This PDF file contains the editorial “Education and Training in Optics and Photonics” for OE Vol. 39 Issue 06

A convenient relation between fractional Fourier transform patterns and diffraction patterns is obtained by applying the Gauss equation of geometrical optics. Thus, Fresnel and fractional domains cannot be considered as independent domains, since one is just a geometrical image of the other, providing a physical and direct connection.

The feasibility of using low-resolution thermal imagers for home security applications is analyzed, taking low cost as the primary consideration. The smallest possible sensor size and resolution are chosen as the operative criteria and derived by simulation, in accordance with the optical constraints of a general home security system and the minimum target feature recognizable using image processing. Lowresolution simulated thermal images were generated by downgrading the high-resolution images captured by an uncooled IR camera, through sampling and modification. Caricatures of human beings and family pets are extracted for recognition using aspect-ratio and neural network methods, which are compared with one another for detection probability. It is demonstrated that highly reliable detection of human beings or pets with a minimal target feature of 8x8 pixels can be obtained using the neural network method. Also, a fire can be detected early using its temporal size variation and higher temperature. Finally, low-cost fabrication of the proposed low-resolution passive infrared imaging system with an uncooled FPA sensor utilizing a fully standard application-specific IC CMOS process is also discussed in detail.

A quantitative imaging method using 2-D single-pulse laser- induced predissociative fluorescence (LIPF) of OH concentrations is developed to study the flame structure in a swirling methane jet flame. A narrowband tunable KrF excimer laser is used to excite the P2(8) rotational line of the A2??X2n?(3,0) transition at ? = 248.46 nm. Though this transition produces a relatively weak signal, LIPF is much less sensitive to collisional quenching in atmospheric flames. Therefore, it is suitable for generating quantitative data. OH concentration data are obtained by careful calibration against flat flame burner data of known fuel- air equivalence ratios using an identical optical setup. Because the distribution of OH concentration has a good correspondence with the flame, the measured 2-D imaging of OH indicates the instantaneous shape of the reaction zone. In the upstream section of the swirling flame, combustion is found to take place in three regions: the shear layer of the fuel jet, the recirculation vortex inside the recirculation bubble, and the thin layer between the recirculation zone and the ambient air. High OH concentration is found in the upstream central portion inside the fuel region. The temperature and radicals of the recirculated hot products appear to accelerate the initial decomposition and radical-generating processes after strong turbulent mixing with fresh fuel and air. This is believed to be superequilibrium OH, because its intensity is higher than that from the recirculated burnt gas and the measured local temperature is low (less than 1200 K). The measured OH concentration structure is strongly influenced by the characteristic swirling flow and flame structures and is also closely related to the NOx formation and flame stabilization in the swirling flame.

Image segmentation is a critical task and many algorithms have been proposed in the literature. However, how to select the best technique when facing a real application is still an open issue. A novel method for optimal selection of segmentation algorithms is introduced and an expert system for determining the best algorithms using evaluation results is proposed. The available segmentation algorithms are first evaluated and their characteristics or behaviors in a number of situations are then determined. The determination of the best algorithm is thus based on the knowledge obtained by objective evaluation of available segmentation algorithms. In other words, the algorithm selection is made according to the properties of the algorithms and images to be segmented. Using this idea, a prototype expert system for algorithm selection is designed and implemented. The design considerations and data structure of this system are detailed. Experiments with various real images are carried out and the results indicate that such an idea is feasible and such a system is suitable for practical segmentation applications.

A fully automatic method is proposed to produce an enhanced image from a very noisy sequence consisting of a translating object over a background with a different translational motion. The method is based on averaging registered versions of the frames in which the object has been motion-compensated. Conventional techniques for displacement estimation are not adequate for these very noisy sequences, and thus a new strategy has been used, taking advantage of a simple model of the sequences. First, the local spatiotemporal spectrum is estimated through a bank of multidirectional, multiscale third-order Gaussian derivative filters, yielding a representation of the sequence that facilitates further processing and analysis tasks. Then, energy-related measurements describing the local texture and motion are easily extracted from this representation. These descriptors are used to segment the sequence according to a local joint measure of motion and texture. Once the object of interest has been segmented, its velocity is estimated applying the gradient constraint to the output of a directional bandpass filter for all pixels belonging to the object. Velocity estimates are then used to compensate the motion prior to the average. The results obtained with real sequences of moving ships taken under very noisy conditions are highly satisfactory, demonstrating the robustness and usefulness of the proposed method.

