This PDF file contains the editorial “Conference Papers and Journal Papers” for OE Vol. 50 Issue 04

We present a Fourier-based regularized method for reconstructing the wavefront from multiple directional derivatives. This method is robust to noise, and is specially suited for deflectometry measurement.

This paper proposes a motion vector coding scheme which uses the optimal predictive motion vector from the surrounding causal motion vectors in the minimum rate-distortion sense. The signaling overhead for the selected predictive motion vector is reduced by a contradiction testing that operates under a predefined criterion at both encoder and decoder for pruning the candidate predictive motion vectors.

Uniform irradiance and color adjustability are the key features in the design of lighting for machine vision inspection systems. A simple and practical design tool of angled light-emitting-diode (LED) ring arrays for uniform near-field irradiance has been developed by introducing a simple model to simplify the complexity of nonrotational symmetric irradiance distribution of angled LEDs. The color distribution and color uniformity of the ring array assembled with RGB LEDs are analyzed based on the analytical model of color mixing. According to the theoretical analysis, the simulated results, and the design exemplifications, the practical design tool offers an easy way to estimate the performance of an RGB LED ring array and can be considered as a starting point to reduce the computation time for exact designs that must use a realistic LED model.

We propose a simple PID (proportional integral differential)-I controller to improve the performance of a CCD-based (charge coupled device) control system for fast steering mirror, which consists of adding an integrator in series to a PID controller, resulting in two integrators in the control loop. The conditions for implementing the PID-I controller into the control system of the fast steering mirror are presented mainly in terms of the closed-loop stability and error attenuation. A model of CCD-based control loop is made to analyze the characteristics of the control loop. Although the error attenuation bandwidth with PID-I controller is a little smaller than that with an integral controller, the error attenuation at low frequency is greatly enhanced. The experimental results are in accordance with the theoretical analysis.

Previous laser illumination systems at Aberdeen Proving Ground and elsewhere required complex pulse timing, extensive cooling, large-scale laser systems (frequency-doubled flash-pumped Nd:YAG, Cu-vapor, Q-switched ruby), making them difficult to implement for range test illumination in high speed videography. Requirements to illuminate through the self-luminosity of explosive events motivate the development of a high brightness imaging technique obviating the limitations of previous attempts. A lensed vertical cavity surface-emitting laser array is proposed and implemented with spectral filtering to effectively remove self-luminosity and the fireball from the image, providing excellent background discrimination in a variety of range test scenarios.

We present a computer simulation and an experimental realization of an optical setup for automatic quality control of microlenses arrays. The method is based on a 4f correlator setup with an amplitude filter. The output intensity signal is simple to analyze and interpret because the intensity is proportional to the first derivative of the distortion of the input wavefront. This method is shift invariant, allows for the examination of single elements, or sets of micro-optical elements simultaneously, and is particularly suitable for assessing the quality of optical elements. However, combining the method with a more detailed analysis based on the Fourier modal method, allows for obtaining quantitative data. Although errors are within the 2-3% range, such an analysis enables a fast and relatively accurate comparison of numerous elements with each other and with the model. The combination has never been applied but allows for a fast and cost-effective analysis that can be used for industrial purposes. Both the methods give separate results for each lens or for all the lenses in the array, simultaneously. In the combination proposed, the analysis is computer-based and done on the basis of the initial single optical measurement.

As a measuring technique, owing to its high throughput and multichannel advantages, interference imaging spectroscopy is widely used in many fields. This technique can be classified as temporally modulated Fourier transform spectrometer (TMFTS) and spatially modulated Fourier transform spectrometer (SMFTS). In contrast to TMFTS-based instruments, instruments using SMFTS are more stable, simple, and compact. In spectrometry, improvements of the spectral resolution and the optical throughput are always the focus points. A new static Fourier-transform imaging spectrometer based on the use of Wollaston prisms is presented. The novelty of this work comes from the use of a longer optical path difference, which provides higher spectral resolution. The principle and the system configuration are described. An experimental system based on the Wollaston prisms has been built and preliminary imaging spectroscopy experiments have been performed with it.

