  Currently planned second-generation gravitational-wave laser interferometers
such as Advanced LIGO exploit the extensively investigated signal-recycling
(SR) technique. Candidate Advanced LIGO configurations are usually designed to
have two resonances within the detection band, around which the sensitivity is
enhanced: a stable optical resonance and an unstable optomechanical resonance -
which is upshifted from the pendulum frequency due to the so-called
optical-spring effect. Alternative to a feedback control system, we propose an
all-optical stabilization scheme, in which a second optical spring is employed,
and the test mass is trapped by a stable ponderomotive potential well induced
by two carrier light fields whose detunings have opposite signs. The double
optical spring also brings additional flexibility in re-shaping the noise
spectral density and optimizing toward specific gravitational-wave sources. The
presented scheme can be extended easily to a multi-optical-spring system that
allows further optimization.

General Relativity and Quantum Cosmology