Silica Optical Fiber Technology for Devices and Components: Design, Fabrication, and International Standards

CHAPTER SIX

Optical Nonlinearity Control in Optical Fibers

6.1   HISTORICAL REVIEW OF OPTICAL NONLINEARITY IN OPTICAL FIBERS

Light as a bosonic particle has been treated as noninteracting until 1950s. Spectrally bright and coherent lasers, however, quickly disclosed that light does interact with optical materials when its intensity exceeds a certain level. Nonlinear optics in bulk media has flourished with the advent of laser throughout 1960s to 1990s and discovered the following facts, which cannot be explained in terms of prior linear optics:

(1) The refractive index of an optical medium changes with the propagating light’s intensity, which subsequently modifies the speed of light in the medium.

(2) The frequency of light can change as the light interacts with a nonlinear optical medium.

(3) The physical quantities of light, such as amplitude, phase, and polarization, can be controlled by other lights through a nonlinear medium.

One of the most evident applications of nonlinear optics in present technologies would be second harmonic generation (SHG), where the frequency of incident light, ω, is doubled to 2ω in a nonlinear crystal. SHG is being widely used in generation of green light out of IR lasers for display, biomedical applications, and commercial laser pointers.

The main constituent material of single-mode optical fibers is vitreous silica and in its bulk form silica glass shows a significantly low nonlinear optical property in comparison to other optical glasses or crystals. ...