This PDF file contains the editorial “Beyond ‘‘Eyeglasses’’!” for OE Vol. 42 Issue 08

Two erbium-doped fiber ring laser configurations are proposed and experimentally demonstrated. Both configurations employ array-waveguide-grating (AWG)-based cavities to select the operation wavelengths. The first experiment can achieve discrete wavelength tuning in a range of 31.8 nm with 2.0-dBm output power for each channel. The second experiment yields four wavelength lasing with –10-dBm output power for all signals after power equalization. The linewidth of either AWG laser is as small as 0.015 nm and the side-mode suppression ratio is over 55 dB.

In this paper, we report the fabrication of a 128-×1024-element cylindrical microlens array in a low-cost inorganic-organic SiO₂/ZrO₂ sol-gel glass using reflowing technique. The fabricated microlens array had excellent surface smoothness and dimension uniformity. The prime advantages of the hybrid sol-gel material are its suitability as an etching-free negative-tone UV-sensitive material, uniformity, and other excellent optical properties. Microfabrication in sol-gel glass using the reflowing technique is demonstrated as a cost-effective and high-volume production technology for micro-optical elements.

A configurable 2-D adaptive digital filter architecture based on 2-D normalized least mean square (TDNLMS) algorithms is proposed. This architecture can be used as a prewhitening filter to enhance the detectability of small objects in digital images. Every tap in this architecture can be configured as one of three types: input, reference, and disable taps. By setting the type of each tap, this architecture can be utilized to implement a TDNLMS adaptive prediction error filter in any type of support region on a 5×5 tap array. This feature allows the adaptive prediction filter to detect small objects whose area changes gradually during the detection process, or to process images with different stochastic characteristics. This architecture can also be configured as an adaptive prediction filter (APF) used in image noise reduction, or a 2-D convolver used in many image processing algorithms. In the calculation of coefficient updating, the power of the input vector is approximate to the power of two, hence the critical path delay is reduced significantly. A local parallel global serial mode is adopted in this architecture to increase the coefficients' word length, and to reduce the finite-precision effect. Simulation results show that TDNLMS APEF based on this architecture can provide satisfactory small object detection performance in various environments.

Anisoplanatism error for the low-order mode and its influence on compensation effects are analyzed both theoretically and experimentally. For non-Kolmogorov turbulence, the anisoplanatism error, the angular correlation function of Zernike polynomials, the long-exposure optical transfer function (OTF), and the residual phase structure function are all discussed. The modal correction coefficient is used to evaluate the influence of anisoplanatism error on the compensation effectiveness of an adaptive optics system used as the low-order mode correction. The numerical calculation results of the modal correction coefficient and long-exposure OTF for light beam horizontal atmospheric propagation are also presented.

Ray-tracing analysis of a particular reflecting axicon, a right circular cone, for use as a retroreflector in active open-path Fourier-transform IR (OP/FT-IR) spectrometry, and the results of testing a 0.305-m aperture right circular cone using a commercial active OP/FT-IR spectrometer are presented. The ray-tracing model is based on the optical characteristics of a commercial single-telescope monostatic OP/FT-IR spectrometer and models the off-axis behavior normally encountered under practical field conditions during field use. Of practical concern are the trends for the diameter of the beam reflected from the retroreflector as a function of the path length between spectrometer and retroreflector and misalignment of the retroreflector with respect to the transmitted beam. Construction and the results of field-testing two smaller epoxy-composite axicons replicated from the 0.305-m master are presented.

Design considerations for a Nomarski reflection microscope to produce a desired differential interference contrast image and the results are presented. Formulas for tracing of rays through the Nomarski prism and calculation of the optical path difference and the angular separation between the orthogonal linearly polarized components and for determining the position of the ray intersection plane are devised. Techniques for the design and fabrication of a Nomarski prism and a complete differential interference contrast microscope are described.

