Pulse Broadening in GI Fibers

• The core refractive index varies radially in case of graded index fibers, hence it supports multimode propagation with a low intermodal delay distortion and high data rate over long distance is possible. The higher order modes travelling in outer regions of the core, will travel faster than the lower order modes travelling in high refractive index region. If the index profile is carefully controlled, then the transit times of the individual modes will be identical, so eliminating modal dispersion.
• The m.s pulse broadening is given as :

                                          … (2.7.1)

where,

σ_intermodal – R.M.S pulse width due to intermodal delay distortion.

σ_intermodal – R.M.S pulse width resulting from pulse broadening within each mode.

• The intermodal delay and pulse broadening are related by expression given by

                                                                       … (2.7.2)

Where τ_g is group delay.

From this the expression for intermodal pulse broadening is given as:

                                                           … (2.7.3)

• The intramodal pulse broadening is given as :

                                                                            … (2.7.4)

 
Where σ_λ is spectral width of optical source. Solving the expression gives :

                                                             …(2.7.5)