OTDR using Rayleigh scattering and reflection to represent the Fresnel characteristics of optical fiber. Rayleigh scattering is caused by the along the fiber produce irregular signal scattering and form. OTDR will measure back to part of the port OTDR scattering light. These backscattering signal would mean that the optical fiber to the attenuation by (loss/distance) degree. The form is a downward trajectory of the curve, it shows the power of the backscattering will decrease, this is due to the transmission distance after a period after the launch of backscatter signal and have loss.

    Given the optical fiber parameters, Rayleigh scattering power can be marked out and, if known, it and the wavelength of the pulse width of the signal proportional: the longer the pulse width, backscattering power is stronger. Rayleigh scattering with the power of the signal wavelength, relatively short wavelengths, power is stronger. That is the signal with 1310 nm track than 1550 nm signal produced the track of Rayleigh backscattering to high.