Fast foci alternation of a spatially divided ferroelectric liquid crystal Fresnel zone plate

Varifocal lenses are highly desirable in imaging, fabrications, and information displays. At present, the shifting among different foci can be realized via reconfiguring the phase profile of a liquid crystal (LC) integrated metalens, alternating the incident polarizations of a series of planar geometric phase lenses, etc. However, the former suffers from a slow response and complicated fabrication, while the latter lacks integration due to the multilayer architecture. In this work, we propose a compact design for a fast-varying focal Fresnel zone plate and demonstrate it with two spatially divided phase diagrams recorded in a ferroelectric liquid crystal (FLC). Under the electrically suppressed helix (ESH) mode, the director of FLC reorients toward ±22.5° with respect to the alignment direction under opposite electric fields (±5 V). An angle of 45° is preset to the alignment direction between the two spatially divided phase diagrams. Thereby, for a properly oriented linear polarization incidence, only one Fresnel zone plate works at the same time. Via alternating the polarity of the electric field, rapid switching of up to ~55 μs between two functions is thus obtained. The dynamic imaging alternation between two objects placed at distinct positions is verified using a non-polarizing-beam-splitter-integrated multiplexed optical path. This work provides a compact and high-speed way for dynamic focusing, which significantly expands the application of FLCs in planar optics and facilitates on-demand functionalities and system miniaturizations in modern informatics.