Chirp Evolution Algorithm of a Dark-Optical-Comb Injection Mode-Locked SOA Fiber Laser Pulses During Soliton Compression

The chirp evolution of a dark-optical-comb injection harmonic mode-locked (HML) semiconductor optical amplifier fiber ring laser (SOAFL) with a nonlinearly driven electro-absorption modulator is demonstrated. The dispersion compensation of the 10-GHz HML-SOAFL pulse with a 100-m-long dispersion compensation fiber is performed to shorten the pulsewidth from 29 to 2.9 ps with a compression factor of 10, and a time bandwidth product (TBP) of 0.5. The soliton compression with a 10-m-long single-mode fiber is employed to deliver the amplified 10-GHz HML-SOAFL soliton pulse with a peak power of 38.2 W and a pulsewidth of 1.6 ps, while the spectrum is broadened from 1.4 to 2.3 nm with a TBP of 0.45. To monitor the dynamic chirp evolution, a second-harmonic generation frequency-resolved optical gating (SHG-FROG) is used to retrieve the amplitude and phase contour profile of the HML-SOAFL. The phase fitting result distinguishes the linear chirp from the nonlinear chirp associated with the HML-SOAFL pulse, which are 0.016 ps² and 0.002 ps³. The Schrödinger equation assists to retrieve the phase evolution of the 10-GHz HML-SOAFL with negative group velocity dispersion. Disregarding the linear dispersion compensation and soliton compression, the original 10-GHz HML-SOAFL pulse with a negative GDD of -5 ps² is quantified.