Optical fibre transmission lines

Optical fibre transmission lines have many advantages over coaxial cables. The most widely used fabrication techniques involve chemical vapour deposition resulting in losses of well below 1 dB/km. Analysis of propagation follows well-defined principles and the results obtained are broadly comparable with those at microwave frequencies, although the wavelength of operation, ¿1 ¿m, is much shorter. By suitable design single-mode fibres can be made to give bandwidth × length products approaching 100 GHz·km. Multimode fibres are now well understood, pose fewer problems and can be excited with light-emitting diodes.