  Gyrotropic properties of multiple quantum well structures are studied
theoretically. Symmetry analysis is performed yielding the gyrotropy tensor
components for structures grown along [001], [110] and [311] crystallographic
directions. Angular dependences of circular dichroism and natural optical
activity signals are established. Phenomenological model and microscopic theory
based on spin-orbit splitting of size-quantized subbands are developed for
photon energies close to the energy of the intersubband optical transition.
Magneto-spatial dispersion effects arising from the diamagnetic shift of the
intersubband energy gap linear in the electron momentum are also considered. It
is demonstrated that the spectral dependence of the gyrotropy and
magneto-spatial dispersion constants represents an asymmetrical peak with a
degree of asymmetry governed by the mean electron energy. The estimates show
that the considered effects are detectable in experiments.
