Free-standing SU-8 subwavelength gratings fabricated by UV curing imprint

Fabrication technique for making subwavelength anti-reflective grating structures has been developed, based on nanoimprint of SU-8, for applications in the near infrared spectral range. The depth and duty cycle of the grating structures optimized for wavelengths around 1550 nm were calculated using rigorous theory of diffraction. The Si mold was made by electron-beam lithography and deep reactive ion etching. The mold structures were transferred to SU-8 by imprinting and followed by UV curing process. A bilayer process using PMMA as sacrificial layer was developed to release the SU-8 layer. The optical properties of the replicated SU-8 gratings were measured over a wide range of spectral wavelength. The general shapes of the curves are in good agreement with the calculations. The reflectivity has been reduced significantly.