This PDF file contains the editorial “Aware of Pollution” for OE Vol. 47 Issue 07

All-optical format conversion from inverse-return-to-zero (inverse-RZ) to non-return-to-zero (NRZ) is realized by using a half-bit-delay Mach-Zehnder delay interferometer. Experimental results demonstrate that the converted NRZ signal has better receiver sensitivity than the back-to-back inverse-RZ signal.

A simple and effective method is presented for fast decoding of H.264 scalable video coding (SVC). The up-sampling operation in H.264 SVC makes the decoder very complex, because convolution and complex memory transactions are inevitable. The proposed method exploits coded modes of neighboring macroblocks (MBs) for determining up-sampling operation on MB by MB. The experimental validation shows considerable improvement in decoding time, and the proposed method reduces the complexity by about 25% on average.

Enhancement and duration of the projector luminance play two key roles in the difficulties of existing projectors. The paper proposes an optimized and novel dual-lamp illumination module, whose designs would be based not only on easy exchange with lamps in existing projector systems, but also on imposing minimal visual burdens on students in conventional classrooms. Applying these requirements to engineering specifications, the illumination module should comply with the following conditions. The total flux on the screen is larger than 1200 lm. The lifetime is longer than 2 years. The lamp module is easily attached to the optical engines in known mass-produced projectors. In order to achieve these conditions, the ray aberrations of burners and the structure of the dual-lamp module are presented and analyzed for optimization. Simulation and experimental results prove that the luminance of the module can be increasesd by about 1.47 times over that of a conventional projector under the stated requirements. Finally, a collateral-type dual-lamp module is also proposed for the further improvement. The simulation results show a further increase of 1.58 times in luminance over the single-lamp module and 11% over the dual-lamp module.

Results of a theoretical analysis on tunable acousto-optic imaging filters using potassium dihydrogen phosphate crystals are presented. It is found that the maximum angular aperture of an imaging filter at the optical wavelength 0.3 μm is equal to 3 deg. The diffraction efficiency in the examined instrument reaches 30% at moderate levels (2 W) of electric driving power. This performance may be obtained in a cell based on the (010) plane of acousto-optic interaction with the cut angle (18.8 deg) evaluated relative to the [100] axis. The device uses a piezoelectric transducer with dimensions 2.7×1.1 cm² generating a slow shear elastic wave in the crystal. The spectral resolution of the filter is equal to 12 cm^-1; the spatial resolution is characterized by 550×800 resolvable pixels in an image processed by means of the filter with linear aperture 0.8×1.1 cm².

Optical systems for scientific instrumentation frequently include lenses with critical mechanical requirements. Position and rotation issues of these components are inextricably bound to the efficiency of the instrument. This work describes the optomechanical design, manufacturing, assembly, and integration of the camera barrel located in the OSIRIS imager/spectrograph for the Gran Telescopio Canarias. The barrel was developed by the Instituto de Astronomía at the Universidad Nacional Autónoma de México (IA-UNAM), in collaboration with the Instituto de Astrofísica de Canarias (IAC), Spain. The camera barrel (CB) includes a set of eight lenses with their respective supports and cells, as well as two compensators: the focusing unit and the passive displacement unit, which uses the third doublet as a thermal compensator to maintain the camera's focal length and image quality with changing ambient temperature. A brief description of OSIRIS, the design criteria, optomechanical requirements, and specifications for misalignment errors and stresses are included. The camera components, analytical calculations, FEA simulations, and error budgets are also described. The iterative process of the optomechanical stages for the development of the camera are also verified and summarized. Finally, notes about fabrication, metrology, assembly, and integration are proposed as guidelines for future developments in optomechanics.

A simultaneous 2-D pulsed digital holographic setup that incorporates a rigid endoscope is used to inspect hidden object areas in order to measure microstrains. The system was tested on the internal surface of a harmonically vibrating rectangular metal box with a fracture on its surface. The simultaneous setup allows the acquisition of displacement data from two different object illumination positions at the same time, so that the system is capable of studying nonrepeatable dynamic events. Further analysis using displacement data generates a gradient strain map where the fracture is successfully detected with the corresponding strain magnitude and direction quantified.