Efficient inspection of an object for deformations and defects requires comparison with an existing real or simulated reference model. Fourier descriptor (FDs) based shape analysis is an effective method for describing a shape using the Fourier transform. This shape representation can be easily modified to achieve shift, rotation, and scale invariance. We propose two new methods, namely the ring sampling and the spiral sampling methods, which enable the usage of FDs in order to detect defects on micro-optical elements like microlens arrays. As an example the measurement data obtained from a confocal microscope has been used to show the effectiveness of the two approaches for both indicating and detecting surface defects. Microlens arrays with different types of defects including global (deformed lenses causing aberrations) and local defects (scratches) were simulated using a confocal microscopy simulation tool to test the reliability of the methods. A classifier differentiates between global and local defective lenses. In order to represent other kinds of objects using FDs, the methods can be easily modified or extended. The whole process has been implemented into an automated multiscale multisensor measurement system, which focuses on fast detection of defects on micro-optical and microelectromechanical systems.

Phase unwrapping, which usually involves complicated and time-consuming procedures, is crucial for phase-measuring profilometry. Unwrapping isolated phase regions with global phase discontinuity is challenging for traditional reliability ordering based phase unwrapping methods. This paper presents a novel method that combines the advantages of digital point array based active triangulation profilometry with a reliability of modulation ordering algorithm. Table entries that store spatial coordinates of sampling points are established, and the true phases measured by geometrical relationships are used to direct phase unwrapping. Different from the proposed 2D spatial unwrapping algorithms until now, the fringe order can be easily identified by referencing the patterns of multiple points. Additionally, unwrapping from the interior part of isolated regions following an optimized path is guaranteed. The prevention of penetration through invalid pixels into isolated regions ensures this new method will alleviate errors due to phase ambiguity. Simulation and experimental results demonstrate that the proposed technique can feasibly measure objects with a wide range of height variation.

Gloss of a product, such as print gloss, is mainly inspected with conventional white light glossmeters both at laboratory or production facilities. However, problems occur in conventional gloss measurement when the inspected surface is vertically moved in the plane of incidence and reflection or when the measurement area is small or curved. For a partial solution to these problems, we have previously introduced diffractive optical element-based glossmeters (DOGs) for the gloss inspection in laboratories and off-line use. We present a new construction of DOG, termed μDOG 1D, for the one-dimensional on-line print gloss measurement, in the form of the reflectance determination normal to the surface. The function of the glossmeter is demonstrated by laboratory tests and on-line measurements at a heat-set web offset printing machine. It is shown that gloss (i.e., normal reflectance) and minute gloss variation of papers and prints can be measured at the printing line using the glossmeter. This glossmeter is expected to be useful in real-time monitoring of the gloss and surface-specific absorption not only in the printing industry but also in inspection of products in other industrial sectors, such as metal finishing, laminating, paper, and construction materials manufacturing.

An ultrafast optical Kerr gate (OKG) in femtosecond time scale was used to determine the scattering coefficients of intralipids, in which the BI₂O₃-B2O₃-SiO₂ oxide glass was employed as the Kerr medium. Because of the joint action of the time gate and a transient spatial gate that was induced in the Kerr materials by the gating beam, more precise scattering coefficients could be obtained. Our experimental results show that, for low turbid media, the scattering coefficients measured using the OKG method are similar to those measured using the collimated transmittance (CT) approach, while for highly turbid media, the results obtained using the OKG method are bigger than those using the CT approach.

Cameras can give useful information for the autonomous navigation of a mobile robot. Typically, one or two cameras are used for this task. Recently, an omnidirectional stereo vision system that can cover the whole surrounding environment of a mobile robot is adopted. They usually adopt a mirror that cannot offer uniform spatial resolution. In this paper, we deal with an omnidirectional stereo system which consists of eight cameras where each two vertical cameras constitute one stereo system. Camera calibration is the first necessary step to obtain 3D information. Calibration using a planar pattern requires many images acquired under different poses so it is a tedious step to calibrate all eight cameras. In this paper, we present a simple calibration procedure using a cubic-type calibration structure that surrounds the omnidirectional stereo system. We can calibrate all the cameras on an omnidirectional stereo system in just one shot.

We use the two-dimensional Chebyshev polynomials as the basis for decomposition of test data over rectangular apertures, particularly for anamorphic optics. This includes simple optics such as cylindrical lenses and mirrors as well as complex optics, such as aspheric cylindrical optics. The new basis set is strictly orthogonal over rectangles of arbitrary aspect ratio and they correspond well with the aberrations of systems containing such type of optics. An example is given that applies the new basis set to study the surface figure error of a cylindrical Schmidt corrector plate. It is not only an excellent fitting basis but also can be used to flag misalignment errors that are critical to fabrication.

