Liquid crystal modal lenses are switchable lenses with a continuous phase variation across the lens. A critical issue for such lenses is the minimization of phase aberrations. In this paper we present results of a simulation of control signals that have a range of harmonics. Experimental results using optimal sinusoidal and rectangular voltages are presented. A lack of uniqueness in the specification of the control voltage parameters is explained. The influence of a variable duty cycle of the control voltage on an adaptive lens is investigated. Finally we present experimental results showing a liquid crystal lens varying its focal length.
We describe two electro-optical systems for adaptive focusing of linearly polarized light. The aperture size is 5 mm and the focal length can be varied from 1 to 4 m for wavelengths from 0.663 to 0.85 μm. The first is a commercially available system including a PC compatible control unit and software, and an adaptive liquid crystal lens. The other is an experimental system consisting of a self-contained unit with an autonomous power supply and an adaptive lens. The safe operating limit in the visible region is 10 W/cm2 with a transmission of 70% without antireflection coating. The switching speed of focus variation from 2 to 1 m and from 1 to 2 m is 780 and 860 ms, respectively. The operating principles of the spherical adaptive lenses and their control units are described. Phase aberrations of the lenses were measured by a Zygo phase shifting interferometer, and the results are presented.
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