Switchable 3D liquid crystal grating generated by periodic photo-alignment on both substrates.

Area of Science:

• Materials Science
• Optics
• Condensed Matter Physics

Background:

• Photo-alignment techniques enable surface patterning for liquid crystal (LC) control.
• Diffraction gratings and interfering light patterns are used to induce complex LC structures.
• Elastic energy minimization is a key principle in LC self-organization.

Purpose of the Study:

• To develop a planar liquid crystal cell with a two-dimensional periodic structure using interfering circularly polarized light.
• To investigate the relationship between alignment pattern periodicity, cell thickness, and the resulting LC configuration.
• To explore voltage-tunable diffraction efficiency in the fabricated LC cell.

Main Methods:

• Illumination of photo-alignment layers with horizontal and vertical diffraction patterns of circularly polarized light.
• Utilizing Q-tensor theory for 3D equilibrium director distribution calculations via Finite Element (FE) simulations.
• Simulating near-field transmission profiles using Jones calculus and performing 2D Fourier transforms to determine diffraction efficiency.

Main Results:

• A complex LC configuration with periodicity in two dimensions was achieved.
• The observed structure's period exceeded the interference pattern's period, suggesting symmetry lowering reduces elastic energy.
• Voltage application allowed for tuning the power distribution across different diffraction orders.
• FE simulations accurately predicted the 3D director distribution and optical properties.

Conclusions:

• The study demonstrates a novel method for creating 2D periodic LC structures with tunable optical properties.
• Symmetry lowering in LC alignment can lead to reduced elastic energy and larger periodic structures.
• The developed LC cell offers voltage-controlled diffraction, opening possibilities for advanced optical devices.