An all fiber laser based upon nonlinear polarization rotation as an effective fast saturable absorber for mode-locking is reported. The absorber can act as passive Q-switching and modelocking. The ring laser with a highly Yb3+-doped fiber as the gain medium, pumped by a semiconductor laser of 976 nm wavelength, can operate in three different stable regimes by proper adjustments of pump power and polarizer orientations: Q-switched, Q-switched mode-locked and continuous wave (CW) mode-locked. The center wavelength of the CW mode-locked pulse is 1.05 μm with a full width at half maximum (FWHM) spectrum of 13.8 nm, the pulse repetition rate is 20 MHz, and an average output power is 15.82 mW with 270 mW pump power. In Q-switched regime, the laser generates 8 μs duration pulses of 4.7 nm FWHM spectrum at a repetition rate of 17.54 kHz. The Q-switched repetition rate is 300 kHz in Q-switched mode-locked regime.