D.E. Jung, V.J. Einck, L. Verrastro, A. Arbabi, J.J. Watkins
University of Massachsuetts,
Keywords: metalens, flat optics, nanoimprint, metasurface
Summary:We report the rapid fabrication of all-inorganic visible wavelength metalenses with numerical apertures of 0.2 and absolute efficiencies of greater than 75% (more than 90% of the design efficiency) using large area masters and nanoimprint lithography (NIL) with imprint cycle times of 2 minutes. We employ atomic layer deposition (ALD) as a post-imprint treatment to enable tuning of the refractive index from 1.9 to 2.2 using a small number of cycles (less than 20), which improves lens efficiency. The ability to tune the RI of the imprinted optics to match that of the substrates removes concerns about the thickness of the residual layer in the device, resolving an issue for the use of NIL in some applications. Additional cycles of ALD can further be used to precisely tune feature dimensions and feature spacings within the device to optimize performance and to offset shrinkage relative to the master. We further demonstrate the excellent optical and material stabilities of the all-inorganic imprinted optics. The approach yields a cost effective, scalable manufacturing platform for planar optics for metalenses, diffractive optical elements, displays, and waveguides for AR/VR.