  Sensitivity of future laser interferometric gravitational-wave detectors can
be improved using squeezed light with frequency-dependent squeeze angle and/or
amplitude, which can be created using additional so-called filter cavities.
Here we compare performances of several variants of this scheme, proposed
during last years, assuming the case of a single relatively short (tens of
meters) filter cavity suitable for implementation already during the life cycle
of the second generation detectors, like Advanced LIGO. Using numerical
optimization, we show that the phase filtering scheme proposed by Kimble et al
[Phys.Rev.D 65, 022002 (2001)] looks as the best candidate for this scenario.
