I used to joke around (most of you who read my editorials know that’s what I do most of the time anyway) that when I wrote my first book, I did it to stay married. My ex-wife was in medical school at the time and studied long hours most nights. So instead of hanging out at the pub, which is what I really wanted to do, I started writing a textbook at night that corresponded to a course in electro-optics that I taught at the University of Memphis. That book took five years to complete.

We proposed a novel scanning method for low-dose computed tomography (CT) that uses an oscillating multi-slit collimator between the x-ray source and the patient. It can be thought as a realization of sparse data sampling that does not require a fast x-ray power switching. A simulation study was performed based on experimentally acquired microCT data of a mouse to demonstrate the feasibility of the proposed method. A numerical collimation was designed to leave only one-fourth of each projection data for use in image reconstruction. A total-variation minimization algorithm was implemented for image reconstruction from the sparely sampled data. We have successfully shown that the proposed method provides a viable option to low-dose CT.

In this article, a cone-beam computed tomography scanning mode is designed using four x-ray sources and a spherical sample. The x-ray sources are mounted at the vertices of a regular tetrahedron. On the circumsphere of the tetrahedron, four detection panels are mounted opposite of each vertex. To avoid x-ray interference, the largest half angle of each x-ray cone beam is 27°22′, while the radius of the largest ball fully covered by all the cone beams is 0.460, when the radius of the circumsphere is 1. A proposed scanning scheme consists of two rotations about orthogonal axes, such that, each quarter turn provides sufficient data for theoretically exact and stable reconstruction. This design can be used in biomedical or industrial settings, such as when a sequence of reconstructions of an object is desired.

The authors fabricated a demountable Ferrule connector/Physical contact connection between silica fiber and a polymer optical fiber (POF) containing a fiber Bragg grating. The use of a connector for POF grating sensors eliminates the limitations of ultraviolet glued connections and increases the ease with which the devices can be applied to real-world measurement tasks.

Increasing communication traffic and plans to increase various services may cause a serious problem towards the power consumption of network equipment. One of the causes of large power consumption in the present network is the multiplexing scheme, such as wavelength division multiplexing (WDM) and electrical routing of the packet signals. WDM requires O/E (optical to electrical) and E/O (electrical to optical) signal conversion circuits with the same number as that of wavelength, resulting in an increase in power consumption. In addition to this electrical signal processing for the IP packet, routing, and switching at the router consumes a large amount of power. If we could process ultrafast signals using electromagnetic light waves without converting to electrical signals, this would reduce the power consumption of routers. One of the ways to overcome these problems is the development of all-optical computing devices. All-optical computing devices are based on the nonlinear interaction of light waves, which is an electromagnetic wave. The use of electromagnetic light waves makes computing, such as switching, possible at very high frequencies of more than 100 GHz. We discuss all-optical computing devices based on semiconductor optical amplifiers with the main emphasis on all-optical logic gates.

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Increasing manufacturing accuracy requirements enforce the development of innovative and highly sensitive measuring tools. Especially for measurement with submicrometer accuracy, the sensor principle has to be chosen appropriately for each measurement surface. Modern multisensor coordinate measurement systems allow automatic selection of different sensor heads to measure different areas or properties of a sample. As an example, different types of optical sensors as well as tactile sensors can be used within the same measuring system. I describe different principles of optical sensors used in multisensor coordinate measurement systems as well as a new approach for tactile measurement with submicrometer accuracy. A special fiber probe has been developed. The tip of the fiber probe is formed as a sphere. The lateral position of this sphere is observed by a microscope objective and can be determined within a fraction of a micrometer. Additionally, a novel optical setup now allows the determination of the z-position of the fiber tip with submicrometer accuracy. For this purpose, an interferometer setup is used. The laser light is coupled into the optical fiber. The light exiting the fiber tip is collected by the microscope objective and superposed with a reference wave, generated directly from the laser. The result is an interference signal that is recorded by the camera and processed by a computer. With this setup, the z-displacement of the fiber sphere can be measured with an accuracy of a fraction of the laser wavelength used.

A new high-precision contact probe with a large scanning range is proposed and validated, which is able to measure miniature components on a micro/nano-coordinate measuring machine (CMM). This scanning probe is composed of a fiber stylus with a ball tip, a mechanism with a wire-suspended floating plate, a two-dimensional (2-D) angle sensor, and a miniature Michelson linear interferometer. The stylus is attached to the floating plate. The wires experience elastic deformation when a contact force is applied, and then the mirrors mounted on the plate are displaced; the displacements can be detected by corresponding sensors. According to industrial demands, such as scanning range, resolution, equal stiffness, contact force, and probe size, several constrained conditions are established, and the optimal structure parameters of the probe are selected. Each component of the probe is designed, fabricated, and assembled in this research. Simulation and experimental results show that the probe can achieve uniform stiffness, ±20-μm scanning range, and 1-nm resolution in x, y, and z directions. The contact force is about 40 μN when the tip ball is displaced 20 μm. It can be used as a contact and scanning probe on a micro/nano-CMM.

In most cases of optical critical dimension metrology, when applying rigorous coupled-wave analysis to optical modeling, a high order of Fourier harmonics is usually set up to guarantee the convergence of the final results. However, the total number of floating point operations grows dramatically as the truncation order increases. Therefore, it is critical to choose an appropriate order to obtain high computational efficiency without losing much accuracy in the meantime. We show that the convergence order associated with the structural and optical parameters is estimated through simulation. The results indicate that the convergence order is linear with the period of the sample when fixing the other parameters, both for planar diffraction and conical diffraction. The illuminated wavelength also affects the convergence of a final result. With further investigations concentrated on the ratio of illuminated wavelength to period, it is discovered that the convergence order decreases with the growth of the ratio, and when the ratio is fixed, convergence order jumps slightly, especially in a specific range of wavelength. This characteristic could be applied to estimate the optimum convergence order of given samples to obtain high computational efficiency.

