Increasing the working range of coherent optical time-domain reflectometer

A new method for increasing the working range of a coherent optical time-domain reflectometer (COTDR) has been theoretically justified and experimentally demonstrated. The proposed method is based on the use of several types of optic fibers with different backscatter coefficients, in which the fiber with a higher backscatter coefficient is connected to the end of a fiber with the minimum absorption coefficient at the working wavelength, the length of which is the maximum possible in order to ensure a preset sensitivity level. It is shown that, using this approach, the COTDR working range can be increased up to 50 km.