Room temperature ultra-fast amplitude modulator of mid-IR laser beams

We have developed a free-space amplitude modulator for mid-IR radiation (λ = 10μm) that can operate up to at least 1.5 GHz (-3dB cut-off at _ 750 MHz) and at room-temperature. The device relies on a semiconductor heterostructure enclosed in a judiciously designed metal-metal optical resonator. At zero bias, it operates in the strong light-matter coupling regime up to 300K. By applying an appropriate bias, the device transitions to the weak coupling regime. The large change in reflectivity due to the disappearance of the polaritonic states is exploited to modulate the intensity of a mid-IR continuous-wave laser up to speeds of more than 1.5 GHz.