After a brief introduction to nulling interferometry, we emphasize the limitations of this technique for the detection of exoplanets, and the need for internal modulation, a recent technique for fast signal chopping. The principles of internal modulation are then discussed and illustrated with an example. Our contribution to the Darwin mission deals with the study of new aperture configurations using internal modulation. the best two configurations identified among an infinity of new possibilities are presented. As compared to the current Darwin configuration, the sensitivity to the planetary signal is improved by a factor of two, resulting in a fourfold speedup in the detection and characterization of exoplanets.