An approach to generate ultrawideband (UWB) monocycle pulses is proposed and experimentally demonstrated, based on a dual-output intensity modulator and tunable optical time delay. Positive and negative pulses are obtained from two output ports of the modulator, respectively, and are coupled together through different time delays. The generated monocycle pulse has a 10-dB bandwidth of 6.5 GHz and a central frequency of 3.7 GHz.

Wavefront coding (WFC) technology can extend the depth of focus of an optical system, which makes the application of this technology to space cameras extremely attractive. This paper introduces the application of wavefront coding to three-mirror anastigmatic optical systems. A transition model is established, in which the secondary mirror is regarded as the wavefront coding element and redesigned according to mathematical calculation. A comparison of modulation transfer function (MTF) behavior between the traditional system and the innovative system with wavefront coding technology is provided. The MTF behavior of both on-axis and off-axis field-of-view points remains the same in spite of the extended depth of focus. It is also observed that the system becomes very insensitive to aberration related to defocus through WFC technology. Errors in optical design and its improvement are discussed. The linear transition model is proven to be an acceptable one. Finally, an extension factor for the depth of focus is defined, and its effect is presented graphically.

After the more than six decades since D. D. Maksutov introduced his aplanatic, catadioptric camera with the meniscus corrector plate and spherical-mirror objective, the system and its variants are well familiar within the design community. But it would have achieved limited enthusiasm had it not been for the singlet corrector's propensity for achromatization, since no balancing aberration is available in the objective. However, the refractor-objective apochromat possesses balancing, chromatic residuals that may be coupled with a Maksutov-like corrector plate to provide improved correction for chromatic aberration. The combination may be further optimized to generate a chromatic error of longitudinal aberration that is only a small fraction of that of the progenitor refractor objective alone. Examples are provided with one and two corrector elements. Caveats are discussed.

Three-dimensional (3-D) imaging is demonstrated using an electronically controlled liquid crystal (LC) optical lens to accomplish a no-moving-parts depth-section scanning in a modified commercial 3-D confocal microscope. Specifically, 3-D views of a standard CDC blood vessel (enclosed in a glass slide) have been obtained using the modified confocal microscope operating at the red 633-nm laser wavelength. The image sizes over a 25-µm axial scan depth were 50×50 µm and 80×80 µm, using 60× and 20× micro-objectives, respectively. The transverse motion step was 0.1 µm for the 60× data and 0.2 µm for the 20× data. As a first-step comparison, image processing of the standard and LC electronic-lens microscope images indicates correlation values between 0.81 and 0.91. The proposed microscopy system within aberration limits has the potential to eliminate the mechanical forces due to sample or objective motion that can distort the original sample structure and lead to imaging errors.

The performance of a Shack-Hartmann wavefront sensor is largely determined by the design of the lenslet array. In its simplest form, there are two available design parameters: the number of lenslets across the diameter of the wavefront, and the focal length. Spatial resolution, sensitivity, accuracy, and dynamic range are all affected by one or both of these parameters. For example, by virtue of increased spot motion under a fixed wavefront slope, longer focal lengths provide greater slope sensitivity. Simultaneously, longer focal lengths reduce the dynamic range, since spots may overlap for smaller wavefront curvatures. This paper presents a graphical approach to lenslet array design where various considerations constrain the possible solutions of the design problem.

Simultaneous phase-shifting ellipsometry based on a grating beamsplitter is presented. In the corresponding setup, an orthogonal grating and analyzer array are used. The latter is composed of four separate analyzers arranged in a 2×2 grid, the polarization axes of which are set to 0, 45, 90, and 135 deg. A mask allows only four diffracted beams of the fist order, having the same optical intensities, to pass. Each beam is incident on one of the analyzers of the array. The intensities of the four beams are simultaneously detected by a quadrant detector. The ellipsometric parameters are obtained using the four intensity signals. The feasibility of simultaneous phase shifting ellipsometry is thus demonstrated.

Thermal barrier coatings (TBCs) are extremely useful in gas turbine engines. The quality of these coatings can be improved by subjecting their surface to laser glazing. A reduction in surface roughness, eliminating open porosity on the surface, and the generation of a controlled segmented crack network, can be achieved. TBCs consisting of atmospheric plasma sprayed (APS) ZrO2-8%wtY2O3 are subjected to a CO2 continuous wave laser glazing process to seal their surface porosity, generating an external dense layer. Different amounts of irradiation are applied to the specimens. The microtopograpic inspection of the samples reveal a significant decrease of the surface roughness after laser treatment. However, a network of surface cracks, dependent on the laser scanning speed and track overlapping, are noticed. The cracks have a tendency to be oriented in two perpendicular directions, one in the direction of the laser beam travel direction, the other perpendicular to it. Cracks parallel to the beam scanning direction are found to be at the overlapping zone, in the edge of the subsequent track.

