Fabrication and performance of efficient thin circular polarization gratings with Bragg properties using bulk photo-alignment of a liquid crystalline polymer
- 115 Downloads
Thin circular polarization gratings, characterized by high diffraction efficiency and large, up to 42°, diffraction angles were created by polarization holography for the first time. The high efficiency of the gratings is the result of the specific properties of a photo-crosslinkable liquid crystalline polymer and a two-step photochemical/thermal processing procedure. A diffraction efficiency of up to 98% at 532 nm has been achieved for gratings with periods of 700 nm. In contrast to polarization gratings with larger periods these gratings exhibit Bragg properties. So one beam is either transmitted or diffracted depending on the direction of the circular polarization of the incident light, whereas the maximal diffraction efficiency is achieved only at the proper incident angle. The fabrication procedure consists of holographic exposure of the film at room temperature which provides the photo-selective cycloaddition of cinnamic ester groups. Upon subsequent thermal annealing above Tg bulk photo-alignment of the LC polymer film occurs enhancing the optical anisotropy within the grating. The holographic patterning provides high spatial resolution, the arbitrary orientation of the LC director as well as high optical quality, thermal and chemical stability of the final gratings. Highly efficient symmetric and slanted circular polarization gratings were fabricated with the proposed technique.
The authors gratefully acknowledge the support of the ZIM Program of the Bundesministerium für Wirtschaft und Technologie (BMWi) of Germany, ZIM/KF Project 2302408UW2. The authors wish to thank to M. Paech for providing the material systhesis and to R. Rosenhauer for her contributions to the material processing procedure and for the films preparation.
- 3.I. Shatalin, V. Kakichashvili, Sh. Kakichashvili: Sov. Tech. Phys. Lett. 13, 1051 (1987)Google Scholar
- 7.E. Nicolescu, M. Escuti, Proc. SPIE. 7050, 1 (2008)Google Scholar
- 9.B. Kress, T. Starner,: Proc. SPIE 8720. 87200A-13 (2012)Google Scholar
- 13.E. Collett, (Polarized Light: Fundamentals and Applications (Dekker, New York, 1993)Google Scholar
- 19.H. Ono, N. Kawatsuki, AZojomo. 1, 1 (2005)Google Scholar
- 21.R. Rosenhauer, Th Fischer, C. Czapla, J. Stumpe, A. Viñuales, M. Pinol, J. Serrano: Mol. Cryst. Liq. Cryst. 364, 295 (2001)Google Scholar
- 24.H. Kogelnik, Bell Syst. Tech. J. 488, 2909 (1969)Google Scholar
- 26.M. Ishiguro, D. Sato, A. Shishido, T. Ikeda: Langmuir. 23, 332 (2007)Google Scholar