Optimizing the efficiency of a periodically poled LNOI waveguide using <i>in situ</i> monitoring of the ferroelectric domains
Yunfei Niu, Chen Lin, Xiaoyue Liu, Yan Chen, Xiaopeng Hu, Yong Zhang, Xinlun Cai, Yan-Xiao Gong, Zhenda Xie, Shining Zhu
Abstract
Lithium niobate on insulator (LNOI) is a unique platform for integrated photonic applications and especially for high-efficiency nonlinear frequency converters because of the strong optical field confinement. In this work, we fabricated a 6-mm-long periodically poled LNOI ridge waveguide with an optimized duty cycle (50:50) using an active domain structure monitoring method. The performance of the single-pass second-harmonic generation and difference-frequency generation in the nanophotonic waveguide was characterized, and the normalized conversion efficiencies were ∼80% of the theoretical values. These high-quality frequency conversion devices can pave the way for the application of LNOI in nonlinear integrated photonics.