This PDF file contains the editorial “Web-based Journalism” for OE Vol. 47 Issue 12

Motion vectors correlate very well with other neighboring motion vectors. Thus, many macroblocks have zero residual motion vectors within their blocks after differential pulse coded modulation using their individually predicted motion vectors. Motivated by this observation, we develop a new joint encoding scheme of motion vectors by defining a new macroblock coding mode called pooled zero motion vector difference coding to jointly code such cases more efficiently. Experimental results with several well-known video test sequences verify that the proposed method improves the coding efficiency up to 6.2% compared to the H.264|advanced video coding (AVC).

Simultaneous transmission of 2.5-Gb/s baseband and 5.8-GHz-band radio frequency (RF) signals on a single wavelength via a fiber link is successfully demonstrated using the optical diplexer and the newly designed novel baseband/RF mixed-signal multiplexer (MUX) with no mixer. The bit error rate (BER) <10⁻¹² of the baseband signal is maintained when the RF input power is less than −14 dBm after 10-km-long distance transmission. The maximum carrier-to-noise ratio (CNR) of the RF signal is measured as 23 dB with no additional amplifier. The measured insertion loss for the RF signal of the mixed-signal MUX is 1.2 dB at 5.8 GHz, and the isolations between the two bands are about 20 dB for the baseband and 30 dB for the RF band, respectively.

We propose, for the first time to the best of our knowledge, a design for a silicon waveguide-based nonlinear directional coupler in order to achieve soliton self-switching. Numerical analysis shows that the proposed design may be quite useful as a soliton switch.

The design and fabrication of an integrated waveguide polarizer in z-cut LiNbO₃ crystals are reported. Single-polarization guiding is achieved by careful selection of Ti diffusion parameters exploiting the transverse electric/transverse magnetic (TE/TM) refractive index anisotropy. Fabricated Ti:LiNbO₃ waveguide polarizers of 1.5 cm length exhibit less than 0.2-dB/cm propagation loss at TM and 33-dB extinction ratio as measured at 1.55-μm wavelength.

A reconfigurable optical add/drop multiplexer (R-OADM) device is proposed based on 2-D photonic crystals (2-D PCs) with a triangular lattice of air holes. It consists of channel add/drop filters, two bends with 120-deg bending angles, and a 2×2 directional coupler switch. Chirp structures are introduced in the directional coupler switch to improve its extinction ratio. At λ=1550 nm, the device is ultracompact with a net footprint 30×22 µm, excluding its external device. It is far smaller in size than other corresponding devices implemented through ring resonators. The device is numerically calculated by the finite-difference time-domain (FDTD) method, and simulation results confirm that the R-OADM device can be used for dynamically wavelength routing.

A simple and stable method is proposed for distinguishing dielectric and metal material surfaces from the polarization images captured by a vision system consisting of a linear polarizer and a digital camera. The polarization state is determined by the transmitted light intensity through the polarizer as a function of polarizing orientation. The degree of polarization (DOP) is estimated from the image intensities through the polarizer. The DOP map is quite effective for material classification around specular highlight on an object surface. We prove that the DOP map is convex for a dielectric surface and concave for a metal surface. The problem of material classification is then reduced to a simple judgment of the convexity of the DOP map obtained around the highlight peak. The proposed method is not a pixelwise local method based on thresholding the Fresnel ratio computed at each pixel but an area-based method based on the DOP map in a highlight area. The feasibility of the method is confirmed in experiments under a variety of conditions.

According to the parameter requirements of a graded reflectivity mirror with a Gaussian profile, the layer structure and the mask pattern are designed using a graded-thickness middle layer. The mask and the automatic mask-switchover equipment are designed considering the actual requirement of the thin films and the specific deposit facility. The uniformity of the layer thickness is analyzed. The measurement results indicate that samples prepared with this technique are basically in accordance with the design parameter. The scattering effect between the material molecules and the mask, thickness errors, and the alignment error between the mask and the substrate are the main factors that influence the deposit result.

A laser interferometer, vision system, and 2-D precision translation stage are used to develop a high precision measuring station with a working range of 18×18 mm. The vision system is installed at the z axis of a coordinate measuring machine (CMM), and the laser, the split and reflection mirrors, and the x-y stage are mounted on the platform of the CMM. The object inspected by the laser-and-vision system is moved using an x-y table so that the camera can take images of the feature points (such as corners) of the object at two different positions. Meanwhile, the displacement of the x-y table is measured using a laser interferometer. Putting these two feature points in one image, the distance between them can be evaluated under the image plane coordinate system. By adding the displacement measured by the laser interferometer, the real distance between these two feature points is obtained. The developed 2-D laser-and-vision measuring system is used to measure the geometric size of several Olympus specimens. Experimental results indicate that the measured values are in good agreement with the Olympus measurements.

