  We consider stationary spin current in a (110)-oriented GaAs-based symmetric
quantum well due to a nonlinear response to an external periodic electric
field. The model assumed includes the Dresselhaus spin-orbit interaction and
the random Rashba spin-orbit coupling. The Dresselhaus term is uniform in the
quantum well plane and gives rise to spin splitting of the electron band. The
external electric field of frequency $\omega$ - in the presence of random
Rashba coupling -- leads to virtual spin-flip transitions between spin
subbands, generating stationary pure spin current proportional to the square of
the field amplitude.
