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The H.264 video coding standard achieves high performance compression and image quality at the expense of increased encoding complexity. Consequently, several fast mode decision and motion estimation techniques have been developed to reduce the computational cost. These approaches successfully reduce the computational time by reducing the image quality and/or increasing the bitrate. In this paper we propose a novel fast mode decision and motion estimation technique. The algorithm utilizes preprocessing frequency domain motion estimation in order to accurately predict the best mode and the search range. Experimental results show that the proposed algorithm significantly reduces the motion estimation time by up to 97%, while maintaining similar rate distortion performance when compared to the Joint Model software.

A nonvolatile reading of erasable polarization holograms in dye-doped liquid-crystal films using the same writing wavelength is presented. The recorded hologram can be easily erased with the illumination of one p-polarized wave; nevertheless, it becomes nonvolatile when reading the hologram with one s-polarized wave. We have proven the nonvolatile reading property is induced by dye adsorption on the substrate of the sample.

A silica spiral photonic crystal fiber is presented here for tailoring two zero dispersion wavelengths (ZDWs) in the visible region. The proposed fiber has two ZDWs (523.1 and 716.8 nm) along with a very high nonlinearity parameter (1060 W−¹ km−¹ at 500 nm) around the visible region. The proposed design shows improvement over the group dispersion control and air holes collapsibility of highly air filled hexagonal photonic crystal fiber (HPCF), and low damage threshold of the soft glass photonic crystal fiber. Besides, the low air filling fraction (≈43%) of the proposed design reduces the probability of sustaining higher order modes in the fiber and also ensures easy fabrication due to fewer air holes.

Densification behavior of alpha silicon carbide (SiC) during vacuum hot pressing was studied up to 1900ºC with sintering additives based on AlN and Y₂O₃ in different proportions. Near theoretical density was obtained with a total sintering additive content of < 4 vol.%. The microstructure of SiC sintered with AlN+Y₂O₃ revealed fine equiaxed grains against the additional elongated grains exhibited by SiC sintered with AlN alone. The SiC having high density exhibited very good strength, elastic modulus, high thermal conductivity, low coefficient of thermal expansion and excellent polishability for telescope mirror applications.

An introduction to the special section by the guest editors.

We investigate optical switching based on stimulated Raman scattering. The circuit consists of two fiber stages connected in series through a bandpass filter. When the pump and signal are launched to the input, the pump is saturated because of the signal amplification in the first stage; the amplified signal is rejected by the filter, so that only low-power pump enters the second stage; and no signal pulses appear at the output. The second stage is fed by 1 mW power at signal wavelength. When the pump only enters at the input, it passes through the first stage without saturation, enters the second stage, and amplifies the signal entering this stage; strong signal pulses appear at the output. We use 2-ns pump pulses at 1528 nm and cw signal at 1620 nm. In the first stage, we use both fibers with normal and anomalous dispersion. In fibers with anomalous dispersion, pump saturation is affected by modulation instability. We find that the contrast may be improved using fibers with normal and anomalous dispersion connected in series in the first stage, provided there is appropriate selection of their lengths. The best contrast we achieve is 15 dB at 6 W pump peak power.

Two-step ion-exchanged waveguides with high surface refractive indices are fabricated under a variety of conditions. By modifying the conventional two-step ion exchange, the losses and the effective diffusion depth can be decreased without a significant effect on the surface refractive index. The influence of the first step, K^+-Na⁺ ion exchange, performed time dependably on the surface refractive index change is investigated. Energy-dispersive x-ray spectroscopy is performed to establish the diffusion profiles of various ions.

We analyze the thermal stability of the power transmission efficiency and the extinction ratio in an asymmetric three-core silicon-on-insulator nonlinear directional coupler with variable Gaussian coupling coefficient. Because the refractive indices of Si and SiO₂ materials are subject to temperature change, the effective refractive index of the nonlinear coupler varies correspondingly. When ratio (LC/b) and ΔT change, the relative transmission efficiency error (Δ) values and relative change of extinction ratio (η) values are obtained. It can be easily shown that variation of Δ and η are negligible under LC/b ≤ 1/2. Therefore, we can set LC/b ≤ 1/2 and ΔT ∈ [-100 K, 100 K] in order to make the power transmission efficiency and the extinction ratio work steadily. This is significant in guiding an actual nonlinear optical pulse switch fabrication.

Rare earth-activated glass-ceramic waveguides constitute a potential significant system to behave as an effective optical medium for light propagation and luminescence enhancement. We present a review on fabrication and optical, structural, and spectroscopic characterization of some kind of rare earth activated oxide glass-ceramic waveguides, obtained by sol-gel route with both bottom-up and top-down approaches, and fluoride glass-ceramic waveguides fabricated by physical vapor deposition.

Based on Wheeler's transformation of multilayer microstrip line, velocity and impedance matching have been analyzed for polymer electro-optic (EO) modulator. Due to the advantages of polymer materials, velocity-matching and impedance-matching can be simultaneously achieved by optimized design for multilayer microstrip electrode. A modified modulator structure has been introduced with a compensation layer placed on the electrode to adjust the microwave index and characteristic impedance. The optimal thicknesses of electrode and compensation layer, and optimal width of electrode can make the EO modulator achieve both velocity matching and impedance matching.

We review the history and current status of ion exchanged glass waveguide technology. The background of ion exchange in glass and key developments in the first years of research are briefly described. An overview of fabrication, characterization and modeling of waveguides is given and the most important waveguide devices and their applications are discussed. Ion exchanged waveguide technology has served as an available platform for studies of general waveguide properties, integrated optics structures and devices, as well as applications. It is also a commercial fabrication technology for both passive and active wave-guide components.