In a light-pen single-camera three-dimensional (3-D) coordinate vision measurement system, a key step is the fast and precise center location for the light spot contour images of the LED control points obtained by the charge-coupled device (CCD)camera. A novel center location scheme for the light spot contour images is proposed in this key step. This scheme uses a geodesic active contour model to obtain every light spot's contour edge simultaneously. Then the center coordinate of every light spot is measured using a subpixel scheme. Compared to the common scheme using the edge detection and the contour tracking, this scheme is highly precise and fast for the center location of every light spot in a CCD image.

A Faraday current sensor using spatially inhomogeneous analyzers is presented. In the proposed optical architecture, the light waves coming from the sensor head travel in free space reaching a space-variant analyzer, and then they are acquired by a (one-or two-dimensional) photodetector array. This allows a full determination of the Faraday rotation induced by the electrical current, even in the case of a nonideal optical system (e.g., analyzer with poor polarization ratio). The proposed method resembles well-known techniques of phase-shifting interferometry. Validation experiments using linearly variant and azimuthal (radial) analyzers are presented and different detection schemes are compared.

A novel technique that uses a single color camera to capture high-resolution three-dimensional (3-D) geometry and the perfectly aligned color texture simultaneously is discussed. A projector projects three phase-shifted black-and-white fringe patterns onto the object, and a color camera captures the fringe images reflected by the object. From these three fringe images, both 3-D shape and the color texture are obtained. Moreover, since only three fringe images are required, this proposed technique permits real-time 3-D shape measurement. Experiments are presented to demonstrate the success of this technique.

We present a noncontact optical-mechatronic device for measuring deviations of straightness of the linearly moving elements of technological equipment. The straightness deviations have been measured by optic-electronic means simultaneously along two axes of coordinates in the plane perpendicular to the direction of motion of the technological machine element. Measurement principles of the device are based on encoding straightness deviation in the difference of phase of signals obtained from the moving and immobile photo sensors when modulated light was applied. The device can be used for measurement, testing, and accuracy analysis of technological machines.

A two-component laser Doppler velocimeter (2D-LDV) prototype for surface-displacement measurement is presented. The system proposed is based on the Doppler differential technique with a backwardscattering configuration. A reference and two frequency-shifted probe beams are generated departing from a single laser beam by means of two beamsplitters and acousto-optic modulators. This configuration has the advantage of using a single-wavelength laser source and a single detector system, while permitting sign detection of the two vector components of the velocity in surface-displacement measurements. It also enables the implementation of a low-cost multitrigger data acquisition system, which is useful in low signal-to-noise ratio (SNR) situations, such as the velocity measurement of low-dispersion surfaces or in hydrodynamic applications. The prototype has been designed to measure velocities up to 3 m per second, both in industrial (solid target) and hydrodynamic applications, with an error well below 1% in the tests performed. The system works in real time with the use of an acquisition card and C++ based software on a PC.

We present, for the first time, comparative studies of laser performance in the mixed vanadate crystals Nd:Y_xGd_1-xVO₄ with direct and indirect pumping. A series of mixed vanadate crystals Nd:Y_xGd_1-xVO₄ with different yttrium and gadolinium composition ratios but the same Nd³⁺ dopant level is prepared under the same fabrication processes and their laser performance in the TEM₀₀ mode operation is studied using the same experimental configuration under direct pumping with laser diodes at 880 nm as well as indirect pumping at 808 nm. Remarkable improvement in laser efficiency and maximum achievable output power is achieved under direct 880-nm excitation over indirect 808-nm excitation. The maximum optical slope efficiency in the TEM₀₀ mode operation is 74% with direct 880-nm pumping, which also produces the maximum overall optical-to-optical conversion efficiency of 59%. The maximum attainable laser power is up to 50% higher under direct 880-nm pumping over the more conventional 808-nm pumping. These achieved results provide valuable insight into crystal composition selection and pump schemes for the mixed vanadate crystals, which have the potential to tailor laser parameters through crystal composition engineering.

A wavelength switchable multiwavelength actively mode-locked fiber-ring laser based on highly nonlinear photonic crystal fiber (PCF) and polarization-dependent mode coupling to multimode-fiber Bragg grating (MMFBG) is proposed. Twenty meters of highly nonlinear dispersion-shifted PCF (DS-PCF) is inserted into the fiber ring cavity to suppress gain competition through the four-wave-mixing (FWM) effect. A mode scrambler is attached to the multimode fiber (MMF) to introduce a polarization-dependent mode coupling to the MMFBG. Through changing polarization in the cavity, stable and switchable one-wavelength, two-wavelength (wavelength spacing of 0.8 and 2.4 nm), and three-wavelength simultaneously actively mode-locked optical pulse trains at a repetition rate of 5 GHz are obtained. We show that high nonlinearity introduced by the nonlinear PCF in the cavity can improve significantly supermode suppression ratio (SMSR) of the multiwavelength pulses generated and a sidemode suppression ratio (SMSR) of 58 dB is realized.

