Distributed phase-sensitive amplification

We propose a phase-sensitive amplifier scheme that balances fiber loss and parametric gain everywhere in a fiber span. We show that, for long links, such a distributed phase-sensitive amplifier has a 3-dB lower noise figure than an ideal distributed phase-insensitive amplifier ( e. g. Raman), even if simple direct detection is employed. This sets the ultimate limit for the optimum noise-nonlinearity trade-off in transmission systems. (c) 2005 Optical Society of America.