We investigated the use of separation, or substrate recovery, layers (SRLs), to enable the reuse of optical substrates after the deposition of multilayer reflective coatings, in particular Mo/Si multilayers as used for EUV lithography. An organic material (polyimide), known from other work to reduce the roughness of the substrate, was applied to the optical substrate. It appeared to be possible to remove the multilayer coating, including the SRL, without any damage or roughening of the substrate surface. The SRL was spin-coated at 1500 to 6000 rpm on different substrate types (Si, quartz, Zerodur) with diameters up to 100 mm. For this range of parameters, the multilayer centroid wavelength value remained unchanged, and its reflectivity loss on applying the SRL was limited typically to 0.7%. The latter was shown to be caused by a minor increase of the SRL surface roughness in the high-spatial-frequency domain. The roughness, characterized with an atomic force microscope, remained constant at 0.2 nm during all stages of the substrate recovery process, independent of the initial substrate roughness.

ZnO thin films were grown on SiO2/Si substrates by radio-frequency magnetron sputtering. Based on the ZnO film, a photoconductive metal-semiconductor-metal ultraviolet detector was fabricated by a liftoff technique. Its I-V characteristics were observed at 365 nm, and a fast response was observed by illumination with a KrF excimer laser.

A technique is described in which electromagnetically induced transparency (EIT) spectra are used to measure laser line width. Two independent sets of EIT measurements are carried out in the presence of 85Rb and 87Rb atomic isotopes. Conventional self-heterodyning detection is used to obtain standard values of laser line width. A comparison shows that the estimated laser line widths in these measurements are very close to each other.

Laser communication is viewed as an enabling technology with great potential in both long-range and “last-mile” applications, serving the needs of individual subscribers, corporate offices, military, and possibly deep-space missions. Indeed, lasers allow for concentration of energy within tightly focused beams and narrow spectral intervals, thus offering high throughput, information security, weight and size of components, and power requirements that cannot be matched by rf systems. A key challenge is that high data rates should be complemented by high-precision wide-bandwidth position control of a laser beam. In many applications, the ability to maintain a link is affected by the complex maneuvers performed by mobile communication platforms, resident vibrations, and atmospheric effects. This work is focused on the application of acousto-optic technology as an alternative to electromechanical devices, which addresses the tracking problems encountered under such conditions. With the realization that an acousto-optic Bragg cell is only a component of the entire system, which should perform complex tasks of pointing and tracking of the remote terminal, we present an attempt to consider this problem from the “systems” point of view. We present the developed electro-optical laboratory prototype, show synthesis of the control system, and feature experimental results that demonstrate excellent tracking performance.

A prototype strain sensor based on a dual fiber-optic Fabry-Perot interferometer (FFPI) was successfully implemented experimentally. The light source was a low-cost communication light-emitting diode, replacing the expensive laser diode. No costly Faraday isolator was required in this sensing system. The dynamic strain modulation in the sensing part of this setup was performed using a piezoelectric transducer. The interesting dynamic strain signal could be extracted at the optical receiver by optical signal demodulation in the reference FFPI. The temperature variation of the sensing part was simultaneously detected as needed.

We have demonstrated a simple method to achieve a high-power single-longitudinal-mode all-fiber ring laser by employing two Sagnac loop filters. In the ring cavity, a high-birefringence Sagnac loop filter is incorporated to limit the affiliated longitudinal modes, and another Sagnac loop filter with unpumped erbium-doped fiber serves as a saturable absorber to ensure single-longitudinal-mode operation. Using such a simple configuration, a single-longitudinal-mode fiber laser with scalable output power of 360 mW has been demonstrated.

A novel scheme to realize optical single-sideband modulation using only one electroabsorption modulator is presented. The scheme is based on the cancellation between the nonlinear phase due to dispersion and the linear phase due to optical delay in a Sagnac loop. Our theoretical analysis and experiment results show that optical single-sideband modulation can be realized in a very simple configuration. The scheme is independent of optical wavelength; it also avoids the problem of coherent interference, resulting in stable generation of optical single-sideband signals.

