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Showing papers in "Applied Optics in 1979"


Journal ArticleDOI
R. Ulrich1, A. Simon1
TL;DR: In twisted single-mode optical fibers the polarization of light is affected by an elastooptically induced optical activity and by a modification of any linear birefringence present.
Abstract: In twisted single-mode optical fibers the polarization of light is affected by an elastooptically induced optical activity and by a modification of any linear birefringence present. These effects are discussed theoretically and demonstrated experimentally. The activity/twist ratio is α/τ ≃ 0.13 … 0.16 universally in weakly guiding silica fibers. Twisted fibers may be used as polarization rotators. A fiber with a ±68° double twist operates as a fast/slow mode interchanger, suitable for delay equalization.

760 citations


Journal ArticleDOI
G. B. Hocker1
TL;DR: The use of a fiber-optic Mach-Zehnder interferometer to measure differences in temperature or pressure between two single-mode fiber arms is described.
Abstract: The use of a fiber-optic Mach-Zehnder interferometer to measure differences in temperature or pressure between two single-mode fiber arms is described. Temperature or pressure changes are observed as a motion of an optical interference fringe pattern. Values are calculated for the pressure and temperature dependence of the fringe motion. Pressure and temperature measurements are made with the interferometer, and the experimental values for sensitivity are in good agreement with those calculated.

669 citations


Journal ArticleDOI
TL;DR: The significance of the feasibility demonstration is that substantial levels of vibrational amplitude reduction were obtained with very small transducers in nonoptimal positions on noncritical portions of the optical structure.
Abstract: We have carried out a preliminary experimental demonstration of the feasibility of using external electronic circuits to damp mechanical vibrations in optical systems. The significance of the feasibility demonstration is that substantial levels of vibrational amplitude reduction were obtained with very small transducers in nonoptimal positions on noncritical portions of the optical structure. The prototype optical structure used in the experiment consisted of a membrane mirror stretched over a 25-cm diam glass frame with complex cross section. Five small piezoelectric transducers (19.05 x 3.18 x 0.28 mm) were applied with Duco cement at arbitrary positions on the glass frame. Acoustic excitation was then used to excite the resonances in the optical structure. These vibrational responses were measured, and one particular mode was chosen for the feasibility test. The structure was driven by external vibrations at the resonant frequency of the chosen mode until the membrane response was visible. One transducer as used to sense the vibrations in the frame, and this output was used to drive a negative feedback amplifier that drove one of the other transducers on the frame. With the feedback circuit active between two points on the frame, the vibrational response of the membrane to the external excitation was substantially reduced (7:1).

459 citations


Journal ArticleDOI
TL;DR: Techniques and calculations are presented that give explicit expressions for the over-all performance of a luminescent solar concentrator in terms of the intrinsic spectral response and quantum efficiency of its constituents.
Abstract: Techniques and calculations are presented that give explicit expressions for the over-all performance of a luminescent solar concentrator (LSC) in terms of the intrinsic spectral response and quantum efficiency of its constituents. We examine the single dye (or inorganic ion) LSC with emphasis on the planar geometry. Preliminary data on the degradation of candidate LSC dyes under severe weathering conditions are also given. Armed with our experimental results and analysis of solar absorption, self-absorption, and solar cell efficiency, we present a new genre of solar concentrator with a theory of operation for the device.

402 citations


Journal ArticleDOI
TL;DR: A fairly accurate analytical expression of the measured reflectance is established for the general case of a non-Lambertian and nonuniform ground by separating the atmospheric and surface effects.
Abstract: A fairly accurate analytical expression of the measured reflectance is established for the general case of a non-Lambertian and nonuniform ground by separating the atmospheric and surface effects. The signal is nearly linear in the function of intrinsic atmospheric reflectance, the actual target reflectance, and two average ground reflectances, angular and spatial, to be defined. Contrast reduction by the atmosphere, defined in the cases of Lambertian and directional ground reflectances, has been evaluated using this formulation.

