Broadband electro-optic polarization conversion with atomically thin black phosphorus

Active polarization control is highly desirable in photonic systems but has been limited mostly to discrete structures in bulky dielectric media and liquid crystal–based variable retarders. Here, we report electrically reconfigurable polarization conversion across telecommunication wavelengths (1410 to 1575 nanometers) in van der Waals layered materials using tri-layer black phosphorus (TLBP) integrated in a Fabry-Pérot cavity. The large electrical tunability of birefringence in TLBP enables spectrally broadband polarization control. We found that polarization states could be generated over a large fraction of the Poincaré sphere through spectral tuning, and that electrical tuning enables the state of polarization conversion to span nearly half the Poincaré sphere. We observed both linear to circular and cross-polarization conversion with voltage, demonstrating versatility with a high dynamic range.