Application of stochastic resonance in gravitational-wave interferometer

We investigate a novel approach which improves the sensitivity of a gravitational-wave interferometer due to the phenomenon of stochastic resonance (SR), performing in a nonlinear cavity (NC). The NC is installed at the output of the interferometer before the photodetector so that the optical signal emerging from the interferometer passes through the NC. Under appropriate circumstances, a specific transformation of the noisy signal inside the NC takes place, which results in the increase of the output signal-to-noise ratio (SNR). As a result, the noisy optical signal of the interferometer becomes less noisy after passing through the NC. The improvement of SNR is especially effective in the bistable NC for wideband (several hundred Hz) detection, when the chirp gravitational-wave signal is detected. Then, for an input SNR of $\ensuremath{\sim}0.05$, the output SNR can be increased up to $\ensuremath{\sim}0.5$. When the detection bandwidth is narrowed, the SR mechanism gradually fades out, and the SNR gain tends to 1. The SNR gain also tends to 1 when the NC is transformed to a linear cavity. Proposed enhancement of the SNR due to SR is not dependent on noise type, which dominates in the interferometer. Particularly, the proposed approach is capable of increasing the SNR at a given amplitude of displacement noise.