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Mikro-Auge basierend auf Glasoptiken und durchstimmbaren Dünnschichtfiltern herstellbar in waferbasierter Fertigung

Subject Area Microsystems
Term from 2011 to 2015
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 214154757
 
Final Report Year 2017

Final Report Abstract

Miniaturized optical systems are of high relevance for many applications ranging from personal miniaturized cameras, e.g., in smartphones, over industrial optical sensor systems to biomedical imaging systems such as endoscopes or remote-control operation systems. This project aimed at investigating components for a tunable single-aperture micro eye mimicking the functionality of a human eye. This artificial eye could find application at the tip of an endoscope or in a sensing system, for example. The investigated components include miniaturized glass lenses, apertures similar to the iris in a human eye, focus-length tuning, intensity-tuning filters mimicking sunglasses, as well as angle steering components corresponding to the motion of an eye. For cost-efficient miniaturization, we envision a wafer-level fabrication procedure. In this procedure, the different types of components are fabricated on separate wafers. Subsequently, the wafers are stacked and bonded. In a final step, the wafer stack is cut to individualize the realized systems. In the project we realized tunable thin-film filters based on reflecting metal layers and thermallytunable polymer layers. We investigated polymer layers with a thickness between 10 µm and 200 µm. The tuning is performed by an electrical current through one of the thin metal layers causing Joule heating. We demonstrate aperture functionality by employing segmented electrodes such that selected surface areas can be tuned to transmission or blocking of light. Using the same principle, intensity tuning is achieved with intermediate actuation currents. These elements work with monochromatic light, for example from a laser, which is often applied in technical applications. The operation wavelength can be adjusted in operation by tuning the polymer layer thickness. For use with polychromatic light, an additional filter is necessary. Originally, we wanted to achieve a focus-length tuning with thin-film filters. Unfortunately, the project results showed that this focus-tuning mechanism is not compatible with miniaturized optics as beams with a small divergence angle are necessary. Therefore, we changed the plan to realize angle tuning thin-film structures. By arranging the tunable thin-film structure as a virtually imaged phased array (VIPA), angle tuning is demonstrated for monochromatic light. In the VIPA light propagates at an angle through the thin-film stack with multiple reflections and interference of the resulting beamlets in the optical far field is utilized. In a second part of the project optical glass lenses were fabricated using a viscous shaping approach. In this approach a glass wafer is bonded with a second wafer structured to define the lens shape. This process allows for aspherical glass lenses for aberration correction. As a third technology piezoelectric actuators were investigated for tilting and displacing optical components. A platform for the optical component is actuated via hinges by driving the piezo-electric actuators with an electric voltage. The operation with a mounted optical component was demonstrated successfully. Thus, the combination of the piezo-electric actuators with the glass lens allows for the desired focus-length tuning. The piezo-electric actuators also allow for a tuning of the viewing angle. All components are fabricated on wafers and wafer-level assembly was realized for several components. To combine the different aspects of the project, we worked on a piezo-electrically tunable VIPA. At the end of the project a first design was realized combining a highly reflective platform with piezo-electric drives. Also, an aperture is integrated into this wafer to couple the incident beam into the device. The combination of this wafer with the glass-lens wafer for focusing of the incident beam and the aperture wafer remains open for future work. In summary, we developed components for an artificial micro eye fabricated with wafer-level processes. We realized miniaturized glass lenses, apertures, focus-length tuning, intensity tuning as well as angle-steering and demonstrated wafer-level assembly of different components. These results are promising for next-generation miniaturized optical systems.

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