Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
A review of optical fiber hydrogen sensors based on palladium (Pd) is presented. Palladium hydrogen optical fiber sensing systems can be considered as a model for other metal hybrid systems. In addition, the Pd hydrogen systems are well characterized in bulk, cluster, or thin film form. We focus on the fiber principles. We then discuss their performances regarding their configurations. We will conclude by introducing the challenges in designing an ideal hydrogen optical fiber sensor based on a metal hybrids approach and which design direction is considered the best to take.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Special Section on Computational Approaches to Imaging LADAR
TOPICS: LIDAR, Sensors, 3D image processing, Digital imaging, Imaging systems, Algorithm development, 3D metrology, Digital holography, Image quality, Radar imaging
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
We assess the accuracy of land surface elevation retrieved from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission through comparisons with the U.S. Geological Survey National Elevation Dataset (NED), Shuttle Radar Topography Mission (SRTM), and the altimetry product from the Geoscience Laser Altimeter System onboard the Ice, Cloud, and Land Elevation Satellite (ICESat). The vertical accuracy of the CALIPSO-derived land surface elevation was tested against these three datasets for about 16 million lidar shots over the continental United States. The results show that the CALIPSO-derived elevation was highly correlated with the elevation result from the NED, SRTM, and ICESat datasets. The overall absolute vertical accuracies of the CALIPSO-derived land surface elevation expressed as the root mean square error (RMSE) are 5.58 and 5.90 m when compared with the SRTM and NED results, respectively. Lower accuracy of the CALIPSO-derived land surface elevation was achieved by comparison with the ICESat results (8.35-m RMSE), primarily due to the several kilometers distance between the CALIPSO and ICESat ground footprints. The results show that the variability in terrain, vegetation, canopy, and footprint size can all influence comparisons between the CALIPSO-derived elevation and the results obtained from NED, SRTM, and ICESat datasets.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
The adaptive spatial filtering method is commonly adopted to extract the +1 term spectrum in digital holography for real-time dynamic analysis. However, the typical filtering method is not satisfactory for automatic analysis, because the reset of the filtering window is needed to extract the area of the +1 term spectrum. Therefore, an adaptive spatial filtering method based on region growing and the characteristic of the spectrum separation is proposed. Its filtering window is automatically formed by region growing. The key parameters, including threshold and seed point, are set by the intensity distribution of the hologram spectrum. Then the adaptive filtering extracting the +1 term spectrum is realized by multiplying the hologram spectrum by the filtering window. Compared to the typical filtering method, the experimental results of a microhole array and a phase step show that the proposed method has better adaptability and a higher precision. Moreover, the applicability of this method for different uses is also demonstrated by experiments with a microhole array and a phase step.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Feature specific imaging is a computational imaging technique that minimizes the number of measurements needed to sufficiently reconstruct a scene by using a priori knowledge (e.g., the scene’s second-order statistics) to judiciously, as well as possibly adaptively, choose the projection vectors to be measured. Here, we have developed an approach to three-dimensional adaptive feature specific imaging that takes into account the obstruction of distant objects by closer objects in the adaption of the projections and in the reconstruction algorithm. The developed system reconstructs the cross-range image of the scene at each range bin from a set of range resolved measurements from all the return from the scene at that range using only a single photodetector, while adapting to the obstruction of the scene by closer objects. Simulations and a proof-of-concept demonstration of adaptive three-dimensional feature specific imaging are presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Several photogrammetry-based methods have been proposed that the derive three-dimensional (3-D) information from digital images from different perspectives, and lidar-based methods have been proposed that merge lidar point clouds and texture the merged point clouds with digital imagery. Image registration alone has difficulty with smooth regions with low contrast, whereas point cloud merging alone has difficulty with outliers and a lack of proper convergence in the merging process. This paper presents a method to create 3-D images that uses the unique properties of texel images (pixel-fused lidar and digital imagery) to improve the quality and robustness of fused 3-D images. The proposed method uses both image processing and point-cloud merging to combine texel images in an iterative technique. Since the digital image pixels and the lidar 3-D points are fused at the sensor level, more accurate 3-D images are generated because registration of image data automatically improves the merging of the point clouds, and vice versa. Examples illustrate the value of this method over other methods. The proposed method also includes modifications for the situation where an estimate of position and attitude of the sensor is known, when obtained from low-cost global positioning systems and inertial measurement units sensors.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
TOPICS: Range imaging, Associative arrays, Sensors, Signal processing, Signal to noise ratio, Imaging systems, Pulsed laser operation, Binary data, Cameras, Signal attenuation
Active range imaging (RI) systems utilize actively controlled light sources emitting laser pulses that are subsequently recorded by an imaging system and used for depth profile estimation. Classical RI systems are limited by their need for a large number of frames required to obtain high resolution depth information. In this work, we propose an RI approach motivated by the recently proposed compressed sensing framework to dramatically reduce the number of necessary frames. Compressed gated range sensing employs a random gating mechanism along with state-of-the-art reconstruction algorithms for the estimation of the timing of the reflected pulses and the inference of distances. In addition to efficiency, the proposed scheme is also able to identify multiple reflected pulses that can be introduced by semi-transparent elements in the scene such as clouds, smoke, and foliage. Simulations under highly realistic conditions demonstrate that the proposed architecture is capable of accurately recovering the depth profile of a scene from as few as 10 frames at 100 depth bins resolution, even under very challenging conditions. The results further indicate that the proposed architecture is able to extract multiple reflected pulses with a minimal increase in the number of frames, in situations where state-of-the-art methods fail to accurately estimate the correct depth signals.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Images measured through the atmosphere are degraded by scattering and absorption from aerosols along the path and by atmospheric turbulence. In the presence of heavy scattering at visible and infrared wavelengths, the distances over which reasonable observations are possible are quite short compared to astronomical imaging paradigms, and aerosol scattering effects dominate the degradation of the point spread function (PSF) due to atmospheric effects. In addition to aerosol-induced blurring, measurement noise effects are present in observed images. We examine the problem of reconstructing images degraded by aerosol blur and measurement noise using estimates of the overall PSF, which account for unscattered and scattered radiation detected by the imaging system. Representative images of a spoke target acquired under various conditions of scattering and photon flux levels were simulated, and reconstruction of the degraded images is performed using two linear reconstruction algorithms: a Wiener filter and a constrained least squares filter. Results of the reconstructions show that spatial resolution can be recovered in badly blurred images up to the limit imposed by the noise effective cutoff spatial frequency of the measurement.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
