Black phosphorus phase retarder based on anisotropic refractive index dispersion

Abstract Black phosphorus (BP) has gained wide interest as a promising layered material for its unique physical properties. In particular, the anisotropic optical property of BP can act as a retarder or a polarizer in nano-optoelectronic devices, for which quantitative qualification of the phase retardation and the anisotropic refractive index dispersion are essential. Here, we report the anisotropic refractive index and extinction coefficient dispersions of BP in the visible and near infrared range of 540–1500 nm, and then characterize optical phase retardation in a BP flake. Cauchy absorbent equations are provided for the refractive index dispersions along both armchair and zigzag directions, which well reproduce the experimentally measured reflectance and transmittance contrast spectra of BP flakes. Furthermore, we demonstrate that a linear polarized light through BP becomes elliptical, a finding that agrees well with simulation results using the obtained anisotropic refractive index dispersions. The two-dimensional phase retarder in this work is expected to find various applications in novel polarization-sensitive nano-optoelectronic devices.