Metasurfaces with freely varying height using grayscale lithography

Metasurfaces have come to the forefront of novel optics research due to their uniqueadvantages over traditional glass optics. Metasurfaces are often limited to consistingof features that are all the same height, due to the use of conventional semiconductorfabrication techniques. In this work, we introduce a grayscale e-beam lithography stepinto the standard ALD-damascene metasurface fabrication process to create dielectricmetasurfaces with varying height that operate in visible wavelengths. We show thatthis additional degree of freedom allows for more independent control of dispersion andphase applied to reflected light. This is due to quasi-periodic oscillations of both thephase and dispersion, which arise as the top of the metasurface becomes aligned withnodes or anti-nodes of the standing wave of the electric field created at a reflectivesurface underneath the meta atom. This novel degree of freedom of height variationof the metasurface can be useful for broadband metasurface applications that requireunique tailoring of dispersion, such as retardance correction in large space telescopes.