This PDF file contains the editorial “Fraud” for OE Vol. 41 Issue 11

Indium-tin oxide films have been deposited by reactive electron beam evaporation of In+Sn alloy both in neutral and ionized oxygen environments. A low-energy ion source (fabricated in-house) has been used. Films deposited with neutral oxygen exhibited very low optical transmittance (5% at 550 nm). Highly transparent (85%) and low-resistivity (5×10–4 cm) films have been deposited in ionized oxygen at ambient substrate temperature. Optical and electrical properties of the films have been studied as a function of deposition parameters.

An externally modulated 1.3-µm simulated 256-quadrature amplitude modulation (QAM) digital signal lightwave transport system using a semiconductor optical amplifier and wavelength-division-multiplexing (WDM) technique transmitted over an 80-km single-mode fiber is proposed and demonstrated for the first time.

We present an artificial retina (AR) large scale integration (LSI) with a high accuracy on-sensor image projection function. The fabricated chip has 32×32 pixels, and each pixel is 56×56 μm² large with a 41.5% fill factor. This AR LSI compresses 1024 bytes of input image data to 64 bytes of data by computing projection at the same time of image detection, on the focal plane. It also has a function of modulating the projection data into the form of spatial and temporal differentiation data, which fit a motion detection algorithm. Effectiveness of this function was proved by a motion detection experiment capturing an electric fan rotating from 775 to 1500 rpm speed. High sensitivity of 20 V/lx sec and wide dynamic range of 66 dB are also beneficial for high frame rates that lead to high-speed motion detection. Therefore, the AR LSI makes it possible to build a high-speed motion detection system even in combination with an 8-bit microcontroller. This proves how effective it is to combine the processing function of the AR LSI and the recognition function of the microcontroller to build up low cost image processing systems.

The diffraction characteristics of a broadband light source from a circular aperture in the far field are clarified theoretically via a prompt and precise mathematical derivation. We provide not only a rigorous treatment of a time-variant Gaussian-shaped pulsed beam passing through a circular aperture, but also give a more accurate and concrete determination of light distributions including the spectral, time-space intensity, and energy distributions.

Polarimetric scattering information provided by fully polarimetric synthetic aperture radar (SAR) is useful for discriminating between different terrain covers. Conventionally, eigenanalysis is used to synthesize a polarimetric matched filter (PMF) that maximizes the contrast between the features of interest, but this involves many algebraic operations, and only one contrast ratio for any two classes can be obtained at one time. This paper describes the application of a genetic algorithm to the contrast enhancement. When it is used, all the contrast ratios characterizing the best discrimination for any two of all possible classes can be obtained simultaneously, providing a new and more convenient way to solve the problem of the optimization of polarimetric contrast enhancement. Two independent sets of L-band fully polarimetric SAR images are used as test data; the results show that the proposed method is very effective and promising.

The even-phase diffractive optical element that produces four equi-intense diffraction orders with maximum efficiency is derived. A full-wave electromagnetic analysis is performed to study the behavior of the device in the resonance domain. Moreover, such full-wave analysis agrees with the scalar prediction in the limit of very large values of the grating period. Design curves for the transmission efficiency as a function of the grating period and of the incidence angle are presented. The effects of quantization of the phase profile to a discrete number of phase levels are considered. The optimization of a simple structure with only four phase levels is reported, showing good results in terms of diffraction efficiency and angular bandwidth.

A document scanner using polymer waveguides with a microlens array was developed. The waveguide grooves and the microlenses were fabricated simultaneously by injection molding. The cores of the waveguides were formed by squeegeeing. The waveguides have multiple sharp bends to minify the image and also to reduce the size of the scanner. The microlens had a root-mean-square wavefront aberration of 0.06 λ(λ = 633 nm), and the waveguide had a transmission loss of less than 0.1 dB/cm at 633 nm. The optical system was designed to be telecentric so that the scanner had a depth of field greater than 6.0 mm (at 4 lp/mm).

