Discrete thin-film layer thickness modulation.
A novel analytical thin-film design method is presented that is based on electrical engineering communication theory. The proposed thickness modulation describes the thickness modulation of discrete, homogeneous thin-film layers of a multilayer coating. One modulation scheme, amplitude modulation, is presented in which analytical equations determine individual layer thicknesses for a given modulation amplitude, carrier frequency (f(c)), direct-current bias, as well as several layers and refractive indices. The spectral performance (especially stop bands) of multilayer coatings with alternating layers of two refractive indices is presented for different carrier frequencies and modulation amplitudes. For f(c) </= 1, the ratio of the center frequencies of the first-order (f(1)) and the next present stop band (f(2)) is determined analytically from the modulation frequency for which f(2)/f(1) = 2f(c) + 1. Particular cases of the carrier frequency produce virtual stop bands below the spectral frequency of the first-order stop band as well as high-frequency harmonics. Degenerate and other cases of thickness-modulated designs are presented, along with other modulation methods.
Perilloux
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