Abstract

Electromagnetic theory is used to study grating diffraction when the grating period optical wavelength are about equal. When electromagnetic theory is used some interesting nonintuitive phenomena have been predicted and subsequently observed through microwave experiments. Consider the experiment of scattering light of wavelength from a grating with period d. To begin d ≫ λ and the usual multiple grating orders are observed. As the wavelength is increased, the grating orders fan out, away from the zero order or specular reflection term. As the orders become parallel to the grating surface they become evanescent or nonpropagating. We eventually reach a point where only three orders propagate: the 0 order and the ±1 orders. Now something interesting happens for oblique incidence. As the wavelength λ approaches the grating period in dimension, only one grating order, the -1 order, appears to be a propagating order. There is virtually no light propagating in either the 0 or +1 diffraction order. As the dimension of the wavelength continues to increase an abrupt, almost discontinuous, change in the diffracted light occurs as the light switches from the -1 order to the 0 order. This effect has been observed in the microwave region and predicted by numerical models. Numerical methods have been developed to deal with 2-D gratings as well as multiple layers of dielectric gratings. Our purpose is to foster greater communication between the microdiffractive optics community and the photonic band gap community.

© 1991 Optical Society of America