What is fiber bandwidth

Optical fiber transmission carrier is light, although the band is extremely wide, but it does not fully utilized, which is due to light in optical fiber with dispersion (mode dispersion, material dispersion and waveguide dispersion) of the reason. Affected in different degrees the fiber bandwidth.

  Mode dispersion is due to different patterns of light in the core - packet interface on the total reflection angle is different twists and turns of the journey of varying lengths. Thus, a beam of light incident optical pulse, it contains a certain distance by each mode of transport to reach the terminal will have the time, which cause pulse broadening. It can show a bunch of narrow pulse wide and 20 ns / km, the corresponding bandwidth of optical fiber is about 20 MHz km.
   Material dispersion is a dispersion of mold. Even though fiber is transmitted laser light, but also contains some broad spectrum of different wavelengths of light weight. For example, GaAlAs semiconductor laser emits the laser spectral width of 2 nm. The transmission of light in the medium speed and refractive index n, whereas the quartz refractive index changes with wavelength, so when a beam of light incident optical pulse, even if the same mode, the transmission wavelength of the light group velocity will be different due to differences , resulting after reaching the end of the pulse broadening, which is the material dispersion. In the vicinity of 1.3 microns, small changes in refractive index with wavelength, so the material dispersion is small (eg 3 ps / km nm). Eliminate the mode dispersion fiber bandwidth can be greatly improved. 1.27 micron in pure quartz has a zero-dispersion wavelength.

  Within the waveguide dispersion is a dispersion model, is due to model changes in the propagation constant with wavelength differences caused by group velocity. Waveguide dispersion is smaller. In the 1.3 micron wavelength, the material dispersion significantly reduced, resulting in roughly the same between the two, and may cancel each other out. Type of fiber by use of the material points, a quartz fiber, multi-component glass fiber, plastic-clad fiber and plastic optical fiber and other categories. Which high purity SiO2 glass silica fiber for fiber-optic materials with low attenuation, frequency bandwidth, etc., in the study and application of dominant. In terms of classification of the main core refractive index and graded index optical fiber mutant fiber. Mode of transmission of light by points, multimode fiber and single mode fiber.