Dual-polarization perfect Janus dipole in near-field coupling

Janus dipoles have exotic features in near-field coupling since they have two distinct faces, namely, the so-called coupling and noncoupling faces. When the out-coupler (e.g., a waveguide) is oriented toward the noncoupling (coupling) face of Janus dipoles, the guided waves can be inefficiently (efficiently) excited. Moreover, the noncoupling face of Janus dipoles can be engineered on demand to fully suppress the excitation of guided waves with either $s$ polarization or $p$ polarization, giving rise to the single-polarization perfect Janus dipole. However, whether it is possible to achieve a dual-polarization perfect Janus dipole in near-field coupling remains elusive. Here we theoretically reveal the possibility to realize a dual-polarization perfect Janus dipole, which requires the judicious design of both the constituent dipole moments of Janus dipoles and the dispersion relation of waveguides. When placing the dual-polarization perfect Janus dipole in the middle of two parallel identical waveguides, we theoretically find that the $p$-polarized guided waves are exclusively excited in one waveguide, while the $s$-polarized guided waves are excited solely in the other waveguide. Our findings might provide an enticing route for the development of polarization-multiplexed photonic devices, quantum routing, and on-chip signal processing.