This PDF file contains the editorial “Special Sections and Kingslake Medal Winner Congratulations” for OE Vol. 49 Issue 08

We propose a priority sorting method that is suitable for H.264/AVC. The proposed method takes into account the unequal importance of encoded video data both in one slice and in one group of pictures. The importance is evaluated by the average distortion over one group of pictures, determined by recursive distortion derivation. A heuristic algorithm is presented to determine the ultimate priority sorting. Experimental results demonstrate that the proposed sorting method provides better error resilience and adaptability.

A microchannel plate (MCP) framing camera is simulated by using the Monte Carlo method. Considering that the laser pulse width has effect on the experimental exposure time, we simulate the experimental exposure time varying with the laser pulse width. The gain characteristics of the MCP framing camera are simulated while the MCP is applied with very short electrical gating pulses. A new method is presented using a nongain MCP instead of a gain MCP.

We present an iterative adaptive hybrid image restoration algorithm for fast convergence. The local variance, mean, and maximum values are used to constrain the solution space. These parameters are computed at each iteration step using a partially restored image at each iteration, and they are used to impose the degree of local smoothness on the solution. The resulting iterative algorithm exhibits increased convergence speed and better performance than typical regularized constrained least-squares approach.

The luminescent photoelastic coating technique is an optical technique to measure the full-field strain on 3-D structural components. A luminescent dye within a photoelastic binder is excited with circular polarized light, and the corresponding coating emission intensity is detected via a digital camera for loaded and unloaded states of the specimen to which the coating is applied. Images are processed to find the relative change in emission with respect to camera analyzer position and subsequently analyzed to determine maximum in-plane shear strain and the principal strain directions. For 3-D structures with moderate movement or deflection in the field of view, especially when implementing an oblique excitation approach to separate the principal strains while accounting for non-strain-related polarization changes due to surface inclination, the image analysis is preferably performed on a 3-D grid. This study describes such an approach and discusses the analysis procedures to separate the principal strains and to obtain full-field strain distribution. The theoretical results are compared to experimental data from both a 2-D and a 3-D test specimen.

In this study, an optical noncontact roughness measurement for the assessment of stress and deformation in lightweight metallic tubular structural parts of autoseats is presented. The deformation of circular section tubes subjected to centered transversal force can be assessed by measuring strain or bending of the tubes. Most frequently contact gauges are used in this process. We employ optical noncontact microtopographic inspection using the MICROTOP.06.MFC microtopographer developed at the Microtopography Laboratory of the Department of Physics at the University of Minho. Bending radius can be directly measured. However, for stronger deformations, bending radius measures become unreliable and full topographic inspection must be performed. If the surface of the tubes in the area where maximum deformation is expected to occur (located by finite element simulation models) is textured to a certain level of roughness, changes in the roughness values after deformation are expected to be measurable. A direct correlation between the deformation state/tension, strain and stress, and surface roughness, in particular average roughness, is found.

We present a method for comparing the optical quality of spectacle lenses based on determining the modulation transfer function (MTF) using random-dot patterns. Furthermore, we determine the precision of the method under repeatability conditions of measurement. The experimental device is composed of a laptop computer in which the LCD monitor presents the random-dot pattern, a liquid-crystal tunable filter, the lens under test, and a charge-coupled device detector connected to its control card installed in another computer. The method proposed has major advantages: the lenses can be characterized at different wavelengths; no additional sources to illuminate the pattern are required, the monitor's lighting source itself is used; and the characteristics of the pattern can be quickly and easily modified, as we install the control software in the laptop computer. We analyze three spherical spectacle lenses (+5 D) from different manufacturers and, in terms of MTF, the greatest difference found between them is 13.7%. The uncertainty associated with this method falls within the range of 0.001 and 0.06. Given the low uncertainty values, differences found between the lenses are significant. Therefore, the method proposed is a versatile and quick technique to distinguish the optical quality of spectacle lenses from different manufacturers.

