| Current Research: Nonliear Fiber Optics
Effects in Optical Fibers
Nonlinear effects in optical fibers originate from the intensity dependence
of the refractive index and stimulated inelastic scattering.
Our group works on different aspects of the fiber nonlinear effects known as
self-phase modulation, cross-phase modulation, four-wave mixing,
stimulated Raman scattering, and stimulated Brillouin scattering.
Design of Microstrctured Fibers (Source: NLFO book)
Conventional optical fibers require long lengths before nonlinear effects
can be observed because of a relatively weak nonlinearity of silica glasses.
In recent years, several new kinds of fibers, known as highly nonlinear
fibers have been developed. Several examples of such
microstructured fibers are shown in the figure above. Typically, the
core diameter in such fibers is reduced to near 1 μm (from 10
μm or so) to enhance the effective nonlinearity of silica fibers. In
another approach, other glass materials (such as lead silicates,
chalcogenides, and bismuth oxide) are used in place of silica to make
optical fibers. Such modifications allows one to observe the nonlinear effects
with lengths as short as a few centimeters.
Highly nonlinear fibers exhibit unique dispersion properties because of a
tight mode confinement. The combination of their unusual
dispersive properties and high nonlinearities has proved valuable and
has provided a new platform for investigating different aspects related to
linear, nonlinear and ultrafast fiber optics. For example, when a
relatively wide intense optical pulse (width 100 ps or more) is launched
close to the zero-dispersion wavelength of the fiber, the combination of
modulation instability, stimulated Raman scattering, and four-wave
mixing creates enough new frequencies within the pulse spectrum that it
can span a wide range. Such a spectrum is called the supercontinuum,
and it can also be created by launching an intense continuous-wave beam
in to a suitable fiber.
Even more interesting effects are observed when an ultrashort pulse
(width 100 fs or less) propagates in the anomalous-dispersion regime of a
highly nonlinear fiber. In this case, fiber dispersion, self-phase
modulation, and stimulated Raman scattering interact with each other so
dramatically and in such a complicated fashion that the supercontinuum
is initiated through a process known as soliton fission
and developed further through two novel phenomena known as
Cheronkov or dispersive radiation and Raman-induced spectral shifts.
Our group discovered in 2004 that the supercontinuum generation process is
very sensitive to the input polarization state of the optical filed, and one
must consider the vector nature of soliton fission. More recent work has focused on
freqyency-comb generation through dual pumping using CW lasers and on the use of
You can consult our list of recent publications by clicking on
"Publications" on the left panel of this page.