Gravity-immune liquid-filled tunable lens with reduced spherical aberration.

The performance of uniform-thickness membrane lenses is severely compromised due to the inherent trade-off between spherical aberration and the sensitivity to gravity effects. This problem can be eliminated by engineering the membrane thickness profile such that a membrane stiff enough to withstand gravity-induced deformations can be shaped into a perfect optical surface under uniform pressure load. We present here a membrane-based liquid-tunable aspherical lens capable of diffraction-limited performance at nominal focal length, with two orders-of-magnitude smaller wavefront error compared to conventional tunable lenses, regardless of the lens orientation, by use of a non-uniform thickness profile of the flexible membrane. The lens has an aperture size of 3 mm, with a nominal focal length of 8 mm and a theoretical diffraction-limited tuning range between 7.2 and 8.8 mm. Between 6 and 12 mm, the cutoff frequency remains above 50% of the diffraction limit, demonstrating a drastic reduction in spherical aberration compared to conventional liquid-tunable lenses.