I’ve been reading about my ancestors from the Driggers side who were in Florida before it became a state in 1845. One such history book is called Gators, Skeeters, and Malary, by Judge E. C. May. The book reminds me about a joke about this elderly man who had lost most of his hearing. He finally decided to go see a specialist, who fitted him with state-of-the-art hearing aids. They worked great, and he could hear everything again. After a few weeks, the man came back to the doctor for a follow up visit, and the doctor noted that the hearing aids were working perfectly. He said, “Everything looks good, I’m glad your hearing has improved so much. Your family must be thrilled that you can hear again.” “Oh no,” the man answered, “I haven’t told any of them about the hearing aids. I just sit quietly, listening to everything they say. I’ve changed my will four times.” I wish I could tell you where that came from originally to give proper attribution, but I can tell you that I did not come up with it even though it cracks me up. I can laugh at this now that I have received an offer from AARP to become a member (I am still thinking about it).

Since the early 1980s when the Airborne Laser Laboratory (ALL) first demonstrated that a high-energy laser flown in a military aircraft was capable of performing both offensive and defensive missions, the concept of a speed-of-light weapon system has been in the mind of future weapons planners. The ALL used a powerful CO₂ laser which lased at 10.6 μm. The maximum intensity at the target for a diffraction-limited beam of power P_o and aperture A is related to the inverse of wavelength λ times distance to the target R squared:

A method for extracting the convection speed and direction of aberrations present in wavefronts due to aero-optical turbulence over the pupil of a turret on the side of an airborne platform is addressed. The method is applied to data from the Airborne Aero-Optics Laboratory (AAOL). Such convection information is useful in designing feed-forward adaptive-optic approaches. The method makes use of a four-beam Malley probe technique derived by constructing a two-dimensional (2-D) local convective velocity-distribution over the beam's aperture. This technique is based on extending the analysis of the Notre-Dame-developed Malley probe. Two wavefront datasets (Azimuth 157 deg and Elevation 40 deg; Azimuth 42 deg and Elevation 43 deg) from the AAOL are analyzed using the derived method, the first where the laser propagates through fully-separated flow and the second where the laser propagates through an attached-flow region. Finally, the 2-D proper orthogonal decomposition is applied to one in-flight measured dataset to determine the spatial requirements of deformable mirrors in an adaptive-optics system. The paper concludes with a discussion that points out the usefulness of the 2-D velocity-distributions in characterizing the various flow structures which convect over the aperture.

We discuss aspects of the development of the Airborne Laser Laboratory. Our discussion is historical in nature and consists of the text from a speech given on the occasion of the Airborne Laser Laboratory leaving Kirtland Air Force Base (AFB) to fly to Wright-Patterson AFB to become an exhibit at the National Museum of the United States Air Force. The last part of the discussion concerns the inception of the study of aero-optics as an area of research and some of the milestones in the understanding of the causes and prediction of aero-optical effects.

Results of recent experimental measurements of aero-optical distortions caused by turbulent boundary layers at subsonic speeds M=0.4…0.6 are presented. Measurements were performed using a high-speed Shack-Hartmann sensor to collect instantaneous wavefronts with high spatial and temporal resolution, accompanied by wavefront measurements with a Malley probe. Effects of different aperture sizes on levels of aero-optical aberrations and detailed statistical analysis of spatial and temporal spectra of aero-optical distortions for both wavefront sensors are presented and discussed.

Recent in-flight aero-optical measurements from the Airborne Aero-Optics Laboratory are provided, along with instrumentation and experimental set-up. Results of an extensive survey of the aero-optical environment at different viewing angles, for both flat-window and conformal-window turrets at different subsonic and low transonic speeds below M=0.65 , are presented, compared and extensively discussed. A comparison between two turret geometries, hemisphere-on-cylinder and hemisphere only, plus the statistical analysis of wavefronts at different viewing angles, are also presented and discussed. Additionally, dynamics of a local shock appearing on the conformal-window turret at transonic Mach number are discussed.

A new method for adaptive prediction and correction of wavefront errors in adaptive optics (AO) is introduced. The new method is based on receding-horizon control design and an adaptive lattice filter. Experimental results presented illustrate the capability of the new adaptive controller to predict and correct aero-optical wavefronts derived from recent flight-test data. The experimental results compare the performance of the new adaptive controller the performance of a minimum-variance adaptive controller previously used in AO. These results demonstrate the reduced sensitivity of the receding-horizon adaptive controller to high-frequency sensor noise.

Numerical databases established by large-eddy simulations of subsonic turbulent boundary layers and separated shear layers are utilized to simulate Malley probe measurements and investigate their accuracy and consistency with the data obtained from two-dimensional (2-D) wavefront sensors. It is found that the Malley probe data give a good approximation for the boundary layer and a reasonable approximation for the separated shear layer in terms of the root mean square of optical path difference (OPD rms ) and the streamwise correlations of OPD. The OPD rms from the Malley probe is slightly smaller than that from the 2-D wavefront sensor with the same streamwise aperture size for both flows. It is shown that the use of multiple Malley probes in the transverse direction of the flow can enhance the accuracy of measurements. The spatial correlations of OPD obtained from simulated multi-Malley-probe data are also examined and compared to those from 2-D wavefront sensors.

We provide a background into aero-optics, which is the effect that turbulent flow over and around an aircraft has on a laser projected or received by an optical system. We also discuss the magnitude of detrimental effects which aero-optics has on optical system performance, and the need to measure these effects in flight. The Airborne Aero-Optics Laboratory (AAOL), fulfills this need by providing an airborne laboratory that can capture wavefronts imposed on a laser beam from a morphable optical turret; the aircraft has a Mach number range up to low transonic speeds. We present the AAOL concept as well as a description of its optical components and sensing capabilities and uses.

The effect of subsonic turbulent boundary layer aero-optical disturbances on a conformal phased array for laser beam projection operating on a high-speed aircraft is considered. We employ a basic model for subsonic boundary layer disturbances developed by Cress et al. which is governed by the displacement thickness δ ∗ to bound the magnitude of the problem, to determine the basic phenomenology affecting phased array performance, and to quantify requirements for compensation of these disturbances in the array subapertures. We used δ ∗ =15  mm as a baseline value in quantifying phased array effects on a 7-aperture hexagonal array with 10 cm subapertures. Boundary layer piston and tilt disturbances dominate array effects, but higher-order disturbances are similar in magnitude to the differential piston over the array and 2× greater in magnitude than an upper bound on free-stream turbulence. Adaptive optics compensation of turbulent boundary layer disturbances in such a phased array requires error rejection bandwidths <1  kHz for high-fidelity array performance.

