An optical phase scrambler is coupled to a laser source to randomly modulate the optical phase. Since the optical phase is continuously changing in a random fashion, at the output of an etalon interferometer formed in the optical path, the two or more components in the interference always have certain time delay between each other, resulting in a random phase different between each other. Therefore, after interference, the fringe amplitude varies randomly as well. Then at the receiver side, the fringe noise is greatly reduced after averaging over time.