We suggest and describe the use of a binary pseudorandom (BPR) grating as a standard test surface for measurement of the modulation transfer function (MTF) of interferometric microscopes. Knowledge of the MTF of a microscope is absolutely necessary to convert the measured height distribution of a surface undergoing metrology into an accurate power spectral density (PSD) distribution. For an ideal microscope with an MTF function independent of spatial frequency out to the Nyquist frequency of the detector array and with zero response at higher spatial frequencies, a BPR grating would produce a flat 1-D PSD spectrum, independent of spatial frequency. For a real instrument, the MTF is found to be the square root of the ratio of the PSD spectrum measured with the BPR grating to the ideal, spatial-frequency-independent PSD spectrum. We present the results from a measurement of the MTF of a Micromap^TM-570 interferometric microscope, demonstrating high efficiency for the calibration method.

The influence of electrothermal feedback and hysteresis on the operation conditions, noise, and performance of a VO₂ transition-edge microbolometer has been evaluated. The material undergoes a first-order semiconductor-to-metal phase transition (SMT) within the temperature range 40<T<70 °C. Due to electrothermal feedback, all device parameters, including the required heat-sink temperature, output voltage and current response, response time, linear dynamic range, responsivity, noise, and detectivity, display complex and nonlinear variations with temperature, electrical biasing conditions, input radiation levels, and hysteresis width. In the constant-current mode, the device responsivity extends over a broad temperature range, but under constant-voltage operation it is sharply localized and restricted to the SMT center. Film quality, as represented by the transition and the hysteresis width and the flicker noise magnitude, crucially affects device performance. In the weak hysteretic case and at low 1/f noise levels, the device detectivity improves substantially in both operation modes. The spectral range of the device is largely determined by the optical absorptivity of the VO₂ film. For operation within the SMT, it extends well into the far IR wavelength region of the atmospheric window, but is substantially smaller for operation in the semiconducting region.

We report on the design and performance test of a multiple laser Mueller matrix ellipsometer (MME). The MME is well conditioned due to the integration of the recently reported achromatic 132-deg compensators based on biprisms, in combination with high-quality Glan-Thompson polarizers. The system currently operates between 300 and 2700 nm, without the need to change any optical components except for the detector. Four lasers are employed as light sources (405, 532, 633, and 1570 nm) to test the performance in both reflection and transmission modes. Thus, the system is used to determine the Mueller matrices and associated optical constants of known optical systems: 1. optical rotatory power of D-glucose in solution, 2. reflection of a native oxide c-Si wafer, and 3. the properties of a liquid crystal spatial light modulator. The results show that the system matrices of the MME have condition numbers between the optimal √3 and 2 during operation, resulting in small experimental errors. To the best of our knowledge, there is no other MME reported with such good conditioning over a comparably wide spectral range.

A microchannel plate is demonstrated as both an optical low-pass filter and a heterodyning modulator. The frequency response function of the microchannel plate indicates it behaves as a low-pass filter. Antialiasing with the microchannel plate is demonstrated using a two-tone amplitude modulated laser beam, with the higher tone above the cutoff frequency being successfully suppressed while the frequency within the bandwidth of the filter is passed through. Selection of different commercially available phosphors controls the filtering and frequency response characteristics of the optical filter, effectively moving the cutoff frequency. By gating the microchannel plate at different frequencies, the microchannel plate can also be used analogously to a heterodyning spectrum analyzer, supplying all of the required functions of a local oscillator, mixer, and filter.

