Atomic‐Layer Graphene as a Saturable Absorber for Ultrafast Pulsed Lasers

TLDR

Monolayer graphene’s optical conductance is governed by the fine‑structure constant, yielding a frequency‑independent absorbance that can be saturated by Pauli blocking under strong excitation. The study demonstrates using atomic‑layer graphene as a saturable absorber to mode‑lock a fiber laser and generate 756‑fs soliton pulses at telecom wavelengths. Atomic‑layer graphene was incorporated into a mode‑locked fiber laser cavity, enabling ultrashort soliton pulse generation. The modulation depth of the graphene saturable absorber can be tuned from 66.5 % to 6.2 % by changing film thickness, demonstrating that ultrathin graphene films offer low saturation intensity, ultrafast recovery, tunable modulation depth, and wideband tunability for fiber lasers.

Abstract

Abstract The optical conductance of monolayer graphene is defined solely by the fine structure constant, α = $e^2 /=\hbar c$ (where e is the electron charge, $\hbar $ is Dirac's constant and c is the speed of light). The absorbance has been predicted to be independent of frequency. In principle, the interband optical absorption in zero‐gap graphene could be saturated readily under strong excitation due to Pauli blocking. Here, use of atomic layer graphene as saturable absorber in a mode‐locked fiber laser for the generation of ultrashort soliton pulses (756 fs) at the telecommunication band is demonstrated. The modulation depth can be tuned in a wide range from 66.5% to 6.2% by varying the graphene thickness. These results suggest that ultrathin graphene films are potentially useful as optical elements in fiber lasers. Graphene as a laser mode locker can have many merits such as lower saturation intensity, ultrafast recovery time, tunable modulation depth, and wideband tunability.