  A novel spin filtering in two-dimensional electron system with nonuniform
spin-orbit interactions (SOI) is theoretically studied. The strength of SOI is
modulated perpendicular to the charge current. A spatial gradient of effective
magnetic field due to the nonuniform SOI causes the Stern-Gerlach type spin
separation. The direction of the polarization is perpendicular to the current
and parallel to the spatial gradient. Almost 100 % spin polarization can be
realized even without applying any external magnetic fields and without
attaching ferromagnetic contacts. The spin polarization persists even in the
presence of randomness.