More and more infrared optical systems work in cryogenic temperatures in order to achieve a high signal-to-noise ratio. Infrared materials' optical properties, such as the refractive index and thermo-optic coefficient (dn/dT) are critical to enable high quality, infrared lens designs for cryogenic temperatures. We show a new cryogenic absolute prism refractometer.

Fringe projection methods using the phase-shifting technique have the advantages of fast 3-D shape measurement and high accuracy. The performance of the fringe projection system, including image quality, nonlinearity of the projected intensity, stability, and switching time for multiple phase-shifted patterns, is essential for fast and accurate shape measurement. A fast and accurate measurement system using a ferroelectric liquid-crystal-on-silicon microdisplay and a high-powered light emitting diode light source is developed. Our results indicate that the nonlinearity of the projected intensity and the stability of the fringe projection were dramatically improved compared with an ordinary commercial liquid crystal display projector. The rapid measurement of the warpage distribution of a flip chip ball grid array electronic package was performed by using the developed system. Nine phase-shifted fringe images with a resolution of 1280×960 pixels were recorded in 1.6 s. In addition, the measurement results obtained by our system agreed well with the results obtained from a micrometer and laser focus sensor. The average error was 2.6 µm, and the standard deviation was less than 10 µm with a 6-mm measurement range.

Full-field chromatic confocal surface profilometry employing a digital micromirror device (DMD) for spatial correspondence is proposed to minimize lateral cross-talks between individual detection sensors. Although full-field chromatic confocal profilometry is capable of enhancing measurement efficiency by completely removing time-consuming vertical scanning operation, its vertical measurement resolution and accuracy are still severely affected by the potential sensor lateral cross-talk problem. To overcome this critical bottleneck, a DMD-based chromatic confocal method is developed by employing a specially-designed objective for chromatic light dispersion, and a DMD for lateral pixel correspondence and scanning, thereby reducing the lateral cross-talk influence. Using the chromatic objective, the incident light is dispersed according to a pre-designed detection range of several hundred micrometers, and a full-field reflected light is captured by a three-chip color camera for multi color detection. Using this method, the full width half maximum of the depth response curve can be significantly sharpened, thus improving the vertical measurement resolution and repeatability of the depth detection. From our preliminary experimental evaluation, it is verified that the ±3σ repeatability of the height measurement can be kept within 2% of the overall measurement range.

A novel metal coated long period fiber grating (LPFG) liquid sensor is presented, in which the dual-peak resonance (DPR) combined with the surface plasma resonance is utilized to improve the sensitivity to liquid concentration. Based on the coupled-mode theory, the double-clad structural model is used to analyze the dual-peak resonant characteristics and refractive index sensing properties of this LPFG. The results show that dual resonant peaks are far away from each other, and shift in opposite directions with an increase of surrounding refractive index. In addition, the influence of metal film thickness and grating structural parameters (grating period Λ, average index change σ) on the sensitivity to refractive index is discussed for this LPFG sensor, which provides a foundation for designing high sensitivity liquid LPFG sensors. Experimentally, the silver films were coated on a LPFG by direct current sputtering, and the dual resonant peaks were observed in this LPFG. Then the salt solution concentration monitoring test was performed. The results indicate the metal coated LPFG based on DPR has higher refractive index sensitivity as compared with dual-peak based non-coated LPFG and general single peak based LPFG, the resolution of liquid refractive index is available to 10−5 for the proposed LPFG with suitable film and grating parameters.

A spectrally resolved interferometry ranging method based on the optical frequency comb of a femtosecond pulse laser was presented. The approach utilized a frequency stabilized Ti:sapphire femtosecond pulse laser to provide a phase-locked summation of discrete quasi-monochromatic light modes of consecutive frequencies, which is seen as an optical comb in the frequency domain. In this method all modes interference signals of the optical frequency comb obtained by the femtosecond light pulses traveling along different optical path between the reference and measurement arms were utilized to measure absolute distance. A Fabry-Perot Etalon was used to filter smaller frequency modes from the broad-bandwidth femtosecond laser pulse produced. The actual measured light spectrum of the femtosecond laser source was used as the input data, the whole process of the spectrally resolved interferometry ranging method was simulated through MATLAB. The simulation results indicate that the spectrally resolved interferometry ranging method could satisfy the demand of the small scale measurement with a nonambiguity range of 5.75 mm and an associated resolution of nanometer level.

Absolute planarity measurement with interferometric data and iterative surface recovering approaches is briefly reviewed. Extension to the case of multiple measurements is outlined, and demonstration with synthetic data is provided. A generalized approach is finally presented, making use of operators representing the manipulations occurred with the surfaces taking part in the generation of the interferograms. The potential advantages of the new interferogram processing technique are pointed out.

Height measurement for a moving human body is a hard task for human body estimation. We propose a novel algorithm for real-time human height measurement without knowing any camera parameter, just having a vertical reference height. As contrasted with the previous research methods in the context of camera calibration, the studied algorithm reduces the complexity of user operations and the economy cost. First, three or more pairs of top-points and bottom-points are extracted by detecting the moving human body to solve the vertical vanishing point and the horizontal vanishing line. Then, the height of the moving human body on ground plane or stepped plane is obtained using the solved vanishing point, the vanishing line, and a given reference height. Considering the importance of the vanishing point and the vanishing line and the sensitivity of both to noise, an optimal approach is adopted. Finally, we show the optimal number and position of the human body in a camera field. Both computer simulation and real testing data validate the robustness and the effectiveness of the proposed algorithm.

Traditional displacement measurement systems by grating, which purely make use of fringe intensity to implement fringe count and subdivision, have rigid demands for signal quality and measurement condition, so they are not easy to realize measurement with nanometer precision. Displacement measurement with the dual-wavelength and single-grating design takes advantage of the single grating diffraction theory and the heterodyne interference theory, solving quite well the contradiction between large range and high precision in grating displacement measurement. To obtain nanometer resolution and nanometer precision, high-power subdivision of interference fringes must be realized accurately. A dynamic tracking down-conversion signal processing method based on the reference signal is proposed. Accordingly, a digital phase measurement module to realize high-power subdivision on field programmable gate array (FPGA) was designed, as well as a dynamic tracking down-conversion module using phase-locked loop (PLL). Experiments validated that a carrier signal after down-conversion can constantly maintain close to 100 kHz, and the phase-measurement resolution and phase precision are more than 0.05 and 0.2 deg, respectively. The displacement resolution and the displacement precision, corresponding to the phase results, are 0.139 and 0.556 nm, respectively.