A silicon p-i-n diode Mach-Zehnder optical modulator integrated with grating couplers is fabricated in 0.18-μm complementary metal oxide semiconductor technology. The device has an ultracompact length of 200 μm. High modulation efficiency with a figure of merit of VπL = 0.22 V mm is demonstrated. A novel pre-emphasis technique is introduced to achieve high-speed modulation, and a data transmission rate of 3 Gbps is present.

In this study isatin and its novel Schiff base as a new red fluorescent material for organic light emitting diodes (OLEDs) are used for red color OLEDs. We fabricated OLEDs with the configuration of indium tin oxide/4.4′-Bis(N-carbazolyl-1,1′-biphenyl/red emitter/HGH₂/Alq₃/Li/Al which the electrical and optical properties of devices have been investigated. Their photoluminescence and electroluminescence properties for isatin and its Schiff base were examined and compared. The electroluminescent spectra of these materials ranges from 593 to 645 nm and their bandgaps are between 2.1 and 1.92 eV. The Commission International De L'Eclairage (1931) coordinates of these two compounds were measured and found to be (0.4325, 0.4329) and (0.4077, 0.4128) for two employed chromophores.

We report a write-once-read-many polymeric memory device that can be read by both electrical and optical methods. The device consists of two layers of conjugated polymer blends sandwiched between a metal electrode and a transparent electrode. One of the polymer blends functions as an ion-trapping, electrochromic layer, while the other polymer blend functions as a light-emitting electrochemical cell. Recording is facilitated by applying a negative writing voltage on the device. Reading can be performed by either probing with a low positive voltage, probing with a laser beam, or by measuring the light emission intensity from the device.

A wide range of applications have emerged for tunable ytterbium fiber lasers as single-frequency sources for spectroscopic applications, pumping source of Pr:ZBLAN amplifier, and Tm:ZBLAN upconversion laser, material processing, and military applications. In this paper, a 975-nm high power fiber coupled high power diode laser module of up to 5 W end pumping a ytterbium-doped multimode D-shaped fiber laser has been investigated. This used a Fabry-Pérot cavity with output coupler reflectivities of 80%, 60%, and Fresnel reflection of 4%. The output laser wavelength was tuned over a wide range of more than 50 nm, from 1041 to 1094 nm for cavity lengths from 1 to 10 m, respectively. An optical-to-optical slope efficiency of 45% was found for a 1-m cavity length, which increased to 60% for a 4-m cavity length. The maximum slope efficiency of 82.1% for a cavity length of 2 m was measured with the Fresnel reflection output coupler, and the measured lowest threshold pump power for this high gain cavity configuration was 130 mW. The threshold lasing pumping powers of 4.3, 4.5, and 4.7 W were dependent on the output coupler reflectivities of 80%, 60%, and Fresnel reflection of 4%, respectively. Also, self-pulsation phenomena were observed only at higher level pumping powers of more than 4 W and at longer cavity length.

Modulation response characteristics of a semiconductor laser with a phase-conjugate feedback mirror is studied. Modulation response equations about the amplitude and frequency chirping of the laser are deduced in detail. It is demonstrated that the amplitude and frequency chirping responses are the function of the modulation angular frequency, optical feedback level, and delayed time. Numerical results illustrate that the amplitude response and modulation bandwidth of the laser are larger than that of the solitary laser when the optical amplitude reflectivity is <0.0022. When the optical amplitude reflectivity is increased further, the peaks of the amplitude response of the laser show periodic variability while the modulation angular frequency at the maximal value of the amplitude response is added; however, the frequency chirping can be enlarged or reduced. The large drive current or the large detuning can enhance the modulation response and frequency chirping.

This study reported the improvement of frequency sensitivity of series photodetector frequency circuit system for fluorescence detection. The 48 MHz series photodetector frequency circuit system matched with polydimethyl siloxane (PDMS) focusing lens was applied to the detection of emissive fluorescence intensity. MEMS technology processes were used to fabricate PDMS focusing lens, the mixing amount of PDMS and the curing temperature were adjusted, and self-improved mold-transfer technology was used to make a 3D planar lens of diameter of 3 to 10 mm. While the series photodetector frequency circuit system matched with PDMS focusing lens of diameter 10 mm was used for fluorescence detection, the relative fluorescence intensity was enhanced by approximately two times, which indicated that the frequency sensitivity of the 48 MHz sensor system was improved. Besides, the bias of the photodetector was also adjusted to improve the frequency sensitivity. According to the optimal conditions of PDMS focusing lens and bias of a photodetector, the detection limit of HEX fluorescence dye concentration 3.3 pmol/L can be measured. The results of the fluorescence experiment also demonstrated that the frequency shift of the 48 MHz sensor system was linearly related to the logarithm of fluorescence dye concentration from 333.3 nmol/L to 3.3 pmol/L.

