Enhanced third-harmonic generation by manipulating the twist angle of bilayer graphene.

Twisted bilayer graphene (tBLG) has received substantial attention in various research fields due to its unconventional physical properties originating from Moiré superlattices. The electronic band structure in tBLG modified by interlayer interactions enables the emergence of low-energy van Hove singularities in the density of states, allowing the observation of intriguing features such as increased optical conductivity and photocurrent at visible or near-infrared wavelengths. Here, we show that the third-order optical nonlinearity can be considerably modified depending on the stacking angle in tBLG.

Optically controlled in-line graphene saturable absorber for the manipulation of pulsed fiber laser operation.

We demonstrate an optically tunable graphene saturable absorber to manipulate the laser operation in pulsed fiber laser system. Owing to the strongly enhanced evanescent field interaction with monolayer graphene, we could realize an efficient control of modulation depth in the graphene saturable absorber by optical means through cross absorption modulation method. By integrating the tunable graphene saturable absorber into the fiber laser system, we could switch the laser operation from Q-switching through Q-switched mode-locking to continuous wave mode-locking by adjusting only the optical power of the control beam.

Monolayer graphene saturable absorbers with strongly enhanced evanescent-field interaction for ultrafast fiber laser mode-locking.

We demonstrate an efficient all-fiber saturable absorber (SA) that evanescently interacts with a graphene monolayer. Strong nonlinear interaction between the graphene sheet and evanescent wave was realized in both experiments and numerical calculations by employing an over-cladding structure on high-quality monolayer graphene that uniformly covered the side-polished fiber. A passively mode-locked Er-doped fiber laser was built, including our in-line graphene SA, which stably generated ultrashort pulses with pulse duration of 377 fs at a repetition rate of 37.

Active control of all-fibre graphene devices with electrical gating.

Active manipulation of light in optical fibres has been extensively studied with great interest because of its compatibility with diverse fibre-optic systems. While graphene exhibits a strong electro-optic effect originating from its gapless Dirac-fermionic band structure, electric control of all-fibre graphene devices remains still highly challenging. Here we report electrically manipulable in-line graphene devices by integrating graphene-based field effect transistors on a side-polished fibre.