Polarization beam-splitting metasurfaces analyzed using the finite-difference time-domain software EMTL

Abstract

Using the FDTD solver EMTL, as well as a new way of thinking about metasurfaces, the primary innovation of this thesis was to take two individual birefringent patterns and interleave them in a checkered pattern. This improved output symmetry, especially with regards to intensity as it ensured that all secondary plasmonic interactions happened with a super-period equal to the common period of the two patterns, instead of happening with the periodicity of either pattern. This shifted the output of the secondary interactions to a separate angle from the desired output angles.

This design alteration was made possible by realizing that contiguousness was not required for the pattern to work, as one could obtain the same directionality by viewing each constituent block type of the metasurface as an infinitely repeating emitter. This analysis showed that the only demand for the metasurface property to be true was that the component size, i.e. the size of the gold nanoblocks on the substrate, had to be sub-wavelength. The EMTL simulations showed that a sparse grating with higher than wavelength separation between the blocks in the period still produced the predicted output.