This is such a great month for me! Ravi Athale is the new permanent electro-optics program officer at the Office of Naval Research (ONR), which means I get to work with him more often. I've known Ravi for the last 15 years or so, and when I talk with him, it's like talking to one of those brothers who you have not seen for a few years, but it feels like you just picked up from your previous discussion yesterday. Ravi started his career at the Naval Research Laboratory, then he was a professor at George Mason University, then he was at DARPA, then MITRE, and now he is back with the U.S. Navy.

Recently, image communications are becoming increasingly popular, and there is a growing need for consumers to be provided with high-quality services. Although the image communication services already exist over third-generation wireless networks, there are still obstacles that prevent high-quality image communications because of limited bandwidth. Thus, more research is required to overcome the limited bandwidth of current communications systems and achieve high-quality image reconstruction in real applications. From the point of view of image processing, core technologies for high-quality image reconstruction are face hallucination and compression artifact reduction. The main interests of consumers are facial regions and several compression artifacts inevitably occur by compression; these two technologies are closely related to inverse problems in image processing. We review recent studies on face hallucination and compression artifact reduction, and provide an outline of current research. Furthermore, we discuss practical considerations and possible solutions to implement these two technologies in real mobile applications.

Atmospheric optics probably started in the 1700s in response to the early curiosity of why the sky was blue. The color of the sky was explained by the clear air and the fact that air molecules scatter more blue light than yellow or red. We have made progress in our understanding of scattering by looking at absorption of the spectrum, C _n ² , water vapor profiling, and scattering through a turbulent medium. Although the initial studies centered around fundamental understanding of light and scattering, we have advanced to the need and ability to image through the atmosphere.

This study encompasses air surface temperature (AST) modeling in the lower atmosphere. Data of four atmosphere pollutant gases (CO, O₃, CH₄, and H₂O_vapor) dataset, retrieved from the National Aeronautics and Space Administration Atmospheric Infrared Sounder (AIRS), from 2003 to 2008 was employed to develop a model to predict AST value in the Malaysian peninsula using the multiple regression method. For the entire period, the pollutants were highly correlated (R = 0.821) with predicted AST. Comparisons among five stations in 2009 showed close agreement between the predicted AST and the observed AST from AIRS, especially in the southwest monsoon (SWM) season, within 1.3 K, and for in situ data, within 1 to 2 K. The validation results of AST with AST from AIRS showed high correlation coefficient (R = 0.845 ?starttoend?0.918), indicating the model's efficiency and accuracy. Statistical analysis in terms of β showed that H₂O_vapor (0.565 to 1.746) tended to contribute significantly to high AST values during the northeast monsoon season. Generally, these results clearly indicate the advantage of using the satellite AIRS data and a correlation analysis study to investigate the impact of atmospheric greenhouse gases on AST over the Malaysian peninsula. A model was developed that is capable of retrieving the Malaysian peninsulan AST in all weather conditions, with total uncertainties ranging between 1 and 2 K.

We present a new approach to remove haze from surveillance video sequences. This approach extracts the background image through the frame differential method, uses the dark channel prior to estimate the atmospheric light, and then calculates a universal transmission map on the intensity component of the background image through a process of multiscale retinex, parameter adjustment, bilateral filtering, and total variation denoising filtering. Finally, it renders haze-free video according to the haze image model. The main advantage of the proposed approach is its speed as this approach adopts a "universal strategy" that applies the same atmospheric light and a universal pseudo-transmission map to a series of video frames. Experiments demonstrate that our method produces visually pleasing defogging results and tends to preserve main details better than previous techniques. A comparative study and quantitative evaluation show the efficiency of the proposed method.

The presence of turbulence over horizontal imaging paths severely reduces the resolution available to imaging systems and introduces anisoplanatic distortions in the image frame. A variety of image processing techniques are being developed which can mitigate these effects, and sequences of high-fidelity images created via simulation are useful in their development. In this paper, we describe a simplification of the split-step wave propagation method that employs a series of uniformly spaced phase screens to accurately simulate turbulence effects on imaging over horizontal paths. Employing this method, a series of 1000 image frames were generated for each of three turbulence conditions. The mean squared error in intensity per pixel is also evaluated for each frame in comparison to a diffraction-limited reference. Examination of the per-frame intensity error statistics indicate these errors are log-normally distributed about a mean value that increases approximately linearly with turbulence strength.

Solar-adaptive optics (AO) are more challenging than night-time AO, in some aspects. A portable solar adaptive optics (PSAO) system featuring compact physical size, low cost, and good performance has been proposed and developed. PSAO can serve as a visiting instrument for any existing ground-based solar telescope to improve solar image quality by replacing just a few optical components. High-level programming language, LabVIEW, is used to develop the wavefront sensing and control software, and general purpose computers are used to drive the whole system. During October 2011, the feasibility and good performance of PSAO was demonstrated with the 61-cm solar telescope at San Fernando Observatory. The image contrast and resolution are noticeably improved after AO correction.

