  We report the fabrication and optical characterization of Yb3+-doped
waveguide amplifiers (YDWA) on the thin film lithium niobate fabricated by
photolithography assisted chemo-mechanical etching. The fabricated Yb3+-doped
lithium niobate waveguides demonstrates low propagation loss of 0.13 dB/cm at
1030 nm and 0.1 dB/cm at 1060 nm. The internal net gain of 5 dB at 1030 nm and
8 dB at 1060 nm are measured on a 4.0 cm long waveguide pumped by 976nm laser
diodes, indicating the gain per unit length of 1.25 dB/cm at 1030 nm and 2
dB/cm at 1060 nm, respectively. The integrated Yb3+-doped lithium niobate
waveguide amplifiers will benefit the development of a powerful gain platform
and are expected to contribute to the high-density integration of thin film
lithium niobate based photonic chip.
