  We investigate optically reconfigurable dielectric metamaterials at gigahertz
frequencies. More precisely, we study the microwave response of a subwavelength
grating optically imprinted into a semiconductor slab. In the homogenized
regime, we analytically evaluate the ordinary and extraordinary component of
the effective permittivity tensor by taking into account the photo-carrier
dynamics described by the ambipolar diffusion equation. We analyze the impact
of semiconductor parameters on the gigahertz metamaterial response which turns
out to be highly reconfigurable by varying the photogenerated grating and which
can show a marked anisotropic behavior.
