Toward photonic–electronic convergence based on heterogeneous platform of merging lithium niobate into silicon

The rapid development of fabrication techniques has boosted the resurgence of integrated photonics based on lithium niobate (LN). While thin-film LN is available and has been a promising photonic platform owing to its superior material properties, it is held back by its non-compatibility with complementary metal-oxide-semiconductor (CMOS) processes and the lack of high-density scaling possibilities. Silicon (Si), despite its less favorable intrinsic properties, was the dominant platform for photonic devices with compact footprints, high density, low cost, and high volume. By embedding thin-film LN into the Si platform, heterogeneous Si/LN photonic devices can be integrated on the same chip, simultaneously leveraging the advantages of the two different materials. In parallel with the development of photonic devices, research in photonic–electronic integrated circuits (PEICs) has flourished. This review begins with the material properties of LN and fabrication approaches for heterogeneous integration. We then introduce various photonic devices involving different functionalities. After that, the advances in photonic–electronic convergence are presented. Taking inspiration from PEICs using Si, we envision the contribution of thin-film LN conjunct with Si in the future PEICs. Finally, some conclusions and challenges are discussed.