  We present an exact, analytic solution of the spin dependent quantum
transport problem with spin-orbit interaction in a one-dimensional mesoscopic
ring with one input and two output leads. We demonstrate that for appropriate
parameters spatial interference in the ring leads to a behavior analogous to
that of the Stern-Gerlach apparatus: different spin polarizations can be
achieved in the two output channels from an originally totally unpolarized
incoming spin state. It is shown that this requires an appropriate interference
of states that carry oppositely directed currents. We find that spin
polarization is possible for several geometries, including the case when the
device is not symmetric with respect to the incoming lead. A clear connection
is established between the Stern-Gerlach like property of the device and the
relevant Aharonov-Casher phases in the loop geometry.
