Abstract

Subwavelength (SW) dielectric transmission gratings can serve as antireflection (AR) devices, wave plates, narrow-band filters, and other optical elements. They are very attractive to future integrated optics, because of the possibility of producing a large array of different optical elements at different locations a substrate by using simple grating structures and a single fabrication step. However, because of the fine period required, most previous investigations were theoretical¹; experimental studies are a few and limited. For example, gratings previously studied were made of low-dielectric-constant materials, such as photoresist,² quartz,³ PMMA (polymethylmethacrylate), and silicon nitride,⁴ giving small refractive-index modulation. Furthermore, all previous experiments have shown consistency with simple-form birefringence theory or effective-medium theory,⁵ which predicts that the gratings should have little polarization, and that birefringence should be almost constant as long as the period is less than the wavelength. In this paper, we report fabrication and investigation of subwavelength amorphous silicon (high refractive index) transmission gratings of various periods on silica substrates. For normally incident light (λ= 633 nm), in addition to large birefringence we observed strong polarization effects.

© 1995 Optical Society of America