We have analyzed the accuracy of the compensating performance of the white-balance mechanism of a 3CCD camera for the three common types of light—fluorescent (F), incandescent (I), and daylight (D). We study the behavior of the camera using the RGB and ClELAB coordinates for a wide set of color samples covering the visible spectrum. CIELAB coordinates are obtained from the tristimulus XYZ. Using linear methods, we obtain the XYZ values from the (RGB)CCD values acquired by a 3CCD camera. We propose two different approaches: the first is specific for each particular light source (F, I, and D); the second considers the equienergetic spectral light source as an approximation for white lighting. We measure the mean color difference in the CIELAB space under a change of illuminant and compare the results in order to evaluate the performance of the response of a 3CCD camera. The transformations that are specific for a given light source allow an improved response under change of illuminant in terms of color constancy.

A fully automatic method for pilling evaluation in fabrics, previously developed from the analysis of Zweigle standard images, is completed for its application to the assessment of real samples. Several aspects are dealt with. As regards the acquisition of input images, a set of primary images sequentially captured under near-tangential illumination from different sides is proposed to obtain complete information of the pill area along with a good pill-to-background contrast. The significant information for the set is concentrated in a single image using the Karhunen-Loeve transform in a later stage of the algorithm. After segmentation, pills appear segmented from the background, and binary noise is reduced by applying a threshold of minimum pill area. This threshold is scale independent when it is expressed in terms of the fabric's thread crossings. From the final segmented binary image, two pill features are measured: the total area of pilling, from which the degree of pilling is assigned, and the pill density. The complete method is applied to 32 real samples, which constitute a wide variety of cases. Three laboratories with their respective panels of experts for visual rating are involved in the assessment of the samples. The results obtained by the image-analysis method and by the visual raters are compared. Finally, the robustness of the method against slight changes in some parameters of the algorithm is evaluated and compared with the degree of agreement of experts.

A novel variable-rate image-coding scheme called the predictive subcodebook search algorithm (PSS) is proposed. In PSS, the initial searched codeword for each input vector is predicted by its encoded neighbors and the closest codeword in the codebook is searched from a specific range (or subcodebook) that is determined dynamically according to the block type of its encoded neighbors. In addition, the relative addressing technique is employed to encode the searched closest codeword. According to the simulation results, it is shown that PSS not only provides better objective image quality peak SNR (PSNR) but also reduces the storage cost for storing multiple codebooks. Furthermore, PSS requires very little computational cost, compared to the full search algorithm for the vector quantization (VQ) scheme. Therefore, it is concluded that PSS indeed provides a good means for variable-rate image coding.

In the field of image simulation, to assess the information content of images, it is necessary to correctly model both objects and backgrounds. This requirement is particularly required to assess the characteristics of images to be generated by future observation instruments, as is the case in earth observation and remote sensing. The physical correction of the models depend basically on the final resolution. Stochastic analysis is a powerful tool to solve problems in domains where deterministic solutions are not satisfactory. There is thus a need to develop efficient and accurate simulation techniques for multidimensional random fields. The turning bands method (TBM) has been used in geophysical sciences, in hydrology, and more recently in remote sensing to simulate medium and large scale data fields, and it can be used to represent realistic topographic surfaces or radiometric nonuniformities induced by unknown factors such as soil thickness of moisture. We present and illustrate two generalizations of the TBM. In the first, we add fractal concepts to the method, thus enabling the synthesis of a 2D stochastic field with a specified fractal dimension. In the second, we extend the TBM to generate nonisotropic fields, which do occur in many fields, in particular in earth resources modeling and classification.

We describe a novel vertical taper structure fabricated at the ends of polymer optical waveguide devices to improve the coupling between channel waveguides and single mode fibers. The taper smoothly converts a highly elliptical waveguide mode into a large and more circular mode for low loss coupling and relaxed fiber alignment tolerances. A vertical taper 0.5 to 2 mm in length is made in the upper cladding to reduce its thickness from a few micrometers to zero. The taper is subsequently covered by an upper cladding. The new upper cladding has an index higher than that of the previous upper cladding but slightly lower than that of waveguide core. In the taper, the channel waveguide mode gradually loses confinement by the upper cladding so that the mode size grows larger as light propagates toward the end of the device, whereas the confinement by the lower cladding and the lateral confinement are not significantly affected. The waveguide mode grows upward away from the lossy ground electrode and substrate commonly found in many polymer devices; therefore, no trade-off between mode size and propagation loss is involved. Two special but simple reactive ion etching techniques, shadow masked etching and etching with a tapered photoresist mask, are developed to make the vertical taper. Mode expansion and a 1.8 dB reduction in coupling loss per tapered end are demonstrated experimentally. The performance of the mode size transformer is found to be insensitive to both waveguide width and polarization.

