Aluminum oxide composite microfiber-based saturable absorber for 1.97 μm picosecond soliton fiber laser

We experimentally demonstrate the generation of a transform-limited soliton pulse with a 1.9 ps pulse width within the 1.97 μm “eye-safe” wavelength band. This was achieved using a microfiber-based saturable absorber (SA) device based on aluminum oxide (Al2O3) microparticles blended within a polydimethylsiloxane matrix to facilitate evanescent field interaction. The Al2O3-SA, fabricated through a heat-assisted solvent exchange and spin-coating technique, exhibited a modulation depth of 4.08% and a saturation fluence of 30 μJ/cm2. By integrating this Al2O3-SA into a thulium-holmium-doped fiber ring resonator, utilizing the combined effects of a long gain fiber length and resonant energy transfer, we achieved an extended lasing wavelength centered at 1971.2 nm. The resonator delivered an output power of 22 mW and a pulse energy of 3.24 nJ. This work highlights the potential of ceramic-based composite materials for next-generation photonic devices in relevant laser applications.