Edge detection remains an important low-level vision problem. Most edge detection methods operate on an image at a single resolution. Edges within an image, however, generally occur at various resolutions, or scales, and represent transitions of different degrees, or gradient levels. Thus, single-resolution edge detection methods that output binary edge maps do not always yield satisfactory results. We develop a multiresolution (MR) edge detection method based on nonlinear image decomposition that produces gray-level edge maps. Unlike linear decomposition methods that tend to blur image features, nonlinear methods can be designed that yield greater control over the scale of structures preserved by the decomposition. The proposed decomposition method utilizes rank-order-based filtering, which preserves visually important cues, such as edges, while eliminating structures smaller than a minimum constraint. The images produced by the decomposition have progressively lower resolution, or more precisely, contain structures of progressively increasing scale. The resulting sequence of images is subject to an edge detection process that incorporates edge strength to yield gray-level edge maps. These edge maps are restricted to form a stacking edge map pyramid. In this formulation, the base edge map contains edges at all scales, while edge pruning, based on edge scale, is performed at subsequent levels. Thus, moving up in the pyramid yields edge maps with fewer small-scale, or detail, edges. The motivation behind this algorithm comes from tactile imaging, an important problem in facilitating access to visual information for blind people. The proposed scheme is suited for such applications because it provides more control over detail (edge scale) level and is compatible with how the mind perceives information, beginning with course information and progressively increasing the detail level. Simulation results are presented on synthetic signals, electron micrographs, and images. A comparison of results with Park's linear decomposition algorithm demonstrate the advantages of the proposed method.

A new method for measuring changes in birefringence (or retardation) by modulating an electro-optic (EO) modulator in a sine-wave signal is developed in a common-path interferometer (polarimeter). The standard heterodyne signal, therefore, can be formed with a new heterodyne scheme, and subsequently the phase shift regarding to changes in birefringence is demodulated by a lock-in amplifier or phase meter. As compared to the conventional techniques, this technique supplies an easier setup, wider modulated frequency, and therefore, a wider frequency response in a sensing system. Finally, the birefringence measurement based on an EO modulator and a new heterodyne scheme in a common-path interferometer is first demonstrated.

In this paper, we propose an optoelectronic two-layer neural network based on the fringe-adjusted joint transform correlator for invariant face recognition accommodating in-plane and out-of-plane 3-D distortions. The neural network is utilized in the training stage for a sequence of facial images and for supervised learning in order to create composite images that are invariant to 3-D distortions. The proposed technique is implemented by using the fringe-adjusted joint transform correlator. Simulation results are presented to verify the performance of the proposed technique. These results are then compared with those obtained using other techniques such as the synthetic discriminant function.

Bound solitons with a soliton pulse width of 326 fs and a pulse separation of 938 fs are obtained in a passively mode locked fiber laser. Its creation and annihilation mechanism is experimentally investigated. Due to the existence of a strong cw laser in the cavity, the generation of bound solitons is found to be different from that of the nonbound normal solitons. We find that the number of stable bound soliton pairs in the cavity can be controlled only under lower pump power.

The static and switching characteristics of a novel wavelength-switching fiber laser source for an optically controlled phased-array antenna (OCPAA) has been studied experimentally. The laser source was configured within a unidirectional ring cavity, with a tunable fiber Fabry-Perot filter, containing two sampled fiber Bragg gratings with a wavelength spacing of about 1.6 nm. It can individually scan the 25 required wavelengths in the fiber Bragg grating array in the OCPAA within 0.08 s. The switching speed, limited by relaxation oscillation, was analyzed. The polarization insensitivity of the ring cavity made the laser output at each wavelength very stable. Side-mode suppression ratios greater than 40 dB for each lasing wavelength were realized.

As a rapidly developing technique of photomechanics, the digital speckle correlation method (DSCM) has attracted attention for its advantages of noncontact, real time, whole field and wide measuring range, etc. Raising the speed of convergence is a developing direction of the method for its great calculation volume. We present an improved DSCM by introducing an optimization theory. It can reduce the computational workload and speed the convergence velocity. This method is used to measure the displacement fields and strain fields in the crack tip region of thin foil, and the stress intensity factor is obtained by the experimental method. Applications show that the DSCM is an effective experimental technique for investigating the mechanical behavior of thin foil materials.

We report the method of accurate diffraction efficiency control for multiplexed volume holographic gratings in dry photopolymer films (DuPont HRF-600). Based on the experimental evaluations of the grating formation characteristics in dry photopolymer films, we present the way to develop the practical recording schedules for the fabrication of holographic gratings under accurate diffraction efficiency control. Using this method, we obtained single holographic gratings with the desired diffraction efficiency (variation 2.5%) and high-efficiency equal-strength (47%/47%) double holographic gratings. As a practical application, we demonstrated the centralized optical backplane architecture with uniform fan-outs using the single and equal-strength double holographic gratings we recorded.

