ROTDR signal is obtained from the Raman Stokes pulses generated by the stimulated Raman scattering (SRS) process in a long fiber. A Q-switched Nd:YAG laser is used for pumping. The optical fiber used are (a) single mode fiber (b) multimode fiber, and the present data are obtained mainly from the multimode fiber 1.7 Km long, using laser output of 6KW.
In this experiment the lengths of single mode and multimode fibers are 120 m and 1.70 Km, respectively. In the fault measurement the fault location-end surface of the fiber-is accurately decided to be 1.70 Km. Also, amplified backward Raman scattered wave, which differs distinctly from usual OTDR signal, is found various analyses.
The characteristics of dichroic filter designed and prepared by vacuum deposition technique is found suitable for use in the OTDR.