1 fiber intrinsic loss
The intrinsic loss of fiber is the inherent loss of fiber, mainly due to the defect of crystal glass of matrix material of fiber machine and containing metal transition impurities and OH-, resulting in scattering, absorption and dispersion in the transmission process of light, which can be generally divided into scattering loss, absorption loss and dispersion loss. The scattering loss is caused by the fluctuation of the atomic density in the material, the density unevenness and the density unevenness in the condensation process. Absorption loss is due to metal transition impurities and OH- absorption in the core, especially in the infrared and ultraviolet spectrum region of glass inherent absorption. Fiber dispersion can be divided into three types according to the causes, namely material dispersion, waveguide dispersion and intermodal dispersion. The single-mode fiber is transmitted by the fundamental mode, so there is no inter-mode dispersion. Among the eigen factors of single-mode fiber, the maximum effect on the connection loss is the diameter of the mode field. The connection loss caused by the single mode fiber intrinsic factor is about 0.014db. When the diameter of the mode field is out of proportion by 20%, the connection loss of 0.2db will be generated. The normalized frequency V>2.404 of multimode fiber has multiple waveguide mode transmission. The larger V value is, the more modes are. In addition to material dispersion and waveguide dispersion, there is inter-mode dispersion. The so-called intermodal dispersion refers to the dispersion caused by different modes of optical fiber with different phase constants at the same frequency and different group velocities.
In addition, optical fiber geometric parameters such as fiber core diameter, cladding outer diameter, core/cladding concentricity, roundness, optical parameters such as relative refractive index, maximum theoretical numerical aperture, etc., as long as one or more mismatches, there will be different degrees of intrinsic loss.
2 fiber additional loss
The additional loss of fiber is composed of radiation loss and application loss. The radiation loss is due to fiber pulling process, fiber diameter, ellipticity fluctuation, expansion and contraction of plastic layer temperature change, and shrinkage of coating at low temperature. Application loss is due to the tension, bending, compression of the fiber caused by macro and micro bending loss.
Post time: Oct-29-2018