We modeled the imaging performance of an acquisition, tracking, and pointing sensor when operating on a high-speed aircraft platform through a turreted laser beam director/telescope. We applied standard scaling relations to wavefront sensor (WFS) data collected from the Airborne Aero-Optics Laboratory test platform operating at Mach 0.5 to model aero-optical aberrations for a λ=1  μm wavelength laser system with a D_ap =30  cm aperture diameter and a 90-cm turret diameter on a platform operating at 30 kft and for speeds of Mach 0.4 to 0.8. Using these data, we quantified the imaging point spread function for each aircraft speed. Our simulation results show Strehl ratios from 0.1 to 0.8 with substantial scattering of energy out to 7.5× the diffraction-limited core. Analysis of the imaging MTF shows a rapid reduction of contrast for low-to-mid range spatial frequencies with an increasing Mach number. Low modulation contrast at higher spatial frequencies limits imaging resolution to <2× diffraction-limit at Mach 0.5 and 5× diffraction-limit at Mach 0.8. Practical limits to usable spatial frequencies require higher image signal to noise ratio in the presence of aero-optical disturbances at a high Mach number. Illuminator laser propagation through aero-optical aberrations produces target illumination modulation at scale sizes near the diffraction-limit of the transmitting laser aperture, thereby producing illumination artifacts that can degrade image-contrast-based tracking algorithms.

Wavefront measurements from wind tunnel or flight testing of an optical system are affected by jitter sources due to the measurement platform, system vibrations, or aero-mechanical buffeting. Depending on the nature of the testing, the wavefront jitter will be a composite of several effects, one of which is the aero-optical jitter; i.e., the wavefront tilt due to random air density fluctuations. To isolate the aero-optical jitter component from recent testing, we have developed an estimation technique that uses only higher-order wavefront measurements to determine the jitter. By analogy with work done previously with free-stream turbulence, we have developed a minimum mean-square error estimator using higher-order wavefront modes to compute the current-frame tilt components through a linear operation. The estimator is determined from computational fluid dynamics evaluation of aero-optical disturbances, but does not depend on the strength of such disturbances. Applying this technique to turret flight test data, we found aero-optical jitter to be 7.7±0.8  μrad and to scale with (ρ/ρ _SL )M² (∼1  μrad in the actual test cases examined). The half-power point of the aero-optical jitter variance was found to be ∼2u _∞ /D_t and to roll off in temporal frequency with a power law between f ^−11/3 and f ^−10/3 .

This paper’s text is taken from a monograph written by the author in 1988. Some of the material contained here has been referenced in the open literature attributed to a private communication. This reprinting of the content of the monograph is and should be viewed as a historic paper documenting the author’s thoughts and knowledge as of 1988 and does not reflect developments since that time.

Spot estimation accuracy of Shack-Hartmann images and its impact on Airborne Aero-Optic Laboratory (AAOL) wavefront statistics are addressed. A study is conducted of an individual spot simulated using a double sinc function under varying degrees of additive non-zero mean Gaussian noise within a 15×15 pixel area-of-interest. The focus of this paper is two-fold. First, the accuracy of four existing centroiding methods including first moment, convolution, Gaussian, and weighted first moment are compared. It is found that the weighted first moment centroid most accurately estimates spot centers but requires significantly more computational time with respect to the first moment method. Second, three image-processing techniques, including gamma correction, thresholding, and windowing, are analyzed to determine their influence on each centroiding method’s spot estimation accuracy. A fourth order gamma correction significantly reduces spot estimation error for three centroiding methods. The key result is that the accuracy of the first moment centroid with an applied gamma correction is comparable to the weighted first moment without the computational burden. Finally, the first moment centroid with gamma correction and weighted first moment centroid are applied to AAOL flight data. Wavefront statistics are computed and compared to the commonly used first moment centroid.

We discuss spatial-temporal characterizations of recent in-flight Airborne Aero-Optics Laboratory wavefront measurements at transonic speeds (Mach 0.65) with a conformal window turret as a function of turret pointing angle. Using both proper orthogonal decomposition and dynamic mode decomposition modal analysis methods, the flow dynamics are characterized. The conformal window wavefronts show shock formation between 85 deg and 90 deg and shear layer formation at a considerably lower turret aft pointing angle than would be expected at subsonic speeds without shock. At larger aft pointing angles, shear layer vortex roll-up dynamics dominate the aero-optical disturbances. In particular, the spatially and temporally periodic vortices grow in width and magnitude while the corresponding oscillation frequency drops with increasing look-back angle, thus maintaining a near constant vortex convection speed equal to about 0.6 times the free-stream velocity. From these results, a modified form of the aero-optics frequency scaling relation is proposed that yields a Strouhal number independent of turret look-back angle in the portion of the flow dominated by such Kelvin-Helmholtz shear layer vortices.

We address the design, development, and testing of a pointer/tracker as a probe beam for the purpose of making high-speed, aero-optical measurements of the flow over a scaled beam director turret. The tracker uses retro-reflection of the probe beam off of a Reflexite annulus surrounding the turret. The constraints of the design required a near-total-commercial off the shelf system that could be quickly installed and removed in a rented aircraft. Baseline measurements of environmental vibrations are used to predict pointing performance; mitigation of line-of-sight jitter on the probe beam is achieved through passive isolation and the design of relay optics. Accommodation of ambient light is made with the use of wavelength filters and track algorithms. Postanalysis of measured data is compared to design estimates.

The Airborne Aero-Optical Laboratory has produced a large database of aero-optical measurements with a high-speed, high-resolution Shack Hartmann wavefront sensor. The data have been collected over a wide range of flight conditions. An analysis of the statistical characteristics of the subsonic and early transonic data is performed to assess the adequacy of the spatial and temporal resolution of the data. Sample rate requirements for a minimum variance phase estimator are also explored. The techniques employed are validated by application to measurements of optical atmospheric turbulence where results can be anticipated based on established Kolmogorov statistics.

In-flight wavefront measurements around a flat-window turret at subsonic Mach numbers are analyzed in instantaneous and time-averaged sense. In addition to the root-mean-squared levels of aero-optical distortions, higher-order spatial statistics are calculated, and their dependence as a function of the viewing angle is discussed. Given the optical data obtained, the applicability of the commonly used large aperture approximation (LAA) is revisited. We show that, for all angles, the LAA consistently underestimates the time-averaged Strehl ratio, so the LAA should be used very cautiously. Some reasons for these discrepancies are traced to non-Gaussian spatial distribution of the optical wavefronts. A different approximation for computing time-averaged Strehl ratios is proposed, and the results are discussed.

Imaging and laser beam propagation from airborne platforms are degraded by dynamic aberrations due to air flow around the aircraft, aero-mechanical distortions and jitter, and free atmospheric turbulence. For certain applications, like dim-object imaging, free-space optical communications, and laser weapons, adaptive optics (AO) is necessary to compensate for the aberrations in real time. Aero-optical flow is a particularly interesting source of aberrations whose flowing structures can be exploited by adaptive and predictive AO controllers, thereby realizing significant performance gains. We analyze dynamic aero-optical wavefronts to determine the pointing angles at which predictive wavefront control is more effective than conventional, fixed-gain, linear-filter control. It was found that properties of the spatial decompositions and temporal statistics of the wavefronts are directly traceable to specific features in the air flow. Furthermore, the aero-optical wavefront aberrations at the side- and aft-looking angles were the most severe, but they also benefited the most from predictive AO.

