I think that it is probably the same thing everywhere, in North America at least. Most of those involved in training of highly qualified personnel very often receive requests for young specialists with excellent skills in optical sys-tem design. This is the most difficult request to respond to. If we look at the way teaching is arranged in our universities, there are well-recognized fields in optics in the same way that there are well-organized areas in physics, chemistry, etc. Having well-organized areas in sciences means that all scientists converge toward the most popular and newly addressed aspects of problems. This is very nice. It attracts new heads in our field, but also permits elimination of heads from certain areas they may have chosen to enter before being exposed to some kind of publicity. Very often, supposedly well-thinking professors will say very discouraging remarks about a colleague who is doing a good and very professional job, but who is doing ‘‘old’’ physics or optics according to their standards.

Active refrigeration of optoelectronic components through the use of monolithically grown thin-film solid-state coolers based on III-V materials is proposed and investigated. Enhanced cooling power compared to the thermoelectric effect of the bulk material is achieved through thermionic emission of hot electrons over a heterostructure barrier layer. These heterostructures can be monolithically integrated with other devices made from similar materials. Experimental analysis of an InP pin diode monolithically integrated with a heterostructure thermionic cooler is performed. Cooling performance is investigated for various device sizes and ambient temperatures. Several important nonideal effects are determined, such as contact resistance, heat generation and conduction in the wire bonds, and the finite thermal resistance of the substrate. These nonideal effects are studied both experimentally and analytically, and the limitations induced on performance are considered. Heterostructure integrated thermionic cooling is demonstrated to provide cooling power densities of several hundred W/cm2. These microrefrigerators can provide control over threshold current, power output, wavelength, and maximum operating temperature in diode lasers.

We propose a new optical encryption technique using the fractional Fourier transform. In this method, the data are encrypted to a stationary white noise by two statistically independent random phase masks in fractional Fourier domains. To decrypt the data correctly, one needs to specify the fractional domains in which the input plane, encryption plane, and output planes exist, in addition to the key used for encryption. The use of an anamorphic fractional Fourier transform for the encryption of two-dimensional data is also discussed. We suggest an optical implementation of the proposed idea. Results of a numerical simulation to analyze the performance of the proposed method are presented.

Printing color images on color printers and displaying them on computer monitors requires a significant reduction of physically distinct colors, which causes degradation in image quality. An efficient method to improve the display quality of a quantized image is error diffusion, which works by distributing the previous quantization errors to neighboring pixels, exploiting the eye's averaging of colors in the neighborhood of the point of interest. This creates the illusion of more colors. A new error diffusion method is presented in which the adaptive recursive least- squares (RLS) algorithm is used. This algorithm provides local optimization of the error diffusion filter along with smoothing of the filter coefficients in a neighborhood. To improve the performance, a diagonal scan is used in processing the image.

This article proposes a new, efficient and cost effective stripe illuminator for active optical triangulation sensors. The long distance stripe-shaped collimation of the light radiated by a linear LED array is achieved by means of a cylindrical parabolic mirror with a focus line coinciding with the internal reflectors of the LEDs. A computer based design process using a model of the LED is presented to find the optimal parabolic shape, radiating aperture and mounting tolerances. A very simple and inexpensive mechanical construction of the light source was realized. Test measurements showed that the light source produces a light stripe with an average incidence between 0.6-5.5 mW/cm2 depending on the range, which enables the detection of objects even with very low reflectivity. The width of the light stripe is 6-10 cm in the 0-2 m range, which allowed a resolution of 5-15 cm using it in a special stripe lighting sensor setup. Test results on an autonomous mobile robot are briefly presented. The eye safety of the source is also discussed.

