RESUMO
An investigation of the losses exhibited by antiresonant ref lecting optical waveguides (ARROW's) formed from solution-deposited solgel films is reported. Solgel layers formed from methyltrimethoxysilane (MTMS) and titanium (iv) propoxide were used to fabricate a simple ARROW structure. Using a combination of MTMS and titanium (iv) propoxide produced good optical quality layers with thicknesses ranging from 1 to 20 microm. Losses as low as 2 dB/cm were measured experimentally for these ARROW devices.
RESUMO
A method is reported for characterizing planar antiresonant reflecting optical waveguides (ARROW's) by use of an unmodified Abbe refractometer. The technique permits the simultaneous determination of the TE-mode effective indices of the allowable modes, the thickness and refractive index of the waveguide core. Results from experimental measurements of an ARROW waveguide compare well with those predicted by a f ield transfer matrix analysis.
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A simple modification to the Fabry-Perot technique for the measurement of semiconductor waveguide losses is described. The modification dispenses with the need for knowing implicitly the reflectivities of end faces of the waveguide, which are usually difficult to ascertain experimentally.
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We present details of a simple method, incorporating first-order perturbation theory, to analyze the birefringence exhibited by elliptical-core fibers by using an equivalent rectangular-core waveguide. The results from this method are compared with those obtained from the finite-element and another approximate technique to demonstrate the accuracy of this simple method. The method may be extended to analyze waveguides of arbitrary geometry.
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It is shown that use of the effective-index method for a rectangular-core waveguide is equivalent to analysis of a pseudorectangular-core waveguide, the dielectric constant of which is higher in some of the cladding regions than that of the actual waveguide. This explains why the effective-index method gives higher values for the propagation constants for the various guided modes than other methods and different results depending on whether one starts with the longer dimension or the shorter dimension to construct the effective-index waveguide.
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A simple analysis is presented for calculating the change in the effective index of a guided mode in an optical fiber with reduced cladding surrounded by an optically nonlinear medium. Using first-order perturbation theory, the optical power required to alter the phase-matched condition in a fiber directional coupler incorporating a nonlinear medium is therefore calculated. This may then be applied to an optically controlled switch, the output of which may be transferred from one port to another by application of a high-intensity pulse. This method may be applied to other fiber components, for example, fiber gratings and polarizers.
Assuntos
Imagem Corporal , Destreza Motora , Cultura , Feminino , Humanos , Inteligência , MasculinoRESUMO
For plethysmographic studies of respiratory mechanics, we selected, from a general population, 51 subjects, aged 25-75 yr, who had never smoked, had no present or past cardiorespiratory symptoms or disease, were alpha1-antitrypsin MM phenotypes, and were normal by physical examination, vectorcardiography, and chest roentgenography. Approximately equal numbers of men and women were represented in each of three age groups; 25-35, 36-64, and 65-75. Both sexes demonstrated loss of lung elastic recoil with age, most significant at high lung volumes, but the rate of loss was less than previously reported. Males had higher lung recoil than females of comparable age, but if lung size was taken into account, there were no sex differences in bulk elastic properties. Maximum expiratory flow diminished with age only at low volumes, suggesting that equal pressure points are more centrally located at low lung volumes in the elderly.
