Liquid Crystal Integrated Dynamic Terahertz Metalenses

Abstract Metasurfaces can freely manipulate the wavefront of electromagnetic waves with the merits of minimization and integration. Dynamic metadevices have continued to be urgently pursued to realize on‐demand functionalities. Among them, dynamic metalenses have attracted particular attention due to their widespread applications, especially in the promising terahertz region. Here, a liquid crystal integrated terahertz metalens with dynamic focusing properties is proposed. Subwavelength silicon columns are specifically designed and set to realize the same lens phase profile for orthogonal linear polarizations, while the rotation of columns additionally introduces a spin‐selective conjugated geometric phase. A photopatterned liquid crystal layer is added to compensate for the geometric phase; therefore, a polarization‐independent single focus is achieved. With a saturated bias applied to the liquid crystal, the phase compensation vanishes; therefore, a spin‐selective bifocal function is realized. When lens and polarization grating profiles are encoded to the geometric phase separately, longitudinal and lateral spin‐dependent focus separations are demonstrated. The metalens can be electrically switched between single‐focus and bifocal functions. The dynamic metalens can be utilized in depth‐of‐field imaging and telecom port selection. The design endows various existing metadevices with dynamic functions.