| dc.description.abstract | In this research, a novel and ultracompact polarization mode converter (PMC) based on mode evolution that converts a quasi-TE$_{00}$ mode in a silicon strip waveguide to a quasi-TM mode in a hybrid plasmonic waveguide (HPW) has been proposed and numerically investigated. A four-section metal structure is introduced asymmetrically/symmetrically on top of a three-section dielectric (Si/SiO$_2$) waveguide to break the structural symmetry drastically. The dominant electric field of the quasi-TE$_{00}$ mode rotates as a result of the excitation of the hybrid plasmonic mode and eventually convert to the polarization state suitable for the quasi-TM mode of the HPW at the PMC output end. By analyzing the polarization extinction ratio (PER) and the propagation loss (PL) across the PMC, the preliminary design of each section is obtained followed by the finite-difference-time-domain method simulations with a mesh size of $Delta x$ = 10 nm, $Delta y$ = 4 nm, and $Delta z$ = 10 nm for more accurate results. The footprint of the optimized PMC is $<$ 7 $ imes$ 0.4 $mu$m$^2$ and the corresponding mode conversion efficiency (MCE), PER, insertion loss (IL), and the polarization conversion efficiency (PCE) are 88.80$\%$, 25.0929 dB, 0.5108 dB and 99.82$\%$, respectively.
The effect of the top metal (Ag) layer is also investigated. The results show that as the Ag film thickness becomes smaller, its capability to rotate the quasi-TE$_{00}$ mode diminishes. Therefore, the ratio of the power of HP quasi-TM mode to the total $z$-directed power decreases at the PMC output end, leading to a smaller MCE and a higher IL. The optimized PMC is shown to be insensitive to wavelength over the span of entire C band. The 80$\%$ bandwidth for the MCE is 103.8 nm (1490.9-1594.7 nm) and the 1-dB bandwidth for the IL is 105.8 nm (1490.0-1595.8 nm). On the other hand, the fabrication tolerances of the Ag film thickness, the straight Ag strip width, and the Ag tip width are 70, 75, and 100 nm for MCE over 80$\%$, respectively.
In the future, it is expected that the combined Si waveguide and HPW would play a key role in achieving highly-integrated photonic circuits. Hence, the research work presented in this thesis may see great potentials and contributions to the field of integrated optics. | en_US |