Electro-tunable achromatic polarization rotator

Manipulating the polarization orientation of light is essential in modern optics, biology, and related fields, but the strong optical dispersion inherent in current polarization rotators severely restricts their use to single-frequency lasers and their flexibility in system design. Many attempts have been made to realize dispersionless polarization rotation, usually by designing a complex set of wave plates with mutually compensated dispersions. Here, enabled by a thin cell of hybrid splay–twist liquid crystal, we demonstrate a tunable achromatic polarization rotator that is free of dispersion engineering. The optic axis distribution in the liquid crystal cell can be dynamically controlled by an applied electric field and allows an input polarization vector to be continuously rotated up to 90° (or 180° in a tandem-cell geometry) in an adiabatic and nondispersive manner. The proposed mechanism can be further implemented to construct spatial light modulators for single-path ultrabroadband generation of complex vector fields from uniformly polarized light.