How the fibre communications revolution began

How thin optical fibres are made

  • Optical fibres are made from glass.
  • The light is guided within a dielectric waveguide. This consists of a core of denser glass surrounded by a cladding glass of lower refractive index.
  • The hair-thin fibres are drawn from a thick glass preform heated at one end.
  • The preforms can be made in various ways. The earlier methods introduced serious losses and are now largely abandoned.
  • The first fibre preforms were made by the “Rod in Tube ” process, in which a rod of denser glass was inserted into a tube of less dense glass. These fibres suffered from high scattering loss due to the imperfect interface between rod and tube.
  • Some unsuccessful attempts were made to draw fibres from liquid rather than a solid preform rod. The “Double Crucible” method offered the possibility of a continuous process, but the fibres made by this method were lossy due to impurities absorbed from the crucible material.
  • Crude large core fibres were made by simply drawing down a silica rod, and coating it with a plastic of lower refractive index. This was an easy way of making large core (Multimode) fibres but they were unsuitable for long distance communication.

Three early optical fibre making processes

  • The succesful methods of manufacture used some form of chemical vapour deposition. The glass was created from oxidation of ultra-pure chemicals, such as Silicon TetraChloride and Germanium TetraChloride.

Silica Fibre Fabrication

  • The heated preform end is then drawn down into a thin fibre.

Heated preform is drawn down into fibre

Images of Fibre Manufacture