A novel method of direct transfer of microstructure into diamond films is presented. A diffractive optical element (DOE) with continuous relief and six annuli was directly fabricated on the diamond films by use of focused ion-beam milling (FIBM). The diamond film was coated via hot filament chemical vapor deposition (HFCVD) on a substrate of fused silica. It is shown by the measurement results of Raman spectrum, transmission, and the refractive index of the diamond film before and after the FIBM that little diamond compound is transferred to the graphite during the FIBM, and the influence of the FIBM on the optical properties of the film can be ignored. The surface roughness of the DOE with an R_a value of 2.374 nm is derived by use of an atomic force microscope (AFM) in a partial square area of 1×1 μm². By the two-dimensional (2-D) profile and three-dimensional (3-D) topography of the DOE it is shown that the surface is smooth and neat, and the relief depth and annulus width of the DOE are in accordance with the design.

The development of an in-line digital microholointerferometer for micromechanical testing is presented. With respect to the specific requirements on the microscopic scheme in micromeasurement, the application of a long-distance microscope is introduced with emphasis. A critical issue, validation of the developed system, is addressed. Aided by finite element analysis and analytical calculation, experimental measurement with the system is examined using a hybrid approach. To evaluate the performance of the system, a microbeam experiment is presented. Results measured with the system, as well as the numerical simulations, are obtained. Quantitative comparisons are carried out in terms of load-induced variations of the test sample, based on which the conclusions are given.

The novel principle of laser feedback displacement sensors is presented and demonstrated. A birefringent dual-frequency laser is used as the light source, which outputs two polarization lights, o light and e light. The two polarization lights are divided by a Wollaston prism and detected separately by two photoelectric detectors. When the feedback mirror is moved along the laser axis, the intensities of both the o light and the e light change periodically. And an increase of o light intensity always accompanies a decrease of e light intensity. If a threshold intensity for the output light is appropriately given by the signal processing circuits, the remaining intensity curves in each period shows four different polarization states: e light, e light and o light, o light, and no light. Each change of polarization state corresponds to a λ/8 displacement of the feedback mirror. We judge the movement direction by the difference of the order of the polarization states that appear. The resolution of the system is 0.079 μm. The possibility of employing the fold feedback cavity is discussed, and its resolution is believed to reach 0.0395 μm.

Ion diffusion of rubidium (Rb) in potassium titanyl phosphate (KTP) creates areas of high Rb concentration. The areas of high Rb concentration have an index of refraction of n_Rb = 1.846 as compared to the index of refraction for the KTP of n_K = 1.842. The small change in the index of refraction is enough to create waveguide structures and integrated optics such as Bragg gratings in the KTP substrate. A tunable external-cavity diode laser is constructed using waveguide structures and integrated optics created by this ion diffusion. The resulting Bragg grating is used to provide optical feedback to control the operating wavelength of an external-cavity laser. Tuning is accomplished using the electro-optic properties of KTP to control the effective period of the Bragg grating. A tuning response of R = 19.5 MHz/V was measured.

Size tolerance of a 4×4 general interference tapered multimode interference (MMI) coupler in a silicon-on-insulator (SOI) structure is investigated by means of a 2-D finite difference beam propagation method (2D-FDBPM), together with an effective refractive index method (EIM). The results show that the tapered multimode interference coupler exhibits relatively larger size tolerance when light is launched from the edgeport than from midport, though it has much better output power uniformity when light is launched from midport. Besides that, it can reduce the device length greatly. The 4×4 general interference tapered MMI coupler has a slightly larger size tolerance compared with a conventional straight multimode interference coupler.

An efficient and robust fiber optic alignment method for locating the optimal coupling position is critical to fiber optic packaging automation, and thus to photonics manufacturing. The often used hill-climbing type alignment method is gradient-based, 1-D "blind" searching, which is difficult for dealing with angular misalignments and the alignment of fiber arrays. This work presents a novel alignment method consisting of the Hamiltonian algorithm and Matlab/Simulink software tools. The Hamiltonian algorithm utilizes the inherent dynamic properties of the system to guide the movement of the fiber tip, and the Matlab/Simulink provides an efficient tool for solving Hamiltonian equations as well as output feedback control. Simulation results are obtained for the active alignment of single-channel fiber optic devices and multichannel-arrayed fiber optic devices, respectively. Trajectories of the searching path are demonstrated to be smooth. It is shown that time for multidegree of freedom alignment is significantly reduced compared to the conventional hill-climbing type alignment method. It is also demonstrated that, for arrayed fiber optic devices, a balanced fiber optic coupling result for all fibers can be easily reached.

