Ultracompact and broadband mid-infrared polarization beam splitter based on an asymmetric directional coupler consisting of GaAs–CaF2 hybrid plasmonic waveguide and GaAs nanowire

In this paper, an asymmetric directional coupler (DC) based on a GaAs–CaF2 hybrid plasmonic waveguide (HPW) and a GaAs nanowire (NW) is designed for the mid-infrared polarization beam splitter (PBS). The mode characteristics of the GaAs–CaF2 HPW and GaAs NW-based PBS are simulated by using the finite element method (FEM). With the appropriate widths of the HPW and NW, the TE polarization mode in the HPW and NW is phase-matched, whereas the TM polarization mode is phase mismatch. Hence, the TE mode undergoes a strong coupling to the GaAs NW while the TM mode pass through the GaAs–CaF2 HPW directly. The results show that the PBS achieves the extinction ratio (ER) of 19.78 dB and insertion loss (IL) of 1.64 dB for the TE mode, ER of 7.78 dB and IL of 2.64 dB for the TM mode at the operating wavelength of 3.5 μm. The PBS based on an asymmetric DC paves the way to achieve integrated waveplates, which has potential applications in the detection and analysis of airborne molecules and the optical communication techniques with large signal transmission capacity.