There is a variety of different typ

There is a variety of different types of fibre optic cable that can be used, and there are a number of ways in which types may be differentiated. There are two major categories:Step index fibre optic cablingGraded index fibre optic cablingThe step index cable refers to cable in which there is a step change in the refractive index between the core and the cladding. This type is the more commonly used. The other type, as indicated by the name, changes more gradually over the diameter of the fibre. Using this type of cable, the light is refracted towards the centre of the cable.Optical fibres or optical fibers can also be split into single mode fibre, and multimode fibre. Mention of both single mode fiber and multi-mode fiber is often seen in the literature.Single mode fiber This form of optical fibre is the type that is virtually exclusively used these days. It is found that if the diameter of the optical fibre is reduced to a few wavelengths of light, then the light can only propagate in a straight line and does not bounce from side to side of the fibre. As the light can only travel in this single mode, this type of cable is called a single mode fibre. Typically single mode fibre core are around eight to ten microns in diameter, much smaller than a hair.Single mode fiber does not suffer from multi-modal dispersion and this means that it has a much wider bandwidth. The main limitation to the bandwidth is what is termed chromatic dispersion where different colours, i.e. Wavelengths propagate at different speeds. Chromatic dispersion of the optical fibre cable occurs within the centre of the fibre itself. It is found that it is negative for short wavelengths and changes to become positive at longer wavelengths. As a result there is a wavelength for single mode fiber where the dispersions is zero. This generally occurs at a wavelength of around 1310 nm and this is the reason why this wavelength is widely used.The disadvantage of single mode fibre is that it requires high tolerance to be manufactured and this increases its cost. Against this the fact that it offers superior performance, especially for long runs means that much development of single mode fiber has been undertaken to reduce the costs.Multimode fiber This form of fibre has a greater diameter than single mode fibre, being typically around 50 microns in diameter, and this makes them easier to manufacture than the single mode fibres.Multimode optical fiber has a number of advantages. As it has a wider diameter than single mode fibre it can capture light from the light source and pass it to the receiver with a high level of efficiency. As a result it can be used with low cost light emitting diodes. In addition to this the greater diameter means that high precision connectors are not required. However this form of optical fibre cabling suffers from a higher level of loss than single mode fibre and in view of this its use is more costly than might be expected at first sight. It also suffers from multi-mode modal dispersion and this severely limits the usable bandwidth. As a result it has not been widely used since the mid 1980s. Single mode fiber cable is the preferred type.