The Transfer Matrix Method (TMM) is the standard method for simulating resonators with internal reflections
occurring in Distributed Feedback (DFB) lasers and other laser types. A restriction of this method is that it
cannot be applied to two dimensions or to time-dynamic simulations. We present a new Finite Element approach
which can be treated as a generalization of the TMM in two or three dimensions. Furthermore, it can be used
for time-dynamic problems as well as for large, tapered structures. We apply it to the time-dynamic simulation
of the optical wave in DFB lasers and show numerical results.