A state-space disturbance model and associated prediction filter for aero-optical wavefronts are described. The model is computed by system identification from a sequence of wavefronts measured in an airborne laboratory. Estimates of the statistics and flow velocity of the wavefront data are shown and can be computed from the matrices in the state-space model without returning to the original data. Numerical results compare velocity values and power spectra computed from the identified state-space model with those computed from the aero-optical data.

Nowadays, we cannot imagine our life without video content and without devices that enable us to acquire and display such content. According to recent research, in 2012, the video content transfer over the Internet was around 60% of the overall Internet data transfer, and the overall video transfer (including the Internet) could reach 90% during the next four years. The TV sets supporting only full high-definition (HD) resolution (i.e., 1080p) are already considered to be outdated due to a dramatic demand for the ultra-HD resolution that often refers to 3840×2160 (4K) or 7680×4320 (8K) resolutions. So, what are the key factors for such tremendous progress? If you are reading this special section on video compression technology, we are sure that you know the answer…

We propose a fast new multiple run_before decoding method in context-adaptive variable length coding (CAVLC). The transform coefficients are coded using CAVLC, in which the run_before symbols are generated for a 4×4 block input. To speed up the CAVLC decoding, the run_before symbols need to be decoded in parallel. We implemented a new CAVLC table for simultaneous decoding of up to three run_befores. The simulation results show a Total Speed-up Factor of 205%∼144% over various resolutions and quantization steps.

A spatial and interlayer hybrid intra-prediction (SILHIP) scheme is proposed in this work to improve the coding efficiency of the scalable video coding (SVC) standard. The SVC standard adopts a line-by-line intra-prediction that predicts the texture information of a block by exploiting the spatial correlation between adjacent blocks. However, the accuracy of the line-by-line intra-prediction deteriorates when a target block lies in the edge region. The proposed SILHIP scheme adaptively predicts a target block by exploiting both the spatial correlation and the interlayer correlation between the base layer and the enhancement layer. To implement the SILHIP scheme, we partition a macroblock into two regions based on the edge map and allow different types of prediction schemes to be used in different regions. It is shown by experimental results that the proposed SILHIP scheme outperforms the conventional one consistently.

The high efficiency video coding (HEVC) video coding standard under development can achieve higher compression performance than previous standards, such as MPEG-4, H.263, and H.264/AVC. To improve coding performance, a quad-tree coding structure and a robust rate-distortion (RD) optimization technique is used to select an optimum coding mode. Since the RD costs of all possible coding modes are computed to decide an optimum mode, high computational complexity is induced in the encoder. A fast learning-based coding unit (CU) size selection method is presented for HEVC intra prediction. The proposed algorithm is based on theoretical analysis that shows the non-normalized histogram of oriented gradient (n-HOG) can be used to help select CU size. A codebook is constructed offline by clustering n-HOGs of training sequences for each CU size. The optimum size is determined by comparing the n-HOG of the current CU with the learned codebooks. Experimental results show that the CU size selection scheme speeds up intra coding significantly with negligible loss of peak signal-to-noise ratio.

Advanced inter-prediction modes are introduced recently in literature to improve video coding performances of both H.264 and High Efficiency Video Coding standards. Decoder-side motion analysis and motion vector derivation are proposed to reduce coding costs of motion information. Here, we introduce enhanced skip and direct modes for H.264 coding using decoder-side super-resolution (SR) and frame interpolation. P- and B-frames are downsampled and H.264 encoded at lower resolution (LR). Then reconstructed LR frames are super-resolved using decoder-side motion estimation. Alternatively for B-frames, bidirectional true motion estimation is performed to synthesize a B-frame from its reference frames. For P-frames, bicubic interpolation of the LR frame is used as an alternative to SR reconstruction. A rate-distortion optimal mode selection algorithm is developed to decide for each MB which of the two reconstructions to use as skip/direct mode prediction. Simulations indicate an average of 1.04 dB peak signal-to-noise ratio (PSNR) improvement or 23.0% bitrate reduction at low bitrates when compared with H.264 standard. The PSNR gains reach as high as 3.00 dB for inter-predicted frames and 3.78 dB when only B-frames are considered. Decoded videos exhibit significantly better visual quality as well.

Improving error resilience of video communications over packet lossy channels is an important and tough task. We present a framework to optimize the quality of video communications based on distributed video coding (DVC) in practical packet lossy network scenarios. The peculiar characteristics of DVC indeed require a number of adaptations to take full advantage of its intrinsic robustness when dealing with data losses of typical real packet networks. This work proposes a new packetization scheme, an investigation of the best error-correcting codes to use in a noisy environment, a practical rate-allocation mechanism, which minimizes decoder feedback, and an improved side-information generation and reconstruction function. Performance comparisons are presented with respect to a conventional packet video communication using H.264/advanced video coding (AVC). Although currently the H.264/AVC rate-distortion performance in case of no loss is better than state-of-the-art DVC schemes, under practical packet lossy conditions, the proposed techniques provide better performance with respect to an H.264/AVC-based system, especially at high packet loss rates. Thus the error resilience of the proposed DVC scheme is superior to the one provided by H.264/AVC, especially in the case of transmission over packet lossy networks.

In error-prone environments, packets could be lost during the transmission of compressed video bitstream, and corrupted errors by the lost packets could be propagated until it meets a refresh point. To defect the error propagation, constrained intra-prediction in high efficiency video coding (HEVC) performs intra-prediction using only neighboring intra-coded samples. However, the errors could be propagated to intra-coded blocks by an in-loop filtering process, since the in-loop filtering is performed regardless of the prediction modes of blocks, even though constrained intra-prediction is used. In this paper, a constrained in-loop filtering is proposed to protect intra-coded samples from error propagation by adaptively applying filters depending on the prediction modes of reconstructed blocks. Simulation results show that the proposed method alleviates the distortion of the decoded pictures and thereby improves both subjective and objective quality compared with the HEVC standard.

Limited computing resources in portable multimedia devices are an obstacle in real-time video decoding of high resolution and/or high quality video contents. Ordinary H.264/AVC video decoders cannot decode video contents that exceed the limits set by their processing resources. However, in many real applications especially on portable devices, a simplified decoding with some acceptable degradation may be desirable instead of just refusing to decode such contents. For this purpose, a complexity-scalable H.264/AVC video decoding scheme is investigated in this paper. First, several simplified methods of decoding tools that have different characteristics are investigated to reduce decoding complexity and consequential degradation of reconstructed video. Then a complexity scalable H.264/AVC decoding scheme is designed by selectively combining effective simplified methods to achieve the minimum degradation. Experimental results with the H.264/AVC main profile bitstream show that its decoding complexity can be scalably controlled, and reduced by up to 44% without subjective quality loss.

