Polarization insensitive graphene saturable absorbers using etched fiber for highly stable ultrafast fiber lasers.

In this paper, we introduce a graphene-based saturable absorber (GSA) with high damage threshold employing symmetrical evanescent wave interaction for highly stable mode-locking of ultrafast fiber lasers. To enhance the evanescent wave interaction between the graphene layer and the propagating light, graphene flakes are mixed with polydimethylsiloxane (PDMS), and the graphene/PDMS composite is coated onto a chemically etched fiber. The GSA exhibits polarization insensitivity due to its symmetric cross-section, which enables stable operation against environmental disturbance such as stress, bending, and temperature variation. Finally, we demonstrate a fiber laser generating 216 fs pulses with an 80 dB signal-to-noise ratio.