  We investigate theoretically the spin-polarized electron transport for a
wide-narrow-wide (WNW) quantum wire under the modulation of Rashba spin-orbit
interaction (SOI). The influence of both the structure of the quantum wire and
the interference between different pairs of subbands on the spin-polarized
electron transport is taken into account simultaneously via the spin-resolved
lattice Green function method. It is found that a very large vertical
spin-polarized current can be generated by the SOI-induced effective magnetic
field at the structure-induced Fano resonance even in the presence of strong
disorder. Furthermore, the magnitude of the spin polarization can be tuned by
both the Rashba SOI strength and structural parameters. Our results may provide
an effective way to design a spin filter device without containing any magnetic
materials or applying a magnetic field.
