Tunable and super-wide angle defocusing lens large phase modulator

Abstract

Traditional terahertz wavefront modulators exhibit significant limitations in controlling optical wavefronts. In order to address the adjustability issues of terahertz wavefront modulators, we have developed a novel optical device based on the tunability of Fermi energy levels. Structurally, we find the ability to modulate the Fermi energy levels of graphene by modulating the carrier concentration. We can also change the phase of the light, causing the transmission path of the light as it passes through the graphene array to change, affecting the position of the backfocusing focal point, thus realizing a dynamically adjustable backfocusing effect. Theoretically, employing Dirac notation and Matrix analyze, reveals the corresponding relationship between Fermi level and phase shift. Specifically, one group Fermi levels induces a set of modulated phase changes. Experimental results demonstrate that the proposed modulator offers a large phase modulation range, enabling 2π phase adjustments. Moreover, it accurately focuses on a predefined focal point located at 400 um, with a numerical aperture of 0.882, a resolution of 30.39, and a full-width at half-maximum of 38. The substantial numerical aperture and small full-width at half-maximum imply that the lens can focus more light while maintaining high resolution, enhanced optical efficiency, and concentrated light focusing. At the same time, by adjusting the position of the Fermi energy level, we have succeeded in realizing a wide-angle focusing effect up to 90°. This capability extends the terahertz wave’s focusing within a wide range, expanding the application scope of traditional focusing devices.