  We present two protocols for the single-photon entanglement concentration.
  With the help of the 50:50 beam splitter, variable beam splitter and an
auxiliary photon, we can concentrate a less-entangled single-photon state into
a maximally single-photon entangled state with some probability. The first
protocol is implemented with linear optics and the second protocol is
implemented with the cross-Kerr nonlinearity. Our two protocols do not need two
pairs of entangled states shared by the two parties, which makes our protocols
more economic. Especially, in the second protocol, with the help of the
cross-Kerr nonlinearity, the sophisticated single photon detector is not
required. Moreover, the second protocol can be reused to get higher success
probability. All these advantages may make our protocols useful in the
long-distance quantum communication.