Polarization holographic gratings transform the polarization state of an incident wavefront. We have studied the diffraction properties of polarization gratings, formed with two orthogonal linearly or circularly polarized waves. For a polarization modulation recorded in the organic material bacteriorhodopsin, the diffraction efficiency and the diffracted wave polarization strongly depend on the polarization state of the readout wave. We have given a simple theoretical treatment using the Fraunhofer diffraction integral. The experimental results have been interpreted in terms of this simplified model.

An all-optical angular sensing system based on volume holography is proposed and demonstrated, where a divergent spherical wave is the reference and reading beam for writing and testing, respectively. Under the paraxial condition, analysis shows that angular selectivity is nearly independent of the distance between the hologram and the light source. By choosing an appropriate distance, the entire energy of the source (e.g., an LED) can be employed while maintaining the same resolution for precise angular sensing.

We propose a new context-based image coding technique using fuzzy logic in the quantization and entropy coding processes. Firstly, we have improved the well-known trellis-coded quantization (TCQ), using previous states of the TCQ symbols and fuzzy logic to predict the current TCQ state of the quantized wavelet coefficient. We designed the fuzzy rules and membership functions using our experiences in image coding. The quantized coefficients were presented with the bit planes, and the bits were coded arithmetically. Secondly, we propose a new probability estimation method for the adaptive arithmetic coder, using fuzzy logic to assign the probability of the coded symbol. Observations of previously coded bits were used as inputs of the fuzzy logic, which assigns the probability of the coded bit according to the fuzzy rules and membership functions. The efficiency of the context-based image coder using fuzzy logic achieves state-of-the-art results with respect to rate distortion.

In the encoding phase of fractal image compression, most of the time is taken in finding the closest match between each range block and a large pool of domain blocks. We use the intrablock variance distributions of domain blocks to reduce the search space. For finding a close match, we need search only the domain blocks whose maximal intrablock variance quadrants are at the same corner as the range block. Thus, we reduce the number of transforms applied on each domain block from eight to two. We also adopt the longest-distance-first vector quantization scheme to divide the large pool of domain blocks into clusters. Thus, the number of domain blocks to be searched is also reduced. The experimental results show that our algorithm can reduce encoding time with only slight loss of quality.

We present an algorithm that can determine the layout of an arbitrary document with great flexibility. The bottom-up approach of pattern extraction and classification provides good segmentation and is insensitive to skew. Soft ordering is a feature that improves segmentation by allowing distinct regions to physically overlap. It is also used to determine the correct order of the document regions. The algorithm can extract and place all the distinct document regions into a logical layout and column structure.

We propose a novel quadrilateral based region segmentation method that is favorable for object tracking. Instead of using groups of pixels or regular blocks, it uses groups of connected quadrilaterals to represent regions. The proposed method derives the vertices of each quadrilateral from the edge map using the concept of center of masses. By merging the quadrilaterals, regions can be represented. The proposed method offers better data reduction than pixelwise region representation and better boundary approximation than block-based segmentation methods. Experimental results show that it generates a more reasonable region map, which is more suitable for object tracking, and a smaller number of regions than the seeded region growing, K-means clustering, and constrained gravitational clustering methods.

We propose two image segmentation algorithms: the integrated sortmap relabel with adjacent-region merging (ISARM), and the self-guided sortmap relabel with adjacent-region merging (SGSARM). Due to the integration of noise reduction and fast merging, ISARM provides a 25% improvement in processing time, as compared to leading existing algorithms such as the region adjacency graph (RAG) algorithm, on a variety of test images. ISARM also provides better segmentation accuracy than the RAG algorithm, by a measure combining the mean squared error and the number of regions obtained. SGSARM is designed for use with large images (say 1024×1024 or larger). It incorporates two levels of processing: an edge detection algorithm of linear complexity, which is applied to large images to detect regions of interest (ROIs), followed by ISARM for finer segmentation of each ROI. SGSARM therefore has significant advantages in speed and accuracy when used in large images. Simulation results are provided to demonstrate the performance of both algorithms.

We describe an optical technique using the principles of a Pohl interferometer and divergent laser beams for measuring optical path changes in the spaces between interdigital electrodes. We present experimental results of the electric-field-induced optical path changes in an electrode space using a LiNbO₃ sample.

A novel null corrector design for use with a white light scatterplate interferometer on a large conic surface is presented. In this design, an aspheric diamond-turned mirror (DTM), hereafter called the null-correcting mirror (NCM), exactly cancels out the spherical aberration of the mirror under test. Low-power refractive elements correct field aberrations over the finite aperture of the scatterplate. The null corrector maintains a phase difference between the test and reference beams of less than ½ wave over the finite field size of the scatterplate for optimal fringe visibility. The null corrector can be certified using another smaller DTM and/or a computer-generated hologram. The design has the significant advantages of being small in size, less expensive than designs using spherical surfaces (due to the small size of the NCM), and useable with other interferometers. We include discussions on the calculation of the surface profile for the NCM and certifying mirror, field correction, and achromatization.

