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 that combine two or more photonic crystals, are promising candidates for the development of structures that control the propagation of electromagnetic waves, also called waveguides. Despite their potential, these materials generally reflect light back in the direction it came from.
This phenomenon, known as light scattering, limits the transmission of data and energy, negatively affecting the materials’ performance as waveguides. Thus, reliably reducing or preventing light scattering in photonic alloys will be an important milestone toward the practical use of these materials.
Researchers from Shanxi University and Hong Kong University of Science and Technology recently fabricated a new photonic alloy with topological properties that enable microwave propagation without light backscattering. This material, introduced in Physical Assessment Letterscould pave the way for the development of new topological photonic crystals.
“Our paper introduces a new concept: the topological photonic alloy as a non-periodic topological material,” Lei Zhang, co-author of the paper, told Phys.org. “We achieved this by combining non-magnetized and magnetized rods in a non-periodic 2D photonic crystal configuration, creating photonic alloys that maintain chiral edge states in the microwave regime.”
The primary goal of Zhang and his colleagues’ recent study was to develop a new photonic alloy that exhibits a topological edge state, inspired by 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 the topological photonic alloy. White dots indicate the positions of the unmagnetized YIG bars, black dots indicate the positions of the magnetized YIG bars, and the blue star indicates the position of the line source. Credit: Qu et al.
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Distribution of chiral edge states in the topological photonic alloy. White dots indicate the positions of the unmagnetized YIG bars, black dots indicate the positions of the magnetized YIG bars, and the blue star indicates the position of the line source. Credit: Qu et al.
“In our experimental setup, a vector network analyzer is used to establish connections between the source and probe antennas,” explains Zhang. “The source antenna is fixed at a specific position within the sample, while the position of the probe antenna is varied to gather valuable information about the intensity and phase of the electromagnetic waves. To facilitate this process, round holes are provided in a metal plate through which both antennas are placed.”
Zhang and his colleagues used a metal coating that served as a “topologically trivial material,” with a Chern number of zero. When this coating covers a photonic topological insulator with a Chern number of 1, a topological edge state is created at the boundary, in accordance with the principle of bulk-edge correspondence.
“The microwave absorber in this setup is intended to suppress the transmission of limit states,” said Zhang. “By using the absorber, we avoid the formation of a closed loop within the entire limit state, which could disrupt the accurate characterization of non-reciprocal phenomena.”
The experiments conducted by this team of researchers have shown that their topological photonic alloy exhibits topological properties even at low doping concentration of magnetized rods without the need for 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 produced without breaking time-reversal symmetry throughout 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 allows the manipulation of different parameters and leads to a wider range of intriguing effects. In addition, we also soon plan to explore the possibility of realizing and capturing similar phenomena in optical frequencies Arguing the relevance of these results for photonics applications would be very intriguing.”
Zhang and his colleagues hope to soon extend their recent findings to the optical domain. This would potentially open up new possibilities for the manipulation of light and the development of innovative photonic devices.
More information:
Tiantao Qu et al, Topological photonic alloy, Physical Assessment Letters (2024). DOI: 10.1103/PhysRevLett.132.223802. On arXiv: DOI: 10.48550/arxiv.2406.05168
Magazine information:
Physical Assessment Letters
arXiv
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