Patent ID: 7593098

Claim:
An optical time domain reflectometer adapted to be coupled to one end of an optical fiber, the reflectometer comprising: a light pulse generator adapted to send a pulse of light into the optical fiber; a photon-counting photodetector adapted to detect a backscattering signal emerging from the optical fiber after the pulse of light is sent therein, and wherein the photodetector generates an output signal; a position circuit to instruct the photodetector to detect the backscattering signal from within a slice of the fiber under test defined between predetermined positions in the optical fiber; and a variable optical attenuator coupled between the optical fiber and the photodetector, the variable optical attenuator to attenuate the backscattering signal if the signal exceeds a predetermined strength; wherein the variable optical attenuator attenuates the backscattering signal at positions in the optical fiber determined by the position circuit.