We describe a technique for fiber Bragg grating multiplexing in a fiber Bragg grating laser sensor. This technique uses an intermodal beating frequency in a fiber laser with a linear cavity formed by a reference Bragg grating and several sensing Bragg gratings. We show the interrogation of an individual Bragg grating in an array formed by two, three, and four Bragg gratings. The longest cavity length used in the experiments was 8.67 km, with a 23-m distance separation between Bragg gratings, which proves the capability for long distance sensors with high spatial resolution. We consider that this technique is suitable for early warning and alarm systems.

The synthesis of fiber Bragg-grating-based all-optical microwave filters using the genetic algorithms is investigated. In the proposed algorithm, all-optical microwave filters employing fiber Bragg gratings as tapping and weighting elements are considered. The coefficients and the tapping intervals of the microwave filters are optimized by the genetic algorithms. Algorithms for fixed and variable tapping intervals are developed and two design examples are presented and discussed.

A theoretical study of a passive fiber ring resonator with a Sagnac loop filter is reported. It is used to construct a stable multiwavelength fiber laser at room temperatures. The gain medium is an elliptical-core erbium-doped fiber. The principle of operation is based on the polarization-dependent gain phenomena in erbium-doped fiber. The effects of the different parameters of the doped fiber and the loop filter are experimentally studied.

We propose a simple tunable chirping technique for uniform Bragg gratings. This technique consists of the application of a uniform Bragg grating to a lateral side of a beam at a particular angle with respect to the beam neutral axis. We demonstrate that it is possible to obtain a tuned linear or quadratic chirp without a center wavelength shift by means of two bending geometries, a beam with simply supported ends and a cantilever beam.

The development of sensors based on no-moving-parts two-beam interferometers has been progressing for many years. These sensors can produce an interferogram sampled simultaneously rather than sequentially, as is done in Michelson-type interferometers in more common use. While similar to Michelson-type interferometers, the rectification of interferograms from digital array scanned interferometers (DASIs) requires somewhat different methods to achieve optimal results. We consider the problem of calibrating a DASI-like sensor using known optical sources. A simple model for a two-beam interferometer is proposed that illustrates the dominant sensor effects that can be present in more complex devices. These effects are (1) the nonlinear relationship between the spatial sampling in the instrument and the temporal sampling of the optical autocorrelation function and (2) the apodization or nonuniform gain, which is applied across the autocorrelation function. The resulting measurement, the interferogram, is a windowed, time-warped version of the true optical autocorrelation function. A method quantifying the time-warping effect using a narrowband optical source is developed. This method treats the interferogram as a sinusoid subject to phase modulation, and uses quadrature demodulation to recover the nonlinear phase that characterizes the time warping. The apodization curve is estimated using simple polynomial curve-fitting. Methods for correcting the interferogram, thus enabling the power spectral density to be computed via standard Fourier transform techniques, are presented.

For the purpose of human-computer interaction (HCI), a vision-based gesture segmentation approach is proposed. The technique essentially includes skin color detection and gesture segmentation. The skin color detection employs a skin-color artificial neural network (ANN). To merge and segment the region of interest, we propose a novel mountain algorithm. The details of the approach and experiment results are provided. The experimental segmentation accuracy is 96.25%.

Decreasing depths of focus, coupled with increasing silicon wafer diameters, place greater restrictions on chucked wafer flatness in photolithography processes. A measurement device is described that measures thickness variation of double-sided polished wafers using an IR source and vidicon detector. Various possible instrument configurations are described with the focus on a setup that uses a collimated wavefront to produce interference fringes between the front and back surfaces of the plane parallel wafer. Experimental results are presented. These tests include (1) a drift test; (2) comparisons between measurements performed using different collimators and, subsequently, wavefronts; (3) an exploration of the impact of phase change on reflection due to the wafer clamping method; and (4) an intercomparison with thickness measurements recorded by a capacitance gage-based instrument and surface measurements obtained using a separate visible wavelength interferometer.

