Ultracompact TE0- and TE1-pass/TM0- and TM1-stop dual-mode polarizer for 1.55/2 µm dual-wavelength using silicon-based cross-like hybrid plasmonic waveguides

Abstract

By leveraging cross-like hybrid plasmonic waveguides (HPWs) and subwavelength gratings, a silicon-based ultracompact T E 0 - and T E 1 - p a s s / T M 0 - and T M 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 T E 0 / T E 1 mode is well supported in the bottom Si layer while the T M 0 / T M 1 mode is confined in the S i O 2 / S i 3 N 4 layer of the HPSNW and thus sees high absorption loss at 1.55/2 µm. Accordingly, the T E 0 / T E 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 T M 0 / T M 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 T E 0 / T E 1 mode and an extinction ratio (ER) of 17.3 dB/29.7 dB for the T M 0 / T M 1 mode at 1.55 µm (an IL of 0.42 dB/0.76 dB for the T E 0 / T E 1 mode and an ER of 33.1 dB/23.3 dB for the T M 0 / T M 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.