Angular microvibrations of platform jitter on the optical inter-orbit communications engineering test satellite are measured in space during ground-to-satellite laser communication links. The microaccelerations are measured by the onboard accelerometers at a sampling rate of 2048 Hz. The angular microvibrations are estimated from the measured microaccelerations using the tracking characteristics of the laser communications terminal and the conversion factor on the basis of microvibration data obtained from ground-based tests. The power spectral density (PSD) of the satellite microvibrations is analyzed by using the fast Fourier transform analysis and the data length is examined according to the frequency resolution of the PSD. The in-orbit measurements of the PSDs are compared with those obtained from the ground test. The angular microvibrational base motion is estimated and a PSD up to 1024 Hz is additionally provided as a database of the real measurement results with previously obtained in-orbit measurements. The measured results will contribute to the angular jitter estimation and the design of a tracking control loop for space laser communication systems in the future.

We demonstrate fast power and wavelength control of a monolithic sampled grating distributed Bragg reflector (SGDBR) laser integrated with semiconductor optical amplifier (SOA). Optical power leveling for different channels can be achieved by tuning SOA driving current. Wavelength switching transients are analyzed experimentally. An appropriate shuttering operation of SOA sections during the channel switching process is implemented to eliminate the impact of transient emitting modes, and greatly improved dynamic performance of the SGDBR laser can be observed. With our design, output power of the laser can be precisely controlled within 0.1 dB and rapidly shuttered within 2 ns.

A linearly scaling optical apodization method for laser beam power profile modulation is induced. Changing an amplitude mask position between the beam-focusing cylindrical lens and the fiber can linearly scale the vertical apodization profile; this, in turn, enables the optimization of the grating apodization. By using this method, an apodized fiber Bragg grating (FBG) that is designed as an uncooled pump laser diode stabilizer with the specifications of 4.5% reflectivity, 1.6 nm bandwidth, and the side-lobe suppression ratio (SLSR) of 30 dB was UV-imprinted with a tiny Gaussian amplitude mask. Using the same apodization method, a nonchirped-type FBG edge filter was written with a very smooth spectrum. The grating specifications of 0.5-dB attenuation bandwidth of 3.6 nm and 96.5% reflectivity were achieved. The half-spectrum ascending bandwidth in the longer wavelength side is 2.2 nm with 27-dB SLSR. The linearly scaling apodization method is highly beneficial for optimizing the apodization process of UV-writing shorter FBGs with strong apodization.

We propose a relatively simple solution that can compensate the signal attenuation due to stimulated Raman scattering cross-talk in a wavelength division multiplexed passive optical network (WDM-PON). The proposed solution also significantly increases the reach of the PON segment, enabling the merger of access and metro network boundaries. This can be accomplished using remote Raman amplification where a continuous wave counter-propagating pump is injected from one of the optical node units. A ~13 dB amplification of the downstream signal is observed with a bit error rate 1×10−12 for a 20-km fiber span. The reach of WDM-PON can be extended to ~40 km for typical 32 splits or up to 25 km for 64 splits using the proposed technique. We also report the effect of pump polarization on the amplification.

We investigate a high-pumping-efficiency and linewidth-broadening, L-band, erbium-doped, superfluorescent fiber source (SFS) using a cascaded dual-backward-pumped configuration. With optimized structural parameters, the design provides an L-band SFS with a mean wavelength of 1578.2 nm, an output power of 132.8 mW, and a spectral linewidth of 52.6 nm without using any external spectral filters under 265-mW pump power. The high pumping efficiency of 50.1% is achieved experimentally. The design relaxes the danger in resonant lasing while enhancing the pumping efficiency and broadening the linewidth.

In a near-ground outdoor (NGOD) environment, a wireless optical communication system usually uses pulse position modulation (PPM) since it provides better power efficiency than on-off keying modulation. In the literature, schemes based on non-return-to-zero PPM have been investigated. We extend this work to a return-to-zero (RZ) PPM scheme with a NGOD application. As a case study, we develop an optimization model to maximize the transmission distance based on a RZ-4PPM system. We show that, with the reduced pulse duration, the transmission distance can be further improved. The model involves three different Gaussian terms, and details of the solution procedure are included.