A hybrid algorithm is proposed for true motion field estimation. This algorithm consists of three steps: block-based initial motion estimation, image segmentation, and wrong-motion-vector detection and correction based on objects. The hierarchical block-matching algorithms are improved for the initial motion estimation. The improved algorithm uses an adaptive technique to propagate motion vectors between hierarchical levels. It produces accurate motion field everywhere, except in the areas of motion occlusion. In order to correct wrong motion vectors in the areas of motion occlusion, the current image is segmented into objects and an object-based method is proposed to process the estimated motion fields. With the object-based method, wrong-motion vectors are detected by approximating the estimated motion field in each object with a motion model, and are corrected using an object-adaptive interpolator. Experimental results show that the improved hierarchical block-matching algorithm outperforms the conventional hierarchical block-matching algorithms. The proposed algorithm results in dense motion fields that are smooth within every object, discontinuous between objects of different motion, and very close to the true motion fields.

We present a method for the extraction of the skeletons of broken handwritten characters. The proposed algorithm is based on a comparison of the directional movement of every segment of a broken character, and on the connection between two points on different boundaries whose direction appears to be contrary. If a segment cannot be connected with another segment with an almost opposite direction, the direction of the segment will be turned at an angle until it connects with another segment. The application of the algorithm smoothes the character and removes small gaps and noise on its boundaries. The noniterative skeletonization process is based on the distances from character pixels to the boundaries. At the intersection, the algorithm will connect two thinned segments that are in a contrary direction and extend the segments that have no proper connecting points.

In order to improve the performance of a linear auto- associator (which is a neural network model), we explore the use of several pre-processing techniques. The gist of our approach is to represent each pattern by one or several pre-processed (i.e., filtered) versions of the original pattern (plus the original pattern). First, we compare the performance of several pre-processing techniques (a plain vanilla version of the auto-associator as a control, a Sobel operator, a Canny- Deriche operator, and a multiscale Canny-Deriche operator) and a Wiener filter on a pattern completion task using a noise degraded version of faces stored. We found that the multiscale Canny-Deriche operator gives the best performance of all models. Second, we compare the performance of the multiscale Canny-Deriche operator with the control condition on a pattern completion task of noise degraded versions (with several levels of noise) of learned faces and new faces of the same or another race than the learned faces. In all cases, the multiscale Canny- Deriche operator performs significantly better than the control.

We describe new methods of denoising images that combine wavelet shrinkage with properties related to the statistics of quad-trees of wavelet transform values for natural images. They are called tree- adapted wavelet shrinkage (TAWS) methods. The shift-averaged version of TAWS produces denoisings that are comparable to state of the art denoising methods, such as cycle-spin thresholding and the cycle- spin version of the hidden Markov tree method. The nonshift averaged version of TAWS is superior to the classic wavelet shrinkage method, and fits naturally into a signal compression algorithm. These TAWS methods bear some relation to the recently proposed hidden Markov tree methods, but are deterministic rather than probabilistic. They may prove useful in settings where speed is critical and/or signal compression is required.

An experimental demonstration of nonmechanical optical image rotation to 20 different angles is described. The optical system consists of a polygon mirror with 20 facets in a half cylinder and a 2-D acousto-optic beam deflector. Experimental details including the requirements of components are described. Various issues such as number of rotation angles, resolution, aberration, and noise are analyzed.

Recently, digital image correlation as a tool for surface deformation measurements has found widespread use and acceptance in the field of experimental mechanics. The method is known to reconstruct displacements with subpixel accuracy that depends on various factors such as image quality, noise, and the correlation algorithm chosen. However, the systematic errors of the method have not been studied in detail. We address the systematic errors of the iterative spatial domain crosscorrelation algorithm caused by gray-value interpolation. We investigate the position-dependent bias in a numerical study and show that it can lead to apparent strains of the order of 40% of the actual strain level. Furthermore, we present methods to reduce this bias to acceptable levels.

