By rotating stacked diffractive optical elements (DOEs) with respect to each other around their central axis, the optical power of the combined element can be precisely tuned. And while monochromatic operation has been previously demonstrated, researchers at Innsbruck Medical University (Innsbruck, Austria) have now extended this principle to demonstrate polychromatic tunable lenses—lenses with the same optical power and diffraction efficiency over the full tuning range at three or more selectable wavelengths. Polychromaticity is achieved by rotating Moiré diffractive optical elements (MDOEs)—higher-order DOEs that are polychromatic at harmonics of a fundamental selected wavelength and have a large optical power tuning range, diffraction-limited focusing, and high diffraction efficiency from 80% up to 100%. Rotation adjusts the phase profiles of the lenses such that, for three or more selected wavelengths, the focal length and diffraction efficiency is equal over the entire tunable range.
Just recently, Austrian startup company Diffractec was founded to exploit the patented technology (U.S. patent 2010/0134869 A1) for novel optical devices, including autofocus and zoom objectives, laser projection, and 3D material processing with lasers. Furthermore, the principle is applicable to other types of rotationally tunable optical elements, including axicons or lenses with arbitrary radial phase profiles, or to variants of diffractive Alvarez lenses that are tunable by a mutual translation. Reference: S. Bernet and M. Ritsch-Marte, Opt. Express, 25, 3, 2469-2480 (2017).
