A pulse shaper for compensating group runtime effects is provided. The pulse shaper comprising a first and a second dispersive element. An optical pulse can be coupled to the pulse shaper along a coupling direction such that said pulse exits from the pulse shaper after passing through the first and the second dispersive element along an exit direction. The first and the second dispersive element are formed and arranged to be movable relative to each other such that the path length to be traversed by the optical pulse through the first and the second dispersive element after coupling to the pulse shaper can be adjusted without any change in an offset between the coupling direction and the exit direction. The first and the second dispersive element are arranged in such a way that the shape of the optical pulse experiences a change as the pulse travels through the pulse shaper.