Giant nonlinear optical activity in chiral metamaterials

We create the first nonlinear chiral metamaterial operating at microwave frequencies that demonstrates giant nonlinear gyrotropy. We show that scattering of electromagnetic waves on such chiral metamaterials can be made highly asymmetric, with the transmission coefficient in two directions different by the factor larger than 65. We demonstrate that this electromagnetic diode possesses extremely large linear and nonlinear optical activity, along with its bistable response.