Measurement and analysis of polarisation effects in optical fibres with a polarimetric OTDR

where, in electrical measurement, a transmitter sends a pulse along a coaxial cable and a receiver and oscilloscope monitor the echoes returning back to the input. Optical TDR was first demonstrated by Barnoski and Jensen in 1976 in multi mode fibres [17] and over the years, it has proved to be an invaluable diagnostic tool for use in both multi mode and single mode optical fibre systems to measure fibre loss, splice losses, locate faults, etc. Nowadays, OTDRs are available from many manufacturers with spatial resolutions as small as one metre. The original principle of POTDR was first proposed by Rogers in 1980 [16] showing that POTDR can measure the birefringence characteristic along fibres with access to only one end. POTDRs, unlike OTDRs, are currently not commercially available and the reasons are various: one is the higher demand on the spatial resolution performance compared to conventional OTDR (as will be discussed) and also the lack of mass commercial interest. However, as stated above, powerful OTDRs are available nowadays and with the growth of interest in PMD, there is now a corresponding interest in an instrument which can measure birefringence (PMD) along a fibre with access to only one end. Moreover, up to now, the analysis of POTDR traces have ignored twist, and given that twist has a large influence on the DGD of the fibre (Chapter 5 and 6), analysis of the influence of twist on the backscattered SOP has been carried out.