PT-symmetric structures in photonic crystals, combining refractive index and gain-loss modulations is becoming a
research field with increasing interest due to the light directionality induced by these particular potentials. Here, we
consider PT-symmetric potentials with axial symmetry to direct light to the crystal central point obtaining a localization
effect. The axial and PT-symmetric potential intrinsically generates an exceptional central point in the photonic crystal
by the merge of both symmetries. This particular point in the crystal lattice causes field amplitude gradients with
exponential slopes around the crystal center. The field localization strongly depends on the phase of the central point and
on the complex amplitude of the PT-potential.
The presented work analyzes in a first stage 1D linear PT-axisymmetric crystals and the role of the central point phase
that determines the defect character, i.e. refractive index defect, gain-loss defect or a combination of both. The interplay
of the directional light effect induced by the PT-symmetry and the light localization around the central point through the
axial symmetry enhances localization and allows higher field concentration for certain phases. The linearity of the
studied crystals introduces an exponential growth of the field that mainly depends on the complex amplitude of the
potential. The work is completed by the analysis of 2D PT-axisymmetric potentials showing different spatial slopes and
growth rates caused by symmetry reasons.
Waqas W. Ahmed, Ramon Herrero, Muriel Botey, and Kestutis Staliunas, "Axisymmetric photonic structures with PT-symmetry," Proc. SPIE 9920, Active Photonic Materials VIII, 99201U (Presented at SPIE Nanoscience + Engineering: September 01, 2016; Published: 16 September 2016); https://doi.org/10.1117/12.2239122.
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