TOPICS: Video, 3D image processing, Clouds, Cameras, Visualization, Optical engineering, Video surveillance, Data modeling, 3D image reconstruction, Feature extraction
The problem of viewpoint variations is a challenging issue in vision-based human action recognition. With the richer information provided by three-dimensional (3-D) point clouds thanks to the advent of 3-D depth cameras, we can effectively analyze spatial variations in human actions. In this paper, we propose a volumetric spatial feature representation (VSFR) that measures the density of 3-D point clouds for view-invariant human action recognition from depth sequence images. Using VSFR, we construct a self-similarity matrix (SSM) that can graphically represent temporal variations in the depth sequence. To obtain an SSM, we compute the squared Euclidean distance of VSFRs between a pair of frames in a video sequence. In this manner, an SSM represents the dissimilarity between a pair of frames in terms of spatial information in a video sequence captured at an arbitrary viewpoint. Furthermore, due to the use of a bag-of-features method for feature representations, the proposed method efficiently handles the variations of action speed or length. Hence, our method is robust to both variations in viewpoints and lengths of action sequences. We evaluated the proposed method by comparing with state-of-the-art methods in the literature on three public datasets of ACT42, MSRAction3D, and MSRDailyActivity3D, validating the superiority of our method by achieving the highest accuracies.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
The classification of eye openness and closure has been researched in various fields, e.g., driver drowsiness detection, physiological status analysis, and eye fatigue measurement. For a classification with high accuracy, accurate segmentation of the eye region is required. Most previous research used the segmentation method by image binarization on the basis that the eyeball is darker than skin, but the performance of this approach is frequently affected by thick eyelashes or shadows around the eye. Thus, we propose a fuzzy-based method for classifying eye openness and closure. First, the proposed method uses I and K color information from the HSI and CMYK color spaces, respectively, for eye segmentation. Second, the eye region is binarized using the fuzzy logic system based on I and K inputs, which is less affected by eyelashes and shadows around the eye. The combined image of I and K pixels is obtained through the fuzzy logic system. Third, in order to reflect the effect by all the inference values on calculating the output score of the fuzzy system, we use the revised weighted average method, where all the rectangular regions by all the inference values are considered for calculating the output score. Fourth, the classification of eye openness or closure is successfully made by the proposed fuzzy-based method with eye images of low resolution which are captured in the environment of people watching TV at a distance. By using the fuzzy logic system, our method does not require the additional procedure of training irrespective of the chosen database. Experimental results with two databases of eye images show that our method is superior to previous approaches.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Digital refocusing is an interesting and useful tool for generating dynamic depth-of-field (DOF) effects in many types of photography such as portraits and creative photography. Since most existing digital refocusing methods rely on four-dimensional light field captured by special precisely manufactured devices or a sequence of images captured by a single camera, existing systems are either expensive for wide practical use or incapable of handling dynamic scenes. We present a low-cost approach for refocusing high-resolution (up to 8 mega pixels) images and videos based on a single shot using an easy to build camera-mirror stereo system. Our proposed method consists of four main steps, namely system calibration, image rectification, disparity estimation, and refocusing rendering. The effectiveness of our proposed method has been evaluated extensively using both static and dynamic scenes with various depth ranges. Promising experimental results demonstrate that our method is able to simulate various controllable realistic DOF effects. To the best of our knowledge, our method is the first that allows one to refocus high-resolution images and videos of dynamic scenes captured by a conventional compact camera.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
A chirped artificial compound eye on a curved surface was fabricated using an optical resin and then mounted on the end of an endoscopic imaging fiber bundle. The focal length of each lenslet on the curved surface was variable to realize a flat focal plane, which matched the planar end surface of the fiber bundle. The variation of the focal length was obtained by using a photoresist mold formed by dose-modulated laser lithography and subsequent thermal reflow. The imaging performance of the fiber bundle was characterized by coupling with a coaxial light microscope, and the result demonstrated a larger field of view and better imaging quality than that of an artificial compound eye with a uniform focal length. Accordingly, this technology has potential application in stereoscopic endoscopy.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Robustly and efficiently tracking pedestrians in the infrared spectrum is a crucial requirement for a number of applications. At the same time, it is also particularly critical due to both the peculiarities of infrared images and pedestrian targets. In fact, low resolutions and high signal-to-noise ratios combined with extremely variable target signatures, chaotic trajectories, and frequent occlusions have forced researchers to develop ever more complex strategies characterized by a neat trade-off between tracking accuracy and computational complexity. Thus, most of the existing techniques might not be capable of ensuring real-time performances with a suitable degree of robustness, especially on limited-resource hardware used, e.g., in automotive or security scenarios. We present a technique that extends an extremely efficient tracking method originally tailored to targets that exhibit a clear and stable hot spot to allow it to deal with pedestrian targets by reusing its core components and integrating an occlusion detection and recovery mechanism. Experimental results obtained on public datasets confirmed that the devised method is able to obtain a robustness that is superior to that of other common approaches by maintaining the high tracking speed of the reference method.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