We report the development of a novel dual-beam laser Doppler vibrometer (LDV) that can eliminate the perturbation due to the vibrometer body vibration without any external reference surface. A residual laser beam from the beamsplitter is used to pick up the vibration of the damper, which is mounted in the vibrometer, and is combined with the reference beam at the photodetector. The output signal of this detector and the main signal are processed to extract the object vibration, using a least-mean-squares adaptive algorithm. It is shown experimentally that the slowly varying statistics of the body vibration, which are valid in most practical cases, can be effectively removed from the measured signal using digital signal processing (DSP) technology.

The U.S. Army has been investigating the differences between various bands in the mid-wave and long-wave infrared spectrum. A holistic approach to quantifying scene information was used in previous research. That is, both natural backgrounds and vehicles were present in scenes when correlation analyses were performed. Similar research has also been performed using hyperspectral imagers. Hyperspectral imagers inherently have poor signal-to-noise ratio (SNR) due to the spectral bandwidth of the individual images. In the new research reported here, a mid-wave infrared broadband sensor is cold filtered to provide four subbands in the mid-wave region. A multiwaveband sensor is used to collect mid-wave infrared imagery of military vehicles and natural backgrounds. Three blackbody sources are placed at the same range as the vehicles for radiometric calibration. The goal is to collect radiometrically corrected data of various vehicle targets and backgrounds. These data are then processed for comparative analysis. The images are segmented to remove all unwanted imagery from the images under observation. Pair-wise correlations between corresponding spectral images are performed to assess the differences in information content between the subbands.

A comparison of phase sensitivity is conducted for two different types of optical fiber designs with the same outer diameter. The optical fibers are subjected to a hydrostatic pressure load. The finite element model validates well with the analytical solutions. The holey fiber selected for this study showed a 130% phase sensitivity gain over a conventional single-mode optical fiber due to its hollow structure, enabling the external pressure load to strain the core beyond that observed in solid optical fibers. The holey fiber's outer coating also enhances the phase sensitivity, with improved performance over conventional single-mode optical fibers with the same coating.

Photonic crystal fibers (PCFs) are quite useful for confining and guiding light with interesting modal properties. The scattering matrix method is used to calculate the higher order modes guided in a PCF. The model is derived from the solution of the boundary condition problem taking into consideration the coupling between the electric and the magnetic fields. Results are presented for novel fibers that allow for only azimuthal modes.

We present an optical finite impulse response (FIR) filter design method. Based on crystal birefringence, an optical FIR filter can be designed to produce arbitrary spectrum output. A mathematic model of the optical FIR filter is introduced from the FIR theory. Details of the mapping relationship between an FIR filter and an optical filter are analyzed. A classical FIR filter design method is directly applied. After using the optical backward transfer method to implement the optical configuration, a design of a green/magenta broadband filter is discussed. The experiment results demonstrate that the theoretical simulation is in accordance with the experiment.

A multichannel ring is designed. Each sublayer network is connected to the ring with an access node (AN), which can transmit data at every wavelength with a tunable laser diode. The data transmission speed at each wavelength is 1.25 Gbit/s. With eight wavelengths, a total bandwidth of 10 Gbit/s can be obtained. With a bandpass filter, the desired optical signal can be dropped down at the access node. On receiving a data packet, the optical signal is split into two parts. One part is converted to an electrical signal and its destination address is extracted and verified. If the data packet belongs to the local subnetwork, it is received. Otherwise, it is retransmitted to the next access node with a selected wavelength. So pipelining data transmission can be achieved among different wavelengths. And this network is a multipipeline structure. The data processing time is less than 300 ns, and all of the processing procedure is implemented via a field programmable gate array (FPGA). So the communication latency and communication overheads can be decreased. Meanwhile, the ring topology has good scalability. More wavelengths can be adopted for a large-scale network with more access nodes.

