What are the reasons for the loss of optical fiber

An important issue in optical fiber communication is to reduce the loss of optical fiber as much as possible. So, what are the reasons for the loss of optical fiber?

What are there? Let's go to find out together.

fiber loss

1. Absorption loss of optical fiber

This is caused by the absorption of light energy by fiber materials and impurities. They consume light energy in the fiber in the form of heat energy, which is an important loss in fiber loss. Absorption losses include the following:

1. Intrinsic absorption loss of the substance This is the loss caused by the inherent absorption of the substance. It has two frequency bands, one is in the near-infrared 8-12μm region, and the intrinsic absorption of this band is due to vibration. The inherent absorption band of another substance is in the ultraviolet band. When the absorption is strong, its tail will be dragged to the 0.7-1.1 μm band.

2. Absorption loss caused by dopants and impurity ions Optical fiber materials contain transition metals such as iron, copper, chromium, etc., which have their own absorption peaks and bands and vary with their valence states. The fiber loss caused by the absorption of transition metal ions depends on their concentration. In addition, the presence of OH- also produces absorption loss. The basic absorption peak of OH- is around 2.7 μm, and the absorption band is in the range of 0.5-1.0 μm. For pure silica fiber, the loss effect caused by impurities can be ignored.

3. Atomic defect absorption loss The optical fiber material will be stimulated by heat or strong radiation to generate atomic defects, resulting in light absorption and loss, but generally this effect is small.

2. Scattering loss of optical fiber

Scattering inside the fiber will reduce the transmitted power and cause loss. The most important of the scattering is Rayleigh scattering, which is caused by the density and composition changes inside the fiber material.

During the heating process of the optical fiber material, due to the thermal disturbance, the compressibility of the atoms is not uniform, the density of the substance is not uniform, and the refractive index is not uniform. This inhomogeneity is fixed during cooling, and its size is smaller than the wavelength of the light wave. When light encounters these inhomogeneous substances with random fluctuations that are smaller than the wavelength of the light wave during transmission, the transmission direction is changed, scattering occurs, and loss is caused. In addition, the uneven concentration of oxides contained in the optical fiber and uneven doping will also cause scattering and loss.

3. Waveguide Scattering Loss

This is due to scattering due to random distortion or roughness of the interface, in fact it is mode conversion or mode coupling caused by surface distortion or roughness. One mode will generate other transmission modes and radiation modes due to the undulation of the interface. Due to the different attenuation of various modes transmitted in the optical fiber, during the long-distance mode conversion process, the mode with small attenuation becomes the mode with large attenuation. After continuous conversion and inverse conversion, although the loss of each mode will be balanced, but The overall mode produces additional loss, that is, the additional loss is generated due to the conversion of the mode, and this additional loss is the waveguide scattering loss. To reduce this loss, it is necessary to improve the optical fiber manufacturing process. For a well-drawn or high-quality fiber, this loss can basically be ignored.

4. Radiation loss caused by fiber bending

Optical fiber is soft and can be bent, but after bending to a certain extent, although the optical fiber can guide light, it will change the transmission path of light. The transmission mode is converted to the radiation mode, so that a part of the light energy penetrates into the cladding or passes through the cladding to become a radiation mode and leaks outward, resulting in loss.