A device for shielding a sub-wavelength-scale object from an electromagnetic wave incident on the device. The device includes a layer of dielectric material, a surface of which has a change of level forming a step. The step is in contact with a medium having a refractive index that is lower than a refractive index of the dielectric material. The sub-wavelength-scale object is located within the device in a quiet zone where an electromagnetic field intensity is below a threshold, the quiet zone extending above said surface, in a vicinity of the step, in a direction of incidence of said incident electromagnetic wave.