The refractive index tailoring in the surface layers of polycarbonate has been carried out with low energy nitrogen ion implantation. The specimens were implanted at 100 keV with nitrogen ions in the fluence range of 1×10¹⁵−to 1×10¹⁷ ions cm−². The refractive index values of virgin and implanted specimens have been calculated from the diffuse reflectivity spectrum obtained by using UV-visible spectroscopy. The refractive indices have been found to increase with implantation dose and wavelength (in visible region). At 400 nm the refractive index changes from 1.58 (for virgin) to nearly 2.34 (at an implantation dose of 1×10¹⁷ ions cm−²). These changes in the refractive indices have been further correlated with the changes observed in conjugation and bonding of carbon atoms investigated using UV-visible absorption and attenuated total reflectance Fourier transform Infrared spectroscopic techniques. The possibility of formation of an optical waveguide using these implanted specimens has been discussed.

Bent waveguide structures (S-, U-, and F-bend) based on buried Er³⁺/Yb³⁺ codoped phosphate glass waveguide channel fabricated by field-assisted annealing have been designed to achieve high-gain C-band integrated amplification. Using a simulated-bend method, the optimal radius for the curved structure is derived to be 0.90 cm with loss coefficient of 0.02 dB/cm, as the substrate size is schemed to be 4×3 cm². In the wavelength range of 1520 to 1575 nm, obvious gain enhancement for the bent structure waveguides is anticipated, and for the F-bend waveguide, the internal gain at 1534-nm wavelength is derived to be 41.61 dB, which is much higher than the value of 26.22 and 13.81 dB in the U- and S-bend waveguides, respectively, and over three times higher than that of the straight one. The simulation results indicate that the bent structure design is beneficial in obtaining high signal gain in buried Er³⁺/Yb³⁺ codoped phosphate glass waveguides, which lays the foundation for further design and fabrication of integrated devices.

Submarine cabled networks are designed to collect valuable data in geophysics, geochemistry, biology, or oceanography. Unfortunately, the development of such a network is expensive and needs complex subsea infrastructures. Once in place, a cabled network cannot be easily relocated. The current cost of cables and their installation are one of the major obstacles to these networks deployment. On the one hand, these cables are necessary to provide power supply and communication data, and on the other hand they drastically reduce the possibilities to extend the cabled observatory network in order to reach a closed area of significant interest. This is why, to address this issue, we propose a quasi-all-optical architecture to easily extend multidisciplinary cabled networks or to create a dedicated submarine hydrophone or seismometer network. This solution consists of using only a single fiber optic to transmit both the energy, required to supply the instrument, and the data, exchanged between the shore station or equivalent. In this paper, we present our proposed architecture, and we discuss its feasibility thanks to experimental results.

Propagation characteristics of an elliptical hollow core optical fiber (EHOF) have been investigated under the application of high lateral and hydrostatic stresses. The simulation results exhibit significant effects of stress on birefringence, polarization mode dispersion (PMD), group velocity dispersion, effective area, and power confinement. High birefringence (~10⁻³), negative dispersion (−22.07 ps/km-nm), low PMD, small effective area, and ultrahigh value of power density (~10³) have been found for EHOF under different stresses. The inclusion of central air hole and asymmetry in geometrical structure of the fiber under stress are responsible for different changes in propagation characteristics.

