Distinguish mode dispersion, which is caused by a large number of modes in the optical fiber and the chromatic dispersion associated with the incoherence of light sources actually operating in a certain range of wavelengths.

c – speed of light
l – fiber length
n ₁ , n ₂ – refractive indices of the core and shell

The most important parameters are the optical fiber loss and attenuation of the transmitted energy. These parameters define the range of the FOC and on its effectiveness. Attenuation in optical fibers due to manifestation of the following losses:

α _c – own loss of fiber waveguides
α _k – additional cable losses
α _ik – absorption loss in the infrared region
α _pr – the loss caused by the presence of impurities in the optical fibers

Proper loss fibers consist, in turn, an absorption loss of α _p and scattering loss α _r :

Attenuation due to the absorption due to the losses on the dielectric polarization depends strongly on the properties of the fiber material and is calculated by the following formula:

tgδ – dielectric loss tangent

The attenuation in the infrared region, situated in the wavelength range of more than 1.6 microns, calculated by the formula:

C and k – constant coefficients. For quartz glass C = 0,9; k = (0,7—0,9) мкм.

Depending on the number of the operating frequency propagating waves (modes) of the fibers and is separated into one multimode. The number of modes is dependent on the ratio of the diameter of the fiber core and the wavelength for optical fibers having step-index is calculated as follows.

α – fiber core radius,
λ – wavelength,
Δ – relative refractive index difference.

Since n ₁ and n ₂ have very similar meanings, the nominal value ∆ for most optical fibers is within

The optical fiber is a thin glass strand bilayer, each element (core and shell) has a different refractive index. The refractive index n of transparent material is the ratio of the velocity of light in vacuo (c - velocity of light) to the speed of light in this material (v), and defined by the following formula:

where ε and μ — respectively, relative dielectric and magnetic permeabilities.

Given that the relative magnetic permeability of the transparent material is usually constant and equal to one, the refractive index of the core for n ₁ = √ε ₁ , and for the shell n ₂ = √ε ₂ .