Increasing repeater span in high-speed bidirectional WDM transmission systems using a new bidirectional EDFA configuration

When fiber-optic systems contain erbium-doped fiber amplifiers (EDFA), reflections are enhanced by the gain of the amplifiers and severe system performance degradations and bit-error-rate (BER) floors can be observed. This provides a very restrictive limit on the usable amplifier gain. We present a new configuration for a bidirectional EDFA that allows for a significantly higher maximum allowable gain while introducing a very small BER penalty. A 2.5 Gb/s, 300 km bidirectional wavelength-division multiplexing (WDM) transmission experiment using the new bidirectional EDFA is reported. Experimental results show that allowable gain of the new EDFA is significantly increased while the associated BER penalty remains negligible.