Advances in Transparent Planar Optics: Enabling Large Aperture, Ultrathin Lenses

Unlike electronics, optics do not follow Moore's law. This statement, expressed by Microsoft's Bernard Kress, refers to the hard challenges to solve in augmented reality hardware. While light sources have undergone numerous revolutions from candles to light emitting diodes, the evolution in transparent optics has been much slower. For transparent materials, variation of the shape, bulk refractive index, and/or its distribution leads to control of the transmitted beam in an optical system. An alternative, the control of the optical axis orientation in an anisotropic material in transparent micrometer‐thin films on a variety of substrates, is explored here. In contrast to metamaterials, these diffractive waveplates have a continuous structure allowing multilayer/multifunctional planar optical systems with close to 100% efficiency across broad bands of wavelengths (ultraviolet to infrared) with customizable spectra. The low‐cost and fast fabrication technology of this fourth generation of optics is scalable to very large aperture sizes. In addition to wearable adaptive optics, the technology enables thin and compact non‐mechanical fast beam steering systems for light detection and ultralight space telescopes. This review will first serve as an introduction to these unique transparent, planar optical films, and then recent advances enabled by specific optical designs will be presented. This review presents an introduction and recent advances in so‐called fourth generation optics, which use geometric phase control to enable novel optical effects. As an alternative to metasurfaces, these diffractive waveplates have a continuous structure allowing multilayer/multifunctional planar optical systems with close to 100% efficiency across a broad band of wavelengths (UV to infrared) with customizable spectra.