Optically generated reconfigurable photonic structures of elastic quasiparticles in frustrated cholesteric liquid crystals

Abstract

We describe laser-induced two-dimensional periodic photonic structures formed by localized particle-like excitations in an untwisted confined cholesteric liquid crystal. The individual particle-like excitations (dubbed "Torons") contain three-dimensional twist of the liquid crystal director matched to the uniform background director field by topological point defects. Using both single-beam-steering and holographic pattern generation approaches, the periodic crystal lattices are tailored by tuning their periodicity, reorienting their crystallographic axes, and introducing defects. Moreover, these lattices can be dynamically reconfigurable: generated, modified, erased and then recreated, depending on the needs of a particular photonic application. This robust control is performed by tightly focused laser beams of power 10-100 mW and by low-frequency electric fields at voltages ~10 V applied to the transparent electrodes.

Subnanowatt Opto‐Molecular Generation of Localized Defects in Chiral Liquid Crystals

“…Optically induced metastable defect structures in chiral liquid crystals have been studied regarding their capabilities in terms of reconfi guration, [ 6 ] large-scale integration, [ 12 ] threedimensional photonic architectures, [ 13 ] phase masks up to millimeter square area [ 14 ] or arrays of microscopic optical vortex generators. [ 15 ] To date their application potential however remains limited.…”

“…Indeed, the reversible generation of a localized defect structure by focused light beams typically requires a 10-100 mW power budget with typical intensities ranging from 1-10 kW cm -2 for low numerical aperture focusing elements up to 0.1-1 MW cm -2 for high numerical aperture. [ 6,12 ] This implies a "point-by-point" laser writing strategy and, consequently, crippling fabrication times when considering the realization of large and dense arrays of them. [ 12,15 ] Still, a few years ago, an approach relying on photo-active achiral dopants has been proposed to reduce the power budget by a few orders of magnitude, down to 10 µW.…”

“…[ 6,12 ] This implies a "point-by-point" laser writing strategy and, consequently, crippling fabrication times when considering the realization of large and dense arrays of them. [ 12,15 ] Still, a few years ago, an approach relying on photo-active achiral dopants has been proposed to reduce the power budget by a few orders of magnitude, down to 10 µW. [ 16 ] However, such an improvement came at the expense of reversibility, as intrinsically irreversible photo-chemical processes are involved.…”

Laser-directed hierarchical assembly of liquid crystal defects and control of optical phase singularities

“…One of the major recent research efforts in soft matter and other branches of condensed matter physics is directed at control of topological defects using fields, colloids, optical tweezers, confinement, chirality, and other means3435363738394041424344. Our findings greatly extend the current capabilities and possibly also the utility of such control of defects.…”

“…The fingers structures can be unwound at applied voltages of 5 V and higher or modified at lower voltages within a typical response time of 5–10 ms, comparable to the response time of nematic LCs confined into cells of similar thickness17. In order to decrease the laser generation times, one can utilize holographic laser tweezers instead of the scanning-beam approach used in our current work212934, which may potentially shorten these times to ∼10 ms, comparable to the LC's response time.…”