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In this study, we investigate tunable broadband optical cavity via a medium with four-level atoms interacting with two strong pump fields and a weak probe field in an N-type configuration. The results indicate the amplitude of the Stokes field causes an additional control mechanism of the dispersion behavior. Moreover, the four-wave mixing condition induces higher linear gain for the probe field. Therefore, it allows the compensation of unavoidable optical losses through the optical cavity. By adjusting the control fields in the four-wave mixing condition, the negative dispersion of the atomic medium is able to balance the normal dispersion of cavity in the zero-absorption area, consequently a white-light cavity with tunable wideband is achievable. The present scheme is interesting for development of white-light-cavity applications such as gravitational wave detection.