Polymer‐Stabilized Monodomain Blue Phase Diffraction Grating

Abstract

are self-assembled in a thermodynamically spontaneous way when chirality is about several hundreds of nanometers. LC directors are doubly twisted at this high chirality and self-assembled into a double-twisted cylinder (DTC). The way that the DTCs are stacked determines the symmetry of the BPLC structure, and the lattice length scale in common includes the visible wavelength, which appears as colorful micrographic textures. From an application perspective, a remarkable breakthrough is that polymer-stabilization method is able to extend their narrow temperature range. [6] Dispersion of nanoparticles (organic/inorganic colloids and perovskite quantum dots) or bent-core LCs and 3D confinement of BPLC like microencapsulation is also reported that it can extend the temperature range of BPs. [7][8][9][10] The polymer-stabilized BPLC (PS-BPLC) by in situ photopolymerization is a promising method not only for extending the BP temperature range but also for enhancing their electro-optic performance, such as optical isotropy, [11] selective reflection, [12] less hysteresis, [13] and fast response time. [14] Despite a successful prototyping into a PS-BPLC display, [4] the PS-BPLC has rather shown their possibility of applying to versatile photonic applications such as a diffraction grating, [15] vortex beam ] have been reported by using BPLC materials because these are advantageous for the non-mechanical beam steering. Such results support that BPLC is one of the promising materials to create such novel functional devices. However, the performance of the device is deteriorated by the multidomain structure of BPLCs. For example, the diffraction efficiency decreases significantly. Despite such importance, less attention has been paid to create and study about monodomain BPLCs for diffraction gratings among several studies previously reported. [16,[25][26][27] Some approaches report that, to resolve the unwanted multiple colors from polycrystalline lattice structure, one can adjust the chiral pitch of BPLCs and have the Bragg wavelength shifted far away from the wavelength of device operation. For instance, when the desired wavelength is within the visible region, one can control the chiral pitch to position the Bragg wavelength within UV region. However, this approach is limited to an The structural beauty of liquid crystalline blue phases is attested not only by their colorful optical micrographic textures but also by optical isotropy. More importantly, the homogeneity of the structures influences greatly to the electro-optic properties. In this work, how the lattice orientation in polymerstabilized blue phase liquid crystal (PS-BPLC) diffraction grating affects phase-modulated diffraction efficiency is elaborated. A well-arranged monodomain structure of blue phase is achieved and its diffraction capability is compared with multidomain PS-BPLC. The diffraction efficiency in the zeroth order of monodomain PS-BPLC is improved by 9% compared to that of multidomain structure. In addition, both driving and threshold voltages in m...

Blue Phase Liquid Crystals with Tailored Crystal Orientation for Photonic Applications

“…The electric field induced the LC birefringence owing to the Kerr effect, causing spatial modulation of the refractive index. Because the regular arrangement of the monodomain BPs has a long coherence length, the driving voltage was reduced by 29% with the improved diffraction efficiency by 9% (Figure 3f,g) [44]. The 3D orientation behavior of the BPs was investigated by observing the phase transitions of the BPs using two types of unidirectionally anchored surfaces [45].…”

Large-scale single-crystal blue phase through holography lithography

“…Usually, the BP fragments form inside the volume simultaneously as a phase transition occurs, leading to polydomain BP structures, which consist of many platelets of different orientations. The mismatches in polydomain BPs increase the scattering in the volume and affect the reflectivity of the Bragg reflection and the optical-electrical properties of BPs 25 – 29 Recent studies indicate that several methods, such as electric fields, 30 – 32 thermal control, 33 and surface treatments 34 – 36 can be applied to form monodomain BPs, which consist of many single-crystal platelets with one lattice plane orientated in the same direction.…”

Dynamic Surface Wrinkles for In Situ Light-Driven Dynamic Gratings

“…The key point for a DDG is the fabrication of dynamic periodic micro/nanostructures; however, most of the periodic grating structures realized by imprint, photolithography, or polarization holography are not dynamic. − Nowadays, several DDGs based only on liquid crystal materials are obtained. − They often require expensive molecules and complicated manufacturing processes . The liquid crystal thermodynamic properties also limit the arrangement of periodic structures and consequently the diversity of the diffraction pattern. ,,, Generally, they cannot be designed top-down.…”