Signal Recycling and Resonant Sideband Extraction
Signal recycling improves the sensitivity of an interferometer by adding a partially reflective mirror at the output port. This improves of the fringe-contrast of the whole interferometer and allows shaping the frequency response of the instrument – tuning it for certain gravitational-wave signals.
GEO600 researched different signal-recycling configurations in detail, which resulted in a considerable sensitivity improvement at high frequencies.
Resonant Sideband Extraction
An interferometer with resonant sideband extraction can be manipulated in such a way that its optical response to effects from gravitational waves can be optimized frequency dependent – independently of other parameters of the interferometer.