This paper describes the design and operation of a stable single-longitudinal-mode medium-power multiwavelength fiber ring laser at room temperature. Single-longitudinal-mode oscillation was achieved by using an unpumped polarization-maintaining erbium-doped fiber inside the cavity as a saturable absorber. To investigate the function of the saturable absorber, erbium-doped fibers with different erbium concentrations and lengths were used. The output characteristics of the laser were studied using a scanning Fabry-Perot spectrum analyzer of resolution 27 MHz and an optical spectrum analyzer of resolution 6.25 GHz. The total output power of the laser obtained was more than 100 mW. The minimum separation between lasing wavelengths for stable single-longitudinal-mode oscillations, number of lasing lines, tunability, and maximum available output power were also explored.

We investigate how to scale a free-space wavelength blocker to implement a spectral phase scrambling system to secure high data rate optical transmissions within a wavelength division multiplexing optical network. This technique belongs to the optical code-division multiple access family, and its implementation can be carried out using a free-space pulse shaping system based, for instance, on a wavelength blocker or spectral equalizer architectures. After a brief recall of the encryption principle, a model of the optical system is given, and we discuss the impact of phase distribution and the scrambling mask used to encrypt the data on penalty sources. We emphasize the importance of correctly choosing certain geometrical parameters, such as the beam waist in the spectral plane and the mask fill factor. The tolerance of this solution with respect to mask positioning errors is then investigated, and we finally discuss how such a solution could be implemented using existing devices, such as a wavelength blocker, for security applications without inducing additional system penalties.

We investigate a new system of photon-entangled recovery states using a fiber ring resonator incorporating an erbium-doped fiber (EDF). We also show that states of weak entangled photons can be regenerated and recovered after circulating in the amplified fiber optic medium. The output entangled photon states can be regenerated by adjusting the polarization controller of the amplified photons. Results obtained show that such a proposed system can be used to perform the polarization entangled recovery states, and the amplified output gain can be achieved. The amplifying noise is also detected and seen on the spectrum output, which affects the entangled photon output visibility. The change in the system temperature is also investigated, which shows that entangled state walk-off compensation is required to obtain the optimum entangled photon visibility.

We investigate the effect of thermal aging on the optical properties of multimode silica fibers. Samples are submitted to several heating-cooling cycles of 8 h each. Analysis is performed using the optical spectrum analyzer, the fixed analyzer method, and the polarization-dependent loss measurements to determine respectively the signal loss values, the differential mode delay, and the polarization-dependent loss. Results show an increase of the attenuation coefficient, the differential mode delay, and the polarization-dependent loss values with the increase of aging time. The obtained results show a degradation of the optical properties of fibers from 1680 h related to structural changes, and to the increase of the optical anisotropy of fibers.

For measurements of the Mueller matrix and other polarization effect matrices in a birefringent optical system, such as an optical fiber, we demonstrate by theoretical analysis and simulation that two input polarization states that are mutually orthogonal in Stokes space statistically have the maximum probability to achieve the optimum measurement accuracy. But in a single test, evident deviation from perpendicularity can be observed for achieving the minimum measurement error. For measurements of both polarization effect matrices and polarization effect vectors, we find that all measurement errors have a bathtub-shaped relationship with the angle between two input polarization states in the range from 0 to 180 deg. This means a limited offset from perpendicularity will only slightly and statistically increase the measurement error in a single test.

A nonlinear-material-based all-optical switching mechanism is utilized to develop the optical flip-flop. As flip-flops are sequential logic circuits, the present state of outputs is dependent on both the present inputs as well as the past outputs. In our present scheme, the outputs are fed back to the former stages instead of the input stages. The output Q and its complemented are obtained simultaneously in our scheme.

Some enhancement measures are studied for improving phase-shifted digital speckle shearography toward time-dependent application, such as the evaluation of materials' time-dependent mechanical behavior. To ensure quick and accurate phase shifting, a liquid-crystal variable retarder and a Wollaston prism are integrated into a compact unit, and an in situ phase-shift calibration procedure is developed. Algorithms are studied, and the most appropriate one is implemented, in which four phase-shifted reference shearograms and one shearogram per deformation state are processed to obtain deformation-related phase changes. Sine-cosine-averaging phase filtering is combined with a multigrid unweighted least-squares phase-unwrapping algorithm to ensure correct real phase extraction. Theories backing the enhancements are illustrated in detail, and verification tests are presented to demonstrate the effectiveness of the suggested improvement measures. The study shows good potential for phase-shifted digital speckle shearography to be applied to time-dependent measurement of surface slope and out-of-plane displacement.

