Showing papers in "Applied Optics in 1987"

System for self-organization of stable category recognition codes for analog input patterns

Abstract: A neural network includes a feature representation field which receives input patterns. Signals from the feature representation field select a category from a category representation field through a first adaptive filter. Based on the selected category, a template pattern is applied to the feature representation field, and a match between the template and the input is determined. If the angle between the template vector and a vector within the representation field is too great, the selected category is reset. Otherwise the category selection and template pattern are adapted to the input pattern as well as the previously stored template. A complex representation field includes signals normalized relative to signals across the field and feedback for pattern contrast enhancement.

Adaptive bidirectional associative memories

Abstract: Bidirectionality, forward and backward information flow, is introduced in neural networks to produce two-way associative search for stored stimulus-response associations (A(i),B(i)). Two fields of neurons, F(A) and F(B), are connected by an n x p synaptic marix M. Passing information through M gives one direction, passing information through its transpose M(T) gives the other. Every matrix is bidirectionally stable for bivalent and for continuous neurons. Paired data (A(i),B(i)) are encoded in M by summing bipolar correlation matrices. The bidirectional associative memory (BAM) behaves as a two-layer hierarchy of symmetrically connected neurons. When the neurons in F(A) and F(B) are activated, the network quickly evolves to a stable state of twopattern reverberation, or pseudoadaptive resonance, for every connection topology M. The stable reverberation corresponds to a system energy local minimum. An adaptive BAM allows M to rapidly learn associations without supervision. Stable short-term memory reverberations across F(A) and F(B) gradually seep pattern information into the long-term memory connections M, allowing input associations (A(i),B(i)) to dig their own energy wells in the network state space. The BAM correlation encoding scheme is extended to a general Hebbian learning law. Then every BAM adaptively resonates in the sense that all nodes and edges quickly equilibrate in a system energy local minimum. A sampling adaptive BAM results when many more training samples are presented than there are neurons in F(B) and F(B), but presented for brief pulses of learning, not allowing learning to fully or nearly converge. Learning tends to improve with sample size. Sampling adaptive BAMs can learn some simple continuous mappings and can rapidly abstract bivalent associations from several noisy gray-scale samples.

Digital phase-shifting interferometry: a simple error-compensating phase calculation algorithm.

Abstract: La difference de phase entre les 2 faisceaux interferant varie de maniere connue et on fait des mesures de la distribution d'intensite a travers la pupille correspondant a au moins 3 dephasages differents

The HITRAN database: 1986 edition.

Abstract: A description and summary of the latest edition of the AFGL high-resolution transmission molecular absorption database (HITRAN) parameters are presented. This new database combines the information for the seven principal atmospheric absorbers and twenty-one additional molecular species previously contained on the AFGL atmospheric absorption line parameter compilation and on the trace gas compilation. In addition to updating the parameters on earlier editions of the compilation, new parameters have been added to this edition such as the self-broadened half-width, the temperature dependence of the air-broadened half-width, and the transition probability. The database contains 348,043 entries between 0 and 17,900/cm. A FORTRAN program is now furnished to allow rapid access to the molecular transitions and for the creation of customized output. A separate file of molecular cross sections of 11 heavy molecular species, applicable for qualitative simulation of transmission and emission in the atmosphere, has also been provided.

Minimum average correlation energy filters

Abstract: The synthesis of a new category of spatial filters that produces sharp output correlation peaks with controlled peak values is considered. The sharp nature of the correlation peak is the major feature emphasized, since it facilitates target detection. Since these filters minimize the average correlation plane energy as the first step in filter synthesis, we refer to them as minimum average correlation energy filters. Experimental laboratory results from optical implementation of the filters are also presented and discussed.

Learning, invariance, and generalization in high-order neural networks

Abstract: High-order neural networks have been shown to have impressive computational, storage, and learning capabilities. This performance is because the order or structure of a high-order neural network can be tailored to the order or structure of a problem. Thus, a neural network designed for a particular class of problems becomes specialized but also very efficient in solving those problems. Furthermore, a priori knowledge, such as geometric invariances, can be encoded in high-order networks. Because this knowledge does not have to be learned, these networks are very efficient in solving problems that utilize this knowledge.

Confocal scanning laser ophthalmoscope.

Abstract: A confocal scanning imager moves an illumination spot over the object and a (virtual) detector synchronously over the image. In the confocal scanning laser ophthalmoscope this is accomplished by reusing the source optics for detection. The common optical elements are all mirrors-either flat or spherical-and the scanners are positioned to compensate astigmatism due to mirror tilt. The source beam aperture at the horizontal scanner is small. Light returning from the eye is processed by the same elements, but now the polygon's facet is overfilled. A solid-state detector may be at either a pupillary or retinal conjugate plane in the descanned beam and still have proper throughput matching. Our 1-mm avalanche photodiode at a pupillary plane is preceded by interchangeable stops at an image (retinal) plane. Not only can we reject scattered light to a degree unusual for viewing the retina, but we choose selectively among direct and scattered components of the light returning from the eye. One (of many) consequences is that this ophthalmoscope gives crisp and complete retinal images in He-Ne light without dilation of the pupil.

