  Semiclassical solutions of two-dimensional Schrodinger equation with
spin-orbit interaction and smooth potential are considered. In the leading
order, spin polarization is in-plane and follows the evolution of the electron
momentum for a given subband. Out-of-plane spin polarization appears as a
quantum correction, for which an explicit expression is obtained. We
demonstrate how spin-polarized currents can be achieved with the help of a
barrier or quantum point contact open for transmission only in the lower
subband.