The contrast of simple achromatic periodic patterns such as square-wave gratings is well defined and agrees with the Michelson contrast, but this is not so for chromatic contrast. It would be desirable to be able to determine the contrast of two colors for use in a general legibility metric. A method for determining the contrast of chromatic square-wave gratings, which is based on the CIE 1976 color difference formula, is proposed. In order to prove the feasibility, we first investigated the contrast sensitivity function of an achromatic grating using Michelson contrast for comparison through sets of psychophysical experiments keeping the mean luminance constant at 22.54cd/m2. Further experiments compared the curve of contrast sensitivity function for red, green, and red-green chromatic square-wave grating in terms of the proposed formula and conventional formula in LMS cone contrast space, which is frequently used in calculating the contrast of color gratings. The results revealed that proposed method is helpful in calculating the contrast of chromatic square-wave gratings and reveals important physical meaning in measuring the contrast of chromatic gratings.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
In spectral-domain optical coherence tomography (SD-OCT), the limited resolution of the spectrometer causes nonuniformity of the interference signal. The latter, in turn, causes the sensitivity of SD-OCT to decrease, thereby limiting the imaging range and decreasing the axial resolution. We addressed this problem by applying nonuniform, nonharmonic analysis (NUNHA) with software that features high-frequency resolution without interpolation. We demonstrate the application of NUNHA in SD-OCT and compare it with conventional frequency analysis methods by simulating nonuniform interference signals. The results suggest that application of NUNHA in SD-OCT can provide acquisition of a clearer tomographic image, accurate analysis of fine and complex structures, and preservation of resolution and sensitivity at regions deep within a sample. This is because it reduces the influence of nonuniformity caused by the spectrometer and is unaffected by distortion due to interpolation.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
A roll-angle measurement interferometer with good stability and high sensitivity is presented. In the system, two sets of spatial parallel beams with different frequencies are formed with the help of a Koster prism, a corner cube, a quarter-wave plate, a wedge prism, and a wedge mirror. The wedge prism is used for the roll-angle sensing component, the roll of which will cause the changes of the optical path of the two beams with different frequencies. This interferometer complies with the principle of common path which minimizes the dead path; the cross talk of straightness, pitch, and yaw errors are avoided in this specific structure which enhances the stability and precision of the measurement. The experimental result fits well with the theoretical analysis and a measurement resolution of 2 μrad is achieved with an electronic interpolation of 2π/512.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
TOPICS: 3D image processing, Fringe analysis, 3D metrology, Phase retrieval, Phase shifts, Digital Light Processing, Reconstruction algorithms, Image processing, Digital filtering, Projection systems
The processing of structured light images in real time is a challenging task for the development of three-dimensional (3-D) shape measurement methods. This paper presents a high speed and low-cost optical profiler implemented using a projection method based on the use of a digital light-processing device to illuminate the object to be measured. The image processing of the reflected structured light pattern allows potential real-time capabilities. The proposed method of absolute phase retrieval for unwrapping the relative phase uses a single additional staircase intensity pattern to determine and correct 2π discontinuities in the phase. Good results are obtained when the method is compared to another which uses three additional fringe patterns to determine the stair phase and then the absolute phase. Since the proposed technique uses only one extra pattern instead of three, it is less costly in terms of computation complexity and is thus faster. The hardware of the developed fringe projection system for a 3-D macroscopic reconstruction is presented and the performance of the method is evaluated. Simulated and experimental results are presented and compared to the other absolute phase-retrieval method. The proposed method is suitable for measuring 3-D object surfaces for a possible implementation in real time.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Blade tip-timing is the most effective method for online blade vibration measurement of large rotating machines like turbine engines. Fiber bundle sensors are utilized in tip-timing system to measure the arrival time of the blade. The model of the tip-timing signal of the fiber bundle sensor is established. Experiments are conducted and the results are in concordance with the model established. The rising speed of the tip-timing signal is analyzed. To minimize the tip-timing error, the effects of the clearance change between the sensor and the blade and the deflection of the tip surface are analyzed. Simulation results indicate that the variable gain amplifier, which amplifies the signals to a similar level, can eliminate the measurement error caused by the variation of the clearance between the sensor and blade. Increasing the clearance between the sensor and blade can reduce the measurement error introduced by deflection of the tip surface.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
A diode laser velocimeter based on laser self-mixing has been developed and characterized as a reliable, precise, comparably cheap, and compact monitor. The resolution of this sensor at different incident angles and for a variety of solid and liquid targets moving at velocities between 0.1 and 50 m/s is presented. This includes a theoretical analysis of the underlying measurement principle, highlighting possibilities to extend the measurement capabilities to even higher velocities by altering the sensor design. Finally, an outlook on future applications of the sensor for detailed studies of supersonic gas jets used in beam diagnostics and atomic physics applications is given.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
In practical optical measurements, the wavefront data are recorded by pixelated imaging sensors. The closed-form analytical base polynomial will lose its orthogonality in the discrete wavefront database. For a wavefront with an irregularly shaped aperture, the corresponding analytical base polynomials are laboriously derived. The use of numerical orthogonal polynomials for reconstructing a wavefront with a general shaped aperture over the discrete data points is presented. Numerical polynomials are orthogonal over the discrete data points regardless of the boundary shape of the aperture. The performance of numerical orthogonal polynomials is confirmed by theoretical analysis and experiments. The results demonstrate the adaptability, validity, and accuracy of numerical orthogonal polynomials for estimating the wavefront over a general shaped aperture from regular boundary to an irregular boundary.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Existing digital image correlation (DIC) using the robust reliability-guided displacement tracking (RGDT) strategy for full-field displacement measurement is a path-dependent process that can only be executed sequentially. This path-dependent tracking strategy not only limits the potential of DIC for further improvement of its computational efficiency but also wastes the parallel computing power of modern computers with multicore processors. To maintain the robustness of the existing RGDT strategy and to overcome its deficiency, an improved RGDT strategy using a two-section tracking scheme is proposed. In the improved RGDT strategy, the calculated points with correlation coefficients higher than a preset threshold are all taken as reliably computed points and given the same priority to extend the correlation analysis to their neighbors. Thus, DIC calculation is first executed in parallel at multiple points by separate independent threads. Then for the few calculated points with correlation coefficients smaller than the threshold, DIC analysis using existing RGDT strategy is adopted. Benefiting from the improved RGDT strategy and the multithread computing, superfast DIC analysis can be accomplished without sacrificing its robustness and accuracy. Experimental results show that the presented parallel DIC method performed on a common eight-core laptop can achieve about a 7 times speedup.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
