Study of black phosphorus anisotropy on silicon photonic waveguide

Due to its unique crystal structure, black phosphorus (BP) shows anisotropic electric and optical properties. In this work, we demonstrate its optical anisotropy by measuring its different absorptions of TE and TM modes travelling in silicon photonic waveguides. In the experiment, when BP crystal armchair axis is aligned perpendicularly to waveguide, the measured absorption coefficients for TE and TM are 0.821 dB/μm and 0.413 dB/μm, respectively. The result matches well with our calculated absorptions of 1.075 dB/μm and 0.581 dB/μm for TE and TM modes. By carefully selecting BP thickness and orientation, it is possible to selectively absorb either TE or TM mode and as an example, TE/TM contrast can reach up to 1.1 dB/μm when BP thickness is 100 nm.