A novel all-fiberized Yb-doped fiber laser configuration for passively sub-nanosecond pulse generation is reported. By splicing a piece of Bi/Cr codoped silica fiber to a section of Yb-doped double clad fiber of 15 m in a fiber Bragg grating constructed fiber laser cavity, stable sub-nanosecond pulse train is obtained with a maximal repetition rate of 50.2 kHz and an average output power of 2 W. The calculated peak power exceeds 30 kW. The linear dependence of the pulse repetition rate on the absorbed pump power is confirmed. It is also found that stimulated Brillouin scattering plays a crucial role in the pulse generation. Broadband infrared supercontinuum emission is detected via the Bi/Cr fiber end, which spans over 1000 nm with spectral intensity variation lower than 5 dB.