  Black phosphorous (BP), a two-dimensional (2D) material, has a direct
bandgap, which fills up the bandgap lacuna left by graphene topological
insulators and transition-metal dichalcogenides because of its dependence on
the layers and applied strains. Theoretically, the direct and tunable band gap
indicates the broadband applications in optoelectronics with high efficiencies
in the spectral range from visible to mid-infrared. Here, a BP broadband
optical modulator is experimentally constructed and the passively modulated
lasers at 639 nm (red), 1.06 um (near-infrared) and 2.1 um (mid-infrared) are
realized by using the BP optical modulator as the saturable absorber in bulk
lasers. The obtained results provide a promising alternative for rare broadband
optical modulators and broaden the application range of BP in photonics.
