  We propose two metamaterial waveguides, operating in the mid-IR, which would
display negative refraction. The first waveguide is a metallic strip
incorporating quantum wells, whereas the second is a dielectric waveguide which
incorporates quantum wells. The negative refraction of both waveguides occurs
around the intersubband transition (ISBT) of the quantum wells and is dependent
upon the 2D concentration of electron within the wells; these materials could
be grown by conventional semiconductor technology (MBE) and the electron
concentration within the wells controlled externally by electric fields or
optically pumping.