296 citations


Journal ArticleDOI
TL;DR: Holographic characteristics of the dichromated gelatin are described, including exposure characteristics with a bulk exposure model, hologram thickness change, and environmental stability.
Abstract: Hardened dichromated gelatin is the best material available today for the fabrication of holographic optical elements (HOEs) because of its low scattering, large refractive index modulation capacity, and other unique properties such as reprocessibility On the basis of experimental data accumulated during the last several years, we describe holographic characteristics of the dichromated gelatin, including exposure characteristics with a bulk exposure model, hologram thickness change, and environmental stability Basic chemistry, hologram formation in the dichromated gelatin, and generalized processing techniques are also discussed

294 citations


Journal ArticleDOI
Wai-Hon Lee1
TL;DR: An accurate numerical method which circumvents two difficulties in using binary Fourier transform holograms and three different techniques for storing amplitude information in the binary computer-generated holograms are discussed.
Abstract: Binary computer-generated holograms are similar to interferograms with fringe patterns hardclipped by a photographic process. Therefore the fringe locations in the binary hologram can be determined by solving a grating equation. However, there are two difficulties in using this approach to make binary Fourier transform holograms. First the discrete Fourier transform provides only data at discrete sampling locations. Second, the phase angles thus calculated are given in terms of the residues of the original phase angles after multiples of 2pi rad are removed. In this paper an accurate numerical method which circumvents these two difficulties is described. Also discussed are three different techniques for storing amplitude information in the binary computer-generated holograms. The different solution methods discussed in this paper are further illustrated by a number of computer-generated holograms and their reconstructed images.

281 citations


Journal ArticleDOI
TL;DR: In this article, various properties of dielectric thin films are discussed, including refractive index and absorption coefficient, light scattering, structure, microstructure, density, gas sorption, chemical composition, homogeneity, adhesion, hardness and mechanical stress, and environmental influences.
Abstract: Various properties of dielectric thin films are discussed in this paper: refractive index and absorption coefficient, light scattering, structure, microstructure, density, gas sorption, chemical composition, homogeneity, adhesion, hardness and mechanical stress, and environmental influences.

272 citations


Journal ArticleDOI
TL;DR: The reflectance map is derived in terms of the bidirectional reflectance-distribution function (BRDF) and the distribution of source radiance in order to improve the understanding of image formation.
Abstract: It appears that the development of machine vision may benefit from a detailed understanding of the imaging process. The reflectance map, showing scene radiance as a function of surface gradient, has proved to be helpful in this endeavor. The reflectance map depends both on the nature of the surface layers of the objects being imaged and the distribution of light sources. Recently, a unified approach to the specification of surface reflectance in terms of both incident and reflected beam geometry has been proposed. The reflecting properties of a surface are specified in terms of the bidirectional reflectance-distribution function (BRDF). Here we derive the reflectance map in terms of the BRDF and the distribution of source radiance. A number of special cases of practical importance are developed in detail. The significance of this approach to the understanding of image formation is briefly indicated.

258 citations


Journal ArticleDOI
TL;DR: An efficient and powerful technique has been developed to treat the problem of wave propagation along arbitrarily shaped single-mode dielectric waveguides with inhomogeneous index variations in the cross-sectional plane based on a modified finite-element method.
Abstract: An efficient and powerful technique has been developed to treat the problem of wave propagation along arbitrarily shaped single-mode dielectric waveguides with inhomogeneous index variations in the cross-sectional plane. This technique is based on a modified finite-element method. Illustrative examples were given for the following guides: (a) the triangular fiber guide; (b) the elliptical fiber guide; (c) the single material fiber guide; (d) the rectangular fiber guide; (e) the embossed integrated optics guide; (f) the diffused channel guide; (g) the optical stripline guide.

237 citations


Journal ArticleDOI
TL;DR: It is shown that for stratospheric measurements below about 25 km, molecular density uncertainties are the dominant source of error for wavelengths shorter than about 1.1 microm during nonvolcanic conditions.
Abstract: A methodology is presented for objective and automated determination of the uncertainty in lidar aerosol measurements. This methodology is based on standard error-propagation procedures, a large data base on atmospheric behavior, and long experience in lidar data processing. Algebraic expressions for probable error are derived as a function of the relevant parameters. The validity of these expressions is then tested by making simulated measurements and analyses in which random errors of appropriate size are injected at proper steps of the measurement and analysis process. An illustrative example is given where the methodology is applied to a new lidar system now being used for airborne measurements of the stratospheric aerosol.