Integrated optical sigma-delta (??) analog-to-digital converters (ADCs) use a pulsed laser to oversample an input signal at two Mach-Zehnder interferometers. A fiber-lattice accumulator is embedded within a feedback loop around a single-bit quantizer to spectrally shape the quantization noise to fall outside the signal band of interest. Decimation filtering is applied to the quantizer output to construct the input signal with high resolution. Applications of integrated optical ?? ADCs include digitizing wideband radio-frequency signals directly at an antenna (digital antenna). In this paper, a novel fiber-lattice accumulator design is presented, and a coherent simulation of an integrated optical first-order, single-bit ?? ADC is reported. The accumulator leakage resulting from a mismatch in the optical circuit parameters is quantified. A time-domain analysis is presented, and the simulation results from an all-electronic ?? ADC are presented for comparison. A frequency-domain analysis of a ten times oversampling (n = 4 bits) simulation is used to compare the dynamic performance parameters, including the spurious-free dynamic range, signal-to-noise-plus-distortion ratio, and effective number of bits. The formation of image frequencies when the accumulator is overloaded (i.e., the optical amplifier gain is too large) is also investigated.

We present a methodology adopted to extract planetary wave information from a set of interferometric data. The data set represent information collected by a Bomem interferometer from 1993 until 1995 in Stockholm, Sweden. We also discuss several procedures other than that adopted for the analysis of this unevenly spaced data and provide the rationale for the adopted procedure. New results on planetary waves are presented. A robust analytical procedure for analyzing gappy data containing information within a known band is also presented. The procedure, consisting of a periodogram method followed by the application of a moving average filter with a correction function, would be used on future data.

Different ways of varying the output pulse duration in laser schemes comprising a powerful master oscillator, a multipass amplifier, and a stimulated Brillouin scattering (SBS) mirror are suggested and realized experimentally. Conditions are determined at which introduction of losses between a SBS mirror and an amplifier allow variation of the output pulse duration without any significant decrease in energy. The use of two different SBS media (SnCl4 and freon) allows construction of a laser where the output pulse duration is varied between 6 and 40 ns and the energy loss is no more than 30%.

A method is proposed to improve the quality of a hole- coupled resonator for a free-electron laser (FEL) oscillator. By using a mesh or grating with a moderate reflectivity to cover the hole, the optical cavity Q can be effectively improved, as is confirmed by three-dimension numerical simulations. The potentiality of the mesh as an electron- transparent mirror to make the FEL device more compact and less expensive is discussed.

The nonlinear response of an erbium-doped fiber amplifier is investigated theoretically through the use of nonlinear Fourier transfer functions, which are derived with the help of Volterra series. The influence of signal power, pump power, and frequency on the amplifier's nonlinear response is investigated. Results computed from the nonlinear transfer functions compare well with the numerical solution of the power evolution and rate equations. Moreover, the nonlinearity-induced distortion product is discussed. The performance evaluation of cascading systems by employing closed-form expressions for nonlinear transfer functions is discussed also.

A novel, simple method is developed and tested (experimentally and by simulations) for effective, high-resolution retrieving of time- resolved lidar profiles for long rectangular-like laser pulses with arbitrary shapes of their leading and trailing edges. Such pulses are typically created by chopping cw optical radiation. The processing algorithm is based on differentiation and iteration procedures and avoids the use of divisions or deconvolutions that are often responsible for some errors and increases in the noise. Comparisons with pulsed and pseudo-random noise modulation lidar methods are given. The method enables a simplification of the entire lidar hardware. No powerful pulsed supplies, high driving pulsed voltages, complicated optical modulations, etc. are required. it could be very attractive for high-resolution, wide-spectral-band lidar measurements in the atmosphere, ocean, etc., using arbitrary optical emitters, especially for closer distances.