The clos network is one of the earliest multistage interconnection networks. Recently, it has been widely studied in parallel optical information processing systems, and there have been many efforts to develop this network. In this paper, a smart and compact Clos network, including Clos(2,3,2) and Clos(2,4,2), is proposed by using polarizing beam-splitters (PBS), phase spatial light modulators (PSLM), and mirrors. PBS features that are s-component (perpendicular to the incident plane) of the incident light beam is reflected, and the p-component (parallel to the incident plane) passes through it. According to switching logic, under control of external electrical signals, PSLM functions to control routing paths of the signal beams, i.e., the polarization of each optical signal is rotated or not rotated 90° by a programmable PSLM. This new type of configuration grants the features of less optical components, compact in structure, efficient in performance, and insensitive to polarization of signal beam. In addition, the straight, the exchange, and the broadcast functions of the basic switch element are implemented bidirectionally in free-space. Furthermore, the new optical experimental module of 2×3 and 2×4 optical switch is also presented by a cascading polarization-independent bidirectional 2×2 optical switch. Simultaneously, the routing state-table of 2×3 and 2×4 optical switch to perform all permutation output and nonblocking switch for the input signal beam, is achieved. Since the proposed optical setup consists of only optical polarization elements, it is compact in structure, and possesses a low energy loss, a high signal-to-ratio, and an available large number of optical channels. Finally, the discussions and the experimental results show that the Clos network proposed here should be helpful in the design of large-scale network matrix, and may be used in optical communication and optical information processing.

With an aim to explore the suitable refractive index profile for maximum coupling, we present a theoretical investigation of coupling optics involving a laser diode and single mode circular core graded index fiber via a hyperbolic microlens on the fiber tip in absence and presence of any possible transverse and angular misalignments. By employing Gaussian field distributions for both the source and the fiber and also ABCD matrix for hyperbolic microlens under paraxial approximation, we formulate analytical expressions for the concerned coupling efficiencies. The investigations are performed for two different light-emitting wavelengths of 1.3 and 1.5 μm for such fibers with different profile exponents in refractive index profile. Further, it is observed that out of the studied refractive index profiles, the triangular index profile having the dispersion-shifted merit comes out to be the most suitable profile to couple laser diode to single mode circular core graded index fiber for two wavelengths of practical interest. The analysis should find use in ongoing investigations for optimum launch optics for the design of hyperbolic microlens either directly on the graded index circular core single mode fiber tip or such fiber attached to single mode fiber to achieve a long working distance.

The processes to derive the associated phase of an interference signal from the data of a series of recorded frames are performed, and we find that the sampling frequency being lower than the Nyquist sampling rate can also be applied to the full-field heterodyne interferometry. Two optimal sampling conditions for a commonly used CCD camera are proposed based on the relation between the heterodyne frequency and the contrast of the interference signal under the condition that the phase error is set to be 0.05 deg.

The holographic gratings on photopolymer films are studied by three different thicknesses for samples A, B, and C. The photopolymer emulsion is prepared with potassium dichromate and nickel (II) chloride hexahydrate in polyvinyl alcohol matrix. The evolution of diffraction efficiency is evaluated during holographic recording with and without voltage as a function of energy exposure by changing the thickness. The curves of diffraction efficiency reach a peak when the films are continuously exposed to energy for a period of time. Sample B obtains the highest diffraction efficiency

The conventional hybrid method of block truncation coding (BTC) and differential pulse code modulation (DPCM), namely the DPCM-BTC method, offers better rate-distortion performance than the standard BTC. However, the quantization error in the hybrid method is easily increased for large block sizes due to the use of two representative levels in BTC. In this paper, we first derive a bivariate quadratic function representing the mean squared error (MSE) between the original block and the block reconstructed in the DPCM framework. The near-optimal representatives obtained by quantizing the minimum of the derived function can prevent the rapid increase of the quantization error. Experimental results show that the proposed method improves peak signal-to-noise ratio performance by up to 2dB at 1.5 bit/pixel (bpp) and by 1.2dB even at a low bit rate of 1.1 bpp as compared with the DPCM-BTC method without optimization. Even with the additional computation for the quantizer optimization, the computational complexity of the proposed method is still much lower than those of transform-based compression techniques.

Modern cameras can cut passengers' faces into boxes in 0.04 s per frame in parallel without time stamps. Unfortunately, that creates random storage without the tracking capability, and one can no longer meet the 5 W's challenge-"who speaks what, where and when." We develop a time-order reconstruction methodology which sorts the boxes as follows. i. A morphological image preprocessing to overcome the facial changes is based on the peripheral invariance of a human visual system when focusing on a maximum overlapping central region. ii. Replacing the Wiener matched filter desired output with an averaged but blurred long exposure, one can select the best matched sharp short exposures called the anchor faces β's. iii. The time-order neighborhood chaining is done by an iterative self-affirmation logic that demands a mutually agreed-upon minimum distance: whether or not the two nearest neighbors of β, namely face A and face C, also consider β to be their two nearest neighbors. The reconstruction procedure mathematically amounts to a product of two triple correlation functions sharing an intermediate state. We have thus demonstrated the time-order helps us associate a video submanifold with the acoustic manifold that solves the 5 W's challenge.

