Mode control with ultra short pulse written fiber Bragg gratings Ultra short pulse lasers are increasingly employed for fiber grating inscription. They allow for the realization of very resilient gratings in non photo sensitive fibers in particular rare earth doped fibers. With this approach fiber gratings can be inscribed largely independent of the fiber geometry: Large cross section fiber Bragg gratings can be realized which cover the whole core of a fiber and its surrounding cladding as well as highly localized FBG which only affect a small part of the core. This thesis explores the resulting possibilities for tailoring the spectral response of few and multi mode fiber gratings as well as coupling to cladding modes.