High-Density Topological Defect Array by Two-Step Interference Photoalignment

Area of Science:

• Nematic liquid crystals (LCs)
• Topological defect engineering
• Photonic device fabrication

Background:

• Topological defects in nematic LCs are crucial for generating laser beams with orbital angular momentum.
• Previous methods using spatial light modulators or digital mirror devices achieved defect arrays but limited defect density.
• Pixel-based approaches restrict the achievable density of topological defects in LC devices.

Purpose of the Study:

• To propose and demonstrate a scalable method for achieving a significantly higher density of topological defects in LCs.
• To overcome the limitations of pixel-based photoalignment techniques.
• To enable the fabrication of novel optical components with enhanced functionalities.

Main Methods:

• A two-step interference illumination process was employed for photoalignment.
• Step 1: Interference of two circularly polarized beams to generate a rotating director pattern.
• Step 2: Two-beam interference for amplitude modulation to introduce defects, with controlled illumination doses and angles.

Main Results:

• Achieved a much higher density of topological defects compared to previous methods.
• Fabricated 2D defect patterns with a minimum spacing of 1.25 micrometers.
• Demonstrated the generation of a high defect density grid through a scalable two-step photoalignment procedure.

Conclusions:

• The proposed two-step interference illumination method is a scalable and effective technique for creating high-density LC topological defects.
• This approach bridges the gap between liquid crystal topological optics and metasurfaces.
• Enables the development of optical components with large-angle diffraction capabilities.