We propose a public-key-based optical image cryptosystem for practical secure communications since conventional optical cryptosystems that use a symmetric algorithm are confronted by the problem of key delivery. The proposed system employs a hybrid architecture in which a double-random-phase encoding is used to cipher and decipher an image and an asymmetric algorithm is used for ciphering and deciphering the session key. To solve this problem of key delivery, the double-random-phase encoding algorithm is analyzed to establish a covert channel and therefore elucidate the phenomenon that the amplitude part of the ciphered image is less sensitive to quantization error than the other parts in the Fourier and output planes. The session key is then hidden in the covert channel setup in the ciphered image and extracted at the receiver side. Experimental results demonstrate that the amplitude parts in the Fourier and output planes are better suited to convey the session key because they enable reconstructed images with a higher visual quality to be obtained.

A novel approach to secret image sharing based on a (k,n)-threshold scheme with the additional capability of share data reduction is proposed. A secret image is first transformed into the frequency domain using the discrete cosine transform (DCT), which is applied in most compression schemes. Then all the DCT coefficients except the first 10 lower frequency ones are discarded. And the values of the 2nd through the 10th coefficients are disarranged in such a way that they cannot be recovered without the first coefficient and that the inverse DCT of them cannot reveal the details of the original image. Finally, the first coefficient is encoded into a number of shares for a group of secret-sharing participants and the remaining nine manipulated coefficients are allowed to be accessible to the public. The overall effect of this scheme is achievement of effective secret sharing with good reduction of share data. The scheme is thus suitable for certain application environments, such as the uses of mobile or handheld devices, where only a small amount of network traffic for shared transmission and a small amount of space for data storage are allowed. Good experimental results proving the feasibility of the proposed approach are also included.

We describe active and passive optical identification tags and readers for remote identification and verification of objects. These include a wavelength-hopped laser encoding and decoding system, and a retroreflective optically phase-modulated ID tag and reader.

We present a multilayered optical storage disk design based on the use of frequency up-conversion in rare earth. This design offers the potential of increased optical storage density. In our experiment, a three-layered sample is prepared by stacking three sections of a thin glass slide on which stripes of Ho³⁺/Yb³⁺ codoped TeO₂ are deposited via a sol-gel technique. The layers are selectively illuminated by a focused 980-nm laser beam by bringing them into the focal plane. The up-converted green luminescence signals from the tracks in the three layers are clearly resolved without any observable interlayer crosstalk, thus demonstrating the successful data retrieval from our multilayered optical disk. Based on the nonlinear property associated with the up-conversion effect, we also perform a theoretical calculation on the bit resolution enhancement in relation to the number of photons involved in the up-conversion process. The use of laser heating to induce phase change from an amorphous state to a polycrystalline one in the sol-gel film for write-once-read-many optical storage is also discussed.

We present a technique that allows us to increment the number of objects to be detected and classified simultaneously in an optical pattern recognition process. It basically consists of the multiplexing of several phase-only filters. The elimination of the convolution signal at the final correlation plane, by means of the direct implementation of phase-only filters, allows an increase in the number of channels to be used in a Vander Lugt correlator. The difference among these composed filters and others proposed before lies in the way they are synthesized. Usually filters are physically implemented by using amplitude media, and it is necessary to perform an encoding of the phase information. In the proposed method, no encoding technique is used to convert the phase values into amplitude ones. The implementation of this kind of filter is carried out by using liquid crystal displays working in phase-only mode. We present in this work numerical simulations and experimental results obtained from the implementation of two different kinds of phase-only filters. Impulse responses and correlation signals are analyzed.

We propose a new image segmentation method that can extract multiple gray objects from a gray image even under nonuniform illumination. Because the minimum area and boundary intensity of the object are the only two parameters used, this new method can be easily applied. The new method is based on the fact that one object can exist in a certain threshold range. Thus, if the original gray image is binarized by successive thresholds, the contours of the object may be different, but it can be found that these contours usually pass through boundary pixels more times than other pixels. We call this observation relation stable state. By using an image to record contours and a new merge-split processing to segment the image, the new method integrates gray value, edge information, and space connectivity smartly. Experiments show it can be used not only in normal cases but also in extracting multiple gray objects even under nonuniform illumination.

