Quantum Limits on the Capacity of Multispan Links With Phase-Sensitive Amplification

Long-distance fiber communication stands as a cornerstone of modern technology. One the underlying principles, preventing signal levels from diminishing below detectability threshold, is optical amplification. In particular, phase-sensitive amplifiers offer promising solution ideally they do not introduce any excess additive noise. Since such devices in principle operate at quantum noise level, natural question whether one can further improve capacity amplified links using principles mechanics it offers much broader scope modulations and detection schemes. We derive ultimate limits determined by laws on multispan with phase sensitive show that advantage over standard approach based quadrature small vanishes for long links.