The Influence Of Higher-order Effects On Raman Soliton Self-frequency Shift In Metamaterials

Metamaterials(MMs) are artificial materials composed of orderly arranged micro-units that are very small even may reach nanometer scale, and their electromagnetic parameters are adjusted by altering the micro-units. Due to the dispersive dielectric permittivity and magnetic permeability, MMs possess many unique electromagnetic properties, such as negative refraction, perfect imaging, etc. Recent years, research on MMs has drawn wide attention in physics, material science, chemistry and engineering areas. In nonlinear optics, with the advent of the nonlinear optical MMs, the propagation of ultrashort pulses has quickly become a new research focus.Based on the model of nonlinear Schrodinger(NLS) equation describing the propagation of ultrashort pulses in MMs with Raman effect, the influence of the higher-order effects, especially saturable nonlinearity(SNL) and the fourth-order dispersion(FOD), on Raman soliton self-frequency shift (SSFS) in abnormal group velocity dispersion(GVD) region of self-focusing MMs is numerically studied by using the split-step Fourier method. The obtained results may provide some references for further studies of the nonlinear propagation of ultrashort pulses in MMs.The main contents are as follows:(1) Introduce the background and status of the MMs and outline the nonlinear propagation of ultrashort pulses and Raman SSFS in MMs.(2) Based on the NLS equation with Raman effect describing the propagation of ultrashort pulses in MMs, the influence of SNL on Raman SSFS is numerically studied. The results showed that in abnormal GVD region of self-focusing negative refraction MMs, the coefficient of SNL effect is negative. The SSFS is accelerated and the soliton spectrum is broadened under the negative SNL effect. In self-focusing positive refraction MMs, the coefficient of SNL effect is positive. The Raman SSFS is suppressed and the soliton spectrum is compressed under the negative SNL effect. In addition, the Raman SSFS is suppressed under the SNL effect combined with self-steepening(SS) effect and the third-order dispersion(TOD).(3) The influence of the FOD on Raman SSFS is numerically studied, which is different from that of SNL effect. In negative refraction MMs, the FOD, which is negative in abnormal GVD region, suppresses Raman SSFS. While in positive refraction MMs, the coefficient of FOD may be negative or positive. The negative FOD effect suppresses Raman SSFS, while the negative FOD promotes it. In addition, the Raman SSFS under the combination of the FOD, SNL effect, SS effect and TOD is also discussed.