Automatic human face recognition is a difficult but significant problem. A method for face recognition based on singular-value feature vectors is discussed. Three algorithms of face recognition based on singular-value feature vectors are proposed. These algorithms are face recognition using principal component analysis based on singular-value feature vectors, face recognition by Fisher linear discriminant analysis based on singular-value feature vectors, and face recognition using the discriminant Karhunen Loeve (DKL) transform based on singular-value feature vectors. Experimental results show that face recognition based on singular-value feature vectors is effective.

We investigate the use of flatbed scanners for photoelasticity. It is found that performing phase shift on red, green, and blue component images extracted from fringe images scanned in white light can produce whole-field phase maps, though low levels of error can only be achieved using red and green component images. Results from a circular photoelastic disk subjected to direct compressive loading show close correspondence with the results from theoretical calculations. The adaptation of photoelasticity into flatbed scanners will yield systems that are simple, cost effective, and compact. These features and the demonstrated ability for automatic analysis using phase shifting should encourage a greater adoption of photoelasticity in the industry.

A phase shift increasing method (PSIM) is proposed to construct a comb-like dispersion profiled fiber (CDPF) with an optimum-designed dispersion map. Using this CDPF, a 10-GHz, 12-ps pulse generated from an actively mode-locked Er³⁺-doped fiber ring laser (AML-EDFL) is compressed to 2 ps without a pedestal. The compressed optical pulse source is used in a 40-Gb/s 247-Km optical time-division multiplexing (OTDM) system with a transmission power penalty of 0.42 dB.

Recent studies have shown that the angular distribution of diffuse reflectance, obtained from bidirectional reflectance distribution function (BRDF) measurements, differs strongly between paper sheets with and without fibers present in the top surface layer. For fiber-containing surfaces, in contrast to pigment-coated paper surfaces, there is a distinct forward scattering at angles much larger than the specular reflection angle. In the search for an explanation of this phenomenon, we have made calculations of reflectance distributions of a simulated paper web, containing randomly distributed hollow fibers. We did this on the assumption that fibers present in paper are considerably larger than the wavelength of visible light, and that the surface microroughness of the fibers can be treated as a diffraction broadening superposed on the ray calculated reflectance distribution. We investigate whether the structural shape and distribution of wood fibers can explain some of the observed forward-scattering phenomenon. We also compare these Monte-Carlo ray tracing calculations qualitatively with experimental BRDF measurements of the diffuse reflectance from a fiber-containing surface. From the calculations we found that the reflection at the inner fiber wall of the hollow fibers constituting the topmost layer plays a major role in forming a forward-scattering reflectance distribution. We also found that the Monte-Carlo-calculated bulk scattering distribution, i.e., the distribution of reflected light after a large number of reflections within the web structure, tended to be elongated perpendicular to the sheet plane of the fiber web, rather than being uniform.

Heterodyne interferometry is a powerful tool for shape measurement. However, there are currently only few papers devoted to full-field, time-dependent heterodyne interferometry. Most known solutions are based on the point measurement, and the shape is obtained by scanning in the examined area. We propose and discuss a full-field heterodyne system using the fringe projection principle and a fast framing Dalsa CA-D1 CCD camera. Due to the frequency shift between interfering beams, the interference pattern travels over the object surface and enables heterodyne registration. The use of a fast camera is a certain approximation of classical heterodyne detection. Quantitative analysis of the influence of some system parameters (geometry, elements, and optical system aberrations) on the measurement result for a chosen object is the basis for developing a final system able to measure two kinds of surfaces: the scattering and specular types. A complete optical system and the geometry of the field heterodyne interferometer realized in the laboratory are shown and discussed. Examples of results obtained are presented, including shape measurement during object movement.