A tunable ring resonator (RR) formed from Si/SiO₂ waveguides with an electro-optic polymer cladding is proposed with emphasis on the trade-off between the tuning voltage and ring radius. The ring resonator circuit combines the advantages of Si/SiO₂ and polymer technologies. The advantages of this hybrid ring design over previously proposed tunable silicon rings include an increased switching speed, from 5 GHz to 20 to 100 GHz, single-polarity instead of dual-polarity voltage tuning and a voltage-independent quality factor. The hybrid design also displays a greater free spectral range (1.85 nm instead of 0.1 nm) and a wider tuning range (0.925 nm instead of 0.05 nm) and is further compatible with silicon devices. Moreover, the device has a high quality factor of 3.4×10⁴.

As a function of the coupling coefficient in step-index (SI) plastic optical fibers (POFs), the coupling length for achieving the equilibrium mode distribution is determined by a simple algebraic equation and graph, separately for light-emitting diode (LED) and laser launch-beam distributions. One benefit of the proposed function is that it simplifies the determination of the coupling length by eliminating the need to numerically solve the power flow equation (or equivalent) repeatedly for all new values of the coupling coefficient.

A collimated heterodyne light enters a modified Linnik microscope, and the full-field interference signals are taken by a fast CMOS camera. The sampling intensities recorded at each pixel are fitted to derive a sinusoidal signal, and its phase can be obtained. Next, the 2-D phase unwrapping technique is applied to derive the 2-D phase distribution. Then, Ingelstam's formula is used to calculate the height distribution. Last, the height distribution is filtered with the Gaussian filter, the roughness topography and its average roughness can be obtained and its validity is demonstrated.

The capability to detect an optical target using laser illumination is typically assessed using an equation commonly referred to as the laser range equation. In practice, however, the laser range equation often produces unreliable predictions when compared to actual results under field conditions. The lack of accuracy is due in large part to the failure of the range equation to account for the effects of atmospheric turbulence on the illuminating laser beam. Retrodirective reflections from a corner cube and a simple lens-mirror system, used as a surrogate for a lens-detector optical system, were studied using near-infrared laser illumination. Each optic was tested under a variety of atmospheric conditions in order to assess the effect of atmospheric turbulence on the returned power. Using established theory, a corrective term for use in the laser range equation that accounts for turbulence-induced beam spreading is developed and compared to experimental results. Additionally, a method for correcting the lab-measured optical cross section of a focused optical system in order to account for the defocusing effects of turbulence is developed. With these corrective terms, the laser range equation was modified to provide accurate return-power predictions under varied atmospheric conditions.

We present a determination of the change with temperature and wavelength of the degree of birefringence of a cold (~30 K) Wollaston prism constructed from antireflection (AR)–coated sulfur-free cadmium selenide (CdSe). We compare the normalized birefringence for the material to that estimated by the Sellmeier-4 formula and to previously published measurements of a warm sample of sulfur-free CdSe. Finally, we measure the transmission as a function of wavelength.

Calibration of the x-ray apparatus is necessary for many applications. Most of the literature on the calibration of x-ray apparatus seem to ignore the imaging deformation. Our main concern is how to apply Tsai's nonlinear camera calibration technique to the calibration of a medical x-ray apparatus with deformation. In order to achieve this goal, two key problems should be solved: The first is how to calibrate some key intrinsic parameters, namely, the imaging center and sampling step of the detector, which are usually provided by the camera manufacturer but are unknown for the x-ray apparatus. The second is how to model the serious imaging deformation. Some practical schema are designed to solve these two problems, and the whole calibration procedure and experimental results are presented.

We present blind noise strength estimation for removing blocking artifacts associated with block-based compression schemes. The proposed framework is based on edge statistics residing across two neighboring blocks. 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 blind noise estimator without any prior information, 2. it models a noise with the combination of block discontinuity and simple noise-shape components, and 3. it adjusts the strength of a filter adaptively for removing the given noise. To evaluate the proposed scheme, several baseline approaches are described and compared in terms of peak signal-to-noise ratio and a quality metric.

