Society Of Photo-Optical Instrumentation Engineers Research Articles

Plasmonic nanopillar coupled two-dimensional random medium for broadband light trapping and harvesting

Random textures have proven to be a better option for light localization and energy harvesting in solar cells. On the other hand, plasmonic structures are significant in localizing the fields into submicron domains. We propose a layered structure design that contains the random dielectric medium with a plasmonic nanopillars array as a back reflector, followed by demon- strating its efficient light trapping ability through simulation means. This structure has shown significant enhancement in the broadband absorption of the light spectrum in the wavelength range UV-IR and a higher extinction in the near-infrared wavelengths. The structure also shows the dependence of reflection on the nanopillar height as well as localization in the nano- pillar region. The broadened and red shifted plasmonic nanopillar resonances (transverse and longitudinal) in a high-index medium are shown as the reasons for enhanced broadband absorption. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1. JNP.9.093061)

Three-dimensional terrain model multiview quality assessment considering human visual system

In the current remote sensing big data era, the huge amount of data, especially the expansion of spatial dimension, brings challenges to the traditional processing and applications in data transferring, processing and visualization. Model quality assessment is usually employed to evaluate the yielding model and select the optimal simplification method, which is used to improve the efficiency of big data processing. The existing three-dimensional (3-D) terrain model assessment methods mainly exploit the data accuracy or geometric features while ignoring the impact of humans or users. We mainly investigate the quality assessment for the 3-D terrain model. The proposed method provides an integration of structural similarity and the human vis- ual system from the multiview angles for the image quality assessment. The visual impact of observers and the structural information retention of the 3-D terrain model have been fully con- sidered. In the experiments, two kinds of models with different simplification ratios are utilized for the terrain model evaluation. The results confirm that the proposed algorithm has a better performance of terrain model quality assessment than other traditional methods. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JRS.9.097290)

Potential of multitemporal Gaofen-1 panchromatic/multispectral images for crop classification: case study in Xinjiang Uygur Autonomous Region, China

Gaofen-1 panchromatic/multispectral (GF-1 PMS) data have both high spatial and temporal resolutions, and this research aims at evaluating the potential of GF-1 PMS data for crop classification. Three PMS images (at days 110, 192, and 274) were acquired in Manas County of Xinjiang. The images were first segmented and all objects were then visually interpreted based on ground reference data. Some indices and textual features were then extracted at the object level. Subsequently, the Jeffries-Matusita (JM) distance was employed to estimate the class separability among all pair-wise comparisons of each time period. Afterward, a random forest algorithm was used to calculate importance scores of all features and classify crop types for every possible image combination. Additionally, to evaluate the influence of feature number on classification accuracy, features were added one by one based on the importance of scores. The result showed that GF-1 PMS images with high-spatial resolution had the potential to identify the boundary of the crop fields. Relatively high JM distance (above 1.5) and classification accuracy (above 90%) indicated that day 192 image contributed the most to the crop identification in the study area. For multi-image combinations, days 110 to 192 combination can achieve high overall accuracy (around 93%) and more images cannot substantially improve the classification performance. As for features, normalized difference vegetation index and near infrared (NIR) band had the highest importance scores and textual features contributed to distinguishing tree from crop land. Finally, classification accuracy increased together with the augmentation of feature number when only a few features were used. After accuracies reached saturation points, however, more features only slightly improved the classification performance. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Efficient and low-latency pixel data transmission module for adaptive optics wavefront processor based on field-programmable gate array

An efficient and low-latency pixel data transmission module for the adaptive optics wavefront processor is presented. A fiber-based custom real-time pixel data transfer protocol is developed, which has the characteristics of long transmission distance, low-latency, and low-protocol overhead. The hardware part of the suite has been verified on different circuit boards with different field-programmable gate arrays. Obtained results demonstrate that the transmission and protocol processing delay are only 413.5 ns, the transmission bandwidth is 3.125 Gbps, and the error rate is less than 10-12. Under the same conditions of 156.25 MHz clock frequencies and length of transmission line, compared with the serial front panel data port protocol adopted by the thirty meter telescope and the european southern observatory, the transmission delay is significantly reduced by 2.82 times and has a remarkably low logic occupancy rate through our solution. Also, the method has been applied in several actual projects. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Fabrication and characterization of carbon/oxygen-implanted waveguides in Nd 3 + -doped phosphate glasses

