Simulation Study of Waveguide and Chromatic Dispersion in a Single Mode Stem Index Optical Fiber

Abstract

Optical fiber is a flexible cylindrical filament of silica glass consisting of highly refractive index of core surrounded by a lower refractive index of cladding. It is widely used in telecommunication instead of copper cables because of its high bandwidth and low transmission loss. It has the characteristics of long distance transmission and large capacity to accommodate signal, but the dispersion in the fiber is one of the most important reasons of signal degradation. Dispersion refers to the pulse broadening over long distance. The major cause of dispersion in single mode fiber is the chromatic dispersion. It is a phenomenon that happens due to different spectral components of light pulse travel at different velocities because of which the pulse reaches the fiber end at different time. As a result pulse gets broaden at the receiver end of the optical fiber link. Hence special care must be taken to compensate this dispersion so that the optical fibers can deliver its maximum capacity.  Chromatic dispersion is divided into two types: waveguide and material dispersion. Material dispersion results in the wavelength dependence of refractive index of fiber material and it cannot be changed. Waveguide dispersion is a type of dispersion caused by the different refractive indexes of the core and cladding of an optical fiber and most significant only in single mode optical fiber. Dispersion depends on various parameters such as the operating wavelength, core radius, relative index difference, source spectral width and length of fiber link. These factors and parameters need to be taken into account during designing a fiber for long transmission distance.

We perform a simulation study of waveguide and chromatic dispersion in the single mode step index fiber. The study has been done by using the simulation software “Understanding Fiber Optics on a PC”.  It has been found that pulse broadening due to waveguide dispersion decreases with increasing refractive index difference between core and cladding for 1310 nm of operating wavelength, 4.5 μm of core radius, 2 nm of spectral width and 50 ps of input pulse width. It is also observed that waveguide dispersion is negative in the single mode fiber region. On the other hand, chromatic dispersion becomes zero for the operating wavelength of 1310 nm, 4.5 μm of core radius, 2 nm of the spectral width, 50 ps of input pulse width and 0.20% of relative refractive index difference. For this zero chromatic dispersion, optical pulse remains unchanged through a large distance of about of 100 km of fiber length. Therefore chromatic dispersion can dominate the effect of waveguide by reducing the pulse broadening for SMSIF.

• Supervision