Everything you always wanted to know about cascaded parametric amplifiers, but were afraid to ask

I will review briefly the properties of optical amplifiers and attenuators, and how they affect the information carried by signals. I will then describe in detail the properties of cascaded parametric amplifiers and transmission links, and explain why such links are signal-phase-insensitive, but have noise figures that are 6-dB lower than standard phase-insensitive links.