Planar lenses based on metasurfaces hold promise to revolutionize optics. However, an issue has traditionally been the so-called “chromatic aberration” inherent in metalenses. Chromatic aberration refers to a focal length whose value varies with wavelength, and makes broadband imaging challenging. In traditional, bulk optics, chromatic aberration must be addressed with combinations of multiple lenses (doublets, triplets, or more) fashioned from various different optical glasses.
Recently, our group reported a specially engineered meta-lens functioning in the visible with a uniform focal length over a 60 nm bandwidth. This, for instance, would be sufficient for imaging over the bandwidth of an LED, a ubiquitous light source. The lens works in reflection, and consists of titanium dioxide nanopillars patterned on a backing mirror of aluminum. Additionally, we have also shown a metalens engineered with reverse chromatic dispersion, a testament to the flexibility with which these phenomena may be engineered with metasurfaces.
This work appears in Nano Letters:
“Achromatic Metalens over 60 nm Bandwidth in the Visible and Metalens with Reverse Chromatic Dispersion”, M. Khorasaninejad, Z. Shi, A. Y. Zhu, W. T. Chen, V. Sanjeev, A. Zaidi, and F. Capasso, Nano Lett.,17 (3), pp 1819–1824, 2017.