Specialized video measuring system (SVMS) is a kind of instruments diagnosing only one special type of part with high performance. In the design of a SVMS, it is necessary to consider the special requirements during the inspection of the parts. We take the video-based inspecting instrument for watch escapement (VIIWE) as an example of SVMS. A method based on least interferences is proposed to determine an optimized movement layout. The quality of image taken by an imaging lens with a limited depth of field (100 μm) may be degraded by two parameters, i.e., the perpendicularity of optical axis to workbench and the parallelism of probe movement plane to workbench. To optimize the two parameters, we calibrate the perpendicularity with a definition function, measure the parallelism with a dial indicator, and develop a mechanism of adjustment. The scheme about movement layout and adjustment has been successfully applied in the VIIWE.

Optimization and active control of the tip clearance of turbine blades has been identified as a key to improve fuel efficiency, reduce emission, and increase service life of the engine. However, reliable and real-time tip clearance measurement is difficult due to the adverse environmental conditions that are typically found in a turbine. We describe a dual-beam fiber optic measurement system that can measure the tip timing and tip clearance simultaneously. Because the tip timing information is used to calculate the tip clearance, the method is insensitive to the signal intensity variation caused by fluctuations in environmental conditions such as light source instability, contamination, and blade tip imperfection. The system was calibrated and tested using experimental rotors. The test results indicated a high resolution of 4.5 μm and measurement accuracy of ±20 μm over the rotation speed range of 2000 to 10,000 rpm.

Optical zoom enables wide and narrow fields-of-view within a single optical system. Traditional zoom designs translate elements along the optical axis, a technique that is generally prohibitive for large diameter optics. Adaptive optical zoom (AOZ) alters system magnification via variable focal length elements, a technique that has the potential to facilitate zoom in large diameter systems. This paper details a novel optical theory developed to design AOZ systems. The developed theory modifies existing techniques for telescope objective design and third-order aberration determination to accommodate the additional degrees of freedom found with AOZ. The derived theory also enables a large-scale tradespace analysis, allowing optical design to begin from a broad perspective and optimize a particular design. Using the tradespace analysis, a Cassegrain AOZ objective with a 3.3Xzoom ratio is designed, demonstrating the capability and validity of the theory.

With the current retinal imaging systems, laser cavities and astronomical spectroscopes, there is the need to employ off-axis reflective systems. These systems, often used in configurations where the object or image are at the infinite with respect to the spherical mirrors, are the most used in this type of instrumentation. Expressions for the wavefront aberrations in an off-axis spherical mirror with image or object at the infinite are presented, analyzed and evaluated. Formulas are derived from the optical path difference between a paroboloid, as reference surface, and a sphere. Exact and approximate expressions, assuming a relative small pupil and a small angle of incidence are presented. They can be used to design and analyze some off-axis reflective systems.

Image reconstruction methods employed in horizontal imaging scenarios must provide the best possible reconstructions over a broad range of conditions. In addition to variations in turbulence conditions, these systems must perform when operated by novice users who may lack knowledge regarding the underlying reconstruction algorithms. Systems that maintain their performance under these conditions and are otherwise immune to factors that cause variability in performance are considered to be robust. We evaluate the effect of varying design parameters, such as the number of input frames, inverse filter parameters, and number of phase estimates parametrically. We find that, for most conditions, it is possible to achieve performance near the limit available from these estimators using as few as 15 input frames, the average of 4 estimates of the object phase, and with only approximate knowledge of the imaging conditions. When operated under these conditions, speckle-imagers can be considered robust. In addition to this analysis, the bispectrum and Knox-Thompson methods were compared as alternative phase estimation techniques. We find that the Knox-Thompson phase estimation method is preferred in situations where minimum computation complexity is desired.

Multiscale designs greatly simplify the large-scale optics needed to realize the resolution of a large aperture. Unlike most monolithic lens systems, multiscale cameras have interdependencies between the optics at various scales. To realize a successful multiscale design, the relationships between microcamera scale and overall camera scale parameters must be understood. Starting with a specification of the multiscale camera, we present a simplified model that allows paraxial optical quantities to be estimated. Based on these quantities, a monocentric objective and a microcamera can be designed. An example of a practical design using spherical glass optics is presented.

We propose a three-dimension (3-D) depth-accuracy enhancement framework of time-of-flight (ToF) depth camera. First, we propose a frame interpolation from unsegmented, unmeshed, and noisy ToF depth video, and a novel temporal interpolative filtering method. This method allows us to increase integration time for given fixed frame rate. Because of the lack of explicit point correspondences between textureless depth images, global rigid motion is estimated from sparse 3-D corner feature matchings between two reference depth frames. Given global rigid motion, a nonrigid iterative closest point detection is adopted to find dense 3-D depth point correspondence for accurate frame interpolation. A temporal interpolative filtering without additional frame memory is introduced to enhance the depth accuracy after the frame interpolation. Experimental results demonstrate the promising performance of accuracy enhancement producing real-time depth video.

Direct measurement of the modulation transfer function (MTF) of focal plane arrays (FPAs) using random laser speckle approaches for the visible/near-infrared wavelength band has been well documented over the last 20 years. These methods have not transitioned to the midwave infrared (MWIR) primarily because other techniques have been sufficient and MWIR laser sources with sufficient output power have been unavailable. However, as the detector pitch decreases, MTF measurements become more difficult due to diffraction, while potential MTF degradation due to lateral carrier diffusion crosstalk makes accurate MTF characterization critical for sensor system design. Here, a random laser speckle FPA MTF measurement approach is adapted for use in the MWIR that utilizes a quantum cascade laser coupled with an integrating sphere to generate the appropriate in-band random speckle. Specific challenges associated with the technique are addressed including the validity of the Fresnel diffraction assumptions describing the propagation of the random speckle field from the integrating sphere to the FPA. Improved methods for estimating the power spectral density (PSD) of the measured speckle that reduce data requirements are presented. The statistics and uniformity of the laser speckle are presented along with PSD measurements and estimated MTFs of a MWIR FPA.