In recent years, time-frequency analysis methods have been significantly developed for the processing of fringe patterns. Among such methods, the short-time Fourier transform (STFT) has been proven a valid method to process noisy fringe patterns. In this paper, the complex phasor and the STFT are used to retrieve instantaneous frequency from a series of holograms based on adaptive windows. Continuous phase maps are calculated by integration of the extracted instantaneous frequency, and phase unwrapping is effectively avoided in both temporal and spatial domains. The validity of this method is verified by an experiment. In addition, a comparison between conventional temporal phase unwrapping and the STFT is presented.

This paper presents a simple approach for removing blocking noise directly in the compressed domain. The proposed framework is based on scattering the noise over the block by controlling the strength of a single filter. First, the block boundary discontinuity is statistically analyzed. Next, the discontinuity is approximated by a simple model, and then filtered by controlling a filter strength according to the contents of the blocks. The main advantages of the proposed algorithm are that (1) it is a one-pass algorithm, (2) it uses a single simple filter, and (3) it performs directly in the compressed domain without any further postprocessing. In order to evaluate the proposed scheme, several baseline approaches are described and compared in terms of peak signal-to-noise ratio and a quality metric.

The light information obtained through a color filter array is sampled as R (red), G (green), and B (blue) based on the intensity of the radiation sensor CCD charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS). Because one pixel in the CCD or CMOS has a wave value for only one color, the information on the other two colors has to be estimated from the samples of the neighboring pixels. This estimation process is called demosaicking, and it plays an important role in the image pipeline. We propose a demosaicking method that uses the correlation among the wavelet coefficients in the high-frequency region of the color channels (R, G, and B). In our method, the high-frequency wavelet coefficients are obtained by linear estimation. The low-frequency coefficients are replaced by the results obtained from bilinear interpolation. We simulate our method and compare it with existing demosaicking schemes. The experimental results show that the proposed method can perform good demosaicking.

We propose an advanced motion-compensated prediction method for improving the coding efficiency in H.264/AVC. Nine separable two-dimensional interpolation filters are applied to precise compensation for motion in various directions. A new optimal cost function, which considers the bit rate and distortion for coding the macroblock, is also proposed. The filter is adaptively selected per macroblock to minimize the proposed cost function. Also, an algorithm for reducing the overhead of transmitting the filter coefficients is described. In experimental results on the various standard QCIF/CIF test video sequences, the proposed method shows improvement in coding efficiency over conventional methods. This leads to approximately a 7.30% (for one reference frame) and 4.46% (for five reference frames) bit-rate reduction on average, compared to H.264/AVC.

Digitalized old films are often degraded by some annoying defects, one of the most common artifacts being line scratches. We present an effective synthesis algorithm for line scratch detection and removal in the overcomplete wavelet expansion (OWE) domain, which is called the OWE-based synthesis algorithm (OSA). OWE is adopted here because of its higher precision in localization than other decimated wavelets. In the detection part, an improved OWE-based cross section method is proposed to find primary line scratches. A morphological refinement method follows, and includes more secondary line scratches. For better scratch removing results, we adopt a pixel-set-based linear interpolation under the criteria of linear minimum square error (LMSE) estimation in every scale. Experimental results show that compared with some classic algorithms, the proposed method can provide higher accuracy and fewer false alarms in line scratch detection, as well as enhanced restoration results.

We propose a novel image authentication and recovery scheme based on discrete wavelet transform (DWT). By using the property of a DWT multiresolution structure, we generate a semifragile watermark from low-frequency bands and embed the recovery information into the high-frequency bands based on the human visual system (HVS) approach. The image authentication system is able to locate precisely any malicious alteration made to the image and restore the altered or destroyed regions based on the recovery mechanism. Therefore, the requirements of ownership protection and tampering detection of digital right management (DRM) are met, and the legal usage of digital content is available. In addition, robustness to mild modifications like JPEG compression and channel additive white Gaussian noise (AWGN) is also achieved with high recovery image quality.

We present a novel and practical algorithm for the self-detection problem of contamination or occlusions on the lens of a camera mounted on a vehicle. First, we analyze the intrinsic characteristics of such contamination on the video image. Based on this, cumulative differences are used to segment the static region in the image. A blurred edge detection algorithm based on wavelet decomposition is introduced to confirm if the static region belongs to contamination or an occlusion. Through the combination of these algorithms, contamination or occlusions can be detected. Experimental data are analyzed to show the detection performance of our algorithm and the effect of different contamination or occlusion material.

Novel nonlinear adaptive composite filters for illumination-invariant pattern recognition are presented. Pattern recognition is carried out with space-variant nonlinear correlation. The information about objects to be recognized, false objects, and a background to be rejected is utilized in an iterative training procedure to design a nonlinear adaptive correlation filter with a given discrimination capability. The designed filter during recognition process adapts its parameters to local statistics of the input image. Computer simulation results obtained with the proposed filters in nonuniformly illuminated test scenes are discussed and compared with those of linear composite correlation filters with respect to discrimination capability, robustness to input additive and impulsive noise, and tolerance to small geometric image distortions.

