Reproducible electronically controlled Fresnel lens based on the principle of dielectric phase separation

Abstract

A Fresnel lens with controllable diffraction efficiency based on the dielectric-induced phase separation was demonstrated. Two immiscible liquids with a large difference in dielectric constants, i.e., nematic liquid crystal (MLC-2140, Δε ∼ 47.6) and optical adhesive (NOA 65, ε_p ∼ 5) are mixed thoroughly and injected into a cell. The cell consists of a bottom substrate featuring a concentric ring-patterned electrode, a top substrate of ordinary glass, with a cell gap of 10 μm. When an external electric field exceeding the threshold is applied, phase separation occurs between the two liquids, the liquid crystal with high dielectric constant moves towards to the edges of the electrode rings and accumulates on the surface of the electrode, while the optical adhesive moves to the gap between the electrodes, finally forming a liquid crystal/optical adhesive Fresnel lenses (LCOFLs) with the aperture of 3.5 mm. Upon removal of the applied voltage, the LCOFLs return to a state where liquid crystal microdroplets are randomly dispersed within the optical adhesive, at which point there is no lensing effect. The LCOFLs can be simply switched between focused and defocused states at a reasonable speed, and the diffraction efficiency can reach 36.3 %, approaching the ideal value of 40.5 %. The proposed LCOFLs exhibits several advantages, including lightweight design, low power consumption, ease of fabrication, and low cost, making it highly promising for applications in various fields such as spectrometers, projection displays, long-distance optical communication, and variable optical data storage systems using a zone plate modulator.