The accuracy of eye gaze estimation using image information is affected by several factors which include image resolution, anatomical structure of the eye, and posture changes. The irregular movements of the head and eye create issues that are currently being researched to enable better use of this key technology. In this paper, we describe an effective way of estimating eye gaze from the elliptical features of one iris under the conditions of not using an auxiliary light source, a head fixing equipment, or multiple cameras. First, we provide preliminary estimation of the gaze direction, and then we obtain the vectors which describe the translation and rotation of the eyeball, by applying a central projection method on the plane which passes through the line-of-sight. This helps us avoid the complex computations involved in previous methods. We also disambiguate the solution based on experimental findings. Second, error correction is conducted on a back propagation neural network trained by a sample collection of translation and rotation vectors. Extensive experimental studies are conducted to assess the efficiency, and robustness of our method. Results reveal that our method has a better performance compared to a typical previous method.

Blind image restoration (BIR) is a useful tool in image processing but too time-consuming to be applied. In order to truly achieve real-time BIR, an ultrafast method for BIR is proposed based on a new concept called the midfrequency region (MR) of an image, which can be used to estimate the point spread function (PSF) and rapidly and accurately restore the image. Also, new MR-based Wiener filtering is derived to accomplish BIR more quickly. Then, using the PSFs of class G that fit numerous imaging systems, a new MR-based algorithm for real-time BIR is derived via independent component analysis and genetic algorithms. Experiments prove that the algorithm is quite effective, speedy, and stable and can truly accomplish real-time image deblurring in on-line systems.

An omni-directional stereo system has a wider field-of-view than conventional cameras, and is widely used in many applications such as robots navigation, depth estimation, and 3D reconstruction. Existing approaches usually use single viewpoint (SVP) systems as the imaging sensor. However, literature proves that an efficient SVP of an omni-directional system can only be achieved with precisely aligned mirrors of parabolic or hyperbolic profile. This enforces rigorous restriction on the configuration of camera and mirrors. In fact, some other profiles, though they do not have the SVP property, are desirable for certain reasons such as cheaper cost and more practical implementation. Therefore, in this paper, we propose both a typical nonsingle viewpoint (non-SVP) omni-directional stereo sensor and its corresponding depth estimation method based on graph-cuts optimization. The sensor comprises a perspective camera and two separate reflective mirrors that could be any radially-symmetric ones. To formulate the depth estimation more consistent with the proposed sensor, we divide the depth space of scenes with a sequence of virtual coaxial cylindrical layers, and model depth estimation as a labeling problem. In the labeling procedure, by considering the characteristics of an omni-directional image, we further devise novel tangential-neighborhood system, radial-neighborhood system, and depth-gradual-changing smoothness constraint which perform better than traditional ones. Depth estimation and 3D reconstruction for both synthesis and real scenes justify the effectiveness of the proposed method.

Three-dimensional (3-D) video technologies are becoming increasingly popular because they can provide high quality and immersive experience to end users. Depth image-based rendering (DIBR) is a key technology in 3-D video systems due to its low bandwidth cost as well as the arbitrary rendering viewpoint. We propose an object-based DIBR method by color-correction optimization. The proposed method first performs temporal consistent rendering to reduce the rendering complexity. Then, by segmenting the depth map into foreground and background, the object-based scalable rendering is performed to improve the rendering quality and reduce the rendering complexity. Finally, the rendered virtual view is further optimized by color-correction operation. Experimental results show that, compared to the results without the above optimization operations, the proposed method can reduce >40% computational complexity while maintaining high rendering quality.

A technique for simultaneous encryption of a color and a gray-scale image is proposed, using single-channel double random-phase encoding in the fractional Fourier domain. Prior to the encryption, the segregated red, green, and blue components of the color image and the gray-scale image are encoded into a single image after changing their bit formats. The format of the encoded image is such that it cannot be perceived by the human eye. The fractional orders of the fractional Fourier transform and two random-phase masks act as key parameters for the encryption. Performance of the scheme is verified against chosen plain-text and known plain-text attacks, respectively. The effect of noise on the performance of the proposed technique is analyzed.

