| 摘要 |
A variable index-of-refraction optical medium of certain minimum thickness and periodicity with respect to the wavelength of incident light-if it meets certain specified constraints with respect to (1) relative indices-of-refraction of both its internal structure and that of its surroundings and (2) relative values of incident wavelength to periodicity and the relative indices-of-refraction-operates to produce both angularly-dependent subtractive-color filter reflection spectra and subtractive-color filter transmission spectra in accordance with its physical parameters. Such filters are suitable for use as authenticating devices for sheet-material authenticated items. |
