Nanoscale of biomimetic moth eye structures exhibiting inverse polarization phenomena at the Brewster angle

Abstract

The unique functionalities of nanoscale structures in the natural world are an inspiration to the development of new nano-manufacturing techniques. For example, the cornea of the moth's eye features a sub-wavelength natural antireflective architecture. To date, almost all optical research into moth eye structures has been focused on their antireflective properties. No studies of inverse polarization phenomena at the Brewster angle have been reported, especially in biomimetic structures. For the first time, we discovered a unique inverse polarization phenomenon on moth eye structures that arises from TM-polarized light having a higher reflectance than TE-polarized light on moth eye structures at angles of incidence near the Brewster angle, unlike the behavior of polarized light on flat interfaces. Herein, we report a one-step colloidal lithography process that allows the fabrication of several kinds of moth eye structures. We characterized these moth eye structures experimentally and through rigorous coupled-wave analysis to understand the mechanism underlying this inverse polarization phenomenon in both visible and near infrared ray (NIR) regimes. Controlling the structural height and degree of non-close-packing of the moth eye structures had a dramatic effect on the extent of inverse polarization. This study is potentially important for various polarization-dependent devices and measurements.