An efficient down/upsampling method to compress a depth map efficiently within the high-efficiency video coding (HEVC) framework is presented. A different edge-preserving depth upsampling method is proposed by using both the texture and depth information. We take into account the edge similarity between depth maps and their corresponding texture images as well as the structural similarity among depth maps to build a weight model. Based on the weight model, the optimal minimum mean square error upsampling coefficients are estimated from the local covariance coefficients of the downsampled depth map. The upsampling filter is combined with HEVC to increase coding efficiency. The objective results demonstrate that we achieve a maximum bit rate saving of 32.2% compared to full resolution method and 27.6% compared to a competing depth down/upsampling method on depth bit rate. The subjective evaluation showed that our proposed method achieves better quality in synthesized views than existing methods do.

Bio-EMD, a biologically inspired fusion of visible and infrared (IR) images based on empirical mode decomposition (EMD) and color opponent processing, is introduced. First, registered visible and IR captures of the same scene are decomposed into intrinsic mode functions (IMFs) through EMD. The fused image is then generated by an intuitive opponent processing the source IMFs. The resulting image is evaluated based on the amount of information transferred from the two input images, the clarity of details, the vividness of depictions, and range of meaningful differences in lightness and chromaticity. We show that this opponent processing-based technique outperformed other algorithms based on pixel intensity and multiscale techniques. Additionally, Bio-EMD transferred twice the information to the fused image compared to other methods, providing a higher level of sharpness, more natural-looking colors, and similar contrast levels. These results were obtained prior to optimization of color opponent processing filters. The Bio-EMD algorithm has potential applicability in multisensor fusion covering visible bands, forensics, medical imaging, remote sensing, natural resources management, etc.

Recognizing degraded faces from low-resolution and blurry images is a common yet challenging task. We propose appealing solutions to this problem without any image reconstruction, without any limitation to blur type, and only using high-quality samples to design a classifier. Short-term Fourier transform (STFT) is an effective and concise transform for face recognition, yet its effectiveness depends on two important issues: one is face representation construction from STFT; the other is a scale-named window size of STFT. To deal with the first issue, we explore the increased discrimination brought by joint coding and using multiple frequency combinations. Specifically, we propose a novel local descriptor in which information of a pixel coming from two frequencies is jointly encoded and multiple two-frequency combinations are jointly utilized so as to construct a more descriptive and discriminative face representation. To deal with the second issue, we propose a multiscale fusion strategy that extracts multiple descriptors corresponding with multiple window sizes of STFT followed by equal weighted summation of outputs given by multiple scales. The experiments conducted on face databases confirm that state-of-the-art performance has been achieved by the proposed novel face representation and multiscale fusion strategy.

When the three-dimensional (3-D) video system includes a multiview video generation technique using depth data to provide more realistic 3-D viewing experiences, accurate depth map acquisition is an important task. In order to generate the precise depth map in real time, we can build a camera fusion system with multiple color cameras and one time-of-flight (TOF) camera; however, this method is associated with depth errors, such as depth flickering, empty holes in the warped depth map, and mixed pixels around object boundaries. In this paper, we propose three different methods for depth error reduction to minimize such depth errors. In order to reduce depth flickering in the temporal domain, we propose a temporal enhancement method using a modified joint bilateral filtering at the TOF camera side. Then, we fill the empty holes in the warped depth map by selecting a virtual depth and applying a weighted depth filtering method. After hole filling, we remove mixed pixels and replace them with new depth values using an adaptive joint multilateral filter. Experimental results show that the proposed method reduces depth errors significantly in near real time.

Recently, it has become necessary to evaluate the performance of display devices in terms of human factors. To meet this requirement, several studies have been conducted to measure the eyestrain of users watching display devices. However, these studies were limited in that they did not consider precise human visual information. Therefore, a new eyestrain measurement method is proposed that uses a liquid crystal display (LCD) to measure a user’s gaze direction and visual field of view. Our study is different in the following four ways. First, a user’s gaze position is estimated using an eyeglass-type eye-image capturing device. Second, we propose a new eye foveation model based on a wavelet transform, considering the gaze position and the gaze detection error of a user. Third, three video adjustment factors—variance of hue (VH), edge, and motion information—are extracted from the displayed images in which the eye foveation models are applied. Fourth, the relationship between eyestrain and three video adjustment factors is investigated. Experimental results show that the decrement of the VH value in a display induces a decrease in eyestrain. In addition, increased edge and motion components induce a reduction in eyestrain.

Quantization operation in the imaging process rounds the measured values of intensities into integers. It neglects the possible differences between the intensities having the same rounded numbers, and therefore lowers the grayscale resolution of images. Although some methods have been proposed for the reconstruction of high-grayscale resolution images from multiple subpixel-shifted low-spatial-resolution and low-grayscale-resolution images, the problems of nonsmooth transition within regions and insufficient intensity levels still exist. A grayscale superresolution method based on fill light and a photographing apparatus are proposed to deal with the problems. The photographing apparatus can add fill lights with slightly different intensities to the captured images without changing the brightness of scenes. Our reconstruction method is based on the method of estimating a float number from several rounded integers. Then, a high-grayscale-resolution image is reconstructed from multiple low-grayscale-resolution images with slightly different intensity fill lights. Simulated data and real-world data have been used for the evaluation of the method, and the experimental results show that our method effectively improves the grayscale resolution. Besides, our method is convenient for a graphics processing unit implementation.

An identification of human eye retinas by applying the covariance function and wavelet theory is presented. The estimations of the autocovariance functions of the two digital images or single image are calculated according to random functions, based on the vectors created from the digital image pixels. The estimations of the pixel’s vectors are calculated by spreading the pixel arrays of the digital images into single column. During the changing of the scale of the digital image, the wave frequencies of the colors of the single pixels are prekept, and the influence of the change of a scale in the procedures of the calculations of the covariance functions does not occur. The Red, Green, Blue (RGB) color model of the colors spectrum for the encoding of the digital images was applied. The influence of the RGB spectrum components and the tensor of colors on the estimations of the covariance functions were analyzed. The identity of the digital images is estimated by analysis of the changes of the correlation coefficient values in the corresponding diapason.

A back propagation artificial neural network (BP-ANN) has good self-learning, self-adaptation and generalization abilities, which we intend to use to interpolate an image. The interpolated pixels are classified into two regions, each region corresponding to one BP-ANN. In order to optimize the structure of the BP-ANN and the process of deinterlacing, three experiments were performed to test the architecture and parameters of region-based BP-ANN. The experimental results show that the proposed algorithm with an 8−16−1 structure provides the best balance between time consumption and visual quality. Compared to the other six advanced deinterlacing algorithms, our region-based BP-ANN method provides about an average of 0.14 to 0.64 dB higher peak signal-to-noise-ratio while maintaining high efficiency.

The development of a target acquisition performance model for an electro-optical imaging system is seriously affected by the description of the target and background characteristics at present. Based on the Hidden Markov Model (HMM), a different clutter metric is proposed to quantify the influence of background on target detection in this article. It first simulates the process of recording a target in the human brain by optimizing the HMM parameters to represent the target as far as possible. And then the background clutter is defined to be the similarity, estimated by the computed model parameters, between the target and background. Finally, the newly proposed clutter metric is applied to the Search2 database, and the experiment results prove its superiority to other metrics.

