Low-voltage electro-optic switching and modulation of second harmonic generation in lithium niobate resonant waveguide gratings assisted by quasi-BICs
Xin Li, Di Liu, Yanyan Huo, Qing-Yang Yue, Tingyin Ning
Abstract
We numerically investigate the low-voltage electro-optic (EO) switching at a telecommunication wavelength and modulation of second harmonic generation (SHG) in lithium niobate (LN) resonant waveguide gratings (RWGs) working at quasi-bound states in the continuum (BICs). The external applied voltage V 0 = 0.4 V can realize the transmission changing from near zero at V 0 = 0 to 70 % in the feasible RWGs nanostructure at quasi-BICs wavelength under both TM-and TE-polarization. The tuning efficiency, i.e. the shift of resonance wavelength at external per-voltage, arrives up to 121 pm/V and 56 pm/V under TM- and TE-polarization, respectively. Besides the switching of linear transmission, SHG from the LN RWGs is also effectively modulated by external voltages. Several orders of magnitude change in SHG conversion efficiency are achieved for the external voltage varying from V 0 = 0 V to 1 V. The low-voltage switching, high tuning efficiency and dramatical modulation of SHG are ascribed to the ultra-high Q -factor at quasi-BICs which is sensitively affected by the refractive index of LN based on EO effect. The results show that the LN RWGs nanostructure working at quasi-BICs is promising for the application in high-performance EO linear and nonlinear devices.