A tunable optofluidic lens based on combined effect of hydrodynamics and electroosmosis

This paper presents the modeling and experimental results of a liquid-core liquid-cladding optofluidic lens under the combined effect of hydrodynamics and electroosmosis. To allow the lens to be tuned by a voltage, the cladding fluids are electrically conducting, while the core fluid is non-conducting. Under constant flow rates, mathematical models of two-dimensional dipole flow in a circularly bounded domain and electric field outside the parallel-plate capacitor were used to predict the curvature of the interface. A test device with a circular lens chamber with 2 mm diameter and 250 mu m height was fabricated in polymethylmethacrylate (PMMA) using thermal bounding method. Two cladding fluids (aqueous NaCl) and the core fluid (silicone oil) are introduced into the circular domain by syringe pumps. External electric fields are applied on the two cladding fluids. Under the same inlet volumetric flow rates, the applied voltages are varied to tune the curvature of the interfaces between the cladding fluids and the core fluid. The interface shape is measured using fluorescence imaging technique. The results show that the interfaces between the cladding fluids and the core fluid have optically smooth arc shape. Under fixed cladding flow rates, the same voltage forms symmetric biconvex lens only. Different voltages can form biconvex lens, plano-convex lens, and meniscus lens. The experimental results agree well with the presented analytical model.