Ultra-short pulse generation in a linear femtosecond fiber laser using a Faraday rotator mirror and semiconductor saturable absorber mirror

An innovative method for obtaining ultra-short and perfectly stable femtosecond pulses in a linear erbium-doped fiber laser is proposed. A commercial semiconductor saturable absorber mirror and a standard Faraday rotator are used in both sides of the linear fiber optic laser configuration to shorten the pulse duration and suppress undesirable effects on the polarization state. The laser operation is investigated theoretically using a physical model and it is verified using experimental results. The main idea of this research is to apply a Faraday rotator mirror for pulse shortening purposes. For this reason, two types of Er-doped fiber optics with different group velocity dispersion parameters are used to achieve the optimum net group velocity dispersion in the cavity. Output results demonstrate good consistency between theory and experimental results. The output power of the linear oscillator is approximately 45 mW with 135 fs pulses at the 23.5 MHz repetition rate without any pulse compression.