Three-dimensionally programmable soft crystals toward geometric phase photonics.

Blue phases (BPs), as highly chiral liquid crystalline phases with soft photonic structures, have recently emerged as competitive candidates for advanced optical applications. However, to date, it is still a big challenge to fabricate monodomains of BPs with programmed lattice orientation and manipulate their geometric phase optical properties, especially for BPI with body-centered cubic structures. In this work, we propose an electrically modulated polarization grating based on polymer-stabilized BP (PSBP) monodomains, with each monodomain being composed of BPI crystals with a programmed azimuthal orientation. The in situ experiments reveal that under a biased direct current (DC) electric field, the BPI crystals confined in polymer networks experience a serial 3D lattice deformation that is different from that of pure BPI crystals, which further enables a reversible tuning of the Bragg reflection band of the element over 200 nm in the visible range with a high diffraction efficiency. Our work provides new insights into the future applications of soft crystals in geometric phase optical elements, such as new displays and integrated photonics with 3D tunable optical properties. [ABSTRACT FROM AUTHOR]