This paper reports two configurations of Bragg reflectors based on liquid crystals confined between two small glass plates. Both approaches employ the efficient electro-optic effect in liquid crystals, which allows tunability of the reflectors by using low voltages. The molecular reorientation induced by an applied electric field implies a refractive index modulation seen by polarized light propagating into the liquid crystal. We show design criteria and profile optimization of the electrodes to induce a liquid crystal refractive index periodic modulation, providing a wavelength selective propagation of confined light in the liquid crystal. The two proposed device configurations differ for the top-bottom electrode configuration in one case and coplanar electrodes in the other case. Modeling of both configurations has been carried by calculating the applied electric field distribution and its interaction with the liquid crystal elastic properties taking into account the boundary conditions due to the alignment layer on the inner faces of the glass substrates. The calculated performance in terms of high wavelength selectivity and ultrawide spectral tuning range indicate that the two designed structures can be proposed for both optical filtering and to produce novel low power integrated distributed feedback resonators in dense wavelength division multiplexed fiber optic systems.

In this work, we experimentally investigated the effects of sodium chloride on the molar absorptivity and surface density of a submonolayer of chlorophyll a adsorbed onto hydrophilic and hydrophobic solid/liquid interfaces. Those investigations were made possible by a broadband spectroscopic platform based on single-mode, integrated optical waveguides, which allows for extremely sensitive spectroscopic detection of analytes immobilized at submonolayer levels. Chlorophyll a with a constant bulk concentration (1.4 μM) was dissolved in phosphate buffer solutions (7 mM) of neutral pH, but with different sodium chloride concentrations. For a buffer solution of 1 mM of sodium chloride, the measured surface density of chlorophyll a was 0.209 pmol/cm² for a hydrophilic and 0.125 pmol/cm² for a hydrophobic surface. For a phosphate buffer solution of 10 mM of sodium chloride, the measured surface density of chlorophyll a was 0.528 pmol/cm² for a hydrophilic and 0.337 pmol/cm² for a hydrophobic surface. Additionally, a hypsochromic shift of the Soret band was observed for the adsorbed pigment in correlation with an increase in buffer ionic strength. The adsorption of chlorophyll a onto different surfaces can play an important role to elucidate several processes found in nature and provide a rationale for bio-inspired new material technologies.

Slab optical waveguides were fabricated in tung-sten-tellurite glass doped with Er³⁺ ions by means of nitrogen ion implantation at 1.5 MeV. A wide range of ion doses (from 5·10¹² to 8·10¹⁶ ions/cm²) was used. Optical characterization, performed by dark-line spectroscopy, revealed that the waveguides were of optical barrier type: the implanted layer exhibited a decrease of the refractive index with respect to the virgin bulk glass, while the region comprised between the sample surface and the end of the ion track acted as an optical guiding structure. It was also demonstrated that a post-implantation annealing process, performed at various temperatures on the samples implanted at higher doses, contributes to the reduction of the barrier region.

Brillouin scattering can be used for determining strain distributions along fibers. This is a convenient way to monitor the structural integrity of large constructions. However, the high cost of the optical circuitry has prevented wide use of this technique. We report on a design study on an integrated optical circuit for a Brillouin optical time domain reflection readout unit with low-cost potential. The circuit contains narrow linewidth tuneable distributed Bragg reflector (DBR) lasers, photodiodes with an optical mixer for coherent detection, a 10-bit digitally switched delay line for frequency tuning, and a switching fabric that allows three modes of operation. Such a circuit can be realized through one of the upcoming foundries in the field of photonic integration.

All-optical networking can be the sole approach to provide the huge bandwidth required for future networks. The essential elements in such an optical network are optical switches. A number of options have been proposed in order to implement them efficiently. We focus on thermo-optical switches. First, the physical principles of the thermo-optic effect are briefly introduced. A description of the most common technologies used for the fabrication of thermo-optic switches is provided along with the values of thermo-optic coefficient for a number of materials. The main steps useful in order to design thermo-optical switches are also briefly introduced. Finally, a bird's-eye view of the main and recent proposals of switches based on the thermo-optic effect is reported and their performances compared.

Aided and automatic target recognition (Ai/ATR) capability is a critical technology needed by the military services for modern combat. However, the current level of performance that is available is largely deficient compared to the requirements. This is largely due to the difficulty of acquiring targets in realistic environments but has also been due to the difficulty in getting new concepts from, for example, the academic community, due to limitations for distribution of classified data. The difficulty of the performance required has limited the fulfillment of the promise that is so anticipated by the war fighter. We review the metrics, imagery data bases, and sensors associated with Ai/ATR performance and suggest possible technical approaches that could enable new advancements in military-relevant performance.

The emerging field of compressed sensing has potentially powerful implications for the design of optical imaging devices. In particular, compressed sensing theory suggests that one can recover a scene at a higher resolution than is dictated by the pitch of the focal plane array. This rather remarkable result comes with some important caveats however, especially when practical issues associated with physical implementation are taken into account. This tutorial discusses compressed sensing in the context of optical imaging devices, emphasizing the practical hurdles related to building such devices, and offering suggestions for overcoming these hurdles. Examples and analysis specifically related to infrared imaging highlight the challenges associated with large format focal plane arrays and how these challenges can be mitigated using compressed sensing ideas.

In this paper, a full-field photothermal imaging technique, which does not require a time consuming scan as used in the conventional photothermal imaging system, is reported. Imaging on gold nanoparticles (70 nm) and a blue polystyrene bead (193 nm) were conducted and the experimental results demonstrate the visualization ability of the photothermal imaging technique on nanotargets that are below the diffraction limit. The photothermal imaging system can be operated in an ambient environment where vacuum is not required.