The method of optical enhancement by means of intersurface-reflection-excited resonance was applied to a single-pixel device filled with a fast-switching electroclinic mixture M68. A contrast ratio of 6.5: 1, which is sufficient for a spatial light modulator (SLM), has been obtained for an electric-field-induced twist angle of 2.97 deg with an electro-optical response time of 162 ns. Success in a single-pixel device should allow very fast multipixel active-silicon-backplane SLMs to be made in the near future. Using this method, we have observed contrast ratios>5 with a field-induced twist angle>2.5 deg. However, better contrast can be achieved with improved alignment of the material used and device fabrication. The thickness effects of the light modulating layer on the resonant behavior were computer-modeled and are discussed in detail. It was found that considerable change occurs even for a thickness variation of 0.1 ?m. However, the effect is much less for a variation of 0.01 ?m. If SLM fabrication cannot control the thickness better than 0.1 ?m, either computer simulation for known thickness or preliminary measurements are needed.

A simple technique is devised to measure the angles of 45deg deflecting (half penta) prisms, without using the expensive spectrometers, autocollimators, and angle gauges.

The properties of volume scattering function measurement at a small angle using only one light detector and data analysis from the detector by the discrete Fourier transform (DFT) linear interpolation (LI) method are presented. The possibility of choice of the data window and its parameters in terms of measurement conditions and the linearity of the equation of the LIDFT method enable its use in the multipoint measurement of scattering light signal and recording of the fast changes of the measured parameters in time.

The longitudinal mode spacing of an external cavity semiconductor laser is dramatically reduced if a high-reflectivity etalon is inserted in the external cavity. By measuring the reduction in the longitudinal mode beat frequency using a microwave spectrum analyzer, a quick and precise method for determining the coating reflectivity is demonstrated.

Two rugged optical fiber telemetry systems for coiled-tubing drilling and other hostile-environment applications are briefly described. One system is a passive uplink; the other is an active simplex link. The transmitter and receiver of the passive uplink are located on the surface. A high-temperature fiber cable connects a serial array of downhole modulators with the surface. Each modulator consists of an intrinsic fiber Bragg grating fixed to a piezoelectric transducer. The simplex link consists of commercial off-the-shelf components: a LED, plastic-clad silica fiber, and a Si pin diode. Both systems performed well when tested at temperatures to 150°C and at vibration levels similar to those downhole. The passive uplink system's performance was unchanged after being tested in actual drilling operations (rotating, drilling, and reaming). The active simplex link's performance was unchanged after being tested at peak vibration levels of 20g. The signal-to-noise ratio of the passive uplinkwas 108 dB/ ?VHz.

A technique for measuring surface roughness in the submicrometer range is developed. The principle of the method is based on laser scattering from a rough surface. A telecentric optical setup that uses a laser diode as a light source is used to record the light field scattered from the surface of a rough object. The light intensity distribution of the scattered band, which is correlated to the surface roughness, is recorded by a linear photodiode array and analyzed using a singlechip microcomputer. Several sets of test surfaces prepared by different machining processes are measured and a method for the evaluation of surface roughness is proposed.

Image processing techniques have seen many developments in recent years. Starting from the pioneering work of Canny, Deriche developed a second order recursive filter capable of detecting stepped contours. However, there are other contour shapes that those filters struggle to detect. We describe a new optimal filter sensu Canny for detecting ridge-line contours. This is a third order recursive and even filter. it is dependent on three parameters by which detection accuracy is adjusted. The results obtained by applying this filter to (possibly noise- affected) images are compared with those in the work by Ziou.

An available and low-cost method for the production of computer-generated phase holograms is presented. Firstly, binary masks are produced by a high-resolution graphic device. The factors that affect the fidelity of the holograms are analyzed. Secondly, enhanced light efficiency is obtained in copies made on holographic emulsions by bleaching them. The reproduction of low spatial frequencies, the usual ones with graphic devices, has been studied using diffraction gratings. We propose the super-Gaussian function to simulate the grating profile. The results obtained with that function present good agreement with the experimental results. The use of this model has enabled us to design a method that has been used to obtain the phase modulation in the bleached emulsion as a function of exposure. Through this study the bleached emulsion has been validated as a good phase material for low spatial frequencies, and has been applied for the production of optical correlation filters. We conclude that the bleached holographic filter improves the efficiency of the master with no significant loss of quality.

The performance assessment of electro-optical (EO) systems with propagation prediction codes requires accurate atmospheric models. The model that is most frequently used for the prediction of aerosols and their effect on extinction in the marine atmosphere is the U.S. Navy aerosol model (NAM) (Gathman, 1983). The nAm was developed for open ocean applications, where it works well. In coastal areas, however, the performance of the NAM may be reduced (Tanguy et al., 1991; De Leeuw, 1993). Based on an extensive series of measurements on the Irish Atlantic coast, an extension of the NAM for the coastal zone is proposed. As in the NAM, the dependence of the aerosol concentration on meteorological parameters is parameterized using empirical coefficients. The effect of the coastal zone is modeled as a function of fetch. A reasonable agreement is found between the model and the aerosol size distributions as measured on the island Inisheer, west of Galway Bay, Ireland.

