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01/13/04 Colloquium
DR. THOMAS WU
UNIVERSITY OF CENTRAL FLORIDA
DEPARTMENT OF ELECTRICAL & COMPUTER ENGINEERING
UNIVERSITY OF CENTRAL FLORIDA
DEPARTMENT OF ELECTRICAL & COMPUTER ENGINEERING
Wave Propagation Through Chiral Photonics Crystal
Abstract: We propose, develop and implement an exact method to analyze the scattering of chiral photonic crystal which can be used as both frequency selective and mode conversion devices in microwave and optoelectronic applications. The method combines the building block approach of multimode network theory with a rigorous mode-matching procedure. Equivalent transmission line networks are introduced both in the cross section and in the longitudinal direction to analyze the eigenvalue problem of period array of chiral slabs and the scattering characteristics of the whole structure, respectively. We have derived a new orthogonality relation for Floquet modes in the period array of chiral slabs to perform mode-matching and derive identities for coupling matrices. Symmetry properties of the structure are also considered to simplify the analysis.At lower frequencies, when only two Floquet modes in the chiral grating are propagating, the chiral periodic structure acts approximately as a uniform chiral slab with parameters equal to the average of those for the periodic layer. We have checked this simplified model and have shown that it is an excellent approximation for wave scattering by chiral periodic structure at low frequencies. At higher frequencies, we have found anomalous peaks and valleys which cannot be explained by a simplified model of uniform chiral slab. But they can be explained by the excitation of leaky waves guided along the periodic layer. The incident wave will couple to a space harmonic of a waveguide mode when phase-matching condition satisfies and excite this waveguide mode. Once excited, this leaky waveguide mode will reradiate using the same space harmonic. We have explained the coupling regions by checking the phase-matching condition.
