Study Of Silicon-Based Hybrid Waveguides For High-Efficiency Broadband Spectra Translation

Mid-infrared band has huge potentials to free-space optical communications,laser radar,laser guidance,and remote sensing.However,photonic technologies and devices in this band are very scarce.In particular,the integrated mid-infrared photonic devices are almost blank.As the bridge of the mid-infrared band and the telecommunication band,mid-infrared spectral translation is considered as the basic key technology to develop mid-infrared devices and applications using the mature technologies in the telecommunication band.Compared with other conventional nonlinear materials,silicon has larger nonlinear coefficient and better compatibility for integration,and its spectrum transparency region covers the telecom band and the mid-infrared band.In this thesis,novel silicon-based hybrid waveguides are designed and the parameters are optimized aiming at realizing high-quality mid-infrared spectra translation.This dissertation is arranged in the aspects as follows:1.A generalized scalar model of nonlinear wave propagation applied to traditional silicon waveguides is introduced.Firstly,a series of important nonlinear effects in nonlinear waveguides are reviewed,and the relations among various nonlinear parameters are derived.Applying weak guidance approximation,the Scalar Nonlinear Schrodinger Equation(SNSE)is derived.Then,according to the scalar model,the parameters of the suspended silicon photonic waveguide were optimized to realize the broadband and efficient spectra translation in mid-infrared band.2.A generalized full vectorial model of nonlinear wave propagation applied to novel silicon-based hybrid waveguides is demonstrated.The novel silicon-based hybrid waveguides in this dissertation have complex transverse structures including inhomogeneous refractive index profiles and subwavelength features.On this occasion,the weak guidance approximation becomes invalid,and the nonlinear effects cannot be described accurately using scalar theory.Here a general vectorially-based Nonlinear Schrodinger Equation(VNSE)is derived for wave propagation through waveguides in the strong guidance regime,a set of nonlinear parameters in SNSE are redefined.Using the reciprocal theorem and perturbation theorem to take dispersion,loss,and nonlinear terms as perturbed terms,a generalized full vectorial amplitude coupled equations is obtained.According to the vectorially-based model,the parameters of two kinds of high-efficient broadband silicon-based hybrid waveguides were optimized to realize the broadband and efficient spectra translation in mid-infrared band.The figure-of-merit(FOM)is proposed to evaluate the performance of the waveguide.3.The silicon waveguides are experimentally demonstrated for spectra translation in mid-infrared band,and the experimental data were compared with simulation results.Finally,the shortcomings of the experimental scheme are analyzed and the improvement methods are proposed.