We use a rigorous Markov approximation-based propagation model to calculate statistical properties of the instantaneous turbulent point spread function (PSF) for weak and strong turbulence conditions. Long-exposure PSF is well-known, and is currently widely used for estimates of optical system performance and simulation of the image distortions caused by turbulence. We discuss some peculiarities of the long-exposure PSF that are related to specifics of propagation in turbulence, which are often overlooked in the literature. Models for the short-exposure PSF have been used since the mid-1960s, and were the subject of some recent publications. We review a recently published model, and present sample calculations of the short-exposure PSF. Based on the available results of the optical propagation theory, we calculate variances of power fluctuations in the instantaneous PSF and the Strehl ratio, and covariance of the total power and the Strehl ratio. Analysis of the calculation results shows that for the most practical situations, the random Strehl ratio is a product of two uncorrelated, random variables-power and axial directivity. This information enables modeling of the instantaneous PSF with random width and height.

An algorithm based on differential evolution (DE) with adaptive strategy selection for remote sensing image registration is designed. The paper has two major contributions. One contribution is the reduction of the computation time for a better result, i.e., fitness function approximate, which is based on multi-resolution processing and histogram matching. The second contribution is an adaptive strategy known as probability matching integration. The probability matching technique is employed in DE to autonomously select the most suitable strategy while solving the problem. To the best of our knowledge, the proposed method is the first adaptive strategy selection-based approach for image registration. In our experiments, the proposed method significantly outperforms previously proposed image registration method based on DE.

The transverse angular (spatial) imaging performance of a laser imaging system through atmospheric turbulence is characterized and described in a practical sense. The system is assumed to scan a far-field scene with a collimated Gaussian beam truncated by a circular aperture and a single channel receiver records the returns. The system point spread function is defined as the average beam profile at the scene and the half-angle beam spread is used to characterize the point spread function. A system modulation transfer function is defined that includes the effects of beam diffraction and turbulence. Spatial sampling of the scene is also considered. A normalized resolution metric (Strehl ratio) is applied to investigate the effects of sampling, beam size, turbulence, and beam truncation. The analysis indicates that resolution will be reduced by more than 90% in homogenous turbulence when the beam waist size is on the order of the atmospheric coherence length. Consistency with conventional imaging performance is discussed.

High resolution ground based solar observations require adaptive optics correction. The next generation of solar telescopes will have large aperture sizes, in the range of 4 m, and will require larger and more complex adaptive optics systems. We study the effects that extended field wavefront sensors have on the correction performance for large aperture size telescopes. These effects are more pronounced for observations at low elevation angles, which are common during high resolution solar observations. Additionally, atmospheric dispersion is strongest at low elevation angle observations and can cause further reductions of the adaptive optics performance. We present a study of the expected correction performance of solar adaptive optics systems in large-aperture solar telescopes using an end-to-end adaptive optics simulation package.

Classification of moving objects in imaging through long-distance atmospheric path may be affected by distortions such as blur and spatiotemporal movements caused by air turbulence. This work aims to study and quantify the effects of these distortions on the ability to classify moving objects in atmospherically degraded video signals. For this purpose, we perform simulations and examine real long-range thermal video cases. In the simulation, we evaluate various geometrical (shape-based) object features for classification at different distortion levels. Furthermore, we examine the influence of image restoration on the classification performances in the real-degraded videos, using geometrical and textural features (combined and in separate) of the objects. Principal component analysis together with both k-nearest neighbor and support vector machines is used for the classification process. Results show how classification performances decrease as the level of blur increases, and how successful digital image restoration for real cases can significantly improve the classification performances.

We analyze the influence of the outer scale of atmospheric turbulence on the quality of optical imaging using the method of moments as applied to the optical transfer function of the "turbulent atmosphere-telescope" system when an averaged image of an incoherent optical source is recorded. The behavior of the integral resolution and three types of limiting values of the spatial scales resolvable by the optical imaging system and determined by the moments of the zero, second, fourth, and sixth orders are analyzed as well. It is shown that the influence of the outer scale of atmospheric turbulence can manifest itself only at small values of the variance of fluctuations of the complex phase of a plane optical wave.

We investigate the effect of orography on the relationship of wind-cloud systems with tropical cyclones (TC). The impact of orography is important for the cloud distribution and wind flow patterns of TC activity. Furthermore, the influence of orography on TCs remains unclear and is an active area of scientific research because of the complexity of orography effects caused by the presence of mountains. We focus on typhoons in the open sea, near coastal regions, and in the mountains. The atmospheric circulation of the level between the troposphere and the stratosphere (TS level) varies when disturbances, such as a high mountain range, occur in the surrounding edges or outflow of a typhoon. Orographic effects can influence the types of clouds (e.g., nimbus and cirrus) that form in different altitudes (high, middle, and low levels of the troposphere). Our results imply that the interaction between TCs and high-altitude topography (e.g., mountains) leads to changes in the features of TCs.

Many techniques have been proposed for active optical remote sensing of the strength of atmospheric refractive turbulence. The early techniques, based on degradation of laser beams by turbulence, were susceptible to artifacts. In 1999, we began investigating a new idea, based on differential image motion (DIM), which is inherently immune to artifacts. The new lidar technique can be seen as a combination of two astronomical instruments: a laser guide star transmitter/receiver and a DIM monitor. The technique was successfully demonstrated on a horizontal path, with a hard-target analog of a lidar, and then a true lidar was developed. Several investigations were carried out first, including an analysis to predict the system's performance; new hard-target field measurements in the vertical direction; development of a robust inversion technique; and wave optics simulations. A brassboard lidar was then constructed and operated in the field, along with instruments to acquire truth data. The tests revealed many problems and pitfalls that were all solvable with engineering changes, and the results served to verify the new lidar technique for profiling turbulence. The results also enabled accurate performance predictions for future versions of the lidar. A transportable turbulence lidar system is currently being developed to support field tests of high-energy lasers.