Shearography is a whole-field, noncontact optical technique that allows the direct measurement of first-order derivatives of deflection on spatial coordinates, depending on the measurement setup. In many cases, the curvatures and twists of an object provide more interesting parameters, as they are directly related to the induced stresses when an object is subjected to external loads. We describe the use of digital shearography for the measurement of these stress-related parameters through phase retrieval when an object is undergoing continuous deformation. A sequence of shearograms is captured by a high-speed camera during the deformation. To avoid the problem of phase ambiguity, either a spatial or temporal carrier is introduced. A comparison of spatial and temporal carrier is also presented. The obtained three-dimensional matrix is then analyzed by Fourier and windowed-Fourier transform in a spatial and temporal domain and a high-quality spatial distribution of the deflection derivative, curvature and twist are extracted at any instant.

The accuracy of optical three-dimensional metrology scanning decreases as the size of the parts for inspection increase to several tens of meters because of accumulated errors. A combined method that includes coordinate and surface metrology is proposed. The method features the use of a laser tracker, photogrammetric system, and a hand-held scanner that identifies fiducials. Each instrument provides a distinct measurement density of point data and ranges which are complementary to each other. The laser tracker is used to position and orient the scanner within a large volume, thus, to ensure accurate measurement, the data captured in the respective sensors' coordinate system is aligned to a common global coordinate system. Close-range photogrammetry is used to improve the speed with which fiducials are measured. The measurements obtained, using the photogrammetric system and laser tracker, are combined to produce highly accurate measurements of part surfaces. The performance, of the combined measurement systems, is verified by measuring calibrated lengths. Results show that the proposed technique enables quick measurement and yields submillimeter accuracy in measuring the absolute distance up to the laser tracker range. Error accumulation is therefore avoided.

In this paper a novel pattern design for camera calibration using planar patterns with the Zhang calibration method is presented. In contrast to other work related to this calibration technique, which deals with the design and extraction of spatial image features, our focus lies on the precise and fully automated extraction of corresponding points by temporal image features using a sequence of planar patterns, which are displayed by a flat screen. The extraction of correspondences in our approach does not utilize areal properties of the images and therefore is hardly influenced by projective distortion, image distortion, or inhomogeneous illumination. Furthermore, not the whole pattern but only parts of it need to be visible in an individual view. In addition, the planarity as well as the physical precision of the control points of the pattern are ensured by the very nature of the flat screen. The overall calibration time may be reduced, as no human interaction is necessary. We compare the results gained from this novel temporal pattern design with those gained from commonly used checkerboard patterns. The proposed approach resulted in an increased precision for the calibration.

Lithium tungsten borate photonic glass is prepared by the conventional melt-quench technique. Due to semiconductor-like behavior of zinc oxide, the glass is doped by ZnO to adapt its optical nonlinearity. Fresnel-based spectrophotometric measurements and Lorentz dispersion theory are applied to study (in a very wide range of photon energy from 0.5 to 6.2 eV) the dispersion of second-order refractive index, two-photon absorption coefficient, and third-order optical susceptibility of the glass. The figure of merit (FOM) needed for optical switching applications is estimated. We reveal the importance of determining the dispersion of the optical nonlinear parameters to find out the appropriate operating wavelength for optimum FOM of the glass.

Point laser probes (PLPs) with charge-coupled device (CCD) are widely used in industry engineering. However, the distance detection accuracy is significantly affected by incident angle, which limits the application in free-form surface measurement. To analyze the influence of incident angle, a reference distance is first determined under normal incidence. Then the detection errors are estimated by the relative differences of non-zero incident angles from the reference. Based on laser ray tracking strategy and superposition principle, an intensity spot is formed on the detector plane. The image deviation is assessed using a robust subpixel algorithm. Therefore the distance detection error can be numerically predicted. As a comparison, a precision calibration system is set up, which is composed of CCD-PLP, data card, human manual interface, pulse controller, step motor driver, and calibration device. A calibration procedure was programmed on the upper PC. Thus data sampling, angle control, and error assessment can be achieved. A series of prediction and calibration tests covering angle range from −55  deg to 55 deg were conducted on a five-axis machining center. The results indicate that the trend of calibration was quite coincident with that predicted. The distance detection error has an approximate linear function of incident angle.

The effects of near-ground wind turbulence-induced laser beam wander on photothermal beam deflection performance are presented. The theories of both photothermal deflection and turbulent beam wander are summarized. The semiphenomenological theory and experiment beam wander curve shapes and magnitudes match well over the range of 10 to 5000 Hz. The photothermal deflection modulation curves are set equal to the turbulence beam wander curves, and an effective turbulence equivalent concentration of the vapor of a chemical analyte can be derived as a function of frequency for the range 10 to 5000 Hz. The results show the limitations of near-ground level photothermal deflection measurements when wind is present in the beam path. The frequency points at which 1 ppbv of acetylene gas can be detected at different wind speeds and pump beam power are obtained. The wind is assumed to propagate parallel to the hard surface.

This paper describes a new technique that was developed for performing three-dimensional (3-D) reconstruction on-the-fly for inspection applications. It is based on the same principles as the traditional depth from focus approach but is able to estimate the three-dimensional structure of a surface as it is undergoing a continuous linear lateral translation, similar to the situation on many types of modern production lines. This has important applications in the area of automated inspection and quality control, since the ability to inspect materials in real-time as they are being manufactured in a continuous process is valuable in a broad range of circumstances. We assume that the relative motion of the surface is known, which is realistic in these types of environments. We demonstrate the technical feasibility of our approach, including its ability to acquire 3-D shape on several different types of structured surfaces.

