2021 - Polarization Manipulation Using a Dielectric Metasurface
Dielectric optical metasurfaces enable us to control transmitted light phase without absorption losses and thus the functionality of traditional optical components can be replicated with high efficiency yet with the reduced footprint. Some of the interactions which determine the change in phase of light after transmission though a metasurface building block (a nanostructure) are polarization sensitive. This fact is used in the presented metasurface, which acts as a half-wave plate. If located between two crossed (or two parallel) polarizers, the metasurface transmits light with defined linear polarization and with two different (additive or subtractive) colors, as illustrated in Fig. 1.
Fig. 1 Basic principle of the metasurface building block functionality. (a) A system of two crossed polarizers by itself does not transmit any light. (b) A system of two parallel polarizers by itself transmits all light. (c) By adding a half-wave-plate metasurface building block into the system of two crossed polarizers, we add a specific (additive) color to the previously null transmission. (d) By adding the same building block into the system of two parallel polarizers, we lower the transmission function of this system and thus obtain a specific (subtractive) color of transmitted light.
The fabrication of the dielectric metasurface was realized in cooperation with the Institute of Scientific Instruments of the Czech Academy of Sciences. There, using high-energy electron beam lithography, a resist mask was created for the preparation of metasurface building block with high aspect ratio between their height and their lateral dimensions (see Fig. 2). The resist mask was filled with titanium dioxide using atomic layer deposition method. The residual oxide layer was removed with ion beam etching thus revealing the resist mask, which was then stripped away by an oxygen plasma.
Fig. 2.Fabriaction of the metasurface. On a fused silica substrate, we spincoated a resist layer which was patterned with electron beam lithography into a masking shape for atomic layer deposition. By repetition of the deposition process, the mask was filled with titanium dioxide and then, the residual TiO2 layer and resist mask were removed with dry etching methods.
The design of individual metasurface building blocks was based on numerical simulations of their optical response in the configuration of two crossed and parallel polarizers. The fabricated metasurface was characterized structurally, using scanning electron microscopy, and optically, to confirm the simulation’s conclusions and verify the designed functionality of the metasurface in experiment. The results of the metasurface building block characterization are summarized in Fig. 3.