A novel polarization atmosphere Michelson interferometer (NPAMI) based on PAMI was designed. We explain the method of NPAMI for atmosphere detecting and then analyze the NPAMI by Jones matrix; the equations of retrieval atmospheric wind velocity and temperature are also derived. In contrast to PAMI, the NPAMI decreases the number of times for the polarizer's rotation and processing data size, thus, highly increasing the speed of detection. This work has great significance on theoretical research, capability improvement, and would be useful for the application on the passive measurement of the wind field of the upper atmosphere.

A high changeover ratio, triple field of view lens assembly was designed for limiting diffraction quality in the mid-wave infrared spectrum for a cryogenically cooled staring detector, and its switching mechanism is described. Three types of nonuniformity correction methods are evaluated using a nonsequential ray tracing method and their illumination uniformity performances are compared. Predicting the image formation of a specific target picture is realized through digital image processing and convolution algorithms.

Physiological changes in the retinal vasculature are commonly indicative of such disorders as diabetic retinopathy, glaucoma, and age-related macular degeneration. Thus, various methods have been developed for noninvasive clinical evaluation of ocular hemodynamics. However, to the best of our knowledge, current ophthalmic instruments do not provide a true color blood flow imaging capability. Accordingly, we propose a new method for the true color imaging of blood flow using a high-speed pulsed laser photography system. In the proposed approach, monochromatic images of the blood flow are acquired using a system of three cameras and three color lasers (red, green, and blue). A high-quality true color image of the blood flow is obtained by assembling the monochromatic images by means of image realignment and color calibration processes. The effectiveness of the proposed approach is demonstrated by imaging the flow of mouse blood within a microfluidic channel device. The experimental results confirm the proposed system provides a high-quality true color blood flow imaging capability, and therefore has potential for noninvasive clinical evaluation of ocular hemodynamics.

Studies have shown that stereo images improve surgeons' visuomotor tasks and therefore constructively affect the outcome of a minimally invasive surgery. Stereo images are captured by a stereo endoscope, which consists commonly of duplicate lens systems. However, stereo images can also be captured by a single lens system following a dual aperture scheme (DAS). DAS creates two spatially separated optical channels by placing a dual aperture plate in the limiting aperture of a single lens system. This paper describes efforts to miniaturize the DAS-based imaging system for use in minimally invasive surgery. To demonstrate feasibility, a prototype was fabricated using lens elements 3 mm in diameter and was tested for its stereo depth effect (SDE). The SDE of the prototype was then compared to a duplicate lens system that was constructed theoretically in the same diameter as the 3-mm prototype. The results show that the prototype yields 4/7 of the SDE of the theoretical model. However, the SDE of the prototype provides sufficient SDE, in a viewing range of 1 to 2.5 cm from the lens, for minimally invasive surgery.

The influence of photon noise to the signal evaluation of digital microscopy using a sinusoidal fringe pattern illumination with incoherent light is shown. The signal is evaluated by calculating the contrast for every charge coupled device (CCD) pixel when the object is defocused and the fringe pattern illumination shifted by a defined phase over the sample for every z -position. Every CCD pixel gets a certain number of irradiance values for every z -position which allows calculating the contrast. The result is the focal depth response (FDR) for every pixel. The FDR is Gaussian shaped and contains the height information of the specimen in the maximum. To accelerate the signal evaluation it is common to compute a fit curve to detect the maximum of the FDR. Due to the statistical photon noise, every measured irradiance value and every computed contrast value contains an error and thus also the maximum of the three-point-Gauss-curve-fit. The error of the maximum of the three-point-Gauss-curve-fit is the uncertainty of the measured height information. A general and a simplified analytical closed form solution are derived to calculate this uncertainty. An easily manageable equation allows calculating the optimal spatial frequency for an incoherent sinusoidal fringe pattern illumination and the corresponding sampling distance.

Infrared (IR) micro-imaging technology, also named chemical imaging, has potential applications in analytical technology. The IR micro-image provides not only the full spectrum information but also the component and structural information for each pixel point. Therefore, various groups of pesticides appear corresponding to the absorption peaks in the specific area of IR spectrum. In this study, the feasibility of using IR micro-imaging to detect chlopyrifos residuals on the surface of apple skin was explored. Different concentrations of chlorpyrifos solutions including 10,000, 1000, and 100  mg/L were sprayed on apple skin. Then IR micro-images were collected with a wavelength range of 4000 to 750  cm −1 . The IR micro-image of chlorpyrifos pure powders was also collected for the contrasted analysis of characteristic absorption peaks. The results showed that there were seven, five, and four characteristic absorption peaks attributed to chlorpyrifos in the IR spectra of apple skin that was sprayed 10,000, 1000, and 100  mg/L chlorpyrifos solutions, respectively. With the decrease of chlorpyrifos solution concentration, the number of characteristic absorption peaks decreased. When the chlorpyrifos solution concentration was as low as 100  mg/L , the peak intensity could be still recognized. The second derivative spectra further validated the above conclusions. The detection limit of quantitative analysis was approximately 0.98  mg/L . The present study indicated that rapid detection of chlorpyrifos on the surface of an apple by IR micro-imaging technology was feasible. It provided useful foundation for the detection of fruits' and vegetables' pesticide residues by IR micro-imaging technology.