We describe a technique to package 15-μm-diam single-mode fibers on a silicon substrate that can be incorporated into an endoscopic probe tip. The single-mode fibers in the array can be used in coherent imaging applications such as optical coherence tomography. Fiber-to-substrate and fiber-to-fiber coupling effects are studied using beam propagation techniques to determine the different design characteristics and the maximum length of the reduced diameter fiber that can be packaged in the probe tip. Single-mode fibers are etched to reduce the cladding diameter from 125 to 15 μm. A 2-μm-thick silica layer is grown in the silicon substrate to minimize the fiber-substrate coupling. Reduced diameter fibers are placed into a 5-mm by 150-μm trench etched in a silicon-silica substrate and fixed with UV curable cement. Active alignment is used to ensure the correct alignment of fibers. The fiber array is experimentally evaluated to test fiber placement accuracy, throughput, and cross talk. Optical coherence tomography images are also obtained with the array.

A simple physical zone model was developed to explain the formation of polychromatic speckle patterns within the Fresnel region. This model represents a reasonable compromise between complex theoretical formulation and simple estimations for practical needs, and allows the speckle contrast to be calculated as a function of geometric parameters for the optics and coherence length of the light source. The model was experimentally verified, and the results are consistent with our previous rigorous theoretical formulation.

Transmission in a 40-Gbit/s alternating-phase (0 and π) duobinary modulation format with 67%, 50%, and 33% pulse width [modulation duobinary carrier suppression (CS) and carrier maximum pulse carving] is demonstrated. A minimum 136-ps/nm dispersion tolerance can be achieved at this transmission rate. At least 5- and 1.2-dB receiver sensitivity improvements are achieved for CS return-to-zero (RZ) 67% and 50% duobinary modulation, respectively, as compared with the experimental measurement under CS RZ differential phase-shift keying transmission over a 320-km three-span optically amplified dispersion-compensated standard single-mode fiber system. A MATLAB Simulink platform is described for simulation of the transmission performance.

We present a new type of single-mode fiber containing 11 radial layers surrounding the core of the fiber and having the same refractive index. The proposed fiber has low propagation losses with nearly zero residual chromatic dispersion for the spectral range of optical communication, and thus it may be a good candidate for transmission of information.

We show that co-optimization of dispersion and power maps in long-haul fiber optic communications can significantly mitigate the effects of group-velocity dispersion (GVD) and self phase modulation (SPM). A genetic algorithm is used for arriving at the optimal (or a near-optimal) link design in reasonable time, since exhaustive search is almost impossible for this intractable problem. Design of a 20-span×80 km/span link that can recover an input Gaussian pulse almost in its original form is presented. This design provides near-optimum values of the required net dispersion, dispersion map, and power map to mitigate the effects of SPM and GVD

A novel scheme of photonic frequency conversion based on two-pump four-wave mixing in a semiconductor optical amplifier is proposed. Characterized by its wide conversion range, the proposed scheme has the potential to generate millimeter waves at much higher frequency and convert several signal channels simultaneously. The system performance is analyzed through a numerical model, and the effect of the pump-signal pulse parameters on the conversion efficiency is discussed.

The onset of supercontinuum generation in a photonic crystal fiber (PCF) is investigated experimentally and numerically as a function of pump optical power with a femtosecond pulse. The pump pulse wavelength is positioned in the normal-dispersion regime close to the zero-dispersion wavelength (ZDW) of the PCF. When the pump power is low, the self phase modulation (SPM) is the dominant nonlinear process. With the increasing pump power, the primary mechanism of spectral broadening is identified as the combined action of stimulated Raman scattering (SRS) and parametric four-wave mixing (FWM). In the experiment, we have also observed the anti-Stokes Raman component, which reveals the importance of the fact that the pump pulses are positioned near the ZDW. Third-order dispersion (TOD) and Raman self frequency shift (RSS) also contribute to the supercontinuum generation. Good agreement between experiment and simulation is obtained.

