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UBC Theses and Dissertations

Nonlinear response of two-dimensional waveguide-based photonic crystals and microstructured fibres Banaee, Mohamad G.


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.

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