Polarization Characteristics Of Silicon Slot Waveguide And Polarization Splitter Based On Silicon Asymmetric Waveguide

Polarization is one of the fundamental properties of light wave. Thus doing research on the polarizations characteristics during light propagation and on the ways to separate different polarization states efficiently, has both theoretical and applicable significance on optical fiber communication, polarization detection and analysis, laser modulation, polarization imaging system and so on. However, in the field of silicon slot waveguide research, most researches pay their attentions mainly to optical transmission characteristics of quasi-TM modes. Therefore, here in this thesis, both the band width properties and the field distributions characteristics associated with dual polarization states(both quasi-TM mode and quasi-TE mode) in a silicon slot waveguide are comprehensively investigated by adoption plane-wave expansion method and finite difference time domain method. Moreover, to satisfy demands of the on-chip applications, a compact polarization beam splitter based on asymmetrical directional coupler is also designed. The main work is as follows:(1) Polarizations characteristics of silicon slot waveguides are investigated by adoption three-dimensional numerical methods in this thesis. By tuning the width of the surrounding silicon region of the slot waveguides, 320.6 nm wide bandwidth for both quasi-TE and quasi-TM modes can be obtained in a dual polarizations single mode slot waveguide, and electric field enhanced in the low index slot zone for quasi-TE fundamental modes is also observed for the whole bandwidth, but there is no magnetic field enhancement for quasi-TM mode in the slot zone. The investigation proposed in this thesis would be served as a basis for the further design of related silicon photonics devices.(2) A compact polarization beam splitter based on asymmetrical directional coupler is designed by using two-dimensional plane-wave expansion method, and the design is verified by finite difference time domain method. The minimum length of the directional coupler in the polarization beam splitter is 2.88 ?m, and the corresponding length obtained by finite difference time domain method is 2.75 ?m. Therefore, the two methods are matched very well, which shows that the polarization beam splitter design would be correct.(3) The influences on extinction ratios and insertion losses, from the length and the bent angle of the s-shaped coupling bent waveguide of the polarization splitter, from the gap between the nanowire and the holey periodic waveguide of the asymmetrical polarization beam splitter are studied systematically. Two dimensional finite difference time domain method simulations demonstrate that when the bent angle is of 16 o, the width of the gap is of 99.05 nm, the optimized polarization beam splitter has 100 nm bandwidth at the central wavelength of 1550 nm, within which the extinction ratio above 15 dB and the insertion loss below 0.8 dB for both polarizations are also observed. The design of this polarization beam splitter would be severed as a basis for design and fabrication miniaturized silicon polarization beam splitters.