Smart micro-optical components are emerging in many novel applications, such as lighting with tunable direction, micro lens with multiple focus lengths in camera and sun light collectors etc.. Most of those applications are based on the mechanical motors which are quite bulky and costly. Micro-electromechanical systems (MEMS) have good advantages (more compact, non-mechanical) for smart components, but it is not applicable for large areas. Liquid crystal has switchable birefringence with electric field above the threshold, if the electric field varies in space, liquid crystal directors at different positions will orient accordingly, and the effective refractive index for a specific polarized light could form lens/prim shape like profile to steer the light. In this study, we use multiple electrodes on one glass substrate and another glass plate with conductive layer (counterglass) to enclose the LCs. With different voltages applied to these strip electrodes, gradient refractive index appears within the device, and deflects the light. Another approach is to use a high resistive layer to form a voltage drop instead of multiple electrodes within one pitch, which can also get the GRIN liquid crystal gratings for light steering.
Fig.1 (a) GRIN liquid crystal gratings with multiple electrodes; (b) GRIN liquid crystal gratings with high resistive layers;
In this study, two approaches are adopted to fabricate the GRIN liquid crystal gratings: multiple electrodes with different voltages and high resistive layer with two terminal voltages in one pitch. Each of them is assembled with conductive counterglass to form the liquid crystal gratings; Several masks with different electrode width and spacing, will be designed for the device fabrications; Different liquid crystal materials including blue phase will be filled into the gratings and optical characterization will be studied in detail with different voltages. At last, successful GRIN LC gratings will be used as demonstrators for the SECONDOS project.