The antibacterial surfaces presented can be one of the solutions for lowering the risk of pathogen outbreaks. Samples were prepared via a multistep physicochemical approach and characterized by terahertz spectroscopy. Properties of modified materials were analyzed using two spectrometers—terahertz pulsed imaging and spectroscopy Spectra [attenuated total reflection (ATR) and transmission module] and Tera optical sampling by cavity tuning. Each sample was measured 3 to 10 times to get accurate results. Observed regions for the transmittance module were set to 0 to 2.6 THz, and 0 to 4 THz for the ATR module. The obtained refractive indices allowed for easy distinguishing between each material. Absorbance spectra were assigned where possible as was the peak position that showed successful bonding of the used monomers/antibacterial agents. Measured dielectric properties described slight changes in materials due to the modification process. The experimentally analyzed transmittance displayed changes in every material up to the 2.6 THz region and Fabry–Perot interferences together with water vapor noise beyond this area. The section containing terahertz imaging of the samples is presented. The present work is one of the first of its kind. The possibility of using terahertz spectroscopy for characterizing materials with antibacterial agents bonded by intermolecular forces onto a treated surface is presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
By correlating bi-Ronchigram images, surface errors without any supposed symmetry are evaluated. No approximation and interference orders are needed. First, only one experimental bi-Ronchigram (Ronchigram with a square grid) image was recorded. Second, given a surface parameter set (curvature radius, conic constant, and/or symmetric and asymmetric deformation coefficients), a bi-Ronchigram image is simulated and correlated with the bi-Ronchigram experimental image. Third, genetic algorithms are used to find the parameters for which the correlation coefficient reaches its maximum value. Finally, the parameters of the experimental surface are estimated. Evaluations of curvature radius, conic constant, and error functions for reflecting surfaces will be shown.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
The temperature field of a horizontal cylinder in natural convection is studied experimentally using a lateral shearing interferometer (LSI) with a large shear amount. Real-time interferograms are obtained with and without the cylinder. The surface temperature of the cylinder dropped from 693.15 K to the ambient temperature 289.03 K. The temperature distribution around the cylinder was reconstructed and fitted using exponential and six-degree-polynomial functions. For high surface temperature, the results indicate that the six-degree-polynomial function has a considerable advantage over the exponential one. Experimental data were compared with that measured by thermocouples within a 0.19% derivation. LSI with a large shear amount can provide accurate measurement of the temperature field around a cylinder with a high surface temperature.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
The idea of using a spatial filtering velocimeter (SFV) to measure the velocity of a vehicle for an inertial navigation system is put forward. The presented SFV is based on a CMOS linear image sensor with a high-speed data rate, large pixel size, and built-in timing generator. These advantages make the image sensor suitable to measure vehicle velocity. The power spectrum of the output signal is obtained by fast Fourier transform and is corrected by a frequency spectrum correction algorithm. This velocimeter was used to measure the velocity of a conveyor belt driven by a rotary table and the measurement uncertainty is ∼0.54%. Furthermore, it was also installed on a vehicle together with a laser Doppler velocimeter (LDV) to measure self-velocity. The measurement result of the designed SFV is compared with that of the LDV. It is shown that the measurement result of the SFV is coincident with that of the LDV. Therefore, the designed SFV is suitable for a vehicle self-contained inertial navigation system.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
We have implemented a simple digital system for long-term frequency stabilization and locking to an arbitrary wavelength of the single-frequency ring CW Ti:Sapphire laser. This system is built using two confocal Fabry-Pérot cavities, one of which is used to narrow the short-term linewidth of the laser and the other to improve the long-term stability of the laser frequency. The length of the second cavity is stabilized using the radiation from an external-cavity diode laser locked to an atomic transition. Our system is an improvement of a commercial Tekhnoscan laser lock. This system has been successfully used in our experiments on high-resolution laser spectroscopy of ultracold rubidium Rydberg atoms.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
TOPICS: Calibration, Error analysis, Star sensors, Integrated modeling, Sensor calibration, Distortion, Stars, Optical engineering, Data modeling, Monte Carlo methods
The performance of star sensors largely depends on the accuracy of the model parameter estimation carried out through calibration. Measurement errors in the calibration data would cause estimated values to deviate from the actual values and couple with one another. Only the intrinsic parameters estimated through calibration are useful to star sensors. Thus, the coupling between estimated intrinsic and extrinsic parameters would affect star sensor accuracy. High-accuracy star sensors are significantly affected by such coupling between the aforementioned parameters. This study investigates the coupling between extrinsic and intrinsic parameters through calibration residual and starlight pointing error. A calibration method based on the decoupling of intrinsic and extrinsic parameters is then proposed. The proposed method uses the invariance of intrinsic parameters and estimates intrinsic parameters through simultaneous optimizations with distinct extrinsic parameters. In both the simulations and the experiment, the decoupling calibration effectively improves the accuracy of the intrinsic parameter estimation. Using the same calibration data, the intrinsic parameters’ estimation precision of a high-accuracy star sensor increased by a range from 50.83 to 86.47%.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
We present the numerical optimization and the technological development progress of x-ray optics based on asymmetric germanium crystals. We show the results of several basic calculations of diffraction properties of germanium x-ray crystal monochromators and of an analyzer-based imaging method for various asymmetry factors using an x-ray energy range from 8 to 20 keV. The important parameter of highly asymmetric monochromators as image magnifiers or compressors is the crystal surface quality. We have applied several crystal surface finishing methods, including advanced nanomachining using single-point diamond turning (SPDT), conventional mechanical lapping, chemical polishing, and chemomechanical polishing, and we have evaluated these methods by means of atomic force microscopy, diffractometry, reciprocal space mapping, and others. Our goal is to exclude the chemical etching methods as the final processing technique because it causes surface undulations. The aim is to implement very precise deterministic methods with a control of surface roughness down to 0.1 nm. The smallest roughness (∼0.3 nm), best planarity, and absence of the subsurface damage were observed for the sample which was machined using an SPDT with a feed rate of 1 mm/min and was consequently polished using a fine polishing 15-min process with a solution containing SiO2 nanoparticles (20 nm).
