Miniature tunable Alvarez lens driven by piezo actuator

Abstract

Alvarez lenses can achieve focal length tuning by shifting a pair of optical elements with cubic surfaces in a direction perpendicular to the optical axis, offering us a series of advantages including compact structures with large varifocal ranges, ease of packaging, and high stability against external disturbances. In this paper, we present a miniature tunable Alvarez lens driven by a piezo actuator integrated with a compact mechanical displacement amplifier. A flexure-guided structure with a displacement amplification ratio of ∼16 is adopted in the mechanical design and a novel method to determine surface profile coefficients in the optical design is employed to optimise the lens performance. Results show that the displacement vs. voltage curve of the mechanical displacement amplifier is nearly linear. A maximum displacement of ∼100 μm is obtained with a 130 V input voltage applied to the piezo actuator. Dynamic tuning of focal length about 2.3 times (from 28 mm to 65 mm) is experimentally demonstrated with the assembled Alvarez lens. Images of a USAF 1951 resolution target through the lens at different focal lengths are captured by a high-resolution camera to evaluate the lens performance. No obvious distortion or blurring of images or performance degradation while tuning are noticed within the whole varifocal range.