Journal ArticleDOI
A. C. Tam1, C. K. N. Patel1
TL;DR: A pulsed dye-laser optoacoustic spectroscopy technique has been used to measure the absorption spectra of light and heavy water at 21.5 degrees C in the visible region and are believed to be the most reliable so far.
Abstract: A pulsed dye-laser optoacoustic spectroscopy technique has been used to measure the absorption spectra of light and heavy water at 21.5 degrees C in the visible region. Basic principles of pulsed optoacoustic spectroscopy technique and the procedure for absolute calibration are discussed with reference to its application in water. Experimental details of the application of optoacoustic spectroscopy to water are given. Our absorption coefficients, of accuracies about +/- 10%, are believed to be the most reliable so far. Light water has a broad absorption minimum near 475 nm where the absorption coefficient is 1.8 x 10(-4) cm(-1). Heavy water exhibits a totally different absorption spectrum and has a broad absorption minimum near 600 nm where the absorption coefficient is 1.9 x 10(-4) cm(-1). Previous measurements of the optical spectra of water were done mostly by long-path transmission measurements, and they display disagreement by factors as large as 10 near the green absorption minimum of light water. We give a critical comparison of our optoacoustic absorption spectra with other existing data.

Journal ArticleDOI
TL;DR: A new image-shearing camera which focuses two laterally sheared images at the film plane and becomes a shearing interferometer, which directly measures the derivatives of the surface displacements.
Abstract: This paper describes a new image-shearing camera which focuses two laterally sheared images at the film plane. With coherent illumination, this camera becomes a shearing interferometer, which directly measures the derivatives of the surface displacements. This strain measuring tool enjoys several advantages over the conventional, holographic, and speckle interferometry, namely, (1) better fringe quality (than speckle interferometry); (2) does not require special vibration isolation; (3) very simple optical setup; (4) direct determination of strains; and (5) extended controllable range of sensitivity.

Journal ArticleDOI
TL;DR: It is shown that, for oblique incidence, the scattering properties of a long slender prolate spheroid resemble those of an infinitely long circular cylinder.
Abstract: In the present paper, the light scattering characteristics of spheroidal particles are evaluated within the framework of a scattering theory developed for a homogeneous isotropic spheroid. This approach is shown to be well suited for computing the scattering quantities of spheroidal particles of fairly large sizes (up to a size parameter of 30). The effects of particle size, shape, index of refraction, and orientation on the scattering efficiency factors and the scattering intensity functions are studied and interpreted physically. It is shown that, in the case of oblique incidence, the scattering properties of a long slender prolate spheroid resemble those of an infinitely long circular cylinder.

Journal ArticleDOI
TL;DR: The computations indicate that the required efficiencies are sufficiently low to account completely for the enhanced reflectance of the ocean's diffuse reflectance near 685 nm in chlorophyll rich waters without resorting to anomalous dispersion.
Abstract: The radiative transfer equation is modified to include the effect of fluorescent substances and solved in the quasi-single scattering approximation for a homogeneous ocean containing fluorescent particles with wavelength independent quantum efficiency and a Gaussian shaped emission line. The results are applied to the in vivo fluorescence of chlorophyll a (in phytoplankton) in the ocean to determine if the observed quantum efficiencies are large enough to explain the enhancement of the ocean's diffuse reflectance near 685 nm in chlorophyll rich waters without resorting to anomalous dispersion. The computations indicate that the required efficiencies are sufficiently low to account completely for the enhanced reflectance. The validity of the theory is further demonstrated by deriving values for the upwelling irradiance attenuation coefficient at 685 nm which are in close agreement with the observations.

