  We demonstrate on-chip light amplification with integrated optical waveguide
fabricated on erbium-doped thin film lithium niobate on insulator (TFLNOI)
using the photolithography assisted chemo-mechanical etching (PLACE) technique.
A maximum internal net gain of 18 dB in the small-signal-gain regime is
measured at the peak emission wavelength of 1530 nm for a waveguide length of
3.6 cm, indicating a differential gain per unit length of 5 dB/cm. This work
paves the way to the monolithic integration of diverse active and passive
photonic components on the TFLNOI platform.
