ABILITY AND LIMITATION OF EFFECTIVE-MEDIUM THEORY FOR SUBWAVELENGTH GRATINGS

In the recent researches of subwavelength relief gratings, the effecti ve refractive indices are used for calculating the coefficients of ref lection and transmission of light waves. The effective refractive indi ces are given by the effective medium theory for light waves propagati ng in a bulky stratified medium. This paper describes the ability and limitation of the theory applied to estimate the performance of such s ubwavelength gratings. The limitation is revealed by numerical calcula tions using a rigorous electromagnetic grating theory and the effectiv e medium theory. As a result, an understanding of the wave behavior in the subwavelength grating has been acquired, which explains the limit ation of the effective medium theory.