The single-mode optical fibre network currently being installed as part of the BT modernisation programme is optimised for 1300 nm operation at 140 Mbit/s. The fibre specification is designed to enable upgrading to higher data rates and longer wavelength operation. Fibre properties at 1.3 um and 1.5 um are discussed and measured results reported.
"Single-Mode Fibre Properties At 1.3 µm And 1.5 µm", Proc. SPIE 0584, Optical Fiber Characteristics and Standards, (15 April 1986); doi: 10.1117/12.950987; https://doi.org/10.1117/12.950987