Dispersion in Optical Fiber
Various wavelengths of the signal have different propagation velocities. Dispersion is the spreading out of a light pulse in time as it propagates down the fiber. Dispersion limits the information carrying capacity of a fiber. It is measured as ps/nm.km
Types of Dispersion–Intermodal dispersion
( Also read about losses in optical fiber )
•Multimode fibers have many different light modes since they have much larger core size.
•The light pulse spreads out in time which can cause signal overlapping.
•The velocity of light through a fiber depends on its wavelength.
•Different wavelengths travel at different velocity due to refractive index, hence the different propagation causes material dispersion.
•Material dispersion at 1300nm for silica is zero.
•Light ray that travels in the cladding travels faster than that in the core causes waveguide dispersion.
•Single mode fiber suffers from waveguide dispersion as it has small core diameter
Polarization Mode Dispersion (PMD)
•Polarization Mode Dispersion (PMD) a form of modal dispersion, causes broadening of the input pulse due to a phase delay between input polarization states.
Effect of Dispersion
•Detection of individual pulse is not easy at receiver.
•Poor BER performance.
•Limit the communication distance.
•Limit the transmission rate.