The Research On Optical Signal Processing In Silicon-graphene Based Nonlinear Devices

Nonlinear optics plays an important role in optical communications. Nonlinear optics based applications mainly focus on areas of optical communication, quantum communication, detection, sensing, imaging and so on. The formation of highly nonlinear effect has long been a hot research topic of the academia. In recent years, nonlinear study based on four-wave mixing, which is an important third-order nonlinear effect, has become a hot subject all over the world. The nonlinear coefficients of silicon structures such as slot waveguide, photonic crystal and surface plasmon waveguide have been greatly enhanced but there are still some problems. Firstly, due to the limitations of silicon’s nonlinear coefficients, signal gains of four-wave mixing are not able to be ideally large; secondly, the response speed of four-wave mixing is limited by the carrier effect in silicon materials. Therefore, combination of new high nonlinear materials with silicon structures could be a prospective trend.Since its discovery in 2004, graphene has raised wide spread concerns of scientists because of its superior characteristics in optoelectronic field, such as high transparency, high electron mobility and high third-order nonlinearity, furthermore, a series of outstanding results have been obtained. We introduce graphene into silicon-based device and use its high nonlinear coefficient to improve the overall nonlinear coefficient of the device. The graphene based nonlinear silicon devices have advantages of small mode area, high integration density, high response rate, and is easy to be integrated with mixed microelectronics. Based on the above mentioned characteristics, they have wide applications in all-optical signal processing, quantum entanglement generation and nonlinear super continuum signals.Innovation points and contributions can be summarized as follows:1) Two kinds of graphene based structures with high nonlinearity are proposed, including silicon straight waveguide and conductor-gap dielectric waveguide. The nonlinear coefficients of the devices are improved by increasing the nonlinear index while reducing the mode field area. The feasibility of this proposal is verified and FWM conversion efficiency is calculated by simulations.2) The fabrication processes of graphene-based silicon straight waveguide devices are described, including the sample preparation of silicon waveguide and graphene and the transfer skills of graphene onto silicon waveguide. The quality of graphene is meanwhile characterized. Four-wave mixing experiments are performed by the fabricated graphene-silicon based nonlinear devices and the influences of graphene on the conversion efficiency are analyzed.3) What’s more, a self-coupled micro-ring resonator is proposed and experimentally demonstrated in this paper. With the mode coupling between micro-ring and self-coupled waveguide, multiple numbers of split resonances can be obtained and devices with this characteristic may have applications in nonlinear signal processing.