An optical delay interferometer (ODI) is employed to suppress the pattern effect manifested on a 10 Gb/s return-to-zero (RZ) data stream when amplified by a semiconductor optical amplifier (SOA) operated in deep gain saturation. The experimental results verify the competence of the scheme to confront the problem for this signal format by achieving a far better performance than that with the SOA alone.

Frequency sweeping interferometry (FSI) is a technique where absolute distance measurements are made without ambiguity, using synthetic wavelengths resulting from frequency sweeps. Accuracy is mainly dependent on the synthetic wavelength measurement using a Fabry-Pérot interferometer to count resonances as frequency sweeps. Measurement uncertainty increases with distance due to propagation of uncertainty in the synthetic wavelength measurement. For large distances, the number of fringes dominates performance, leading to a linear decrease of accuracy with range. To overcome this problem, the dual FSI concept was introduced, where the measurement process for large distances is reduced to the close-range case, by limiting the interferometer optical path difference. This is achieved by increasing the reference arm with a long reference fiber, and using an ancillary interferometer to calibrate the fiber length continuously. This dual FSI concept was implemented and fully tested in view of ESA-PROBA3 space mission. The sensor is composed of an external cavity diode laser, a high-finesse Fabry-Pérot interferometer, and a dual measurement system. Accuracies better than 32 µm for a measurement range from 51 to 61 m were achieved using a reference fiber with 71 m, while maintaining the reduced complexity inherent to FSI technique, which is mandatory for space applications.

A setup for observing formation of light-induced diffraction grating in LiNbO₃:Fe in real time is presented. The utilization of this setup allows monitoring the temporal dependence of the diffraction efficiencies of several diffraction orders and observing the temporal evolution of the grating by means of the Mach-Zehnder optical interferometer at the same time. The part of the setup responsible for imaging of the space-time distribution of the refractive index changes in a crystal is advantageous to those making long-period gratings in various photorefractive materials because of easy and direct readout of both the grating spacing and the amplitude of the refractive index modulation. These two parameters are well controlled, and the recording of the grating can be stopped after desired values are reached.

Optical tweezer experiments have partially unveiled the mechanical properties of processive motor proteins while driving polystyrene or silica microbeads in vitro. However, the set of forces underlying the more complex transport mechanisms in living samples remains poorly understood. Several studies have shown that optical tweezers are capable of trapping vesicles and organelles in the cytoplasm of living cells, which can be used as handles to mechanically interact with engaged (active) motors, or other components regulating transport. This may ultimately enable the exploration of the mechanics of this trafficking mechanism in vivo. These cell manipulation experiments have been carried out using different strategies to achieve dynamic beam steering capable of trapping these subcellular structures. We report here the first trapping and manipulation, to our knowledge, of such small motor-propelled cargos in living cells using holographic technology.

A hologram provides a scene similar to the real world, and it can be used to display a virtual scene because it can be simulated numerically. However, the simulation is a computationally extensive task. Therefore, we accelerate it by enhancing the detail driven method. The design of the original method allows us to reduce the number of samples and limit the variability of elements without restricting scene contents. The proposed enhancements neither limit the diffusiveness of a surface nor require a minimum distance between a scene and a hologram. The computation time is reduced approximately 5× in the case of a typical scene. Hence, the method is able to calculate a hologram of 4096×4096 samples from a scene of 800 triangles in about 3.1 h on a regular 2.4-GHz CPU without any special hardware. This shows flexibility of the method and indicates that the method is acceptable for practical use.

The decoding performance of the 4/9 code, which depends on the accuracies of similarity comparisons for the code and the positional marker, was computationally evaluated in response to translation disturbances. The reproduction bright spot size () was constrained to be smaller than the image-sensor pixel pitch (p) for the code, and >p was necessary for the marker. These contradictory requirements were solved by a reproduction method in which a large numerical aperture (NA) was set for the code and a small NA was set for the marker. A bit error rate of 10−4 and a position detection resolution of ~p/10 were confirmed in the read-only-type holographic memory where the above method using two different NAs was applied.