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
We design and simulate six- and seven-port optical routers based on Mach–Zehnder interferometer switches that are suitable for photonic networks-on-chip. The routers are composed of 12 and 22 switching elements as the possible 30 input/output and 42 input/output routing paths are verified at a data transmission rate of 20 Gbps for six- and seven-port optical routers, respectively. We use an OptiSystem simulator to evaluate the proposed optical routers from the aspects of insertion loss, Q-factor and minimum bit error ratio.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Wavefront coding involves the use of an asymmetrical phase mask to extend the depth of field of incoherent imaging systems. The performance of wavefront coding systems depends on designing a suitable phase profile to generate the defocus-invariant imaging characteristic. We proposed a square-root phase mask with two profile factors for achieving a steadier defocused modulation transfer function (MTF). Several evaluation methods are employed for the purpose of performance comparison between the proposed phase mask and the previously suggested phase masks under the constraint condition that the phase parameters are optimized at the same level of noise gain. Numerical results show that the square-root phase mask yields better properties in extended depth of field imaging, especially in acquiring defocus-invariant MTFs and eliminating image artifacts associated with the decoded images.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Reddish-orange emitting Eu3+-activated Ba3Gd(PO4)3 phosphors have been successfully synthesized by a conventional solid-state reaction. X-ray powder diffraction confirmed the phase formation. The photoluminescence excitation and emission spectra were investigated. The band gap of Ba3Gd(PO4)3 was estimated to be about 3.68 eV from the diffuse reflection spectrum. The temperature-dependent luminescence of Ba3Gd(PO4)3:Eu3+ was discussed, and the activation energy for thermal quenching was calculated as 1.74 eV. The fluorescence decay curve and the commission internationale de L’Eclairage value of Ba3Gd(PO4)3:Eu3+ phosphors were also investigated in detail. The phosphor presented high color purity. Ba3Gd(PO4)3:Eu3+ might be a promising reddish-orange emitting phosphor used in white light-emitting diodes.35104
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Physical optics modeling requires propagating optical wave fields from a specific radiometric source through complex systems of apertures and reflective or refractive optical components, or even complete instruments or devices, usually to a focal plane or sensor. The model must accurately include the interference and diffraction effects allowed by the polarization and coherence characteristics of both the initial optical wave field and the components and media through which it passes. Like a spherical wave and a plane wave, a Gaussian spherical wave (or Gaussian beam) is also a solution to the paraxial wave equation and does not change its fundamental form during propagation. The propagation of a Gaussian beam is well understood and easily characterized by a few simple parameters. Furthermore, a paraxial Gaussian beam can be propagated through optical systems using geometrical ray-trace methods. The decomposition of arbitrary propagating wave fields into a superposition of Gaussian beamlets is, thus, an alternative to the classical methods of propagating optical wave fields. This decomposition into Gaussian beamlets has been exploited to significant advantage in the modeling of a wide range of physical optics phenomena.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Chiral metamaterials have been a research area for many researchers due to their polarization rotation properties on electromagnetic waves. However, most of the proposed chiral metamaterials are designed depending on experience or time-consuming inefficient simulations. A method is investigated for designing a chiral metamaterial with a strong and natural chirality admittance by optimizing a grid of metallic pixels through both sides of a dielectric sheet placed perpendicular to the incident wave by using a genetic algorithm (GA) technique based on finite element method solver. The effective medium parameters are obtained by using constitutive equations and S parameters. The proposed methodology is very efficient for designing a chiral metamaterial with the desired effective medium parameters. By using GA-based topology, it is proven that a chiral metamaterial can be designed and manufactured more easily and with a low cost.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
In the high-power laser facility (SG-III), focusing 48 laser beams into the target center better than 50 microns (RMS) within a few picoseconds is dependent on the stringent specifications of thousands of large optics and also puts huge challenges on the engineering characteristics of the design and mounting. A parametric optomechanical method is proposed to evaluate the performance of a 400 mm large-aperture transport mirror. With theoretical modeling and numerical analysis, the impacts of assembly structure, manufacturing errors, mounting loads, and gravity on the mirror surface aberrations are calculated and discussed in detail. With field experiments and case studies, the proposed method shows a powerful performance on the mirror surface aberrations’ evaluation, and negative impacts of currently used mounting techniques for the mirror are found. Finally, a new assembly design is presented based on a discussion of its advantages.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
TOPICS: Modulation, Free space optics, Atmospheric turbulence, Polarization, Phase shift keying, Signal detection, Scintillation, Turbulence, Atmospheric optics, Signal to noise ratio
A transmission scheme is proposed which loads differential phase shift keying (DPSK) information and circular polarization shift keying (CPolSK) information on the same optical carrier for free space optical links through an atmospheric turbulent channel. Theoretical models of modulation and demodulation are derived and a design is specified to detect and recover the information with two mutually independent branches in order to meet the requirement for a high real-time transmission capacity and to entirely remove modulation-induced cross talk. Simulation results show that the CPolSK/DPSK system has a high tolerance to intensity scintillation and phase noise caused by atmospheric turbulence. A bit error rate performance comparison of a CPolSK system, a DPSK system, and a CPolSK/DPSK system is also presented to comprehensively demonstrate that the CPolSK/DPSK system outperforms the other two modulation techniques in terms of a high real-time transmission capacity.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
