  Lithium niobate on insulator (LNOI), as an emerging and promising optical
integration platform, faces shortages of on-chip active devices including
lasers and amplifiers. Here, we report the fabrication on-chip erbium-doped
LNOI waveguide amplifiers based on electron beam lithography and inductively
coupled plasma reactive ion etching. A net internal gain of ~30 dB/cm in
communication band was achieved in the fabricated waveguide amplifiers under
the pump of a 974-nm continuous laser. This work develops new active devices on
LNOI and will promote the development of LNOI integrated photonics.
