  We design an effect protocol for protecting the single-photon entanglement
from photon loss and decoherence. The protocol only requires some auxiliary
single photons and the linear optical elements. By operating the protocol, the
photon loss can be effectively decreased and the less entangled single photon
state can be recovered to the maximally entangled state with some probability.
Moreover, the polarization information encoded in the single photon state can
be perfectly contained. The protocol can be realized under current experimental
condition. As the single photon entanglement is quite important in quantum
communication, this protocol may be useful in current and future quantum
information processing.
