Selective Crosslinking of Polyimide for Photonic Devices

Abstract

Vertically aligned nematic (VAN) liquid crystals (LC) are interesting for many photonics applications. The performance of VAN cells depends on different factors; the boundary interactions between the LC monolayer and the alignment layer surface are the most important ones. These interactions are determined by anchoring energy. A set of procedures have been developed to modify by crosslinking the alignment properties of a specific polyimide (PI) for VAN cells; this PI produces vertical alignment with a small pretilt. We used two diepoxides as crosslinking agent of PI. The cells show different switching voltages for crosslinked and not crosslinked areas in the device. A small variation of the voltage, such as 1–2 V, can be adequate to generate phase grating with vertically aligned cell.

Keywords:

• alignment layer
• crosslinking
• liquid crystals
• polyimide

Acknowledgments

The authors would like to acknowledge the financial aid from the project CIMA-CLIQ from the Ministerio de Educación y Ciencia of Spain. The authors would like to thank X. Nie and S.T. Wu, University of Central Florida, for helpful discussions regarding the polar anchoring measurements.