A binary descriptor for representing 3-D tree objects is presented. This descriptor is based on chain coding. These 3-D tree objects correspond to natural existing 3-D tree structures, such as plants, live trees, blood vessels, and so on. Due to the fact that the proposed descriptor for representing trees is binary, only this kind of tree structures are considered. Three-dimensional trees are digitalized and represented by a notation called the binary-tree descriptor. Thus, 3-D trees are composed of constant straight-line segments using only orthogonal directions. Therefore, using the proposed binary descriptor it is possible to represent any 3-D binary-tree object via a chain of base-2 digit strings (0 and 1) suitably combined by means of parentheses. The proposed descriptor is invariant under translation, rotation, scaling, and can be starting-point normalized. Also, we define the complementary chain of a 3-D binary-tree object, which produces the mirror image of the tree. Note that there are many methods for representing trees. However, the proposed descriptor preserves the shape of the trees (and the shape of their branches), enabling us to know their geometrical and topological properties. Furthermore, it is a very compact method of tree representation.

Extracting effective features for texture classification is always a difficult problem in texture analysis. We present a method for texture features extraction by independent component analysis (ICA) of Gabor features (called ICAG). It has three distinguished aspects. First, Gabor wavelet transformation first produces distinct textural features characterized by spatial locality, scale, and orientation selectivity. Second, principal component analysis (PCA) and ICA then reduce the dimensionality and redundancy of these features. Thus, the resulting independent components are taken as texture features for classification. Third, in the ICA procedure, two different frameworks are discussed. Framework I, called ICAG I, regards pixels as random variables and represents them as a column vector by reshaping all the transformed images row by row, while framework II, called ICAG II, treats the statistical features, namely, the mean and standard deviation, as random variables. Thus, the statistical features of all the transformed images construct a column vector. Finally, comparative experiments between ICAG and the other traditional methods—ICA and Gabor wavelets—are performed on two composite images (five narrowband textures and five natural textures with broader bands). The results indicate that ICAG provides the best performance and ICAG II is more efficient and applicable.

The increasingly extensive applications of the latest video coding standard H.264 creates an urgent need to transcode the widely available MPEG-2 compressed video to H.264 compressed format. This paper presents a novel fast variable block-size selection algorithm for inter macro block (MB) based on the MB motion information aiming for providing low-complexity transcoding technique. The edge pattern of the MB residual as well as motion vector is employed for analyzing the MB motion characteristics. An optimal block size is decided based on the characteristics without conducting motion reestimation. Experiment results show that this method reduces the transcoder complexity dramatically with little compression performance degradation.

The point spread function (PSF) is asymmetric in a wavefront coding (WFC) system with cubic phase mask (CPM). The image formation of the WFC system is described as the generalized Sylvester matrix equation. With Tikhonov regularization, a global generalized minimal residual method (Gl-GMRES) algorithm is used to obtain the restored sharp image. For this large-scale, linear, and discrete, ill-posed problem, we introduce a Kronecker product approximation of the blurring operator to reduce the computation consumption. To eliminate ringing effect, four boundary conditions (BCs) are considered in the image restoration: periodic BCs, zero BCs, reflective BCs, and antireflective BCs. Analysis and numerical results show that the antireflective BCs provide better results than others. The experiment results show that the Gl-GMRES algorithm with antireflective BCs is more effective than the classic Wiener filter.

Based on an analysis of maximum stripe deformation (due to depth change on surfaces) and measuring resolution limits, a principle of spatial periodicity used for coding is proposed. When spatial periodicity is used for coding, the resolution is greatly improved, or the number of patterns is greatly reduced for real-time structured light systems. A novel coded pattern for real-time structured light systems is presented, which is based on spatial periodicity. The coding pattern allows range scanning of moving objects with easy implementation of decoding and high measurement resolution. Using alternate time-space coding in a structured light system, we achieve a measurement speed of 20 frames per second with two stripe patterns.

A lithography technique for fabricating subwavelength surface relief grating features based on evanescent waves interference is investigated by both analytical and numerical approaches. The analytical expressions for the intensity profiles of evanescent waves interference generated by both s- and p-polarized incident plane waves are deduced. The corresponding resist topologies are computed using a numerical scheme based on a modified cellular automata model, as proposed. The influences of polarization and exposure duration on patterning by evanescent waves interference lithography are investigated. The results suggest that this technique is capable to achieve nanoscale line features with linewidths as small as 15 nm, a pitch size of 105 nm, and an aspect ratio as high as 10.7 by appropriate choice of exposure duration and state of polarization for the incident beams.

This PDF file contains the errata for “OE Vol. 47 Issue 12 Paper 3054186” for OE Vol. 47 Issue 12

This PDF file contains the errata for “OE Vol. 47 Issue 12 Paper 3062203” for OE Vol. 47 Issue 12