Ultrafast (≈10 GHz) mid-IR modulator based on ultrafast electrical switching of the light–matter coupling

Abstract

We demonstrate a free-space amplitude modulator for mid-infrared radiation (λ ≈ 9.6 μm) that operates at room temperature up to at least 20 GHz (above the −3 dB cutoff frequency measured at 8.2 GHz). The device relies on the ultrafast transition between weak- and strong-coupling regimes induced by the variation of the applied bias voltage. Such transition induces a modulation of the device reflectivity. It is made of a semiconductor heterostructure enclosed in a judiciously designed array of metal–metal optical resonators, that—all-together—behave as an electrically tunable surface. At negative bias, it operates in the weak light–matter coupling regime. Upon application of an appropriate positive bias, the quantum wells populate with electrons, and the device transitions to the strong-coupling regime. The modulator transmission remains linear with input radio frequency power in the 0–9 dBm range. The increase in optical powers up to 25 mW exhibit a weak beginning of saturation a little bit below.