We propose a new family of hyperbolic kernels Φ_hyperbolic(θ,τ) = [sech(βθτ)]ⁿ, where n = 1,3,5,... for a joint time-frequency distribution. The first-order hyperbolic kernel sech(βθτ) is mainly considered. Theoretical aspects of the new hyperbolic kernel are examined in detail. The effectiveness of a kernel is determined by three factors: cross-term suppression, auto-term resolution, and noise robustness. The effectiveness of the new kernel is compared with other kernels including Choi-Williams, Wigner-Ville, and multiform tiltable exponential using two different signals: complex-exponential and chirp.

We describe a unique implementation of an optical-in/optical-out focal plane processor whose functionality is derived from a biological retina. The retina chip has increased control over the output through a novel differential difference amplifier and a clocked analog scheme. Processing is done on-chip to produce an edge-detected version of the optical input signal. However, the output signal is also optical, enabled by a liquid crystal spatial light modulator on the chip. We present experimental results from a 19×19 array and demonstrate how the edge information can be controlled on-chip and read out in parallel from each processing cell.

Currently, two principal operation modes are utilized by interferometric synthetic aperture radar (IFSAR) systems for data collection. The first mode is a one-antenna, two-pass IFSAR operation mode, where the aircraft platform possesses a single antenna and flies by the scene of interest twice collecting data. The two-antenna, one-pass IFSAR operation mode is the second mode, in which the aircraft platform possesses two antennas and flies by the scene of interest once while collecting data. Each one of these IFSAR operation modes possesses certain strengths and weaknesses. The one-antenna, two-pass mode allows for large baselines but suffers from imprecise knowledge of the baseline length, and consequently does not possess accurate target height scaling. Alternatively, the two-antenna, one-pass mode allows for precise knowledge of baseline length, but often at the expense of a limited baseline length, and consequently suffers from increased height noise. We describe an innovative IFSAR operation mode for overcoming these weaknesses by combining the two current IFSAR operation modes into a new two-antenna, two-pass IFSAR operation mode. By accurately estimating the antenna baseline between the two flight passes from the data itself, target height scaling accuracies are improved to the equivalent of a two-antenna, one-pass IFSAR system with the height-noise performance commensurate with the larger baseline. This, in turn, allows for more accurate information about target ground position locations and heights.

The tracking of multiple maneuvering targets in a dense clutter environment is investigated. An effective parallel processing algorithm based on state fusion and fast joint probabilistic data association (FJPDA) is proposed. State fusion and feedback of all state information are used to fit different movements of targets. The FJPDA, combining cluster matrix decomposition with a fast data association algorithm, is used for tracking multiple targets. The advantages of this algorithm are not only keeping the accurate estimation and fast response for target maneuvering, but also reducing the computational burden of data association from N! to N/4*(4!). Three examples are simulated to prove the validity and reliability of the proposed new algorithm.

The fractal dimension is a fascinating feature highly correlated with the human perception of surface roughness, and has been successfully applied to texture analysis, segmentation, and classification. Several approaches have been developed to estimate the fractal dimension. Among them, the box-counting (BC) method is nonstochastic and popular in estimating the fractal dimension of a two-tone image. The differential box-counting (DBC) method, a generalization of the classical BC method, was proposed to compute the fractal dimension for a 2-D gray-level image. However, the classical BC and the DBC methods have several major drawbacks, such as overcounting and undercounting the number of boxes. Hence, the real value of the fractal dimension cannot be reached. In this work, two algorithms that can obtain more accurate estimates of the fractal dimension are proposed. The first one, a modified algorithm of the DBC method, is called the shifting DBC (SDBC) algorithm, and the second one is called the scanning BC (SBC) algorithm. We theoretically prove that the SDBC algorithm approaches the estimated value closer to the exact fractal dimension than the DBC method. Simulation results show that the two proposed algorithms can resolve the drawbacks that the BC and the DBC methods possess. Compared to the DBC method, the two proposed algorithms consistently give more satisfactory results on synthetic and natural textured images.

This PDF contains a comment on the paper "Method for measuring the cell gap in liquid-crystal displays"

This PDF contains a comment on the paper "Method for measuring the cell gap in liquid-crystal displays."