  Polarization conversion of light reflected from quantum wells governed by
both magnetic field and light propagation direction is observed. We demonstrate
that the polarization conversion is caused by the magneto-spatial dispersion in
quantum wells which manifests itself in the reflection coefficient contribution
bilinear in the in-plane components of the magnetic field and the light
wavevector. The magneto-spatial dispersion is shown to arise due to structure
inversion asymmetry of the quantum wells. The effect is resonantly enhanced in
the vicinity of the heavy-hole exciton. We show that microscopically the
magneto-spatial dispersion is caused by the mixing of heavy- and light-hole
states in the quantum well due to both orbital effect of the magnetic field and
the in-plane hole motion. The degree of the structure inversion asymmetry is
determined for GaAs/AlGaAs and CdTe quantum wells.
