Fiber dispersion refers to a physical phenomenon of optical signal distortion which is caused by different group velocities of different frequencies or modes of the signals that a fiber transports. Group velocity refers to the transmission rate of optical energy in a fiber. Optical signal distortion refers to pulse broadening.
Types of fiber dispersion:
Fiber dispersion is classified into material dispersion, waveguide dispersion and polarization mode dispersion (PMD). The material dispersion and waveguide dispersion are also called intramodal dispersion; the PMD is also called intermodal dispersion.(1) Material dispersionrefers to the pulse broadening which is a result of the phenomenon that the refractive index of fiber material varies with the light source frequency and different light source frequencies are propagated at different group velocities.
(2) Waveguide dispersionrefers to the pulse broadening which is a result of the phenomenon that the modular propagation constant varies with the wavelength. The waveguide dispersion is relevant to the fiber waveguide parameters and its value parallels the value of material dispersion. The material dispersion and waveguide dispersion exist in both the single-mode fiber and multimode fiber.
(3) PMDrefers to the pulse broadening which is a result of the phenomenon that the group velocities of the same light source frequency in different transmission modes are different. The PMD mainly exists in the multimode fiber.
In a word, both the material dispersion and waveguide dispersion are caused by different frequencies of transmission signals in a fiber; the PMD is caused by different modes of transmission signals in a fiber.
