Chapter 12
Nonlinear Processes in Optical Fibers
Abstract This chapter discusses several different nonlinear effects that start to
appear in an optical fiber link as the optical power increases beyond a certain level.
This can occur in a fiber when the core area is made small or when several highstrength optical fields from different signal wavelengths are present in a fiber at
the same time. Consequences of nonlinear effects for signal levels include power
gain or loss at different wavelengths, wavelength conversions, and crosstalk between
wavelength channels. In some cases the nonlinear effects can degrade WDM system
performance, while in other situations they might provide a useful application.
The design of a lightwave transmission system requires careful planning and consideration of factors such as fiber selection, choice and tuning of optoelectronic components, optical amplifier placement, and path routing. The goal of these efforts is to
create a network that meets the design criteria, is reliable, and is easy to operate
and maintain. As the previous chapters describe, the design process must take into
account all power penalties associated with optical signal-degradation processes.
Intuitively, it seems natural to let the input optical power be as large as possible to
overcome the power penalty effects to achieve the link design goals. However, this
works only if the fiber is a linear medium; that is, if the fiber properties are independent
of the optical signal power level. In an actual fiber several different nonlinear effects
start to appear as the optical power level increases beyond a certain level [1–5].
High optical power densities can occur in a fiber when the core area is made small
or when several high-strength optical fields from different signal wavelengths are
present in a fiber at the same time. Nonlinear effects arise when the electromagnetic
fields from these high power densities interact with acoustic waves and molecular
vibrations. To avoid nonlinear effects, the total power in the fiber must not exceed a
specific level. This restriction limits the power per WDM channel. For example, if
the nonlinear threshold for the total launched power into a fiber is 17 dBm (50 mW),
then for a 64-channel DWDM link the power limit per wavelength is −1.0 dBm
(0.78 mW). Consequences of nonlinear effects for signal levels of this magnitude or
greater include power gain or loss at different wavelengths, wavelength conversions,
and crosstalk between wavelength channels. In some cases the nonlinear effects can
degrade WDM system performance, while in other situations they might provide a
useful application.
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
G. Keiser, Fiber Optic Communications,
https://doi.org/10.1007/978-981-33-4665-9_12
477
Nonlinear Processes in Optical Fibers
Abstract This chapter discusses several different nonlinear effects that start to
appear in an optical fiber link as the optical power increases beyond a certain level.
This can occur in a fiber when the core area is made small or when several highstrength optical fields from different signal wavelengths are present in a fiber at
the same time. Consequences of nonlinear effects for signal levels include power
gain or loss at different wavelengths, wavelength conversions, and crosstalk between
wavelength channels. In some cases the nonlinear effects can degrade WDM system
performance, while in other situations they might provide a useful application.
The design of a lightwave transmission system requires careful planning and consideration of factors such as fiber selection, choice and tuning of optoelectronic components, optical amplifier placement, and path routing. The goal of these efforts is to
create a network that meets the design criteria, is reliable, and is easy to operate
and maintain. As the previous chapters describe, the design process must take into
account all power penalties associated with optical signal-degradation processes.
Intuitively, it seems natural to let the input optical power be as large as possible to
overcome the power penalty effects to achieve the link design goals. However, this
works only if the fiber is a linear medium; that is, if the fiber properties are independent
of the optical signal power level. In an actual fiber several different nonlinear effects
start to appear as the optical power level increases beyond a certain level [1–5].
High optical power densities can occur in a fiber when the core area is made small
or when several high-strength optical fields from different signal wavelengths are
present in a fiber at the same time. Nonlinear effects arise when the electromagnetic
fields from these high power densities interact with acoustic waves and molecular
vibrations. To avoid nonlinear effects, the total power in the fiber must not exceed a
specific level. This restriction limits the power per WDM channel. For example, if
the nonlinear threshold for the total launched power into a fiber is 17 dBm (50 mW),
then for a 64-channel DWDM link the power limit per wavelength is −1.0 dBm
(0.78 mW). Consequences of nonlinear effects for signal levels of this magnitude or
greater include power gain or loss at different wavelengths, wavelength conversions,
and crosstalk between wavelength channels. In some cases the nonlinear effects can
degrade WDM system performance, while in other situations they might provide a
useful application.
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
G. Keiser, Fiber Optic Communications,
https://doi.org/10.1007/978-981-33-4665-9_12
477