  A one-way quantum key distribution scheme based on intrinsically stable
Faraday-mirror type Michelson interferometers with four-port polarizing
beampslitters has been demonstrated which can compensate for birefringence
effects automatically. The encoding is performed with phase modulators, but
decoding is accomplished through measurement of the polarization state of Bob's
photons. An extinction ratio of about 30dB was maintained for several hours
over 50km of fiber at 1310nm without any adjustment to the setup, which shows
its good potential for practical systems
