Transmission of wideband DC-coupled analogue signals over fibre

Transmission of wideband analogue signals has long presented severe design problems concerning provision of a DC-coupled response. The paper presents details of a novel split-spectrum transmission method which achieves optimum spectral performance by combining separate high- and low-frequency routes, each employing its own modulation technique. The resulting DC-coupled analogue system displays an upper frequency limit of 400 MHz with an extremely low long-term DC offset of better than 50 μV over a 1 km length of optical fibre. Extension of the upper frequency limit is possible simply by specifying improved high-frequency components and is constrained neither by the low-frequency elements nor the spectral-splitting approach adopted