The ability of a chromotomosynthetic imaging (CTI) system to accurately represent spatial and spectral characteristics of a spectrally diverse set of extended sources was evaluated. The goal is to evaluate CTI hyperspectral imagery for the remote classification of widely separated combustion events against a dark background. Accuracy is determined by comparing results to those of a liquid crystal tunable filter (LCTF). The reconstructed CTI two-dimensional (2-D) image was equivalent to a wideband, undispersed image for images reconstructed using 1 deg projection separation. The Colsher discrepancy metric degrades from 0.44 for the 1 deg sampling to 0.72 for a 10 deg sampling, with 5 deg sampling still equivalent to the image obtained by integrating the spectral frames of the LCTF. Hyperspectral data cubes are reconstructed with image quality dependent primarily on source intensity, not wavelength. Through nearly the entire range, narrower spectral lineshapes are attained from CTI data with little degradation in results from the 1 deg, 5 deg, and 10 deg sampled projections. The measured spectral locations were in agreement between the CTI and LCTF for most elements in the mosaic. Spectral and spatial artifacts are observed in the CTI hyperspectral imagery particularly for dim objects adjacent to bright and spectrally similar sources. As a scene becomes more continuous with spatially and spectrally similar sources, more complex processing will be necessary to avoid degraded performance.

Planar optical waveguides are the key elements in a modern, high-speed optical network. An important problem facing the optical fiber communication system is optical-axis alignment and coupling between waveguide chips and transmission fibers. The advantages and disadvantages of the various algorithms used for the optical-axis alignment, namely, hill-climbing, pattern search, and genetic algorithm are analyzed. A new optical-axis alignment for planar optical waveguides is presented which is a composite of a genetic algorithm and a pattern search algorithm. Experiments have proved the proposed alignment's feasibility; compared with hill climbing, the search process can reduce the number of movements by 88% and reduce the search time by 83%. Moreover, the search success rate in the experiment can reach 100%.

Electromagnetic theory shows that a thick-screen frequency selective surface (FSS) has many advantages in its frequency response characteristics. In addition, it can be used to make a stealth radome. Therefore, we research in detail how machining accuracy affects the frequency response properties of the FSS in the gigahertz range. Specifically, by using the least squares method applied to machining data, the effects of different machining precision in the samples can be calculated thus obtaining frequency response curves which were verified by testing in the near-field in a microwave dark room. The results show that decreasing roughness and flatness variation leads to an increase in the bandwidth and that an increase in spacing error leads to the center frequency drifting lower. Finally, an increase in aperture error leads to an increase in bandwidth. Therefore, the conclusion is that machining accuracy should be controlled and that a spatial error less than 0.05 mm is required in order to avoid unwanted center frequency drift and a transmittance decrease.

We present a three-dimensional (3-D) shape profiling method that involves the projection of two shifted strictly binary (square wave) fringe patterns, whose adequately weighted average allows to synthesize a sawtooth pattern. We demonstrate that the deformed fringes (after unwrapping) provide an intensity pattern proportional to the depth profile of the surface. The proposed technique overcomes the nonlinear response (i.e., the "gamma problem") of digital cameras and commercial video projectors without previous calibration. The two binary patterns can be encoded in the color components of a single color image, which allows a reliable 3-D profiling surface reconstruction at large time-rates. Validation experiments are presented.

For most off-the-shelf cameras, the lens distortion is inevitable. An accurate template-based calibration method for the lens distortion of an area array digital camera is proposed. A checkerboard template is employed as a standard object in this method and only one image of the template is needed. The mapping relationship in distortion-free imaging is described by a homography matrix and the discrepancy between an observed image point and its ideal location is used to find the distortion center and distortion coefficients. It is straightforward and efficient. For distortion correction, it is known that applying a forward distortion model which transforms the ideal image coordinate (distortion-free) of an image point to its observed image coordinate (with distortion) in a calibration process makes the calibration much more accurate. However, in many cases, it is necessary to calculate the ideal image coordinates for some specified points from their observed image coordinates. Generally, it is often difficult to derive the inverse function of a complex forward distortion model. A distortion-table interpolation method is proposed to accomplish the transformation. Both computer simulation and real data are used to validate the proposed methods and good results are obtained.

We theoretically analyze waveguide coupled surface plasmon resonance structure to investigate the coupling phenomenon between waveguide resonance and plasmonic resonance. Variations of types of metals as well as changes of thickness of the waveguide layer produce some interesting phenomena in the context of coupled plasmonics. Different modes that are generated are found to have dual contributions of waveguide and plasmonic effects. Field enhancement and reflectance contour plots with simultaneous angular and wavelength interrogation give some insight into the effect of waveguide resonance on the performance of nanoplasmonic structure. Figure of merit calculations and comparison of angular and wavelength differential curves of different nanoplasmonic structures can be used to determine the right candidature as regarding the better sensing performance compared to conventional SPR based sensor. Moreover, the important role played by the thickness of the waveguide layer is also established with supporting simulations.

