Ultrafast Nonlinear Optics And Applications In SOI Waveguides

In recent years, silicon-on-insulator (SOI) optical waveguides with larger refractive index contrast between silicon core and insulator cladding has attracted much attention because it is considered as an ideal platform for optoelectronics integration, in which both theoretical and experimental investigations become booming nowadays. For comparison with the conventional optical fiber waveguides case, SOI has stronger nonlinear optical properties such as nonlinear Kerr effect and stimulated Raman scattering (SRS), etc., and unique nonlinear processes such as two-photon absorption (TPA), free-carrier absorption (FCA) and free-carrier dispersion (FCD), and so on, due to the influences of waveguide structure and material character of SOI.In the thesis, based on both theoretical and experimental modeling for optical signal propagating in SOI optical waveguides, all kinds of linear and nonlinear processes experienced are investigated for ultrafast optical pulse with only time duration ranging from femtosecond to picosecond in SOI waveguides. Various application models are explored and designed by utilizing these nonlinear phenomena.Based on generalizing and analyzing the research progress of optical signal processing in SOI, the linear and nonlinear propagation equations for ultrafast pulse evolving in ridge silicon waveguide are improved further, which include linear processes such as waveguide linear loss, group velocity dispersion, and third-order dispersion, and so on, and nonlinear processes such as self-phase modulation, degenerate two-photon absorption, free carrier absorption, and free carrier dispersion. In addition, the nonlinear processes such as cross-phase modulation, non-degenerate two-photon absorption, and stimulated Raman scattering must also be considered for double wavelengths propagating in waveguide. Because the nonlinear equation can not be solved analytically in common cases, the operation processes of the classical split-step Fourier and four-order Runge-Kutta methods are introduced in detail. However, the dynamic evolution of ultrafast pulse in waveguide can also be observed by means of the analytical results of propagation equations under especial conditions and reasonable assumptions. Investigation results show that when ignoring the dispersion effects, the time domain and spectrum widths of picosecond pulse will be extended and compressed, respectively, by TPA dominance, nevertheless which will be compressed and extended, respectively, by FCA dominance because of the absorbed trailing edge. Furthermore, the pulse symmetry is destructed. In addition, although the FCD will not influence on the time domain waveform, the spectrum will be extended rapidly. When the time duration of pulse is shortened into femtosecond region, the influence of dispersion on the pulse should be considered. By the combined effects of dispersion and various nonlinearities, the optical wave breaking is observed for the first time, when high intensity pulse evolving in waveguide. After the launching pulse is determined, the properties of optical wave breaking depend strongly on the sign and intensity of dispersion parameters.When several ultrafast pulses are propagating simultaneously, nonlinear processes such as cross-phase modulation (XPM), cross non-degenerate TPA, SRS and four-wave mixing (FWM), and so on, will be considered. One of the nonlinear processes will play dominance for various conditions. The strong pump pulse will change the spectrum of weak signal pulse by the XPM effect as a result that the time domain waveform of weak signal pulse is also changed remarkably by combining the dispersion effect. Hence, the models of signal pulse compression and optical switching based on the Mach-Zehnder interferometer (MZI) configuration are designed by employing the principle of XPM. Moreover, the signal pulse can also be compressed effectively under the condition of larger pulse walkoff effect, but which has some pedestal due to the influence of third-order dispersion. The switching window can be controlled by adjusting the energy of control pulse, where the outcome pulse can be formed into a series of ultrashort pulse with the increase of input control pulse. By using the non-degenerate TPA absorption process between both of pulses, a novel project if explored for compressing and shaping the self-compression pulse induced by FCA, in which shaping of self-compression can be optimized by adjusting the initial delay time and control pulse energy. In addition, the operations of ultrafast all-optical modulation and logic NOR gate are achieved by utilizing the non-degenerate TPA effect. In optical modulation, both the dispersion and initial chirp will change the modulation depth of pulse modulated. When the frequency detuning between both of pulses satisfies the condition of Raman resonance, energy transfer will occur from pump to signal pulse. After the signal pulse obtains enough high energy, the pump pulse will be depleted further, leading to gain level suppressed. Therefore, the pump pulse will evolve into asymmetric two peaks. By the SRS effect, the models of ultrafast logic AND gate, high speed inverted and non-inverted all-optical wavelength conversion, and femtosecond pulse generation are explored and designed, where the quality of AND gate pulse is strongly related to waveguide length and launching pulse energy, and the wavelength conversion of single-to-dual and simultaneously inverted and non-inverted conversion is achieved by controlling the frequency detuning between signal and continue probe wave, and by the SRS effect of ultrafast dark pulse and continue wave, we have obtained ultrafast femtosecond bright pulse with time domain width of only several tens of femtosecond, whose properties is dependent on the launching energy, waveguide length and dark pulse width. Under the condition with phase mismatch of zero, we realize the degenerate ultrafast FWM process, in which the signal pulse will be amplified effectively owing to parameter gain. By adopting different FWM processes, pulse shaping and Tbps all-optical wavelength conversion are achieved.