Fiber optic transmission has various advantages over other transmission methods like copper or radio transmission. Fiber optic cable which is lighter, smaller and more flexible than copper can transmit signals with faster speed over longer distance. However, many factors can influence the performance of fiber optic. To ensure the nice and stable performance of the fiber optic, many issues are to be considered. Fiber optic loss is a negligible issue among them, and it has been a top priority for many engineers to consider during selecting and handling fiber optic. This article will offer detailed information of losses in optical fiber.
When a beam of light carrying signals travels through the core of fiber optic, the strength of the light will become lower. Thus, the signal strength becomes weaker. This loss of light power is generally called fiber optic loss or attenuation. This decrease in power level is described in dB. During the transmission, something happened and causes the fiber optic loss. To transmit optical signals smoothly and safely, fiber optic loss must be decreased. The cause of fiber optic loss located on two aspects: internal reasons and external causes of fiber optic, which are also known as intrinsic fiber core attenuation and extrinsic fiber attenuation.
Internal reasons of fiber optic loss caused by the fiber optic itself, which is also usually called intrinsic attenuation. There are two main causes of intrinsic attenuation. One is light absorption and the other one is scattering.
Light absorption is a major cause of losses in optical fiber during optical transmission. The light is absorbed in the fiber by the materials of fiber optic. Thus light absorption in optical fiber is also known as material absorption. Actually the light power is absorbed and transferred into other forms of energy like heat, due to molecular resonance and wavelength impurities. Atomic structure is in any pure material and they absorb selective wavelengths of radiation. It is impossible to manufacture materials that are total pure. Thus, fiber optic manufacturers choose to dope germanium and other materials with pure silica to optimize the fiber optic core performance.
Scattering is another major cause for losses in optical fiber. It refers to the scattering of light caused by molecular level irregularities in the glass structure. When the scattering happens, the light energy is scattered in all direction. Some of them is keeping traveling in the forward direction. And the light not scattered in the forward direction will be lost in the fiber optic link as shown in the following picture. Thus, to reduce fiber optic loss caused by scattering, the imperfections of the fiber optic core should be removed, and the fiber optic coating and extrusion should be carefully controlled.
Intrinsic fiber core attenuation including light absorption and scattering is just one aspect of the cause in fiber optic loss. Extrinsic fiber attenuation is also very important, which are usually caused by improper handling of fiber optic. There are two main types of extrinsic fiber attenuation: bend loss and splicing loss.
Bend loss is the common problems that can cause fiber optic loss generated by improper fiber optic handling. Literally, it is caused by fiber optic bend. There are two basic types. One is micro bending, and the other one is macro bending (shown in the above picture). Macro bending refers to a large bend in the fiber (with more than a 2 mm radius). To reduce fiber optic loss, the following causes of bend loss should be noted:
- Fiber core deviate from the axis;
- Defects of manufacturing;
- Mechanical constraints during the fiber laying process;
- Environmental variations like the change of temperature, humidity or pressure.
fiber optic splicing is another main causes of extrinsic fiber attenuation. It is inevitable to connect one fiber optic to another in fiber optic network. The fiber optic loss caused by splicing cannot be avoided, but it can be reduced to minimum with proper handling. Using fiber optic connectors of high quality and fusion splicing can help to reduce the fiber optic loss effectively.
The above picture shows the main causes of losses in optical fiber, which come in different types. To reduce the intrinsic fiber core attenuation, selecting the proper fiber optic and optical components is necessary. To decrease extrinsic fiber attenuation to minimum, the proper handling and skills should be applied.
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