Abstract

Graded index coatings and step down multilayers in which the index is progressively decreased from the substrate index to the medium index are known to be excellent broadband antireflectors. The modified Fourier transform techniques developed and implemented at the NRCC are well suited to the synthesis of graded index films. They can also yield homogeneous multilayers. However they normally assume that the media on either side of the coating are the same. This obviously rules out the design of AR coatings. We have recently described preliminary results obtained by applying our computer program to a problem in which the external media were different, namely to the synthesis of graded index broadband AR coatings on germanium.¹ No constraints were imposed on the refractive indices. In this talk, we discuss the effects of restraining the refractive indices within a specified range of values. We show that good solutions continue to be possible. We give examples with refractive index profiles and optical performances that are quite comparable to published results obtained by other methods.

© 1990 Optical Society of America