Fiber Optic Tutorials

Fiber Design and Fabrication

Mar 22, 2020

In this tutorial, we discuss the engineering aspects of optical fibers made using either silica glass or a suitable plastic material. Manufacturing of fiber cables, suitable for use in an actual lightwave system, involves sophisticated technology with attention to many practical details. we begin with silica fibers and then consider plastic fibers. Both types of materials have been used in recent years to make microstructured fibers too. 1. Silica Fibers In the case of silica fibers, both the core and the cladding are made using silicon dioxide (SiO2) or silica as the base material. The difference in their refractive indices...

Nonlinear Optical Effects

Mar 21, 2020

The response of any dielectric to light becomes nonlinear for intense electromagnetic fields, and optical fibers are no exception. Even though silica is intrinsically not a highly nonlinear material, the waveguide geometry that confines light to a small cross section over long fiber lengths makes nonlinear effects quite important in the design of modern lightwave systems. We discuss in this tutorial the nonlinear phenomena that are most relevant for fiber-optic communications.

Fiber Loss

Mar 20, 2020

Fiber loss is another fundamental limiting factor as it reduces the average power reaching the receiver. Since optical receivers need a certain minimum amount of power for recovering the signal accurately, the transmission distance is inherently limited by fiber loss. In fact, as discussed earlier, the use of silica fibers for optical communications became practical only when the loss was reduced to an acceptable level to achieve a transmission distance of 10 km or more. This tutorial is devoted to a discussion of various loss mechanisms in optical fibers.

Dispersion-Induced Pulse Broadening

Mar 20, 2020

Pulse broadening discussed previously is based on an intuitive phenomenological approach. It provides a first-order estimate for pulses whose spectral width is dominated by the spectrum of the optical source rather than by the Fourier spectrum of the pulse. In general, the extent of the pulse broadening depends on the width and the shape of the input pulse. This tutorial discusses pulse broadening by using the wave equation derived previously.

Dispersion in Single-Mode Fibers

Mar 19, 2020

The main advantage of single-mode fibers is that intermodal dispersion is absent simply because the energy of the injected pulse is transported by a single mode. However, pulse broadening does not disappear altogether. The group velocity associated with the fundamental mode is frequency dependent because of chromatic dispersion. As a result, different spectral components of the pulse travel at slightly different group velocities, a phenomenon referred to as group-velocity dispersion (GVD), intramodal dispersion, or simply fiber dispersion.

Intramodal dispersion has two contributions known as material dispersion and waveguide dispersion. This tutorial considers both of them and discusses how GVD limits the performance of lightwave systems employing single-mode fibers.