Gratings of dielectric material can act as homogeneous birefringent materials if the wavelength of the incident radiation is greater than twice the period of the grating. For the case of square profile gratings, simple equations predict the birefringence versus linewidth-to-period ratio of the gratings. By using x-ray lithography and reactive ion etching, 240-nm period gratings of polymethylmethacrylate and silicon nitride were fabricated with various linewidths. The birefringence of these was measured at 632.8 nm and found to agree closely with the theory. Silicon nitride gratings which act as half-wave and quarter-wave plates in the visible were made.

Uniform crystallographic orientation of silicon films, 500 nm thick, has been achieved on amorphous fused-silica substrates by laser crystallization of amorphous silicon deposited over surface-relief gratings etched into the substrates. The gratings had a square-wave cross section with a 3.8-μm spatial period and a 100-nm depth. The 〈100〉 directions in the silicon were parallel to the grating and perpendicular to the substrate plane. We propose that orientation of overlayer films induced by artificial surface patterns be called graphoepitaxy.

Spatial-period (320-nm) square-wave gratings fabricated on amorphous SiO2 substrates were used to produce uniform alignment of the director in nematic and smectic liquid-crystal layers. This demonstrates that molecular alignment can be achieved using surface structures fabricated by a planar process. A novel method of producing twisted-nematic liquid-crystal displays using surface gratings is described.