Causes of Fiber Attenuation

What is the cause of fiber attenuation? The optical power in the fiber decreases gradually along the vertical axis. The reduction in optical power depends on the wavelength. In fiber optic links, the main causes of optical power reduction are scattering, absorption, and optical power loss caused by connectors and splices. The unit of attenuation is dB.

Causes: There are many reasons for fiber attenuation, mainly including: absorption attenuation, including impurity absorption and intrinsic absorption; scattering attenuation, including linear scattering, nonlinear scattering and incomplete structure scattering; other attenuation, including microbend attenuation, etc. Chief among these is attenuation due to impurity absorption.

Optical fiber attenuation coefficient: the attenuation value of optical signal power per kilometer of optical fiber. Unit: decibel/km.

Fiber Bending Loss

Optical fibers are very sensitive to bends, excessive bending = light spillage. If the bend radius is less than 20 times the outer diameter, most of the light will escape through the coating. Single-mode fiber-optic cables are more sensitive to bend loss than multi-mode fiber-optic cables.

Optical losses occur in two types of bends: macrobends and microbends.

How is the fiber attenuation coefficient defined? It is defined as the attenuation (dB/km) per unit length of a uniform optical fiber in a steady state.

What is insertion loss? It refers to the attenuation caused by inserting optical devices (such as inserting connectors or couplers) in optical transmission lines.

What is the bandwidth of optical fiber related to? The bandwidth of an optical fiber refers to the modulation frequency at which the amplitude of the optical power is 50% or 3dB lower than the amplitude of the zero frequency in the fiber transfer function. The bandwidth of an optical fiber is approximately inversely proportional to its length, and the product of the bandwidth length is a constant.

How many types of dispersion are there in optical fiber? what is it about The dispersion of optical fiber refers to the expansion of group delay in optical fiber, including mode dispersion, material dispersion and structural dispersion. Depends on the characteristics of the light source and fiber.

Optical pulse broadening in optical fibers caused by different group velocities at different wavelengths in the spectral composition of the light source.

material dispersion

The refractive index of the optical fiber material quartz glass has different values for different wavelengths of transmitted light. This proves that sunlight of many different wavelengths can be divided into seven different colors after passing through a prism. Due to the above reasons, the refractive index of the material changes with the wavelength of light, and the phenomenon of pulse broadening is called material dispersion.

waveguide dispersion

Since the refractive index difference between the core and the cladding of the fiber is very small, when total reflection occurs at the interface, part of the light may enter the cladding. After this part of the light travels a certain distance in the cladding, it may return to the core to continue transmission. The intensity of this part of the light entering the cladding is related to the wavelength of the light, that is, the length of the light transmission path varies with the wavelength of the light.

The light pulse emitted by a light source with a certain spectral width is injected into the optical fiber. Since the light transmission paths of different wavelengths are not completely the same, the time to reach the end point is also different, resulting in pulse broadening. Specifically, the longer the wavelength of the incident light, the greater the proportion of light intensity that enters the cladding, and the longer the distance that this part of light travels.