  We present theoretically calculated optical functions for Cu$_2$O quantum
well (QW) with Rydberg excitons in an external, homogeneous electric field
parallel to the QW planes for the energy region above the gap, suitable to
observe the Franz-Keldysh (FK) oscillations. We quantitatively describe the
amplitudes and periodicity of FK modulations and the influence of both Rydberg
excitons and confinement effect on this phenomenon.