Journal ArticleDOI
TL;DR: Both procedures showed performance limits to be functions of the square root of the flux density coupled into the target-illuminating fiber(s) by the electroluminescent source.
Abstract: Intrinsic performance limits of noncontacting fiber lever displacement measuring systems are quantitatively described. Generalized relationships linking displacement detection limit, frequency response, dynamic range, linearity, and working distance to fiber diameter, illumination irradiance and coupling angle, photo-detector characteristics, and reflection and transmission losses were obtained by analysis and confirmed by measurement. Both procedures showed performance limits to be functions of the square root of the flux density coupled into the target-illuminating fiber(s) by the electroluminescent source. Displacement detection and bandwidth limits achievable with tungsten or LED sources were in the 2 × 10−11 to 2×10-12m/Hz and MHz, range respectively. A basis for optimizing levers for different applications and determination of intrinsic performance limits is provided.

Journal ArticleDOI
TL;DR: The cylindrical lens method is shown to be most efficient, with a coupling loss of 1.8 dB under optimum alignment conditions, and the optimum radius of a cylINDrical lens, which gives maximum coupling efficiency, is derived by theoretical calculation, using the ray matrix method.
Abstract: Promising results of various coupling experiments between laser diodes and single-mode fibers to determine the optimum coupling method are reported. The cylindrical lens method is shown to be most efficient, with a coupling loss of 1.8 dB under optimum alignment conditions. More than −2 dB coupling efficiency is attained with a cylindrical lens whose radius is less than 8 μm. The laser to fiber coupling characteristics are estimated by Gaussian beam approximation. The optimum radius of a cylindrical lens, which gives maximum coupling efficiency, is derived by theoretical calculation, using the ray matrix method. The cylindrical lens alignment tolerance is also shown theoretically and experimentally.

Journal ArticleDOI
TL;DR: Antireflective (AR) coatings, which are produced from organometallic driven solutions containing oxide constituents in a chemically polymerized form, are presented and showed as much as 49% improvement in efficiency over the uncoated state.
Abstract: Antireflective (AR) coatings, which are produced from organometallic driven solutions containing oxide constituents in a chemically polymerized form, are presented. These solutions leave a film on substrates which, upon heat treatment, converts to a glasslike oxide film having the desired optical thickness and index of refraction. The index can be varied continuously from 1.4 to 2.4; thus the AR coatings can be fine-tuned for different substrates and for specific wavelengths of light. Silicon solar cells AR-coated by this technique showed as much as 49% improvement in efficiency over the uncoated state. The real advantage of the process, however, lies in the fact that it is simple, well-suited for automated mass production of photovoltaic cells, and reduces the cost of coating application from an estimated $0.20 per W-package to about $0.01 per W-package.

Journal ArticleDOI
TL;DR: Using residue arithmetic it is possible to perform additions, subtractions, multiplications, and polynomial evaluation without the necessity for carry operations.
Abstract: Using residue arithmetic it is possible to perform additions, subtractions, multiplications, and polynomial evaluation without the necessity for carry operations. Calculations can, therefore, be performed in a fully parallel manner. Several different optical methods for performing residue arithmetic operations are described. A possible combination of such methods to form a matrix vector multiplier is considered. The potential advantages of optics in performing these kinds of operations are discussed.

Journal ArticleDOI
TL;DR: The results from this analysis indicate that aerosol, ozone, and neutral density vertical profiles can be retrieved to an accuracy better than 10% with about 1-km vertical resolution over most of the stratosphere.
Abstract: The paper discusses a possible data retrieval technique for the spaceborne Stratospheric Aerosol and Gas Experiment (SAGE). The SAGE instrument has four radiometric channels located at selected intervals in the 0.38-1.0-micron wavelength range. A data reduction procedure is described for minimization of experimental errors on the basis of a detailed simulation of the measurement sequence. An efficient and accurate inversion method is then used for the retrieval of all the constituent vertical profiles. Also, the effects of horizontally inhomogeneous distributions of the constituent vertical profiles are studied based on available data of their global distributions. A simple horizontally inhomogeneous model of stratospheric aerosol and ozone is employed to estimate the perturbation on the retrieval accuracies.

