Abstract
In this work, we present the results of the opto–electro–mechanical characterization of tunable micro-lenses, Tlens®, performed with a single-spot optical measuring system. Tested devices are composed of a transparent soft polymer layer that is deposited on a supporting glass substrate and is covered by a glass membrane with a thin-film piezoelectric actuator on top. Near-infrared optical low-coherence reflectometry is exploited for both static and low-frequency dynamic analyses in the time domain. Optical thickness of the layers and of the overall structure, actuation efficiency, and hysteretic behavior of the piezo-actuator as a function of driving voltage are obtained by processing the back-reflected signal in different ways. The use of optical sources with relatively short coherence lengths allows performing interferometric measurements without spurious resonance effects due to multiple parallel interfaces, furthermore, selecting the plane/layer to be monitored. We finally report results of direct measurements of Tlens® optical power as a function of driving voltage, performed by redirecting a He-Ne laser beam on the lens and monitoring the focused spot at various distances with a digital camera.
Highlights
Cameras in mobile devices are extensively used for capturing sharp images, and commonly used autofocus mechanisms rely on electromagnetic voice-coil [1] or ultrasonic motors [2]
In the past we have demonstrated the great capabilities of semiconductor laser feedback interferometry for optical microelectromechanical systems (MEMS) characterization with spot optical measurements [29,30,31], whereas in the case of the Tlens®, we looked at a measuring technique that allowed to detect static as well as dynamic properties, with an instrumental configuration intrinsically capable of separating the contributions coming from the various layers forming the lens
We have reported the results of the experimental characterization of Tlens® tunable micro-lenses
Summary
Cameras in mobile devices are extensively used for capturing sharp images, and commonly used autofocus mechanisms rely on electromagnetic voice-coil [1] or ultrasonic motors [2]. Micro-lenses with tunable focus length have recently been fabricated, exploiting microelectromechanical systems (MEMS) technology [3,4,5,6,7]. Piezoelectrically actuated micro-lenses have been demonstrated, based on the deformation of a transparent fluid or soft polymer [8] placed between glass membranes or layers of other transparent materials. Actuated membranes are the basic building blocks for other MEMS devices, such as micropumps [9,10]. For demonstrating the actual functionality of the fabricated devices, as well as for providing feedback to the design and process engineers, several parameters related to the opto–electro–mechanical properties of piezoelectrically tunable micro-lenses deserve to be directly measured. The thin glass membrane, and the underlying polymer, can be deformed by a voltage applied across
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