Diffractive optical elements (DOEs) are increasingly used as miniaturized and lightweight components in photonic devices. Efficient steering of light can be obtained with the help of photoaligned liquid crystal (LC) devices that modulate the geometric phase of light. We study a multitude of diffractive LC structures, ranging from simple one-dimensional gratings with a periodically rotating surface alignment, to highly dispersive gratings, multi-stable gratings and different types of lenses. All these components are enabled by photoalignment technology, that allows to control the geometric phase of the transmitted or reflected light by locally varying the azimuthal anchoring direction of the LC. Next to the standard nematic LCs, we also investigate the use of chiral nematic LCs (with different chiral pitches) and dual-frequency nematic LCs. The use of short pitch chiral LC gives rise to highly efficient diffraction in reflective devices, as we have demonstrated in linear gratings and on- and off-axis lenses. Dual-frequency LC on the other hand allows to substantially enhance the diffraction efficiency over large angles in transmissive devices. Imposing well-designed anchoring patterns at the substrates also allows to obtain highly dispersive configurations or structures with hysteresis switching as a function of the applied electric field. In all case, the working principles of the component can be understood with the help of finite element Q-tensor simulations for the LC director.
Flat diffractive optics utilizing chiral liquid crystal (CLC) has gained a lot of interest as a potential in- and out-coupling technology for applications such as augmented reality and head-up display systems. The unique properties of CLC together with a photoalignment technique capable of inducing controlled variation of the optical axis within a thin liquid crystal layer make it possible to obtain a range of efficient optical components. These components typically operate in reflection mode and can possess a variety of optical functionalities. In this study, we investigate 2D diffraction gratings and holographic lenses that combine diffraction grating and lens functionalities.
Using the principle of photo-alignment it has become possible to pattern the orientation of liquid crystal on a substrate. With this approach liquid crystal gratings and lenses with high optical quality have been realized. Recently we have demonstrated that the period of the photo-alignment can be reduced below one micrometer. Chiral liquid crystal that is deposited on this photo-alignment layer will tilt its helical axis and circularly polarized light is diffracted over a certain angle with high yield. The resulting device behaves as a volume hologram with interesting properties: high reflectivity in a certain wavelength range, tunable diffraction angle and low scattering.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.