A quantum-mechanical study of optical regenerators based on   nonlinear-loop mirrors
  We present a quantum-mechanical analysis of a nonlinear interferometer that achieves optical switching via cross-phase modulation resulting from the Kerr effect. We show how it performs as a very precise optical regenerator, highly improving the transmitted bit-error rate in the presence of loss. 
Giacomo M. D'Ariano and Prem Kumar (Department of Electrical and   Computer Engineering Northwestern University, Evanston, I...