Controlling the propagation of hyperbolic polaritons with near-field excitation

Researchers from Huazhong University of Science and Technology and China University of Geosciences, led by Professor Xinliang Zhang, Professor Peining Li, and Professor Zhigao Dai, have made significant progress in the field of nanophotonics by developing a novel technique for controlling the excitation and propagation of polaritons at the nanoscale. Their findings, published in eLight, pave the way for the development of integrated nanophotonic devices, circuits, and chips.

The team focused on hyperbolic polaritons (HPs), which are ultra-confined and highly directional particles crucial for advancing nanophotonics. While high-symmetry crystals have been extensively studied for this purpose, they suffer from reduced directionality and energy-transporting efficiency due to the presence of four mirror-symmetric beams during in-plane HP propagation.

To overcome this limitation, the researchers explored low-symmetry monoclinic crystals, where they discovered a new class of polaritons called hyperbolic shear polaritons. These polaritons exhibit enhanced directional propagation, albeit with higher losses. The asymmetry of these shear polaritons arises from the unique properties of the low-symmetry crystals, which are not present in high-symmetry counterparts.

The team’s study focused on investigating the effects of linearly polarized in-plane sources on generating symmetry-broken HPs with improved directional propagation in high-symmetry, low-loss systems. Through theoretical analyses and experimental demonstrations, they successfully showed that by controlling the near-field excitation source, they could configure the excitation and propagation of in-plane HPs, thereby breaking mirror symmetry without relying on low crystalline symmetry.

This source-configured approach introduced a new degree of freedom for manipulating the propagation of asymmetric polaritons across a wide frequency range. The ability to dynamically and robustly control light guiding and propagation at the nanoscale opens up new possibilities for reconfigurable polaritonic devices, such as polarization-dependent nanophotonic circuits and optical isolation.

The research conducted by this team provides valuable insights into harnessing the potential of polaritons for advanced nanophotonics and represents a significant step toward the development of practical applications in integrated nanophotonic systems.

Source: Chinese Academy of Sciences

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