  The consistent quantum theory of self-phase modulation (SPM) and cross-phase
modulation (XPM) for ultrashort light pulses (USP) in medium with electronic
Kerr-nonlinearity are developed. The approach makes use of momentum operator of
electrical field which takes account of the inertial behaviour of the
nonlinearity. The spectrum of quantum fluctuations of squeezed-quadrature
component as a function of response time of nonlinearity and values of
nonlinear phase shifts due to the SPM and XPM effects, is investigated.
