Optical time domain reflectometry on optical amplifier systems and its application to future optical transmission systems and networks

Experimental results are presented which demonstrate that the established technique of optical time domain reflectometry (OTDR) can be employed on fibre systems containing optical amplifiers (semiconductor or fibre amplifiers). The technique relies upon optical amplification of both the forward travelling OTDR probe pulses and the returning backscatter, thus the most important requirement is that the transmission system does not contain in-line optical isolators. Experimental results are available which confirm that systems without isolators are feasible. After a discussion of the main OTDR equipment requirements, the optical amplifier characteristics which affect the operation of the OTDR are briefly summarized. System measurements are presented on fibre links containing two and three cascaded amplifiers demonstrating that the technique will allow system fault location and supervisory functions to be carried out from the terminal ends of long-span transmission systems containing cascaded in-line optical amplifiers. Finally, possible future improvements are identified, enabling an estimate to be made of the system lengths for which OTDR can be used for fault location and supervisory functions