This paper presents a 3-D water-flow reconstruction algorithm for use on stereo-camera systems. It contains two major contributions. The first is the stereo-camera calibration method. A vanishing line is used to get a closed-form solution of the parameters of one camera and then the bicamera parameters are recursively updated for more precise results. The second contribution is the stereo matching of particles in the water flow. The difficulty here is that the correspondence of the maximum-correlation-coefficient method is not right for all water flow particles, because the illumination environment is not uniform and the aperture of the two cameras is different. We use relaxation labeling and template matching to cluster the water particles into group sets and compute the best correspondence of these sets based on epipole and camera geometry. The experimental results are reliable.

A dual representation of spectral functions called the composite model is proposed. Its key point is to decompose all spectra into a smooth background and a collection of spikes. This duality not only reflects the physical emission and light-material interaction, but also provides a mathematical basis to effectively handle the opposing characteristics of spectra?frequency space is effective for smooth components, but wavelength space for spikes. In this paper, we represent the smooth part through Fourier coefficients, and spikes through delta functions. We show the sufficiency of a low-dimensional representation analytically through evaluating errors based on CIE color space and approximating the CIE color-matching functions in terms of Gaussian functions. To improve performance, we propose resampling smooth functions that are reconstructed from Fourier coefficients, and as a result spectral multiplications are greatly reduced in complexity. Overall, our composite model eliminates the drawbacks of previous one-fashion representations and is able to satisfy all identified representation criteria with aspect to accuracy, compactness, computational efficiency, portability, and flexibility. This new model has been demonstrated to be crucial for realistic image synthesis, especially for rendering spectral optical phenomena such as light dispersion and diffraction, and has promise in other research areas such as image analysis and color science.

Discrete formulas to calculate aerial imaging on the wafer for photolithography are presented, and physical fundamental of inverse Fourier transform convolution filtering to improving resolution is discussed. The larger contrast for dense L/S group with the pitch of 0.27 µm is obtained with an ArF 193 nm stepper with a numerical aperture of 0.60 and partial coherent coefficients of 0.3.

Phase shifting masks (PSMs) provide us with a breakthrough in the future semiconductor industry by extending submicrometer lithography further. PSMs have been used for several years, and their requirements are changing due to the development of other technologies. First, it became possible to use a high transmittance attenuated PSM (HT-Att- PSM) because of improvement in the photoresist technology. Second, continuous improvement in the inspectional equipment technology lowered the inspection wavelength. Now, we are provisionally targeting to make HT-Att-PSM having 20±5% transmittance at the ArF line and to choose the KrF line as the inspection wavelength. We simulate the optimum conditions for HT-Att-PSM using the matrix method. The simulation is performed to find the optimum range of the variables that yield 180 deg phase shift and 20±5% transmittance at the exposure wavelength, and less than 40% transmittance at the inspection wavelength. Based on the simulation results, we find the optimum fabrication condition of HT- Att-PSM. Using measured optical constants as a function of film composition, we determine the optimum film composition yielding 20±5% transmittance and 180 deg phase shift at the exposure wavelength and below 40% transmittance at the inspection wavelength. As a result, Cr2Al8O15 film with thickness of 124 nm is found to be suitable for an ArF line HT-Att-PSM.

By the z-scan method, we investigated the photobleaching processes of a nonlinear optical polymer film made of poly (methyl methacrylate) with a dispersed red (PMMA/DR1) side chain at the 488 nm wavelength of an argon ion laser. It provides a simple method to determine the parameters in a bleaching model that describes the polymer photobleaching processes.

Optical properties of spherical and nonabsorbing styrene- acryl copolymer pigment spheres with concentric spherical shells were studied by wavelength-dependent reflectance from the slurry. The data were analyzed using a light-scattering model and Wiener bounds. The object was to obtain estimates for the refractive index of a particle shell as a function of wavelength. © 2000 Society of Photo-Optical Instrumentation Engineers.

Multiplexed holograms recorded in purple-membraned bacteriorhodopsin (BR) films are investigated. Calculations of the reconstruction selectivity and crosstalk noise of BR-based holographic memory, along with experimental results, are presented. We also show that the properties of BR films can be effectively used for constructing holographic free-space optical interconnections that are reconfigurable in real time.

