Abstract
By leveraging cross-like hybrid plasmonic waveguides (HPWs) and subwavelength gratings, a silicon-based ultracompact ${{\rm{TE}}_0}$- and ${{\rm{TE}}_1}$-${\rm{pass}}/{{\rm{TM}}_0}$- and ${{\rm{TM}}_1}$-stop dual-mode polarizer for 1.55/2 µm dual-wavelength is proposed and analyzed in detail. The HPWs are located above the bottom Si waveguide to form a hybrid plasmonic silicon nitride waveguide (HPSNW), in which the ${{\rm{TE}}_0}/{{\rm{TE}}_1}$ mode is well supported in the bottom Si layer while the ${{\rm{TM}}_0}/{{\rm{TM}}_1}$ mode is confined in the ${\rm{Si}}{{\rm{O}}_2}/{\rm{S}}{{\rm{i}}_3}{{\rm{N}}_4}$ layer of the HPSNW and thus sees high absorption loss at 1.55/2 µm. Accordingly, the ${{\rm{TE}}_0}/{{\rm{TE}}_1}$ mode at 1.55/2 µm can directly pass through the device once it is transited from input waveguide to the HPSNW. In contrast, the ${{\rm{TM}}_0}/{{\rm{TM}}_1}$ mode at 1.55/2 µm suffers from great mode radiation and mode attenuation, respectively, caused by the modal mismatch and metal absorption, leading to mode blocking. Therefore, a polarizer with dual-mode/dual-wavelength operation is realized for the first time, to the best of our knowledge. Numerical results show that the proposed polarizer has an insertion loss (IL) of 0.37 dB/0.29 dB for the ${{\rm{TE}}_0}/{{\rm{TE}}_1}$ mode and an extinction ratio (ER) of 17.3 dB/29.7 dB for the ${{\rm{TM}}_0}/{{\rm{TM}}_1}$ mode at 1.55 µm (an IL of 0.42 dB/0.76 dB for the ${{\rm{TE}}_0}/{{\rm{TE}}_1}$ mode and an ER of 33.1 dB/23.3 dB for the ${{\rm{TM}}_0}/{{\rm{TM}}_1}$ mode at 2 µm) in an ultracompact length of 6.5 µm. The operating bandwidth is up to 630 nm when the ER is over 18.5 dB/19.7 dB and the IL is below 0.52 dB/1 dB for fundamental/first-order mode, indicating an ultrabroadband operation. Additionally, fabrication tolerances of the proposed device are investigated, and electric field evolution is also illustrated.
© 2020 Optical Society of America
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