Perturbation theory of quantum solitons: continuum evolution and optimum squeezing by spectral filtering

We study the quantum-noise properties of spectrally filtered solitons in op tical fibers. Perturbation theory, including a quantum description of the c ontinuum, is used to derive a complete analytical expression for the second -order correlator of the amplitude quadrature. This correlator is subsequen tly used to optimize the frequency response of the filter numerically in or der to achieve the minimum photon-number noise. For propagation distances u p to three soliton periods, the length at which the best noise reduction oc curs, a square filter is found to be approximately optimum. For longer dist ances, more-complicated filter shapes are predicted for the best noise redu ction. (C) 1999 Optical Society of America.