an optical fiber is a tiny and flexible glass thread made up of two parts core and clouding which have different refractive index according to Disney's law the light beam generated by a LED or a laser introduced into the fiber enters a defined acceptance angle remains confined in the heart the advantages of using an optical fiber are total immunity from electromagnetic disturbances the high transmission capacity up to tens of terabits per second the low attenuation approximately equal to 0.1 decibel per kilometer depending on the wavelength and the small size and low costs at the same time however we have some disadvantages namely they are difficult to connect to each other and with connectors their small radius of curvature and complex regeneration the standard size of the diameter of the fibers is 0.25 mm and with the external coating it reaches 0.25 mm a simplified but precise analysis until the dimensions of the fiber are much greater than those of the wavelength can be carried out by applying the laws of geometric optics according to Snelli's law in fact made two means called 1 and 2 the refractive index of a medium n 1 for the sine of alpha 1 will be equal to the beginning of the refraction n 2 for the sine of alpha 2 and ralph a one equal to alpha there can go fractional form an angle alpha 2 of 90 degrees in fact at the facci is equal to the sine to the minus one of the ratio between n 2 and n 1 and alpha 1 and greater than alpha c the wave is reflected by the separation surfaces and therefore remains trapped inside the core there are two types of optical fiber multimode and single mode the multimode ones allow more modes of propagation the mode consists of a configuration of the energy that propagates in the fiber is obtained from the solution of maxwell's equations finally the most widespread is the choice 2.5 125 the modal ones allow only one mode of propagation and have a very small color dimension the modal dispersion consists of a set of rays that propagate along paths of different lengths which correspond to different propagation times this places a limit on the minimum duration of a pulse and therefore limits the maximum transmission speed there are two phenomena of modal dispersion step index is large and index the step index is characterized by a constant refractive index between the center to the periphery of the core the refractive index of the increases sharply with a step step entering the planning the large and index whose refractive index profile gradually bars along the diameter of the fiber passing from a maximum value at the center the core and of the gradually increasing until it assumes a minimum value at the border between running and clegg thing the modal index is equal to 2pi greek for ragio runs between d'Olanda and all x the root of n 1 the second apple n 2 the second for vi minardi 2.405 the fiber is monomodal therefore decreasing there is no modal dispersion in the case of chromatic dispersion the game is told tower of light distributes the light energy on two wavelengths the dispersion depends on the fact that each wavelength has a different propagation speed to reduce in a phenomenon of chromatic dispersion you must use very narrow band light sources almost monochrome laser instead of led