TOPICS: Orthogonal frequency division multiplexing, Modulation, Distortion, Optical engineering, Nonlinear optics, Receivers, Data communications, Interference (communication), Data conversion, Signal generators
High peak-to-average power ratio (PAPR) of the orthogonal frequency division multiplexing (OFDM) signal is one of the limitations to the transmission performance of an optical OFDM system. Many PAPR reduction techniques have been proposed in previous works. However, most of them only consider a single scheme while overlooking the complementary features of these techniques. We propose a twofold PAPR reduction technique called Hadamard transform combined with a partial transmit sequence (PTS) (HTCP). The proposed HTCP scheme combines the merits of two complementary techniques, i.e., Hadamard transform and PTS, to improve the performance of the optical OFDM system in terms of PAPR and bit error rate (BER). Furthermore, the side information generated in PTS is transmitted by pilot sequences which increase the utilization of subcarriers. Least square estimation is used to estimate the pilot signal’s phase to recover the side information. The HTCP scheme is theoretically analyzed in a direct-detection optical OFDM system. Simulation results show that the HTCP scheme has a better performance with regards to PAPR and BER compared with the case of applying only the Hadamard transform or PTS technique.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Traditional cable television (CATV) network configuration is mainly a branch topology. When fibers break, there are always disconnections of CATV and Internet access. Meanwhile, network service providers usually cannot be instantly informed of network breakage; network problems are noticed only after the users call for services. Network breakage location detection and repair are, in general, costly and time-consuming. This paper proposes a new framework to protect CATV fiber optic networks, where a HUB with multiple optical protection switching (OPS) is constructed between the head end and the fiber nodes. The first layer ranging from the head end to the HUB forms a 1+1 protection path ring structure. The second layer ranging from the HUB to the fiber nodes forms multiple 1+1 protection path ring structures. The framework can form a four fiber optic path protection architecture with multiple ∞-shapes between the head end and the fiber nodes. When the CATV network system experiences a malfunction, such as fiber optic cable breakage or poor signal quality, OPS can immediately switch the fiber transmission path in order to maintain uninterrupted CATV network traffic. After simulation tests on fiber path switching time automatic protection switching, frame loss, packet jitter, latency, bit errors, and system traffic flow monitoring by manually switching OPS and pulling broken fiber optic cable, results show that the fiber path protection switching mechanism can react immediately, and test data results show that network traffic is unaffected, so the proposed framework can effectively enhance the survivability and quality of service of CATV network systems.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
A dual-parameter optical fiber sensor is proposed and demonstrated. It is based on an intermodal interferometer (IMI) with an inline embedded fiber Bragg grating (FBG). The IMI is formed by cascading a taper structure and a spherical-shaped structure through a segment of a single-mode fiber. Due to the different wavelength shifts of the IMI and FBG to temperature and liquid level, simultaneous measurement can be achieved. Experimental results indicate a good linear relation between the wavelength shift and external parameters (temperature and liquid level). The sensitivities of 0.066 nm/°C and −0.133 nm/mm are achieved experimentally for temperature and liquid level, respectively. The interesting properties of the sensor include good operation linearity, compact size, and high sensitivity.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Acousto-optically Q-switched operation of a Ho:SSO laser is reported for the first time. An average power of 2.23 W was obtained at a pulse repetition frequency from 5 to 20 kHz, with a corresponding to optical-to-optical conversion efficiency of 14.4% and a slope efficiency of 20%. The highest energy per pulse of 0.44 mJ in 28 ns was achieved at 2112 nm with a repetition rate of 5 kHz and peak power of 15 kW. The lifetime of Ho3+ in the Sc2SiO5 crystal host was also measured.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
The orthogonal frequency division multiplexing (OFDM) modulation technique has been used widely in visible light communications (VLC) systems to combat intersymbol interference. At the same time, the inherent drawback of OFDM with a high peak-to-average power ratio (PAPR) is brought into OFDM visible light communications (VLC-OFDM). Furthermore, considering the limited dynamic range characteristics of light-emitting diodes, the performance degradation caused by a high PAPR is more serious in VLC-OFDM. In this paper, we propose a partial transmit sequence (PTS) technique based on the combination of a genetic algorithm (GA) and a hill-climbing algorithm (GH-PTS) to solve the problem of high PAPR. GH-PTS is a modified PTS technique based on GA-PTS. Essentially, GH-PTS is a local optimization of GA-PTS. Simulation results show that the optimized technique is able to reduce PAPR more effectively without any loss of bit error rate performance than the GA-PTS technique in VLC-OFDM system.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
The gain flatness of an L-band erbium-doped fiber amplifier (EDFA) is still an open issue. We improve the conventional single-pass two-stage configuration by placing a fiber Bragg grating (FBG) with the center wavelength at 1529.4 nm. Then, a weak lasing resonance cavity is formed by this FBG and a fiber isolator, which is able to increase the pump conversion efficiency by reflecting the residual amplified spontaneous emission and compressing the raised gain around 1570 nm based on the gain-clamped effect. The experimental results show that by adopting the proposed scheme, the gain un-flatness of the L-band EDFA is controlled within ±0.4dB in the range of 1570 to 1610 nm, and an ∼29 dB average gain is simultaneously maintained.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
