Bidirectional optical amplifier delivering high gain

For long distance transmission of highly accurate time or stable frequency it is important to keep the reciprocal propagation path. It allows us to improve transmission stability (slow effect will cancel in first order) and also to establish active compensation of propagation fluctuations. Unfortunately, single fiber transmission introduces necessity of bidirectional symmetrical amplifiers in order not to lose advantage of a reciprocal path. In case of time transfer, quasi-bidirectional amplification might be acceptable. It means that amplifiers contain short nonreciprocal path, e.g. wavelength routers or even active fibers. But the ultra-stable frequency transfer requires truly single path optical amplifiers that are considered further. This paper proposes the new idea of using bidirectional EDFA amplifier with optical channel monitor for to detect and suppress unwanted laser of amplifier.