1: Solitons and noise
A coherent soliton can be represented as a superposition of a classical hyperbolic secant light pulse and the quantum fluctuations of the field (left). The quantum fluctuations or "noise" lead to uncertainties in the soliton's position in time and space, its central frequency, its photon number or electric-field amplitude, and the phase of its electric field. (a) The frequency uncertainty, coupled with the frequency-dependent refractive index of the fibre, causes the pulse to "jitter" in its time-window. The photon-number uncertainty is responsible for the shot noise observed when coherent light is detected.
(b) The photon-number uncertainty, coupled with the fibre nonlinearity, also causes the phase of the pulse to spread. (From Drummond et al.)