Analysis of almost-periodic distributed feedback slab waveguides via a fundamental matrix approach.

Abstract: A unified approach to obtain the characteristics of almost-periodic grating slab waveguides including gain in the waveguide is reported. In this approach the waveguides are divided into short segments, and in each segment the gratings are assumed to be periodic, that is, parameters such as coupling coefficient, grating phase, deviations from the Bragg frequency, and gain in the waveguide are independent of a propagation direction z. Then characteristics of almost-periodic grating slab waveguides can be obtained by multiplying each F matrix of a short segment with the proper grating phase conditions at the interface between two adjacent segments. The appropriateness of this approach is shown for typical aperiodic grating waveguides such as tapered, chirped, and phase-shifted gratings. The results obtained by this method are compared with others and prove to be in good agreement with the results obtained by other methods. In addition to these characteristics, it is shown that the F matrix can be used to obtain the threshold conditions for distributed feedback laser oscillations including reflections from cleaved edges.

Synthesis of digital holograms by direct binary search

Abstract: A new approach to the design of computer-generated holograms makes optimal use of the available device resolution. An iterative search algorithm minimizes an error criterion by directly manipulating the binary hologram and observing the effect on the desired reconstruction. Several measures of error and efficiency useful in assessing the optimality of digital holograms are defined. Methods for designing digital holograms that are based on projections and error diffusion are presented as established techniques for comparison to direct binary search.

Color and spatial structure in natural scenes.

Abstract: Digitized records of terrain scenes were produced using a technique of photographic colorimetry. Each record consisted of three tristimulus images (X,Y, and Z) which were analyzed for their color statistics, spatial frequency content, and image correlation. Interactions between color and space were examined using a cone receptor transformation. It is shown that the scene amplitude spectra follow an approximate reciprocal variation with frequency, and that the correlation function can be described by a one-step autoregressive model. The results are discussed in terms of methods for optimum image coding in human and machine vision.

New measurement system for fault location in optical waveguide devices based on an interferometric technique

Abstract: A new measurement system for fault location in optical waveguide devices is presented. The system consists of a fiber-optic Mach-Zehnder and a bulk-type Michelson interferometers. The spatial resolution of the scatter distribution is <380 microm, which is limited by the averaging time. The minimum detectable backscattered power is -116 dB relative to the light power propagating in the waveguides. Preliminary experimental results using single-mode fibers <10 cm long are demonstrated.

Aging of the human lens

Abstract: The optical density of the human lens changes during life. Literature concerning both the spectral density function and the rate of such changes is reviewed. Analysis indicates that two components govern the spectral lens density function, with one increasing gradually during life. The average lens density increases linearly at 400 nm by 0.12 density unit per decade between the ages of 20 and 60 and by 0.40 density unit per decade above age 60. A tabulation of the two components of the average 32-yr old lens is given, as are equations to derive the average spectral lens density functions for observers aged 20–80.

Joint transform image correlation using a nonlinear spatial light modulator at the fourier plane

Abstract: The present invention is a nonlinear joint transform image correlator which employs a spatial modulator operating in a binary mode at the Fourier plane. The reference and input images are illuminated by a coherent light at the object plane of a Fourier transform lens system. A image detection device, such as a charge coupled device, is disposed at the Fourier plane of this Fourier transform lens system. A thresholding network detects the median intensity level of the imaging cells of the charge coupled device at the Fourier plane and binarizes the Fourier transform interference intensity. The correlation output is formed by an inverse Fourier transform of this binarized Fourier transform interference intensity. In the preferred embodiment this is achieved via a second Fourier transform lens system. This binary data is then applied to spatial light modulator device operating in a binary mode located at the object plane of a second Fourier transform lens system. This binary mode spatial light modulator device is illuminated by coherent light producing the correlation output at the Fourier plane of the second Fourier transform lens system. The inverse Fourier transform may also be formed via a computer. In an alternative embodiment, the Fourier transform interference intensity is thresholded into one of three ranges. An inverse Fourier transform of this trinary Fourier transform interference intensity produces the correlation output.

