Field-Effect Induced Linear Dichroism in Black Phosphorus from the Visible to Mid-Infrared

The incorporation of electrically tunable materials into photonic structures such as waveguides and metasurfaces enables dynamic control of light propagation, a critical functionality for emerging optical technologies. Atomically-thin, 2D crystals are ideal materials for this application, as their optical properties are modulated effectively by electrostatic gating. Few-layer black phosphorus is uniquely promising, as its absorption edge is tunable with thickness from the visible to the mid-infrared, and its optoelectronic properties exhibit strong anisotropy within the Van der Waals plane.

In this Abstract we report the first demonstration of broadband, electrically tunable dichroism, observed here in few-layer black phosphorus. By exploiting the quantum-confined Stark effect, Burstein-Moss shift, and selection rules for forbidden transitions under application of an external electric field, we are able to control the material intersubband absorbance along the armchair axis and, consequently, the in-plane optical anisotropy. This behavior persists from the band gap energy (~0.3 eV) to the visible (1.8 eV), and we observe large BP oscillator strength modulation, approaching unity for some combinations of frequency and BP thickness.