We propose and demonstrate a novel radio-over-fiber (ROF) architecture by using only one phase modulator and one optical filter to generate an optical millimeter (mm) signal and realize wavelength reuse for upstream data connection. In the central office, the rf signals are generated by an electrical mixer that mixes the local oscillator (LO) and downstream data, and a phase modulator is used to generate an optical millimeter-wave signal. In the base station, an optical interleaver with two output ports is used to separate the optical carrier and the first-order sidebands. The separated first-order sidebands are used to generate optical millimeter-wave signals with a double LO frequency, while the separated optical carrier is reused for an uplink connection. There is no additional laser source for the upstream data generation in the base station and no dc-bias controller for phase modulator. By this method, we simplify the configuration of the radio-over-fiber system and reduce the cost of the system.

The optical burst switching (OBS) technique is a realistic solution to the mismatch of the capacity of optical fiber and electrical switching in backbone photonic networks. One of the critical issues in OBS networks is to avoid burst contention at transit nodes. This problem induces the rapid growth of burst-transmission delay time under heavy traffic loads. We propose a low-delay burst transmission scheme using burst segmentation at source nodes to suppress the growth in burst-transmission delay. In our scheme, a control packet refers the reservation table of each transit node within the range of offset time to approach routes, and reserves available periods for the burst-transmission temporarily. The influence of tentative reservation on burst-transmission delay is considered, and we clarify capabilities of the proposed scheme by using a simulation model. From the evaluation, it is shown that the proposed scheme prevails in the case of heavy traffic loads and large numbers of transit nodes such as four or more.

Based on the Sagnac interferometric structure, a simple novel ultrafast scheme of an all-optical nonreturn-to-zero (NRZ) to return-to-zero (RZ) is proposed. The operations of this scheme at 40 Gbit/s 2⁷-1 PRBS sequences are simulated correctly with an output extinction ratio of more than 19.1 dB. Through a built theoretical model and numerical analysis, the operating characteristics of the scheme are illustrated. Furthermore, the carrier recovery time of the semiconductor optical amplifier (SOA) is no longer a crucial parameter to restrict the operation speed of this scheme. This scheme is potentially capable of all-optical NRZ-to-RZ format converter operation speeds to 80 Gbit/s thus far.

A transmission ellipsometer with the configuration of modified Mach-Zehnder heterodyne interferometer is demonstrated. Two acousto-optical modulators are employed to generate a 20-kHz beat frequency. The scheme offers high resistance to environmental turbulence because of the interferometric components passing through the same path. A single layer of indium tin oxide on a glass substrate was measured, and an error up to several nanometers of the sample thickness is observed. The polarization mixing error is mainly due to the imperfection of polarizing beamsplitters (PBSs) and to the elliptical polarization and nonorthogonality of the light beams produced by the laser source and wave plates. The mechanism governing the error and its influence on measurement accuracy is analyzed with the Jones matrix method. In contrast with interferometric reflection ellipsometry using a Zeeman laser, the theoretical analysis indicates that only second-order error is introduced in this system. The elliptical polarization and nonorthogonality, occurring only before the light splitting, have little influence on measurement accuracy; the imperfection of PBSs is the major contributor to the polarization mixing error.

Third-generation thermal cameras have high dynamic range (up to 14 bits) and collect images that are difficult to visualize because their contrast exceeds the range of traditional display devices. Thus, sophisticated techniques are required to adapt the recorded signal to the display, maintaining, and possibly improving, objects' visibility and image contrast. The problem has already been studied in relation to images acquired in the visible spectral region, while it has been scarcely investigated in the infrared. In this work, this latter subject is addressed, and a new method is presented that combines dynamic-range compression and contrast enhancement techniques to improve the visualization of infrared images. The proposed method is designed to meet typical requirements in infrared sensor applications. The performance is studied through experimental data and compared with that yielded by three well-established algorithms. Evaluation is performed through subjective analysis, assigning each algorithm a score on the basis of the average opinion of human observers. The results demonstrate the effectiveness of the proposed technique in terms of perceptibility of details, edge sharpness, robustness against the horizon effect, and presence of very warm objects.

