MENISCUS SHAPE AND OPTICAL PERFORMANCE OF A MEMS-BASED LIQUID MICRO-LENS SYSTEM

It is very difficult to fabricate tunable optical systems having an aperture below 1000 micrometers with the conventional means on macroscopic scale. Krogmann et al. (J. Opt. A: Pure Appl. Opt. vol. 8, 2006, pp. S330-5336) presented a MEMS-based tunable liquid micro-lens system with an aperture of 300 micrometers. The system exhibited a toning range of back focal length between 2.3 mm and infinity by using the electrowetting effect to change the contact angle of the meniscus shape on silicon with a voltage of 0-45V. However, a serious optical aberration was found in their lens system. In the present study, a numerical simulation is performed for this same physical configuration by solving the Young-Laplace equation on the interface of the lens liquid and the surrounding liquid. The resulting meniscus shape produces a back focal length that agrees with the experimental observation excellently. To eliminate the optical aberration, an electric field is applied on the system. The electric field alters the Young-Laplace equation and thus changes the meniscus shape and the quality of the lens system. The numerical result shows that the optical aberration of the lens system can be essentially eliminated when a proper electric field is applied.