▎ 摘　　要

In contrast with graphene oxide (GO), carboxyl-functionalized graphene oxide (GO-COOH) is more appropriate for fabricating saturable absorbers (SAs) with high modulation depth and low nonsaturable loss because of its higher solubility in water. Here, we present a femtosecond mode-locked ytterbium-doped fiber (YDF) laser based on GO-COOH SA and a nonlinear polarization rotation effect. A mode-locked laser with a center wavelength of 1027 nm, an average output power of 53.5 mW (44.3% conversion efficiency), a fundamental repetition rate of 22 MHz, a pulse duration of 239 fs, and a signal-to-noise ratio of up to 75 dB is obtained. (C) 2018 The Japan Society of Applied Physics