Silicon nitride polarizing beam splitter with potential application for intersubband-transition-based all-optical gate device

In this paper, we present the design, fabrication, and characterization of a silicon nitride polarizing beam splitter, which has potential applications in an all-optical gate device based on an intersubband-transition-induced cross-phase modulation. On the basis of a Mach–Zehnder interferometer (MZI) configuration consisting of two directional coupler structures, the splitter can realize a high extinction ratio, wide operation bandwidth, and negligible inherent excess loss. The directional coupler is designed on the basis of the coupled mode theory and supermode theory, which can work as a 3-dB coupler for transverse electrical (TE) light and realize a complete cross-coupling for a transverse magnetic (TM) wave. Thus, the TE light can couple to the cross port while the TM wave is output from the through port under the MZI configuration. An extinction ratio of 37 dB at approximately 1554 nm wavelength and a 38 nm bandwidth with an extinction ratio of higher than 20 dB can be achieved. More application prospects beyond the polarization splitting in optical communications could be expected for the current device.