The development of an automated distributed fiber optic sensor based on the Brillouin loss principle is presented. A description of the system configuration and signal processing techniques used in the measurement and control system are included. The system can achieve 0.5-m spatial resolution with ±1°C temperature or ±20 ?m/m strain measurement precision.

A theoretical and experimental study of self-referencing fiber optic intensity sensors based on Michelson and on Mach-Zehnder configurations is conducted. Via the definition of the measurement parameter R, sensor linearity and sensitivity are analyzed. Theoretical and experimental results are compared, considering the problem of sensor design and optimization. The choice between the two configurations is addressed; the Michelson one is recommended for practical reasons.

A new optical strain sensor is developed to rival the traditional electrical strain gauge. It directly measures in-plane strains using a high frequency grating and two position-sensitive detectors (PSDs). The strain measurement is independent of the rigid body motion of the grating. A high frequency diffraction grating attached to the surface of a specimen is illuminated by a focused or collimated laser beam. The centroids of the two symmetric diffracted beam spots from the grating are determined by the PSD sensors connected to a personal computer. The shift of diffracted beam spots due to the specimen deformation is transformed to strain components. Several measures are taken to improve strain sensitivity including residual strain error due to the misalignment of laser and grating. The measured strain is directly displayed on the monitor in both digital and graphical forms in real time. Strain sensitivity of 1 x strain and a spatial resolution of 0.1 mm can be achieved.

. We explore alternative ways to assign a measure to dynamic speckle patterns produced by different phenomena. Both the power spectrum and the autocorrelation of the intensity are considered. First, we describe an experimental study of the statistics of the Fresnel speckle patterns produced by illuminating a diffuser with laser light as a phenomenon where some control can be maintained on the dynamic variables. The diffuser rotates in a plane with constant angular speed. A correlation is established between some parameters of the autocorrelation or the power spectrum of the intensity fluctuations of the speckle patterns and the tangential speed corresponding to different distances from the rotation axis. A scale correction is suggested to estimate the number of points of the autocorrelation function that should be included in the calculations before speckle crosstalk starts. The defined parameters are then applied to characterize the activity of the dynamical speckle produced in the drying of paint. This is considered as a starting point for the understanding and assessment of more complex situations including biological activity.

In laser front projection display, the observer in the far field of the image pixels on the screen will observe serious speckle noise. For the first time we show a way to eliminate speckles in the far field by modulating a laser beam with traveling ultrasonic waves in a liquid cell. The resulting running interference fringes in a pixel on the screen will produce a boiling speckle pattern, which will be time-averaged in the eye of the observer. By superposition of ultrasonic waves of different frequencies, the speckle contrast can be reduced even further. We optimized the modulation frequencies, as well as the scattering properties of different screen materials. The intensity modulation depth of the speckle pattern could be reduced to a few percent without noticeable influence on the beam quality.

We describe a laboratory test article developed to capture the dynamics and control problems anticipated for future space-based telescopes: the Space Interferometry Mission (SIM) and the Next Generation Space Telescopes (NGST). We motivate the design of the Origins Testbed (OT) by identifying three operational events common to spacebased telescopes and requiring the OT to simulate them in a laboratory: large-angle slew, optical capture (alignment), and observation. The OT is the first spacecraft-like testbed to include nanometer phasing and a large-angle slew capability in the presence of spacecraftlike disturbances. The OT is discussed in detail, including the testbed’s dynamics and control sensors and actuators, with particular emphasis on the optical system. We present the necessary optics to capture the phasing of SIM and NGST using three interferometer channels. Pointing optics are detailed, with a description of an implemented spiral-based autoalignment algorithm. Initial slew control is discussed, and experimental results are presented. Future experiments performed on the OT will provide critical heritage for control techniques to be implemented on SIM and NGST.

