Fiber optical experiment technology, about a man who is engaged in the optical research is not strange, if can grasp some fiber optic test technology, to complete their test is very help!
Today, we summarizes some common knowledge of optical fiber, and fiber optic test components, these knowledge are also in my own summary groping in experiment study, hope to help everyone's test.
The structure of the fiber optical fiber is the typical structure of multilayer concentric cylinder, by inside and outside, in order: fiber core and cladding and coating layer three layer structure, fiber core is used to convey the light, cladding reflected light, the protective coating layer, the diagram below: light is only able to communicate within the optical fiber in the fiber core, because the total reflection, the refractive index of fiber core is bigger than the refractive index of cladding.
And the fiber core of intrusive usually from several um to 100 um, single-mode optical fiber in the fiber core is less than 10 um, it is conceivable that each regulate optical fiber coupling is how difficult.
The main composition of the classification of the fiber optical fiber is high purity silica, if mixed with refractive index is higher than in the quartz quartz dopant, can make the fiber core of the fiber.
Also, if the mixed with refractive index is lower than in the quartz quartz dopant, it can be used as cladding material.
According to the refractive index distribution, can be divided into three categories: mutant multimode optical fiber, the graded-index multimode optical fiber and single mode fiber.
Mutant multimode optical fiber core refractive index for n1 remains unchanged, the cladding Russia into n2.
This optical fiber core usually 2 a = 50 ~ 80 microns in diameter, light to convey line shape along the axis of fiber core base direction, is characterized by large signal distortion.
Graded-index multimode fiber in the fiber core refractive index base n1, maximum to the periphery along the radial r became smaller, until the package layer into n2.
This optical fiber core usually 2 a 50 microns in diameter, light to sine shape along the axis of fiber core base direction, characterized by small signal distortion.
Step-index single-mode fiber refractive index distribution and similar step-index optical fiber, fiber core only 8 ~ 10 microns in diameter, shape of light in a straight line along the fiber core base axis direction.
Because this kind of optical fiber transmission only one mode (
Only transfer main mode)
, so called single-mode fiber, the signal distortion is small.
You may feel very strange, why single-mode light is along a straight line shape convey?
Because the single mode optical divergence Angle is small, and multimode optical divergence Angle is bigger, so the single mode light is approximate shape along a straight line.