Journal ArticleDOI
TL;DR: Analytic and numerical results are given for the elastic scattering of evanescent electromagnetic waves by dielectric spheres and some polarization and symmetry effects not found in Lorenz-Mie scattering are noted.
Abstract: Analytic and numerical results are given for the elastic scattering of evanescent electromagnetic waves by dielectric spheres. Some polarization and symmetry effects not found in Lorenz-Mie scattering are noted. The possibility of experimental studies is also discussed.

Journal ArticleDOI
TL;DR: It is shown that both plate- and columnlike ice crystals show a strong backscattering and the effect of orientation on the light scattering, and that columnlike crystals randomlyoriented in a plane behave rather like spherical particles and not like columns randomly oriented in space.
Abstract: The classical ray optics approximation has been applied to compute the angular scattering of light by finite-sized hexagonal ice crystals in the form of columns and plates. The results are presented at a wavelength of 0.55 μm for a random orientation of the crystals either in space or in a plane. The results are also compared to those of ice spheres. For the first time the angular light scattering of platelike crystals and a quantitative description of the 46° halo are given. Contrary to earlier studies, it is shown that both plate- and columnlike ice crystals show a strong backscattering. In agreement with previous studies, ice spheres are found to scatter—when compared to ice prisms—less energy at angles near 90°. With regard to the effect of orientation on the light scattering, it is shown that columnlike crystals randomly oriented in a plane behave rather like spherical particles and not like columns randomly oriented in space.

Journal ArticleDOI
TL;DR: A novel system for real-time heterodyne interferometry of extended objects is demonstrated, featuring the direct measurement of the optical path difference, eliminating the sometimes troublesome interpretation of the fringe patterns of traditional interferometer.
Abstract: A novel system for real-time heterodyne interferometry of extended objects is demonstrated. Featured in this system is the direct measurement of the optical path difference, eliminating the sometimes troublesome interpretation of the fringe patterns of traditional interferometry. High spatial and temporal resolutions are available in real time for a properly instrumented system. The concept, its performance, and applications are presented along with results from a breadboard system, where phase accuracy of better than λ/100 is demonstrated.

Journal ArticleDOI
TL;DR: The dependence of the coupling strength of titanium-diffused lithium niobate directional couplers upon fabrication parameters and guided wavelength has been investigated and good comparison was obtained with theoretical results calculated using an effective index method.
Abstract: The dependence of the coupling strength of titanium-diffused lithium niobate directional couplers upon fabrication parameters and guided wavelength has been investigated. Measurements of the coupling strength as a function of interguide separation have been made at He-Ne, GaAs, and Nd:YAG wavelengths. To good approximation, the coupling strength depends exponentially upon guide separation. Rather strong dependence upon the metal thickness diffused and the guided wavelength were observed. Good comparison was obtained with theoretical results calculated using an effective index method. Transfer lengths as short as 200 microm have been obtained. Fabrication parameters for which the coupling strength for the TE and TM modes are equal were determined.

Journal ArticleDOI
TL;DR: A laser Doppler technique which provides a means of obtaining absolute measurements of the speed of red blood cells flowing in individual retinal vessels is described and preliminary measurements obtained using a prototype instrument are presented.
Abstract: A laser Doppler technique which provides a means of obtaining absolute measurements of the speed of red blood cells (RBCs) flowing in individual retinal vessels is described. Doppler-shift frequency spectra of laser light scattered from the RBCs are obtained for two directions of the scattered light. Each spectrum exhibits a cutoff frequency that is directly related to the maximum RBC speed (V(max)). The difference in cutoff frequencies is used to obtain an absolute measure of V(max) that is independent of the exact orientation of the vessel and of the relative direction of the incident and scattered beams with respect to the flow direction. Preliminary measurements obtained using a prototype instrument are presented.

