Chromatic-aberration correction in geometric-phase lenses, for red, green, and blue operation (Conference Presentation)

Abstract

All diffractive lenses manifest chromatic aberration/dispersion. If the focal length f0 at a given wavelength λ0 is known, then the focal length f(λ) = f0 λ0 / λ at other wavelengths λ. This can be considerable, even for lenses of a few diopters. Geometric-phase lenses (GPLs), are no exception, which manipulate incident light’s wavefront by the Pancharatnam-Berry phase effect. Several years ago, we developed achromatic coatings based on photo-aligned chiral liquid crystals that achieve nearly 100% efficiency into the primary and conjugate waves, and more recently we demonstrated fast, defect-free GPLs down to F/1.5 for red light. Until now, no one has reported how to generally reduce chromatic aberration and ensure that two or more wavelengths can have the same focal length. Here, we report on a new approach to correct for chromatic aberration using a stack of GPLs and retarders to arrange red, green, and blue wavelengths to have precisely the same focal length. A simple arrangement of these elements results in a thin, monolithic, and flat GPL, which can either converge or diverge three wavelength sources (R/G/B) with the same focal length, positive or negative, depending on the handedness of the circular input polarization. Here, we describe the concept and characterize our first prototypes by evaluating focal lengths, efficiency, and polarization contrast. We also discuss the realistic opportunities and limitations for this approach.