The optical fibre cable is used to carry light and sends information coded in a beam of light down a glass or plastic pipe.
These cables are made up of incredibly thin strands of glass or plastic known as optical fibres. One cable can have only two strands or a hundred strands. Each strand is less thick than a human hair and can carry something like 25,000 telephone calls, so an entire fibre-optic cable can easily carry several million calls.
There are major three types of Optical Fibre cables that are mainly used in electric transmission and these types are mentioned below:
- Single-mode step index
- Multimode step index
- Multi-mode graded index
1 Single-mode step index:
Single mode or mono mode has a very thin core of about 5 μm diameter and usually has a large cladding which is mainly made from plastic or glass. As these cables have a very thin core, it has a strong monochromatic light source i.e. a laser source is used to send light signals within it. It carries the fibres which are used for long-distance transmission of signals. Since the light travels in a straight direction, there are fewer losses, and it can be used in applications requiring long-distance connections.
2 Multimode step index:
As the name says, it has multiple modes of light to travel along their axis. The wavelengths of light waves in multimode fibres are in the visible spectrum ranging from 850 to 1300 nm. Due to its large diameter such as 50 μm, it is useful for only short distances. Lower order modes are moderately transverse or even completely straight and hence fare better comparatively.
3 Multimode graded index:
A multi-mode graded index is another type of optical fibre cable. This fibre has a core which ranges in between a diameter from 50 to 1000 μm. As compared to other modes, it has a core of relatively high refractive index and the refractive index decreases gradually from the middle to the outer surface of the fibre. There is no boundary between the core and the cladding. This type of fibre is useful for long-distance applications in which white light is used. The mode of transmission of light through this type of fibre is also the same,i.e, continuous refraction from the surface of smoothly decreasing refractive index and total internal reflection from the boundary of the outer surfaces.
These are the types of fibre optic cables that can be used in transmitting a large amount of data with a high speed, in carrying the light in computer networking, telephones and lighting.
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