An automated approach for detecting the presence of watercraft in a maritime environment characterized by regions of land, sea, and sky, as well as multiple targets and both water- and land-based clutter, is described. The detector correlates a wavelet model of previously acquired images with those obtained from newly acquired scenes. The resulting detection statistic outperforms two other detectors in terms of probability of detection for a given (low) false alarm rate. It is also shown how the detection statistics associated with different wavelet models can be combined in a way that offers still further improvements in performance. The approach is demonstrated to be effective in finding watercraft in previously collected short-wave infrared imagery.

The modulation transfer function (MTF) is widely used as the image quality criterion of choice for imaging applications where fine detail in extended images needs to be specified or evaluated. We present a parametric analysis of the effect of scattered light upon the MTF of an imaging system and illustrate the results for three specific applications: (1) a visible Newtonian telescope with moderately good optical surfaces which produce no significant effect upon the MTF, (2) an extreme ultraviolet Newtonian telescope where scattering effects can dominate both diffraction effects and aberrations in the resulting image degradation even for state-of-the-art optical surfaces, and (3) a visible system made up of three diamond-turned off-axis aspheric mirrors where we use the predicted MTF to estimate whether post-polishing is required (huge cost and schedule impact) to meet a specific image quality requirement.

A new and simple method for measuring the refractive index of liquid substances is presented. In this method, a laser beam impinges transversely on a glass tube (cylindrical cell) filled with the liquid to be measured. The laser beam incident on the cylindrical cell is deviated when it propagates through the wall of the cell and the liquid contained in it. By measuring the deviation of the principal ray of the laser beam when it emerges from the cylindrical cell, we can determine the refractive index of the liquid. To show the feasibility of the method, we measured the refractive index of pure water with a He-Ne laser.

The goal of phase retrieval is to extract the phase of an optical wave field from intensity measurements. The transport-of-intensity equation (TIE)-based method is a popular deterministic solution and has been applied in various fields such as optical microscopy, electron microscopy, and x-ray imaging. For macro-imaging, a camera is often used to capture the images, and thus the phase modulation of the lens should be considered. A new formulation is proposed to extend TIE for phase retrieval in a lens-based wave propagation model. To obtain the defocus step, a data-collection-reading device is designed by equipping a camera with a micrometer caliper. Simulation and real experiments are conducted to test the proposed method.

A photon model is proposed, and the parameter equations of the photon are obtained. This model can explain the polarization, total reflection, evanescent wave, and Goos-Hanchen shift of a single photon. The evanescent waves of photons with different frequencies are refractively dispersed. The Goos-Hanchen shift is dependent on the difference between the two refractive indices of media, the incident angle, and the frequency of the photon. According to this model, an evanescent wave of light does not decay exponentially along the z direction and does not propagate along the x direction infinitely. The laws of refraction and reflection for a single photon can be derived. The refractive dispersion of light can be explained. According to this model, every photon is polarized. Polarization is the intrinsic nature of the photon. The motion of a single photon is either clockwise or counterclockwise. The so-called unpolarized light refers to light that consists of an equal number of photons with clockwise motion and counterclockwise motion. The trajectories of two photons with the same frequency but opposite spiral directions are mirror-image isomers. They cannot be superimposed upon each other.

Through modulating the Bessel–Gaussian radially polarized vector beam by the cosine synthesized filter under a reflection paraboloid mirror system with maximum focusing semi-angle of π/2 , arbitrary-length super-Gaussian optical needles are created with consistent beam size of 0.36λ (full width at half maximum) and the electric field being pure longitudinally polarized (polarization conversion efficiency greater than 99%). Numerical calculations show that the on-axis intensity distributions are super-Gaussian, and the peak-valley intensity fluctuations are all within 1% for 4λ , 6λ , 8λ , and 10λ long light needles. The method remarkably improves the nondiffraction beam quality, compared with the subwavelength Gaussian light needle, which is generated by a narrow-width annular paraboloid mirror. Such a light beam may suit potential applications in particle acceleration, optical trapping, and microscopy.

A method to calculate element misalignments in optical systems is presented. The method uses the wavefront information in the exit pupil in the form of Zernike coefficients and a function that relates them to the misalignment values. Three different functions with its calculation procedures have been studied: in the first one, a nonlinear equations system is used by the authors to show the complexity around misalignments computing; in the next two, a single artificial neural network (ANN) and a procedure with two ANNs overcome the limitations of the equations systems. It is shown that for misalignments being small perturbations of position around the nominal value, the Zernike coefficients’ behavior in front of misalignments can be approximated with a polynomial expression. But for combinations of both decenter and tilt the problem becomes too complex to be solved analytically, therefore, we have used ANNs to solve it. The method is validated by simulation for each of the functions, using a triplet where the second lens is misaligned, and the results are compared.

Exploratory research has been conducted with the aim of completely determining the polarization signatures of selected particulates as a function of wavelength. This may lead to a better understanding of the interaction between electromagnetic radiation and such materials, perhaps leading to the point detection of bio-aerosols present in the atmosphere. To this end, a polarimeter capable of measuring the complete Mueller matrix of highly scattering samples in transmission and reflection (with good spectral resolution from 300 to 1100 nm) has been developed. The polarization properties of Bacillus subtilis (surrogate for anthrax spore) are compared to ambient particulate matter species such as pollen, dust, and soot. Differentiating features in the polarization signatures of these samples have been identified, thus demonstrating the potential applicability of this technique for the detection of bio-aerosol in the ambient atmosphere.

A new algebraic reconstruction technique (ART), nonlinear auto-adjusting iterative reconstruction technique (NAIRT), is proposed and applied to reconstruct a section of an actual thermal air flow field. With numerical simulation, NAIRT was tested to reconstruct a complicated field to demonstrate its superior reconstructive capability. In contrast, three typical ARTs, the basic ART, simultaneous ART (SART), and a modified SART (MSART), were simulated to demonstrate the reconstructive capability improvement attained through the use of the proposed NAIRT. The calculated results were discussed with mean square error (MSE) and peak error (PE). A thermal air flow field was produced with an alcohol burner and was detected by a laser beam. With laser beam projections, a cross-section of the field was reconstructed by NAIRT. As a result, the reconstructive capability was improved much by NAIRT. The MSE decreased by 95.5%, and PE by 97.2% from that of the basic ART. Only NAIRT converged without filters while its reconstructive accuracy improved. By increasing the projections from 42 to 84, the accuracy of NAIRT without filters was improved significantly. NAIRT could effectively reconstruct the section of the thermal field. The proposed NAIRT needed no filter for its convergence and it had the highest reconstructive accuracy and simplest iterative expression of those analyzed.

