Schematic diagram of a topological photonic alloy. The red star indicates the position of the line source and the arrow indicates the direction of propagation of the chiral edge state. Credit: Qu et al.
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Schematic diagram of a topological photonic alloy. The red star indicates the position of the line source and the arrow indicates the direction of propagation of the chiral edge state. Credit: Qu et al.
Photonic alloys, alloy-like materials combining two or more photonic crystals, are promising candidates for developing structures that control the propagation of electromagnetic waves, also known as waveguides. Despite their potential, these materials typically reflect light back in the direction it came from.
This phenomenon, known as backscattering of light, limits the transmission of data and energy and adversely affects the performance of materials as waveguides. The reliable reduction or prevention of light backscattering in photonic alloys will thus be a key milestone towards the practical use of these materials.
Researchers from Shanxi University and the Hong Kong University of Science and Technology recently produced a new photonic alloy with topological properties that allows microwaves to propagate without backscattering light. This material, presented in Physical Review Letterscould pave the way for the development of new topological photonic crystals.
“Our paper introduces a new concept: a topological photonic alloy as a non-periodic topological material,” Lei Zhang, co-author of the paper, told Phys.org. “We achieved this by combining unmagnetized and magnetized rods in a non-periodic configuration of a 2D photonic crystal. This resulted in photonic alloys that maintain chiral edge states in the microwave regime.”
The primary goal of a recent study by Zhang and his colleagues was to develop a new photonic alloy exhibiting a topological edge state, drawing inspiration from the unique physical properties of alloys. The researchers created their material by randomly mixing yttrium iron garnet (YIG) rods and magnetized YIG rods composed of substitutional or interstitial alloys.
Distribution of chiral edge states in a topological photonic alloy. The white dots indicate the positions of the unmagnetized YIG rods, the black dots indicate the positions of the magnetized YIG rods, and the blue star indicates the position of the conduction source. Credit: Qu et al.
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Distribution of chiral edge states in a topological photonic alloy. The white dots indicate the positions of the unmagnetized YIG rods, the black dots indicate the positions of the magnetized YIG rods, and the blue star indicates the position of the conduction source. Credit: Qu et al.
“In our experimental setup, a vector network analyzer is used to establish the connection between the source and probe antenna,” Zhang explained. “The source antenna is fixed at a specific position in the sample, while the position of the probe antenna is changed to collect valuable information regarding the intensity and phase of the electromagnetic waves. To facilitate this process, circular holes are present in the metal plate through which both antennas are inserted.”
Zhang and his colleagues used a metal cladding that served as a “topologically trivial material” with a Chern number of zero. When this cladding covers a photonic topological insulator with a Chern number of 1, a topological edge state appears at their boundary, in accordance with the bulk-edge correspondence principle.
“The microwave absorber in this setup is supposed to suppress the transfer of boundary states,” Zhang said. “By using an absorber, we prevent the formation of a closed loop within the entire boundary state, which could disrupt the accurate characterization of non-reciprocal phenomena.”
Experiments conducted by this team of researchers demonstrated that their topological photonic alloy even exhibits topological properties with a low doping concentration of magnetized rods without requiring order. This remarkable finding could open new possibilities for the experimental realization of topological edge states, as it suggests that chiral edge states can be created without breaking the time-reversal symmetry in a crystal.
“In our next studies, we plan to explore multi-component topological photonic alloy systems,” Zhang added. “Multi-component systems have a greater number of degrees of freedom, which enables the manipulation of various parameters and leads to a wider range of interesting effects. In addition, we soon also plan to explore the possibility of realizing similar phenomena in optical frequencies and determining the relevance of these results for photonic applications would be very interesting.”
Zhang and his colleagues hope to soon extend their recent discoveries to the optical domain. This would potentially open up new opportunities for manipulating light and developing innovative photonic devices.
More information:
Tiantao Qu et al, Topological Photonic Alloy, Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.132.223802. On arXiv: DOI: 10.48550/arxiv.2406.05168
Information from the diary:
Physical Review Letters
arXiv
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