Femtosecond graphene mode-locked Er:ZBLAN fiber laser at 2.8 μ m

The mid-infrared (MIR) spectral region is an attractive band for major applications, such as spectroscopy owing to the presence of many molecular absorption signatures. Fiber lasers operating in this spectral region are highly sought after because of their compactness and ease of integration into detection systems. Considerable effort has been invested in advancing the ultrafast operation of such lasers, particularly in the 3 μm spectral range where erbium ions exhibit broadband gain under 976 nm pumping. However, achieving passively mode-locked femtosecond operation with erbium fiber oscillators remains challenging due to the complexities involved in designing saturable absorbers, particularly with adapted carrier recovery time. In this study, we present a compact setup for the sub-picosecond operation of an erbium fluoride fiber laser. The passive mode-locking operation is enabled by a graphene film on a gold mirror fabricated in-lab using a wet chemical transfer process. The laser produced a record pulse duration of 656 fs at 2.8 μm and delivered energies of up to 4.93 nJ. This work explores the soliton dynamic operation of the laser and paves the way for the further development of such MIR femtosecond fiber oscillators.