Abstract
A square geometry for the diaphragm of microelectromechanical systems (MEMS) tunable lenses with circular pupils is often used. This square diaphragm introduces aberrations that would not be present for a circular diaphragm and the question arises of whether it could be advantageous to also consider other than circular geometries for the pupil. To investigate this question, we have extended a previously established modeling framework for piezoelectrically actuated MEMS tunable lenses to devices with general polygonal-shaped pupils. It models the static optoelectromechanical coupling for symmetric configurations based on laminated-plate theory, linear piezoelectricity, and ray tracing. The framework helps to find geometrical parameters that give a diffraction-limited tunable lens with a minimum F-number. The tunable lens’ optical performance and its focusing capability, alone and in combination with a fixed lens, were calculated in terms of object distances and actuation voltages. Using the modeling framework, we show that the modulation transfer function of the tunable lens and the fixed lens combination remains the same up to a ±10-deg field of view after voltage adjustment to refocus on near objects. In addition, we found that pupil masking of the tunable lens can provide a beneficial tradeoff between the lens dioptric power and its RMS wavefront error.
Highlights
An autofocus mechanism, which allows image capturing with sharp details, has become an essential feature in mobiledevice cameras
We focus our attention on the optical performance of piezoelectrically actuated MEMS tunable lenses with differently shaped pupils
The MEMS tunable lenses that we study here bend a transparent diaphragm by piezoelectric actuation to modify the interface slope between air and a polymer[8] or air and a fluid.[7]
Summary
An autofocus mechanism, which allows image capturing with sharp details, has become an essential feature in mobiledevice cameras. Microelectromechanical systems-(MEMS)based tunable focus lenses are recently trending in providing low-power microscale solutions with faster scanning rates over the focusing range.[3,4,5,6,7,8] MEMS autofocus lenses have no sliding parts within the camera housing, consume less power during focus adjustment, and cause no loss in the field of view, as compared to the conventional technologies. One tunable liquid lens uses the electrowetting phenomena to make the interface between two polar liquids convex or concave.[6] Piezoelectrically actuated lenses deform a transparent membrane between two refractive media. These media can be air and a fluid,[7] or air and a polymer as in the TLens case.[8]. Akram, and Halvorsen: Optical performance of piezoelectrically actuated MEMS tunable
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