Efforts in developing a synthetic environment for testing light detection and ranging (LADAR) sensors in a hardware-in-the-loop simulation are continuing at the Aviation and Missile Research, Engineering, and Development Center of the U.S. Army Research, Engineering and Development Command (RDECOM). Current activities have concentrated on evaluating the optical projection techniques for the LADAR synthetic environment. Schemes for generating the optical signals representing the individual pixels of the projection are of particular interest. Several approaches have been investigated and tested with emphasis on operating wavelength, intensity dynamic range and uniformity, and flexibility in pixel waveform generation. This paper will discuss some of the results from these current efforts at RDECOM's System Simulation and Development Directorate's Electro Optical Technology Development Laboratory.

The image quality of two active matrix organic light emitting diode (AMOLED) smart-phone displays and two in-plane switching (IPS) ones was visually assessed at two levels of ambient lighting conditions corresponding to indoor and outdoor applications, respectively. Naturalness, colorfulness, brightness, contrast, sharpness, and overall image quality were evaluated via psychophysical experiment by categorical judgment method using test images selected from different application categories. The experimental results show that the AMOLED displays perform better on colorfulness because of their wide color gamut, while the high pixel resolution and high peak luminance of the IPS panels help the perception of brightness, contrast, and sharpness. Further statistical analysis of ANOVA indicates that ambient lighting levels have significant influences on the attributes of brightness and contrast.

A new method to optimize transmission of photonic crystal filter composed of coupled cavities is proposed. This method can improve transmission without changing 3 dB bandwidth and it is achieved by shifting the defect rods in two cavities centripetally to shorten the distance between energy distribution centers within two cavities. Finally, an ultra compact four-channel demultiplexer is demonstrated by using this optimization method, and this device satisfies the coarse wavelength division multiplexing standard of ITU-T G.694.2 with transmission 99% for each channel.

By considering the influence of the turn-off time and the modulation frequency of the acousto-optic (AO) modulator, the coupled rate equations for a diode-pumped doubly Q-switched and mode-locked (QML) laser with AO modulator and Cr4+∶YAG saturable absorber under Gaussian approximation are given. By numerically solving these equations, the key parameters of an optimally coupled doubly QML laser including the gain medium, the saturable absorber and the resonator as well as the modulation frequency of AO modulator are obtained, which can maximize the pulse energy of singly Q-switched envelope. A diode-pumped doubly QML Nd∶GdVO4 laser with AO modulator and Cr4+∶YAG saturable absorber is constructed and the experimental results are in agreement with the numerical simulations.

We propose a simple method to fabricate graphene saturable absorber (GSA) through drop casting the graphene dispersion prepared by liquid-phase exfoliation of graphite onto quartz plate and realize the passively mode-locked of an Erbium-doped fiber laser by this saturable absorber (SA). In contrast with previous GSAs, due to the incorporation of additional free space alignment from the SA component, we are able to deliberately control the laser radiation spot size and location on GSA, leading to flexibility in mode-locked performance. Finally, we can obtain stable soliton pulse emission with central wavelength at 1564.42 nm, 3 dB bandwidth of 1.02 nm, and pulse duration of 2.89 ps, and also note that soliton parameters (pulse energy, central wavelength, and pulse duration) sensitively depend on the position of GSA, which could be traced back to nonuniformity of saturable absorption from the nonhomogeneous morphology of the as-prepared graphene sample.

Damage sites as large as 600 μm in fused silica surface were successfully mitigated with a new protocol by hydrofluoric acid (HF) etching combined with carbon dioxide laser treatment. The damage sites were first etched in 40% HF solution to blunt the fractures, and then the etched damage sites were smoothed with a CO₂ laser. It has been found that the etching rate of damaged material in the lateral direction is larger than in the longitudinal direction; thus, an optimized etching time was chosen to etch the damage sites based on the etching ratio. Three types of damage test methods were used to confirm the mitigation efficiency of the protocol. The results indicate that the damage resistance capability of mitigated sites can recover to the level of pristine substrate.

Raman distributed temperature sensing (RDTS) is widely used in many fields. The system configuration, devices, and data processing methods have been well studied and improved, but research on sensing fiber itself is rare. We design a multimode fiber for RDTS based on experimental results from a series of conventional multimode fibers. The optimized multimode fiber offers temperature sensing at a distance less than 10 km. It has a much larger nonlinear effect than conventional multimode fibers, so the spontaneous anti-stokes signal under the same optical input is 1.5 to ∼ 2.4 times higher. Its loss and dispersion within the wavelength range from 1400 to 1650 nm is acceptable. Therefore, under the same system configuration, a higher anti-stokes signal is received by the data acquisition card, which makes signal acquisition and processing easier and improves temperature sensitivity, accuracy, and resolution without sacrificing other characteristics, such as spatial resolution and measuring distance.

A novel star detection approach based on color filter array detectors that simultaneously measures both the centroid position and spectral properties of the observed stars is proposed.This additional color information can be used to supplement the geometric measurements that form the basis of most modern star-matching routines used in star trackers. We present a candidate model for star detection, based on bivariate Gaussian intensity function with separate color magnitude parameters (i.e., red, green, and blue). The model is fit to the observed point spread function using a nonlinear least squares algorithm. We consider several parameterizations to our model and explore the performance of these alternate schemes using laboratory and night-sky testing. These studies demonstrate that consistent color measurements are possible with well-designed optics.

A metamaterials (MTM)-core slab waveguide overlaid with a MTM buffer layer was used to enhance an evanescent field. The guided modes were graphically obtained by a new dispersion equation of the four-layered MTM-core slab waveguide modeled to have four layers, including an air layer, buffer layer, slab waveguide layer, and substrate layer. With the tuning of the refractive index and width of the MTM-buffer layer, abuffer layer with one-tenth of the core-layer width was obtained together with the refractive index of 1.7, making the evanescent field increase up to 1.8 times.