Many composite correlation filter designs have been proposed for solving a wide variety of target detection and pattern recognition problems. Due to the large number of available designs, however, it is often unclear how to select the best design for a particular application. We present a theoretical survey and an empirical comparison of several popular composite correlation filter designs. Using a database of rotational target imagery, we show that some such filter designs appear to be better choices than others under computational and performance constraints. We compare filter performance in terms of noise tolerance, computational load, generalization ability, and distortion in order to provide a multifaceted examination of the characteristics of various filter designs.

We present a camera calibration technique to determine the focal length and the extrinsic parameters of a camera merely by using one perspective view of two coplanar circles with arbitrary radii and topological configuration. We believe our effort is valuable, in that the position of a camera and its focal length are frequently adjusted in many vision applications. In contrast to the iterative optimization technique in previous work, whose convergence relies heavily on proper initialization, we propose a closed-form solution on the basis of simple matrix operations, which turns out to be computationally efficient. It can also be used to initialize existing algorithms for higher accuracy and speed. Our method is based on the projective equation of a circle, first presented here, which naturally encodes the intrinsic and extrinsic camera parameters and the degenerate conic envelope spanned by the image of circular points. Extensive experiments with both synthetic data and real images verify the efficiency and robustness of our technique.

Until now, most research on iris recognition has been focused on recognition algorithms and iris camera systems. There has been little research into fake iris detection, although recently its importance has been greatly emphasized. Fake iris detection refers to the process of detecting and defeating fake iris images. In this work, we propose a new method of defeating fake iris attacks using Purkinje images based on gaze position. Our research presents the following four improvements over previous works. First, we calculate the theoretical positions and distances between the Purkinje images based on the 3-D human eye model. Second, by using these positions and distances (which changed according to gaze positions), we design a more robust way of detecting fake irises. Third, since it is not necessary to align the center of the user's eyeball with the optical axis of the camera, the proposed method can be used in practical iris systems. Fourth, by activating the illumination infrared-light-emitting diode (IR-LED), the distance-measuring IR-LED and the Purkinje IR-LED alternatively, we obtain accurate positions for the Purkinje images according to the user's gaze position. Experimental results show that the false rejection rate (FRR) is 0.2% and the false acceptance rate (FAR) is 0.2%.

With the increasing needs in security systems, iris recognition is reliable as one of the important solutions for biometrics-based identification systems. This work presents an effective approach for iris recognition by analyzing iris patterns. To improve the rate of recognition, we divide the normalized iris image into several regions to keep the iris image away from several noise factors, such as eyelids, eyelashes, and motion blur. For feature extraction, the local edge pattern (LEP) operator is designed to capture local characteristics of the iris image to produce discriminating texture features in every region. A resulting 2D feature vector is mapped into a low-dimensional subspace using two dimension linear discriminant analysis (2DLDA), and then the minimum distance classifier (MDC) is adopted for recognition. Experiments on the public and freely available iris images taken from the CASIA (Institute of Automation, Chinese Academy of Sciences) and UBIRIS databases confirm the advantage of the proposed approach in terms of speed and accuracy.

Based on vectorial Debye theory, the expressions for the distribution of the light field and orbital angular momentum (OAM) of tightly focused vortex beams have been derived. A Bessel-Gaussian (BG) beam is set as the model of the vortex beam. The phase distribution of the field component in the x direction near focus is analyzed as usual by presenting phase contours. It is found that circular edge dislocations exist in the focal plane, but they evolve as screw wavefront dislocations in observation planes away from the focus. Moreover, the dependence of the distribution of phase contours and OAM in the focal plane on the numerical aperture is shown. The distribution of OAM along the z axis is studied; it is found that the optimal location for applications of OAM of vortex beams along the z axis is near the focal plane.

We investigate the practical design of a complex-encoded key mask for optical encryption and decryption based on joint transform correlation architecture. The mask is created by using two coupled liquid-crystal spatial light modulators, one operating in amplitude mode and the other in phase mode. We develop a modified iterative Fourier transformation algorithm to design an optimal complex key mask, which is applied and mapped to the complex modulation of the liquid-crystal devices for optical implementation. The limitations of the devices on the system design are investigated and analyzed. The width constraints of the key mask are also derived, based on the joint transform correlation architecture for optical realization. Experimental results show the decryption performance and the shift-invariance of the complex key mask.