Simultaneous $Q$ -Switching of a Tm3+:ZBLAN Fiber Laser at $1.9~\mu$ m and $2.3~\mu$ m Using Graphene

We demonstrate a passively Q-switched, dual-band Tm
³⁺
:ZBLAN fiber laser operating simultaneously around 1895 and 2315 nm using bidirectional pumping at 795 nm and a graphene saturable absorber. The Q-switched pulse trains at 1895 and 2315 nm have a synchronized repetition rate from 10.8 to 25.2 kHz with pulse durations as short as 4.5 and 4.9 μs, respectively.