To further validate that the SBS noise does not introduce interference, the average intensities of the transmitted and backscattered signals were measured at different input powers, as plotted in Fig. 3. The red-triangles, blue-triangles, and black-asterisks represent the cases of single fibers A, B, and interference signals, respectively. The pink circles represent the sum of single fibers A and B (labeled as sum AB). As seen in the figures, SBS starts to occur when the input power reaches 4.8 mW. In the transmitted case, the average intensities of sum AB are different from that of the dual-arm interference signals, indicating the coherent property of the transmission. For backscattered signals, due to the lack of interference, sum AB are the exactly the same as that of the dual-arm configuration. Note that in this measurement, an average time of 0.5 s was applied to suppress the random noise while at the same time partially retaining the coherence information of the signal.