dc.description.abstract | For realizing high-density photonic integrated circuits, subwavelenth waveguides are essential. Hybrid plasmonic waveguides (HPWs) have been regarded as a promising solution for its subwavelength field confinement capability and low loss characteristic compared to traditional plasmonic waveguides. In this research, two hybrid-plasmonic-mode-evolution-based polarization mode converters (PMCs) for rotating and coupling the photonic quasi-TE$_{00}$ mode in an embedded silicon waveguide to the HP$_{01}$ mode in a HPW have been presented. Both designs are silicon-on-insulator-compatible and consist of four-section asymmetric/symmetric top silver (Ag) structures.
The design principle is based on considering the whole PMC as a cascade of HPW slices, each of which having its eigenmodes along the propagation direction. The gradient ascent of the transverse magnetic polarization fraction and the minimum rate of change in the modal index (real part) of the eigenmode are used to rapidly obtain sub-optimum designs and are proved to effectively reduce heavy reliance on parameter sweeps using numerical computations. The former describes the mode evolution process, while the later deals with the propagation loss problem.
The footprints of the two numerically optimized PMCs are <6$ imes$0.43 $mu$m$^2$ and<7$ imes$0.6 $mu$m$^2$, respectively. The mode conversion efficiency (MCE), polarization conversion efficiency (PCE), polarization extinction ratio (PER), and the insertion loss (IL) of the first (second) PMC design are found to be 87.58 % (90.09 %), 99.87 % (99.96 %), 27.9114 dB (34.3846 dB), and 0.5899 dB (0.4592 dB), respectively, at the operating wavelength of 1550 nm. Under the conditions of MCE>80 %, PCE>92 % and IL>80 %, the corresponding spectral range of the first (second) design is 133 nm (176 nm), 182 nm (>200 nm) and 139 nm (181 nm), all covering the entire $C$ band of optical telecommunication. The fabrication tolerances of the top Ag structure and the silica spacer are also discussed. The PMCs presented here whose performance are rigorously evaluated are not only well-designed and ultracompact in size, but also support the novel design principle for mode-evolution-based PMCs presented in this work. | en_US |