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Bifocal liquid lens zoom objective for mobile phone applications

: Wippermann, F.; Schreiber, P.; Bräuer, A.; Craen, P.


Blouke, M.M. ; Society for Imaging Science and Technology -IS&T-; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Sensors, cameras, and systems for scientific/industrial applications VIII : 30 January - 1 February 2007, San Jose, California, USA; Proceedings of Electronic imaging, science and technology
Bellingham, WA: SPIE, 2007 (SPIE Proceedings Series 6501)
ISBN: 978-0-8194-6614-3
Paper 650109
Conference "Sensors, Cameras, and Systems for scientific/Industrial Applications" <2007, San Jose/Calif.>
Annual Symposium Electronic Imaging, Science and Technology <19, 2007, San Jose/Calif.>
Conference Paper
Fraunhofer IOF ()
zoom objective; liquid lens; electrowetting

Miniaturized camera systems are an integral part of today's mobile phones which recently possess auto focus functionality. Commercially available solutions without moving parts have been developed using the electrowetting technology. Here, the contact angle of a drop of a conductive or polar liquid placed on an insulating substrate can be influenced by an electric field. Besides the compensation of the axial image shift due to different object distances, mobile phones with zoom functionality are desired as a next evolutionary step.
In classical mechanically compensated zoom lenses two independently driven actuators combined with precision guides are needed leading to a delicate, space consuming and expansive opto-mechanical setup. Liquid lens technology based on the electrowetting effect gives the opportunity to built adaptive lenses without moving parts thus simplifying the mechanical setup. However, with the recent commercially available liquid lens products a completely motionless and continuously adaptive zoom system with market relevant optical performance is not feasible.
This is due to the limited change in optical power the liquid lenses can provide and the dispersion of the used materials. As an intermediate step towards a continuously adjustable and motionless zoom lens we propose a bifocal system sufficient for toggling between two effective focal lengths without any moving parts. The system has its mechanical counterpart in a bifocal zoom lens where only one lens group has to be moved.
In a liquid lens bifocal zoom two groups of adaptable liquid lenses are required for adjusting the effective focal length and keeping the image location constant. In order to overcome the difficulties in achromatizing the lens we propose a sequential image acquisition algorithm. Here, the full color image is obtained from a sequence of monochrome images (red, green, blue) leading to a simplified optical setup.