For multihologram recording, especially in a disk-shaped storage medium, a simple cost-effective method to implement the peristrophic, angular, and spatial multiplexing techniques together is studied and its experimental demonstration is presented. Holographic storage with both peristrophic and angular multiplexing is realized by controlling the reference beam directly with a pair of wedge prisms, while the storage with spatial multiplexing is achieved by shifting the storage medium. The area storage density of our system is strongly dependent on the f numbers of the lenses in the signal and reference arms. For a given f number of the lens in the reference arm, we show that the area storage density becomes maximal when the f number of the lens in the signal arm is approximately twice that in the reference arm. The proposed method can be used for 3-D holographic disk memories to enhance their area storage density.

We fabricated x-ray mirrors for hard x-ray (? 10 keV) telescopes using multilayer coatings and an improved epoxy-replicated aluminum foil (ERAF) nonvacuum technology. The ERAF optics have ~1 arcmin axial figure half-power diameter (HPD) and passed environmental testing. Reflectivity measurements at 8 keV on ERAFs with and without multilayer coatings show a 4.4 to 4.8 Å root mean square (rms) microroughness for correlation lengths ?15 µm. To reduce the dominant contribution of mirror assembly and large-scale distortion in the overall telescope HPD, we designed a figure metrology system and a new mounting technique. We describe a cylindrical metrology system built for fast axial and roundness figure measurement of hard x-ray conical optics. These developments lower cost and improve the optics performance of the HEFT (high-energy focusing telescope) and Constellation-X missions.

The laser Doppler vibrometer (LVD) has been the favorite instrument for precision dynamics measurement due to its noncontact nature, high accuracy, and high resolution. However, LDV can give only the dynamic data of a particular locate on the entire feature. To acquire the whole field data, a laser beam scanning mechanism must be implemented. Currently, a motor-driven scanning mirror is used to move the measurement probe from one point to another, and the mechanical vibrations of the scanning mirror reduce the measurement accuracy. We introduce a novel scanning LDV optical system embodying an acoustooptic deflector scanning mechanism, which can improve the measurement accuracy since there is no mechanical motion involved. One main advantage of this system is that it generates laser scanning in parallel, which is different from the beam scanning in a conventional scanning LDV. Promising results are obtained from the preliminary experiments carried out for measurement of a hard disk suspension.

Theoretical study indicates the potential for fabricating a noncircle cylindrical microlens array, a circle-shaped cylindrical microlens array, and a microprism array. Experimental results show that the cylindrical microlens arrays with surface profiles of a circle and an ellipse in a Si substrate have good surface quality and high uniformity. The relation curves between the Ar ion energy and the Ar ion-beam etching rate in several substrate materials such as ZrO2, InP, SiO2 (quartz glass), and Si and the photoresist (BP212) mask materials consolidated at relatively high temperature are given. The techniques utilized can be applied to fabricate a large-area cylindrical microlens array with different surface profiles and microprism array.

A novel method of manufacturing micro-optical elements with continuous relief by focused ion beam (FIB) is described in detail. Microfabrication of diffractive optical elements (DOEs) with feature sizes as small as the submicronmeter range is realized in this way. Making use of direct milling by FIBs, the microstructure on any substrate (metal and nonmetal) and the mold used for micro-optical element replication are realized easily without any other procedures. The DOEs are duplicated by hot-embossing with relief surface roughness [root mean square (rms) value] of 3 nm measured in a 2 x2 µm2 area, which is higher than the 5 nm achieved with conventional methods. In addition, other examples such as a microlens mold, a microcylindrical lens, and a 3 x3 DOE array are introduced briefly.

