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Register a new userA parametric study of the lensing properties of dodecagonal photonic quasicrystals
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Added by
Emiliano Di Gennaro Dr.
Publication date
2007
fields
Physics
and research's language is
English
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We present a study of the lensing properties of two-dimensional (2-D) photonic quasicrystal (PQC) slabs made of dielectric cylinders arranged according to a 12-fold-symmetric square-triangle aperiodic tiling. Our full-wave numerical analysis confirms the results recently emerged in the technical literature and, in particular, the possibility of achieving focusing effects within several frequency regions. However, contrary to the original interpretation, such focusing effects turn out to be critically associated to local symmetry points in the PQC slab, and strongly dependent on its thickness and termination. Nevertheless, our study reveals the presence of some peculiar properties, like the ability to focus the light even for slabs with a reduced lateral width, or beaming effects, which render PQC slabs potentially interesting and worth of deeper investigation. Key words: Photonic quasicrystals; negative refraction; superlensing.
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We present the key results from a comprehensive study of the refraction and focusing properties of a two-dimensional dodecagonal photonic ``quasicrystal (PQC), carried out via both full-wave numerical simulations and microwave measurements on a slab made of alumina rods inserted in a parallel-plate waveguide. We observe anomalous refraction and focusing in several frequency regions, confirming some recently published results. However, our interpretation, based on numerical and experimental evidence, differs substantially from the one in terms of ``effective negative refractive-index that was originally proposed. Instead, our study highlights the critical role played by short-range interactions associated with local order and symmetry.
We report a general description of quasi-phase-matched parametric process in nonlinear photonic crystals (NLPC) by extending the conventional X-ray diffraction theory in solids. Under the virtual wave approximation, phase-matching resonance is equivalent to the diffraction of the scattered virtual wave. Hence a modified NLPC Ewald construction can be built up, which illustrates the nature of the accident for the diffraction of the virtual wave in NLPC and further reveals the complete set of diffractions of the virtual wave for both of the air-dielectric and dielectric-dielectric contacts. We show the two basic linear sequences, the anti-stacking and para-stacking linear sequences, in one-dimension (1D) NLPC and present a general rule for multiple phase-matching resonances in 1D NLPC. The parameters affecting the NLPC structure factor are investigated, which indicate that not only the Ewald construction but also the relative NLPC atom size together determine whether a diffraction of the virtual wave can occur in 2D NLPC. The results also show that 1D NLPC is a better choice than 2D NLPC for a single parametric process.
We report on the formation and development of the photonic band gap in two-dimensional 8-, 10- and 12-fold symmetry quasicrystalline lattices of low index contrast. Finite size structures made of dielectric cylindrical rods were studied and measured in the microwave region, and their properties compared with a conventional hexagonal crystal. Band gap characteristics were investigated by changing the direction of propagation of the incident beam inside the crystal. Various angles of incidence from 0 degree to 30degree were used in order to investigate the isotropic nature of the band gap. The arbitrarily high rotational symmetry of aperiodically ordered structures could be practically exploited to manufacture isotropic band gap materials, which are perfectly suitable for hosting waveguides or cavities.
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A high repetition rate, picosecond THz parametric amplifier (TPA) with a LiNbO3 (LN) crystal has been demonstrated in this work. At 10 kHz repetition rate, a peak power of 200 W and an average power of 12 {mu}W have been obtained over a wide range around 2 THz; at 100 kHz repetition rate, a maximum peak power of 18 W and average power of 10.8 {mu}W have been obtained. The parametric gain of the LN crystal was also investigated and a modified Schwarz-Maier model was introduced to interpret the experimental results.
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