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

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 pi 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.(c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement