Liquid crystal micro-Fresnel zone plate with fine variable focusing properties

Abstract

This study presents a liquid crystal micro-Fresnel zone plate (LC-MFZP) with fine variable focusing properties. The LC-MFZPs are fabricated via photochemical processes without any mechanical process. The focusing properties are investigated through numerical simulations and experiments. LC-MFZPs can generate a focusing spot with a specific incident wavelength such that the transmitted phase difference between their adjacent ring zones is π rad. When this difference is changed by the electrical reorientation of the LCs, the focusing spot disappears because the diffraction condition is no longer satisfied. Subsequently, another focusing spot at a specific incident wavelength is generated to satisfy the diffraction condition. The positions of these focusing spots differ because the focal lengths depend on the incident wavelength. Consequently, LC-MFZPs can be used to electrically control the focal length. This study may find applications in optical manipulation and optical trapping.