The optical fiber consists of a number of glass fibers which transmit information as light. The transmission of information is through these fibers results in loss of information. The losses in optical fiber are Absorption loss, scattering loss, dispersion loss, radiation loss and coupling loss.
Losses in Optical Fiber
Absorption loss:
Due to the presence of impurities in the fiber cable some of the residues still remain resulting in the absorption. The composition of the fiber and its fabrication of fiber results in absorption loss. There is dissipation of optical power in the fiber cable. The wavelength of light and its concentration affects the amount of absorption. The two types of absorption losses as explained below:
a. Intrinsic absorption
The electronic absorption bands in the UV region are the main cause of this type of absorption loss. When a photon interacts with an electron it is excited to a higher energy level and results in absorption. The characteristic vibration frequency of atomic bonds results in the absorption loss in the IR region. The electromagnetic field and the interaction of vibration bonds is the main cause of intrinsic absorption.
b. Extrinsic absorption
Extrinsic absorption is more common than intrinsic loss. They are the outcome of impurities in the fiber during manufacturing. In iron, nickel and chromium there is transition of metal ions to higher energy levels. We can reduce the impurity level to 1 part in 1010 through modern fabrication techniques.
Radiative losses:
The bending losses or radiative losses are more predominant when the fiber is curved. Also, Micro bending losses and Macro bending losses are two types of radiative or bending losses.
Scattering loss:
Within the fiber when there is interaction of light with density fluctuation scattering losses occur. There is density change in the optical fiber when manufactured.
- Linear Scattering Losses: Linear scattering occurs when the energy is transferred from dominant mode to the adjacent mode. In dominant mode the linear scattering is proportional to the input power injected. Mie scattering and Rayleigh scattering are two types of linear scattering.
- Non- Linear Scattering Losses: The optical fiber is said to operate in non-linear mode when the optical power at the output of the fiber does not change proportionally with the power change at the input of the fiber. Stimulated Raman Scattering and Stimulated Brillouin Scattering are two categories of non-linear scattering losses.
Dispersion loss:
In Dispersion the temporal spreading that occurs when light pulse propagates through an optical fiber. Sometimes, the propagation time delay causes the pulse to broaden. Delay distortion is another name for dispersion loss.