First Demonstration of Waveguide-Integrated Black Phosphorus Electro-Optic Modulator for Mid-Infrared Beyond 4 μm

We demonstrate the first black phosphorus (BP) electro-optic modulator integrated with Si waveguide for the mid-infrared (MIR) spectrum from 3.85 to 4.1 μm. Optical properties of BP were effectively modulated by a vertical electric field from a top gate through Burstein-Moss and Franz-Keldysh effects. With a gate bias of -4 V, a modulation depth of ~5 dB was achieved with a small active footprint of merely 225 μm
²
. The modulation depth was observed to increase with decreasing light power. The results are promising for operations under weak-light condition with low-power consumption and compact footprint at room temperature. Our device lays a stepping stone towards realizing on-chip MIR systems for applications such as bio-sensing and environment monitoring.