The Nonlinear Propagation Of Ultrashort Pulse In The Silicon Waveguides

Silicon photonic waveguides have been extensively studied in recent years, due to their extraordinary capability to tightly confine optical mode, enhanced nonlinearity and the good compatibility with mature CMOS technologies. Some photonic phenomenon has been demonstrated in silicon photonic waveguides, such as temporal soliton-effects compression, four-wave-mixing, Roman amplification, optical switching, all-optical modulation, and all-optical wavelength conversion. The temporal and spectral properties of the ultrafast pulse propagation in the silicon photonic waveguides are of much necessity to be investigated to support its application.We studied the temporal and spectral properties of ultrafast pulse in both silicon nanowire waveguides and silicon photonic crystal waveguide. The physical mechanism of pulse acceleration is analyzed in detail and the influences of input pulse energy and waveguide length on the temporal and spectral properties are discussed. Additionally, the temporal and spectral properties of the signal pulse propagation are studied when both pump and signal pulses are propagating in the silicon waveguide. The main contents of this paper are as follows:Firstly, the experimental system, the ultrafast pulse detection system, is presented as well. This system is with the capability of both Frequency Resolved Optical switch(FROG) and Cross Correlation Frequency Resolved Optical gating(XFROG). The temporally and spectrally properties of the ultrafast pulse propagation in the silicon photonic waveguides are investigated in detail by the numerical simulation of Nonlinear Schrodinger Equation and the detection of the frequency of cross-correlation frequency-resolved optical gating. The main results are as follows:1, The nonlinear pulse broadening of the picosecond pulse evolution in the silicon nanowire waveguide was investigated, and physical mechanism of nonlinear pulse broadening is demonstrated to be the two-photon absorption. On the other hand, the input pulse energy and waveguide length which influence the nonlinear pulse broadening are analyzed as well.2, In the experiments, we observed the phenomenon of pulse acceleration in the silicon nanowire waveguides for the first time. Our research shows that the pulse acceleration is induced by the free carrier absorption. The input pulse energy and waveguide length which play important roles in the absorption are analyzed.3, We study the spectral blue shift of the picosecond pulse by the detection of the XFROG and the simulation of NLSE mode. The physical mechanism of the spectral blue-shift was demonstrated to be the free carrier dispersion. The characters of the chirped pulse propagation in the silicon nanowire waveguides are discussed and the influences of initial chirp on the pulse propagation are analyzed.4, The properties of the femtosecond pulse evolution in the silicon nanowire waveguides are investigated by generalized nonlinear Schr?dinger equation, and the pulses exhibit high-order soliton compression, splitting and spectral red-shift. We also analyzed the influence of the dispersion and the higher-order nonlinear effects on the properties of the femtosecond pulse evolution.Secondly, the temporal and spectral properties of the ultrafast pulse propagation in the slow light photonic crystal waveguide are investigated by the simulations of nonlinear Schr?dinger equation model and the detections of cross-correlation frequency-resolved optical gating. The main results are as follows:1, The analysis on the pulse compression in the slow light photonic crystal waveguide shows that the compression factor is 2.16 in the photonic crystal waveguide with 1.3mm length, although the two photon absorption is considering. We demonstrated the physical mechanism of pulse acceleration in the silicon photonic crystal waveguide, which shows that the pulse acceleration is induced by the free carrier dispersion. We demonstrated that the pulse compression,the pulse acceleration are and the spectrum blue shift extremely enhanced by the slow light effect.2, The temporal direction of the reference pulse was determined by the XFROG measurement and NLSE simulation, and we found that the time direction of the input pulse and the reference pulse can be confirmed, with the sub-peak at the tailing edge of the pulse. The method can overcome the limit of traditional FROG measurement method of ulrashort pulses, with ambiguous temporal direction.Thirdly, the temporal and spectral properties of signal pulse are discussed by cross-pulse nonlinear Schrodinger equation when both pump pulse and signal pulse are propagating in a silicon nanowire waveguides or a silicon photonic crystal waveguide. The interaction of pump pulse and signal pulse are influenced by the pump pulse energy and the temporal difference of these two pulses. Our research indicated that the temporal and spectral properties of output signal pulse are determined by the pump pulse energy and the temporal difference of these two pulses, in support of the application of silicon waveguides.Our researches support the analysis of the properties of silicon waveguides with functionality, performing with ultrashort pulses. Our researches have potential values for the next generation of optical computing and communication system, matrix light controlling.