A route of delivering ultra-short laser pulses through a polarization-maintaining single-mode fiber has been investigated experimentally. The group velocity dispersion was well compensated, and the self-phase modulation was depressed in fiber. Finally, a 40-fs laser pulse with the energy of 70 pJ was obtained at the output of the transmitted fiber with the length up to 4 m in our fiber-delivery system. The route exhibits distinguishing features of compactness and flexibility, and this 40-fs laser pulse can be used not only to generate broadband terahertz (THz) radiation but also to detect broadband THz radiation, which is much better than the 150-fs laser pulse used previously.

We propose and experimentally demonstrate a low cost, low power consumption technique for ultra-wideband pulse shaping. Our approach is based on thermal apodization of two identical linearly chirped fiber Bragg gratings (LCFBG) placed in both arms of a balanced photodetector. Resistive heating elements with low electrical power consumption are used to tune the LCFBG spectral responses. Using a standard gain switched distributed feedback laser as a pulsed optical source and a simple energy detector receiver, we measured a bit error rate of 1.5×10−4 at a data rate of 1  Gb/s after RF transmission over a 1-m link.

An imprinted polymeric wavelength-independent coupler (WINC), which is one of the core components used in optical fiber communications and fiber-to-the-home systems, was designed with a beam propagation method. Its designed structure has the form of the Mach-Zehnder interferometer. The polymer core size of the WINC was optimized at 8×8  μm using an imprinting technique, the hot embossing process. Optical properties of the polymeric WINC were evaluated by measuring its insertion loss and transmission spectrum. The insertion loss values for channels 1 and 2 were 3.5 and 4.2 dB, respectively, and the transmission spectrum was flat over a range of 1260 to 1640 nm.

A high-sensitivity temperature sensor based on fiber Bragg gratings (FBGs) in liquid-filled photonic crystal fibers (PCFs) is proposed. PCF is designed using the full-vector finite-element method. To achieve the maximum difference of the core-mode effective index of PCF as the temperature change, the structural parameters of PCF are optimized via genetic algorithms. The calculated Bragg wavelength shift (BWS) value of FBGs in liquid-filled PCF is 263  pm/°C as the temperature changes from −15°C to 65°C.

A Mueller-Stokes analysis of the polarization characteristics of a photonic crystal fiber (PCF) with a mechanically induced long-period fiber grating (MLPFG) is presented. Results show that the diattenuation and the polarizance parameters, and the anisotropic degree of depolarization, increase greatly with the LPFG in the PCF. The depolarization index, the Q (M) depolarization scalar metric, the theorem of Gil-Bernabeu, and the degree of polarization, provide consistent results that indicate the existence and the increasing of depolarization effects due to the presence of the LPFG in the PCF. Finally, the polarization dependent loss also increases when the LPFG is present in the fiber for a wavelength illumination centered at 1064 nm. As a conclusion, the PCF with LPFG cannot be described by the Jones matricial formulism. One important result we have found here is that the PCF we employed has an intrinsic anisotropic degree of depolarization.

A new technique of terahertz (THz) frequency carrier generation for multi-channel radio frequency identification (RFID) use is proposed. The dense wavelength division multiplexing signals can be obtained by using a Gaussian pulse propagating within a modified add-drop filter known as a PANDA ring resonator. The THz device system can be made contributions to the promising applications, especially in high-speed switching, demultiplexing, and wavelength conversion of optical signals, in which the effect of THz control is also required and essential for the potential application to ultra-high speed wireless digital interconnects for computer chips with ultra-high clock rates. In principle, the high-density frequency (wavelength) can be generated and used to form the RFID; moreover, the tiny device system is another advantage, which can be constructed to incorporate the currently used system. The results obtained have shown that higher density and increasing channel capacity can be obtained and are useful for the large demand for RFID applications.

Arbitrary operating conditions, such as the temperature dependence in the fiber link impose a challenge for the extension of radio-over-multimode fiber techniques. Temperature impairment characterization is analyzed over the broadband transmission bands that can be present in the frequency response of multimode fiber (MMF) supporting multiple-GHz carriers delivering schemes. Experimental results show that these transmission bands are dramatically influenced by the hysteresis of heating and cooling temperature cycles, respectively. The influence of the MMF graded index exponent tolerance on frequency response at higher bands is also analyzed. And this variation can be directly attributed to environmental temperature changes that could affect the MMF link. Additionally, selective mode-launching schemes combined with the use of narrow line-width optical sources are experimentally demonstrated to enable broadband transmission, not only at short but also at middle-reach distances over MMFs.

High quality permanent connection between optical fibers is a significant issue in optics and communication. Studies on room temperature optical large diameter fiber-fiber direct bonding, which is essentially surface interactions of glass material, are presented here. Bonded fiber pairs are obtained for the first time through the bonding technics illustrated here. Two different kinds of bonding technics are provided-fresh surface (freshly grinded and polished) bonding and hydrophobic surface (activated by H2SO4 and HF) bonding. By means of fresh surface bonding, a bonded fiber pair with light transmitting efficiency of 98.1% and bond strength of 21.2 N is obtained. Besides, in the bonding process, chemical surface treatment of fibers' end surfaces is an important step. Therefore, various ways of surface treatment are analyzed and compared, based on atomic force microscopy force curves of differently disposed surfaces. According to the comparison, fresh surfaces are suggested as the prior choice in room temperature optical fiber-fiber bonding, owing to their larger adhesive force, attractive force, attractive distance, and adhesive range.

This paper proposes a novel indoor positioning algorithm using visible light communications (VLC). The algorithm is implemented by preinstalled light-emitting diode illumination systems. It recovers the VLC channel features from illuminating visible light and estimates receiver locations by analytically solving the Lambertian transmission equation group. According to our research, the algorithm is able to provide positioning resolution higher than 0.5 mm, in a practical indoor environment. The performance significantly exceeds conventional indoor positioning approaches using microwaves.

