Sub-1.2 ps Pulse in Thulium-Doped Fiber Laser using ZIF-8 Derived Nanoporous Carbon Hybrid Saturable Absorber

In this work, sub-picosecond pulses near the 2.0 µm region are obtained from a thulium-doped fiber laser (TDFL) using a combination of a nanoparticle-doped component (NPC) derived from zeolitic imidazolate framework-8 (ZIF-8) as a physical saturable absorber (SA) together with the naturally occurring nonlinear polarization rotation (NPR) phenomenon in the laser cavity. The NPC, synthesized via direct carbonization at 700 °C, exhibited a high modulation depth of 17.47% with a saturation intensity of 2.8 MW/cm 2 . Initial testing with the standalone NPR configuration generated 1.3 ps pulses at 1988.24 nm with a 47.3 dB signal-to-noise ratio (SNR). The integration of the NPC into the NPR cavity, to form a hybrid SA, resulted in a 10.8% reduction in pulse width to 1.16 ps and a shift in the lasing wavelength to 1944.32 nm. Furthermore, the hybrid configuration significantly enhanced the operational stability, achieving an improved SNR of 51.1 dB. The results indicate that ZIF-8-derived nanoporous carbon is a highly effective nonlinear material for enhancing the performance of ultrafast fiber lasers.