FIBRE OPTICS – INTERESTED IN THE THEORY OF FIBRE OPTICS?

This is how fibre optics technology works

A glass fibre is a fibre made of glass that is as thin as a human hair (just 125 to 250 microns across). The fibre consists of two types of glass, namely a wafer-thin core that is fused with a thicker casing. Since the light in the glass fibre only hits the outer edge of the fibre at a very shallow angle, reflection is guaranteed and the light remains inside the fibre thanks to internal reflection. A laser sends the light through each glass fibre. The quicker that the laser gives the on and off signals, the more quickly the information is sent. There are two types of glass fibre: multi-mode and single-mode.

Multi-mode glass fibre

The multi-mode fibre is suitable for shorter distances with lower speeds and high bandwidths. Compared to single-mode, the equipment needed is cheaper because LED or VCSEL technology is used instead of a laser. Depending on the manufacturing method used, the cores of multi-mode fibres may have detrimental transfer properties because they scatter light (the diagonal arrows). This can lead to loss of bandwidth. The core of multi-mode glass-fibre cables has a larger diameter that contains multiple paths. A range of wavelengths are used in the glass-fibre core.

Single-mode glass fibre

Single-mode is suitable for longer distances and high bit-rates and requires equipment that contains relatively expensive lasers. The single-mode fibre makes possible data transmission with speeds of more than a terabit a second. Single-mode fibres have a small core and transmit just a single light beam. Since just a single path goes through the core, the light moves to the centre of the core. Unlike with multi-mode fibres, the light beam does not bounce back off the core’s exterior.