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Loss Mechanism In Optical Fiber
  • July 4,2018.

Electromagnetic energy loss propagated in the fiber due to material absorption, material scattering, waveguide scattering caused by imperfect interface, mode loss caused by fiber bending, and foreskin loss.

Plastic Fiber Optics

1 Material Absorption

Impure glass materials contain residual impurities and hydrogen/oxygen atoms, which are the main causes of absorption loss. The wavelength with the largest attenuation (maximum absorption) is caused by (OH) strontium ions. In quartz fiber, this wavelength is λ = 2.7 μm. In the spectral region below this wavelength, there are absorption bands of 1.38 μm, 1.24 μm and 720 nm.

Propagating short-wave light in a quartz fiber (such as UV λ = 210 nm) causes a loss mechanism called "sun exposure." There is an absorption center in the quartz where the electrons replace the anion. These electrons are easily activated in the case of resonance. These regions in the crystal are also referred to as "color centers" because of the chromatic fading of typical colored neutral crystals such as NaCl.

2 Material Scattering

A key scattering mechanism is "Rayleigh scattering." There is a change in density in the fiber material (ranging less than one wavelength), which changes the refractive index and causes light scattering. The intensity of the scattered light is proportional to 1/λ4, and the backscattering effect is obvious in various scattering.

Another scattering mechanism is "microscattering", which primarily leads to forward scatter. This scattering is mainly due to impurities in the material in the larger wavelength spectrum.

"Stimulated Raman Scattering" and "Stimulated Brillouin Scattering" are effects of nonlinear radiation exceeding a certain intensity limit, which occurs only after the laser has passed this limit.

3 Special Scattering Mechanism Of Optical Fiber

"Intrinsic properties of the fiber" can cause energy loss. Including: changing core diameter, refractive index difference, refractive index distribution state, mode coupling (dual mechanism), scattering in leather glass. The transition of the core mold to the cladding mode causes losses.

4 Scattering Loss Caused By Macroscopic Bending

The bending of the fiber with the same bending radius is called "macro bending". Small diameter, high numerical aperture fiber mode losses are minimal.

Another notable problem in curved fibers is the loss of light energy caused by the difference in light propagation speed.

5 Loss Caused By Microscopic Bending

The fiber will periodically or randomly bend along the length, and the amplitude of the bend changes continuously.

6 Fiber Coupling Loss

Separate fibers may be connected. There may be intrinsic (pure optical) and external (mechanical connection) losses at the joint. The figure below shows the different structures and transmission values after the multimode fiber is disconnected.

Glass Fibers

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