Blue-phase liquid crystals: synthesis and prospective applications in nonlinear image processing and self-action sensor protection

Conventional methods of synthesizing large areal size monocrystalline Blue-Phase liquid crystals (BPLC’s) are extremely slow (take hours). We have discovered that using only an applied electric field at the high temperature end of the BPI phase near the BPI/BPII transition, one can rapidly (in minutes) obtain stable and large-areal size monocrystalline BPLC of various crystalline symmetries. In the so-called Reverse Electrostriction Directed Assembly technique, the polycrystalline BPLC sandwiched between alignment treated and ITO-coated cell windows is first brought to the uniformly aligned nematic phase by a strong millisecond-long electric field; the electric field is then abruptly reduced to and held at predetermined lower levels to allow molecular self-assembly in a controlled manner that prohibit random crystallite formation and at the same time direct the merging of the crystallites into a large crystal with all principal crystal axes in alignment. Using REDA, large areal size monocrystalline BPLCs of various symmetries (tetragonal, orthorhombic, cubic) form and stabilize in minutes and remain stable even after the applied field is turned off. Due to crystalline uniformity over a large area, monocrystalline BPLC’s possess several advantageous features compared to their polycrystalline counterparts such as improved efficiency, resolution and overall image quality in optical wave-mixing based real time holography and image processing as well as passive optical limiting applications. Nonlinear optical responses of a BPLC or a BPLC/nanostructure (e.g., metasurface) layer may also be used as nonlinear function in optical neural network operations, enabling intensity-dependent transformations essential for computing tasks.