Neural dynamics of attentionally modulated Pavlovian conditioning: blocking, interstimulus interval, and secondary reinforcement

Abstract: Selective information processing in neural networks is studied through computer simulations of Pavlovian conditioning data. The model reproduces properties of blocking, inverted-U in learning as a function of interstimulus interval, anticipatory conditioned responses, secondary reinforcement, attentional focusing by conditioned motivational feedback, and limited capacity short-term memory processing. Conditioning occurs from sensory to drive representations (conditioned reinforcer learning), from drive to sensory representations (incentive motivational learning), and from sensory to motor representations (habit learning).The conditionable pathwas contain long-term memory traces that obey a non-Hebbian associative law. The neural model embodies a solution to two key design problems of conditioning, the synchronization and persistence problems. This model of vertebrate learning is compared with data and models of invertebrate learning. Predictions derived from models of vertebrate learning are compared with data about invertebrate learning, including data from Aplysia about facilitator neurons and data from Hermissenda about voltage-dependent Ca(2+) currents. A prediction is stated about classical conditioning in all species, called the secondary conditioning alternative, and if confirmed would constitute an evolutionary invariant of learning.

Step height measurement using two-wavelength phase-shifting interferometry.

Abstract: Two-wavelength phase-shifting interferometry is applied to an interference phase-measuring microscope enabling the measurement of step features. The surface is effectively tested at a synthesized equivalent wavelength lambda(eq) = lambda(a)lambda(b)/| lambda(a) - lambda(b)| by subtracting phase measurements made at visible wavelengths lambda(a) and lambda(b). The rms repeatability of the technique is lambda/1000 at the equivalent wavelength. To improve the precision of the data, the phase ambiguities in the single-wavelength data are removed using the equivalent wavelength results to determine fringe orders. When this correction is made, a measurement dynamic range (feature height/rms repeatability) of 10(4) is obtainable. Results using this technique are shown for the measurement of an optical waveguide and a deeply modulated grating.

Interferogram analysis using Fourier transform techniques

Abstract: Fourier transform techniques have been used to map the complex fringe visibility in several types of interferogram. A Gerchberg-type iterative technique is used to eliminate edge effects. Results are presented for two specific cases: seeing measurements and interferometric tests.

Automated single-cell manipulation and sorting by light trapping

Abstract: Following the recently reported trapping of biological particles by finely focused laser beams, we report on the automated micromanipulation of cells and other microscopic particles by purely optical means as well as on a newly observed interaction between particles in the trapping beam. A simple instrument is described which allows single cells to be positioned with high accuracy, transported over several millimeters, and automatically sorted on the basis of their optical properties. These operations are performed inside a small enclosed chamber without mechanical contact or significant fluid flow. Potential applications of this technique in experimental cell biology are discussed.

Second harmonic generation and accurate index of refraction measurements in flux-grown KTiOPO 4

Abstract: Accurate index of refraction measurements have been performed in flux-grown KTiOPO(4). These measurements give good agreement between experiment and theory for angle phase matching in Type II second harmonic generation at 1.064 microm. These refractive-index data have allowed us to calculate the propagation angles for second harmonic generation at wavelengths of interest other than 1.064 microm such as 1.34 microm. Type II second harmonic energy conversion efficiency of 1.064 micro m of up to 59% in this material has also been demonstrated with higher efficiencies possible. Limits to conversion efficiency are discussed.

Optical properties of Au, Ni, and Pb at submillimeter wavelengths

Abstract: Measurements of the optical properties, and thus the optical constants, of metals at submillimeter wavelengths are almost nonexistent. We used a nonresonant cavity to measure at ambient temperature the angle averaged absorptance spectra P(ω) of gold, nickel, and lead in the 30–300-cm−1 wave-number region. The real part of the normalized surface impedance spectrum z(ω) = r(ω) + ix(ω) was determined from P(ω). The r(ω) spectrum was combined with previous measurements by others at higher frequencies, and Kramers-Kronig analyses of the resultant r(ω) spectra provided ∊(ω) = ∊1(ω) + i∊2(ω) and N(ω) = n(ω) + ik(ω) for gold and nickel in the 35–15,000-cm−1 region and for lead in the 15–15,000-cm−1 region. We also derived an exact analytical expression for P(ω) of a metal.

Guided-wave reflectometry with micrometer resolution.

Abstract: We describe a new type of optical reflectometry which is useful in testing single-mode lightguide systems. This technique uses a scanning Michelson interferometer in conjunction with a broadband illuminating source and cross-correlation detection. High resolution is achieved through the limited coherence of the backscattered radiation. With this approach it is possible to distinguish scattering centers separated by only a few micrometers. In some cases loss may be estimated for components in the transmission path of a test lightguide. The basic principles of this diagnostic technique, along with some performance characteristics, are illustrated for an all-fiber reflectometer. We also discuss several laboratory applications which serve to demonstrate the resolution capabilities of this measurement concept.

Optical microscope system for standardized cell measurements and analyses.

