There are many types of optical fibers are designed. They are devided on two major types – single-mode and multimode fibers. Mode as known from the Theory of Oscillations and Waves is the type oscillation, i.e. how the light goes through the fiber. On this basis, single-mode fiber is constructed so there's only one main mode is propagated ("can get through") through the fiber and this mode has the lowest order. On the other hand, multimode fiber has such parameters of its light conductor core, that the light can move through it using multiple types of oscillation or modes (up to hundreds).

Typically, single-mode fiber is better and more expensive than multimode one, and that's why – in the multimode fiber signals propagate by unpredictable modes, and sometimes transform from one to other mode, etc. This causes a dispersion distortions to appear, wavefront loses clarity, "smeares", chandes itself from square to the Gaussian-blurred form, which is why the communication range for multimode fiber is limited. However, such a fiber is much easier to manufacture - it has a fiber core diameter variyng from 50 to 62,5 microns, while for single mode fiber laws of physics require a core diameter of at least 7 and not more than 10 microns. To improve the quality of wave distribution over multimode fiber, it can be manufactured without a step change in the material's refractive index, but with a gradient change (the so-called “selfoc” - self-focusing fibers). In such fibers, the light moves by not the polygonal path, but by the smooth curved path, so the effect of dispersion is reduced, and the quality of the output signal is increased.

Manufacturing technology of single-mode fiber is more complex and costly, but if you can achieve that all the signal was moving on one mode, the effect of dispersion distortions fall hundreds of times. Naturally, for input of optical radiation in a single-mode fiber, special laser with optical system should be used. For multimode fiber, radiation can be inputed using inexpensive LED.

Standardly for optical communication uses frequencies in the infrared, where the quartz glass of which fiber is made has a windows of transparency, the second - 1310 nm and the third - 1550 nm. There are devices for the diagnostics of fiber, they input eye visible red light to the fiber, but this light is attenuated in the fiber of about a mile, and at large distances is not used.

All types of fibers have external reflective-acting (with low refractive index) shell with diameter of 125 microns.

In general, single-mode fiber is now used successfully for communication on distances up to 100 km at a speed of up to 10Gbit/s while multi-mode fiber theoretically can be used at a distance of 4-5 km with the reduced speed of up to 1 Gbit/s, but in practice its technical limit is 500-600 meters - for example, installation of local networks in the buildings.