White-light cavity with competing linear and nonlinear dispersions

We experimentally demonstrate that broad, tunable bandwidth of an optical ring cavity can be achieved by making use of the negative dispersion of the Kerr nonlinear refractive index in the three-level electromagnetically-induced transparency medium. For a given cavity field intensity, the white-light cavity condition can always be satisfied by choosing the appropriate coupling beam parameters. This white-light cavity scheme can be used effectively to achieve large buildup intensity in the signal-recycling cavity with a broad bandwidth in future advanced gravitational wave detectors.