Reconfigurable Broadband Metasurface with Switchable Functionalities in the Visible Range

In this article, we propose a broadband reconfigurable multifunctional meta-structure for the first time in the visible range. This device can be reconfigured between an achromatic metalens and a broadband absorber by switching the state of the phase change material (VO₂). Our designed VO₂ based novel multistage meta-atoms helped us overcome the inherent limitation of small optical contrast between PCM states in the visible regime, which hinders the realization of reconfigurable multifunctional devices in this band. We have used the finite-difference time-domain (FDTD) technique to characterize the designed multifunctional device. The structure showed a maximum switching ratio of 21.1dB between the on and off states, the highest among previously reported broadband metalens-absorber systems in any design band. A small focal length shift within $\pm5\%$ in the on state within the 678nm to 795nm band verifies the achromatic focusing characteristics. Our device proves the feasibility of reconfigurable metasurfaces with switchable functionalities in the visible band and has the prospects to bring about a revolution in next-generation integrated photonic platforms.