We propose and experimentally demonstrate a hybrid CATV/16-QAM-Digital CATV/16-QAM-OFDM in-building network over a 40-km single-mode fiber and graded index-plastic optical fiber/10-m visible light communication. The application of external injection technology with the addition of an optoelectronic feedback that raises the resonance frequency of the laser diode results in increased system transmission capability. Good performances of carrier-to-noise ratio, composite second-order, and composite triple-beat are obtained for the CATV signal. A low bit-error-rate value is achieved for the 16-QAM-Digital CATV/16-QAM-OFDM signal.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Contradictions among receiver optical power, bandwidth of photodiode, and transmission distance are ubiquitous in visible light communication (VLC) systems. In order to moderate such contradictions and improve the performance of VLC systems, we proposed a space diversity receiver for a light-emitting diode (LED)-based VLC system and experimentally demonstrated the highest data rate for an RGB LED with a 1.4 Gbit/s data rate employing two detectors located in different space positions at the same time. The maximal ratio combining algorithm was used in the VLC system for the first time. As a result, the bit error ratios of the receivers can be reduced by 48.08 dB (red LED), 12.04 dB (green LED), and 27.48 dB (blue LED) compared with any separate detector. The performance of the VLC system was significantly improved. It turned out that it was highly desirable to use multiantennas in the VLC system.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Molybdenum oxide (MoOx) and nickel oxide (NiOx) thin films were deposited by reactive biased target ion beam deposition. MoOx thin film resistivity varied from 3 to 2000 Ω·cm with a temperature coefficient of resistance (TCR) from −1.7% to −3.2%/K, and NiOx thin film resistivity varied from 1 to 300Ω·cm with a TCR from −2.2% to −3.3%/K, both easily controlled by varying the oxygen partial pressure. Biased target ion beam deposited high TCR MoOx and NiOx thin films are polycrystalline semiconductors and have good stability in air. Compared with commonly used vanadium oxide thin films, MoOx or NiOx thin films offer improved process control for resistive temperature sensors.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Negative refractive-photonic crystal (NR-PC) lenses that can exceed the diffraction limit of focus resolution for imaging and target detection in the near field have gotten more and more special attention in recent years. Three flat lens groups with Ag defects based on NR-PC are designed, and the focusing imaging in the NR-PC three flat lens groups is concluded with the extension of Snell’s law, and the influence on the resolution for a target detection dynamic scanning scheme is simulated by using the finite difference time domain method. An optimal-doped structure with Ag defects is achieved by different simulation combinations. The refocusing resolution 0.18834λ is achieved in the optimal structure and there is approximately a 0.06806λ improvement in the refocusing resolution compared to those undoped with Ag (0.2564λ); it also possesses distinct smaller side-lobes than a single flat lens doped with Ag. This means the optimal detecting ability for the three NR-PC flat lens groups with Ag defects is more improved than that for a single undoped and doped with Ag. This is significant for the perfect imaging being achieved for a particle structure.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
We present the design of a parabolic multimode waveguide used as a spot size width converter. The designed structure allows reducing the input spot size width an order of magnitude using a very short structure with respect to linear or conventional tapers. An illustrative example of spot width reduction from 10 microns to a Si wire of 1 micron with a small length in the order of 17 microns and a coupling efficiency of ∼90% is presented. Using a linear taper structure with a taper length >100 μm, the coupled power is still less than that obtained by the parabolic multimode interference (PMMI) guide. This means that the PMMI offers a length reduction of more than 5× with respect to the linear taper to achieve the same spot reduction.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
In order to reduce the polarization-induced impact on the incoherent optical frequency domain reflectometry based single-mode fiber-optic distributed temperature sensor, a synchronous polarization scrambling technique with a low-speed electrically driven polarization controller (EPC) is presented. The polarization-induced error is derived by error analysis. By simulating the distribution of the states of polarization on the Poincare sphere, optimized EPC driven parameters are selected. The polarization scrambling process is synchronous with the frequency response measurement of the Raman backscattered light. Additionally, the scrambling period is set to be equal to the measurement time of each frequency response. Experimental results show that the polarization-induced error is ∼±3°C, and it is basically in accord with the result of a theoretical error analysis. By using the synchronous polarization scrambling technique, the polarization-induced fluctuation of the measured temperature distribution has been almost eliminated.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
An efficient temperature measuring and monitoring method in an interferometric fiber-optic gyroscope (FOG) for space application is presented. Resource-saving digital temperature sensors and integrated optical-circuit temperature sensors are designed and separately implemented in a field programmable gate array and the second closed loops of FOG. A multipoint temperature measurement in FOG is conducted using both kinds of temperature sensors. An FOG status-monitoring strategy is proposed by defining a status index based on multipoint temperature information and heat-transmission model of our four-axis FOG structure. Temperature measurement and status-monitoring strategy are verified by experimental results.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
The effect of an oxygen atmosphere on the expansion dynamics of a laser-produced vanadium-oxygen plasma has been investigated using a fast intensified charged-coupled device camera. We find regimes of the plasma plume expansion ranging from a free plume at vacuum and low oxygen pressures, through collisional and shock-wave-like hydrodynamic regimes at intermediate oxygen pressure, finally reaching a confined plume with subsequent thermalization of the plume particles at the highest pressure of the oxygen gas. Vanadium oxide nanostructures thin films were synthesized from this plasma and the resulting vanadium oxide phases studied as a function of the plume dynamics. We found monoclinic vanadium dioxide (VO2) (M1) and VO2 (B) nanoparticles in thin films deposited at 0.05 mbar. Pure phases of vanadium trioxide (V2O3) smooth and pentoxide (V2O5) nanorods thin films were detected at 0.01 and 0.1 to 0.2 mbar, respectively. Thin films containing VO2 (M1) were found to have a reversible metal-to-insulator transition at 61°C. This work paves the way to VO phase control by judicious choice of laser and plasma conditions.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
