Multi-twist retarders: broadband retardation control using self-aligning reactive liquid crystal layers

Area of Science:

• Optics and Photonics
• Materials Science

Background:

• Polarization control is crucial in various optical systems.
• Traditional retarders often suffer from limited bandwidth and complex assembly.
• Achieving broadband achromatic polarization control remains a significant challenge.

Purpose of the Study:

• To introduce and characterize a new class of birefringent elements: Multi-Twist Retarders (MTRs).
• To demonstrate the potential of MTRs for effective broadband polarization transformation.
• To explore MTRs for achromatic quarter- and half-wave applications.

Main Methods:

• Development of MTRs using two or more twisted liquid crystal layers on a single substrate with a single alignment layer.
• Utilizing a numerical design method for optimizing MTR performance.
• Fabrication and experimental validation of quarter-wave MTRs using a polymerizable liquid crystal.

Main Results:

• MTRs exhibit continuously varying optic axis due to direct layer-to-layer alignment, simplifying fabrication and ensuring registration.
• Achieved excellent achromaticity in quarter-wave MTRs across broad bandwidths (450-650 nm and 400-800 nm).
• Performance of two- to three-layer MTRs matches or surpasses traditional multi-retarder approaches.

Conclusions:

• MTRs offer a promising solution for broadband polarization control with simplified fabrication.
• The design flexibility of MTRs makes them suitable for patterned achromatic retarders.
• MTRs can be engineered for large bandwidth and low retardation variation across visible to infrared spectra.