Semiconductor saturable absorber mirror in the 3-5 mu m mid-infrared region

Semiconductor saturable absorber mirrors (SESAMs) have been regarded as a revolutionary technology for ultrafast mode-locked lasers, producing numerous landmark laser breakthroughs. However, the operating wavelength of existing SESAMs is limited to less than 3 mu m. In this study, we create a 3-5 mu m mid-infrared (MIR) SESAM by engineering an InAs/GaSb type-II superlattice. Bandgap engineering and the strong coupling between potential wells in a superlattice enable a broadband response of saturable absorption in the 3-5 mu m spectral range. Using the fabricated SESAM, we realize a SESAM mode-locked Er:ZBLAN fiber laser at 3.5 mu m, which delivers MIR ultrashort pulses with high long-term stability. The breakthrough of SESAM fabrication in the MIR will promote the development of MIR ultrafast coherent sources and related application fields. (C) 2022 Optica Publishing Group