In some computer vision applications, it is necessary to calibrate the geometry relationships of nonoverlapping cameras. However, due to lacking a common field of view, the calibration of this camera topology is quite difficult. A calibration method for nonoverlapping cameras is proposed and investigated. The proposed method utilizes several light planes, which can be generated by a line laser projector or a rotary laser level, as the calibration objects. The fact that local light planes available in different cameras are identical in global coordinates is used to recover the geometries. Results on both synthetic and real data show the validity and performance of the proposed method. The given method is simple and flexible, which can be used to calibrate geometry relationships of cameras located in large-scale space without expensive equipment such as theodolites and laser trackers.

The simple filtering procedure, high spatial resolution, and low computation time benefits of Fourier normalized-fringe analysis are verified. For this, both the fringe-pattern normalization method by parameter estimation using the least squares method and the standard Fourier transform method are implemented. This proposal, or any Fourier normalized-fringe analysis scheme, has the advantage that the filter’s properties are not very critical because the zero-order spectrum is suppressed by the normalization stage. Then, the simple half-plane filter is applied in the filtering procedure which, in addition, increases the spatial resolution. Both a computer simulation and the experimental results show the functionality and feasibility of the suggested scheme.

Using multiple optical channels increases the number of design possibilities for the objectives of mobile imaging devices. For easy wafer-level fabrication, we start from a single optical element—a monocentric plano-convex lens. The quality of the areal image is used to select the size of the field of each channel. Each channel optics is axially positioned to reduce the effect of the image field curvature. The resulting device has a small number of channels and it images a full field of view of ±40 deg with an f -number of 3. Details of the optical design, of the fabrication process, and of the device performance are reported.

Semiconductor quantum-dot-sensitized TiO ₂ thin-film solar cells have been assembled by incorporating CdS quantum dots into the TiO ₂ porous film. The influence of acid treatment on TiO ₂ electrode, dipping time, and the effect of electrolytes on the performance of solar cells have been investigated. Two types of solar cells have been fabricated, one using a liquid electrolyte and the other one using a quasi-solid-state polymer electrolyte. It has been found that quantum-dot-sensitized solar cells exhibits better photovoltaic performance when the TiO ₂ electrode was acid-treated. When the TiO ₂ electrode was acid-treated, the short-circuit current, open-circuit voltage, fill factor, efficiency, and even the amount of quantum dots absorbed by the TiO ₂ film was found to increase appreciably. The quantum dot solar cells fabricated using liquid electrolyte were observed to exhibit better efficiency than the quasi-solid-state polymer-electrolyte-based solar cells.

Thin-film computations are often a time-consuming task during optical design. An efficient way to accelerate these computations with the help of graphics processing units (GPUs) is described. It turned out that significant speed-ups can be achieved. We investigate the circumstances under which the best speed-up values can be expected. Therefore we compare different GPUs among themselves and with a modern CPU. Furthermore, the effect of thickness modulation on the speed-up and the runtime behavior depending on the input data is examined.

Based on the elastic–plastic deformation theory, status between abrasives and workpiece in magnetorheological finishing (MRF) process and the feasibility of elastic polishing are analyzed. The relationship among material removal mechanism and particle force, removal efficiency, and surface topography are revealed through a set of experiments. The chemical dominant elastic super-smooth polishing can be fulfilled by changing the components of magnetorheological (MR) fluid and optimizing polishing parameters. The MR elastic super-smooth finishing technology can be applied in polishing high-power laser–irradiated components with high efficiency, high accuracy, low damage, and high laser-induced damage threshold (LIDT). A 430×430×10  mm fused silica (FS) optic window is polished and surface error is improved from 538.241 nm [peak to valley (PV)], 96.376 nm (rms) to 76.372 nm (PV), 8.295 nm (rms) after 51.6 h rough polishing, 42.6 h fine polishing, and 54.6 h super-smooth polishing. A 50×50×10  mm sample is polished with exactly the same parameters. The roughness is improved from 1.793 nm [roughness average (Ra)] to 0.167 nm (Ra) and LIDT is improved from 9.77 to 19.2  J/cm ² after MRF elastic polishing.

Soliton-like pulses with a 1984-nm center wavelength are produced from a Tm-doped mode-locked fiber laser. The linear cavity has a graphene saturable absorber mirror at one end and a fiber Bragg grating as the output coupler. The laser operates without dispersion compensation, and the repetition rate was tuned from 20 to 5 MHz by the addition of SMF-28 fiber. The dry transfer process used to place the graphene on a mirror could be extended to any optical substrate. This enables integration of graphene with optics such as an optical window coated with a graphene filter or a graphene-saturable absorber placed directly on a semiconductor laser facet.

The development of a very compact, highly efficient, megawatt peak power, subnanosecond pulse width, 266 nm ultraviolet (UV) microlaser is reported. It contains a specially designed passively Q-switched Nd∶YAG/Cr ⁴⁺ ∶YAG microchip laser whose high output peak power of 13 MW enables an efficient wavelength conversion without using any optics before the nonlinear crystals. The subnanosecond pulse width region, which delivers high peak power even at moderate pulse energy, is very useful for an efficient wavelength conversion. We achieve 73% second harmonic generation efficiency using a LiB ₃ O ₅ (lithium triborate) crystal and 45% fourth harmonic generation efficiency using a β−BaB ₂ O ₄ (β -barium borate) crystal. As a result, we obtain 650 μJ, 4.3 MW peak power, 150 ps, and 100 Hz pulse output at 266 nm. We use an original design for the nonlinear crystal holders to reduce the size of the microlaser. This palm-top size 266 nm UV microlaser will be useful for many applications, such as materials microprocessing, pulsed laser deposition, UV laser induced breakdown spectroscopy, and photoionization.

We use a chaotic laser, instead of thermal light, as the light source in temporal ghost imaging. This laser is generated by employing an external optical feedback. The imaging magnification is varied by adjusting the group-delay dispersion parameters of the fibers. The temporal ghost imaging result is the convolution between the transmission function of the object and the temporal correlation functions of the chaotic laser. The simulation experiment, which uses a controllable time switch as the object, shows the effectiveness of our scheme. This scheme could find applications in the time-domain tomography of pulses.

A prototype of a 160 GHz millimeter-wave (mm-wave) generator is proposed and analyzed. In the scheme, two lasers with 100 GHz frequency interval serve as sources. Then, a frequency 16-tupling feed-forward modulation technique is employed to generate two-phase correlated sidebands with a 160 GHz interval. The desired sidebands can be selected by using optical interleavers. A 160 GHz mm-wave signal free of phase noise can be achieved.

We describe a method based on multichannel time-delay estimation with linear fitting correction for laser time-of-flight (TOF) measurement. The laser TOF measurement system is constructed with a laser source, a stop receiver channel, a reference receiver multichannel, an analog to digital converter (ADC) sampling unit, and a digital signal processing unit. Limited by the sampling rate, the precision of laser TOF measurement is restricted no more than the ADC sampling period in conventional methods. As this problem is considered, multichannel correlation time-delay estimation with linear fitting correction is devised. It is shown that the measuring precision is better than 2 ns with multichannel time-delay estimation and not influenced by signal-to-noise ratio. The experimental results demonstrate that the proposed method is effective and stable.

