Two-dimensional hole-type hexagonal lattice photonic crystals with low and high dielectric materials have been investigated for the aim of achieving all-angle negative refraction for subwavelength imaging. Structures composed of Si (εSi = 12 at IR) and PbTe (εPbTe = 36 at mid-IR) have been regarded, as sample materials. All-angle negative refraction has been achieved for the TM polarization in the second band under the light line in a broad bandwidth of 26% and 31% for low and high dielectric materials, respectively. The optimized radii for low and high dielectric PCs equal to 0.31a and 0.35a and provide the spatial full width at half maximum of 0.37λ and 0.38λ, respectively. The structures present TE gap in the operating wavelength range, and this feature of the structures can be applied to design polarization beam splitters in integrated space division multiplexing.
A comprehensive study has been performed to achieve all-angle self-collimation in basic two-dimensional square array photonic crystals with cylindrical scatterers. Based on plane wave expansion and finite difference time domain analysis for both rod- and hole-type structures, we report on all-angle self-collimation (SC) in the first band of the structure, which results in loss suppression due to out-of-plane scatterings. A lower threshold for index contrast has been obtained to achieve all-angle SC, which offers more design flexibility regarding structural parameters. Furthermore, it has been shown that a minimum and maximum coupling efficiency enhancement of ∼40% and 80% can be achieved for the proposed structure, respectively, by introducing a row of scatterers with proper radius at the input and the output air/photonic crystal interfaces.
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