  We have studied theoretically optical reflection spectra from the Bragg
multiple quantum well structures. We give an analytical explanation of the
presence of two special frequencies in the spectra at which the reflection
coefficient weakly depends on the quantum well number. The influence of the
exciton nonradiative damping on the reflection spectra has been analyzed. It
has been shown that allowance for the dielectric contrast gives rise to the
third special frequency at which the contributions to the reflectivity related
to the dielectric contrast and the exciton resonance mutually compensate one
another.
