  We put forward an effective amplification protocol for protecting the
single-photon entangled state of the time-bin qubit. The protocol only requires
one pair of the single-photon entangled state and some auxiliary single
photons. With the help of the 50:50 beam splitters, variable beam splitters
with the transmission of $t$ and the polarizing beam splitters, we can increase
the fidelity of the single-photon entangled state under $t<\frac{1}{2}$.
Moreover, the encoded time-bin information can be perfectly contained. Our
protocol is quite simple and economical. More importantly, it can be realized
under current experimental condition. Based on the above features, our protocol
may be useful in current and future quantum information processing.
