Near-unity and high-Q circular dichroism reversal enabled by chiral guided mode resonance in planar dielectric metasurfaces

Realizing low-loss circular dichroism (CD) tuning and reversal is highly desirable for diverse applications, such as chiral sensing and optical encryption. Here, we demonstrate a strategy for achieving near-unity and high-Q CD reversal by manipulating chiral guided mode resonance (GMR) in planar dielectric metasurfaces. By simply rotating the etching curves around the center, the CD of the GMR can be continuously tuned from −0.996 to +0.754 at a fixed wavelength. More notably, by translating the curves, a near-unity normalized CD reversal from −0.996 to +0.985 is achieved, while the Q factor of GMR consistently exceeds 10 ³ . This reversal of chiral GMR excitation originates from the modulation of the phase difference between the GMR fields excited by two orthogonal linearly polarized components, which interchanges constructive and destructive interferences under opposite circularly polarized light incidence. Finally, the refractive index sensing performance of the chiral GMR and quasi-bound state in the continuum modes is investigated, demonstrating comparable sensitivities and high-Q CD resonances. By enabling CD sign reversal through phase-difference-controlled spin-selective interference rather than geometric chirality inversion, the chiral GMR provides a promising route for low-loss manipulation of chiroptical responses.