Nonlinear Science at the Dawn of the 21st Century (9).pdf

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9
Nonlinear Fiber Optics
Govind P. Agrawal
1 Introduction
Nonlinear fiber optics concerns with the nonlinear optical phenomena oc-
curring inside optical fibers. Although the field ofnonlinear optics traces
its beginning to 1961, when a ruby laser was first used to generate the
second-harmonic radiation inside a crystal [1], the use ofoptical fibers as
a nonlinear medium became feasible only after 1970 when fiber losses were
reduced to below 20 dB/km [2]. Stimulated Raman and Brillouin scatter-
ings in single-mode fibers were studied as early as 1972 [3] and were soon
followed by the study of other nonlinear effects such as self- and cross-
phase modulation and four-wave mixing [4]. By 1989, the field ofnonlinear
fiber optics has advanced enough that a whole book was devoted to it [5].
This book or its second edition has been translated into Chinese, Japanese,
and Russian languages, attesting to the worldwide activity in the field of
nonlinear fiber optics.
Nonlinear fiber optics has continued to grow during the decade of1990s,
perhaps even more dramatically than anticipated. This growth is motivated
by several recent advances in lightwave technology, the most important be-
ing the advent ofhigh-capacity fiber-munication systems [6]. In
such systems, the transmitted signal is amplified periodically by using op-
tical amplifiers pensate for residual fiber losses. As a result, the
nonlinear effects accumulate over long distances, and the effective interac-
tion length can exceed thousands ofkilometers! Among other fiber devices
in which nonlinear effects are ing increasingly important are mode-
locked fiber lasers, distributed fiber amplifiers, and fiber Bragg gratings. It
is impossible to review the entire field ofnonlinear fiber optics in a chapter
of this size. The focus therefore is on optical solitons and optical switch-
ing, the two topics that are driven by advances in the field offiber-optic
communications and are lik