Rigid tools can confer advantages at certain stages of manufacturing off-axis mirror segments, but the misfit due to surface asphericity and asymmetry poses constraints on their application. Types of misfit are classified and, using least squares, the best-fit tool forms with different distances from the pole of the parent asphere are calculated. The outer mirror segment for the European extremely large telescope is taken as a case-study, assuming a rigid tool size of 150 mm. A simple independent approximation validates the calculation. A close parallel is wavefront misfit in subaperture interferometry, which is also considered.

A theoretical model for calculating the refractive index profile of gradient refractive index rod lens is established. Gradient refractive index rod lenses are prepared using double ion exchange processes, and their optical characteristics have been evaluated for the first time to the best of our best knowledge. The theoretical and the experimental results show that they agree well with each other. Moreover, the refractive index profile and the optical performance of gradient refractive index rod lens in the two-step ion exchange process are superior to them in the one-step ion exchange process.

A new approach called dynamic-scan-detection is presented to detect the focal spot on nonplanar surfaces, which is a key technique for laser direct writing on nonplanar surfaces. From the depth response properties of a confocal system on a nonplanar surface, the approach scans the axial shift of intensity response peak by oscillating the modified pinhole in the axial direction, and demodulates the defocus by measuring the length of time between two peaks of measured intensity waveform in one period. Compared with conventional methods, this approach features easy implementation, wide depth measurement range without deterioration of the depth discrimination property, dynamically adjustable scan amplitude, and more importantly, suppression of common-mode noise or variable system factors.

Replacement of a bulk pentaprism with a mirror-based pentaprism (MBPP) in slope-measuring instruments, such as long trace profilers and autocollimator-based deflectometers, is a well-established way to significantly improve the reliability of surface slope measurements. This is due to the elimination of systematic errors introduced by inhomogeneity of the optical material and fabrication imperfections of bulk pentaprisms. Proper use of an MBPP requires precision mutual alignment of its mirrors. In a recent work we have reported on an original experimental procedure for optimal alignment of MBPP mirrors. The procedure has been verified with numerical ray tracing simulations and via test experiments with the developmental long trace profiler, a slope measuring profiler available at the Advanced Light Source Optical Metrology Laboratory. In the present article, we provide an analytical derivation and verification of easily executed optimal alignment algorithms for two different designs of mirror-based pentaprisms. We also provide an analytical description for a mechanism for reduction of the systematic errors introduced by a typical high quality bulk pentaprism. It is also shown that residual misalignments of an MBPP introduce entirely negligible systematic errors in surface slope measurements with scanning deflectometric devices.

A low-cost mechanical artifact is developed for the metrological verification of photogrammetric measurement systems. It is mainly composed of five delrin spheres and seven cubes manufactured in different sizes. A set of circular targets are fixed on these elements to perform the photogrammetric restitution. The artifact is used in order to compare three photogrammetric systems defined by three different cameras (Canon 5D with 14-mm lens, Nikon D200 with 20-mm lens, and Jai BB500GE with 8-mm lens). Photomodeler Pro and Matlab software are used for the data processing. The precision of the systems is evaluated using the standard deviation of the geometric coordinates calculated from the restitution of the circular targets. The accuracy is calculated using two different procedures: one of them uses the distance between the center of the spheres and the other uses the distance between the faces of the cubes. The comparison between the photogrammetric systems and their associated calibration files reveals that the Jai camera produces the best results in terms of precision and accuracy, while the Canon camera produces the poorest ones. The bad results from the Canon system are primarily related to the low quality of the calibration procedure.

Using a coherent detection technique, the measurement of the phase-relation between transmitted and reflected paths for beam splitters is presented. A change in the phase of p and s polarization components of the reflected and transmitted light for a beam splitter can be determined. Two measurement schemes are presented: one for polarizing beam splitters and one for nonpolarizing beam splitters. Experimental results for the case of a polarizing beam splitter are discussed.

There is a constant search for a more accurate measurement, which generally leads to higher cost, greater complexity, or devices that do not lend themselves to manufacturing environments. We present a method of using statistical sampling to improve metrological accuracy without these undesirable effects. For metrology of flat surfaces and steps between flat surfaces, this method demonstrated precision improvement up to a factor of 55, and accuracy increase of at least a factor of 10. The corresponding precision and accuracy improvements on a spherical surface were both factors of 8. Since this accuracy improvement can be implemented in software, it does not affect the speed of measurement or the complexity of the hardware, and it can be used to improve the accuracy of a wide range of metrology systems.

For optical axis alignment when light deflection control of a MEMS mirror is done at high speed, we propose a method based on identifying the quadratic surface shape. The method uses information about the optical power monitored when the mirror is inclined to a small angle. It is shown that the search for maximum optical power is possible by using this method. We also designed a control system with a band-stop filter for resonance frequency to decrease residual vibration generated when the mirror is moved at high speed. We confirm that the searchable level of optical power can be improved.

In this paper, we propose an optical switch based on a metal-insulator-metal plasmonic waveguide with Si₃N₄ core sandwiched between two gallium (Ga) metal layers. Combining the unique structural phase transition property of gallium, within a total length of only 400 nm, an extinction ratio as high as 7.68 dB can be achieved in the proposed nanoplasmonic structure. The phase transition may be achieved by changing the temperature of the waveguide or by external light excitation.

Computational holography becomes highly complicated and demanding when it is employed to produce real three-dimensional (3D) images. Here we present a novel algorithm for generating a full parallax 3D computer generated hologram (CGH) with occlusion effect, which is an important property of 3D perception, but has often been neglected in most CGH related works. The ray casting technique is introduced to handle the occlusion issue. Horizontally and vertically distributed rays are projected from each hologram sample to the 3D objects to obtain the complex amplitude distribution. The proposed algorithm has no restriction on-or approximation to-the 3D objects, and it can produce reconstructed images with correct shading effect and no visible artifacts. An optical experiment is performed to validate our approach, using a phase-only spatial light modulator to optically reconstruct a 3D scene. The experimental result confirmed that the CGHs produced by our algorithm can successfully reconstruct 3D images with full parallax and occlusion effect.

