We have previously shown through simulation that an optical beam deflector based on the Pancharatnam (geometric) phase can provide high efficiency with up to 80° deflection using a dual-twist structure for polarization-state control [Appl. Opt.54, 10035 (2015)]. In this report, we demonstrate that its optical performance is as predicted and far beyond what could be expected for a conventional diffractive optical device. We provide details about construction and characterization of a ± 40° beam-steering device with 90% diffraction efficiency based on our dual-twist design at a 633nm wavelength.
Liquid crystal photonic devices are becoming increasingly popular. These devices often present a challenge when it comes to creating a robust alignment layer in pre-assembled cells. In this paper, we describe a method of infusing a dye into a microcavity to produce an effective photo-definable alignment layer. However, previous research on such alignment layers has shown that they have limited stability, particularly against subsequent light exposure. As such, we further describe a method of utilizing a pre-polymer, infused into the microcavity along with the liquid crystal, to provide photostability. We demonstrate that the polymer layer, formed under ultraviolet irradiation of liquid crystal cells, has been effectively localized to a thin region near the substrate surface and provides a significant improvement in the photostability of the liquid crystal alignment. This versatile alignment layer method, capable of being utilized in devices from the described microcavities to displays, offers significant promise for new photonics applications.
In this work, the detailed studies of surface polymerization stabilizing liquid crystal formed on an azodye sublayer are presented. The surface localized stabilization is obtained by free-radical polymerization of a dilute solution of a bi-functional reactive monomer (RM) in a liquid crystal (LC) solvent. To optimize the process for surface localized stabilization, we investigate the effects of several process parameters including RM concentration in LC hosts, the types of materials (either RM or LC), the photo-initiator (PI) concentration, ultra-violet (UV) polymerization intensity, and the UV curing temperature. The quality of surface localized stabilization is characterized and/or evaluated by optical microscopy, electro-optical behavior (transmission/voltage curve), the life test, and photo-bleaching. Our results show that, by carefully selecting materials, formulating mixtures, and controlling the polymerizing variables, the RM polymerization can be realized either at the surface or through the bulk. Overall, the combination of surface localized stabilization and photo-alignment offers an elegant and dynamic solution for controlling the alignment for LC, which could play a profound role in almost all liquid crystal optical devices.
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