210-km bidirectional transmission system with a novel four-port interleaver to facilitate unidirectional amplification

A novel bidirectional transmission system is proposed and experimentally demonstrated using a four-port interleaver to enable unidirectional amplification. Following bidirectional transmission through 210 km of standard single-mode fibers, sensitivity variations of less than 0.2 dB, with a bit-error rate level of 10/sup -9/ at 10 Gb/s, were observed between bidirectional and unidirectional transmissions.