  We consider enhancing the sensitivity of future gravitational-wave detectors
by adding optical filters inside the signal-recycling cavity -- an intracavity
filtering scheme, which coherently feeds the sideband signal back to the
interferometer with a proper frequency-dependent phase. We study three cases of
such a scheme with different motivations: (i) the case of backaction noise
evasion, trying to cancel radiation-pressure noise with only one filter cavity
for a signal-recycled interferometer; (ii) the speed-meter case, similar to the
speed-meter scheme proposed by Purdue and Chen [Phys. Rev. D 66, 122004 (2002)]
but without the resonant-sideband-extraction mirror, and also relieves the
optical requirement on the sloshing mirror; (iii) the broadband detection case
with squeezed-light input, numerically optimized for a broadband sensitivity.