A new method of optical cryptography using dark-bright soliton conversion control within a modified add/drop optical filter is proposed. A pair of optical keys is randomly generated and transmitted into the transmission line, where finally the corrected keys between Alice (sender) and Bob (receiver) can be retrieved. In principle, the coincidence (orthogonal) dark-bright soliton pair has shown promising behaviors, especially when they propagate into the π/2 phase shifter, i.e. beamsplitter, the shift in phase of π/2 between dark and bright solitons is occurred and separated. Such behaviors can be used to form the orthogonal light modes (solitons), which are useful for cryptographic application, where in this case the long-distance cryptography can be easily managed. We have derived and presented a new concept of multi-orthogonal solitons generated by using dark-bright soliton pulses within the modified add/drop optical filter, which is known as a PANDA ring resonator. By using the dark-bright soliton conversion control, the obtained output of the dynamic states can be used to randomly form the multi-orthogonal soliton pairs, which can be available for computer and communication security applications, especially for long-distance link.

An interferometric technique for three-dimensional phase measurement of optically transparent microscopic phase samples is presented. An obliquely aligned polarizer-masked cube beam-splitter, an infinity-corrected microscope objective, and a couple of simple polarization phase-shifting components serve as the setup for such a measurement. Surface phase profiles are then extracted using standard phase-shifting algorithms. The salient features of the proposed technique are its simple design, in-line configuration, possibility of integration with standard microscopic systems, and inherent compensation of the substrate phase. Experimental results are presented. The overall lateral magnification is restricted due to the low numerical aperture offered by the microscope objective and cube beam-splitter combination.

A digital micro-mirror device (DMD) acting as a real-time hologram is an emerging technology in dynamic holographic projection. This paper presents a lensless image magnification method in DMD holography by using a Fresnel hologram. By analyzing the diffraction order distribution in the image plane of a hologram produced by DMD, we find the factors that limit the size of the magnified image. We perform a lensless magnification experiment that shows good magnified images in accordance with the numerical results. Finally, we discuss methods to eliminate longitudinal error and chromatic aberration in three-dimensional (3-D) and color projection, respectively, and present a 3-D image reconstruction result that shows lensless magnification of a 3-D image without distortion. It is believed that this technique can be used in future real-time holographic projection based on digital light processing technology.

A new shape of blackbody cavity composed of a conical generatrix and a flat inclined bottom is developed for absolute optical radiation measurement in space. For the new-shape cavity with specular isothermal cavity walls, the Monte Carlo method was used to obtain the optimal cavity geometrical parameters, such as the conical angle and inclination angle of the bottom. Distribution maps of the number of reflections over the aperture for traced rays were depicted for demonstrating the performance of the new cavity. Finally, the new-shape cavity was simulated as a blackbody absorber in cryogenic solar absolute radiometer (CSAR). Calculation results reflect that the new-shape cavity can get high absorptivity and achieve high accuracy measurements in CSAR from space.

Aiming at the space target and two dominant background sources including the sun and earth-atmosphere system, their radiation models are established, and the background influence on the space target detection for the space-based infrared imaging system are discussed in the long wave infrared (8 to 14 μm) range. From the numerical calculation and analysis, we find that the earth-atmosphere system is the strongest background interference source and will form a big detection blind zone, followed by the sun, whose irradiance is about 1.6% of that from the earth-atmosphere system. Compared with these two intense radiations, the space target radiation acting on the space-based infrared detector is so weak that it may be submerged once the target appears in the earth-atmosphere or solar backgrounds. Thus, in order to reduce the influence of the background interferences, necessary measures must be taken to control the space-based infrared detector and its host platform in real time, such as adjusting the flight attitude, changing the detection angle, transferring operating orbit, and so on.

Hyperspectral unmixing is a process aiming at identifying the constituent materials and estimating the corresponding fractions from hyperspectral imagery of a scene. Nonnegative matrix factorization (NMF), an effective linear spectral mixture model, has been applied in hyperspectral unmixing during recent years. As the data of hyperspectral imagery analyzed deeper, prior knowledge of some signatures in the scene could be available. In several scenes such as mining areas, a few surface substances like copper and iron are easy to identify through field investigation. Thus, their spectral signatures can be used as prior knowledge to unmix hyperspectral data. In such a context, we propose an NMF based framework for hyperspectral unmixing using such prior knowledge, referred to as NMFupk. Specifically, our algorithm supposes that some spectral signatures in the scene are known and then utilizes the prior knowledge of the spectral signatures to unmix the hyperspectral data. In a series of experiments, we test NMFupk and NMF without prior knowledge on both synthetic and real data. Results achieved demonstrate the efficacy of the proposed algorithm.

A challenge for current edge-preserving image decompositions is to deal with noisy images. Gradient- or magnitude difference-based techniques regard the noise boundary as edges, while the local extrema-based method suffers from averaging noisy envelops. We introduce local anisotropy derived from nonlinear local structure tensor to differentiate edges from fine-scale details and noises. Providing low smoothness weights to the places with large local anisotropy rather than a large gradient under the improved weighted least squares optimization framework, we present a noise-resistant, structure-preserving smoothing operator. By either progressively or recursively applying this operator we construct our structure-preserving multiscale image decomposition. Based on the key property of our algorithm, noise resistance, we compare our results with existing edge-preserving image decomposition methods and demonstrate the effectiveness and robustness of our structure-preserving decompositions in the context of image restoration, noisy image abstraction, and noisy image dehazing.

A novel depth estimation and occlusion boundary recovery approach for a single outdoor image is described. This work is distinguished by three contributions. The first contribution is the introduction of a new depth estimation model, which takes the camera rotation and pitch into account, thus improving the depth estimation accuracy. The second contribution is a depth estimation algorithm, in which we classify the standing object region with visible ground-contact points into three cases according to the information of vanishing point for the first time, meanwhile, we propose the depth reference line concept for estimating the depth of the region with depth change. Two advantages can thereby be obtained: improving the depth estimation accuracy further and avoiding the occlusion mismarked phenomenon. The third contribution is the depth estimation method for the standing object region without visible ground-contact points, which takes the mean of minimum and maximum depth estimation result as region depth and prevents the missing phenomenon of occlusion boundaries. Extensive experiments show that our works are better than previously published results.