A combination of erbium (Er), ytterbium (Yb), and neodymium (Nd), in fiber amplifiers, is examined. This combination extends the pumping wavelength spectrum by creating a new pumping path. Furthermore, the Nd addition enables pumping the amplifier from within the amplifier center, and thereby decreases the amplified spontaneous emission at the amplifier ends. A mathematical model is presented relating the excited population density, the signal power along the amplifier, the energy transfer among the ions, and the amplified spontaneous emissions. The study compares the amplifier characteristics of Er-Yb-Nd co-doped amplifier with a traditional Er-Yb amplifier for various combinations. The new configuration adds flexibility into the amplifier design. By properly selecting its parameters, one can increase the output signal power and decrease the amplified spontaneous emission, to comply with various requirements.

A simultaneous Q-switched and mode-locked (QML) Nd:LuVO₄ laser with an acousto-optic (AO) modulator and GaAs was presented. By inserting an AO modulator into the laser cavity, the stability of the QML pulses was improved and the pulse width was compressed significantly. The pulse energy and the peak power of mode-locked pulses under the Q-switched envelope had greatly increased. Considering the influences of the turnoff time and the modulation frequency of the AO modulator, a rate equation model for dual-loss modulated QML lasers was given and the numerical solutions of the rate equations were in good agreement with the experimental results.

It is an effective approach to obtain high-power laser output by spectral beam combining (SBC) technologies. In this paper, a simple SBC system based on the superimposed reflective volume Bragg grating (RVBG) is proposed to reduce the scale of the SBC system. Considering the cross-coupling between the two gratings in a volume, two structure models of the superimposed RVBG-the superimposed RVBG with the same period and the superimposed RVBG with a different period-are analyzed and compared by using the rigorous coupled wave analysis, and their applications for SBC system are discussed. Numerical results show that the superimposed RVBG is easy to be fabricated and has the potential to combine multiple lasers with one volume. Cross-coupling can be neglected for the same period structure when the slant angle divergence is larger than 0.01 rad and for the different period structure when the spectral separation is larger than 1.0 nm. The superimposed RVBG with a different period can achieve high diffraction efficiency simultaneously for each grating with a small slant angle divergence, and is convenient to combine multiple beams with small spectral separation. The effect of wavelength shift on diffraction efficiency can be ignored.

Fiber Bragg gratings have has been widely used in sensors. We analyze the transmission and polarization properties of magneto-optical fiber Bragg gratings based on coordinate conversion. The simulations demonstrate the influence of magnetic field intensity on the transmission spectrum, the polarization properties by the coupled mode theory, and the Jones formalism. The results show that while a small magnetic field can hardly be detected in the grating amplitude response, it leads to significant polarization properties such as the third normalized Stokes parameter, polarization dependent loss, and ellipticity. We demonstrate that these polarization properties contain information about the magnetic field and can thus be used for magnetic field sensing purposes. The sensitivity and dynamic range depend on the physical parameters of the grating.

Several key optical components in a reflective fiber optic current sensor (R-FOCS) show error characteristics, which induces linearly polarized light wave in polarization maintaining (PM) fiber and circularly polarized light wave in sensing fiber to be an elliptically polarized light wave. Therefore, nonreciprocal phase shift induced by magnetic field of the current is interrupted by the wrong polarization state. Focused on optical polarization error in R-FOCS, we analyze the characteristics of polarization errors associated with optical components in R-FOCS theoretically, and demonstrate the methods to build optical polarization error models by using Poincaré sphere and Jones matrix, respectively. Then, based on a model of polarization states in R-FOCS, we theoretically investigate the effect of several main error factors on optical polarization characteristics, including polarizing performance of polarizer, phase delay in quarter-wave retarder, splice angular between quarter-wave retarder and PM fiber, birefringence in sensing head and mirror reflection phase shift error. Finally, we quantify a nonreciprocal phase shift to be detected in R-FOCS with optical polarization error respectively, and propose measures.

A thermo-optical tunable filter based on the Vernier effect of cascaded microring resonators, which can expand the free spectrum range (FSR) and the tuning range, has been designed and simulated. The FSR of the filter with a radius of 48 μm for the first stage and 50 μm for the second stage microring can be expanded to 75.6 nm, which is, at present, the largest FSR to our best knowledge. A tuning range covering all of the above mentioned FSR can be reached under 103.1 mW heating power, which is also the largest one for silicon-based thermo-optical tunable microring resonator filters. The response time, calculated by solving the two-dimensional heat conduction equation with finite element method, of the designed tunable filter with 48/50 μm radius rings is 3.5 μs for the rise edge and 0.8 μs for the fall edge, which is much quicker than most of the reported silicon microring-based thermo-optical tunable filters.

We propose a novel method of an optical cryptography using the dark-bright soliton conversion control in a modified add/drop optical filter. By using the control arrangement, the obtained outputs of the dynamic states of dark-bright soliton can be used to form the key suppression for communication security application, in which the key recovery can be obtained by controlling the add/drop filter outputs. The optical cryptography consists of an add/drop filter which is used to generate the encryption and decryption keys from the optical keys (LIP signals). A Mach-Zehnder interferometer is used for multiplexing and de-multiplexing operations. Simulation results obtained shows, that the proposed system can be used to form a high security communication system.

