Moving refractive index fronts in waveguides with dispersion is a special type of spatio-temporal modulation. The interaction of light with that front allows frequency conversion, light stopping, optical delays, and bandwidth and pulse duration manipulation. Here, we present examples of signal transmission, reflection, trapping and stopping. We will geometrically consider indirect transitions in the dispersion relation using the phase continuity relation at the front and present numerical solutions of the linear Schrödinger equation which follows from the slowly varying envelope approximation of the wave equation.
