Abstract
A graphene-silicon hybrid waveguide with a dielectric spacer is proposed to enhance the nonlinear response in ultra-wide wavelength range by applying graphene’s broadband highly nonlinear optical properties. The chemical potential of the graphene layer is tuned to satisfy the resonance condition and hence a low propagation loss is obtained. The dielectric spacer is used for avoiding additional free-carrier-absorption loss due to carrier interchange between the silicon core and the graphene layer. Aiming at the special waveguide structure with ultra-thin graphene layer, a full-vectorial theoretical model is developed to analyze its nonlinear properties. The waveguide dimensions are optimized in terms of the nonlinear parameter. The proposed hybrid waveguide exhibits high nonlinearity enhancement in an ultra-broad wavelength region covering near-infrared and mid-infrared bands. The conversion efficiency for a degenerate four-wave mixing process reaches −18.5 dB only with a pump power of 0.5 W and a waveguide length of tens of microns. In the wavelength range of 1.3–2.3 μm, the conversion efficiency can be kept stable by adopting suitable waveguide geometry and length. The corresponding 3-dB bandwidth can reach 40–110 nm for each fixed pump. The graphene-silicon hybrid waveguide has the potential to support chip-scale nonlinear applications in both near- and mid-infrared bands.
Highlights
As we know, a monolayer of pristine graphene exhibits a considerable wavelength-independent absorption (≈ 2.3% per layer) in an ultra-broadband wavelength region involving infrared and visible optical band[14]
Without the precondition of weak guidance approximation, a vectorial nonlinear Schrödinger equation for nonlinear pulse propagation has been derived in ideal lossless waveguides with complex transverse structure[30], which provides a platform for generalizing nonlinear processes like self-phase modulation (SPM), cross-phase modulation (XPM), four-wave-mixing (FWM), Raman and Brillouin scattering
We find that, as the wavelength increases, graphene’s imaginary part of the third-order susceptibility may change its sign near the resonance points of photon absorption, the loss of graphene cannot be treated as either two-photon absorption (TPA) or absorption saturation
Summary
A graphene-silicon hybrid waveguide with a dielectric spacer is proposed to enhance the nonlinear response in ultra-wide wavelength range by applying graphene’s broadband highly nonlinear optical properties. We will numerically investigate the wave dynamics upon propagation in the proposed graphene-silicon hybrid waveguide and discuss its nonlinear performance (nonlinear parameter, conversion efficiency and conversion bandwidth) in the near- and mid-infrared wavelength range. In order to achieve the best nonlinear performance of a DFWM process in the graphene-silicon hybrid waveguide, the cross section dimensions should be designed to maximize the nonlinear parameter at the pump wavelength λp, and the waveguide length and pump power should be optimized for the highest conversion efficiency. The results show that the designed graphene-silicon hybrid waveguide can support broadband nonlinearity enhancement in an ultra-broad wavelength range covering both near- and mid-infrared band. A graphene-silicon hybrid waveguide with a dielectric spacer is proposed to enhance the nonlinearity using the high third-order susceptibility of graphene in an ultra-broad wavelength range covering near- and mid-infrared bands. The proposed hybrid waveguide structure has a stable nonlinear enhancement from 1.3–2.3 μm, which exhibits that the micron-scale graphene-silicon hybrid waveguide has the potential to support chip-scale nonlinear applications in both near- and mid-infrared bands
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