It is well known that normal-incidence aplanatic telescope designs perform better at small field angles than ones corrected only for spherical aberration. This is why most large astronomical telescopes fabricated in the past fifty years have been of the Ritchey-Chretien (aplanatic) design rather than of the classical Cassegrain design. For the relatively new field of x-ray astronomy, the Wolter type I grazing incidence design has been extensively utilized. it consists of a paraboloidal primary mirror coaxial with a confocal hyperboloidal secondary mirror. Aplanatic versions of the Wolter type I grazing incidence x-ray telescope have been discussed in detail in the literature, and are widely touted as being superior designs. However, scattering effects from residual optical fabrication errors and other practical engineering error sources prevent these grazing-incidence telescopes from being near diffraction-limited (even on axis) at the very short operational x-ray wavelengths. A systems engineering analysis of these error sources indicates that they will dominate coma at the small field angles, and of course astigmatism, field curvature, and higher-order aberrations dominate coma at the large field angles. Hence, there is little improvement in performance when going to an aplanatic design. Comparison of performance predictions for the classical versus aplanatic Wolter type I x-ray telescope are presented for the special case of the Solar X-Ray Imager (SXI) baseline design. SXI is expected to become a standard subsystem aboard the next generation of NOAA/GOES weather satellites.

Two types of optical schemes are considered for telescopes with a fast spherical primary: the first for an afocal system, and the second for a focusing system. Both are strictly corrected for spherical aberration. In the extreme case the relative aperture of the spherical primary is 1/0.35 and the length of the system is 2.8 times smaller than the diameter of the primary. Exact analytical expressions describing a profile of the aspheric secondary are presented. The field of view of the system is highly limited by coma. It is shown that this drawback might be slightly compensated by field scanning by means of rotation of the secondary about either its vertex or the center of curvature of the fixed primary. Such schemes can be used for many different purposes, such as studies of point sources, laser-beam transformation, transmission and reception of infrared emission, and indication of telescope pointing errors.

This paper presents the implementation of two optical methods for characterizing the state of fabric surfaces: a multidirectional roughness meter and a hairiness meter. A textile fabric has a complicated texture in that the relevant components (fibers) are not very small (usually at least 10 ?m in diameter), but in the fabric are partly ordered (in the yarn) and partly disordered (in the superficial hairiness). Hairiness is important in giving a textile fabric a characteristic surface. It makes the effective surface three-dimensional with many hidden areas. Thus, characterizing the state of a fabric surface requires special devices. On the one hand, the presented roughness meter measures essentially the fabric-reflected rays in all surface directions, because the fabric is rotated in its plane during the measurement. A Fourier temporal analysis of the reflected beam scanned across the fabric surface allows the fabric structure periods to be determined, because these periods yield peaks in the frequency spectrum. Two examples are given that show that the peak heights characterize the state of the fabric surface. On the other hand, the hairiness meter measures the hairiness of the fabric surface by an edge extraction method, which separates hairiness and structural information. The two devices are complementary and allow the processes that modify the fabric surface to be understood and controlled.

Operation and management of wavelength division multiplexing (WDM) systems require the monitoring of optical channel frequency and power. We propose a simple and low-cost solution for tracking the frequency of WDM channels, based on the thermooptic tuning of single or coupled-cavities Fabry-Perot silicon optical filters. The fabricated structures are single-cavity filters exhibiting, thanks to a suitable coating stack on both cavity sides, high finesse and narrow bandwidth. Moreover, the free spectral range is large compared to the channel spacing, enabling the monitoring of one carrier frequency at a time. By means of a heater, we change the cavity refractive index and move the transmission peaks, thus scanning the WDM frequency set. In particular, we demonstrate the possibility to resolve up to seven 50-GHz-spaced channels with a crosstalk of -10 dB at wavelengths around 1550 nm. Better performances, in terms of resolvable channels and crosstalk can be obtained by using two coupled cavities, having a common resonance peak and different free spectral ranges. The global optical transfer function of such a cascade shows only one transmission peak in a frequency range of about 30 nm, and can be thermally tuned in this range.

A fast method for chip pin location inspection based on the Harr wavelet transform is presented. A cross line at the pin tip is analyzed, and the method locates the central line of a pin according to the zero crossing position of the transform of the 1-D cross line without theoretical error. The requirement of being theoretically error free is that the constant segment of the pin image is wider than 2 pixels. The experiment shows a measurement precision of 1/40 pixel.

Pattern recognition techniques are widely used in many applications particularly in the area of industrial inspection where objects are identified from features in an image. In particular, the Radon transform ~RT! and the Hough transform ~HT! are known1,2 to be powerful tools for feature extraction. The digital techniques used to implement the RT and the HT require a large number of calculations, however, and as such are limited to non-real-time applications.

This PDF contains the communications section which includes "Analysis of Slyusarev optical wedge distortion".