High-Nonlinearity in Glass Fibers and Cross-Phase Modulation - Optical Signal Processing by Silicon Photonics - page 51

Chapter 5
High-Nonlinearity in Glass Fibers and
Cross-Phase Modulation
Abstract In this chapter, the effects of nonlinearity in optical fiber communica-
tion link have been discussed and highlighted. Desirable effects of nonlinearity in
general and undesirable effects, in particular, in an optical fiber are enumerated
with examples. Cross-phase modulation (XPM) and high-nonlinearity (HNL)
glasses along with their advantages and disadvantages are spelled out with the
help of their theories and applications in practical systems.
Keywords Nonlinear • Pulse broadening • Polarization luctuation • Pulse walk-off
5.1 Introduction to Linearity and Nonlinearity
Nonlinearity is very interesting and important phenomena particularly in the field
of engineering and its applied areas. Usually, a misconception prevails about non-
linearity and its subsequent applications in engineering systems, which in fact,
is incorrect. On the contrary, nonlinear behavior can effectively be exploited for
many useful applications in engineering design and analysis. In order to under-
stand nonlinearity in true prospective, the under-mentioned examples from daily
life could be helpful for the purpose.
While driving a vehicle, when a driver presses accelerator, the car speeds up
proportionally to the acceleration, if the car gains 100 km/h speed in 6 s, this is a
total linear behavior.
On the other hand, if a person visits a departmental store where a single bar
of chocolate costs $5; however, in case a deal is offered, that is, if a person buys
more than one bar of chocolate, 20 % discount is offered. This exhibits a nonlin-
ear behavior as the purchased items (chocolates) is not proportional to the money
paid. Both of the above-mentioned examples complement the fact that nonlinearity
can be at times useful as well.