Fiber absorption loss. It is connected with transformation of one type of energy to another. Electromagnetic wave with defined length cause the changing of electron orbit in some chemical elements, and that leads to the fiber heating. Obviously, the wave absorption process as fast, as the wave is short and the fiber material is pure.
Dispersion losses. The cause of the signal power loss is that a part of a light flux comes out of a wave-propagating system. It is based on imperfections of the material refraction index. The dispersion losses increase when the the wavelength decrease.
In theory, it is possible to reach better rates of common attenuation at the intersection of absorption and spreading curves. The reality is more complicated and connected with the chemical composition of the environment. In quartz fiber (SiO2) silicon and oxygen become active when the length of the wave reaches defined value and very impair the transmission capacity.
As a result, three low-loss transmission windows appear , where the attenuation has the minimal value. The most common values of wavelength is: 0.85; 1.3; 1.55; mkm.
For the analog transmission use waves with length 850 and 1310 mkm.
Special heterojunction laser was created for these diapasons, and modern FOCL are based on it.
Nowadays, fiber-optic with such specifications is considered to be out-dated. The output of AllWave ZWP fiber-optic has been mastered long time ago. In this fiber-optic type hydroxyl ions were removed from the silica glass composition. This glass has not a window, but an aperture with diapason 1300 – 1600 nm.
All the low-loss transmission windows are laying in infra-red, i.e. the light, which is transmitted in the FOCL, is invisible for the men’s eye. It is worth noting that it is possible to add visible light into the standard fiber-optic. Small blocks, which can be found in some reflectometer, are used for this reason. Also, a little converted laser pointer can be used for the same thing. With the help of these devices it is possible to find cord breaks. At the place, where the fiber-optic is broken, will be a bright shine. This kind of light is usable in a short distances (1 km maximum) because it is fading fast in the fiber.