  We propose two efficient entanglement concentration protocols (ECPs) for
arbitrary less-entangled single-photon entanglement (SPE). Different from all
the previous ECPs, these protocols not only can obtain the maximally SPE, but
also can protect the single qubit information encoded in the polarization
degree of freedom. These protocols only require one pair of less-entangled
single-photon entangled state and some auxiliary single photons, which makes
them economical. The first ECP is operated with the linear optical elements,
which can be realized in current experiment. The second ECP adopts the
cross-Kerr nonlinearities. Moreover, the second ECP can be repeated to
concentrate the discard states in some conventional ECPs, so that it can get a
high success probability. Based on above properties, our ECPs may be useful in
current and future quantum communication.
