Reinforced design method for moiré metalens with large spacing

Although metalens has attracted many research interests for its advantages of light weight, ultrathin size, and high design freedom in realizing achromatic and aberration-free optical devices, it still lacks adjustability in zoomable optical systems. Moiré metalens, which consists of two cascaded metasurface layers, can realize large focus tuning range by the mutual rotation of the two layers, and becomes a possible solution to realize real application of reconfigurable metalenses. However, due to the spacing between the two metasurface layers, it suffers from aberration caused by diffraction, leading to a dramatically decreased efficiency with the spacing. In this paper, we propose a reinforced design method for moiré metalenses with large spacing based on diffraction optics. Simulation results demonstrate that at the wavelength of 810 nm, when the spacing of the two metasurfaces is 10λ, the focusing efficiency of the reinforced moiré metalens is 3.4 times larger than the traditional moiré metalens. Furthermore, in order to consider the situation that the spacing between the two metasurfaces cannot be controlled precisely, we also propose a reinforced design method for multiplex spacings, which can make the device maintain a high focusing efficiency (3 times larger than the traditional moiré metalens) for the spacing in a range of 6λ∼10λ. The new design method is anticipated to be applied in realizing tunable metalenses in integrated continuously zoomable optical systems.