This study used the novel fluorescence based deep-blue-emitting molecule BPVPDA in an organic fluorescent color thin film to exhibit deep blue color with CIE coordinates of (0.13, 0.16). The developed original organic RGB color thin film technology enables the optimization of the distinctive features of an organic light emitting diode (OLED) and thin-film-transistor (TFT) LCD display. The color filter structure maintains the same high resolution to obtain a higher level of brightness in comparison with conventional organic RGB color thin film. The image-processing engine is designed to achieve a sharp text image for a TFT LCD with organic color thin films. The organic color thin films structure uses an organic dye dopant in a limpid photoresist. With this technology, the following characteristics can be obtained: 1. high color reproduction of gamut ratio, and 2. improved luminous efficiency with organic color fluorescent thin film. This performance is among the best results ever reported for a color-filter used on TFT-LCD or OLED.

We investigate a new type of high-power light emission diode module with glass encapsulation instead of conventional polymer. To the best of our knowledge, this work could be the first very early attempt to make a glass encapsulation light-emitting diode module into a prototype.

Mercury cadmium telluride (HgCdTe) processing must be performed at a low temperature in order to reduce Hg depletion. To meet demand, low-temperature plasma enhanced atomic layer deposition (PE-ALD) is an emerging deposition technology for highly conformal thin films. We comparatively studied the effectiveness of low-temperature PE-ALD by measuring the ALD film roughness, thickness, and dielectric values. Conformal deposition was investigated through scanning electron microscopy images of the Al₂O ₃ film deposited onto high aspect ratio features dry-etched into HgCdTe. PE-ALD demonstrated conformal coatings of trenches, pillars and holes in advanced HgCdTe infrared sensor architectures.

A method is introduced for small signal gain measurement in a low-saturation regime using an amplified spontaneous emission (ASE) footprint of a gain media. By this method, the ratio of intensities, with and without a reflector, is measured beside the bandwidth of the ASE, hence two equations are formed. An iterative solution of these equations will simultaneously determine both the small signal gain and the loss.

The performance of a multibeam laser system is evaluated for coherent and incoherent beam combination under tactical scenarios. For direct comparison, identical aperture geometries are used for both, coherent or incoherent, combination methods. The analysis assumes a multilaser source coupled with a conventional 0.32 m diameter, on-axis, beam director. Parametric analysis includes variations over residual errors, beam quality, atmospheric effects, and scenario geometry. Analytical solutions from previous results are used to evaluate performance for the vacuum case, providing an upper bound on performance and a backdrop for organizing the multitude of effects as they are analyzed. Wave optics simulations are used for total system performance. Each laser in the array has a wavelength of 1.07 μm, 10 kW (25 kW) output power, and Gaussian exitance profile. Both tracking and full-aperture adaptive optics are modeled. Three tactical engagement geometries, air to surface, surface to air, and surface to surface, are evaluated for slant ranges from 2.5 to 10 km. Two near-median atmospheric profiles were selected based upon worldwide climatological data. The performance metric used is beam propagation efficiency for circular target diameters of 5 and 10 cm.

To suppress spatial hole burning, a direction related polarizer is adopted in Er-doped fiber ring laser gyroscope. To decrease the frequency drift caused by fluctuation of environment temperature, the polarization maintaining (PM) fiber is substituted for single mode fiber in the ring cavity. To obtain better reciprocity, two 90-deg rotations of PM fiber are introduced. Through the manners, the stable single-mode continuous wave lasers are observed simultaneously in both output directions. At last, better performance of the ring laser gyroscope based on Er-doped fiber is achieved.

An optical sensor for measuring the moisture level of clay has been realized by a couple of telecommunications lasers at 1300 and 1550 nm. The sensor can operate directly during building material production. The measurement principle is based on the measurement of the optical reflection at different wavelengths in the infrared region. Custom low-noise electronics allows rejecting disturbances of ambient light, and a digital processing makes the system independent on the clay distance. By means of a proper calibration, the sensor can monitor the moisture level during brick production, without moving parts or optical filters.

The propagation characteristics of the surface plasmon waves supported inside the metal-insulator-metal (MIM) waveguide are studied. The resonance wavelengths are significantly related to the effective index of the mode in the slit and the length of the slit. Actually, the effective index is defined by the width of the slit and the relative permittivity of the metal and the insulator. When the effective index is obtained, the resonance wavelengths in the MIM waveguide can be estimated. Furthermore, a series of slot cavities, which perform as the drop waveguides, can be designed in the MIM waveguide with the positions of half of the resonance wavelengths. The resonance wavelengths can be coupled out from the corresponding slot cavities. Therefore, a plasmonic filter with multiple exports that respectively supply a specific pass band is achieved. The device can be developed as an optical demultiplexing component.

Based on the Sagnac effect, a resonator micro-optic gyro (RMOG) is a novel optical sensor used for measuring rotation velocity. Due to the advantages of small volume, narrow linewidth, and tunable wavelength, an external cavity laser diode (ECLD) is adopted. By analyzing the working mechanism of the ECLD, a new scheme of constant temperature and driving current tuning control is determined. First, a theoretical resonance curve is calculated. Then the laser frequency is successfully tracked in the RMOG. Finally, a bias stability of 1.6  deg/s over 600 s is obtained in the RMOG with a silica waveguide resonator of 12.8 cm.

