In this article we report on the fabrication of 100 nm pitch gratings over a large area (similar to 10 cm(2)) using a simple, low-cost, fast process. This method includes (1) generation of the grating pattern using, interferometric lithography and spatial frequency doubling and (2) pattern replication using nanoimprint lithography. The form birefringence of a 100 nm pitch Si -rating was studied using ellipsometry. Measurements show an index difference of Delta n > 0.9 at a wavelength of 632.8 nm. The experimental data are in good agreement with effective medium theory. This indicates the possibility of using, these structures for wave plates and other subwavelength optical devices operating in the visible.