Aspherical high-speed varifocal mirror for miniature catadioptric objectives.

We present a varifocal mirror based on a piezo-actuated glass membrane that can be used as a secondary mirror in miniature Cassegrain-type mirror- or catadioptric objectives. The mirror section has a diameter of 10 mm on a clear membrane diameter of 23 mm, with a focal range of ±8 m and a response time on the millisecond-scale. The two piezo layers enable an aspherical tuning range that covers the elliptic, parabolic and hyperbolic regime over most of the focal range. We demonstrate the application of the mirror in a simple catadioptric telefocus objective with a focal length of 68 mm at an aperture of 22 mm and a thickness of 16.6 mm.