The design, fabrication, and characteristic of the plastic optical fiber (POF), beam splitter, for the automotive network, has been demonstrated. The fabricated 1×2 POF beam splitter consisted of a poly(methylmethacrylate) (PMMA) core, which had a structure of circular waveguide and a diameter of 0.98 mm, UV curable epoxy (PC-414) clading of 0.02 mm thickness, and three POF pigtails with multimedia oriented system transport standard ferrules. A 1×2 PMMA waveguide, which was designed to have an optimal angle of 15.8 deg at the beam splitting point, was fabricated using the injection molding method for mass production. The total volume of the fabricated 1×2 POF beam splitter is 48×18×12 mm³ with 1.2 m length input and output POF pigtails. From the measurement results, we experimentally confirm that the fabricated 1×2 POF beam splitter has excellent properties such as a beam splitting ratio of 50:50 ± 10 % and excess loss of less than 3.52 dB and it works well up to 250 Mbps for the automotive network.

Since wireless optical communication (WOC) systems can offer several potential advantages over their radio frequency counterparts, there has been a growing interest in WOC systems. Influenced by the complicated optical propagation environment, there exists diffuse propagation phenomena. In order to eliminate the effect of multipath propagation caused by diffuse reflection, much attention should be concentrated on the channel estimation in diffuse WOC systems. This paper focuses on the complementary sequences (CSs) for estimating a channel impulse response in WOC systems. Based on the "two-sided" training sequences (a preamble and a postamble sequence are included in the data frame), this paper studies the channel estimation in WOC systems. Further, a simple expression for Cramer-Rao bound (CRB) is proposed to evaluate the two-sided channel estimation errors. By minimizing the CRB, the CS-based channel estimation method is proposed. Moreover, the sequence detection performance measured by a bit error ratio is also investigated. Simulation results show that the channel estimation and sequence detection performance can be significantly improved by employing the CS-based channel estimation.

We propose novel correlator receiver architecture with a PnpN optical thyristor operating as optical hard-limiter, and demonstrate a multiple-access interference rejection of the proposed correlator receiver. The proposed correlator receiver is composed of the 1×2 splitter, optical delay line, 2×1 combiner, and fabricated PnpN optical thyristor. The proposed correlator receiver enhances the system performance because it excludes some combinations of multiple-access interference patterns from causing errors as in optical code-division multiple access systems with conventional optical receiver shown in all previous works. It is found that the proposed correlator receiver can fully reject the interference signals generated by decoding processing and multiple access for two simultaneous users.

Photonic millimeter wave (mm-wave) signal generation employing a differential Mach-Zehnder modulator (DMZM) and a semiconductor optical amplifier (SOA) is proposed and evaluated by theoretical analysis and simulation. This paper presents the theoretical study of the generation of a co-polarized and phase-locked dual-pump for four-wave mixing and optical mm-wave signal, the propagation of the optical mm-wave signal in single mode fiber, and the coherent demodulation of the electrical mm-wave signal at the base station. Performance analysis and optimization design of the proposed scheme are conducted via simulations. The generation of mm-wave signals at 30, 40, and 60 GHz is simulated and analyzed. The influence of SOA and the input optical signal on the mm-wave generation and transmission is investigated. Simulation results present useful insight for the practicality of photonic mm-wave signal generation and distribution in the next-generation access network.

A simple and robust photonic radio frequency multiplication with continuously tunable multiplication factor by using a Fabry-Pérot laser diode (FP-LD) is proposed and demonstrated. In a FP-LD, the four-wave mixing effect can create new harmonic components, and the injection-locking behavior is able to lock and amplify one of the sidebands. When the output signal beats on a high speed photodetctor, the multiplication frequencies with a factor more than 41 can be obtained. The tunability is implemented by detuning the injection wavelength. In the experimental demonstration, the frequency components around 20 GHz are generated from a 500 MHz (or 1 GHz) sinusoidal signal. The measured single sideband phase noise is −95 dBc/Hz at a 10 kHz frequency offset.

Performance analysis has been carried out to evaluate the performance of a free-space optical terrestrial system using on-off keying in the presence of scattering and absorption due to atmospheric gas molecules and aerosols, and pointing error phenomenon due to the link missalignment. It is found that in order to achieve a bit error rate (BER) of 10−⁹ at a visibility of 1.9 km, a 13.2 dB power penalty is incurred for atmospheric channel in haze condition and for atmospheric channel in rain condition, a heavy rainfall rate of 25 mm/h produces a high atmospheric attenuation coefficient α, and thus almost 18 dB power penalty is induced to achieve a BER of 10−⁹. However, for the atmospheric channel in a fog condition, the visibility can reach 1.1 km and induces a power penalty of 25 dB to maintain the BER of 10−⁹. The power penalty increases when the visibility is reduced, rainfall intensity increased, and an additional power penalty of more than 25 dB is incurred in the presence of pointing error for atmospheric channel of 1.3 km visibility in a light fog condition compared to clear weather condition.

This paper represents a power transfer function (PTF)-based chromatic dispersion (CD) monitoring method applicable to signals with different duty cycles and optical signal-to-noise ratio (OSNR). Our method relies on phase-mismatched four wave mixing to provide a steep PTF that maps the CD experienced by the signal onto the average power of the output signal. The steep PTF greatly enhances the monitoring sensitivity, thus solves the problem that former PTF-based methods cannot be applied to signals with high duty cycles and low OSNR because of low output contrast. Furthermore, because the optical power required is low, our method is optically efficient and easy-to-implement. Numerical simulations are then used to demonstrate the effectiveness and efficiency of this monitoring method.

