Interferometric characterization of pyroelectrically activated micro-arrays of liquid lenses in lithium niobate crystals S. Grilli, L. Miccio, V. Vespini and P. Ferraro Istituto Nazionale di Ottica Applicata del CNR (CNR-INOA) Viale Campi Flegrei 34, 80078 Pozzuoli (NA), Italy simonetta.grilli@inoa.it , pietro.ferraro@inoa.it ABSTRACT In recent years a wide variety of liquid based optical elements have been conceived, designed and fabricated even for commercial products like digital cameras. The impressive development of microfluidic systems in conjunction with optics has led to the creation of a completely new field of investigation named optofludics. Among other things, the optofluidic area deals with the investigation and the realization of liquid micro-lenses. Different methods and configurations have been proposed in literature to achieve liquid variable micro-lenses. This paper reports about the possibility to achieve lensing effect by a relatively easy to accomplish technique based on an open microfluidic system consisting of a tiny amount of appropriate liquid manipulated by the pyroelectric effect onto a periodically poled LiNbO 3 substrate. Basically, an electrowetting process is performed to actuate the liquid film by using the surface charges generated pyroelectrically under temperature variation. The configuration is electrode-less compared to standard electrowetting systems, thus improving the device flexibility and easiness of fabrication. The curvature of the liquid lenses has been characterized by interferometric techniques based on the evaluation of the phase map through digital holography. The results showing the evolution of the lens curvature with the temperature variation will be presented and discussed. Keywords: Microlens array, Lithium Niobate; Pyroelectric effect; Digital Holography. 1. INTRODUCTION The possibility to realize tunable and adaptive optical elements has attract scientist attention in last years. These devices are well suitable in several field such as optical communication, multiplex focusing components or biological applications. One way to accomplish lens with tunable focal length is to employ liquids using their capability to modify own shape changing the surface tension, this feature is useful in particular for sub-millimeter devices. Lensing effect by liquids is very common and several examples in nature can be found [1]. Two classes of microfluidic liquid lenses exists: one based on the elettrowetting effect and another based on the hydrostatic pressure. The first class comprises many configurations: sometimes two immiscible liquids are used inside special cases made of hydrophobic coating and electrodes. The applied voltage changes the equilibrium among the forces acting on the liquid-liquid and solid-liquid interfaces causing a changing in the curvature of the meniscus at the liquid-liquid interface. In this way, the applied voltage variation allows to switch between converging and diverging lens with flexible focal lengths [2-7]. In some cases a free standing sessile liquid drop is placed on a plane surface acting as first electrode while the second one is a needle just immersed on the top of the drop [8]. The second class of liquid lenses makes use of small liquid reservoir having flexible and transparent membranes. By changing the pressure in the liquid volume it is possible to change the shape of the lens [9, 10]. The hydrostatic pressure is responsible for changing the focal power of the microfluidic lens. Electro-wetting or more in general studies on wettability and de-wettability [11-22] of surfaces have been studied and investigated since long time with the aim to pattern liquids on surfaces. An interesting overview about scope, methods and results is given in ref. [15]. Interferometry XIV: Applications, edited by Erik L. Novak, Wolfgang Osten, Christophe Gorecki, Proc. of SPIE Vol. 7064, 706404, (2008) · 0277-786X/08/$18 · doi: 10.1117/12.796076 Proc. of SPIE Vol. 7064 706404-1 2008 SPIE Digital Library -- Subscriber Archive Copy