Our goals in hyperspectral point target detection have been to develop a methodology for algorithm comparison and to advance point target detection algorithms through the fundamental understanding of spatial and spectral statistics. In this paper, we review our methodology as well as present new metrics. We demonstrate improved performance by making better estimates of the covariance matrix. We have found that the use of covariance matrices of statistical stationary segments in the matched-filter algorithm improves the receiver operating characteristic curves; proper segment selection for each pixel should be based on its neighboring pixels. We develop a new type of local covariance matrix, which can be implemented in principal-component space and which also shows improved performance based on our metrics. Finally, methods of fusing the segmentation approach with the local covariance matrix dramatically improve performance at low false-alarm rates while maintaining performance at higher false-alarm rates.

How to protect secret information is a most important issue in military technology. In this paper, a (p,n) secret sharing method using Blakley's concept is proposed to protect the security of secret images. Even though enemies know p-1 of n shadow images, they cannot obtain any information about the secret image. Only p or more than p shadow images can reconstruct it. Experimental results show that the proposed method has the advantage of smaller shared images, which can greatly reduce the storage space.

Color similarity between foreground and background causes many foreground segmentation algorithms to fail. In this paper, a new algorithm is presented to segment foreground from similarly colored background. First, model precision and model recall are presented to quantify the model accuracy of various foreground models. Model accuracy tests show that the more accurate the foreground model is, the more accurate the segmentation is. Second, a new foreground model, which is more accurate than the general foreground model, is the developed by blending in different historical segmentations. Finally, the foreground is segmented using the new foreground model combined with a likelihood modification technique. Experimental results on typical sequences show that many foreground pixels misclassified by previous algorithms can be correctly classified by the new algorithm

A modified partial distortion search algorithm considering the neighboring-block correlation property is proposed for fast motion estimation. The motion vector information of neighboring coded blocks is used to predict the possible occurrence region of the global-minimum-distortion position of the current block. In addition, a dynamic search-range decision algorithm is also proposed for automatically changing the size of the search range. Afterwards, the normalized partial distortion search is performed in the selected region instead of the whole search window. Through the proposed algorithms, the computational complexity can be significantly reduced with slight objective quality degradation.

We propose a new method for finding flippable pixels in binary images. Instead of finding them in the traditional spatial domain, we find them in the binary wavelet transform (BWT) domain. It is shown that flippable pixels can be found more easily and efficiently by investigating high frequency components of BWT coefficients.

Projection-based image registration algorithms use the sum of the pixel values along a given axis of an image to detect spatial changes in temporally separated images. These algorithms have been shown to be computationally efficient and effective for aligning temporally separated images and for visually detecting sensor motion. Registering images via projections has also been shown as a method for overcoming registration errors caused by the presence of fixed pattern noise. This work describes a method that exploits the statistical properties of images with significant local correlation to improve the performance of projection-based image registration algorithms. The algorithm is shown to operate in low signal-to-noise ratio (SNR) conditions and to significantly improve registration performance by as much as a factor of 5.5 in mean squared error over existing projection-based registration algorithms at a minimal computational cost.

We propose an a posteriori kernel orthogonal subspace technique to segment texture images. It is a nonlinear version of the signature subspace classifier (SSC) derived on the basis of an unconstrained least-square estimation. In this approach, the linear subspace mixture model for the SSC is first reformulated in feature space via nonlinear mapping. Then the SSC in feature space is kernelized in terms of the kernel functions so that the dot products in the high dimensional feature space can be implicitly calculated by kernels. The obtained kernel SSC (KSSC) is equivalent to a nonlinear SSC in the input space. After that, the KSSC is applied to segment the texture images. To reduce the computational requirement in segmentation, the multiresolution-based technique (MKSSC) is developed. Experimental results demonstrate that the proposed MKSSC approach can effectively segment texture images and outperforms the MSSC method.

