Ultra-high Q lithium niobate microring monolithically fabricated by photolithography assisted chemo-mechanical etching.

As one of the element photonic structures, the state-of-the-art thin-film lithium niobate (TFLN) microrings reach an intrinsic quality (Q) factor higher than 107. However, it is difficult to maintain such high-Q factors when monolithically integrated with bus waveguides. Here, a relatively narrow gap of an ultra-high Q monolithically integrated microring is achieved with 3.8 µm, and a high temperature annealing is carried out to improve the loaded (intrinsic) Q factor with 4.29 × 106 (4.04 × 107), leading to an ultra-low propagation loss of less than 1 dB/m, which is approximately 3 times better than the best values previously reported in ion-slicing TFLN platform.