Nanowerks has a spotlight on the work of Dingyuan Tang from Nanyang Technological University and Professor Kian Ping Loh from National University of Singapore with the first breakthrough in using few-layer graphene as a saturable absorber for the mode locking of lasers.
Graphene can be used for telecommunications applications and that its weak and universal optical response might be turned into advantages for ultrafast photonics applications.
The addition of a layering structure could tune graphene’s electronics properties, thus influencing its photonics nature as well as its saturable absorption property.
Graphene’s tunable photonic property will guarantee graphene with brilliant photonic applications given that the ability to extensively control and tune materials’ properties is now at the center of modern photonics.
The chemical modification of graphene could bring completely new physics.
It is envisaged that many new photonic properties of graphene will be discovered, and new concepts on graphene based ultra-fast photonic devices will emerge. It definitely paves the way to graphene based ultra-fast photonics applications for ultra-fast micro-processing, bio-medical, sensing, military and telecommunications systems.
We have demonstrated large energy mode locking of an erbium-doped fiber laser with atomic layer graphene as the saturable absorber. Stable mode locked pulses with single pulse energy as high as 7.5nJ and 415 fs pulse width have been generated. Our experimental results shown that atomic layer graphene could be a promising saturable absorber for high power laser mode locking.
Starting from the laser mode locking threshold, the output power increased linearly with the pump power with a slope efficiency of 6.7%. The maximum achieved single pulse energy is as high as ~7.3 nJ. To the best of our knowledge, this is the highest pulse energy reported for ultrafast erbium doped fiber lasers mode locked with a real saturable absorber in cavity. At the maximum output power, the pulse width is ~415fs, which gives the maximum peak power of 17.6 kW.
The optical conductance of monolayer graphene is defined solely by the fine structure constant, = (where e is the electron charge, 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.
Due to its unique electronic property and the Pauli blocking principle, atomic layer graphene possesses wavelength-independent ultrafast saturable absorption, which can be exploited for the ultrafast photonics application. Through chemical functionalization, a graphene-polymer nanocomposite membrane was fabricated and first used to mode lock a fiber laser. Stable mode locked solitons with 3 nJ pulse energy, 700 fs pulse width at the 1590 nm wavelength have been directly generated from the laser. We show that graphene-polymer nanocomposites could be an attractive saturable absorber for high power fiber laser mode locking
We report on the dark pulse emission of an all-normal dispersion erbium-doped fiber laser with a polarizer in cavity. We found experimentally that apart from the bright pulse emission, under appropriate conditions the fiber laser could also emit single or multiple dark pulses. Based on numerical simulations we interpret the dark pulse formation in the laser as a result of dark soliton shaping.