  In this paper we represent nonperturbative calculation for one-loop Quantum
Electrodynamics (QED) vacuum birefringence in presence of strong magnetic
field. The dispersion relations for electromagnetic wave propagating in strong
magnetic field point to retention of vacuum birefringence even in case when the
field strength greatly exceeds Sauter-Schwinger limit. This gives a possibility
to extend some predictions of perturbative QED such as electromagnetic waves
delay in pulsars neighbourhood or wave polarization state changing (tested in
PVLAS) to arbitrary magnetic field values. Such expansion is especially
important in astrophysics because magnetic fields of some pulsars and magnetars
greatly exceed quantum magnetic field limit, so the estimates of perturbative
QED effects in this case require clarification.