All-optical logic gates are the basic components of all-optical signal processing and computing. Among all other logic gates, exclusive-OR (XOR) plays a significant role on optical computing, switching, and networking. We propose a novel and simple scheme for all-optical exclusive-NOR and XOR logic gates using single mode Fabry-Pérot laser diode (SMFP-LD). The logic gates are based on the multi-input injection locking and supporting beam principle to suppress the intensity of the dominant mode of the SMFP-LD. The working principle of the proposed scheme is explained, and the experimental results are presented at the data rate of 10 Gbps input signals for the logic operations. We observed clear eye openings with an extinction ratio of about 12 dB and a rising/falling time of about 35 ps of the logic outputs. The demonstrated scheme can be used to implement all-optical computing and switching networks.

In this paper, a crosstalk expression and equivalent circuit model have been proposed based on RLC line model and interconnect parameters for wire-bonded and flip-chip bonded multichannel optoelectronic modules. The analytical expression and model are accurate for computing crosstalk of interconnects used in chip packaging. In addition, full-wave simulation and experimental results from total crosstalk measurement are discussed.

Remote sensing provides a new idea and an advanced method for lithology identification, but lithology identification by remote sensing is quite difficult because 1. the disciplines of lithology identification in a concrete region are often quite different from the experts' experience; 2. In the regions with flourishing vegetation, lithology information is poor, so it is very difficult to identify the lithologies by remote sensing images...An intelligent method proposed in this paper for lithology identification based on support vector machine (SVM) and adaptive cellular automata (ACA) is expected to solve the above problems. The method adopted Landsat-7 ETM+ images and 1:50000 geological map as the data origins. It first derived the lithology identification factors on three aspects: 1. spectra, 2. texture and 3. Vegetation cover. Second, it plied the remote sensing images with the geological map and established the SVM to obtain the transition rules according to the factor values of the samples. Finally, it established an ACA model to intelligently identify the lithologies according to the transition and neighborhood rules. In this paper an ACA model is proposed and compared with the traditional one.

In medical x ray computed tomography (CT) imaging devices, the x ray tube usually emits a polychromatic spectrum of photons resulting in beam-hardening artifacts in the reconstructed images. The bone-correction method has been widely adopted to compensate for beam-hardening artifacts. However, its correction performance is highly dependent on the empirical determination of a scaling factor, which is used to adjust the ratio of the reconstructed value in the bone region to the actual mass density of bone-tissue. A significant problem with bone-correction is that a large number of physical experiments are routinely required to accurately calibrate the scaling factor. In this article, an improved bone-correction method is proposed, based on the projection data consistency condition, to automatically determine the scaling factor. Extensive numerical simulations have verified the existence of an optimal scaling factor, the sensitivity of bone-correction to the scaling factor, and the efficiency of the proposed method for the beam-hardening correction.

Image inpainting, an art of modifying or recovering an image in an undetectable way by ordinary observers, has been drawing considerable attention in recent years. In this paper, we propose a novel algorithm to address this problem based on the variation of variances and the linear weighted filling-in under the local patch consistency constraints on pixel values and the first-order gradient. First, a variation of variances of neighboring source patches approach is applied to assign priority to target patches on the image structures (e.g., edges or corners). Second, a linear weighted filling-in scheme, which uses the combinational information of source patches rather than a single source patch, is applied to reconstruct the estimated patches among which the best matching patch is selected. Moreover, the technique of rotating the on-edge patches is introduced to extend the sample space. Experiments on natural images and comparisons with representative existing algorithms show that our proposed method can more robustly discriminate structures and textures, estimate the best matching patch with more known information, and improve the visual quality.

A novel contrast enhancement scheme for infrared (IR) image using detail-preserving stretching (DPS) is presented in this paper. Unlike CCD images, the histogram of the IR images is not distributed to the entire dynamic range of the input image. Therefore, in order to enhance the contrast, the proposed method adopts contrast stretching since it has a low computational complexity and preserves the global contrast of the original. However, the stretching often produces unpleasant images that do not contain clear details by limiting the output dynamic range. To solve this problem, we propose a new contrast stretching method based on gradient-domain processing (GDP) that can enhance the local image contrast while preserving the global contrast as well as the image details. Experimental results demonstrate that the proposed method outperforms the conventional stretching-based and other image enhancement methods with respect to the visual quality and computational complexity.

A range scan of a building's interior typically produces an immense cloud of colorized three-dimensional data that represents diverse surfaces ranging from simple planes to complex objects. To create a virtual reality model of the preexisting room, it is necessary to segment the data into meaningful clusters. Unfortunately, segmentation algorithms based solely on surface curvature have difficulty in handling such diverse interior geometries, occluded boundaries, and closely placed objects with similar curvature properties. The proposed two stage hierarchical clustering algorithm overcomes many of these challenges by exploiting the registered color and spatial information simultaneously. Large planar regions are initially identified using constraints that combine color (hue) and a measure of local planarity called planar alignment factor. This stage assigns 72 to 84% of the sampled points to clusters representing flat surfaces such as walls, ceilings, or floors. The significantly reduced data points are clustered further using local surface normal and hue deviation information. A local density driven investigation distance (fixed density distance) is used for normal computation and cluster expansion. The methodology is tested on colorized range data of a typical room interior. The combined approach enabled the successful segmentation of planar and complex geometries in both dense and sparse data regions.

The view synthesis prediction (VSP) method utilizes interview correlations between views by generating an additional reference frame in the multiview video coding. This paper describes a multiview depth video coding scheme that incorporates depth view synthesis and additional prediction modes. In the proposed scheme, we exploit the reconstructed neighboring depth frame to generate an additional reference depth image for the current viewpoint to be coded using the depth image-based-rendering technique. In order to generate high-quality reference depth images, we used pre-processing on depth, depth image warping, and two types of hole filling methods depending on the number of available reference views. After synthesizing the additional depth image, we encode the depth video using the proposed additional prediction modes named VSP modes; those additional modes refer to the synthesized depth image. In particular, the VSP_SKIP mode refers to the co-located block of the synthesized frame without the coding motion vectors and residual data, which gives most of the coding gains. Experimental results demonstrate that the proposed depth view synthesis method provides high-quality depth images for the current view and the proposed VSP modes provide high coding gains, especially on the anchor frames.