Navigation involves the integration of methodologies and systems for estimating the time-varying attitude of moving objects. A fiber strapdown inertial navigation system (FSINS) is presently used in several applications related to vehicle navigation. However, the absolute attitude and position from FSINS contain an error that increases with time. In order to improve the performance of FSINS based on our present inertial sensors, the auto-compensation of inertial sensor bias in rotation error modulation was proposed. The aim is to develop a rotary FSINS, in which the significant sensor bias is automatically compensated by rotating the inertial measurement unit (IMU), to offer the comparable navigation performance to navigation-grade IMU. In the proposed rotational technology, the IMU is rotated back and forth in azimuth through four orthogonal positions relative to the vehicle’s longitudinal axis. Simulation and experimental testing are conducted for the prototype, and the results showed that the rotary FSINS’s navigation performance is improved.

Through integrating advantages of optical and wireless communications, the Fiber-Wireless (FiWi) has become a promising solution for the “last-mile” broadband access. In particular, greening FiWi has attained extensive attention, because the access network is a main energy contributor in the whole infrastructure. However, prior solutions of greening FiWi shut down or sleep unused/minimally used optical network units for a single segment, where we deploy only one optical linear terminal. We propose a green mechanism referred to as energy-efficient ring (EER) for multisegment FiWi access networks. We utilize an integer linear programming model and a generic algorithm to generate clusters, each having the shortest distance of fully connected segments of its own. Leveraging the backtracking method for each cluster, we then connect segments through fiber links, and the shortest distance fiber ring is constructed. Finally, we sleep low load segments and forward affected traffic to other active segments on the same fiber ring by our sleeping scheme. Experimental results show that our EER mechanism significantly reduces the energy consumption at the slightly additional cost of deploying fiber links.

The impact of power transients stemming from channel reconfiguration on erbium-doped fiber amplifier (EDFA) gain dynamics in wavelength division multiplexing (WDM) optical networks is investigated. The impact of power transients on EDFA gain dynamics leads to error bursts and impact on the network performance. First, we model an EDFA simulator with one-dimensional nonlinear differential equation that describes the time-dependent population density. For the model to show gain flattening multiplexed channels at different wavelengths, new function blocks are used. Next, to simulate the noise performance of EDFA, forward amplified spontaneous emission noise blocks are designed that add noise dynamically at signal wavelength. Finally, EDFA simulator is used as an in-line amplifier for amplitude shift keying-modulated WDM fiber communication link where the gain clamping facility is provided to protect power imbalance at the receiver. Next, we apply the mentioned model in the estimation on the link performance parameters, like signal-to-noise ratio and bit error rate, and variations in these values by channel add/drop results from variation in incremented signal output of EDFA. The variations are almost equal at different wavelengths in C- or L-band, which is due to flat gain and also the gain clamping facility of the present EDFA simulator.

Ultrafast-photonic logic circuits are crucial elements to perform ultrafast-optical signal processing functions in the next-generation ultrahigh-speed networks. A 160  Gbit/s all-optical data distributor based on cross-phase modulation in a single highly nonlinear fiber is investigated and demonstrated. The numerical calculation is conducted, and the result shows that the data distributor can be realized in 160  Gbit/s for the data signals of return-to-zero format with logical correctness and high quality. To evaluate the performance of the scheme, the Q-factor of the output signal on signal wavelength, the peak power of signals, the initial delay, and the filter position are calculated and discussed, respectively. The proposed data distributor is suitable for ultrafast applications for the emerging all-optical networks.

An integrated model of photonic crystal (PC) demultiplexer that can be used to combine dense wavelength-division multiplexing (DWDM) and coarse wavelength-division multiplexing (CWDM) systems is first proposed. By applying the PC demultiplexer, dense channel spacing 0.8 nm and coarse channel spacing 20 nm are obtained at the same time. The transmission can be improved to nearly 90%, and the crosstalk can be decreased to less than −18  dB by enlarging the width of the bus waveguide. The total size of the device is 21×42  μm ² . Four channels on one side of the demultiplexer can achieve DWDM in the wavelength range between 1575 and 1578 nm, and the other four channels on the other side can achieve CWDM in the wavelength range between 1490 and 1565 nm, respectively. The demonstrated demultiplexer can be applied in the future CWDM and DWDM system, and the architecture costs can be significantly reduced.

The channel estimation problem for asymmetrically clipped optical orthogonal frequency division multiplexing wireless communication systems is investigated. In order to resolve the noise-sensitive problem of traditional least squares-based channel estimation method, a new channel estimation method which is based on superimposed training sequence and guarantees the linear minimum mean square error estimate is proposed. Cycle training sequence is added at variable power ratio to the information sequence at the transmitter prior to transmission. Then, statistical average method is employed to separate training and information sequences at the receiver. Simulation results show that the power ratio of training sequence needs to balance between the mean square error (MSE) of estimation and the error bit rate. Moreover, compared with the traditional least squares-based method, the proposed method has significantly improved the estimation performance under the condition of low signal-to-noise ratio, especially, when the MSE of the estimation reduces 1 to 2 orders.

The effect of higher-order amplified spontaneous scattering in Raman amplification is investigated. With the effect, a structure of third-order distributed fiber Raman amplifier (DFRA) is introduced and its bandwidth is studied and optimized. A method of multiorder pumps with multiwavelengths is adopted, which is different from that of multiwavelength pumps for the conventional DFRA. Simulation results indicate that pumps in different orders have different functions: the first-order pump can improve the gain flatness and extend the bandwidth, the second-order pump can increase the gain value, whereas the third-order pump can provide powers for pumps in other orders and improve the noise figure (NF) together with them; a flat spectrum with the bandwidth of 80 nm, gain of 24 dB, ripple of less than 1 dB, and a low NF over a span of 120 km is achieved. All these results are beneficial to design a broadband higher-order Raman pumping DFRA in future experimental work. A modified genetic algorithm is also proposed in optimizing the bandwidth.

We propose a duplex multiple-user radio over fiber-passive optical network (ROF-PON) system based on multitone generation and sextupling technique. A dual-drive Mach–Zehnder modulator (DD-MZM) is used to realize the multitone generation. By controlling the modulation voltage of the DD-MZM, the odd carriers can be suppressed which makes the adjacent frequency gap twice the frequency of the local oscillator frequency. Due to the multitone generation and pure carrier reuse technique, the base stations (BSs) are also source-free. The system can support more than one BS simultaneously for a transmission length more than 50 km. The proposed multiuser ROF-PON is scalable and cost-effective, and its feasibility is successfully verified by simulation.

