Abstract

An ultra-compact and ultra-broadband polarization-selective bidirectional vertical coupler is proposed. The coupler is designed by coupling unique two-plane chiral $\pi$-shaped plasmonic nanoantennas on top of a silicon-on-insulator waveguide. By taking advantage of the spin-directional locking principle and coupled nanoantennas, a circularly polarized incident light can be coupled into a specific direction through the waveguide, depending on its spin. Based on the full-vectorial finite element method, for a beam radius of 0.53 µm, the coupler with a size of $1.07 \times 0.5\;{{\unicode{x00B5}{\rm m}}^2}$ provides maximum coupling efficiency and an extinction coefficient of ${-}{6.9}\;{\rm dB}$ and 16.9 dB across the telecommunication C to U bands, respectively, with a 2 dB bandwidth of ${\gt}{160}\;{\rm nm}$. The proposed coupler has potential applications in telecommunications, vertical cross-chip communications, and quantum information processing.

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