In order to realize optical fiber communication, an important problem is to reduce the loss of optical fiber as much as possible. Fiber loss refers to the attenuation of fiber per unit length in dB/km. The loss of fiber directly affects the transmission distance or the distance between relay stations.
After the optical signal is transmitted through the optical fiber, the optical power is reduced due to absorption, scattering, and the like. Fiber loss is an important indicator of fiber transmission and has a decisive influence on the transmission distance of fiber communication.
An important issue in achieving fiber-optic communication is to reduce the loss of the fiber as much as possible.
Impure glass materials contain residual impurities and hydrogen/oxygen atoms, which is the main cause of absorption loss. The results show that the attenuation is greatest in a small wavelength region. Is the biggest wavelength (maximum) absorption attenuation caused by (OH) ˉ ion. In quartz fiber, the wavelength is lambda =2.7 microns. Below this wavelength are absorption bands of 1.38, 1.24 and 720nm.
There is a minimum attenuation "window" between these wavelength bands. These spectral regions are: 850nm(first window), 1300nm(second window) and 1550nm (third window). These spectral regions can be used for data transmission (communication technology).
Impurities include metal ions such as Cr3+,Fe2+ and Cu2+. The corresponding absorption band is between 500nm and 1000nm. Bandwidth varies depending on the glass fiber material and the metal ions it contains.
Propagation of short-wavelength light (like ultraviolet lambda =210nm) in quartz fibers causes a loss mechanism known as sunburn. There are absorption centers in quartz where electrons replace anions. These electrons are easily activated by resonance. These areas in the crystal are also known as "color centers", because normal color neutral crystals (such as NaCl) produce temperamental fading