Doping titanium dioxide (TiO2) with impurities has been extensively investigated for the optimal use of solar energy in order to improve photocatalyst performance. Density functional theory calculations are performed to investigate the effects of Tm doping on the energy band structures and optical properties of anatase TiO2 with various doping concentrations. The results show that Tm doping can effectively reduce the band gap of pure anatase TiO2 by introducing Tm 4f states above the top of the valence band, and thus results in a red shift in the optical absorption edges. Furthermore, the calculations of optical properties indicate that Tm doping TiO2 at low levels presents the prominent optical absorbance in the low energy region. Our results have important implications for the understanding and further development of photocatalytic functionalities of anatase TiO2 by introducing a dopant for effective band gap engineering.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
In recent years, considerable research has been carried out relative to the electromagnetic (EM) propagation and refraction characteristics in metamaterials with emphasis on the origins of negative refractive index. Negative refractive index may be introduced in metamaterials via different methods; one such is the condition whereby the Poynting vector of the EM wave is in opposition to the group velocity in the material. Alternatively, negative refractive index also occurs when the group and phase velocities in the medium are in opposition. The latter phenomenon has been extensively investigated in the literature, including recent work involving chiral metamaterials with material dispersion up to the first order. This paper examines the possible emergence of negative refractive index in dispersive chiral metamaterials with material dispersion up to the second order. The motivation is to determine if using second- as opposed to first-order dispersion may lead to more practical negative index behavior. A spectral approach combined with a slowly time-varying phasor analysis is applied, leading to the analytic derivation of EM phase and group velocities, and the resulting phase and group velocities and the corresponding phase and group indices are evaluated by selecting somewhat arbitrary dispersive parameters. The results indicate the emergence of negative index (via negative phase indices along with positive group indices, as reported in the literature) or negative index material (NIM) behavior over information bandwidths in the low RF range. The second-order results are not significantly better than those for first-order results based on the theoretical analysis; however, greater parametric flexibility exists for the second-order system leading to the higher likelihood of achieving NIM over practical frequency bands. The velocities and indices computed using the Lorentzian and Condon models yield an NIM bandwidth around 200−400Mrad/sec, about 2 orders of magnitude higher than that for the parametric approach; more importantly, NIM is found not to occur in the first order when using practical models.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
The phase-only liquid crystal on silicon (LCOS) spatial light modulator has been used as a wavefront generator and reconstruction device for display applications due to its phase-only modulating property of incident light. In order to achieve the best reconstructed phase modulated wavefront, the properties of LCOS have to be fully known. The intensity of reflected light from LCOS decreases under normal incidence by going through a beam splitter. In order to improve the intensity of the reflected light beam, the oblique incidence is preferred during many applications. The oblique incidence characterization of a parallel aligned LCOS is investigated at a working wavelength of 532 nm on the basis of double-hole interferometric method. Through experiments, the phase modulation characterization of LCOS under the oblique incidence is obtained. In addition, an image postprocessing method is proposed to overcome the effect of flicker and coherent noise by simplifying the computation and increasing the measurement accuracy. The comparison of experimental results for different incident angles indicates that it plays an important role in the performance of phase modulation of LCOS, where the phase modulation decreases with the increasing angle of incidence.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
This paper reports on the investigation of the electrically controlled multifocus, multi-imaging characteristics of an on-axis holographic polymer-dispersed liquid-crystal (H-PDLC) Fresnel lens. The Fresnel lens is examined within a PDLC cell through the analysis of interference fringes generated by on-axis plane and spherical waves. Experiments are conducted to investigate the multifocus and multi-imaging phenomena of the H-PDLC Fresnel lens, and a corresponding geometrical optical analysis is also provided. It is then demonstrated that the H-PDLC Fresnel lens is a plane-surface diffractive optical device which modulates the phase of incident light through a periodic change of refractive index and forms multiple symmetrical images. Its diffraction properties, which can be controlled electrically, have further potential applications in this field.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.
A comprehensive study has been performed to achieve all-angle self-collimation in basic two-dimensional square array photonic crystals with cylindrical scatterers. Based on plane wave expansion and finite difference time domain analysis for both rod- and hole-type structures, we report on all-angle self-collimation (SC) in the first band of the structure, which results in loss suppression due to out-of-plane scatterings. A lower threshold for index contrast has been obtained to achieve all-angle SC, which offers more design flexibility regarding structural parameters. Furthermore, it has been shown that a minimum and maximum coupling efficiency enhancement of ∼40% and 80% can be achieved for the proposed structure, respectively, by introducing a row of scatterers with proper radius at the input and the output air/photonic crystal interfaces.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.