We propose an adaptive corner detector based on the degree of sharpness of the contour, which can detect the corners efficiently and accurately. First, we extract edges from an image using an edge detector, such as Canny, Sobel, etc. Second, we define a degree-of-sharpness variable and calculate its value for each point on the edge. Then we use an adaptive threshold of the degree of sharpness to find the initial corner candidates for each edge. Third, we propose a method of making a projection for an edge segment toward the edge's fitting line to remove salient points. Finally, if some neighboring corner candidates are detected in a support area, we offer an effective method to merge them into one point, and the final corners are reserved. The proposed detector is compared to a classical corner detector and two state-of-the-art methods on planar curves and gray-level images, respectively. The experimental results show that the proposed detector has high correctness in finding true corners. In addition, the algorithm is robust to the additive noise and can detect the circular contour well.

A Bayesian approach for data reduction based on spatial filtering is proposed that enables detection of targets partly occluded by natural forest. The framework aims at creating a synergy between terrain mapping and target detection. It is demonstrates how spatial features can be extracted and combined in order to detect target samples in cluttered environments. In particular, it is illustrated how a priori scene information and assumptions about targets can be translated into algorithms for feature extraction. We also analyze the coupling between features and assumptions because it gives knowledge about which features are general enough to be useful in other environments and which are tailored for a specific situation. Two types of features are identified, nontarget indicators and target indicators. The filtering approach is based on a combination of several features. A theoretical framework for combining the features into a maximum likelihood classification scheme is presented. The approach is evaluated using data collected with a laser-based 3-D sensor in various forest environments with vehicles as targets. Over 70% of the target points are detected at a false-alarm rate of <1%. We also demonstrate how selecting different feature subsets influence the results.

An improved algorithm integrating wavelet decomposition, multilevel filtering, and an additive operator splitting (AOS)-based level-set framework for infrared small target detection is proposed. This model has two components: a filtering operation, and level-set evolution. In the filtering step, the original image is first decomposed using a wavelet transform. After determining the location of sea-sky line, we construct a subimage based on the sea-sky-line position, and then execute multilevel filtering on this subimage. This filtering framework provides the input image for the level-set evolution. Using the level-set formulation, complex curves can be detected while naturally handling topological changes of the evolving curves. To reduce the computational cost required by an explicit implementation of the level-set formulation, a new solver named AOS is proposed. Additionally, the quantitative analyses for our algorithm are also given. Experiments on real infrared image sequences indicate that our method is efficient and robust.

A subwavelength grating with resonant behaviors can be used to exploit security productions with characteristics of anisotropic color variation, i.e., its color has been changed when the grating is rotated on its own plane. In this paper, a novel grating structure with potentials of broadening its spectral bandwidths and improving its color aspects is proposed and its design principles and fabrication methods are also provided. The design of it is completely based on rectangular gratings with a filling factor of 0.5, but the grating regions of fabricated structures have profiles of sinusoidal gratings. Reflection spectra of such two structures are simulated and compared using vector diffraction methods and compared. Moreover, a security grating with unique characteristics of color change has been successfully designed and fabricated, and the changes of color aspects of it have also been verified from both theory and experiment. The proposed structure and its related fabrication methods are feasible in practical application of security and have better values and potentials for mass productions through holographic embossing equipments.

The green up-conversion emissions corresponding to the ²H11/2→4I15/2 and 4S3/2→4I15/2 transitions of the Er³⁺ doped borosilicate glass were recorded, using a 978-nm semiconductor laser diode as an excitation source. The fluorescence intensity ratio (FIR) of the green up-conversion emissions at about 524 and 550 nm was studied as a function of temperature over the temperature range of 296 to 723 K. The maximum sensitivity and the temperature resolution derived from the FIR of the green up-conversion emissions were approximately 0.0038 K−1 and 0.2 K, respectively. It was demonstrated that the prototype optical temperature sensor based on the FIR technique from the green up-conversion emissions in the Er³⁺ doped borosilicate glass plays a major role in temperature measurement.

Herein, we sincerely make an apology to readers for our misguidance. We have made a mistake on the analysis of the optical path difference produced by the Savart polariscope which resulted in the improper design of a wide-field-of-view Savart polariscope. The correct statements are presented.

This PDF file contains the errata for “OE Vol. 50 Issue 04 Paper OE ERR-APR2011-1” for OE Vol. 50 Issue 04