We numerically investigate the nonlinear transmission performance of 112  Gb/s coherent transmission systems using polarization multiplexed quadrature-phase-shift-keying (QPSK), offset QPSK (OQPSK) and minimum-shift-keying (MSK) formats, and compare the fiber nonlinear tolerances of the three modulation formats. Simulation results show that in both single channel and wavelength-division-multiplexed (WDM) systems, OQPSK is slightly more resistant to fiber nonlinearities than QPSK, and MSK has the best fiber nonlinear tolerance. The advantage of MSK format over QPSK and OQPSK is particularly notable in WDM systems. When digital back propagation (DBP) is used in the digital coherent receiver for intra-channel fiber nonlinearity compensation, system performance is improved with better Q-factor, enlarged input optical power range and extended transmission distance. It is found that the use of DBP brings the largest performance improvement in QPSK system and the least performance improvement in MSK system although MSK system has better fiber nonlinear tolerance.

We describe a homodyne optical Costas loop receiver intended to detect weak coherent states with diffused phase and suppressed carrier phase modulation. In order to get the information contained in the quadrature components of the optical field, we implement an 8-port receiver operating at 1550 nm, based on the manipulation of the state of polarization of both the local oscillator and the data signal. Employing binary phase-shift keying, we make measurements in the time and frequency domain of the quantum noise and bit error rate using an optimum loop filter, and compare the performance of our receiver against the standard quantum limit for the simultaneous quadrature detection, considering both ideal conditions and the overall efficiency of our set up.

In optical burst switching (OBS) networks, burst contentions in OBS core nodes may cause data loss. To reduce this data loss, a retransmission scheme has been applied. However, uncontrolled retransmission may significantly increase network load and data loss probability, thus defeating the retransmission purpose. In addition, in a priority traffic existing OBS network, OBS nodes may apply different retransmission mechanisms to priority bursts for quality-of-service (QoS) support. We present a controlled retransmission scheme for prioritized burst segmentation to support QoS in OBS networks. Different from previous work in the literature, we set a different value to retransmission probability at each contention and propose a retransmission analytical model for a burst segmentation contention resolution scheme. In addition, we apply the proposed retransmission scheme to the prioritized burst segmentation for QoS support. We take into account the load at each link due to both the fresh and the retransmitted traffic and calculate the path-blocking probability and the byte loss probability for high-priority and low-priority bursts to evaluate the network performance. An extensive simulation is proposed to validate our analytical model.

As an alternate to fast Fourier transform-based orthogonal frequency-division multiplexing (OFDM), wavelet packet transform (WPT)-based OFDM (WPT-OFDM) does not require cyclic prefix to avoid inter-symbol-interference. The wavelet has many varieties and therefore, it can provide more freedom for system design to suit different applications. We propose a real-valued WPT-OFDM that uses intensity modulation/direct detection. We also conduct an experiment to verify its performance through a 75-km standard single-mode fiber.

The impact of the optical multiplexing/demultiplexing filter on ultradense wavelength-division multiplexing transmission based on polarization-multiplexed quadrature phase-shift keying (PM-QPSK) modulation at the Nyquist spectral efficiency limit is studied through simulations. We analyze 10×111  Gbit/s PM-QPSK systems with baud-rate channel spacing for both back-to-back and long-haul nonlinear transmission cases. We show that, although a higher-order filter generally leads to better system performance at the optimal filter bandwidth, this benefit comes at the cost of reduced tolerance to variations in filter bandwidth and center-frequency shifts.

The arbitrary-waveform-decomposition technique is employed to study the arbitrary-waveform pulse that propagates over optical fibers and the evolution process is strictly governed by the dispersion-managed Schrödinger equation. Through decomposing the initial signal waveform into sub Gaussian pulses, we can simply yield the approximately analytical solutions when incorporating the second- and third-order dispersion terms into the Schrödinger equation, with the form of combination of Gaussian functions and Airy functions, and the error between the solution derived by our method and the exact solution is strictly dependent on curve-fitting during the decomposing process. Our results should be useful for predicting the evolution characteristics of arbitrary-waveform pulse in various forms of optical communications systems.

In order to ensure the communication link stability in mobile free-space optical communication (FSO) system, a novel omni-directional regular icosahedron-shaped optical antenna is designed and its beam control method is proposed. The beam control strategy is studied in detail, which includes the switch between the transmission units on the same transmitting surface and the switch between the transmitting surfaces, and the numerical simulations are carried out. When the movement of the antenna is random and the number of the transmission units in each transmitting surface is designed as 820, the number of the transmission units on the same surface changes from 0 to 560 and the number of the switched transmitting surfaces is from 1 to 17, which is basically consistent with the actual situation. The results show that the transmission units of the antenna can be switched effectively according to the terminal's movement. Our proposed method is suitable for mobile FSO in all-directions.

We propose a design of tellurite and As2S3-based chalcogenide tapered photonic crystal fibers (TPCF) for broadband coherent mid-infrared supercontinuum (SC) generation in the few-optical-cycle regime. We optimize the soliton self-compression by injecting pre-chirped femtosecond pulses. More than one octave-spanning SC spectra were generated in 8 mm-long in both tellurite and chalcogenide TPCF with low input pulse energies of 1 nJ and 100 pJ at pump wavelengths of 2.9 and 4.7 μm, respectively.

We address the average bit error rate (BER) performance of free-space optical communications over weak turbulence channel with pointing errors. With atmospheric attenuation, turbulence, and pointing errors, we present a statistical model for the optical intensity fluctuation at the receiver. The average BER performance is analyzed in the channel environment and a closed-form expression is obtained. The simulation results indicate that the derived closed-form expression matches with the simulation results.

