Strong optical force and its confinement applications based on heterogeneous phosphorene pairs.

We study the plasmonic properties of face-to-face phosphorene pairs, including their optical constraints and optical gradient forces. The symmetric and anti-symmetric plasmonic modes occur due to the strong anisotropic dispersion of phosphorene. Compared with the anti-symmetric mode, the symmetric mode has a stronger optical constraint and much larger gradient force. Especially, the optical constraint of the symmetric mode can even reach as high as 96% when the two phosphorene layers are along the armchair and zigzag direction respectively. We also propose a scheme of an ultra-small phase shifter using phosphorene-based photonic devices.