Electrically tunable VO₂–metal metasurface for mid-infrared switching, limiting and nonlinear isolation

We demonstrate an electrically controlled vanadium dioxide (VO₂)–metal metasurface for the mid-wave infrared regime that simultaneously functions as a tunable optical switch, an optical limiter with a tunable limiting threshold and a nonlinear optical isolator with a tunable operating range. The tunability is achieved via Joule heating through the metal comprising the metasurface, resulting in an integrated optoelectronic device. As an optical switch, the device has an experimental transmission ratio of ~100 when varying the bias current. Operating as an optical limiter, we demonstrated the tunability of the limiting threshold from 20 to 180 mW of incident laser power. Similar degrees of tunability are also achieved for nonlinear optical isolation, which enables asymmetric (non-reciprocal) transmission.