Optical planar waveguides in Nd-3-Hdoped phosphate glasses are fabricated by a 6.0-MeV carbon ion implantation with a dose of 6.0 x 1014 ions/cm2 and a 6.0-MeV oxygen ion implantation at a fluence of 6.0 x 1014 ions/cm(2), respectively. The guided modes and the corresponding effective refractive indices were measured by a modal 2010 prism coupler. The refractive index profiles of the waveguides were analyzed based on the stopping and range of ions in matter and the RCM reflectivity calculation method. The near-field light intensity distributions were measured and simulated by an end-face coupling method and a finite-difference beam propagation method, respectively. The comparison of optical properties between the carbon-implanted waveguide and the oxygen-implanted waveguide was carried out. The microluminescence and Raman spectroscopy investigations reveal that fluorescent properties of Nd3- ions and glass microstructure are well preserved in the waveguide region, which suggests that the carbon/oxygen-implanted waveguide is a good candidate for integrated photonic devices. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Mapping stresses in high aspect ratio polysilicon electrical through-wafer interconnects

Electrical through-wafer interconnect technologies such as vertical through-silicon vias (TSVs) are essential in order to maximize performance, optimize usage of wafer real estate, and enable three-dimensional packaging in leading edge electronic and microelectromechanical systems (MEMS) products. Although copper TSVs have the advantage of low resistance, highly doped polysilicon TSVs offer designers a much larger range of processing options due to the compatibility of polysilicon with high temperatures and also with the full range of traditional CMOS processes. Large stresses are associated with both Cu and polysilicon TSVs, and their accu- rate measurement is critical for determining the keep-out zone (KOZ) of transistors and for optimizing down- stream processes to maintain high yield. This report presents the fabrication and stress characterization of 400-μm deep, 20-Ω resistance, high aspect ratio (25:1) polysilicon TSVs fabricated by deep reactive ion etching (DRIE) followed by low-pressure chemical vapor deposition (LPCVD) of polysilicon with in-situ boron doping. Micro-Raman imaging of the wafer surface showed a maximum stress of 1.2 GPa occurring at the TSV edge and a KOZ of ∼9 to 11 μm. For polysilicon TSVs, the stress distribution in the TSVs far from the wafer surface(s) was not previously well-understood due to measurement limitations. Raman spectroscopy was able to overcome this limitation; a TSV cross section was examined and stresses as a function of both depth and width of the TSVs were collected and are analyzed herein. An 1100°C postanneal was found to reduce average stresses by 40%. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JMM.14.2.024001)

Digital image analysis around isotropic points for photoelastic pattern recognition

Fringe tracking and fringe order assignment have become the central topics of current research in digital photoelasticity. Isotropic points (IPs) appearing in low fringe order zones are often either overlooked or entirely missed in conventional as well as digital photoelasticity. We aim to highlight image processing for characterizing IPs in an isochromatic fringe field. By resorting to a global analytical solution of a circular disk, sensitivity of IPs to small changes in far-field loading on the disk is highlighted. A local theory supplements the global closed-form solutions of three-, four-, and six-point loading configurations of circular disk. The local theoretical concepts developed in this paper are demonstrated through digital image analysis of isochromatics in circular disks subjected to three-and four-point loads. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Image data compression with hierarchical pixel averaging and fully adaptive prediction error coder

The fully adaptive prediction error coder (FAPEC) is an entropy coder that typically offers better results than the adaptive Rice compressor. It uses basic preprocessing stages such as delta preprocessing, but it can also be combined with a discrete wavelet transform. We describe a new algorithm called hierarchical pixel averaging (HPA). It divides an image into blocks of 16 x 16 pixels, which are subsequently divided into smaller blocks, up to the basic level where one block corresponds to one pixel. Average pixel values are determined for each level from which differential coefficients are extracted. HPA allows the introduction of controlled losses with several quality levels, also allowing to progressively decompress a given image from lower to higher quality. It achieves better resolution in sharp image edges when compared to other lossy algorithms. HPA is based on simple arithmetic operations, allowing a very simple (thus quick) implementation. It does not use any floating-point operations, which is an interesting feature for satellite or embedded data compression. We present a first implementation of HPA and the results obtained on a variety of images, both for the lossless and lossy cases with different quality levels. Our results indicate that HPA + FAPEC offer a performance comparable to that of CCSDS 122.0. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Bioinspired molecular electrets: bottom-up approach to energy materials and applications