In multiresolution analysis, the total structures of images are characterized by an approximate component, and the specific features such as lines, edges, and contours are contained in detail components. This paper proposes a fusion scheme to combine the structure information representing the background of source images and the directive contrast information representing the features of lines, edges, and contours along different directions in source images into a single image. Here, the structure information can be attained by structure similarity methods. And the directive contrast is defined as the ratio of the local maxima of the detail components in a Gaussian window and the mean of the corresponding approximate components. The visual and statistical results show that the proposed method has improved the fusion performance compared to the existing fusion schemes, especially in term of the visual effects.

Hyperspectral remote sensing is widely used in many fields suchas agriculture, military detection, mineral exploration, and so on. Hyperspectral data has very high spectral resolution, but much lower spatial resolution than the data obtained by other types of sensors. The low spatial resolution restrains its wide applications. On the contrary, we easily obtain images with high spatial resolution but insufficient spectral resolution (like panchromatic images). Naturally, people expect to obtain images that have high spatial and spectral resolution at the same time by the hyperspectral image fusion. In this paper, a similarity measure-based variational method is proposed to achieve the fusion process. The main idea is to transform the image fusion problem to an optimization problem based on the variational model. We first establish a fusion model that constrains the spatial and spectral information of the original data at the same time, then use the split bregman iteration to obtain the final fused data. Also, we analyze the convergence of the method. The experiments on the synthetic and real data show that the fusion method preserves the information of the original images efficiently, especially on the spectral information.

The traditional local binary pattern (LBP) histogram representation extracts the local micropatterns and assigns the same weight to all local micropatterns. To combine the different contributions of local micropatterns to face recognition, this paper proposes a weighted LBP histogram based on Weber's law. First, inspired by psychological Weber's law, intensity of local micropattern is defined by the ratio between two terms: one is relative intensity differences of a central pixel against its neighbors and the other is intensity of local central pixel. Second, regarding the intensity of local micropattern as its weight, the weighted LBP histogram is constructed with the defined weight. Finally, to make full use of the space location information and lessen the complexity of recognition, the partitioning and locality preserving projection are applied to get final features. The proposed method is tested on our infrared face databases and yields the recognition rate of 99.2% for same-session situation and 96.4% for elapsed-time situation compared to the 97.6 and 92.1% produced by the method based on traditional LBP.

In this paper, an online adaptive decision fusion framework is developed for image analysis and computer vision applications. In this framework, it is assumed that the compound algorithm consists of several sub-algorithms, each of which yields its own decision as a real number centered around zero, representing the confidence level of that particular sub-algorithm. Decision values are linearly combined with weights that are updated online according to an active fusion method based on performing orthogonal projections onto convex sets describing sub-algorithms. It is assumed that there is an oracle, who is usually a human operator, providing feedback to the decision fusion method. A video-based wildfire detection system is developed to evaluate the performance of the algorithm in handling the problems where data arrives sequentially. In this case, the oracle is the security guard of the forest lookout tower verifying the decision of the combined algorithm. Simulation results are presented.

In this paper, we present a multi-vehicle tracking method that uses integrated position and motion tracking methods to minimize missing and false detection. No existing state-of-the-art vehicle detection method can detect all the vehicles on the road and remove all false positive alarms. Therefore, a robust tracking-by-detection algorithm is necessary to minimize the number of false positive and false negative alarms. In multi-vehicle tracking, there are three types of errors such as false negative alarms, false positive alarms, and track identity switches. False negative and false positive alarms are caused by an imperfect detection algorithm, while track identity switches are caused by measurement-to-track pair confusion. Our tracking-by-detection method minimizes these errors while processing in real-time for online application. Sparse false positive alarms are reduced by a track initialization procedure. Motion tracking with selected features can minimize false negative alarms. A data association algorithm with complementary global and local distance prevents tracks from connecting measurements incorrectly. The proposed method was evaluated and verified in challenging, real road environments. The experimental results demonstrate that our multi-vehicle tracking method remarkably reduces false positive and false negative alarms and performs better than previous methods.

Event detection for video surveillance is a difficult task due to many challenges: cluttered background, illumination variations, scale variations, occlusions among people, etc. We propose an effective and efficient event detection scheme in such complex situations. Moving shadows due to illumination are tackled with a segmentation method with shadow detection, and scale variations are taken care of using the CamShift guided particle filter tracking algorithm. For event modeling, hidden Markov models are employed. The proposed scheme also reduces the overall computational cost by combing two human detection algorithms and using tracking information to aid human detection. Experimental results on TRECVid event detection evaluation demonstrate the efficacy of the proposed scheme. It is robust, especially to moving shadows and scale variations. Employing the scheme, we achieved the best run results for two events in the TRECVid benchmarking evaluation.

Moment invariants have received a lot of attention as features for identification and inspection of two-dimensional shapes. In this paper, two sets of novel moments are proposed by using the auto-correlation of wavelet functions and the dual-tree complex wavelet functions. It is well known that the wavelet transform lacks the property of shift invariance. A little shift in the input signal will cause very different output wavelet coefficients. The autocorrelation of wavelet functions and the dual-tree complex wavelet functions, on the other hand, are shift-invariant, which is very important in pattern recognition. Rotation invariance is the major concern in this paper, while translation invariance and scale invariance can be achieved by standard normalization techniques. The Gaussian white noise is added to the noise-free images and the noise levels vary with different signal-to-noise ratios. Experimental results conducted in this paper show that the proposed wavelet-based moments outperform Zernike's moments and the Fourier-wavelet descriptor for pattern recognition under different rotation angles and different noise levels. It can be seen that the proposed wavelet-based moments can do an excellent job even when the noise levels are very high.