We perform unsupervised image classification based on texture features by using a novel evolutionary clustering method, named manifold evolutionary clustering (MEC). In MEC, the clustering problem is considered from a combinatorial optimization viewpoint. Each individual is a sequence of real integers representing the cluster representatives. Each datum is assigned to a cluster representative according to a novel manifold-distance-based dissimilarity measure, which measures the geodesic distance along the manifold. After extracting texture features from an image, MEC determines partitioning of the feature vectors using evolutionary search. We apply MEC to solve seven benchmark clustering problems on artificial data sets, three artificial texture image classification problems, and two synthetic aperture radar image classification problems. The experimental results show that in terms of cluster quality and robustness, MEC outperforms the K-means algorithm, a modified K-means algorithm using the manifold-distance-based dissimilarity measure, and a genetic-algorithm-based clustering technique in partitioning most of the test problems.

Nonlinear dimensionality reduction (recently called manifold learning) is crucial in many research fields. Maximum-variance unfolding (MVU) is one of the most important approaches to it. Unfortunately, due to too strict local constraints, MVU cannot unfold the manifold when short-circuit edges appear or the embedded mapping is conformal but not isometric. A relaxed version, relaxed MVU (RMVU), is proposed. Neighbors are adaptively assigned when short-circuit edges appear, and local distance is rescaled when the manifold is assumed to be angle-preserving. RMVU can effectively solve the preceding problems with MVU. More importantly, RMVU also performs better than MVU in general cases, and hence it has huge potential in many fields. Additionally, the proposed two strategies can also be used in other manifold learning algorithms. Experiments, accompanied with numerical comparisons, were performed on both synthetic and real data sets to demonstrate the effectiveness of RMVU.

A new method for improving detection performance of modified amplitude-modulated joint transform correlators by using a smoothed amplitude-modulated filter (AMF) is proposed. Smoothing of the filter is done to reduce dependence of the detection performance on a threshold value. Simulation results show that recognitions of intratarget scenes can be optimized by using a single smoothed AMF generated at low threshold.

In the steel-making industry, both the quality and quantity of the products are critical. This work presents a real-time defect detection method for high-speed steel bar in coil (BIC). For good performance characteristics, the detection algorithm must be robust to problems associated with the cylindrical shape of BICs, the presence of noise and nonuniform brightness distribution of images, the various types of defects, and so on. Furthermore, because the target speed is very high, it should have a fast processing time. Therefore, a defect detection algorithm should satisfy the two conflicting requirements of reducing the processing time and improving the efficiency of defect detection. This work proposes an effective real-time defect detection algorithm that can satisfy these conditions. Moreover, to reduce cost, the proposed algorithm is implemented on a PC-based real-time defect detection system without a professional digital signal processing (DSP) board. Experimental results show that the proposed algorithm guarantees both real-time processing and accurate detection.

We try to incorporate a graphical model to solve the problem of object recognition, which is a fundamental problem in computer vision. Adopting the multiscale feature keypoint technique, we present an object recognition algorithm that establishes the center, scale factor, and rotation angle of the object in the images. First, the local invariant features are detected in template and scene images. Second, the belief propagation algorithm is used to compute the correspondence considering the spatial constraints. Third, each correspondence point records a vote to the object's center, scale factor, and rotation angle. Finally, we keep the densest point on the vote map as the recognition result. Experimental results demonstrate the robustness of the algorithm on real images.

A study of compression efficiency of 3-D chain codes to represent discrete curves is described. The 3-D Freeman chain code and the five orthogonal change chain directions (5OT) chain code are compared. The 3-D Freeman chain code consists of 26 directions, in 3-D Euclidean space, with no invariance under rotation. The 5OT chain elements represent the orthogonal direction changes of the contiguous straight-line segments of the discrete curve. This chain code only considers relative direction changes, which allows us to have a curve descriptor invariant under rotation, and mirroring curves may be obtained with ease. In the 2-D domain, Freeman chain codes are widely used to represent contour curves. Until now, the authors have had no information of implementing Freeman chain codes to compress 3-D curves. Our contribution is how to implement the Freeeman chain code in 3-D and how to compare it with the recently proposed 5OT code. Finally, to probe our results, we apply the proposed method to three different cases: arbitrary curves, cube-filling Hilbert curves, and lattice knots.