© 2015 Society of Photo-Optical Instrumentation Engineers (SPIE). The diversity of life on Earth is made possible through an immense variety of proteins that stems from less than a couple of dozen native amino acids. Is it possible to achieve similar engineering freedom and precision to design electronic materials? What if a handful of nonnative residues with a wide range of characteristics could be rationally placed in sequences to form organic macromolecules with specifically targeted properties and functionalities? Referred to as molecular electrets, dipolar oligomers and polymers composed of non-native aromatic beta-amino acids, anthranilamides (Aa) provide venues for pursuing such possibilities. The electret molecular dipoles play a crucial role in rectifying charge transfer, e.g., enhancing charge separation and suppressing undesired charge recombination, which is essential for photovoltaics, photocatalysis, and other solar-energy applications. A set of a few Aa residues can serve as building blocks for molecular electrets with widely diverse electronic properties, presenting venues for bottom-up designs. We demonstrate how three substituents and structural permutations within an Aa residue widely alter its reduction potential. Paradigms of diversity in electronic properties, originating from a few changes within a basic molecular structure, illustrate the promising potentials of biological inspiration for energy science and engineering.

Broadband and omnidirectional antireflection of SiN composite nanostructures–decorated Si surface for highly efficient Si solar cells

SiN composite nanostructures (CNs), composed of SiN nanorods and the underlying SiN film, are formed on Si substrate through SiN deposition, nanosphere lithography, and dry etching. The antireflection performance of Si samples decorated by the SiN CNs with different morphology is experimentally investigated. All the SiN CNs decorated Si samples exhibit antireflection over 300 to 1000 nm and a wide view. Their antireflection performance varies with the height of the nanorods (H) and the thickness of the underneath film (T). A reflectivity of less than 10% over 300 to 1000 nm and an incident angle of 8 deg and 65 deg are achieved in the optimal antireflection structures with H = 240 nm, T = 750 nm and H = 500 nm, T = 300 nm, respectively. Furthermore, antireflection behavior in the SiN CNs decorated Si sample with H = 500 nm, T = 300 nm is compared with that in Si samples decorated by 565- and 60-nm thick SiN film. A weighted reflectance of about 5% is achieved in an SiN CNs decorated Si sample in any incident angle, which is much lower than that in any SiN film coated Si sample. Moreover, such a performance is beyond the limitation of interface reflectivity of Si and SiN materials, and should benefit Si solar cells to simultaneously enhance the absorption and surface passivation. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Photodynamic therapy: a review of applications in neurooncology and neuropathology.

Photodynamic therapy (PDT) effect is a promising adjuvant modality for diagnosis and treatment of brain cancer. It is of importance that the bright fluorescence of most photosensitizers provides visualization of brain tumors. This is successfully used for fluorescence-guided tumor resection according the principle to see and treat. Non-oncologic application of PDT effect for induction of photothrombotic infarct of the brain tissue is a well-controlled and reproducible stroke model, in which a local brain lesion is produced in the predetermined brain area. Since normal neurons and glial cells may also be damaged by PDT and this can lead unwanted neurological consequences, PDT effects on normal neurons and glial cells should be comprehensively studied. We overviewed the current literature data on the PDT effect on a range of signaling and epigenetic proteins that control various cell functions, survival, necrosis, and apoptosis. We hypothesize that using cell-specific inhibitors or activators of some signaling proteins, one can selectively protect normal neurons and glia, and simultaneously exacerbate photodynamic damage of malignant gliomas. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI:

Data correction techniques for the airborne large-aperture static image spectrometer based on image registration

We propose an approach to correct the data of the airborne large-aperture static image spectrometer (LASIS). LASIS is a kind of stationary interferometer which compromises flux output and device stability. It acquires a series of interferograms to reconstruct the hyperspectral image cube. Reconstruction precision of the airborne LASIS data suffers from the instability of the plane platform. Usually, changes of plane attitudes, such as yaws, pitches, and rolls, can be precisely measured by the inertial measurement unit. However, the along-track and across-track translation errors are difficult to measure precisely. To solve this problem, we propose a co-optimization approach to compute the translation errors between the interferograms using an image registration technique which helps to correct the interferograms with subpixel precision. To demonstrate the effectiveness of our approach, experiments are run on real airborne LASIS data and our results are compared with those of the state-of-the-art approaches. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

