Half-wave phase retarder working in transmission around 630nm realized by atomic layer deposition of sub-wavelength gratings

The realization of half wave phase retarders based on subwavelength periodic gratings typically requires small periods with large aspect ratio features. The required aspect ratio of the grating features can be considerably decreased when high refractive index materials are employed. Because the nano-structuring and processing of such dielectrics is quite difficult, we have designed and developed a half-wave retarder relying on (low index) fused silica (SiO2) gratings that are over-coated by titanium dioxide (TiO2) using atomic layer deposition. The period and depth of the fabricated structures are 400nm and 1700nm, respectively. Half-wave retardation is achieved at 628nm and the total transmission lies above 90%.