, respectively. Then we obtain the rough shadow detection result by means of synthesizing the above two results efficiently. Finally, post processing is put forward to modify misclassified pixels for acquiring the refined shadow detection result. Extensive experiments and comparisons of various scenes prove that the proposed method can detect cast shadows automatically and effectively and outperforms some well-known methods.

Video-based rapid traffic accident detection is very important for intelligent transport systems. Traditional methods are either not fast enough or not stable with working environments. A rapid and environment-adaptive method is proposed. The inspiration of the method is originated from the key observation that the traffic accident brings abundant information on motion directions. This method includes three steps. First, the orientation map for each video frame is constructed based on the optical flows. Then, for each orientation map, the connected regions are formed. An entropy-like energy function is used to measure the orientation information of the connected region. The higher the energy value, the more moving directions exist. The highest measure of these connected regions in each orientation map is considered as its energy measure. Finally, based on the energy sequence of orientation maps, a Gaussian model is established to learn the normal energy fluctuation range for some environment. In the detection process, if the energy of one orientation map burst out of the normal range, it means there exists a traffic accident. The advantages of our method include the fast processing speed, a compact parameter set, and the robustness to the different environments and illuminations. Experimental results confirm the above advantages of the proposed approach.

An efficient algorithm named modified directional gradient descent searches to enhance the directional gradient descent search (DGDS) algorithm is presented to reduce computations. A modified search pattern with an adaptive threshold for early termination is applied to DGDS to avoid meaningless calculation after the searching point is good enough. A statistical analysis of best motion vector distribution is analyzed to decide the modified search pattern. Then a statistical model based on the characteristics of the block distortion information of the previous coded frame helps the early termination parameters selection, and a trade-off between the video quality and the computational complexity can be obtained. The simulation results show the proposed algorithm provides significant improvement in reducing the motion estimation (ME) by 17.81% of the average search points and 20% of ME time saving compared to the fast DGDS algorithm implemented in H.264/AVC JM 18.2 reference software according to different types of sequences, while maintaining a similar bit rate without losing picture quality.

In H.264/advanced video coding (AVC), low-pass filtering is performed on neighboring coded pixels before intra prediction is applied to reduce the effect of quantization errors. However, reducing the effect of quantization errors by conventional methods is difficult in some areas, depending on the image characteristics. To alleviate this issue, we need to consider the prediction direction. We propose a mode-dependent filtering technique to reduce the effect of quantization errors. Our method has a threshold to adaptively choose between the conventional and proposed methods to reduce the number of flag bits that are sent to the decoder. The method is compared with other benchmark methods in terms of their average bit-saving and peak signal-to-noise ratio. Simulation results show that the average bit-rate reduction is about 1.222% in test sequences.

The enhancement of absorption in a thin-film amorphous silicon solar cell based on guided mode resonance is theoretically investigated. This is achieved by patterning a single- or double-groove grating with a waveguide layer as the absorbing layer. The optimized grating parameters are obtained by use of rigorous coupled-wave analysis and the simulated annealing algorithm. The averaged integrated absorptions are weakly dependent on the angle of incidence in both grating structures. It is shown the optimized solar cell with double-groove grating has better optical performance than single-groove grating structures. The qualitative understanding of enhanced absorption based on guided-mode resonance and double-groove grating structure is presented. An antireflective grating structure is proposed and discussed for reducing reflection and enhancing absorption. The solar cell with antireflective grating has much better performance than those without an antireflective grating. The designed solar cells have high integrated absorption and are weakly dependent on the incident angle, which should be highly interesting for practical application.

Resonance domain diffraction gratings with local periods near the wavelength may have very high diffraction efficiencies. Unfortunately, they are difficult to fabricate, especially for use with light in visible and shorter wavelengths. We present several methods for fabricating surface relief resonance domain diffraction gratings used in the visible spectral region. We also optimize the relevant fabrication parameters and compare the resulting performance for each method. For the fabrication, we resort to e-beam lithography and reactive ion etching. Characterization is performed with environmental scanning electron microscopy, atomic force microscopy, and optical measurements on representative structures. Nearly 100% Bragg diffraction efficiency can be achieved with transmission resonance domain binary gratings formed in fused silica and having a period of 0.5 μm and a groove depth of 1 μm.

A stable amplitude squeezed-state light was generated by utilizing the nondegenerate optical parametric amplifier based on periodically poled KTiOPO₄ crystal at 1064 nm. We observed - 4.93 dB of squeezing with a local oscillator phase locked in homodyne measurement. The imaging experiments of the resolution target have shown that the imaging resolution, which was based on squeezed-state light, is 1.41 times as much as the resolution that was acquired using coherent light as light source. In addition, the squeezed-state light was applied for imaging of the virtual object. It was found that the characters on the board were much more easily discerned with squeezed light as a light source than with coherent light. This result paves the way for further improvements of imaging resolution by use of the squeezed-state light.

We investigate the terahertz (THz) transmission characteristics of complex slot arrays with various order of rotation symmetry. Our experimental results reveal that an asterisk-shaped aperture with sixfold rotational symmetry is the most appropriate shape for realizing polarization-independent, highly efficient, and frequency-selective transmission of THz radiation. A systematic understanding of the THz transmission characteristics is useful for achieving versatile platforms and custom-designed metallic devices with specific electromagnetic responses.

We present results for a rapid, precise, and wide field-of-view scanning antenna for use at millimeter and submillimeter wavelengths, based on the photo-injected Fresnel-zone plate antenna (piFZPA) method. In this paper, we demonstrate the potential of this technology as a viable solution for a range of applications demanding real-time imagery or high flexibility and beam fidelity at these frequencies. We present proof-of-principle experiments at 94 GHz that incorporate a commercial display technology operating at visible wavelengths. The 100-mm-diameter piFZPA achieves 37-dBi directivity, excellent beam symmetry, beam steering in two dimensions over a ±20-deg field of view, and precise beam control and repeatability. Preliminary results of a piFZPA-based, short-range, 94-GHz, three-dimensional imaging radar are also presented.

This article [Opt. Eng.. 51, , 077008 (2012)] was originally published on 18 Jul. 2012 with reversed captions in Figs. 3 and 4. The corrected figures and captions are reprinted below.