New geo-portal for MODIS/SEVIRI image products with geolocation-based retrieval functionality

A large number of remote sensing data sets have been collected in recent years by Earth observation instruments such as the moderate resolution imaging spectroradiometer (MODIS) aboard the Terra/Aqua satellite and the spinning enhanced visible and infrared imager (SEVIRI) aboard the geostationary platform Meteosat Second Generation. The advanced remote sensing products resulting from the analysis of these data are useful in a wide variety of appli- cations but require significant resources in terms of storage, retrieval, and analysis. Despite the wide availability of these MODIS/SEVIRI products, the data coming from these instruments are spread among different locations and retrieved from different sources, and there is no common data repository from which the data or the associated products can be retrieved. We take a first step toward the development of a geo-portal for storing and efficiently retrieving MODIS/ SEVIRI remote sensing products. The products are obtained using an automatic system that processes the data as soon as they are provided by the collecting antennas, and then the final products are uploaded with a one day delay in the geo-portal. Our focus in this work is on describing the design and efficient implementation of the geo-portal, which allows for a user- friendly and effective access to a full repository of MODIS/SEVIRI advanced products (com- prising tens of terabytes of data) using geolocation retrieval capabilities. The geo-portal has been implemented as a web application composed of different layers. Its modular design provides quality of service and scalability (capacity for growth without any quality losing), allowing for the addition of components without the need to modify the entire system. On the client layer, an intuitive web browser interface provides users with remote access to the system. On the server layer, the system provides advanced data management and storage capabilities. On the storage layer, the system provides a secure massive storage service. An experimental evaluation of the geo-portal in terms of efficiency and product retrieval accuracy is also presented and discussed. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JRS.9.096079)

Effects of last barrier thickness on the hot–cold factor of GaN-based light-emitting diodes

The study of thermal properties for GaN-based light-emitting diodes (LEDs) with various last barrier thicknesses was reported. It was found that the LED output power decreased as we increased the thickness of the last barrier. It was also found that the LED output powers decrease with the increase of temperature for the LEDs with 12-, 24-, and 48-nm-thick last bar- riers. However, it was found that the LED output power increases with the increase of temper- ature for the LED with a 72-nm-thick last barrier due to the fact that more holes could enter the multiquantum well active region at elevated temperatures. Furthermore, it was found that the output power decreased by 0.15%/°C, 0.15%/°C, and 0.11%/°C for the LEDs with 12-, 24-, and 48-nm-thick last barriers, respectively, but increased by 0.09%/°C for the LED with a 72-nm-thick last barrier. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI:

Gap-optimized Moiré phase imaging alignment for proximity lithography

The proposed four-quadrant Moire alignment scheme to detect the misalignment between mask and wafer for proximity lithography can achieve the alignment accuracy with nanometer level. When implementing the scheme, however, the distribution of Moire fringes associated with the mask-wafer gap indeed goes against the alignment, making the gap optimization highly urgent. The optimization model is established, and numerical simulation as well as experimental verification is also provided. Furthermore, an alignment accuracy of similar to 3 nm with the illumination wavelength of 632.8 nm is experimentally attained. Simultaneously, the design mechanism of alignment marks for improving the availability of the alignment scheme is discussed. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Spatially dispersive functional optical metamaterials

Functional optical metamaterials usually consist of absorbing, anisotropic, and often noncentrosymmetric structures of a size that is only a few times smaller than the wavelength of visible light. If the structures were substantially smaller, excitation of higher-order electromag- netic multipoles in them, including magnetic dipoles, would be inefficient. The required non- negligible size of metamolecules, however, makes the material spatially dispersive, so that its optical characteristics depend on the light propagation direction. We consider the possibility to use this usually unwanted effect. We present a theoretical model that allows one to study the interaction of such spatially dispersive metamaterials with optical beams. Applying the model, we show that a strong spatial dispersion, combined with optical anisotropy and absorption, can be used to efficiently control propagational characteristics of optical beams and create new types of optical elements. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1 .JNP.9.093097)

