We present a passive mode-locked Raman laser incorporating SWCNT (Single-Wall Carbon Nanotubes) as saturable absorbers operating in O-band. We construct two single mode fiber lasers to generate ultrashort pulses near zero dispersion wavelength fiber. As results, pulse-trains were achieved in two different regimes and we compared the output bandwidth, rate repetition and pulse durations from both lasers. With high accumulated dispersion, nanoseconds square duration pulses were generated from laser cavity. So we study the pulse duration behavior introducing a dispersion shifted fiber (DSF) inside the cavity and verified a strong relation between pulse shortening and DSF length.