Atmospheric turbulence imparts phase distortions on propagating optical waves. These distortions couple into amplitude fluctuations at the pupil of a telescope, which, for strong enough phase distortions, produce zeros in the amplitude called branch points. In our earlier work, we presented the case that branch points can be utilized as a source of information on the turbulent atmosphere. Using our bench-top data, we have demonstrated several properties of branch points including motion, density, persistence and separation. We have shown that the pupil plane motion of subsets of branch points scales to the velocities of atmospheric turbulence layers and identifies the number of branch point producing layers. We have identified empirical relationships for density and separation as functions of the strength and altitude for a single layer. All of this work has been done using a bench-top adaptive optics system utilizing a two-layer atmospheric turbulence simulator. In this paper, we use simulations to verify these previous results by showing that all of these branch point properties follow similar behaviors in independently anchored wave optics simulations.

Two-point correction-based nonuniformity correction of a scan-based long wave infrared camera can be successful in normal working environments. However, the method produces strong fixed-pattern noise in cluttered aerial environments. We analyze the mechanism of such phenomena and propose a nonuniformity correction method by combining a reference-based approach and a nonlinear filter-based residual offset estimation method. The nonlinear filtering process of row directional minimum filtering after two-point correction can remove the nonuniformity around cluttered aerial infrared images. Experimental results validate the feasibility of the proposed method.

The balanced enhancement for color images refers to the ability of improving the visual quality of both highlights and dark areas. To this end, a symmetric Naka-Rushton formula (SNRF) is proposed. Particularly, SNRF is symmetric around a pixel-wise threshold which is devised as the adaptive criterion for highlights. Treating RGB channels separately, SNRF regulates each pixel according to the anisotropic local intensity, thus avoiding halos and protecting uniform areas. Further, the color-constancy extension of SNRF (SNRFCC) is presented by incorporating conventional image statistics with the adaptive threshold. Different from traditional color-constancy algorithms that focus on color correction, SNRFCC accomplishes color and lightness adaptation simultaneously. Finally, a postprocessing technique is designed to compensate for the slightly compressed contrast due to the balanced adaptation. Compared with other tone-mapping methods, SNRF achieves more vivid color and details especially in highlights. Besides, comparisons with other color-contrast enhancement algorithms confirm that SNRFCC features the merit of less residual color cast when implementing color constancy on images under varying light.

Estimating depth has long been a major issue in the field of computer vision and robotics. The Kinect sensor's active sensing strategy provides high-frame-rate depth maps and can recognize user gestures and human pose. This paper presents a technique to estimate the depth of features extracted from video frames, along with an improved feature-matching method. In this paper, we used the Kinect camera developed by Microsoft, which captured color and depth images for further processing. Feature detection and selection is an important task for robot navigation. Many feature-matching techniques have been proposed earlier, and this paper proposes an improved feature matching between successive video frames with the use of neural network methodology in order to reduce the computation time of feature matching. The features extracted are invariant to image scale and rotation, and different experiments were conducted to evaluate the performance of feature matching between successive video frames. The extracted features are assigned distance based on the Kinect technology that can be used by the robot in order to determine the path of navigation, along with obstacle detection applications.

We propose using certain blind image quality metrics to tune the inverse filter used for amplitude recovery in speckle imaging systems. The inverse filter in these systems requires knowledge of the blurring function. When imaging through turbulence over long horizontal paths near the ground an estimate of the blurring function can be obtained from theoretical models incorporating an estimate of the integrated turbulence strength along the imaging path. Estimates provided by the user in these scenarios are likely to be inaccurate resulting in suboptimal reconstructions. In this work, we use two blind image quality metrics; one metric is based on image sharpness, and the other on anisotropy in image entropy, to tune the value of integrated turbulence in the long exposure atmospheric blurring model with the goal of providing images equivalent to the minimum mean squared error (MMSE) image available. We find that both blind metrics are capable of choosing images that differ from the MMSE image by less than 4% using simulated data. Using the image sharpness metric, it was possible to produce images within 1% of the MMSE on average. Both metrics were also able produce high quality reconstructions from field data.

A major problem for obtaining target reflectance via hyperspectral imaging systems is the presence of illumination and shadow effects. These factors are common artefacts, especially when dealing with a hyperspectral imaging system that has sensors in the visible to near infrared region. This region is known to have highly scattered and diffuse radiance that can modify the energy recorded by the imaging system. A shadow effect will lower the target reflectance values due to the small radiant energy impinging on the target surface. Combined with illumination artefacts, such as diffuse scattering from the surrounding targets, background or environment, the shape of the shadowed target reflectance will be altered. We propose a new method to compensate for illumination and shadow effects on hyperspectral imageries by using a polarization technique. This technique, called spectro-polarimetry, estimates the direct and diffuse irradiance based on two images taken with and without a polarizer. The method is then evaluated using a spectral similarity measure, angle and distance metric. The results of indoor and outdoor tests have shown that using the spectro-polarimetry technique can improve the spectral constancy between shadow and full illumination spectra.