Multispectral images enable robust night vision (NV) object assessment over day-night conditions. Furthermore, colorized multispectral NV images can enhance human vision by improving observer object classification and reaction times, especially for low light conditions. NV colorization techniques can produce the colorized images that closely resemble natural scenes. Qualitative (subjective) and quantitative (objective) comparisons of NV colorization techniques proposed in the past decade are made and two categories of coloring methods, color fusion and color mapping, are discussed and compared. Color fusion directly combines multispectral NV images into a color-version image by mixing pixel intensities at different color planes, of which a channel-based color fusion method is reviewed.

The range image has received considerable attention in the automatic target recognition field; however, a mass of range images are generally difficult to be collected in a real application. Therefore, with small samples of laser radar (ladar) range images, classifier ensembles-support vector machine (SVM) ensembles and back propagation neural networks (BPNN) ensembles-are applied to improve the performance of target recognition in this paper. There are three aspects of experiments. First, the performances of SVM and BPNN are compared with different numbers of training sets. Secondly, the SVM ensembles and the BPNN ensembles are applied to improve the performance. Thirdly, the performances of the SVM ensembles and the BPNN ensembles are analyzed with the view angle of the tested samples changing while the view angle of the trained samples is invariant. The experimental results demonstrate that the recognition rate is effectively improved by classifier ensembles. The SVM is superior to the BPNN when the number of the training sets is not less than the feature dimensions; however, the BPNN has a better approximating ability when the number of training sets is small and lower than feature dimensions.

Here, we present a new application of the supervised learning based classifier in stereo matching. In particular, the chosen classifier is a balanced neural tree. The tentative matches are obtained using the speeded-up robust feature (SURF) matching. The feature vector corresponding to each tentative match is formed based on a similarity measure between SURF descriptors and their neighborhoods in the two stereo images, and these feature vectors are classified into inlier or outlier classes. Further, accuracy of the obtained results have been evaluated in terms of stereovision applications such as in the estimation of the homography and rectification matrices between two stereo images. The experiments based on these stereo estimates show the applicability of the proposed application in the stereo vision.

A feature extraction algorithm based on spectral clustering with adaptive multiparameters is proposed for synthetic aperture radar automatic target recognition (SAR-ATR). Spectral clustering has been widely applied in computer vision for its good performance. Meanwhile, the spectral mapping step in it has the property of feature space transformation. Spectral clustering based target feature extraction for SAR-ATR is constructed according to the framework of out-of-sample extensions in weighted kernel principal component analysis. To avoid the scaling parameter selection in spectral feature analysis (SFA) and eliminate the influence of scaling parameter on feature extraction performance as well, the multiple scaling parameters are calculated adaptively by local neighborhoods. Because the local statistics of the neighborhood of each point are taken into consideration, its performance is better than using only one fixed parameter. Based on the extracted features, target recognition is performed by the support vector machine for its good generalization capability. The experimental results show that the multiparameter SFA outperforms the principal component analysis, kernel principal component analysis and SFA with the selected scaling parameter for SAR target recognition in terms of recognition accuracy.

Zernike moments (ZM) have potentials in pattern recognition, image analysis/processing, and in computer vision. Their invariance and orthogonality are attractive in many applications. Unfortunately, direct computation of factorials in them is time consuming and discouraging. Also, people have shown poor invariance for Cartesian ZM in the discrete case. Need of a faster computing algorithm with better rotational invariance is already felt in various research communities. To find a solution, we have examined a completely new approach which comprises a unique mapping of a gray-level image on a discrete circular disk to compute Cartesian as well as polar ZM through a new recursive relation. Such a map does not require any special sampling. The proposed new recursion is based on the computational structure of the radial polynomial embedded in the ZM. Fast computation of ZM, in our case, uses the developed new recursion and the properties of discrete circles, e.g., symmetry, uniqueness, and hole-free generation of discrete disk. This discrete circular map helps not only the fast computation of ZM but also lends its support to provide better rotational invariance for polar ZM over that of Cartesian ZM. The invariance is useful in recognition.

We studied numerically the Anderson localization of light in the two-dimensional square photonic lattice, optically induced in both linear and nonlinear dielectric media. We investigated the combined influence of nonlinearity and disorder on Anderson localization in bulk media, as well as when there is interface between the linear and nonlinear medium. In bulk, there exist strongly nonlinear regimes in which localization is less pronounced than in the linear regime. We found that in the defocusing nonlinear regime, the localization is always less pronounced than in the linear regime. We also studied surface-localized modes near the interface between linear and nonlinear dielectric media with an optically induced photonic lattice, and observed the threshold for their existence. We demonstrate suppression of the localization at the interface for lower disorder levels, compared with both pure linear and pure nonlinear media.

The effect of concentration on the optical nonlinearity of gold nanoparticles is investigated. Gold nanoparticles were synthesized by nanosecond-pulsed laser ablation of a high-purity gold plate in distilled water. The size of nanoparticles was measured using dynamic light scattering (DLS) method and was calculated from full width half maximum of their plasmonic absorption peak using Mie theory. Different nonlinear characteristics of gold nanoparticles are observed by considering their effects under irradiation with a second harmonic beam of a continuous-wave low power Nd-YAG laser at 532 nm. Low-power optical limiting with low limiting threshold is obtained in the sample using different apertures at different points of the laser beam path. The nonlinear optical responses are characterized by measuring the intensity dependent refractive index of medium using the z-scan technique. Results show that the linear absorption coefficient and nonlinear refractive index of samples are increased with increasing the concentration of gold nanoparticles in distilled water. Increasing the intensity of the probe beam leads to increasing the magnitude of nonlinear refractive index.

This article [Opt. Eng.. 51, , 060901 (2012)] was originally published on 5 June 2012 with duplicated characters in Eqs. (21) and (22). The corrected equations appear below. Δν=2*V λ (21). Δϑ=λ 2L (22). . The paper was corrected online on 21 August 2012.