What is Optical Fiber Attenuation？
Optical fiber attenuation refers to the attenuation per unit length of the optical fiber, in dB/km. The level of fiber attenuation directly affects the transmission distance or the distance between relay stations.
What is the maximum value of Optical Fiber Attenuation？
What is the theoretical maximum attenuation value of the optical fiber? It depends on what type of fiber you are using and what purpose. Even if the attenuation of the optical fiber is large, the luminous power of the equipment interconnected by the optical fiber is large, and the optical power received after transmission through the optical fiber is still passable within the receiving range.
Generally speaking, the maximum allowable attenuation of optical fiber is -40DB, but in order to achieve a stable effect, it is recommended that the optical attenuation should not be greater than -25DB, because -25DB is the critical value for the normal and stable operation of optical terminal equipment.
Scattering attenuation of optical fiber
Scattering attenuation is caused by the light power coupling out or leaking out of the fiber core due to the slight fluctuation of atomic density in the fiber components or the structural defects of the fiber waveguide.
Intrinsic scattering is the most important scattering of materials, and its attenuation power has a linear relationship with the power of the propagation mode. It is due to the non-uniformity of the material atoms or molecules and the material structure, which causes the microscopic non-uniformity of the refractive index of the material and causes the scattering of the transmitted light waves. This kind of scattering is inherent to the material and cannot be eliminated. It is the lowest limit of fiber attenuation. Rayleigh scattering belongs to this category. The Rayleigh scattering attenuation is inversely proportional to the fourth power of the wavelength. When working at a long wavelength, the attenuation of the fiber can be greatly reduced.
Another type of intrinsic scattering is caused by uneven doping. In fiber manufacturing, in order to change the refractive index of the glass, some kind of oxide needs to be doped. This kind of scattering will be caused when the oxide concentration is uneven or fluctuating.
Non-linear scattering includes stimulated Brillouin scattering and stimulated Raman scattering. When the medium is under the action of strong light power density, when the incident photon collides with medium molecules inelastically, phonons will be generated. When the light is scattered by the propagating acoustic phonons, it is called Brillouin scattering; when the light is vibrated by the molecules or when it is scattered by optical phonons, it is called Raman scattering. Both types of stimulated scattering have a threshold power, which will only occur when this value is exceeded. In a common optical communication system, the optical power of the input fiber is generally low, and non-linear scattering is usually not generated.
Irregular attenuation of optical fiber structure
The irregular structure attenuation is the attenuation caused by the small structural fluctuations on the core-clad interface and the uneven waveguide structure inside the fiber. When the fiber structure is irregular, the mode conversion will occur, and part of the transmission energy will be emitted out of the core to become a radiation mode, which increases the attenuation. This attenuation can be reduced by improving manufacturing technology.
Optical fiber bending attenuation
Bend attenuation is the attenuation caused by the bending of the fiber axis. Any deviation of the optical fiber axis from a straight line that is visible to the naked eye is called bending or macro bending. The bending of the fiber will cause the coupling between the modes in the fiber. When the energy of the propagating mode is coupled into the radiating mode or the leakage mode, bending attenuation occurs. This attenuation increases exponentially as the radius of curvature decreases. Another type of attenuation is caused by the random micron-level lateral displacement of the fiber axis, which is called microbend attenuation. The reason for the microbending is that the optical fiber is subjected to excessive uneven lateral pressure or longitudinal stress during the process of coating, cable forming, sheathing, installation, etc., or the temperature expansion coefficient of the coating or outer jacket after the optical fiber is manufactured caused by the inconsistency of the optical fiber.
Post time: 2021-02-22