...
A practical use of material and waveguide dispersion is to combine them in a way that produces zero chromatic dispersion at a desirable operating wavelength (normally between 1530 and 1620 nm). This can be done by changing waveguide dispersion since material dispersion is usually undesirable to change due to desirable intrinsic properties of chosen material for optical fiber (most likely silica). The following figure shows how material dispersion, waveguide dispersion and chromatic dispersion vary with wavelength in nonzero dispersion-shifted fiber and indicates zero chromatic dispersion at 1.5-micrometer wavelength.
Figure 1: Combine material dispersion and waveguide dispersion to produce zero chromatic dispersion at 1500 nanometers. Pictures taken from Hecht, J. (2011). Understanding fiber optics (5th ed.)
Figure 2: Common Singlemode Refractive Index Profiles. Pictures taken from youtube.
4. Polarization mode dispersion: Since in multimode optical fiber, the effect of polarization mode dispersion is relatively small compared with modal and chromatic dispersion; it is usually ignored. In single-mode fiber, pulses are transmitted in two distinct polarization modes and the electric fields of two modes are perpendicular to each other. In ideal situation where all forces acting on optical fiber are perfectly symmetrical, these two modes cannot be distinguished. However, in real world, stress during manufacturing process as well as environmental stresses due to factors as temperature, sea water loading and low-level vibration cause slight differences in the refractive index experienced by light pulses in two polarization modes. This phenomenon is called birefringence.
...
In case of short distance transmission or low data rates (2.5 Gb/s or less), polarization mode dispersion is less compared with chromatic dispersion. However, adequate control is critical for long distance transmission at higher speed.
Figure 3: Pulse spread out due to Polarization-mode dispersion. Pictures taken from Hecht, J. (2011). Understanding fiber optics (5th ed.)
Figure 4: Polarization mode dispersion in singlemode optical fiber. Pictures taken from youtube.
Since these dispersions are independent of each other, they are added to form the total dispersion. Hence, total pulse spreading is give by the formula:
...