Nonlinear Fabry-Perot interferometers, in the form of nonlinear semiconductor etalons, have been proposed and demonstrated some years ago as pulse shaping elements 1,2. Such etalons can shorten the pulse duration drastically if their finesse is high enough. On the other hand, the nonlinear Fabry-Perot interferometer is also, under certain conditions, a bistable element 3,4, and the fast switching associated with this property may also be used to reshape optical pulses. However, the switching time and the pulse shortening ability of such nonlinear interferometers are limited by the finite lifetime of the cavity and transient effects5. A shorter cavity requires a stronger nonlinearity, most often associated with a significant absorption, and a long response time.