Effective-medium theory of sinusoidally modulated volume holograms

Zeroth-order effective-medium theory is applied to sinusoidally modulated volume holograms for which the period of the grating is much smaller than the illumination wavelength. These holograms can be modeled as negative uniaxial films, with the effective ordinary and extraordinary permittivities being determined by the small-period quasi-static approximation. The limits of validity of the small-period approximation are examined as a function of the wavelength-to-grating-period ratio (A:A) by rigorous coupled-wave theory. The limits are shown to be more restrictive for slanted holograms and for conically incident waves than for unslanted holograms and nonconically incident waves.