A spectrally sliced, single-mode, optical transmission system installed in the UK local loop network

Described is a four-channel spectrally sliced transmission system installed in field trials in the UK local-loop network. Each channel supported a 2-Mb/s data stream and generated over a 3.5-km section of single-mode fiber. This enabled the connection of field-located 30-channel primary multiplexers to a digital switch located in the central office, making possible the provision of 120 POTS (plain old telephone systems) channels. Grating-based WDM (wavelength division multiplexing) components were used for both multiplexing and demultiplexing functions, enabling the system to operate with >4 dB of margin. An electrooptic primary multiplexer was linked to the public switched telephone network via the system, with no degradation being observed. It has also been shown that critical system components must be carefully specified to ensure that attenuation remains within the system limits over a range of conditions and that multilevel line codes must be considered unsuitable for future spectrally sliced system development