Kee, H.H., Lees, G.P. and Newson, T.P.
A method of increasing the range of 1.65µm long range OTDR system based on Raman amplification.
In, 12th International Conference on Optical Fibre Sensors, Williamsburg, US,
28 - 31 Oct 1997.
Optical Time Domain Reflectometry (OTDR) is an efficient and reliable technique for locating fibre faults and determining the loss distribution along the fibre. An OTDR system operating at a wavelength of 1.65µm is more sensitive to fibre macro-bending and micro-bending losses than those at the region of 1.3/1.55µm, thus providing an early detection of system faults and reducing the risk of total system failure. The current limitation in the maximum dynamic range of OTDR systems is due to the low power of 1.65µm laser diodes. Raman amplification has been employed to amplify a 1.66µm laser diode pulse by 24.8dB before launching it down the end of a sensing fibre. We propose a novel method of increasing the dynamic range of a 1.65µm OTDR system through the use of delayed Raman amplification within the sensing fibre. By delaying the pump pulse with respect to the OTDR pulse, amplification of the latter may be delayed by tens of kilometres
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