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.