This invention discloses a fiber Chirped Pulse Amplification (CPA) laser system. The system includes a fiber mode-locking oscillator for generating a seed laser. The laser system further includes a stretching stage for stretching the seed laser for projecting to an Yb doped amplifier. The Yb doped amplifier is implemented for taking advantage of a self phase modulation (SPM) to broaden a spectrum whereby an amplification of the laser pulse is without narrowing down the spectrum. The amplifier has a gain spectrum corresponding to a broaden spectrum by taking advantage of the SPM in the amplifier. The amplifier is further connected to an output fiber having a predefined length with a predefined level of SPM for broadening a spectrum.