Achromatic optical processing systems can perform a variety of operations with temporally incoherent (polychromatic) light, without color blurring. The system design is a complicated task, since usually the scale at the output depends on the wavelength. The design goal is to eliminate this scale dependence as well as two other wavelength- dependent defects. Such a goal is generally achieved by modifying lens design procedures. Here we do it in a different manner. Specifically, we resort to matrix algebra, applied to the Wigner distribution function. The resulting Wigner matrix includes elements that characterize wavelength- dependent parameters of the optical systems. Such a characterization provides a clear insight into what is needed to reduce the wavelength dependence, and indeed achieve the achromatization of the systems. This design approach is valid with either wave optics or geometrical optics. The basic principles and specific design examples of achromatic optical Fourier transformers and Fourier processing systems with low chromatic aberrations over the entire visible spectrum are presented.

Piezoelectric bimorphs are inexpensive and can be applied to a wide variety of purposes. We took two bimorphs to move one end of a mirror upward (downward), and two more piezoelectric bimorphs to move the other end downward (upward). The new aspect of this approach is that the angle of the mirror is much larger than that driven by the bending of each bimorph alone due to mechanical amplification. The optical scanner has a static and nonresonance mirror rotation of up to 4.6 deg. The power consumption at resonance with maximum driving voltage was calculated at 2.6 mW, which we consider to be low power consumption.

A noninvasive method for the estimation of internal temperature in chicken meat immediately following cooking is proposed. The external temperature from iR images was correlated with measured internal temperature through a multilayer neural network. To provide inputs for the network, time series experiments were conducted to obtain simultaneous observations of internal and external temperatures immediately after cooking during the cooling process. An iR camera working at the spectral band of 3.4 to 5.0 µm registered external temperature distributions without the interference of close-to-oven environment, while conventional thermocouples registered internal temperatures. For an internal temperature at a given time, simultaneous and lagged external temperature observations were used as the input of the neural network. Based on practical and statistical considerations, a criterion is established to reduce the nodes in the neural network input. The combined method was able to estimate internal temperature for times between 0 and 540 s within a standard error of ± 1.01°C, and within an error of ± 1.07°C for short times after cooking (3 min), with two thermograms at times t and t+ 30 s. The method has great potential for monitoring of doneness of chicken meat in conveyor belt type cooking and can be used as a platform for similar studies in other food products.

The novel principle for changing a single HeNe laser to a displacement sensor is presented and demonstrated. By inserting a birefringence element in laser cavity, we split a frequency of the laser light into two (o-light and e-light) with an orthogonal linear polarization and a tunable frequency difference. When one mirror of the laser is moved along the laser axis, the polarization of the output light of the laser changes periodically. Each period corresponds to both the ?/2 displacement, by which the cavity mirror moves, and the variation of one longitudinal mode interval, by which the two frequencies drift. In each period, four different polarization states in the laser output (e-light, e-light and o-light, o-light, no-light) appear continuously. If the frequency difference and the cavity length are appreciated, each polarization state corresponds to both X/8 displacement of the mirror and the drift of the two frequencies by 1/4 longitudinal mode interval. Therefore, when a onetime change of the polarization is sensed by optoelectric detectors and circuits, we know that the mirror has moved by ?/8, and by counting the number of occurrences of ?/8 we can calculate the displacement of the mirror. We judge the direction of mirror movement by sensing the order of the four polarization states that appear. The moving mirror is attached to and moved with the object to be measured. This system reaches an accuracy of 0.079 µm, a measurement range of 8 mm, and a linearity of 0.0036%, and it has the function of self-calibration in accordance with laser wavelength.

Laser radar, like other electro-optic sensors being used in the marine environment, can be strongly affected by atmospheric conditions. We calculate statistical distributions of coherent laser radar performance based on an extensive set of observed weather conditions for several littoral locations at selected wavelengths from 1 to 10 µm. The analysis shows that the best performance can generally be achieved in the mid-IR wavelength region around 3.8 µm. This wavelength region is less affected by aerosol scattering and atmospheric turbulence compared to the near iR and also less affected by water vapor absorption compared to the long-IR band.

