  We propose an alignment-free two-party polarization-entanglement transmission
scheme for entangled photons by using only linear-optical elements, requiring
neither ancillary photons nor calibrated reference frames. The scheme is robust
against both the random channel noise and the instability of reference frames,
and it is subsequently extended to multi-party Greenberger-Horne-Zeilinger
state transmission. Furthermore, the success probabilities for two- and
multi-party entanglement transmission are, in principle, improved to unity when
active polarization controllers are used. The distinct characters of a simple
structure, easy to be implemented, and a high fidelity and efficiency make our
protocol very useful for long-distance quantum communications and distributed
quantum networks in practical applications.
