Tunable optical elements based on light actuated fluid-fluid interface

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Tunable optical elements are gaining increased attention over the conventional solid based optical systems, as they provide a potential route towards the realization of portable optical or optofluidic devices. Tuning optical properties utilizing semiconductor technology, deformable solid materials, liquid crystals, porous nanostructures and fluid-fluid interfaces have been reported. However, fluid-fluid interface offers added advantages such as dynamic, reconfigurable, and self-healing capabilities with less complex fabrication steps compared to the solid based optical elements. Electrowetting, dielectrophoretic effect magnetic actuation, thermal actuation and pneumatic actuation are the widely followed fluid based techniques to realize tunable optical components. The major disadvantages of these methods are the use of peripheral components/specific fluids which limit their applicability. Methods utilizing optically actuated interface can overcome these limitations as they provide a non-contact and additive free way of manipulating the interface. In our lab, we try to address these challenges and attempts to provide new optofluidic strategies to realize reconfigurable optical elements. In this regard, we had demonstrated a dual functional optofluidic strategy where a single device can operate as either optical switch or liquid lens with variable focal length, or both the functions simultaneously. The strategy relies on light-controlled expansion/contraction of an air plug confined in a minichannel filled with water. The air plug acts as a mediator for switchable total internal reflection (TIR) (light switch) and a liquid actuator (liquid lens).