High-Q-factor chiral quasi-BIC LiNbO3 metasurface enabling versatile electro-optic modulation

It is challenging to construct nano-scaled meta-structures enabling efficient and versatile electro-optic modulations, especially those related to circular dichroism (CD), which is useful in detection of chiral molecules and optical manipulation. In this study, we have modeled chiral metasurfaces based on single-crystal LiNbO3 using finite element method. The numerical calculation and characterization indicate that a quasi-BIC(q-BIC) resonance with a high Q-factor optical signal of 9.3 × 10⁴ and a peak CD signal of 0.89 at 972.76 nm could be obtained by breaking the structural symmetry of the chiral metasurface. The pockels effect of LiNbO₃ is enhanced via q-BIC resonance, resulting in a highly efficient electro-optic modulation of the CD signal. The modulation efficiency was found to be 1 nm/1.25×10⁵ V/m at 972.76 nm. Furthermore, we have investigated in detail the polarization-dependent electro-optic properties of the LiNbO₃ metasurface. The polarization states of the output far-field radiation can be actively tuned by electro-optic modulation efficiently. The modulation ranges of polarized rotary angle were found to be 55° and 48° for right-handed and left-handed polarization, respectively. The ellipticity can be tuned in a range of 62° and 3.3° for right-handed and left-handed polarization, respectively. Benefiting from the high Q-factor, this metasurface shows a high sensitivity to environmental refractive index of 590nm/RIU and a high figure of merit of 5.9×10⁴. These results show that the studied metasurface is promising as an electro-optic modulator and for applications in sensing of chiral responses.