OTDR manufacturing principles:
It is made based the light backscattering and Fresnel reflection principle
Backscatter method (1): the starting end in the optical fiber cable within the numerical aperture of the measurement of the Rayleigh scattering of light reflected back a non-destructive measurement method of the fiber loss;
Backscatter method (2): The high-power narrow pulse light injected into the fiber under test, and then detecting the scattered light power is returned back along the fiber at the same end;
Rayleigh scattering: it is the material molecular scattering of light waves produce a physical phenomenon;
Rayleigh scattering light: it can only be within the numerical aperture along the optical fiber transmission, and because the fiber exists loss, so the scattered light is gradually reduced along the propagation direction, and the degree of reduction depends on the attenuation coefficient and length of the fiber.
Based on the above reasons, the starting end in the optical fiber to accept the return of scattered light within the numerical aperture, the same having a fiber loss of the information. Which is facing away from the principles of the measured fiber loss of the scattering method. Works made using this instrument, called optical time domain reflectometer, also known as the OTDR.