We propose a novel specularity removal method based on reflection component separation and joint bilateral filtering. In general, specularities in images are represented as the linear combination of diffuse and specular reflection components in homogeneous objects. Although diffuse and specular components are correctly classified by reflection component separation, some illumination effects still remain in diffuse images due to the inaccurate illumination chromaticity estimation. Therefore, we refine the separated diffuse components using a joint bilateral filter. We test our method on both synthetic and real images, and the experimental results demonstrate that the proposed method outperforms the state-of-the-art ones in specularity removal.

The optimization of image fusion is researched. Based on the properties of nonsubsampled contourlet transform (NSCT), shift invariance, multiscale and multidirectional expansion, the fusion parameters of the multiscale decompostion scheme is optimized. In order to meet the requirement of feedback optimization, a new image fusion quality metric of image quality index normalized edge association (IQI-NEA) is built. A polynomial model is adopted to establish the relationship between the IQI_NEA metric and several decomposition levels. The optimal fusion includes four steps. First, the source images are decomposed in NSCT domain for several given levels. Second, principal component analysis is adopted to fuse the low frequency coefficients and the maximum fusion rule is utilized to fuse the high frequency coefficients to obtain the fused coefficients and the fused result is reconstructed from the obtained fused coefficients. Third, calculate the fusion quality metric IQI_NEA for the source images and fused images. Finally, the optimal fused image and optimal level are obtained through extremum properties of polynomials function. The visual and statistical results show that the proposed method has optimized the fusion performance compared to the existing fusion schemes, in terms of the visual effects and quantitative fusion evaluation indexes.

Algorithms that mimic the computation and learning capabilities of the human brain are feasible solutions to many information-processing problems. We present a theoretical model based on the observation that images of similar visual perceptions reside in a complex manifold in an image space. To model the pattern manifold, we present a novel learning algorithm using a recurrent neural network based on the behavior of the brain. In designing a recurrent neural network, convergence dynamics of the network needs special consideration. We propose to modify this picture: If the brain remembers by converging to the state representing familiar patterns, it should also diverge from such states when presented with an unknown encoded representation of a visual image belonging to a different category. Based on this, we have developed a self-organizing line attractor to learn new patterns. A nonlinear dimensionality reduction technique is used to embed the points to a lower dimensional space that preserves the intrinsic dimensionality and metric structure of the data to enable fast and accurate recognition. Experiments performed on UMIST, CMU AMP, FRGC version-2, Japanese female face expression, and Essex Grimace databases show the effectiveness of the proposed approach in accurate recognition of complex patterns.

We propose a new three-dimensional (3-D) crosstalk minimization method for the active shutter glasses-type 3-D liquid crystal displays (LCD) television (TV). The crosstalk was reduced from 43% to 10% on average with the proposed technology. Furthermore, we propose a user-friendly method to reduce the 3-D crosstalk without any measurement equipment, which enables consumers to make their TVs crosstalk free. It is found that the results of the proposed crosstalk minimization method and user-friendly method are matched well. Thus, 3-D TV consumers can easily minimize the 3-D crosstalk with their eyes only.

This paper proposes an efficient intra-field deinterlacing algorithm which implements a filter switching interpolation method (FSID) according to different local region features, which produces outstanding visual results. In this method, a bilateral filter is used for smooth regions to interpolate the missing line due to its accurate interpolation performance through use of the closeness and similarity among the neighboring pixels. On the other hand, a trilateral filter is used for complex regions to interpolate the missing line since it has high edge-preserving ability due to taking into accountthe closeness and similarity among neighboring pixels, but also the pixel gradient. Experimental results show that the proposed FSID algorithm provides satisfactory performances in terms of both objective and subjective image quality. In addition, the algorithm exploits the local spatial similarity among the neighboring pixels without complex preset-conditions, which is easier to implement than many other existing algorithms.

We present grayscale laser image formation from a programmable binary mask using a digital micromirror device (DMD) followed by a telescope with an adjustable pinhole low-pass filter. System performance was measured by comparing the intensity conformity with respect to the target image and by the energy conversion efficiency. A theoretical analysis of image precision proved high-precision image formation and inspired the iterative pattern refinement process based on the point spread function of a single DMD pixel to seek optimized image quality. We derived the diffraction efficiency formula of the DMD and discussed the overall system energy efficiency with operation wavelengths. Actual image precision performance was evaluated by measuring the root-mean-square (RMS) error of a series of sinusoidal-flattop profiles with different system bandwidths. We produced grayscale laser images with different spatial spectral content using intensity profiles of Laguerre-Gaussian, Hermite-Gaussian, and Lena-flattop beams. Measured RMS errors of all examples of various bandwidths were consistent with the image precision of the sinusoidal reference patterns. The ripple effect caused by the sharp-edged pinhole was the major contributor to the residual error in the output images. Error histograms had a zero-mean Gaussian distribution with standard deviation equal to the value of the RMS error.

This article [Opt. Eng.. 51, , 073607 (2012)] was originally published on 17 July 2012 with errors on p. 2 and in Tables 2 and 4. On p. 2, the last sentence has been changed from "Therefore, taking the value of the distance point to point from z rta+ trans   to z rta   we get:" to "Therefore, taking the value of the distance point to point from z rot+ trans   to z rta   we get:"Also, on the left side of Table 2, row 6, the value of A₃ should be negative. On the left side of Table 4, row 5, mm −7 should be mm −5 . In the right side of row 6, mm −9 should be mm −7 . The corrected tables appear below.