Quantitative evaluation of observation capability of GF-1 wide field of view sensors for soil moisture inversion

Currently, many satellite data are used to invert soil moisture. However, there is no study about quantitative evaluation of observation capability of GF-1 wide field of view (WFV) sensors for soil moisture inversion. Therefore, we proposed a method to evaluate it. We used WFV, Landsat8 Operational Land Imager (OLI), and Moderate-resolution Imaging Spectroradiometer (MODIS) data to invert soil moistures in Wuhan from September 2013 to September 2014 based on the Perpendicular Drought Index (PDI) and modified PDI (MPDI). From the estimated results, the R 2 values, and standard error, we found that both the PDI and MPDI had a significantly negative linear correlation with soil moisture (P < 0.01). Through the values of R, mean absolute error, mean relative error, and root mean square error, we found that a strong relativity existed between the estimated and observed soil mois- tures. It was evident from the results for the WFV, OLI, and MODIS that the performances of WFV and OLI were consistent and that WFV performed better than MODIS. All the results indicated that WFV sensors had a high observation capability for soil moisture inversion in Wuhan. The comprehensive evaluation results for the performance of the PDI and MPDI proved that the MPDI performed better for soil moisture inversion than did the PDI. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JRS.9.097097)

Optimization of structure parameters of concentric plasmonic lens for 355 nm radially polarized illumination

We propose and optimize two designs of plasmonic lens structures, concentric grooves with a central hole (CGH) and concentric grooves with a central pillar (CGP), based on a traditional structure of concentric grooves (CG). The numerical investigation based on COMSOL Multiphysics is performed to optimize the three kinds of structures by a 355 nm radially polarized laser illumination. It is found that full-width at half maximum (FWHM) is closely related to the size of the center-position, and the field enhancement effect depends on the resonant wavelength of surface plasmon polaritons, permittivity, film thickness, and groove number. Compared to a FWHM of λ∕3 (λ is the wavelength of the laser beam) with the conventional CG type, the combination of localized and extended surface plasmons results in CGP and CGH parameters achieving their optimal value with a much smaller spot size of λ∕8 and higher intensity enhancement for a variety of the aspect ratios of central pillar and hole. A focused ion beam was used to fabricate the three type nanostructures with high accuracy. The CGH type with a central hole 20.88 nm in diameter and the CGP type with a central pillar 55.45 nm in diameter have been successfully fabricated approximately to their optimization results. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JNP.9

Quantitative estimation of density variation in high-speed flows through inversion of the measured wavefront distortion

A simple method employing an optical probe is presented to measure density variations in a hypersonic flow obstructed by a test model in a typical shock tunnel. The probe has a plane light wave trans-illuminating the flow and casting a shadow of a random dot pattern. Local slopes of the distorted wavefront are obtained from shifts of the dots in the pattern. Local shifts in the dots are accurately measured by cross-correlating local shifted shadows with the corresponding unshifted originals. The measured slopes are suitably unwrapped by using a discrete cosine transform based phase unwrapping procedure and also through iterative procedures. The unwrapped phase information is used in an iterative scheme for a full quantitative recovery of density distribution in the shock around the model through refraction tomographic inversion. Hypersonic flow field parameters around a missile shaped body at a free-stream Mach number of 5.8 measured using this technique are compared with the numerically estimated values. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)

Investigation of atmospheric insect wing-beat frequencies and iridescence features using a multispectral kHz remote detection system

Quantitative investigation of insect activity in their natural habitat is a challenging task for entomologists. It is difficult to address questions such as flight direction, predation strength, and overall activities using the current techniques such as traps and sweep nets. A multispectral kHz remote detection system using sunlight as an illumination source is presented. We explore the possibilities of remote optical classification of insects based on their wing-beat frequencies and iridescence features. It is shown that the wing-beat frequency of the fast insect events can be resolved by implementing high-sampling frequency. The iridescence features generated from the change of color in two channels (visible and near-infrared) during wing-beat cycle are presented. We show that the shape of the wing-beat trajectory is different for different insects. The flight direction of an atmospheric insect is also determined using a silicon quadrant detector. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE) (Less)