A numerical analysis on the refractive index modulation in first and second order of type I fiber Bragg gratings (FBGs) written by prism interferometer fringes is presented. The analysis of FBG written by biprism interferometers has been carried out to optimize the writing position and by Lloyd prism interferometer to optimize FBG length with respect to ultraviolet (UV) beam parameter. It is analytically shown that in the biprism fringe depth, the fiber positions of maximum reflectivity in first and second orders are different and both are less than the distance of maximum beam overlap. The refractive index modulation of FBGs written by Lloyd prism varies along the FBG length. The evolution and saturation of the FBGs written by biprism and Llyod prism are different due to difference in magnitude and/or profile of the UV fringes contrast in the FBG writing plane.

The effects of cutting speed and assist gas pressure on laser cutting of 1-mm thick Al 1050, AZ31, and Ti6Al4V lightweight alloys are experimentally investigated. Fiber laser cutting of these materials is not broadly investigated and the acquisition of a new level of knowledge is of fundamental importance for applications like sheet metal trimming in automotive industry. The main process outputs are in depth compared with results reported in literature and obtained by cutting with CO ₂ and Nd∶YAG lasers. The good cut quality, the high productivity, and the easy delivery of the beam obtained at the same time, corroborate the advantage of using fiber lasers for thin sheets lightweight alloys cutting.

Conventionally, in intelligent buildings in a metropolitan area network and in small-scale facilities in the optical access network, optical connectors are joined manually using an optical connection board and a patch panel. In this manual connection approach, mistakes occur due to discrepancies between the actual physical settings of the connections and their management because these processes are independent. Moreover, manual cross-connection is time-consuming and expensive because maintenance personnel must be dispatched to remote places to correct mistakes. We have developed a fiber-handling robot and optical connection mechanisms for automatic cross-connection of multiple optical connectors, which are the key elements of automatic optical fiber cross-connect equipment. We evaluate the performance of the equipment, such as its optical characteristics and environmental specifications. We also devise new optical connection mechanisms that enable the automated optical fiber cross-connect module to handle and connect angled physical contact (APC) optical connector plugs. We evaluate the performance of the equipment, such as its optical characteristics. The evaluation results confirm that the automated optical fiber cross-connect equipment can connect APC connectors with low loss and high return loss, indicating that the automated optical fiber cross-connect equipment is suitable for practical use in intelligent buildings and optical access networks.

An evanescent waveguide–based optical sensor incorporating composite planar waveguide geometry using silicon oxynitride as core layer has been designed and developed. The proposed waveguide of length ∼10,000  μm and core width ∼50  μm was embedded on silica/silicon wafer and tailored for sensing glucose concentration in aqueous solution with high waveguide sensitivity ∼0.95 , as an evidence of the design and development. We derived the dispersion relation from the wave equation of the structure for estimating the propagation constants of transverse electric and transverse magnetic modes and then modeled the sensor response to the change of the sensing layer refractive index. The enhancement of waveguide sensitivity is shown by using simple effective index method based on sinusoidal modes. The sensor structure is polarization independent. The theoretical results are in good agreement with the results obtained experimentally. The experimental results have revealed strong enhancement in terms of waveguide sensitivity which is ∼10 times more than that of the existing planar waveguide sensors and five times more than asymmetric waveguide sensor. This proposed waveguide sensor requiring minimal sample volume has the potential to realize for online monitoring of blood glucose levels in the near future.

The utilization of adaptive equalization in the design of atmospheric laser link transceiver architectures that can be used for television and broadcast signal interconnect between the external place of event and the master control room is suggested. At the transmitter side of the proposed transceiver; an array of atmospheric laser sources, digital signal processing, and optical radiators are used to send light waves in free space. At the receiver side, an adaptive finite impulse response least mean square (LMS) equalizer with activity detection guidance (ADG) and tap decoupling (TD) is used to mitigate the effect of channel impairments. The performance of the suggested adaptive equalizer is compared with that of the conventional adaptive equalizer based only on the standard LMS algorithm. The simulation results revealed that the adaptive LMS equalizer with ADG and TD is a promising solution for the inter-symbol interference problem in optical wireless communication systems.

A polarization beam splitter (PBS) based on cascaded step-size multimode interference (MMI) coupler is demonstrated on silicon on insulator. The total area of MMI sections is smaller than 7×600  μm ² . This PBS shows 25-nm bandwidth for transverse-electric polarization and 20-nm bandwidth for transverse-magnetic polarization with an extinction ratio more than 20 dB. The length of this PBS is reduced to about one ninth of that of the conventional design in MMI sections.

An innovative inertial vibration sensor based on moiré fringe, which was generated by the relative movement of a pair of parallel gratings, is presented. One of the gratings was mounted on an inertial mass which was a part of the spring–mass–damping system, whereas the other was fixed to the sensor shell. The relationship between the moiré fringe and the vibration state of the measurand was discussed in detail. By using the signal processing system board, together with a unique algorithm of subdivision and direction recognition, the moiré fringes were converted into the direction and amplitude of the relative displacement with high resolution. The maximum amplitude of the relative displacement measurement is 2.5 mm with maximum error of 0.056 μm and the measurement resolution can reach to 0.028 μm. Furthermore, a temperature compensation circuit was also designed and tested, which indicates temperature immunity when taking photoelectric conversion into account. Finally, a digital compensatory filter for broadening the dynamic bandwidth with flat frequency response was developed to meet the demand in vibration measurement in the low frequency range. As a result, a linear response over a broad frequency range from 0.1 to 1000 Hz was realized.

A typical model of the flattened-vortex beam propagating through the turbulent atmosphere in a slant path is established, and the analytical formulas of the average intensity distribution at the observation plane are derived based on the extended Huygens-Fresnel principle. Under the H-V 5/7 turbulence model, the characteristics of the average intensity distribution at the observation plane are investigated, and the influences of the optical topological charge, the propagation distance, and the zenith angle of the propagation path are numerically analyzed.

The polarizability of an arbitrarily shaped electrically small particle of an isotropic dielectric material embedded in an isotropic dielectric host material given in a recent article [Opt. Eng.52, 051205 (2013)] is incorrect. In particular, the polarizability cannot be a scalar (unless the particle is either spherical or cubical), but must be a dyadic.

The authors respond to the comments by Mackay and Lakhtakia.First of all, we would like to thank Mackay and Lakhtakia1 who have carefully read our paper and for their valuable comments on our manuscript. We agree that the polarizability is a dyadic.For our aims (analytical models, full-wave simulations, and sensitivity analysis), we have assumed the impinging electromagnetic field as a plane wave having the electric field E parallel to the nanoparticle principal axis (x -axis as depicted in the Fig. 1 of the paper). In this case, Eq. (1) and the following equations refer only to scalar component x ^ x ^ of the dyadic polarizability α − − − − (sufficient to evaluate the nanoparticle response under the aforementioned excitation condition).We have to point out that for sensing applications the analyzed polarization is crucial in order to obtain the best sensitivity performances.

This article [Opt. Eng.. 52, (7 ), 073104 (2013)] was originally published on 9 July 2013 with an error in Table 2. For Subject number 19, the value in the last column (EC) should be 0.7314, not −0.7314 . The corrected table is reprinted below.