Rate multiplication by double-passing Fabry-Perot filtering

We present a new technique for extending the decay time of the impulse response function of a Fabry-Perot filter while simultaneously maintaining a large bandwidth. It involves double passing through the filter and it can be used for the easy multiplication of the repetition rate of optical sources. We apply the concept to a 10-GHz pulse train to demonstrate experimentally the rate quadruplication to 40 GHz.