Main factors causing fiber attenuation
Optical fiber attenuation is an important factor hindering the long-distance transmission of digital signals. The level of fiber loss directly affects the transmission distance or the distance between relay stations.
The main factors causing fiber attenuation are:
Intrinsic, bending, extrusion, impurities, unevenness and butt joint, etc.
Intrinsic: It is the inherent loss of the fiber, including: Rayleigh scattering, inherent absorption, etc.
Bending: When the fiber is bent, part of the light in the fiber will be lost due to scattering, resulting in loss.
Squeeze: The loss caused by the slight bending of the optical fiber when it is squeezed.
Impurities: Impurities in the optical fiber absorb and scatter the light propagating in the optical fiber, resulting in losses.
Inhomogeneity: The loss caused by the inhomogeneity of the refractive index of the fiber material.
Butt joint: the loss generated when the fiber is docked, such as: misalignment (the concentricity of single-mode fiber is required to be less than 0.8 μm), the end face is not perpendicular to the axis, the end face is uneven, the butt core diameter does not match, and the welding quality is poor.
Classification of Fiber Loss
Optical fiber loss can be roughly divided into the inherent loss of the optical fiber and the additional loss caused by the use conditions after the optical fiber is made. The specific breakdown is as follows:
Optical fiber loss can be divided into intrinsic loss and additional loss.
Intrinsic loss includes scattering loss, absorption loss and loss caused by imperfect fiber structure.
Additional losses include microbending losses, bending losses, and splicing losses.
Additional loss
The additional loss is artificially caused during the laying of the optical fiber. In practical applications, it is inevitable to connect the optical fibers one by one, and the optical fiber connection will cause loss. Microbending, extrusion, and stretching of optical fibers will also cause loss. These are the losses caused by the conditions of use of optical fibers. The main reason is that under these conditions, the transmission mode in the fiber core changes. Additional losses can be avoided as much as possible.
Additional losses include microbending losses, bending losses, and splicing losses.
There are two forms of fiber bending:
The bend whose radius of curvature is much larger than the diameter of the fiber is called a bend or a macrobend;
The fiber axis produces micron-scale bending, and this high-frequency bending habit is called microbending.
intrinsic loss
Among the intrinsic losses, scattering loss and absorption loss are determined by the characteristics of the fiber material itself, and the intrinsic losses caused by different operating wavelengths are also different. It is of great significance to understand the mechanism of loss and quantitatively analyze the loss caused by various factors for the development of low-loss optical fiber and the rational use of optical fiber.
The absorption peak generated by electronic transition in quartz glass is around the wavelength of 0.1-0.2 μm in the ultraviolet region. As the wavelength increases, its absorption gradually decreases, but the influence area is very wide, until the wavelength above 1 μm. However, UV absorption has little effect on silica fibers operating in the infrared region. For example, in the visible light region with a wavelength of 0.6 μm, the ultraviolet absorption can reach 1dB/km, and it drops to 0.2-0.3dB/km at a wavelength of 0.8 μm, while at a wavelength of 1.2 μm, it is only about 0.ldB/km.
The infrared absorption loss of the quartz fiber is produced by the molecular vibration of the material in the infrared region. There are several vibration absorption peaks in the band above 2 μm.