We present a novel feature extraction algorithm for face recognition called the uncorrelated and discriminative graph embedding (UDGE) algorithm, which incorporates graph embedding and local scaling method and obtains uncorrelated discriminative vectors in the projected subspace. An optimization objective function is herein defined to make the discriminative projections preserve the intrinsic neighborhood geometry of the within-class samples while enlarging the margins of between-class samples near to the class boundaries. UDGE efficiently dispenses with a prespecified parameter which is data-dependent to balance the objective of the within-class locality and the between-class locality in comparison with the linear extension of graph embedding in a face recognition scenario. Moreover, it can address the small sample-size problem, and its classification accuracy is not sensitive to neighbor samples size and weight value, as well. Extensive experiments on extended YaleB, CMU PIE, and Indian face databases demonstrate the effectiveness of UDGE.

Robust multiple people tracking is very important for many applications. It is a challenging problem due to occlusion and interaction in crowded scenarios. This paper proposes an online two-stage association method for robust multiple people tracking. In the first stage, short tracklets generated by linking people detection responses grow longer by particle filter based tracking, with detection confidence embedded into the observation model. And, an examining scheme runs at each frame for the reliability of tracking. In the second stage, multiple people tracking is achieved by linking tracklets to generate trajectories. An online tracklet association method is proposed to solve the linking problem, which allows applications in time-critical scenarios. This method is evaluated on the popular CAVIAR dataset. The experimental results show that our two-stage method is robust.

Compressed video bitstreams are very sensitive to transmission errors. If we lose packets or receive them with errors during transmission, a video decoder normally applies error concealment techniques to repair the damaged frame. The effectiveness of these error concealment schemes relies on the performance of the error detection algorithm. In this paper, we present a new error detection scheme based on a fragile watermarking algorithm to support error concealment. We verified that the proposed algorithm generates good performances in peak signal-to-noise ratio and objective visual quality test through the computer simulation by H.324M mobile simulation set.

We propose a new public digital watermarking technique for video copyright protection working in the discrete wavelet transform (DWT) domain. The proposed scheme is a combination of spread-spectrum and quantization-based watermarking. The proposed scheme is characterized by two achievements: (i) a spread-spectrum technique is used to spread the power spectrum of the watermark data and (ii) an error correction code is applied and embeds the watermark with spatial and temporal redundancy. The goal of these two achievements is to increase robustness against attacks, protect the watermark against bit errors, and achieve a very good perceptual quality. The effectiveness of the proposed scheme is verified through a series of experiments in which a number of video and standard image-processing attacks are conducted. The proposed scheme achieves a very good perceptual quality with mean peak signal-to-noise-ratio values of the watermarked videos of >40 dB and high resistance to a large spectrum of attacks.

The performance of intra coding is important in many broadcasting and professional applications, because repeated insertion of intra frames usually requires a large portion of video data. In order to improve such intra coding performance, this paper proposes an advanced intra prediction scheme, systematically increasing prediction precision via optimal linear predictors for weakly-predicted subspace. Experimental results show that the proposed scheme outperforms the conventional and the recent best intra prediction methods by up to 11.41% and 9.08% of bitrate reduction, respectively.

Intra coding of an RGB video is important to many high fidelity multimedia applications because video acquisition is mostly done in RGB space, and the coding of decorrelated color video loses its virtue in high quality ranges. In order to improve the compression performance of an RGB video, this paper proposes an inter color prediction using adaptive weights. For making full use of spatial, as well as inter color correlation of an RGB video, the proposed scheme is based on a residual prediction approach, and thus the incorporated prediction is performed on the transformed frequency components of spatially predicted residual data of each color plane. With the aid of efficient prediction employing frequency domain inter color residual correlation, the proposed scheme achieves up to 24.3% of bitrate reduction, compared to the common mode of H.264/AVC high 4:4:4 intra profile.

Based on the vectorial Raleigh-Sommerfeld diffraction integral, an analytical propagation equation of vectorial nonparaxial hollow Gaussian beams (HGBs) through an annular aperture is derived. The corresponding closed-forms for a circular aperture, a circular black screen, and unapertured case are given as special cases of the general results. The typical numerical examples are given to illustrate our analytical results. It is shown that the f parameter plays an important role in determining the nonparaxiality of vectorial apertured HGBs.

Optical beams of Bessel-type, whose transverse intensity profile remains unchanged under free-space propagation, are called nondiffracting beams. In this paper, we propose a simple and effective method to generate spiral beams whose intensity remains invariant during propagation using amplitude masks. We show how the interaction between two incomplete annular beams leads to the formation of a spiral structure. Experimental observations are presented to show the characteristic features of the spiral structure generated. We can modulate the nondiffracting beam modifying the amplitude mask.

Multibiometric systems have been recently developed in order to overcome some weaknesses of single biometric authentication systems, but security of these systems against spoofing has not received enough attention. In this paper, we propose a novel practical method for simulation of possibilities of spoof attacks against a biometric authentication system. Using this method, we model matching scores from standard to completely spoofed genuine samples. Sum, product, and Bayes fusion rules are applied for score level combination. The security of multimodal authentication systems are examined and compared with the single systems against various spoof possibilities. However, vulnerability of fused systems is considerably increased against spoofing, but their robustness is generally higher than single matcher systems. In this paper we show that robustness of a combined system is not always higher than a single system against spoof attack. We propose empirical methods for upgrading the security of multibiometric systems, which contain how to organize and select biometric traits and matchers against various possibilities of spoof attack. These methods provide considerable robustness and present an appropriate reason for using combined systems against spoof attacks.