NEWS and LATEST RESEARCH
Jared Sisler, Wei Ting Chen, Alexander Y. Zhu and Federico Capasso, "Controlling dispersion in multifunctional metasurfaces," APL Photonics 5, 056107 (2020).
Conventional metasurfaces are usually designed at a wavelength to implement a target phase profile. In this paper, we report a more general design strategy by considering phase and group delay profiles at design wavelengths. This enables multi-functional metasurface devices with controlled dispersion characteristics. To proof the concept, we design and simulate metalenses with dual focal lengths and tailored focal length shifts in two discrete bandwidths in the visible spectrum as well as a metalens capable of achromatically focusing an incident plane wave to Airy disk and vortex spots for red and blue wavelengths.
W. T. Chen, A. Y. Zhu, J. Sisler, Z. Bharwani, F. Capasso, "A broadband achromatic polarization-insensitive metalens consisting of anisotropic nanostructures," Nat. Commun. 10, 355 (2019).
Polarization-insensitive metasurfaces usually comprise isotropic nanostructures. This greatly restricts the number of geometric parameters available in design. I demonstrated a polarization-insensitive metalens using otherwise anisotropic nanofins which offer additional control over the dispersion and phase of the output light. The polarization-insensitive metalens is achromatic across nearly the entire visible spectrum from wavelength λ = 460 nm to 700 nm with diffraction-limited performance. The metalens can image color objects, such as circular rainbow and letters of "R", "G" and "B" of three preliminary colors.
W. T. Chen, A. Y. Zhu, J. Sisler, Y.-W. Huang, K. M. A. Yousef, E. Lee, C.-W. Qiu, F. Capasso, "Broadband Achromatic Metasurface-Refractive Optics," Nano Lett. 18, 7801-7808 (2018).
Existing methods of correcting for chromatic aberrations in optical systems are limited to two approaches: varying the material dispersion in refractive lenses or incorporating grating dispersion via diffractive optical elements. I circumvent this limitation and design a metacorrector consisting of TiO2 nanofins with a tunable phase and artificial dispersion to correct spherical and chromatic aberrations in a large spherical plano-convex lens. The effectiveness of this approach is further validated by designing a metacorrector, which greatly increases the bandwidth of a state-of-the-art immersion objective (composed of 14 lenses and 7 types of glasses) from violet to near-infrared wavelengths.