  We calculate the efficiency of infrared optical spin injection in
single-layer graphene with Rashba spin-orbit coupling and for in-plane magnetic
field. The injection rate in the photon frequency range corresponding to the
Rashba splitting is shown to be proportional to the ratio of the Zeeman and
Rashba splittings. As a result, large spin polarization can be controllably
achieved for experimentally available values of the spin-orbit coupling and in
magnetic fields below 10 Tesla.
