Dispersion is due to light waves in different frequency components at different transmission speeds to produce a physical effect of different time delays. Digital transmission, dispersion caused by the optical pulse broadening, resulting in around pulse overlap, causing ISI mathematics signals, resulting in increased error rate; for analog transmission, it will limit the bandwidth, harmonic distortion, making SNR system decreases. Dispersion including material dispersion, waveguide dispersion, mode dispersion, polarization mode dispersion, and other.

Material dispersion: pulses with different wavelengths of light transmitted through the optical fiber, the different wavelengths of the electromagnetic waves can cause the refractive index of the core material is not the same, so that different transmission speeds, which leads to pulse broadening, resulting in the dispersion.

Waveguide dispersion: dispersion is determined by the geometry of the optical fiber, wherein the cross-sectional size of the fiber play a major role. When the light in the fiber core and cladding interface by by total reflection effect, is limited to propagation in the core. But if the fluctuations occur along the fiber axis transverse dimension, in addition to leading to the mode change between modes, there are likely to cause a small part of the high frequency of light entering the cladding, transport in the cladding, and the low refractive index cladding propagation velocity Large (V = C/n), which will cause light pulse broadening, leading to dispersion.

Mode Dispersion: refers to the same wavelength of light, even if their patterns are different, the propagation speed is different, thus causing the dispersion. Fiber dispersion pattern exists only in the multimode fiber, the arrival time of each mode fiber has different terminals, resulting in pulse broadening, so that dispersion occurs.

PMD (Polarization Mode Dispersion): Due to the structure of the fiber itself or external factors formed defects (e.g. irregular geometry of the core, uneven internal stress) caused by birefringence in the optical fiber such that two orthogonal polarization modes It will be in a different group velocity in optical output to produce different delay, so that the light pulse broadening, which led to the dispersion. It exists only in the single-mode optical fiber.