We report the theoretical analysis of a quasi-distributed sensor system for absorption measurements based on the frequency- modulated continuous wave (FMCW) technique combined with frequency modulation spectroscopy (FMS). The laser diode injection current is sawtooth modulated to provide a linear scan of the output over a certain frequency/wavelength range and the output is also externally modulated at radio frequencies. The sensor units consist of a series of open-path micro-optic cells constructed from graded index (GRIN) lenses, each with a unique beat frequency. By arranging for only one sideband of the modulation to be attenuated by the absorption feature, a new signal, proportional to the absorbance, appears in the output spectrum at a frequency corresponding to the difference between the rf- modulation frequency and the beat frequency of a cell. The method is highly sensitive and applicable to a variety of chemical species with narrow absorption lines, such as in trace gas analysis. We present the mathematical analysis of the proposed method for single and multiple cell systems, using methane detection as an example.

We present an optical fiber voltage sensor for 420 kV electric power lines. The sensor exploits the converse piezoelectric effect of quartz and measures the voltage by a line integration of the electric field. The alternating voltage is partitioned to a series of four cylinder-shaped quartz crystals, which are embedded in polyurethane resin within a 3.2-m long insulator tube of fiber reenforced epoxy. The alternating piezoelectric deformations of the crystals are sensed by a common elliptical-core dual-mode fiber, which is wound onto the circumferential crystal surfaces. The fiber is interrogated using low coherence interferometry. We determine the dielectric design of the sensor from a numerical analysis of the electric field distribution within and in the vicinity of the sensor. We experimentally verify the dielectric reliability under ac overvoltages up to 520 kV root mean square (rms) and lightning and switching impulse voltages up to 1425 and 1050 kV, respectively. Further, we investigate the sensor performance including accuracy, dynamic range, bandwidth, and temperature dependence.

A new multichannel optical sensor for monitoring large structures, consisting in an eight-optical-fiber ribbon pultruded in composite material, has been realized and completely characterized. Both strain and temperature sensitivity, and both dynamic and thermal strain response, as well as birefringence tests and mechanical characterization are reported. The experimental results confirm the capabilities of pultru- sion to realize multichannel optical sensors for large structures that are able to operate in a severe environment. The sensor can fulfill mechanical, chemical, and electrical custom requirements with quality consistency at low cost. The sensors have been used as strain sensors for an 85-m-long oil-rig riser.

An analysis of temperature-induced transient noise for a thermal detector prepared with Pb(Zr, Ti)O3-Pb(Sb0.5Nb0.5)O3 (PZT-PSN) pyroelectric ceramics as the sensing element is conducted by measuring its oven noise as a function of the junction field-effect transistor (JFET) characteristics, gate resistance, low-temperature heat treatment, chemical composition and the grain size of the pyroelectric ceramic. Pyroelectric wafers are prepared by the mixed oxide technique, and thermal sensors are fabricated with a PZT-PSN ceramic wafer, JFET, chip-type gate resistor, alumina PCB (printed circuit board) and a TO-5 package with antireflective (AR)-coated Si window. Thermal detector noise depends on the chemical composition of the pyroelectric sensing element. The temperature-induced transient JFET noise varies with its characteristics and gate resistance and is reduced by connecting a pyroelectric sensing element with high capacitance. The pyroelectric ceramic sensing element generates burst noise in the region from 7 to ?10°C during cooling, which is remarkably reduced by reducing the grain size of the pyroelectric ceramic and/or by cyclic heat treatment at a low temperature. Thus, burst noise has a strong relationship with the elastic energies within the ceramic sensing element and the bonding material between the sensing wafer and the PCB, originating in the different thermal expansion between pyroelectric sensing wafer and alumina PCB.

Beamsplitters play an important role in most sensitive optical experiments such as interferometry, holography, phase conjugation, etc. For all these experiments, proper splitting of beams (either 50:50 or 25:75) is essential, and to achieve it the proper design of a beamsplitter is important. Beamsplitters consist of a thin window, on each side of which a different type of coating is deposited.