Planar Freeform Metasurfaces with Customized Circular Dichroism Responses

ABSTRACT Chiral metasurfaces have emerged as a versatile platform for manipulating chiral light‐matter interactions in diverse applications. However, the design of arbitrary chiroptical responses remains challenging because conventional parameterized geometries severely constrain the accessible design space. To address this issue, we present a design framework for planar freeform chiral metasurfaces (FCMs) in the near‐infrared regime, enabling on‐demand inverse engineering of customized circular dichroism (CD) responses. The proposed framework allows flexible control over key CD spectral characteristics, including spectral feature position, amplitude, line shape, and bandwidth. Experimental and numerical results demonstrate representative capabilities. Specifically, high CD responses can be designed at selected target wavelengths, and tailored CD spectra with Fano, single‐Gaussian, dual‐Gaussian, and gate‐shaped profiles can be further realized. In addition, multiple fabrication‐compatible FCM candidates with distinct geometries can be obtained for the same target response. Good agreement between simulations and experiments confirms the reliability and flexibility of the proposed strategy. This work provides a practical route toward the on‐demand realization of customized CD responses in freeform metasurfaces.