High‐Q Chiral Metasurfaces: Broadband Spectral Tunability with Angle‐Dependent Response

Abstract Chiral metaphotonics are essential for many applications such as enantioselective sensing where high‐quality factor (Q) resonances and strong chiroptical activity are demanded. Furthermore, spectral tuning using the same structure without compromising high‐Q and chiral responses is highly desirable. This study presents a silicon‐based metasurface that maintains high‐Q and broadband chiral responses across its full operational band, enabling spectral tuning through adjusting the in‐plane wavevector while preserving high Q factors and circular dichroism (CD) values. The metasurface, composed of silicon pillars on a silicon slab, demonstrates full chiral bands in both wavevector directions. This is confirmed by both mode CD calculated from the eigenfields and transmittance CD from the far‐field spectra in the full‐wave simulations. The angle‐dependent transmittance spectra measured from the fabricated structure exhibit a quality factor of 1100, a CD value of 0.61, and an angular tuning range of 12°, in good agreement with numerical predictions. Additionally, enhanced third harmonic generation from this nonlocal metasurface exhibits further improved nonlinear CD (0.95), which can also be spectrally tuned by varying the incident angle. These findings lay the groundwork for advanced chiral metasurfaces operating over extensive angular ranges, with significant implications for applications requiring precise spectral matching and tunable chiroptical responses.