Journal ArticleDOI
TL;DR: The shape of the resultant predicted gain-voltage transfer characteristic for the MCP fits well with experimental data, confirming the assumption made and permitting the use of curve matching techniques to determine such important MCP parameters as the average number of active dynodes, the gain per stage, the crossover potential, the transit time through the multiplier, etc.
Abstract: It is shown that microchannel plates (MCPs) tend to act as if they were discrete stage electron multipliers with a fixed number of stages or dynodes if a plausible assumption is made regarding the behavior of the secondary electrons emitted from the semiconducting sidewalls of tubular channel electron multipliers under the grazing incidence conditions predominantly encountered in these multipliers. The shape of the resultant predicted gain-voltage transfer characteristic for the MCP fits well with experimental data, confirming the assumption made and permitting the use of curve matching techniques to determine such important MCP parameters as the average number of active dynodes, the gain per stage, the crossover potential for the MCP wall material, the transit time through the multiplier, etc.

Journal ArticleDOI
TL;DR: Both the mode eigenvalues and mode weights, which are necessary for determining the impulse response, can be obtained with high accuracy from a numerical Fourier transform of the complex field-correlation function by the use of digital-filtering techniques.
Abstract: Methods are developed for extracting from a numerical propagating-beam solution of a scalar wave equation the information necessary to compute the impulse-response function and the pulse dispersion for a multimode graded-index fiber. It is shown that the scalar Helmholtz equation and the parabolic wave equation have the same set of eigenfunctions in common and that the eigenvalues for the two equations are simply related. Thus one can work exclusively with the simpler parabolic equation. Both the mode eigenvalues (propagation constants) and mode weights, which are necessary for determining the impulse response, can be obtained with high accuracy from a numerical Fourier transform of the complex field-correlation function by the use of digital-filtering techniques. It is shown how a solution obtained in the absence of profile dispersion can be simply corrected for the presence of profile dispersion. In an illustrative example a graded-index fiber with a central dip in its profile is considered.

Journal ArticleDOI
TL;DR: A method for detecting sound using a single step-index multimode fiber is presented and it is found that this approach is approximately 10(-3) less sensitive than the single-mode interferometer arrangement.
Abstract: A method for detecting sound using a single step-index multimode fiber is presented. The detected signal results from differences in acoustically induced phase shifts between two different waveguide modes propagating in the fiber. The relative sensitivity of this technique compared with a two-path interferometer was experimentally determined and agreed with that calculated using the fiber parameters. Because the sensitivity of this approach is proportional to the difference in propagation constants for modes in the fiber, it is approximately 10−3 less sensitive than the single-mode interferometer arrangement.

Journal ArticleDOI
TL;DR: The experimental value for the density derivative of refractive index rho(dn/drho)T deviates by only a small amount from the value calculated from the Lorentz-Lorenz equation, which is the expected result for molecular solids.
Abstract: The following parameters have been obtained for Plexiglas 55 and Lexan: refractive index n at 486.1 nm, 589.3 nm, and 656.3 nm, the thermooptic constant dn/dT at 632.8 nm, the linear thermal expansion coefficient; the photoelastic constants q(11), q(12), p(11), and p(12); and the elastic moduli c(11), c(12), s(11), and s(12). The experimental value for the density derivative of refractive index rho(dn/drho)T deviates by only a small amount from the value calculated from the Lorentz-Lorenz equation. This is the expected result for molecular solids. The density variation with temperature is the dominant contribution to dn/dT.

Journal ArticleDOI
S. H. Wemple1
TL;DR: A three-parameter description of optical fiber material dispersion is proposed which fits the available data and reveals the key roles played by bond length, lattice structure, chemical valence, average energy gap, and atomic mass.
Abstract: A three-parameter description of optical fiber material dispersion is proposed which fits the available data and reveals the key roles played by bond length, lattice structure, chemical valence, average energy gap, and atomic mass. Using broadly applicable trends in electronic and phonon oscillator strengths, simple expressions are deduced for material dispersion including the zero crossover wavelength λc. These results impose severe constraints on fiber design which essentially limit the possibilities for significantly improving on pure silica to sulfates (particularly Li2SO4) and to BeF2. The predicted value of λc for the latter material is 1.05 μm.