We present the results of a detailed characterization of electro-optical and nonlinear optical properties of liquid crystals with nanoparticulate internal structures. The experiments revealed three different states of transmission of the material: diffusive, translucent, and semitranslucent. Transformations between them are induced by electric fields and laser beams. A threshold power exists for a laser beam to change the transmission state of the material. An increase in the strength of laser/material interaction with an increase of scan speed of the beam across the material was observed. One- and two-dimensional diffraction gratings were recorded using two techniques: overlap of two 1-D gratings, and modulation of the speed of laser beam scan. We show that information pixels that are recorded in such materials may possess microstructures for certain laser power and exposure times. We also report the observation of "netquake," a phenomenon of long-range propagation of thermal shocks at high laser beam power levels.

The possibility of using smectic liquid crystals in active waveguide devices is explored through the analysis of both an integrated electro-optic switch and a continuously tunable filter. The two devices are based on a Bragg grating in planar waveguide with a liquid crystal overlayer, which enables changing the spectral behavior of the device. The fast and bistable switching of smectic C^* in the surface-stabilized liquid crystal structure is used to investigate the possibility of realizing an integrated electro-optical switch. The principal advantage of this device is its spectral signature, which enables us to overcome the problems of intensity dependent devices. The soft-mode of smectic A^* liquid crystals, enabling a continuous modulation of extraordinary refractive index, is used to design an integrated wavelength filter in the wavelength range of interest for optical communications. The principal advantages of such device include fast tuning speed, wide tuning range, low power dissipation, and low cost.

We present a simple method to measure the focal length of a lens of any size. This method consists in measuring the displacement of the transmitted spot image that occurs when a Gaussian beam impinges on a laterally displaced lens. It is shown that the method is consistent with alternative methods.

Cr/Sc multilayers have been grown on Si substrates using dc magnetron sputtering. The multilayers are intended as condenser mirrors in a soft x-ray microscope operating at the wavelength 3.374 nm. They were designed for normal reflection of the first and second orders, with multilayer periods of 1.692 and 3.381 nm, and layer thickness ratios of 0.471 and 0.237, respectively. At-wavelength soft-x-ray reflectivity measurements were carried out using a reflectometer with a compact soft-x-ray laser-plasma source. The multilayers were irradiated during growth with Ar ions, varying both in energy (9 to 113 eV) and flux, in order to stimulate the adatom mobility and improve the interface flatness. It was found that to obtain a maximum soft x-ray reflectivity with a low flux (Cr = 0.76, Sc = 2.5) of Ar ions a rather high energy of 53 eV was required. Such energy also caused intermixing of the layers. By the use of a solenoid surrounding the substrate, the arriving ion-to-metal flux ratio could be increased 10 times and the required ion energy could be decreased. A high flux (Cr = 7.1, Sc = 23.1) of low-energy (9 eV) Ar ions yielded the most favorable growth condition, limiting the intermixing with a subsistent good surface flatness.

Testing methods commonly used for ophthalmic lenses produce a power distribution map that treats the lens as an independent element. This map, however, does not necessarily correspond to the refractive correction state of the lens when the observer looks through it. We describe a method to obtain a refractive correction map of an ophthalmic lens, which is an improved representation of its actual performance.

An analytical model to analyze the effect of light on the dc and rf characteristics of a GaN metal semiconductor field effect transistor (MESFET) is presented. The photovoltaic effect in the depletion region and gate length modulation in the active channel is considered using an unidimensional approach. The parasitic resistances are made illumination dependent by considering the photovoltage developed across the Schottky barrier, causing gate-voltage modulation in the ungated portions of the channel. Also, the sidewall capacitance is evaluated, taking into account the illumination-modulated fringing charge. These effects are then used to predict the cut-off frequency, admittance parameters, and scattering parameters of the device.

Based on the theory of synthetic discriminant function, several subreference images are synthesized to realize distortion-invariant recognition. Using a phase-encoding technique and amplitude modulation on a joint power spectrum, the proposed joint transform correlator greatly reduces the intensity and width of the strong dc component, sharpens the correlation peak, and eliminates cross-correlations between each input target and the conjugate cross-correlation between the reference and input targets, which exist in the classical joint transform correlator. All these achievements are accomplished in only one step. At the end, a computer simulation is given, which proves the efficiency of the proposed method.

