Stable resonance in dielectric metasurfaces: a quasi-BIC approach to ultrahigh-Q chiroptical performance

The physics of high-index dielectric materials has led to the appearance of all-dielectric meta-photonics, which provides a low-loss platform for effective subwavelength control and manipulation of electromagnetic waves. This paper presents a metasurface that supports ultrahigh-Q chiroptical resonance at the gamma point. We propose a design that manipulates quasi-bound states in the continuum (q-BICs) through in-plane and out-of-plane perturbations to achieve unit chirality in a lossless planar metasurface. By varying the in-plane asymmetry parameter, we enhance the quality factor while keeping the resonant wavelength stable. The design is done in such a way that by changing the in-plane asymmetry parameter to increase the quality factor, the resonant wavelength remains stable. The design achieves a Q -factor of 5.9×10 6 and a circular dichroism (CD) of 0.99 at visible wavelengths by breaking the out-of-plane symmetry. Our findings open up new possibilities for precise chiral sensing technologies.