Design and fabrication of etchless lithium niobate photonic crystal nanobeam cavity for efficient photon manipulation

Recently, a novel approach that uses low-refractive-index polymers as loading materials coated on lithium niobate (LN) can dramatically simplify fabrication challenges for etching LN. On this platform, various devices operating in the transverse magnetic (TM) polarized state based on optical bound states in the continuum (BIC) have been demonstrated. However, in this configuration, the propagation loss of TM mode exhibits sensitivity to waveguide width, which limits design flexibility in waveguide structures. To this end, we designed transverse magnetic electric (TE) polarized photonic crystal structures with the same fabrication process using a y-cut LN on insulator (LNOI) substrate. The fabricated photonic crystal nanobeam cavity (PCNBC) achieves a Q factor over one order of magnitude higher than any previously reported PCNBCs on the etchless LNOI platform and retains a high transmission. To verify the strong photon manipulation ability, additional experiments such as thermo-optic tuning and optical bistability generation have been made. These results demonstrate the potential of our devices for efficient on-chip photon manipulation.