Figure 5
Fluctuations of OTDR traces versus measurement times. (a) OTDR traces from taking the first measurements 60 s (orange), 600 s (blue) and 1800 s (red). As the measurement time increases, both signal counts and noise counts go up. But, the signal counts increase faster than the noise counts, thus the dynamic range increases. (b) The dynamic ranges (dynR) versus measurement time tm. (c)~(e) Variations of the OTDR traces from 175 km to 215 km at different measurement times. Scales of the vertical axes are proportional to 
. In each case, the experimental variations are well confined between the upper boundary (blue) and lower boundary (red). Both boundaries are calculated from a Poisson distribution statistics.
