A slot-waveguide-based polarization beam splitter assisted by epsilon-near-zero material

Abstract

A slot-waveguide-based polarization beam splitter (PBS) assisted by “epsilon-near-zero” (ENZ) material is proposed and investigated. Because of the tunable complex refractive indices of indium tin oxide (ITO), ENZ effect can be achieved in the 1.55 μm regime. By embedding ITO in the slot region of the silicon waveguide, the modal characteristics of the TM mode are significantly modified, whereas that of the TE mode is nearly unchanged. Based on this feature, an asymmetric directional coupler is constructed as a PBS in which the TE mode undergoes a strong coupling to the slot waveguide nearby while the TM mode can pass through the waveguide directly. The results show that with 5.6 μm coupling length and 200 nm gap, the PBS offers 31.1 dB and 31.9 dB extinction ratio (ER) and 0.69 dB and 0.97 dB insertion loss (IL) for TE mode and TM mode, respectively. Furthermore, the impact of carrier concentration and operation wavelength on the PBS performance are investigated in detail. The proposed PBS is compatible with most of the newly developed ITO-based active photonic devices and can be a useful component for on-chip signal processing.