The characteristics of light diffraction by graded index diffraction gratings, formed in glasses by ion-exchange techniques, and the minimum periodicity of such gratings are theoretically evaluated on the basis of a simple physical model. It is shown that spontaneous thermal ion-exchange can be used for the formation of gratings demonstrating Raman-Nath type light diffraction only. Electrically stimulated ion exchange can be applied for the formation of gratings diffracting similar to 60-80% of incident light in one diffraction order. However, thick diffraction gratings demonstrating high angular selectivity can hardly be formed by this method. The range of achievable grating periodicities and phase modulation depths are estimated based on the glass parameters, the temperature of the ion-exchange process, and driving electric field strength. (c) 2005 Elsevier B.V. All rights reserved.
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