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The various losses in optical fiber are due to either intrinsic or extrinsic factors. Fiber attenuation, which is also called signal loss or fiber loss, is the consequence of the intrinsic properties of an optical fiber (multimode and single mode fiber). Apart from the intrinsic fiber losses, there are some other types of losses in the optical fiber that contribute to the link loss, such as splicing, patch connections, bending, etc.
Intrinsic Optical Fiber Losses
Absorption losses in optical fiber are the major cause of optical fiber losses during the transmission. When the photon interacts with the components of the glass, an electron or metal ions, the light power is absorbed and transferred into other forms of energy like heat, due to molecular resonance and wavelength impurities.
Dispersion losses are the results of the distortion of optical signal when traveling along the fiber. Dispersion losses in optical fiber can be intermodal or intramodal. Intermodal dispersion is the pulse broadening due to the propagation delay differences between modes in multimode fiber. Intramoal dispersion is the pulse spreading in single mode fiber, because the refractive index or the propagation constant varies with wavelength.
Scattering losses in optical fiber are due to microscopic variations in the material density, compositional fluctuations, structural inhomogeneities and manufacturing defects.
The above three factors are the intrinsic attenuation losses in optical fiber. According to EIA/TIA-568 standards, the fiber losses for different fiber types are as following:
| Fiber Type | Wavelength | Fiber Loss |
|---|---|---|
| Multimode 50/125 µm (OM2/OM3/OM4) | 850 nm | 3.5 dB/km |
| Multimode 62.5/125 µm (OM1) | 850 nm | 3.5 dB/km |
| Single-mode 9 µm | 1310 nm | 0.4 dB/km |
| Single-mode 9 µm | 1550 nm | 0.3 dB/km |
Extrinsic Optical Fiber Losses
Fiber optic splicing is another type of loss in optical fiber. By joining two optical fibers end-to-end, splicing aims to ensure that the light passing through it is almost as strong as the virgin fiber itself. But no matter how good the splicing is, the splicing loss is inevitable. Fusion splicing losses of multimode fiber are 0.1-0.5 dB, 0.3 dB being a good average value. For single mode fiber, the fusion splicing loss typically can be less than 0.05 dB.
Connector losses or insertion losses in optical fiber, are the losses of light power resulting from the insertion of a device in a transmission line or optical fiber. Multimode connectors will have losses of 0.2-0.5 dB (0.3 typical). Factory made single mode connectors will have losses of 0.1-0.2 dB and field terminated single mode connectors may have losses as high as 0.5-1.0 dB (0.75 dB, TIA-568 max acceptable).
Bending is the common problem that can cause optical fiber losses generated by improper fiber optic handling. There are two basic types. One is micro bending, and the other one is macro bending (shown in the picture below). Macro bending refers to a large bend in the fiber (with more than a 2mm radius).
