Abstract
We study the nonlinear optical properties of graphene integrated onto Si3N4 waveguides under picosecond and subpicosecond pulsed excitation at telecom wavelength. Saturable absorption of graphene under guided-mode excitation is measured, and the temporal effects related to the photoexcited carrier dynamics in graphene are highlighted. Thereafter, a model of photoexcited carriers in graphene is implemented into the nonlinear Schrodinger equation in order to simulate the pulse propagation across the hybrid graphene/Si3N4 waveguide. This allows us to extract phenomenological parameters of graphene saturable absorption in chip-based devices, which could provide some guidelines for the design of nonlinear elements in photonic integrated circuits.
Highlights
Over the past decade, graphene, a bi-dimensional lattice of carbon atoms, has generated plenty of interest for both fundamental and applied research in microelectronics and more recently in optoelectronics.1,2 Its unique properties,3 mostly related to the Dirac cone electronic dispersion,4 make it an outstanding material candidate for both electronic and photonic device applications.5–8 Among all relevant properties, the optical nonlinearity of graphene was pointed out to be much larger than those in traditional semiconductor and glass materials.9–11 In addition, this nonlinear response could be dynamically tuned through electrical gating,12–15 with the prospect of realizing fast, reconfigurable, and flexible nonlinear devices
We first present the nonlinear transmission of graphene/Si3N4 waveguides when excited by subpicosecond pulses at 1547 nm with increasing peak power and a fixed pulse duration (∼0.2 ps, for an Erbium Doped Fiber Amplifier (EDFA) pump current of 160 mA)
To reemphasize the link between the EDFA pump current and the pulse duration, we present in Fig. 6(d) the related normalized transmission vs the pulse duration inferred from these measurements for the case Lgr = 2.3 mm and EDFA pump current below 170 mA
Summary
Graphene, a bi-dimensional lattice of carbon atoms, has generated plenty of interest for both fundamental and applied research in microelectronics and more recently in optoelectronics. Its unique properties, mostly related to the Dirac cone electronic dispersion, make it an outstanding material candidate for both electronic and photonic device applications. Among all relevant properties, the optical nonlinearity of graphene was pointed out to be much larger than those in traditional semiconductor and glass materials. In addition, this nonlinear response could be dynamically tuned through electrical gating, with the prospect of realizing fast, reconfigurable, and flexible nonlinear devices. By varying the pulse duration from the picosecond to subpicosecond, we report a variation of the absorption saturation of graphene, thereby revealing some dynamics of this effect We correlate these measurements with a nonlinear pulse propagation model taking into account graphene interaction length, the linear and nonlinear response of the hybrid waveguide, power-dependent loss in graphene, and the associated dynamics of free carrier relaxation. These studies attempt to clarify the interplay between saturable absorption and third-order nonlinear refractive processes in graphene, which should help realize more efficient graphene based nonlinear devices on a chip
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