Numerical modeling and simulation of active and passive silicon photonic waveguides

2017-01-31T04:16:47Z (GMT) by Dissanayake, Chethiya Meghawarna
This research was undertaken with the aim of establishing a comprehensive simulation platform for the investigation of light propagation in active and passive silicon photonic structures. It is essential to perform detailed numerical simulations to gain a clear insight into the interplay of optical nonlinearities in silicon for improving the performance of silicon based photonic devices. Such detailed numerical simulations may also lead to novel device concepts and substantially extend the capabilities of silicon photonics in the future. The well-established finite-difference time-domain (FDTD) technique is preferred for such detailed simulations because the FDTD scheme allows electromagnetic field equations to be solvedwithminimal assumptions. Moreover, unlike most other simulation models, the FDTD models are restricted neither by the single-mode assumption nor by the slowly varying envelope approximation. In the first stage of the research, a two-dimensional FDTD simulator that takes into account the linear and nonlinear optical properties of silicon was developed. The dominant linear optical effects included in this FDTD algorithm were material dispersion and linear absorption in silicon, while the dominant nonlinear optical effects included were stimulated Raman scattering, the Kerr effect, two-photon absorption, free-carrier absorption, and free-carrier dispersion. The developed simulator was used to investigate the Raman-mediated nonlinear interaction of co-propagating and counter-propagating pulses inside silicon waveguides. This analysis shows unambiguously that second-order Stokes and anti-Stokes sidebands of sufficiently high intensities can develop from noise when the two pulses are co-propagating, but these sidebands are absent when these pulses counter-propagate, due to an inherent phase mismatch. In addition, the evolution of interacting pulses in the temporal and frequency domains was studied using the developed two-dimensional simulator. In stage two, by incorporating the anisotropy of silicon optical nonlinearities and the vectorial nature of the electromagnetic field, a fully functional three-dimensional FDTD algorithm was developed for the analysis of silicon photonics devices. Modeling of the anisotropy of the Kerr effect, two-photon absorption, and stimulated Raman scattering was undertaken and presented. Under certain realistic conditions that prevent generation of the longitudinal optical field inside the waveguide, thismodel was simplified considerably and was represented by a computationally-efficient algorithm, suitable for numerical analysis of complex polarization effects. Using this FDTD simulator, polarization dependence for several nonlinear effects, including self-phase modulation, cross-phase modulation, and stimulated Raman scattering, was studied. Owing to its generality in handling complex waveguide geometries and short optical pulses, the proposed three-dimensional FDTD algorithm is very useful for testing the suitability of anisotropic nonlinearities for different siliconbased photonic devices. In addition, this research has resulted in the development of several essential post-processing tools for the analysis of FDTD simulation results. These tools include a spectrummonitor for transforming the time domain results into the frequency domain, an energy flow monitor for investigating the propagation of energy within the silicon structures, and a visualization tool for investigating the evolution of electromagnetic wave polarization.