Ultrahigh Extinction Ratio Topological Polarization Beam Splitter Based on Dual-Polarization Second-Order Topological Photonic Crystals

A novel configuration of dual-polarization second-order topological photonic crystal (SOTPC) is presented, which is constructed by drilling 8-shaped air holes on the dielectric background, and propose a scheme to achieve a wide common bandgap within this SOTPC for both transverse-magnetic (TM) and transverse-electric (TE) polarizations. The dual-polarization topological transport of edge states along three different straight waveguides is demonstrated. Then proposed, for the first time, a T-shaped SOTPC-based topological polarization beam splitter (TPBS) and validate the ability of this TPBS to effectively separate TM and TE modes over a broad operating bandwidth. Ultrahigh extinction ratios of 108 dB for TM polarization and 112 dB for TE polarization are simultaneously achieved at the wavelength of 1550 nm. Moreover, it is demonstrated that the polarization beam splitting effect, along with the corresponding performance of the TPBS, exhibits significant robustness against structural defects. Given the excellent features of the proposed TPBS, such as very compact footprint, ultrahigh extinction ratios and wide operating bandwidth, its potential is anticipated as a promising platform for applications in polarization multiplexing photonic integrated circuits and optical communication systems.