Room-temperature nanoimprint lithography to fabricate TiO2 subwavelength phase retarder

A room-temperature nanoimprint lithography (RT-NIL) is presented to fabricate subwavelength phase retarders by combining high-refractive-index TiO2 material, which shows some unique advantages in terms of lower cost, higher efficiency and better performances. The TiO2 subwavelength phase retarders are designed and analyzed by the rigorous coupled wave analysis, where the phase retardations of 130° to 60° from 370 to 780 nm are achieved. The phase retarders are fabricated by the RT-NIL, where the fabrication process is described in details, and SEM images of fabricated gratings are shown. Further, phase retardations and transmittances of the fabricated phase retarders are measured, which shows that the transmittances of TE polarization and TM polarization are stronger than 76 % and 85 % in visible region respectively, and the measured phase retardations agree well with the theoretical results, and the proposed RT-NIL technique is expected to find wide applications in fabrication of subwavelength optical devices in future.