BRILLOUIN OTDR EMPLOYING OPTICAL FREQUENCY SHIFTER USING SIDE-BAND GENERATION TECHNIQUE WITH HIGH-SPEED LN PHASE-MODULATOR

In order to measure spontaneous Brillouin backscattered lights, which are related to fiber-distributed tensile strain and temperature, by us ing a highly sensitive self-heterodyne coherent detection technique, a wideband optical frequency shifter is required to reduce the beat sig nal frequency between the Brillouin backscattered signal and the LO li ght to the IF bandwidth of the conventional coherent receiver. We cons tructed a highly stable optical frequency shifter with a 14 GHz bandwi dth and 20 kHz frequency resolution which employs side-band light gene rated by a high-speed LN phase-modulator. The structure is simple and the insertion loss is low. We applied this shifter to B-OTDR and measu red the distributed tensile strain in a 30-km dispersion-shifted optic al fiber with a 100-m spatial resolution.