Reliable target detection and tracking within strong clutters in outdoor infrared video sequences present great challenges. This is caused by several artificial and natural conditions, such as luminance change resulted from automatic gain adjustment in the IR camera, and other extreme granularity and uncontrolled environmental factors. In some important applications, the targets of interest include vehicles in motion and people in transit. We propose a new integrated solution to address all these issues. The system is composed of the following components: a region masking algorithm to divide a video frame into reliable and unreliable regions, a novel motion pattern recognition module, and an automatic walking-person recognition module. Such a comprehensive technique makes it possible for real-world outdoor infrared surveillance applications, where environmental interferences are uncontrolled and target motion are complex. Extensive experiments were carried out on real-world outdoor infrared videos provided by General Dynamics. In all tested sequences, the proposed algorithm had successfully detected and tracked the targets consistently throughout the life cycle of the targets, even when some targets were seriously blurred or occluded. Our results show that the proposed algorithm is practical, robust, and reliable for low-quality outdoor infrared videos.

In the case of optical computed tomography (OpCT) reconstructions for the field comprising obstacle objects, parts of the projection data are lost; hence, the image reconstruction would be always imprecise with conventional OpCT algorithms if no other preprocessing or interpolation approaches are adopted. To solve the problem of the reconstruction with incomplete data, a Lagrange interpolation reprojection-revising (LIRR) algorithm is proposed. First a Lagrange interpolation polynomial is adopted to preestimate the lost projection data. By comparing to the reprojection of the rough reconstructed image in the iteration, the unbiased Lagrange interpolation estimations are retained; otherwise, the biased estimations are revised, ray by ray, with the weighed superposition of the interpolation and the reprojection data. These steps are repeated until all estimations for lost data are acceptable. Reconstruction results of some known algorithms and the LIRR algorithm for two typical tested images, including a circle round opaque object, were compared. Additionally, an emission spectral tomography experiment was also designed to evaluate the LIRR. The simulation and experiment results show the LIRR makes a great improvement in reconstruction precision over the traditional OpCT algorithms and hence has potential application of OpCT reconstructions with incomplete data.

The reversible steganographic technique allows extraction of secret messages and restoration of original images without any distortion from the embedded image. In this work, a statistical adaptive reversible steganographic technique is proposed to improve difference expansion (DE)-based schemes, consisting of two parts. First, bicubic interpolation is adopted as the pixel prediction to obtain more embeddable pixels. Meanwhile, since differences are generated between the accurate predicted value and its original value, quality of difference is also considered. Second, a statistical adaptive reversible embedding algorithm is proposed to overcome the restriction of the embedding capacity under single-layer embedding. The relationship between the complexity of the neighboring pixels and the difference distribution for the image is generalized as the variance conditional in statistics. With the maximum modifiable degree of the predicted pixel, the proposed scheme provides a suitable embedding capacity for all embeddable pixels with less additional information. The experimental results demonstrate advantages of the proposed scheme and prove that it is able to provide high capacity with good visual quality for the embedded image.

Representing an object with multiple image fragments or patches for target tracking in a video has proved to be able to maintain the spatial information. The major challenges in visual tracking are effectiveness and robustness. We propose a robust fragments-based tracking algorithm with adaptive feature selection. The best discriminate feature is used for tracking, which can improve tracking effectiveness. A set of likelihood images corresponding to the most discriminative features are fused to divide the object into some fragments, which can maintain the spatial information. By weighting the fragment and background colors, more robust target and candidate models are built. Given these advantages, the novel tracking algorithm can provide more accurate performance and can be directly extended to a multiple object-tracking system.

In thin-film silicon solar cells, a flexible optical design for light collection is developed that can lead to zero reflection loss and enhance the optical path length in the absorber layer. In this work, we demonstrate two-filling-factor asymmetric binary gratings on the top of the solar cells and metallic diffraction gratings as a back reflector. The potential of the structures in the solar cells is investigated by means of numerical simulations, i.e., the rigorous coupled wave analysis enhanced by the modal transmission line theory. The impact of the structure parameters of the gratings on reflectivity is investigated. The results show that a close to zero reflection can be achieved by the two-filling-factor asymmetric binary gratings, and the path length of the transmitted light can be increased within the absorber layer by the metallic diffraction gratings.