Atomically thin optical lenses and gratings

Two-dimensional (2D) materials have emerged as promising candidates for miniaturized optoelectronic devices due to their strong inelastic interactions with light. On the other hand, a miniaturized optical system also requires strong elastic light–matter interactions to control the flow of light. Here we report that a single-layer molybdenum disulfide (MoS2) has a giant optical path length (OPL), around one order of magnitude larger than that from a single-layer of graphene. Using such giant OPL to engineer the phase front of optical beams we have demonstrated, to the best of our knowledge, the world’s thinnest optical lens consisting of a few layers of MoS2 less than 6.3 nm thick. By taking advantage of the giant elastic scattering efficiency in ultra-thin high-index 2D materials, we also demonstrated high-efficiency gratings based on a single- or few-layers of MoS2. The capability of manipulating the flow of light in 2D materials opens an exciting avenue towards unprecedented miniaturization of optical components and the integration of advanced optical functionalities. More importantly, the unique and large tunability of the refractive index by electric field in layered MoS2 will enable various applications in electrically tunable atomically thin optical components, such as micro-lenses with electrically tunable focal lengths, electrical tunable phase shifters with ultra-high accuracy, which cannot be realized by conventional bulk solids. Optical components that are just a few atomic layers thick have been made from the two-dimensional material molybdenum disulfide (MoS2). Researchers from the Australian National University and the University of Wisconsin in the USA fabricated a miniature concave optical lens that was just 6.3 nm thick by etching a several-layer-thick flake of MoS2 into a bowl shape. The lens had a focal length of –240 μm. In addition, the team fabricated highly efficient gratings by milling periodic patterns into MoS2 flakes up to six layers thick. Such ultrathin optical devices can be realized due to the very strong interaction between light and MoS2. In particular, the optical path length and elastic scattering efficiency of MoS2 are much larger than those of other materials.