| Summary: | The nonlinear response of two-dimensional waveguidebased
photonic crystals and photonic crystal fibres is investigated
in this thesis. First, the third order nonlinear
response of planar waveguide-based photonic crystals
is studied theoretically to estimate the influence of this
nonlinear susceptibility on the specular reflectivity spectrum
of these structures. It is shown that coupling of
the incident field with leaky photonic modes introduces
features in the specular reflectivity spectrum that are dependent
on the input intensity. By changing the input intensity,
the reflectivity of this structure at a desired wavelength
can, theoretically, be switched from zero to one.
This nonlinear property might have potential application
in all-optical switching devices. Both degenerate (single
beam) and nondegenerate (dual beam, pump/probe) geometries
are considered.
In the second part of the thesis, the output spectrum
of a microstructured fibre, which has a two-dimensional
photonic crystal cladding is investigated as a function of
power when ~100 fs laser pulses are launched into the
fibre at an 80 MHz repetition rate. For launched average
powers of ~20 mW to ~100 mW, the output spectrum is
dramatically shifted and broadened compared to the input
laser spectrum. This occurs through a combination
of nonlinear optical effects that are not currently understood.
The detailed nature of the spectrum and the
temporal properties of the light emitted from the photonic
crystal fibre depend on the excitation wavelength
and the coupling geometry. Under some conditions the
spectrum consists of a series of discrete red-shifted components
that shift monotonically further to the red at
higher input powers. In this case the temporal shape
of the output beam is found to be strongly asymmetric,
with a rapid leading edge, and a slower decay. Under
other conditions, the spectrum is more like a continuum,
and the behaviour in the time domain is symmetric. === Science, Faculty of === Physics and Astronomy, Department of === Graduate
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