Abstract: A fully integrated optical microscope and computer workstation for the pathology laboratory is described along with a system module for that workstation, the Cell Measurement Program (cmp). This module allows for the acquisition and storage of digitized microscope images; measurement of a standard set of cell features, or descriptors, calibrated for accurate densitometry; and a comprehensive set of statistical analyses and display procedures. This system is useful in research in cell biology and in cancer research, allowing the investigator to use the microscope as a measuring instrument.

Evaluation of blood flow by laser speckle image sensing. Part 1.

Abstract: A new method is proposed to visualize the microcirculation map using a dynamic laser speckle effect. A skin surface is illuminated by He-Ne laser line spot and its image speckle is detected by a CCD array sensor. The erence between a pair of output data for successive scannings of the image speckles at the sensor plane was calculated and integrated for each pixel. The results were displayed in color graphics showing the spatial variation of the flow level in the area of interest.

Computer generated holograms: an historical review

Abstract: Since Gabor's first hologram, the meanings of that term have grown with increased use of the invention. Computers expanded applications further, and this paper surveys the methods and techniques of computer generated holograms.

Pump/probe method for fast analysis of visible spectral signatures utilizing asynchronous optical sampling

Abstract: We report the results from a new pump/probe spectrometer for potential use in combustion diagnostics that employs asynchronous optical sampling. The instrument consists of two frequency-doubled mode-locked Nd:YAG lasers operating at slightly different repetition rates, synchronously pumping two dye lasers (rhodamine 6G) to generate the pump and probe beams. The spectral and temporal capabilities of the instrument are examined by obtaining a spectrum and an excited state decay of rhodamine B. The instrument response is shown to be proportional to pump power, probe power, and sample absorptance. Different frequency synthesizers and different modes of triggering are used to study their effect on signal stability.

Neural network model for selective attention in visual pattern recognition and associative recall.

Abstract: A neural network model of selective attention is discussed. When two patterns or more are presented simultaneously, the model successively pays selective attention to each one, segmenting it from the rest and recognizing it separately. In the presence of noise or defects, the model can recall the complete pattern in which the noise has been eliminated and the defects corrected. These operations can be successfully performed regardless of deformation of the input patterns. This is an improved version of the earlier model proposed by the author: the ability of segmentation is improved by lateral inhibition.

Confocal imaging for 3-D digital microscopy.

Abstract: Optical serial sectioning based on the depth-discriminating ability of confocal laser scanning can be combined with digital image processing to realize fast and easy-to-use 3-D microscopy. A great advantage as compared with traditional methods, e.g., using a microtome, is that the specimen is left undamaged. An account is given of an instrument designed for this purpose and of feasibility studies that have been carried out to assess the usefulness of the method in fluorescence microscopy.

Dielectric totally internally reflecting concentrators

Abstract: Dielectric totally internally reflecting concentrators (DTIRCs) which can achieve concentrations close to the thermodynamically allowed limits are introduced. General design methodologies are given explicitly. Geometrical and optical properties of DTIRCs are discussed.

Antireflection effect in ultrahigh spatial-frequency holographic relief gratings.

Abstract: An interpretation model for low reflectivity in ultrahigh spatial-frequency holographic relief gratings is proposed. The model is based on the concept that the grating effective index, caused by grating ultrahigh spatial frequency, is graded in the depth direction and forms an antireflective constitution similar to the multilayer coating. Numerical results show that a sinusoidal grating is antireflective over wide groove depth, wavelength and incident angle ranges, and a grating with nearly triangular section, having a circle arc index distribution, has a very low reflectivity, >10(-4)%. Reflectivity vs groove depth, obtained experimentally for a holographically recorded photoresist grating, agrees fairly well with the numerical results.

Intermodulation distortion and compression in an integrated electrooptic modulator.

Abstract: We have characterized the intermodulation distortion and compression properties of an integrated optical modulator at microwave frequencies by measuring the third-order intercept and 1-dB compression points. Values of +30.0 and +21.4 dBm, respectively, were measured and agree well with theory. When operated in the shot-noise-limited regime, these devices can have spurious free dynamic ranges in excess of 100 dB, making them attractive as potential alternatives to conventional diode mixers in special applications.

Molecular line parameters for the atmospheric trace molecule spectroscopy experiment

Abstract: During its first mission in 1985 onboard Spacelab 3, the ATMOS (atmospheric trace molecule spectroscopy) instrument, a high speed Fourier transform spectrometer, produced a large number of high resolution infrared solar absorption spectra recorded in the occultation mode. The analysis and interpretation of these data in terms of composition, chemistry, and dynamics of the earth's upper atmosphere required good knowledge of the molecular line parameters for those species giving rise to the absorptions in the atmospheric spectra. This paper describes the spectroscopic line parameter database compiled for the ATMOS experiment and referenced in other papers describing ATMOS results. With over 400,000 entries, the linelist catalogs parameters of 46 minor and trace species in the 1-10,000/cm region.