School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang, Avenue, Singapore 639798.
Lab Chip. 2012 Oct 7;12(19):3680-7. doi: 10.1039/c2lc40406k.
This paper numerically and experimentally investigates and demonstrates the design of an optofluidic in-plane bi-concave lens to perform both light focusing and diverging using the combined effect of pressure driven flow and electro-osmosis. The concave lens is formed in a rectangular chamber with a liquid core-liquid cladding (L(2)) configuration. Under constant flow rates, the performance of the lens can be controlled by an external electric field. The lens consists of a core stream (conducting fluid), cladding streams (non-conducing fluids), and auxiliary cladding streams (conducting fluids). In the focusing mode, the auxiliary cladding stream is introduced to sandwich the biconcave lens to prevent light rays from scattering at the rough chamber wall. In the diverging mode, the auxiliary cladding liquid has a new role as the low refractive-index cladding of the lens. In the experiments, the test devices were fabricated in polydimethylsiloxane (PDMS) using the standard soft lithography technique. Ethanol, cinnamaldehyde, and a mixture of 73.5% ethylene glycol and 26.5% ethanol work as the core stream, cladding streams and auxiliary cladding streams. In the numerical simulation, the electric force acts as a body force. The governing equations are solved by a finite volume method on a Cartesian fixed staggered grid. The evolution of the interface was captured by the level set method. The results show that the focal length in the focusing mode and the divergent angle of the light beam in the diverging mode can be tuned by adjusting the external electric field at fixed flow rates. The numerical results have a reasonable agreement with the experimental results.
本文通过数值模拟和实验研究，展示了一种基于压力驱动流和电渗流的协同作用，设计出一种用于平面内双凹透镜的光焦度和光束发散度的光流控双凹透镜。该凹透镜在具有液体芯-液体包层（L(2)）结构的矩形腔中形成。在恒定流速下，透镜的性能可以通过外部电场进行控制。透镜由一个核心流（导电流体）、包层流（非导电流体）和辅助包层流（导电流体）组成。在聚焦模式下，引入辅助包层流来夹在双凹透镜之间，以防止光线在粗糙腔壁上散射。在发散模式下，辅助包层液体具有新的作用，即作为透镜的低折射率包层。在实验中，使用标准的软光刻技术在聚二甲基硅氧烷（PDMS）上制造测试设备。乙醇、肉桂醛和 73.5%的乙二醇和 26.5%的乙醇混合物分别作为核心流、包层流和辅助包层流。在数值模拟中，电场力作为体力。控制方程通过笛卡尔固定交错网格上的有限体积法求解。界面的演化通过水平集方法捕捉。结果表明，在固定流速下，通过调节外部电场，可以调节聚焦模式下的焦距和发散模式下光束的发散角。数值结果与实验结果吻合较好。
