Noise suppression using modified NOLM for stealth signal receiving in optical steganography system

A modified nonlinear optical loop mirror (NOLM) by adding tunable bandpass filter (TBPF) is demonstrated for the stealth signal receiving in the optical steganography system. For the promotion of the noise suppressing ability, we investigate the optimal couple ratio, offset spectral and bandwidth of the TBPF in the NOLM. With the parameters we get, the modified NOLM can provide stable thresholding ability and improve the sensitivity of the stealth channel nearly 4dB over the classical NOLM.