LAUSR

The subwavelength grating microlens has attracted much attention due to its variety of potential applications. Instead of the vertical sidewall profile normally considered by most recent works, a tapered sidewall profile is often obtained during current fabrication processes, especially during the fabrication of high aspect ratio structures. In this work, we have discovered that a tapered sidewall profile may have a significant destructive effect on the concentration properties of subwavelength concentrating lenses/metasurfaces. This is caused by the phase shift from the tapered profile that affects each individual phase shifter. More interestingly, we have further discovered that there exist some period/fill-factor combinations for phase shifters that "resist" the phase shift from the tapered structure. This study will provide an important avenue for the design of subwavelength concentrating lenses/metasurfaces when dealing with the tapered sidewall profile.