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

Abstract

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 37.7 MHz. The corresponding 3-dB spectral bandwidth of the laser was measured to be 8.6 nm at the central wavelength of 1607.7 nm. We also experimentally observed that the spectral bandwidth and pulse duration of the laser output could be controlled by proper selection of the refractive index of the over-cladding material on the monolayer-graphene SA.

Reprogrammable Electro-Optic Nonlinear Activation Functions for Optical Neural Networks

“…Similarly, a fixed nonlinear response may also limit the performance of very deep ONNs with many layers of activation functions since the optical signal power drops below the activation threshold, where nonlinearity is strongest, in later layers due to loss in previous layers. For example, with optical saturable absorption from 2D materials in waveguides, the activation threshold is on the order of 1-10 mW [16][17][18], meaning that the strength of the nonlinearity in each subsequent layer will be successively weaker as the transmitted power falls below the threshold.…”

High extinction ratio D-shaped fiber polarizers coated by a double graphene/PMMA stack

“…Recently, graphene [7][8][9] has attracted enormous attention due to its unique electronic and photonic properties, including strong nonlinearity, high carrier mobility, ultrafast broadband response, high efficiency for light-matter interaction, and high thermal conductivity. Graphene-based structures have been exploited to realize saturable absorbers of fiber lasers [10][11][12], all-optical modulators [13,14], sensors [15] and broadband polarizers [16]. As far as polarizers are concerned, owing to the linear dispersion of Dirac electrons, graphene can selectively support TE or TM surface plasmon mode [16][17][18].…”

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

“…The inline GSA was fabricated by transferring a large area and uniform monolayer graphene onto the side-polished fiber (SPF). By employing additional overcladding on the SPF, we could realize strongly enhanced evanescent field interaction with monolayer graphene with reduced non-saturable scattering loss [25]. We describe the details of the optical tuning behavior of the GSA by applying control beam at 980 nm to the SA.…”

“…After transferring the graphene, the optical absorption of the SPF was increased to 0.58 dB with slight polarization dependent loss (PDL) of 0.03 dB. We then applied an overcladding with matched refractive index to increase the graphene-light interaction that also significantly increased the PDL to 13dB [25]. With this structure, the graphene SA demonstrate strong small signal absorption and large modulation depth at the wavelength of the signal beam at 1550 nm.…”