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Liquid lenses are becoming important optical devices for a wide range of applications, from mobile-phone cameras to
biological imaging modalities. Their biggest advantage is their potential to have a variable focus that can be changed to
obtain a different radius of curvature and thus optical power. The tunability of such micro-lenses could be of great
interest to the field of micro-optics thanks to the possibility to achieve focus tuning without moving parts and thus
favouring the miniaturization of the optical systems. A special class of tunable liquid micro-lenses is presented here.
They are generated by electro-wetting effect under an electrode-less configuration. The lensing effect is induced by the
pyroelectric effect on polar dielectric crystals we named pyroelectric-electrodeless-electro-wetting (PEEW). If a thin
liquid film is spin coated on a z-cut lithium niobate wafer, the pyroelectric effect causes surface-charges at the liquidsolid
interface when the substrate suffers temperature changes. Electric charges build up on the substrate's surface by
pyroelectricity and are responsible for the variation of the liquid contact angle, thus forming liquid micro-lenses. The
temperature variation can generate a pattern of electric charges onto the surface of the crystal when ferroelectric domain
pattern is micro-engineered. Different types of lenses: spherical, cylindrical and toroidal have been formed. Any
temperature change allows the liquid layer to become a tunable micro-lens array, showing a strong focusing effect. A
digital holography technique is used to characterize the transmitted wavefront during focusing and focal length variation
in the millimetre range is observed. Formation process is illustrated while interferometric characterization and imaging
properties are analyzed and discussed.
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