  Effective spin-orbit coupling can be created in cold atom systems using
atom-light interaction. We study the BECs in an optical lattice using the
Gross-Pitaevskii equation with spin-orbit coupling. Bloch states for the linear
equation are numerically obtained, and compared with stationary solutions to
the Gross-Pitaevskii equation with nonlinear terms. Various vortex lattice
states are found when the spin-orbit coupling is strong.
