Tunable doublets: piezoelectric glass membrane lenses with an achromatic and spherical aberration control

We present two versions of tunable achromatic doublets based on each two piezoelectrically actuated glass membranes that create the surface of fluid volumes with different dispersions: a straightforward back-to-back and a more intricate stack of the fluid volumes. In both cases, we can control the chromatic focal shift and focal power independently by a suitable combination of actuation voltages on both active membranes. The doublets have a large aperture of 12 mm at an outer diameter of the actuator of 18 mm, an overall thickness of 3 mm and a short response time of around 0.5 ms and, in addition, provide spherical aberration correction. The two designs have an achromatic focal power range of ±2.2 m^-1 and ±3.2 m^-1 or, for the purpose of actively correcting chromatic errors, a chromatic focal shift at vanishing combined focal power of up to ±0.08 m^-1 and ±0.12 m^-1.