Design studies of varifocal rotation optics

We present the design of a varifocal freeform optics consisting of two lens bodies each with a helical-type surface structure of azimuthally varying curvatures. This arrangement allows for tuning the optical refraction power by means of a mutual rotation of the lens bodies around the optical axis. Thus, the refraction power can be tuned continuously in a defined range. The shape of the helical-type surfaces is formed by a change in curvature subject to the azimuthal angle α. At the transition of the azimuthal angle from α = 2π to α = 0, a surface discontinuity appears. Since this discontinuity will seriously affect the imaging quality, it has to be obscured. In the initial state, i.e., zero-degree rotation, the curvatures of the opposing surfaces result in a specific refraction power, which is constant over the entire circular aperture. Rotating one of the lens bodies by an angle φ around the optical axis will change the opposing curvatures and result in a change of refraction power. Two circular sectors with different tunable optical refraction powers are formed, thus resulting in a tunable bifocal optics. Obscuring the minor sector will result in a tunable monofocal rotation optics. In contrast to conventional tunable lens systems, where additional space for axial or lateral lens movement has to be allocated in design, rotation optics allowing for a more compact design. A performance analysis of the rotation optics based on simulations is presented in dependence on aperture size as well as approaches to compensate for spherical aberrations.