Lithium niobate on insulator (LNOI) is an emerging photonic platform with great promise for use in future optical communications, nonlinear optics, and microwave photonics. An important integrated photonic building block, active waveguide amplifiers, however, are still missing in the LNOI platform. Here, we report an efficient and compact waveguide amplifier based on erbium-doped LNOI waveguides, achieved using a sequence of erbium-doped crystal growth, ion slicing, and lithography-based waveguide fabrication. Using a compact 5 mm long waveguide, we demonstrate an on-chip net gain of > 5 d B for 1530 nm signal light with a relatively low pump power of 21 mW at 980 nm. The efficient LNOI waveguide amplifiers could become an important fundamental element in future lithium niobate photonic integrated circuits.

Lithium niobate on insulator (LNOI) has already become a promising material platform for ultracompact, high‐performance, and low‐cost passive microphotonic devices. However, studies on an active LNOI platform are relatively slow. Current work aims at developing an important integrated photonic piece, an active LNOI thin film and waveguide. Herein, it is first demonstrated that a full wafer‐scale (3 in. in diameter) Er³⁺‐doped LNOI (Er:LNOI) wafer can be fabricated by directly ion‐beam slicing a commercially bulk Er³⁺‐doped lithium niobate wafer. Then, a number of rib‐type waveguides with a cross‐section <1 μm² are patterned on its surface using mature nanostructuring technologies. Further optical and spectroscopic characterization results confirm the applicability of the Er:LNOI wafer to the fabrication of an active waveguide. The success in fabrication of Er³⁺‐doped LNOI thin film and waveguides enables the establishment of an active LNOI platform and opens the possibility of developing ultracompact active microphotonic devices, which may find wide applications in the fields of optical communications, nonlinear optics, microwave photonics, and novel photonic systems such as parity‐time symmetric systems.