MEASUREMENT OF RAYLEIGH BACKSCATTERING IN SINGLE-MODE FIBERS BASED ON COHERENT OFDR EMPLOYING A DFB LASER DIODE

Rayleigh backscattering in a single-mode optical fiber is measured by coherent-OFDR employing a frequency variable DFB laser diode. Backscattered power from the neighborhood of the far end of a 0.5 km long fiber is measured with a spatial resolution of 50 cm. The insertion of a delay line fiber in the reference optical path and an acoustooptic frequency shifter in the signal optical path enable us to measure backscattering in a long optical fiber in spite of the short coherence length of the DFB-LD.