Laser ablation was applied to X-cut Z-propagation Ti:LiNbO₃ waveguides. The effective refractive index change of the waveguides after the ablation was measured for both TE and TM modes. The change is more sensitive to the ablation for the TE than for the TM mode. This phenomenon was confirmed by measuring the modal effective refractive indices of a nonablated and an ablated planar Ti:LiNbO₃ waveguide with the m-line method. A photoelastic effect that may cause the different effective index changes of the waveguide modes after ablation is discussed.

The stabilization of line of sight (LOS) against vehicle-induced disturbance is an essential feature of an electromechanical gimbaled sighting system with an optical sensor for sighting. We describe the design of a high-performance controller for an electromechancial target-tracking system with an optical sensor for sighting. The control law is obtained using a linear model of the electromechanical system. The modeling of the system is carried out using the experimental frequency response data. The H∞ control methodology is used to design a high-performance controller so as to control the rate of the line of sight. The mixed sensitivity optimization problem is posed and weighting functions are selected so that they not only encapsulate all the design goals but also accommodate the modeling uncertainties. A stabilizing controller with excellent robustness properties is obtained.

A simple technique is devised for making prisms with submultiple or half angles. As an application of these prisms, methods are suggested to measure the angles of the Pechan and Pellin-Broca prisms without using expensive spectrometers, autocollimators, and angle gauges.

A solid-state dye laser for potential application as an ozone lidar transmitter is described. The solid-state dye laser material is made from a polymer host polymethyl methacrylate (PMMA) injected with a pyrromethene laser dye PM-597. The laser oscillator cavity is end-pumped by a Q-switched Nd:YAG laser at 532 nm. Broadband and narrowband laser oscillator cavities were constructed and tested. For the broadband oscillator, slope efficiency as high as 79% was achieved. A narrowband laser oscillator was constructed to generate radiation at 578 and 600 nm with 390-pm linewidth. This output was frequency doubled to 289 or 300 nm using a beta-barium borate (BBO) crystal. The oscillator cavity generated a maximum energy of 11 mJ at 578 nm when pumped by 100 mJ, 532 nm, at 10-Hz repetition rate. Maximum output energy of 380 μJ was achieved at a wavelength of 289 nm.

The monochromatic response as a Fourier transform infrared (FTIR) spectrometer apparatus functions is determined to estimate the influence of optical system aberrations on the measurement precision. Exemplary results for the third-order spherical aberration are presented. General conclusions concerning the influence of wave aberrations in the spectrometer channel with moving mirror are formulated.

Guided-mode resonances in subwavelength gratings are strongly dependent on incident angles. A beam selector with high sensitivity is designed based on this property. A guided-mode resonant silicon nitride (Si₃N₄) grating on a silicon dioxide (SiO₂) substrate is presented as an example of such a device with a 1.55 μm wavelength. The calculated reflection resonance has an incident angle FWHM of Δθ~0.0042 radians, and a normal-incident peak efficiency of ~99.9%. In addition, we propose that this type of beam selector be applied to select transverse modes of semiconductor lasers.

Restoration of vibrated images can be performed with or without knowledge of the motion function. The algorithms based on the known motion function are more accurate. However, sensing of the motion function in the real-world environment is often difficult to implement accurately. We propose a differential scheme for sensing vibrations. It is shown that the differential scheme permits one to obtain a true rotational motion function, which is often the main blurring factor in remote sensing systems. An experiment was set up and the results are presented. The proposed sensing scheme was implemented in real time and then the obtained image was restored from motion blur with a personal computer. The fine accuracy of the restoration results derives from the accuracy of the proposed motion sensing scheme.

We report on the feasibility of a polarization-independent multiplexer for two visible wavelengths region with a spectral separation of 2.4 nm and an angular separation of 4 deg. To construct this device, holographic gratings are recorded in an iron-doped lithium niobate crystal via the photorefractive effect. Thermal fixing is employed to avoid optical erasure and increase the lifetime of the recorded gratings. It is shown that the two polarization modes associated with each wavelength propagate collinearly outside the crystal. Furthermore, it is shown that the signal power depends only marginally on the incident polarization, and its variation is less than 5%. No polarization crosstalk is detected, and the wavelength crosstalk is suppressed by 8 to 11 dB.

This PDF contains the communication "Diffraction efficiency of nonsynchronously sampled diffraction gratings."