Tunable polarization volume gratings based on blue phase liquid crystals

Area of Science:

• Materials Science
• Optics
• Crystallography

Background:

• Chiral liquid crystals, specifically blue phases (BPs), exhibit unique optical properties due to their three-dimensional ordered structures.
• Polarization volume gratings (PVGs) are crucial optical components with applications in various photonic devices.

Purpose of the Study:

• To demonstrate a large-angle polarization volume grating (PVG) with circular-polarization selectivity.
• To investigate the alignment and structural behavior of blue phase liquid crystals on patterned substrates.
• To explore the tunability of the PVG for potential applications.

Main Methods:

• Fabrication of a PVG using blue phase II liquid crystal with simple cubic symmetry.
• Utilizing periodically patterned substrates to achieve defect-free alignment of the blue phase crystal.
• Employing Kossel diagrams and far-field diffraction patterns to analyze the crystal structure and lattice behavior.
• Exploiting the external field-responsivity of blue phases for tunability.

Main Results:

• Successful demonstration of a large-angle PVG with circular-polarization selectivity.
• Achieved defect-free alignment of the blue phase crystal on substrates with periods as small as 700 nm.
• Observed lattice slant within the cell to accommodate the imprinted pattern, confirmed by diffraction analysis.
• Demonstrated tunability of the PVG by applying external fields.

Conclusions:

• The developed PVG, based on blue phase liquid crystals, offers high performance in terms of angle and polarization selectivity.
• The ability to tune the PVG using external fields significantly enhances its applicability.
• This technology holds promise for advanced tunable photonics and augmented reality systems.