Patent ID: 6570649
Filing Date: 2003-05-27
Classification: G01M

Abstract:
An optical fiber characteristics measuring device comprising:a pulse driving circuit for supplying a pulse driving current having a long pulse period and a duty ratio larger than 2000:1 to a laser diode which concurrently emits a pulse light and continuous light having the same frequency; a bias circuit for supplying a continuous driving current to the laser diode at all times during operation; a first optical directional coupler for branching the light output from the laser diode into a signal light arid a reference light; a second optical directional coupler for sending the signal light to an optical fiber to he measured and for branching a returned backward scattered light front the optical fiber into a third optical directional coupler; the third optical directional coupler for incorporating the reference light output from the first optical directional coupler and the backward scattered light output from the second optical directional coupler and coupling the backward scattered light onto the reference light; and a photoelectric transducer for converting an optical signal output from the third optical directional coupler into an electric signal and for outputting the electric signal; wherein the frequency of the backward scattered light is detected based on the electric signal.