A switchable and rotatable chiral nematic liquid crystal diffraction grating for beam-steering technology

This paper presents a switchable and rotatable chiral nematic liquid crystal (LC) diffraction grating that can be operated using low applied voltages at room temperature. A chiral nematic LC mixture is prepared such that the thickness (d) to pitch (p) ratio is set to 1.85, enabling the formation of a uniform lying helix configuration when combined with homeotropic alignment layers and the appropriate electric field conditions, resulting in the formation of a diffraction grating. The addition of a small concentration by weight of the LC dimer, CB7CB, is found to lead to an asymmetry in the flexoelectro-optic tilt angle, generating torque on the helix axis, which in turn enables a uniform 360° in-plane rotation of the diffraction grating and the corresponding far-field diffraction pattern. Results are presented to demonstrate that this rotation of the diffraction grating and subsequent rotation in the diffraction pattern requires the application of tailored voltage waveforms with adjustable temporal parameters. Furthermore, analysis of the normalized intensity of the zero-order reveals systematic correlations with the temporal parameters of the waveform, while exhibiting dependence on the incident light polarization. These findings offer promising insights into the potential development of advanced beam-steering devices.