High-Density Well-Aligned Single-Walled Carbon Nanotubes for Application as a Saturable Absorber with a High-Pass Filter Effect in an Erbium-Doped Ultra-Short-Pulse Fiber Laser

We report on the experimental study of the stability of ultrashort pulse (USP) generation. Two types of mode-locking (ML) mechanisms were carried out in an Er-doped fiber laser: first, passive ML based on the nonlinear polarization evolution (NPE) and second, hybrid ML based on high-density, well-aligned single-walled carbon nanotubes (HDWA-SWCNT) as a saturable absorber (SA). The output pulse characteristics of both states were compared. The average output power was 28.8 and 29.96 mW, with pulse durations of 174 and 211 fs for NPE-based ML and hybrid ML, respectively. The maximum level of the relative intensity noise (RIN) was -130.35 dBc/Hz for NPE-based ML and -133.83 dBc/Hz for HDWA- SWCNT-based ML in the frequency range of 476 mu Hz to 100 kHz. This result provides direct evidence of the high-frequency filter effect in the nanotubes used. Furthermore, the measured value of the deviation of the pulse repetition frequency in a time interval equal to 1 s was 1.9610(-7) and 1.3310(-7) for the ML mechanisms of the NPE and hybrid modes, respectively.