  Here we demonstrate the capacity to manipulate the optical spring (OS) effect
by employing an optical parametric amplifier (OPA) within an optical cavity. We
observed more than a factor of 2 increase in the OS frequency shift with the
OPA. We also showed for the first time that the OS can be tuned by solely
adjusting the OPA phase and showing an un-detuned cavity exhibiting an optical
spring. The method can be applied to gravitational wave detectors in the signal
recycling configuration to realize narrow bandwidth high sensitivity. The OS
can be tuned to align the detector peak sensitivity frequency to known
frequency continuous gravitational wave signals, dynamically tuned to track the
gravitational wave signal from merging compact binaries or tuned to search for
the post-merger signal of known binary coalescence.
